Nerang River Catchment Hydrological Study · 2019-06-23 · River catchment based on design...

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Nerang River Catchment

Hydrological Study

August 2015

Version 3 – August 15 TRACKS-#41849138-v6-REPORT_NERANG_RIVER_HYDROLOGICAL_MODELLING_REPORT_AUGUST_2015

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Title: Nerang River Catchment Hydrological Study

Author:

Study for: City Planning Branch

Planning and Environment Directorate

The City of Gold Coast

File Reference: WF50/44/01(P1)

TRACKS #41849138

Version history

Version Comments/Change Changed by

& date Reviewed by &

date

1.0 Draft for Consultation

2.0 Reviewed by Don

3.0 Update to Word 2010

4.0 Grammar Review

Distribution list

Name Title Directorate Branch

NH Team PE City Planning


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1. Executive Summary

The main objective of the study was to develop a hydrological model for the Nerang River Catchment based on URBS modelling software, calibrated and verified against available data, and fully documented to a consistent standard. The calibrated model was used to estimate flood discharges for design events ranging from 2 year Average Recurrence Interval (ARI) to Probable Maximum Flood (PMF).

The hydrological modelling of the Nerang River catchment was undertaken using an approach and methodology consistent with the other catchments in the Gold Coast City area. Previous reports separate Worongary and Mudgeeraba catchments which are contained within the Nerang River catchment. For this study, these models were combined into the Nerang URBS model and reported as one. The model parameters were kept global and the model configuration was kept as simple as possible. The URBS model has been configured based on current catchment land uses.

For design event discharges, both current climate and a 10% increase in rainfall intensity to account for the impact of climate change have been demonstrated in this report.

Model Calibration and Verification

The Nerang URBS model, including Mudgeeraba and Worongary Creeks, has been calibrated against five historical flood events (January 1974, March 2004, November 2004, June 2005 and January 2008) and then verified against another four historical flood events (March 1999, February 2001, May 2009, and January 2013). The selected calibration and verification events cover a wide range of discharges across the catchment. It is worthwhile to note that there is only 1 water monitoring station at Worongary Creek which was installed in 2010. Hence, only the January 2013 event was verified for this creek.

The emphasis of the model calibration was to achieve the best possible fit between the predicted and recorded discharge hydrographs at key stations in the Nerang River catchment for the selected calibration events. For these stations, the calibration attempted to match the predicted and recorded flood peaks and volumes, and also the shape of the hydrographs. The calibrated model was then verified by comparing the model predictions against the recorded discharge hydrographs at various gauging stations for the selected verification events using the calibrated model parameters.

Rainfall losses were adjusted to achieve the best possible hydrograph shapes and flood volumes for each historical flood event.

A single set of model parameters were adopted for the model and maintained for all calibration and verification events. The model parameters were adjusted to achieve the best calibration across all events, resulting in a compromise between model accuracy and model simplicity. It is noted that calibration of the models for individual events can be improved by adopting a different set of model parameters for each of the different events. The adopted model parameters for the Nerang URBS model are shown below:


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Table 1 Adopted Catchment and Channel Parameter Values for the Nerang River Catchment

URBS Parameter Adopted Value

(Channel Lag Parameter) 0.1

(Catchment Lag Parameter) 1.5

m (Catchment non-linearity) 0.7

Calibration and Verification Results

A reasonable calibration and verification was achieved throughout the catchment, with the URBS model generally reproducing recorded flood discharges satisfactorily for most calibration and verification events.

The model calibration is considered generally reasonable, considering that a single set of global parameters were adopted. Gauges upstream of the Clearview gauge and Hinze Dam are well calibrated. The calibration results for gauging stations downstream of Clearview are uncertain because of the unavailability of well rated gauging stations. The gauges downstream of Clearview are affected by downstream tide water levels. In addition, the effects and operation of the Boobegan lock during the historical events are unknown (from a hydrological perspective) to adequately calibrate the model to flows at this location.

At Mudgeeraba Creek TM gauging station, the hydrograph timing, shape and volume at this station are good for the November 2004, June 2005 and January 2008 calibration events, although modelled predicted peak discharges are slightly higher than the recorded peak rated discharges.

At Worongary Creek ALERT station, only recorded water level is available and hence the calibration is undertaken using a hydraulic model. More information is further discussed in the hydraulic report (Ref 40).

Design Flood Discharges

The calibrated URBS model was used to estimate design flood discharges throughout the Nerang River catchment based on design rainfall intensity – frequency – duration (IFD) data (Ref 1). Design flood discharge hydrographs were estimated for a range of storm durations from 0.5 hour to the 120 hour event for the 2, 5, 10, 20, 50, 100, 200, 500, 2000 year ARI events, and up to the 120 hour event for the Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) events. The design rainfall data and associated procedures and input data (including IFD, temporal patterns, areal reduction factors, spatial distribution and design rainfall losses) adopted in the study are based on a comprehensive review of the latest available data and information (Ref 2).


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The peak design discharges estimated in this study have been compared with the peak design discharges reported in previous studies (Ref 3, 4, 5, 6, 8 and 9). The current study estimates the 100 year ARI peak design discharge at the Hinze Dam outflow (Hinze Dam Stage 2) is 964 m3/s and 1045 m3/s at Clearview, compared with previous studies as seen in Table 2.

Table 2 Peak Discharge Comparison, Hinze Dam Stage 2

Estimated Peak 100 year ARI Discharge (mᶟ/s)

Hinze Dam Outflow Clearview

Current Study 964 1045

Council's 2011 Update (Ref 4) 1045 1099

Hinze Dam Alliance 2009 (Ref 8) 740 ‐

WRM 2010 (Ref 3) 919 968

Council 2001 (Ref 6) 1119 1201

GHD 1999 (Ref 5) 938 1007

It is worthwhile to note that the 1999, 2001 and 2009 studies used unfiltered AWE (Ref 10) temporal patterns and design rainfalls (Ref 1) without the application of areal reduction factors (ARFs). Further, previous studies did not attempt to reconcile their URBS model design discharge estimates with flood frequency analysis (FFA) results, with the exception of GHD study in 1999 (Ref 5)

The Hinze Dam design outflows (100 year ARI) estimated by the 2009 HDA study (Ref 8) for both Stage 2 and 3 of the dam are lower than the estimates from this study. The 2009 HDA study (Ref 8) used the Monte-Carlo (i.e. joint probability) modelling approach to estimate design discharges. Rainfall events more frequent than 1000 years ARI used an initial reservoir level at Hinze Dam from a distribution of sample drawdowns derived from simulated reservoir levels. For rainfall events rarer than 1000 years ARI, the Hinze Dam was assumed full to provide a reasonable degree of conservatism (Ref 8).

This study used a differing method whereby the design flows were estimated with the dam assumed full at the commencement of all design storm events.

Flood Frequency Analysis

Flood frequency analyses (FFA) was undertaken using the methodology recommended in Australian Rainfall and Runoff (Ref 11) by fitting a Log-Pearson Type III distributions to annual series of recorded peak flood discharges at Clearview and Neranwood gauging stations. These were the only two gauging stations with a sufficiently long record to undertake a useful FFA for the Nerang River Catchment.

The FFA results were compared with FFA results from the 1999 GHD (Ref 5), 2000 GCCC (Ref7) and 2010 WRM (Ref 3) studies.

The URBS model estimated peak design discharges were also compared with the FFA results to assess the consistency between the discharge estimates and reconcile any differences from the two methods.


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The FFA comparative results at Clearview (Pre-Hinze Dam) are displayed in Table 3. The design peak discharges estimated by the URBS model corresponded well to the FFA estimates of the current study for all ARIs up to the 100 year. The FFA results from all studies are relatively similar across all ARIs with the exception of the 50 and 100 year ARI from the WRM 2010 study (Ref 3), which is slightly higher than the current study results.

Confidence is achieved in the current studies values of the design peak discharges for ARIs up to 100 years at the Clearview gauging station as a result of the similarity between the URBS and FFA outputs.

Table 3 FFA Comparison @ Clearview (Pre-Hinze Dam)

FFA Estimated Peak Discharge (m3/s)

ARI (Years)

GHD 1999 (Ref 5)

GCCC 2000 (Ref 7)

WRM 2010 ( Ref 3)

Current Study

URBS Current Study (mᶟ/s)

5 920 965 808 828 868

10 1163 1212 1192 1148 1195

50 1833 1885 2237 1953 2061

100 2182 2232 2754 2335 2399

Joint Probability Analysis

Joint Probability approach or Monte Carlo approach has also been undertaken using the Total Probability Theorem approach (TPT) and Cooperative Research Centre – Catchment Hydrology approach (CRC-CH). Joint probability techniques offer an alternative to the design event approach in estimating peak discharges for various ARI events.

The results of the Monte Carlo approach gave further support of the discharges obtained from the Design Event Approach with comparable discharges achieved across all ARIs (Figure 1).


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Figure 1 Monte Carlo Approach (TPT & CRC-CH) compared to Design Event Approach

Conclusion

A URBS model of the Nerang River catchment was satisfactorily calibrated and verified against available data, and then used to estimate design flood discharges at key locations in the catchment for design events ranging from 2 year ARI to PMF.

In addition, the URBS model design discharge estimates have been further supported by the peak discharges determined within the FFA and Joint Probability approach. All analyses in this study have been undertaken using a methodology consistent with the hydrologic modelling currently being undertaken for other catchments in the Gold Coast. In addition, the methodology and results of this study have been fully documented to a consistent standard.

Peak Flow (m3/s) vs ARI @ Clearview St2

0

500

1000

1500

2000

2500

1 10 100 1000 10000

ARI

Dis

ch

arg

e (

m3

/s)

Design Event Approach

TPT Approach

CRC-CH Approach


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Table of Contents

1. Executive Summary ...................................................................................................................... 3

2. Introduction ................................................................................................................................. 16

Overview ............................................................................................................................ 16 2.1

Study Objectives and Scope .............................................................................................. 16 2.2

Limitation Statement .......................................................................................................... 16 2.3

Acknowledgement ............................................................................................................. 17 2.4

Previous Studies ................................................................................................................ 17 2.5

2.5.1 Nerang Catchment ................................................................................................... 17

2.5.2 Mudgeeraba Catchment ........................................................................................... 19

2.5.3 Worongary Catchment .............................................................................................. 19

3. Catchment Description ............................................................................................................... 21

Overview ............................................................................................................................ 21 3.1

3.1.1 Upper Catchment ..................................................................................................... 22

3.1.2 Middle Catchment..................................................................................................... 23

3.1.3 Lower Catchment ..................................................................................................... 23

Landuse ............................................................................................................................. 23 3.2

Stream Gauging Stations ................................................................................................... 25 3.3

4. Methodology ................................................................................................................................ 27

Comprehensive Review of Existing Models and Data ....................................................... 27 4.1

Model Construction ............................................................................................................ 27 4.2

Model Calibration and Verification ..................................................................................... 27 4.3

Design Discharge Estimation ............................................................................................. 28 4.4

4.4.1 Monte Carlo Simulation ............................................................................................ 28

Preparation of Study Report .............................................................................................. 28 4.5

5. Available Data .............................................................................................................................. 29

Topographic Data .............................................................................................................. 29 5.1

Land Use Data ................................................................................................................... 29 5.2

Rainfall Data ...................................................................................................................... 29 5.3

5.3.1 Pluviograph Data ...................................................................................................... 29

Daily Data .......................................................................................................................... 32 5.4

5.4.1 January 1974 Event.................................................................................................. 35

Streamflow and Water Level Data ..................................................................................... 35 5.5

Storage Data ...................................................................................................................... 38 5.6

5.6.1 Little Nerang Dam ..................................................................................................... 38

5.6.2 Hinze Dam ................................................................................................................ 38

Rating Curves .................................................................................................................... 41 5.7


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5.7.1 Nerang River at Whipbird (146011A) ....................................................................... 43

5.7.2 Nerang River at Glenhurst (Clearview TM) (146002B) ............................................. 43

5.7.3 Little Nerang Creek at 4.0Km (146009A) ................................................................. 44

5.7.4 Little Nerang Creek at Little Nerang Dam (146907) ................................................. 45

5.7.5 Nerang River at Hinze Dam ALERT (146906) .......................................................... 46

5.7.6 Mudgeeraba Creek at Mudgeeraba TM (Springbrook Rd) (146020a) ...................... 48

5.7.7 Mudgeeraba Creek at Mudgeeraba ALERT (146912) .............................................. 48

5.7.8 Boobegan Creek Lock ALERT (146801) .................................................................. 49

5.7.9 Worongary Creek ALERT (540597) ......................................................................... 49

5.7.1 Bonogin Creek ALERT (540453) .............................................................................. 49

Peak Annual Flow Data ..................................................................................................... 49 5.8

6. Model Development .................................................................................................................... 51

Model Description .............................................................................................................. 51 6.1

Model Configuration ........................................................................................................... 52 6.2

6.2.1 Adopted Land Uses .................................................................................................. 53

Dam Routing ...................................................................................................................... 55 6.3

7. Model Calibration and Verification ............................................................................................ 56

Selection of Calibration and Verification Events ................................................................ 56 7.1

Calibration Methodology .................................................................................................... 57 7.2

Assignment of Total Rainfalls and Temporal Patterns ....................................................... 58 7.3

Adopted Model Parameters ............................................................................................... 58 7.4

Initial and Continuing Losses ............................................................................................. 59 7.5

Initial Dam Water Levels .................................................................................................... 61 7.6

Calibration Results ............................................................................................................. 61 7.7

7.7.1 General Calibration/Verification Overview ................................................................ 61

7.7.2 January 1974 Event.................................................................................................. 61

7.7.3 March 2004 Event .................................................................................................... 62

7.7.4 November 2004 Event .............................................................................................. 64

7.7.5 June 2005 ................................................................................................................. 65

7.7.6 January 2008 Event.................................................................................................. 67

Verification Results ............................................................................................................ 68 7.8

7.8.1 March 1999 Event .................................................................................................... 68

7.8.2 February 2001 Event ................................................................................................ 70

7.8.3 May 2009 Event........................................................................................................ 71

7.8.4 January 2013 Event.................................................................................................. 73

8. Design Flood Estimation ............................................................................................................ 75

Methodology ...................................................................................................................... 75 8.1

Rainfall Depth Estimation .................................................................................................. 82 8.2

8.2.1 Frequent to Large Design Events (up to and including 100 years ARI flood) ........... 82

8.2.2 Rare to Extreme Design Events (200 to 2000 year ARI flood) ................................. 82


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8.2.3 Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) Design Events .......................................................................................................... 83

Temporal Patterns ............................................................................................................. 83 8.3




Areal Reduction Factors .................................................................................................... 86 8.4




Rainfall Losses .................................................................................................................. 87 8.5




Spatial Distribution ............................................................................................................. 88 8.6




Initial Water Level for Dams ............................................................................................... 88 8.7

Modelled Design Discharges for Hinze Dam Stage 2 ........................................................ 89 8.8




8.8.4 Comparison with Previous Studies ........................................................................... 95

Modelled Design Discharges for Hinze Dam Stage 3 ........................................................ 97 8.9




8.9.4 Comparison with Previous Studies ......................................................................... 100

Climate Change (10% increase in rainfall intensity) ........................................................ 101 8.10

8.10.1 Modelled Design Discharges for Hinze Dam Stage 2 with Climate Change ...... 101

8.10.2 Modelled Design Discharges for Hinze Dam Stage 3 with Climate Change ...... 103

9. Flood Frequency Analysis ........................................................................................................ 105

Method of Analysis .......................................................................................................... 105 9.1

Analysis and Results ....................................................................................................... 105 9.2

9.2.1 Clearview (Pre-Hinze Dam) .................................................................................... 105


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9.2.2 Neranwood ............................................................................................................. 106

Comparison with Previous FFA Studies .......................................................................... 109 9.3

9.3.1 Clearview FFA (Pre-Hinze Dam) ............................................................................ 109

9.3.2 Neranwood ............................................................................................................. 110

Comparison with URBS Results ...................................................................................... 110 9.4

9.4.1 Clearview (Pre-Hinze Dam) .................................................................................... 110

9.4.2 Neranwood (Pre-Hinze Dam) ................................................................................. 111

10. Joint Probability Approach (Monte Carlo Simulation) ........................................................... 112

Monte Carlo Results ........................................................................................................ 114 10.1

11. Conclusions ............................................................................................................................... 116

Overview .......................................................................................................................... 116 11.1

Model Calibration and Verification ................................................................................... 116 11.2

Design Flood Discharges ................................................................................................. 117 11.3

Flood Frequency Analysis ............................................................................................... 117 11.4

Monte Carlo Simulations .................................................................................................. 117 11.5

Spreadsheets ................................................................................................................... 117 11.6

12. Recommendations .................................................................................................................... 118

13. Reference ................................................................................................................................... 119

14. APPENDICES ............................................................................................................................. 122

Appendix A - URBS Model Sub-Catchment Areas and Land Uses ............................................. 122

Appendix B - URBS Catchment Definition File (Design Event) ................................................... 124

Appendix C- Design Temporal Patterns ......................................................................................... 133

Appendix D – Probable Maximum Precipitation (PMP) Calculation ............................................ 135

D.1 PMP Method Selection ..................................................................................................... 135

D.2 Generalised Short Duration Method (GSDM) .................................................................. 136

D.3 Generalised Tropical Storm Method Revised (GTSMR) ................................................. 138

Appendix E - Calibration and Verification Hydrographs .............................................................. 142

E.1 January 1974 Calibration .................................................................................................. 142

E.2 March 2004 Calibration .................................................................................................... 145

E.3 November 2004 Calibration ............................................................................................. 149

E.4 June 2005 Calibration ....................................................................................................... 153

E.5 January 2008 Calibration .................................................................................................. 157

E.6 March 1999 Verification .................................................................................................... 161

E.7 February 2001 Verification .............................................................................................. 164

E.8 May 2009 Verification ...................................................................................................... 168

E.9 January 2013 Verification .............................................................................................. 172

Appendix F - Design Event Discharge Hydrographs (Hinze Dam Stage 2 Current Climate)..... 176

Appendix G - Design Event Discharge Hydrographs (Hinze Dam Stage 3 Current Climate). ... 178


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Appendix H – Hydrological Modelling Utilities .............................................................................. 180

H.1 URBS Control Centre ........................................................................................................ 180

H.2 Subrain (Calibration Only) ............................................................................................... 183

H.3 IFD (Design Event Only) .................................................................................................. 184

H.4 Combine IFD .................................................................................................................... 185

H.5 MaxQ ................................................................................................................................ 186

H.6 MaxMaxQ ......................................................................................................................... 186

H.7 Detain ............................................................................................................................... 187

H.8 Convert to dfs0 ................................................................................................................ 187

H.9 Frequency Adjustment Factor (FAF) ............................................................................... 187

Appendix I – Previous Hydrology IFD and Temporal Pattern Source (Ref 2) ............................. 189

Appendix J – Monte Carlo Results ................................................................................................. 190

List of Figures Figure 1 Monte Carlo Approach (TPT & CRC-CH) compared to Design Event Approach ................ 7

Figure 2 Locality Map, Nerang Catchment ...................................................................................... 22

Figure 3 Landuse in the Nerang catchment .................................................................................. 24

Figure 4 Rainfall Station Location Map, Nerang River Catchment ................................................. 34

Figure 5 Location of EHP/DERM gauging stations .......................................................................... 42

Figure 6 Available and Adopted Rating Curves, Nerang River at Whipbird (146011A) ................... 43

Figure 7 Available and Adopted Rating Curves, Nerang River at Glenhurst (146002B) ................. 44

Figure 8 Available and Adopted Rating Curve, Little Nerang Creek at 4.0Km (146009A) ............... 45

Figure 9 Available and Adopted Rating Curve, Little Nerang Creek at Little Nerang Dam (146907)... ........................................................................................................................................... 46

Figure 10 Available and Adopted Rating Curve, Nerang River at Hinze Dam Stage 2 (146906) . ................................................................................................................................. 47

Figure 11 Adopted Rating Curve, Nerang River at Hinze Dam Stage 3 (146906) ................... 47

Figure 12 Available and Adopted Rating Curves, Mudgeeraba Creek at Springbrook Rd (146020A) ................................................................................................................................. 48

Figure 13 Available and Adopted Rating Curve, Mudgeeraba Creek at Mudgeeraba Alert (146912) ................................................................................................................................. 49

Figure 14 Nerang URBS Model Configuration .......................................................................... 53

Figure 15 Jan 1974 Modelled (C) and Recorded (R) Flows at Clearview (146905) ................. 62

Figure 16 March 2004 Modelled (C) and Recorded (R) Flows at Clearview (146905) ............. 63

Figure 17 November 2004 Modelled (C) and Recorded (R) Flows at Clearview (146905) ...... 65

Figure 18 June 2005 Modelled (C) and Recorded (R) Flows at Clearview (146905) ............... 66

Figure 19 June 2008 Modelled (C) and Recorded (R) Flows at Clearview (146905) ............... 68

Figure 20 March 1999 Modelled (C) and Recorded (R) Flows at Clearview (146905) ............. 69

Figure 21 February 2001 Modelled (C) and Recorded (R) Flows at Clearview (146905) ........ 71


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Figure 22 May 2009 Modelled (C) and Recorded (R) Flows at Clearview (146905) ................ 72

Figure 23 January 2013 Modelled (C) and Recorded (R) Flows at Clearview (146905) .......... 74

Figure 24 Anomalies for events > 100 year ARI @ Clearview, Hinze Dam Stage 2 (Ref 9) .... 75

Figure 25 Comparison of URBS Model Design Discharges and Flood Frequency Distribution, Nerang River at Clearview (146002 A & B) - Pre-Hinze Dam, 1920-1975 ......................................... 106

Figure 26 Comparison of URBS Model Design Discharges and Flood Frequency Distribution, Little Nerang Creek at Neranwood (146004A) ................................................................................... 107

Figure 27 Schematic Illustration of Design Event Approach ................................................... 112

Figure 28 Schematic Illustration of Joint Probability Approach ............................................... 113

Figure 29 Comparison of Peak Discharges for Hinze Dam stage 2 at Clearview .................. 115

Figure 30 Comparison of Peak Discharges for Hinze Dam stage 3 at Clearview .................. 115

List of Tables Table 1 Adopted Catchment and Channel Parameter Values for the Nerang River Catchment .... 4

Table 2 Peak Discharge Comparison, Hinze Dam Stage 2 ............................................................. 5

Table 3 FFA Comparison @ Clearview (Pre-Hinze Dam) ............................................................... 6

Table 4 Stream Gauge Stations in Nerang River Catchment ........................................................ 25

Table 5 Pluviograph Data Availability for the Nerang River Catchment ........................................ 30

Table 6 Daily Rainfall Data Availability for the Nerang River Catchment. ..................................... 32

Table 7 Stream Gauge Data Availability for the Nerang River Catchment .................................... 36

Table 8 Adopted Stage-Storage-Spillway Discharge Relationship, Little Nerang Dam ................. 38

Table 9 Hinze Dam Levels ............................................................................................................. 38

Table 10 Adopted Stage-Storage-Spillway Discharge Relationship, Hinze Dam Stage 2 ................ 39

Table 11 Adopted Stage-Storage-Spillway Discharge Relationship, Hinze Dam Stage 3 ................ 39

Table 12 Summary of Annual Peak Series Data .............................................................................. 50

Table 13 Nerang River Catchment Land Use Categories ............................................................... 54

Table 14 Adopted Land Use Breakdown, Nerang River URBS model ............................................. 55

Table 15 Recorded Peak Discharges for Calibration and Verification Events .................................. 57

Table 16 Adopted Catchment and Channel Parameter Values for the Nerang River Catchment .... 59

Table 17 URBS Parameter Ranges(Ref 25) ........................................................................................ 59

Table 18 Adopted Initial and Continuing Losses (Calibration Events) .............................................. 60

Table 19 Adopted Initial and Continuing Losses (Verification Events) ............................................. 60

Table 20 Recorded and Modelled Peak Discharges at Key Gauging Stations, January 1974 Flood Event ........................................................................................................................................... 61

Table 21 Recorded and Modelled Peak Discharges at Key Gauging Stations (March 2004 Flood) 63

Table 22 Recorded and Modelled Peak Discharges at Key Gauging Stations, November 2004 Flood Event .......................................................................................................................................... 64

Table 23 Recorded and Modelled Peak Discharges at Key Gauging Stations, June 2005 Flood Event ............................................................................................................................................................. 65


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Table 24 Recorded and Modelled Peak Discharges at Key Gauging Stations, January 2008 Flood Event ........................................................................................................................................... 67

Table 25 Recorded and Modelled Peak Discharges at Key Gauging Stations, March 1999 Flood Event .................................................................................................................................................... 69

Table 26 Recorded and Modelled Peak Discharges at Key Gauging Stations, February 2001 Flood Event .................................................................................................................................................... 70

Table 27 Recorded and Modelled Peak Discharges at Key Gauging Stations, May 2009 Flood Event ........................................................................................................................................... 72

Table 28 Recorded and Modelled Peak Discharges at Key Gauging Stations, January 2013 Flood Event .................................................................................................................................................... 73

Table 29 Summary of Recommended Methodology for Design Event Analysis .............................. 76

Table 30 Adopted Rainfall Depth (IFD) Source for the Nerang Catchment ...................................... 80

Table 31 Adopted Temporal Pattern Source for the Nerang Catchment .......................................... 81

Table 32 10 Historical Storm Temporal Patterns used for PMF ....................................................... 84

Table 33 Adopted Areal Reduction Factors ...................................................................................... 86

Table 34 Adopted Initial and Continuing Loss Values, 2 year to 100 year ARI Events .................... 87

Table 35 Adopted Initial Losses and Continuing Loss Rates, 200, 500, 1000 and 2000 Year ARI Events .................................................................................................................................................. 87

Table 36 Adopted Initial Losses and Continuing Loss Rates, PMP and PMF Events ...................... 88

Table 37 Nerang River URBS Model (Hinze Dam Stage 2) Design Discharges, 2 year to 100 year ARI Events ........................................................................................................................................... 89

Table 38 Nerang River URBS Model (Hinze Dam Stage 2) Critical Storm Durations, 2 year to 100 year ARI Events ................................................................................................................................... 90

Table 39 Nerang River URBS Model (Hinze Dam Stage 2) Design Discharges, 200, 500, 1000 and 2000 year ARI Events .......................................................................................................................... 91

Table 40 Nerang River URBS Model (Hinze Dam Stage 2) Critical Storm Durations, 200, 500, 1000 and 2000 year ARI Events ................................................................................................................... 92

Table 41 Nerang River URBS Model (Hinze Dam Stage 2) Discharges and Critical Durations, PMPDF Event ....................................................................................................................................... 94

Table 42 Nerang River URBS Model (Hinze Dam Stage 2) Discharges and Critical Durations, PMF Event ........................................................................................................................................... 94

Table 43 Comparison of Peak Design Discharges Estimated in Different Studies for Nerang River Catchment, Hinze Dam Stage 2 ........................................................................................................... 96

Table 44 Comparison of Estimated Hinze Dam Stage 2 Design Outflows with 2007 HDA Results (Ref 8) and WRM Results (Ref 3) ........................................................................................................ 96

Table 45 Comparison of Estimated Hinze Dam Stage 2 Design Outflows with GHD (Ref 18) and WRM Results (Ref 3) ........................................................................................................................... 97

Table 46 Nerang River URBS Model (Hinze Dam Stage 3) Design Discharges, 2 year to 100 year ARI Events ........................................................................................................................................... 98

Table 47 Nerang River URBS Model (Hinze Dam Stage 3) Critical Storm Durations, 2 year to 100 year ARI Events ................................................................................................................................... 98

Table 48 Nerang River URBS Model (Hinze Dam Stage 3) Design Discharges, 200, 500, 1000 and 2000 year ARI Events .......................................................................................................................... 99


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Table 49 Nerang River URBS Model (Hinze Dam Stage 3) Critical Storm Durations, 200, 500, 1000 and 2000 year ARI Events ................................................................................................................... 99

Table 50 Nerang River URBS Model (Hinze Dam Stage 3) Discharges and Critical Durations, PMPDF Event ..................................................................................................................................... 100

Table 51 Nerang River URBS Model (Hinze Dam Stage 3) Discharges and Critical Durations, PMF Event ......................................................................................................................................... 100

Table 52 Comparison of Estimated Hinze Dam Stage 3 Design Outflows with 2007 HDA Results (Ref 8) and WRM Results (Ref 3) ...................................................................................................... 101

Table 53 Nerang River URBS Model (HD 2) Design Discharges with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events .......................................................................................... 101

Table 54 Nerang River URBS Model (HD 2) Critical Storm Durations with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events .......................................................................................... 102

Table 55 Nerang River URBS Model (HD 3) Design Discharges with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events .......................................................................................... 103

Table 56 Nerang River URBS Model (HD 3) Critical Storm Durations with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events .......................................................................................... 104

Table 57 FFA Results, Nerang River at Clearview (146002A & B) - Pre- Hinze Dam .................... 106

Table 58 FFA Results, Little Nerang Creek at Neranwood (146004A) - Pre-Dams. ...................... 107

Table 59 FFA Comparison, Nerang River at Clearview (146002 A & B) - Pre-Hinze Dam ............ 109

Table 60 FFA Comparison, Little Nerang Creek at Neranwood (146004A) ................................... 110

Table 61 Comparison of URBS model and FFA Estimated Peak Design Discharges, Clearview .. 110

Table 62 Comparison of URBS model and FFA Estimated Peak Design Discharges, Neranwood ..... ......................................................................................................................................... 111


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2. Introduction

Overview 2.1

Over recent years, City of Gold Coast (City) has developed numerous hydrological models of its catchments and waterways. These models have been developed by Council staff and/or consultants, using a range of approaches and assumptions. The standard of these models, with respect to their configuration, calibration, use for design discharge estimation and documentation, vary significantly.

To provide a consistent basis for floodplain management and local government planning, Council commissioned WRM Water & Environment Pty Ltd (WRM) in December 2007 to undertake a comprehensive study to review and update its hydrological models to a consistent standard of methodology and documentation. Based on the review, a set of recommendations were provided to update the 10 models in a consistent manner across the city area using the latest data and modelling approaches. These recommendations provide the basis for the current model upgrades. Details of the model review and its findings are given in WRM (Ref 2).

Previously, separate hydrological modelling studies have been undertaken for Mudgeeraba Creek and Worongary Creek catchments, both sub-catchments within the Nerang River catchment. However, these two models are now combined into the Nerang River model developed in this study.

This report describes the development, calibration and use of a URBS model for the Nerang River catchment.

Study Objectives and Scope 2.2

The main objective of the study was to develop a hydrological model for the Nerang catchment, which included the Mudgeeraba and Worongary catchments using the URBS hydrological modelling software (URBS), calibrated and verified against available data, and fully documented to a consistent standard. Once this objective is achieved, the calibrated model was used to estimate design flood discharges using a consistent methodology.

The scope of work was as follows:

Review existing models and data Update the existing model to a standard consistent with other catchments Review and update model calibration and verification Review and update the FFA Undertake Monte Carlo Simulations

Estimate design discharges and extreme event discharges at key locations throughout the catchment using current industry standard methodology; and

Document the adopted methodology, tasks and results to a standard consistent with other updated models.

Limitation Statement 2.3

The following limitations apply in the preparation of this report.


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This report was prepared based on available information at the time of writing.

The analysis and approach by this study is specifically prepared for internal use. Use of contents of this report is prohibited unless a written approval is obtained from Gold Coast City Council.

The result of this study is accurate only for its intended purpose.

Acknowledgement 2.4

The assistance provided by the Bureau of Meteorology, and in particular, for this study is gratefully acknowledged. The Bureau provided GCCC with a copy of their Nerang River URBS model (BOM, 2008) used for flood forecasting purposes and all the historical rainfall and streamflow data used in this study for model calibration and verification.

Previous Studies 2.5

There are many studies of relevance to the hydrological modelling of the Nerang River catchment which are briefly described below.

2.5.1 Nerang Catchment

1992 Kinhill (Ref 14)

This study updated and consolidated the work undertaken in a major flood study in 1987 and additional investigations undertaken up to 1990. These investigations used a calibrated RORB model for the Nerang River catchment and the model included the Mudgeeraba Creek and Worongary Creek sub-catchments. The RORB model was used to estimate design discharges along the Nerang River and investigate flood mitigation options in the catchment. The results were also used as input to the Nerang River hydraulic model. It is noted that design discharges in these studies were calculated using temporal patterns given in Australian Rainfall and Runoff (1977) patterns (Ref 13) and not the Australian Rainfall and Runoff (1987) patterns (Ref 11) which were current in 1992.

1999 GHD (Ref 5)

This study developed and calibrated a URBS model of the Nerang River catchment for the estimation of design discharges and use in real-time flood forecasting. The URBS model was calibrated against 13 historical flood events from June 1967 to March 1999, including the extreme event in January 1974. The calibrated model was then used to estimate design discharges for 1 to 72 hour storm durations for 5 to 500 Year ARI events. The URBS model was divided into 46 sub-areas and included the Mudgeeraba and Worongary Creek catchments. Design discharges were estimated using AWE (Ref 1) design rainfall intensity-frequency-duration data and AWE design rainfall temporal patterns (Ref 10). Rainfall aerial reduction factors were not used in this study.

2000 GCCC (Ref 7)

This study reviewed previous Nerang River hydrology studies undertaken between 1987 and 1999. Five studies in total, comprising 3 studies undertaken by Kinhill Cameron McNamara including 1992 Kinhill (Ref 14), 1998 BoM (Ref 15) and 1999 GHD (Ref 5), were reviewed. The study concluded that


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the results of the 1999 GHD study should be accepted by Council because it is based on the most up to date inputs to the adopted hydrological model.

2001 GCCC (Ref 6)

This study followed on from the recommendations in the 2000 GCCC (Ref 7) report and updated the 1999 GHD URBS modelling to include revised design rainfall temporal patterns, sub-catchment specific design rainfalls and more conservative loss rates. The study produced design discharge estimates that are higher than the 1999 GHD estimates but concluded that the new estimates should be viewed as conservative.

The 2003 Gold Coast Planning Scheme uses the output from this study as the designated flood level for the Nerang catchment.

2005 GHD (Ref 16, 17 and 18)

This suite of studies estimated design extreme rainfalls up to the Probable Maximum Precipitation (PMP) event and used these design rainfalls to estimate extreme flood discharges up to, and including, the PMP Design Flood (PMPDF) and the Probable Maximum Flood (PMF) events. These studies were undertaken using the 2001 GCCC version of the URBS model to incorporate a revised rating curve Hinze Dam Stage 2 and assess several options for Hinze Dam Stage 3.

2009 Hinze Dam Alliance (Ref 8)

This study, which was undertaken as part of the Hinze Dam Stage 3 upgrade design investigations, updated the previous flood hydrology estimates for Hinze Dam. A RORB model, which was calibrated to the results of the 1999 GHD URBS model, was used in this study. Further, this study adopted a Monte-Carlo simulation (i.e. joint probability) approach to estimate design discharges in the Nerang River catchment. This approach allowed their design simulations to start with Hinze Dam initial reservoir levels that are less than full.

In addition, more up to date design rainfalls (including CRC-FORGE data) were used. The study found that the AWE (Ref 10) design rainfall temporal patterns had some limitations, including embedded bursts which could bias the design flood estimates. These temporal patterns were filtered to remove the embedded bursts prior to use in the study, but the filtering methodology and the results are not presented in the report.

1998 BOM (Ref 15)

The Bureau of Meteorology (BOM) developed a URBS model for the Nerang River catchment for their flood forecasting purposes. The model was calibrated against 12 historical flood events between 1967 and 1996. The BOM model was not used to estimate design discharges.

2009 WRM (Ref 3, 19 and 20)

WRM was commissioned by GCCC to undertake a comprehensive study to review and to update the hydrological models to a consistent methodology and to calibrate to recent flood events.


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2010 Addendum (Ref 4)

GCCC updated the WRM hydrological model in 2011 to include the final storage curve for the Hinze Dam Stage 3 upgrade. The output of this study was meant to be used in the 2012 Gold Coast Planning Scheme.

2013 GCCC (Ref 9)

An independent review of GCCC hydrological model was undertaken by Don Carroll Project Management Pty Ltd. Recommendations from this review were later adopted for the present study. It is envisaged that the study output will be used in the new 2015 City Plan.

2.5.2 Mudgeeraba Catchment

2004 GCCC (Ref 21)

In 2004, GCCC undertook a catchment wide hydrological modelling study of the Mudgeeraba Creek catchment using the URBS model. The Mudgeeraba Creek (including Bonogin Creek) catchment was divided into 20 sub catchments. Although there was no calibration undertaken for this study, it compared the modelled peak discharges at Pacific Highway with the equivalent peak discharges obtained from Council’s Nerang URBS model (Ref 7). The Mudgeeraba model was used to estimate design discharges for 5, 10, 20, 50, 100, 200 and 500 year ARI design events.

2007 GCCC (Ref 22)

A further update to the hydrological model was undertaken in 2007 to calibrate to historical events and to regenerate all design events using new rainfall data files and the original model parameters. This 2007 model estimated the 2, 5, 10, 20, 50, 100, 200 and 500 year ARI design discharges at key locations in the catchment.

2008 WRM (Ref 19)


2010 GCCC (Ref 45)

In 2010, GCCC updated the WRM hydrological model to recalibrate to historical events and to adjust model parameters, as well as to recalculate the flood frequency curves. The output of this study was meant to be used in the 2012 Gold Coast Planning Scheme.

2.5.3 Worongary Catchment

2004 GCCC (Ref 21)

In 2004, GCCC undertook a catchment wide hydrological modelling study of the Worongary Creek catchment using the URBS model. The Worongary Creek catchment was divided into 33 sub catchments. Although there was no calibration undertaken for this study, it compared the modelled


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peak discharges at Pacific Highway with the equivalent peak discharges obtained from Council’s Nerang URBS model (Ref 7). The Worongary model was used to estimate design discharges for 5, 10, 20, 50, 100, 200 and 500 year ARI design events.

2008 WRM (Ref 20)


2010 GCCC (Ref 46)

In 2010, GCCC updated the WRM hydrological model to recalibrate to historical events and to adjust model parameters, as well as to recalculate the flood frequency curves. The output of this study was meant to be used in the 2012 Gold Coast Planning Scheme.


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3. Catchment Description

Overview 3.1

The Nerang River has its headwaters in the McPherson Ranges along the Queensland / New

South Wales border and flows in a generally north-easterly direction towards the coast where it

discharges into the Broadwater. The Nerang River catchment has a total area of approximately

492 km2 and includes a number of significant tributaries including Worongary, Mudgeeraba, Little

Nerang and Little Tallebudgera Creeks. Mudgeeraba Creek has a catchment area of 84 km2 to

the Pacific Motorway and Worongary Creek has a catchment of 17 km2 to the Pacific Motorway

(as shown in Figure 2).

The topography of the catchment varies from steep hills, valleys and mountainous terrain in the

upper catchment to wide, flat floodplains and canal waters in the middle and lower reaches of the

river. Catchment elevations range from approximately 1150 m in McPherson Ranges to less than

2 m at the river mouth and through the canal areas. The catchment contains two major dams,

Hinze Dam on the Nerang River and Little Nerang Dam on Little Nerang Creek, several on-river

weirs and locks and a significant number of canals through the lower catchment. The major land

uses are forest and pasture in the upper catchment and rural residential in the middle. The lower

catchment contains medium to high density residential and a number of major urban centres

including Nerang, Southport, Broadbeach, Surfers Paradise, Robina and Burleigh.


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Figure 2 Locality Map, Nerang Catchment

3.1.1 Upper Catchment

The Nerang River catchment upstream of the Hinze Dam is referred to as the upper catchment.

This catchment comprises the Nerang River itself, which has its headwaters in Border Ranges


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National Park, and a major tributary called Little Nerang Creek. Little Nerang Creek drains to the

two major dams in the Nerang River Catchment, Little Nerang Dam and Hinze Dam. It has a

catchment area of some 35 km2 to Little Nerang Dam and 52 km2 to Hinze Dam.

In the upper catchment, the Nerang River itself is generally quite narrow. The river channel in the

upper reaches is relatively incised, with the average channel slope from the upstream extent of

the catchment to Hinze Dam (some 29 km) being approximately 0.4%. The average channel

slope was calculated from 50 m contours using the equal area slope method (Ref 23).

Hinze Dam, which is located on the Nerang River, is a significant storage located in the upper

catchment. The dam has a catchment area of 207 km2. Stage 1 of the dam was completed in

1976 and had a full supply volume (FSV) of 42,315 ML. Stage 2 of the dam was completed in

1989 and had a FSV of 161,073 ML (Spillway level of 82.2 m AHD) (Ref 24). Stage 3 of Hinze

Dam was completed at the end of 2011, increasing the FSV of the dam to 310,730 ML (Spillway

level of 94.5 m AHD) (Ref 24). Hinze Dam has a significant impact on downstream flood flows in

the Nerang River.

Little Nerang Dam is located upstream of Hinze Dam on Little Nerang Creek. Little Nerang Dam,

which was completed in 1965, has a catchment area of 35 km2 and a FSV of 9,200 ML. Little

Nerang Dam has little impact on downstream flood flows in the Nerang River.

3.1.2 Middle Catchment

The Nerang River Catchment downstream of Hinze Dam and up to the Pacific Highway is

referred to as the middle catchment. This catchment includes the Nerang River itself through the

town centre of Nerang and a number of significant tributaries including Mudgeeraba and

Worongary Creeks. Through the middle catchment area, Nerang River has an average slope of

approximately 0.14%. Worongary and Mudgeeraba Creeks both have average slopes of

approximately 0.4%. The average channel slope was calculated from 1m contours using the

equal area slope method (Ref 23).

3.1.3 Lower Catchment

The Nerang River Catchment downstream of the Pacific Highway is referred to as the lower

catchment. This catchment is low lying and contains a number of different canal networks and

minor tributaries. Most of the area is also tidally affected. Through this area the average slope of

the Nerang River is approximately 0.01%. The average channel slope was calculated from 1m

contours using the equal area slope method (Ref 23).

Landuse 3.2

The major land use in the upper Nerang River catchment is forest, with pasture and small areas

of rural residential living located close to the river. The land use in the middle catchment is

predominately rural residential and low density residential with a minor urban area located at

Nerang. The land use in the lower catchment is predominately residential (medium and high


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density) with a number of significant urban areas (Surfers Paradise, Broadbeach, Burleigh) along

the coast and major urban areas (Robina, Carrara) located closer to the Pacific Highway.

The landuse information is later used by the model as characterisation parameters (Further

details are discussed in Section 6.2.1 .

Figure 3 Landuse in the Nerang catchment


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Stream Gauging Stations 3.3

Table 4 shows the key stream gauging sites in the Nerang River catchment, the length of the

channel and the catchment area draining to each site. The period of operation of each station is

also shown. The locations of the gauging sites are shown on Figure 2. The ALERT stations are

maintained by GCCC and BOM whereas the TM stations are maintained by EHP. They measure

water levels. Further information is explained in Section 5.5 .

Table 4 Stream Gauge Stations in Nerang River Catchment

River Station Number (AWRC No)

Station Name Stream Name

Period of Operation

Gauge Zero (m AHD)

Catchment Area (km2)

146907 Little Nerang Dam ALERT

Little Nerang Creek

2006 - Present 168.02 35

146004A Neranwood

TM Little Nerang

Creek 1926 - 1962 102.85 40

146927 Nerangwood

ALERT Mudgeeraba 2008 - Present 34.31 -

146009A 4.0km TM Little Nerang

Creek 1962 - 1974 24.50 53

146011A Whipbird TM Nerang River 1965 - 1986 66.83 123

146904 Hinze Dam Nerang River 1988 - 2010 82.20 209

146906 Hinze Dam

ALERT Nerang River 2010 - Present 94.50 209

146002A Neranga Nerang River 1919 - 1970 0.72 240

146002B Clearview

TM/Glenhursta Nerang River 1967 - Present 2.85 240

146905 Clearview ALERTa Nerang River 1992 - Present 2.77 240

146914 Carrara ALERT

Nerang River 2002 - Present 0 270

146020A

Mudgeeraba TM

(Springbrook Rd)

Mudgeeraba Creek

1989 - Present 5.01 36


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River Station Number (AWRC No)

Station Name Stream Name

Period of Operation

Gauge Zero (m AHD)


146912 Mudgeeraba

ALERT Mudgeeraba

Creek 1989 - Present 0 84

146801 Boobegan Creek Lock

ALERT

Boobegan Creek

1997 - Present 0 121

540597 Worongary

Creek ALERTb

Worongary Creek

2008 - Present 2.60 -

540453 Bonogin

Creek ALERT (Hardys Rd) b

Bonogin Creek

2008 - Present - -

aNerang, Glenhurst, Clearview ALERT and Clearview TM are referred to collectively as “Clearview” in this

study.

b Worongary and Bonogin Ck ALERT stations were installed in 2008 and hence only recorded water level

are available post-2008.


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4. Methodology

The hydrological modelling of the Nerang River catchment was undertaken using an approach and methodology consistent with the other catchments in the Gold Coast City area. The study adopted a systematic approach that consisted of the following steps:

Comprehensive Review of Existing Models and Data 4.1

The specific tasks included:

Review of previous studies.

Review of storage-discharge characteristics of Hinze Dam and Little Nerang Dam.

Review of available rainfall and stream gauging data.

Review and update of key gauging station rating curves.

Review of existing land-use data and update them based on current land-uses identified from aerial photography and land use planning scheme maps.

Model Construction 4.2


Delineation of catchment and sub-catchments boundaries based on latest DTM and drainage network data for the Nerang catchment.

Generation of catchment (network) files with appropriate output locations and calibration locations for the URBS model.

Model Calibration and Verification 4.3


Selection of calibration and verification events.

Processing of rainfall and streamflow data for calibration and verification events.

Rainfall analysis of all selected events to create sub-catchment specific rainfall to generate rainfall definition file for the URBS model.

Calibration and verification of Nerang URBS model for five calibration events and four verification events.

Adoption of global model parameters for the Nerang URBS model.


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Design Discharge Estimation 4.4


Estimation of design rainfalls and loss rates for the Nerang URBS model for storm events ranging from 2 Years Average Recurrence Interval (ARI) to Probable Maximum Precipitation (PMP).

Undertaking of design event model runs for storm durations of up to 120 hours and storm severities ranging from 2 Years ARI to PMP and the Probable Maximum Flood (PMF).

Undertaking of flood frequency analysis (FFA) for peak discharges in the Nerang River at Clearview and Little Nerang Creek at Neranwood.

Reconciliation of URBS model design events and flood frequency analysis results.

Estimation of design discharges at key locations throughout the catchment for the full range of design events investigated.

4.4.1 Monte Carlo Simulation

Undertake Monte Carlo simulations using both the CRC-CH and TPT method, for further verification

of the discharges obtained from the Design Event Approach (DEA).

Preparation of Study Report 4.5


Documentation of the adopted methodology, tasks and results to a standard that is consistent with other updated models.


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5. Available Data

Topographic Data 5.1

The topographic datasets available for this study were as follows:

GCCC’s 5m grid DTM (covering GCCC area and immediate surrounds)

1:250,000 topographic maps for the entire Nerang River catchment

1:25,000 topographic maps for parts of the catchment

EHP’s GIS drainage network layer, showing all watercourses and waterbodies throughout the catchment.

Land Use Data 5.2

The following land use datasets were available for the study:

Cadastral boundaries for GCCC

Land use planning scheme maps for GCCC

GCCC GIS land use database information

Aerial and Satellite photography.

Rainfall Data 5.3

Rainfall data for pluviograph and daily rainfall stations in, and adjacent to, the catchment was provided by the BOM (for ALERT stations) and EHP (for TM stations). Figure 4 shows the locations of the rainfall stations.

5.3.1 Pluviograph Data

Table 5 shows the availability of pluviograph data from rainfall stations within and adjacent to the Nerang River catchment for the selected model calibration and verification events; except for the January 1974 event (selection of these events is discussed in Section 7.1

Available pluviograph stations located within the catchment for each selected historical event is detailed below.

January 1974 (refer Figure )

March 2004 (refer FigureE-)

November 2004 (refer Figure )

June 2005 (refer FigureE-1)


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January 2008 (refer Figure )

March 1999 (refer Figure)

February 2001 (refer Figure)

May 2009 (refer Figure)

January 2013 (refer Figure).

Table 5 Pluviograph Data Availability for the Nerang River Catchment

Station No

Station Name

Pluviograph Data Available

Mar 1999

Jan 2001

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

040881 Air Sea Rescue ALERT

Y Y Y Y Y Y Y Y

040844 Beechmont

ALERT Y Y Y Y Y Y Y Y

540360 Biggera Ck

Dam ALERT - - Y Y Y Y Y -

040845 Binna Burra

ALERT Y Y Y Y Y Y Y -

540352 Bonogin Creek

ALERT - - Y Y Y Y Y Y

540253 Boobegan Ck Lock ALERT

Y - Y - Y Y Y Y

540290 Canungra

Army ALERT - - - Y Y Y -- --

7240 Canungra

TM - Y - - - - - -


- - Y Y Y Y Y -

540291 Clagiraba Rd

ALERT - - Y Y Y Y Y Y

040846 Clearview

ALERT Y Y Y Y Y Y Y -

040416 Clearview

TM - Y Y Y - Y - -


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Station No

Station Name


Mar 1999

Jan 2001

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

540320 Coplicks Br

ALERT - - Y Y Y Y - -

540318 Evandale ALERT

- - - Y Y Y Y Y

040764 Gold Coast

Seaway - - Y Y Y - - -

040847 Hinze Dam

ALERT Y Y Y Y Y Y - -

040930 Laheys Lookout ALERT

- - Y Y Y Y - -


Y Y Y - Y Y - -

540238 Loders Creek

ALERT - - Y - Y Y - -

540359 Loders

Creek Dam ALERT

- - - - - Y Y -

540428 Molendinar

ALERT - - - - - Y Y -

540353 Mt Nimmel

ALERT - - Y Y Y Y Y -

040335 Mt

Tambourine ALERT

Y Y Y Y Y Y Y -

040197 Mt

Tambourine Fern St

- - Y Y Y Y - -

540254 Mudgeeraba

ALERT Y Y Y Y - - Y -

540440 Neranwood - - - - - - Y Y

040882 Numinbah

ALERT Y Y Y - Y Y Y -

540438 Numinbah

Valley ALERT

- - - - - - Y -


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Station No

Station Name


Mar 1999

Jan 2001

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

540252 Oyster Ck

ALERT - Y Y Y Y - - -

040848 Springbrook

Lower ALERT

Y Y Y Y Y Y Y -

540287 Tallai

ALERT - - - - - Y - -

540366 Tallebudgera

Ck Dam ALERT

- - - - Y Y - -

540356 Tallebudgera

Ck Rd ALERT

- - Y Y Y Y - -

040376 Tyungun ALERT

Y Y Y Y Y - - -

540400 Upper

Springbrook ALERT

- - - - - Y - -

540597 Worongary

ALERTa - - - - - - - Y

a Worongary and Bonogin Ck ALERT stations were installed in 2008 and hence only recording post-2008

are available.

Daily Data 5.4

Table 6 shows the data availability from daily rainfall stations (measured at 9am every day) within and adjacent to the Nerang River catchments for the selected model calibration and verification events, except the January 1974 event.

For the January 1974 event, only daily rainfall data is available. It is noted that no daily rainfall station data was available for the March 1999, January 2001, May 2009 or January 2013 events.

Table 6 Daily Rainfall Data Availability for the Nerang River Catchment.

Station No

Station Name


Mar 1999

Jan 2001

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

040558 Glengaven - - Y Y Y Y - -

040417 Miami

Bardon Ave - - - Y Y Y - -


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Station No

Station Name


Mar 1999

Jan 2001

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

040160 Nerang

Gilston Rd - - - Y Y Y - -

040162 Numinbah State Farm

- - - - Y - - -

040190 Southport Ridgeway

Ave - - - - - Y - -

040607 Springbrook

Rd - - - - - Y - -

040750 Springbrook

TM - - - Y Y - - -


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Figure 4 Rainfall Station Location Map, Nerang River Catchment


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5.4.1 January 1974 Event

Rainfall data available for the 1974 event is limited to only four stations; two of those stations are within the Nerang River catchment located at Springbrook and Nerang. Data is also available at Tambourine bordering the catchment and Beenleigh which is located 30km north of the catchment. Processed data used for the centroids in the BOM URBS model were available and used in this study.

Streamflow and Water Level Data 5.5

Table 7 shows the availability of water level data from stream gauging stations located within the Nerang River catchment for the selected model calibration and verification events (See Section 7.1 ). Figure 2 shows the locations of the stream gauges as listed in Table 7.

The following is of note with respect to:

Some stream gauging stations have both Telemetry (EHP) and ALERT (BOM) data transmission whereby both are referred to by different station numbers; however it is understood that both record and transmit data from the same location and instrument but transmit separately to EHP and BOM. As a result, some stations are repeated in Table 7 as they are listed under different station numbers.

Only EHP stations have rating curves based on actual gaugings. The maximum gauged height and/or gauged discharge at each of the EHP (or DERM) stations are shown in Table 4 and Table 7. Rating curves for common gauges are generally based on the EHP (or DERM) rating curve for the site, but some have been modified by BOM for use in their URBS models.

The water level is converted to flow by a pre-defined rating curve. An assessment of the available rating curves for each gauging station is given in Section 5.7

Version 3 – August 15 TRACKS-#41849138-v6-REPORT_NERANG_RIVER_HYDROLOGICAL_MODELLING_REPORT_AUGUST_2015 of 191

Table 7 Stream Gauge Data Availability for the Nerang River Catchment

Station No

Station Name

Stream Name


Station Operator

Max. Gauged Height (m)

Max. Gauged Flow (m3/s)

Streamflow or Water Level Data Available

Jan 1974

Mar 1999

Jan 1999

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013


Little Nerang Creek

35.2 BOM - - - Y Y Y Y Y Y Y -

146011A Whipbird TMa Nerang River 123.7 EHP 2.85 205 Y - - - - - - - -

146009a 4.0km TM a Little Nerang

Creek 53.3 EHP 1.07 8.2 Y - - - - - - - -

146906 Hinze Dam

ALERT Nerang River 212.5 BOM - - - Y Y Y Y Y Y Y Y

146905 Clearview

ALERT Nerang River 239.3 BOM - - - Y Y Y Y Y Y Y Y

146002b Glenhurst (Clearview

TM) Nerang River 239.3 EHP 7.95 b 904.75 b Y - - - - - - - -


Nerang River 270.3 BOM - - - - - Y Y Y - Y Y

146020a

Mudgeeraba TM

(Springbrook Rd) c

Mudgeeraba Creek

36.0 EHP 3.35 107 - Y - Y Y Y Y - -

146912 Mudgeeraba

ALERT c Mudgeeraba

Creek 84.2 BOM - - - - Y Y Y Y Y Y Y

146801 Boobegan Creek Lock

ALERT

Boobegan Creek

120.9 BOM - - - - - Y Y Y Y Y Y


Station No

Station Name

Stream Name


Station Operator

Max. Gauged Height (m)

Max. Gauged Flow (m3/s)

Streamflow or Water Level Data Available

Jan 1974

Mar 1999

Jan 1999

Mar 2004

Nov 2004

Jun 2005

Jan 2008

May 2009

Jan 2013

540597 Worongary

Creek ALERTd

Worongary Creek

BOM - - - - - - - - - - Y

540453 Bonogin Creek

ALERTd

Bonogin Creek

BOM - - - - - - - - - - Y

asubmerged after construction of Hinze Dam Stage 2 brecorded before construction of Hinze Dam cused in the Mudgeeraba Creek catchment URBS modeld Worongary and Bonogin Ck ALERT stations were installed in 2008 and hence only recorded water level are available post-2008.


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Storage Data 5.6

5.6.1 Little Nerang Dam

Table 8 shows the adopted stage-storage-discharge relationship for Little Nerang Dam which was constructed in 1965. Note that the elevation data was interpolated from the rating curve for the discharges noted in the provided storage-discharge curve.

Table 8 Adopted Stage-Storage-Spillway Discharge Relationship, Little Nerang Dam

Stage (m above Spillway)

Storage (ML) Spillway Discharge (m3/s)

0.0 9200 0

1.2 9340 109

2.3 9473 307

3.5 9600 565

4.8 10336 891

5.4 10550 1071

7.5 11050 1712

5.6.2 Hinze Dam

Table 9 lists the Hinze Dam configuration for all Hinze Dam stages. Table 10 and Table 11 show the adopted stage-storage-discharge relationship for Hinze Dam, stage 2 and 3 respectively. Stage 1 of the dam was constructed in 1976, Stage 2 was completed in 1989 and Stage 3 was completed in 2011. Stage-storage and spillway discharge data for Hinze Dam was provided by SEQ Water.

Table 9 Hinze Dam Levels

Hinze Dam Stage Spillway (m AHD) Full Supply Volume (ML)

Dam Crest (m AHD)

1 64.6 42 315 -

2

82.2

(89.2 High Level Crest)

161 073 93.5

3

94.5

(100.3 High Level Crest)

310 730 108.5


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Table 10 Adopted Stage-Storage-Spillway Discharge Relationship, Hinze Dam Stage 2

Stage (m AHD) Storage (ML) Spillway Discharge (m3/s)

82.2 161073 0

84 179370 100

85 189976 200

86 200945 350

87 212297 540

88 224046 720

89 236209 930

90 248794 1200

91 264797 1600

92 275217 1960

93 289068 2520

94 303362 3040

95 318098 3510

96 333281 4120

97 348926 4710

98 365255 5360

99 381583 6030

100 398597 6740

101 416066 7331

102 433987 7975

103 452361 8619 Source: WRM 2010 Study (Ref 3)

Table 11 Adopted Stage-Storage-Spillway Discharge Relationship, Hinze Dam Stage 3


94.5 310730 0

95 318098 8

95.5 325690 21

96 333281 39

96.5 341104 61

97 348926 86

97.5 357090 114

98 365255 142

98.5 373419 175


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99 381583 210

99.5 390090 246

100 398597 285

100.5 407332 334

101 416066 429

101.5 425027 556

102 433987 708

102.5 443174 878

103 452361 1077

103.5 461777 1291

104 471193 1525

104.5 480839 1771

105 490484 2038

105.5 500359 2317

106 510233 2614

106.5 520341 2924

107 530449 3246

107.5 540792 3583

108 551135 3931

108.5 561717 4296

109 572299 4668

109.5 583123 5049

110 593947 5449

110.5 604971 5860

111 615996 6275

111.5 627302 6711

112 638609 7144

112.5 650160 7557

113 661711 7973

113.5 673507 8393

114 685303 8814

114.5 697346 9238

115 709388 9667

115.5 721678 10100

116 733968 10537

116.5 746506 10978

117 759044 11422


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117.5 771832 11870

118 784619 12322

118.5 797656 12776

119 810694 13234

119.5 823982 13694 Source: SEQ Water

It is worthwhile to note that during the construction of the Hinze Dam Stage 3, an interim rating curve was used in the 2008 WRM (Ref 3) and 2009 HDA (Ref 8) studies. A comparison of the interim and adopted rating curve is documented in the 2011 GCCC study (Ref 4). The final rating curve was provided by SEQWater.

Rating Curves 5.7

The rating curves are used in the hydrological modelling to convert recorded water levels to estimated/rated discharges. EHP supplied current and historical rating curves for the following key stations:

Nerang River at Whipbird (146011A)

Little Nerang Creek at 4.0Km (GS 146009A)

Nerang River at Glenhurst (Clearview) (146002B)

Mudgeeraba Creek at Mudgeeraba TM (Springbrook Road) (146020A).

Rating curves for all of the above gauging stations (except Little Nerang Creek at 4.0Km) were also available from BOM’s URBS model (Ref 15). BOM generally have modified the EHP (or DERM) rating curves for use in their URBS models. These modifications have been done during the matching of model predictions against recorded rated discharges for a number of historical events used for model calibrations.

For the other three key non-EHP stations in the catchment (Little Nerang Dam, Hinze Dam (outflows), and Mudgeeraba ALERT), BOM has developed rating curves from correlations between their URBS model predicted discharges and recorded peak flood heights.

Note that some BOM rating curve data was also available for Nerang River at Evandale and Carrara, and Boobegan Creek at Boobegan Creek Lock. However, the water levels at these stations are tidally influenced and therefore were not used for calibration.


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Figure 5 Location of EHP/DERM gauging stations


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5.7.1 Nerang River at Whipbird (146011A)

The available and adopted rating curves for Whipbird station are shown in Figure 6. The EHP/DERM rating curve for Whipbird is based on gauged data up to 205 m3/s (2.85 m gauge height). BOM has adopted a modified curve for this station which deviates significantly from the EHP curve for discharges greater than approximately 400 m3/s. The BOM curve has been adopted for this study because it produces more consistent results for the historical events modelled.

Figure 6 Available and Adopted Rating Curves, Nerang River at Whipbird (146011A)

5.7.2 Nerang River at Glenhurst (Clearview TM) (146002B)

The available and adopted rating curves for Glenhurst (Clearview) are shown in Figure 7. The EHP/DERM rating curve for Glenhurst (Clearview TM) is based on gauged data up to 904 m3/s (7.95 m gauge height). BOM modified the EHP curve slightly for discharges between 1000 m3/s and 1800 m3/s at this station. The BOM curve has been adopted for this study.


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Figure 7 Available and Adopted Rating Curves, Nerang River at Glenhurst (146002B)

5.7.3 Little Nerang Creek at 4.0Km (146009A)

The available and adopted rating curves for 4.0 km Little Nerang Creek are shown in Figure 8. The EHP/EHP rating curve used for this study is based on gauge data up to 8.2 m3/s (1.07 m gauge height) and has been extrapolated above this point. This rating curve is only used for calibration of the January 1974 event.


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Figure 8 Available and Adopted Rating Curve, Little Nerang Creek at 4.0Km (146009A)

5.7.4 Little Nerang Creek at Little Nerang Dam (146907)

The available and adopted rating curves for Little Nerang Dam are shown in Figure 9. No available EHP/EHP rating curve or gauging data were available for this study. The BOM rating curve has been used for this study.


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Figure 9 Available and Adopted Rating Curve, Little Nerang Creek at Little Nerang Dam (146907)

5.7.5 Nerang River at Hinze Dam ALERT (146906)

The BOM rating curve was adopted for Nerang River at Hinze Dam ALERT (which records outflows from Hinze Dam) and is shown in Figure 10. No rating curve or gauging data was available from EHP however; the stage discharge data is available from the 2004 Cardno study (Ref 24). The Cardno data was used as verification of the BOM rating curve.

The BOM rating curve has been used for this study for flood events prior to 2012. As discussed in Section 5.6.2 , Hinze Dam Stage 3 upgrade was completed at the end of 2011, with the upgraded spillway being overtop in the January 2013 flood event.

For flood events post 2012, the rating curve in Figure 11 (Hinze Dam Stage 3) should be used, which was obtained from SEQWater.


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Figure 10 Available and Adopted Rating Curve, Nerang River at Hinze Dam Stage 2 (146906)

Figure 11 Adopted Rating Curve, Nerang River at Hinze Dam Stage 3 (146906)


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5.7.6 Mudgeeraba Creek at Mudgeeraba TM (Springbrook Rd) (146020a)

The available and adopted rating curves for Springbrook Road are shown in Figure 12. The EHP/DERM rating curve is based on gauged data up to 107 m3/s (3.35 m gauge height), and is extrapolated above this point. Both EHP and BOM have adopted the same rating curve for this station and so this curve was adopted for this study as well.

Figure 12 Available and Adopted Rating Curves, Mudgeeraba Creek at Springbrook Rd (146020A)

5.7.7 Mudgeeraba Creek at Mudgeeraba ALERT (146912)

The adopted rating curve for Mudgeeraba ALERT is shown in Figure 13. As there is no EHP/DERM rating curve or gauging data available for this station, the BOM rating curve has been used for this study.


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Figure 13 Available and Adopted Rating Curve, Mudgeeraba Creek at Mudgeeraba Alert (146912)

5.7.8 Boobegan Creek Lock ALERT (146801)

Boobegan Creek Lock is located at Carrara and provides access and maintains the water level for Robina Lakes and Clear Island Waters to the tidally affected reaches of the Nerang River. No stage-storage or discharge curves were available for the lock and hence the lock is not incorporated into the URBS model.

5.7.9 Worongary Creek ALERT (540597)

This ALERT station is located at Worongary Creek, near Mudgeeraba Road. As this station is relatively new, no stage-storage or discharge curves were available for the lock and hence the lock is not incorporated into the URBS model.

5.7.1 Bonogin Creek ALERT (540453)

This ALERT station is located at Bonogin Creek, near Mudgeeraba Road. As this station is relatively new, no stage-storage or discharge curves were available for the lock and hence the lock is not incorporated into the URBS model.

Peak Annual Flow Data 5.8

The peak annual discharges recorded at the selected gauge sites were obtained from the EHP/DERM website which was used for Flood Frequency Analysis (refer Section 9). A summary of the available peak series data for each gauge is given in Table 12, noting the following:

Mudgeeraba Alert

0

1

2

3

4

5

6

7

0 200 400 600 800 1000 1200

Discharge (m^3/s)

Height (m

GH)

BOM Rating


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The annual data was assessed for water years (i.e. October – September).

Data used for the Clearview FFA was a combination of data from Nerang (146002a) and Glenhurst (146002b). The Nerang gauge was decommissioned in 1970 and the Glenhurst gauge began recording in 1967.

The analysis for the Clearview data was split into two periods: the period before and after the construction of Hinze Dam stage 1 (1975).

No recorded annual peak series data was available for Clearview for 1968.

Table 12 Summary of Annual Peak Series Data

Gauging Station Name

Gauging Station No

Stream Name Years Without Data

Years of Available Data

Clearview / Glenhurst) 146002A & B 1920 – 1975a,

Pre-Hinze Stage 1

1 55

Clearview / Glenhurst 146002B 1989b - 2005, Post-Hinze

Stage 2 0 17

Neranwood 146004A 1928 - 1961 0 34 aStage 1 of Hinze Dam was completed in 1976; bStage 2 of Hinze Dam was completed in 1989


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6. Model Development

Model Description 6.1

URBS is a networked (i.e. sub-catchment based) runoff-routing model that estimates flood hydrographs by routing rainfall excess through a module representing the catchment storage. In URBS, the storages are arranged to represent the drainage network of the catchment. The distributed nature of storage within the catchment is represented by a separate series of concentrated storages for the main stream and for major tributaries to provide a degree of physical realism. The storages in the model are generally non-linear, but linear storages can be used.

The model provides a number of options for conceptualising the rainfall-runoff process. Rainfall excess is first estimated from rainfall data using one of several available techniques (i.e. loss models) before it is applied to the runoff-routing component of the model to compute the surface runoff hydrograph. Baseflow, if significant, is estimated separately and added to the surface runoff hydrograph to provide the total catchment hydrograph. The model can easily incorporate the effects of land use change, construction of reservoirs, changes to channel characteristics and other changes in the catchment.

The model provides different options for runoff routing. The user is given the option of lumping the catchment runoff and channel flow components into a single routing component or modelling them as separate routing components. The latter option (i.e. the ‘Split’ model) was adopted for the Nerang River catchment.

In the Split model, the rainfall excess for each sub-catchment is first determined by subtracting losses from the rainfall hyetograph. The rainfall excess is then routed through a conceptual catchment storage to determine the local runoff hydrograph for the sub-catchment. The storage - discharge relationship for catchment routing is:

m

2

2

catch QU

FAS

)1(

)1(

Where:

β is the catchment lag parameter; A is the area of sub-catchment (km2); U is the fraction urbanisation of sub-catchment; F is the fraction of sub-catchment forested; m is the catchment non-linearity parameter; and Scatch is the catchment storage (m3 h/s). In the above equation, β is determined during model calibration and is a global parameter.

The local runoff hydrograph is then combined with runoff from the upstream sub-catchment and routed through a channel storage to obtain the outflow hydrograph for the sub-catchment. Channel routing is based on the non-linear Muskingum Model. The channel routing storage-discharge relationship is given by:


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ndu

c

chnl ))1((*

QxQxS

LnfS

Where:

α is the channel lag parameter f is the reach length factor; L is the length of reach (km); Sc is the channel slope (m/m); QU is the inflow at upstream end of reach (includes catchment inflow) (m3/s); Qd is the outflow at downstream end of the channel reach (m3/s); x is the Muskingum translation parameter; n is the Muskingum non-linearity parameter (exponent); n* is the Manning's 'n' or channel roughness; and Schnl is the channel storage (m3 h/s).

In the above equation, α and f are the principal calibration parameters. Note also that α is a global parameter, whereas f can be varied for each channel reach.

URBS allows the user to select one of several standard loss models. The available options are: initial and continuing loss model; proportional loss model; Manley-Phillips infiltration model; and water balance model. The initial and continuing loss model was adopted for the Nerang River catchment. This model assumes that there is an initial loss of ‘il’ mm before any rainfall becomes runoff. After this, a continuing loss rate of ‘cl’ mm per hour is applied to the rainfall, subject to the limit of the soil infiltration capacity (IFmax). The loss rates can be specified ‘globally’ to the entire catchment or ‘individually’ to each sub-catchment. Global loss values were adopted for the Nerang River catchment.

Full details of the URBS model and its features are given in the URBS User Manual (Ref 25).

Model Configuration 6.2

The Council’s previous Nerang River URBS model (Ref 6) and the additional WRM update (Ref 3) formed the backbone of the current model. The model parameters of the Nerang URBS model were configured similar to the other Gold Coast models with model configuration kept as simple as possible. The adopted catchment configuration for the URBS model is shown in Figure 14. The Nerang River URBS model includes the Mudgeeraba and Worongary catchments which were previously separated into their own individual catchments (Ref 19 and 20). It is of note that the Nerang URBS model has been configured based on current catchment land uses only.

In total, the Nerang Catchment model consists of 104 sub-catchments, including; 52 in Nerang, 33 in Worongary and 19 in Mudgeeraba. Table in Appendix A shows the adopted Nerang River sub-catchment areas and land uses, with the Nerang sub-catchment IDs from 1-52, Worongary sub-catchment IDs from 101-133 and the Mudgeeraba sub-catchment IDs from 201-219.

Little Nerang Dam is included in the model at sub-catchment 17 using details given in Section 5.6.1 Hinze Dam is included in the model in sub-catchments 11, 12, 13, 19, 20 and 21. The Hinze Dam


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wall is located at the upstream end of sub-catchment 22. The area inundated by the dam extends from sub-catchment 19 on Little Nerang Creek and sub-catchment 11 on Nerang River.

Figure 14 Nerang URBS Model Configuration

6.2.1 Adopted Land Uses

Table 13 shows the adopted five major land use categories for the purpose of URBS modelling and the corresponding City of Gold Coast land classifications.


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Of the five different land uses, four relate to the amount of urbanisation in the catchment, affecting both the percent imperviousness (losses) and the routing characteristics. The forested land use only affects the routing characteristics.

Forest effects on catchment routing within the URBS model are based on a study within Papua New Guinea on tropical forests (Ref 25). This study multiples the forest factor by 0.5 or halves the forested effect, to more realistically represent forest conditions seen in the South East Queensland Area (Ref 25).

Table 14 shows the sum of adopted land use breakdown for each of the URBS sub-models.

Table 13 Nerang River Catchment Land Use Categories

Nerang River

URBS Model Land Use Classification City of Gold Coast Classification

UF (Forested) Forest

Forest/Grassland

UR (Rural Land) Grassland - Urban/Suburban

Grazing

Open - Ground

Recreation (Facilities & Sub/Urban Parks)

Rural Residential

Tourism Recreation Park

Vacant Land

Waste Disposal

UH (High Density Urban)a Access - Restriction Strip

Commercial

Constructed Waterway - Lake

Industrial

Marina

Residential Choice

Tourism - Accommodation

Transport (Rail, Road & Paved Areas)

Utilities - Infrastructure

Water

Wetlands

UM (Medium Density Urban) Detached Dwelling

UL (Low Density Urban) Park Living

Tourism - Caravan Park

UL/UM/UHb Highly Disturbed - Under Development

Urban Residential a Roads are included in this category. b Appropriate classification selected based on aerial photos and site inspections.


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Table 14 Adopted Land Use Breakdown, Nerang River URBS model

Nerang River

Total Catchment Area (km2)

Urban Low Density (%)

Urban Medium Density (%)

Urban High Density (%)

Rural Land (%)

Forested (%)

492 1.75 6.93 14.78 35.29 41.25

Dam Routing 6.3

For design events, to ensure that the maximum flood extent was achieved, the dam was set as full within hydrologic model setups. This option is available in ‘u’ file where the parameter ‘Dam Route’ is prescribed. Below is the command used for the Hinze Dam stage 2 design runs;

DAM ROUTE VBF=0 FILE = HINZEST2.SQ

The volume below full supply (VBF) is the volume available in the storage which must be filled before any discharge will occur. The VBF parameter has been specified in the catchment file as a volume (in megalitres). VBF values were set to zero in design event ‘.u’ files, to set the dams (Little Nerang and Hinze Dam) as full. If there is no volume to be filled, then discharge occurs soon as water is routed through the dam. The “SQ” file refers to the storage discharge relationship described in section 5.6.2 .


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7. Model Calibration and Verification

Selection of Calibration and Verification Events 7.1

Calibration data from BOM for a total of 24 flood events between 1947 and 2013 were available. The available rainfall and stream flow data for early events are very limited and of poor quality. Therefore, the selected calibration and verification events are generally the most recent events, with the exception of the January 1974 event, which is the largest on record. The selected events are as follows:

January 1974 Calibration

March 2004 Calibration

November 2004 Calibration

June 2005 Calibration

January 2008 Calibration

March 1999 Verification

February 2001 Verification

May 2009 Verification

January 2013 Verification.

The selected events cover a wide range of discharges across the Nerang River catchment. Table 15 shows the recorded peak (rated) discharges for each event at each of the key gauging stations used for model calibration and verification.

The key stream gauging stations used for calibration of the Nerang River URBS model are listed below.

Little Nerang Creek at Little Nerang Dam (146907)

Little Nerang Creek at 4.0km (146009a)

Nerang River at Whipbird (146011a)

Nerang River at Hinze Dam (146906)

Nerang River at Clearview (146905/146002)

Mudgeeraba Creek at Mudgeeraba ALERT (146011a)


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Mudgeeraba Creek at Mudgeeraba TM (146020A)

Worongary Creek at Worongary Creek ALERT (540597).

The calibration emphasis was placed on the recorded data at the key gauge sites listed above. Due to a number of reasons, including lack of adequate upstream pluviograph data, rating curve quality concerns, tidally affected stations, missing or incorrect recorded data and insufficient number of upstream URBS sub-catchments, the remainder of the stream gauges listed in the following table were used only to achieve the general timing and shape of predicted hydrographs at the gauging stations.

Table 15 Recorded Peak Discharges for Calibration and Verification Events


Gauging Station No

Recorded Peak Discharge (m3/s)

Jan-74

Mar-99

Feb-01

Mar-04

Nov-04

Jun-05

Jan-08

May-09

Jan-13

Little Nerang 146907 - 80 - 129 - 112 513 74 395

Whipbird TM 146011a 718 - - - - - - - -

4.0km TM 146009a 403 - - - - - - - -

Hinze Dam 146906 - 31 114 0 0 0 12 114 194

Clearview 146905 1460 86 160 76 118 137 81 54 210

Carrara 146914 - - - 177 486 671 - 174 585

Mudgeeraba 146011a - - 149 230 192 - 494 168 494

MudgeerabaTM 146020A - - - 118 63 128 183 - 228

Boobegan 146801 - - - 492 484 690 540 324 876

Worongarya 540597 - - - - - - - - - b Only water level recording is available for Worongary Ck ALERT.

Calibration Methodology 7.2

The emphasis of the model calibration was to achieve the best possible fit between the predicted and recorded (or rated) discharge hydrographs at key stations along the main streams of the Nerang River catchment for the selected calibration events. For these stations, the calibrations attempted to match the predicted and recorded flood peaks and volumes, and also the shape of the hydrographs. The calibrated model was then verified by comparing the model predictions against the discharge hydrographs recorded at various gauging stations for the selected verification events.

Due to the lack of available rainfall data for most events and the lack of detailed rainfall data where data were available, the URBS model cannot be expected to accurately reproduce flood behaviour for all events and at all gauging stations. As such, calibration emphasis was placed more on large events (January 1974), as the accuracy of small events are impacted significantly by spatial and temporal variation in rainfall. A single set of model parameters was adopted for the model, and maintained for all calibration and verification events. The model parameters were adjusted to achieve the best calibration across all events, resulting in a compromise between model accuracy and model simplicity. It is noted that calibration of the model for individual events can be improved by adopting a different set of model parameters for each of the different events.


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Rainfall losses were adjusted to achieve the best possible hydrograph shapes and flood volumes. A uniform initial loss and continuing loss rate were adopted for each flood event. Again, it is noted, that calibration of the model for individual events can be improved by adopting variable initial and continuing losses across the catchment.

For the 1974 calibration event, Hinze Dam was not yet constructed and was excluded from the URBS model. For the January 2013 flood event, Hinze Dam stage 3 is included in the URBS model. For all other historical events Stage 2 of Hinze Dam (completed in 1989) was used within the URBS model.

Assignment of Total Rainfalls and Temporal Patterns 7.3

Rainfalls for each sub-catchment were generated from available pluviograph and daily rainfall station data using an inverse distance squared method based on the nearest 4 rainfall stations to the sub-catchment centroid.

For Daily Stations, the nearest available pluviograph temporal pattern was adopted. This method ensures that all of the available data are used, and that the rainfall pattern for the nearest pluviograph is assigned to the sub-catchment.

Adopted Model Parameters 7.4

The adopted model parameters for the Nerang model (including Mudgeeraba and Worongary) are shown in Table 16. The adopted model parameters were applied uniformly across the catchment, and were maintained for all calibration, verification, Monte Carlo and design events.


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Table 16 Adopted Catchment and Channel Parameter Values for the Nerang River Catchment

URBS Parameter Adopted Value

(Channel Lag Parameter) 0.1

(Catchment Lag Parameter) 1.5

m (Catchment non-linearity) 0.7

The parameters used within this study are within the typical range (Table 17) as outlined in the URBS user manual (Ref 25).

Table 17 URBS Parameter Ranges(Ref 25)

URBS Parameter Typical Range

(Channel Lag Parameter) 0.1 - 0.3

(Catchment Lag Parameter) 1 - 9

m (Catchment non-linearity) 0.6 - 1

Initial and Continuing Losses 7.5

Table 18 and Table 19 show the adopted initial loss and continuing loss rates for the calibration and verification events respectively. It is of note that losses across the Nerang catchment were adjusted to produce the best calibration, and as such the amount and quality of available rainfall data for each event will have some effect on the adopted initial and continuing losses.


Table 18 Adopted Initial and Continuing Losses (Calibration Events)

January 1974 March 2004 November 2004 June 2005 January 2008

Catchment Initial Loss (mm)

Continuing Loss (mm/hr)

Initial Loss (mm)


Initial Loss (mm)


Initial Loss (mm)


Initial Loss (mm)


Nerang 60 2.5 50 1.0 50 2.00 60 5.0 50 3.0

Table 19 Adopted Initial and Continuing Losses (Verification Events)

January 2013 March 1999 February 2001 May 2009

Catchment Initial Loss (mm)


Initial Loss (mm)


Initial Loss (mm)


Initial Loss (mm)


Nerang 75 5.0 20 2.5 50 2.50 50 2.0


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Initial Dam Water Levels 7.6

The recorded water levels in Hinze and Little Nerang dams for each calibration and validation event were used, if available, to estimate the URBS ‘volume before filled’ (VBF parameter) for each event. The estimated VBFs for each dam were then ‘fine-tuned’ to produce the best calibration downstream of the dam. For events where recorded dam levels were not available, the initial dam water levels were established by trial and error.

Calibration Results 7.7

7.7.1 General Calibration/Verification Overview

A good calibration was achieved throughout the Nerang River catchment, with the URBS model generally reproducing recorded flood discharges satisfactorily for all calibration events.

The model calibration is considered generally good, considering that a single set of global parameters were adopted. Gauges upstream of the Clearview gauge and Hinze Dam are well calibrated. The calibration results for gauging stations downstream of Clearview are uncertain because of the unavailability of well rated gauging stations. The gauges downstream of Clearview are affected by downstream water levels. In addition, the affects and operation of the Boobegan lock during the historical events is unknown to adequately calibrate the model to flows at this location.

More weighting was given to the 1974 historical flood event during calibration, as it was the largest recorded flood event experienced within the Gold Coast. The 1974 event produced a peak discharge at Clearview of 1460 m3/s (pre-Hinze Dam), with the next largest being the 2013 flood event (Hinze Dam stage 3) with 210 m3/s.

It is worthwhile to note that even though the 1974 event was given higher priority in the calibration process, the next largest and most recent flood event (Jan 2013) has a very good match between recorded and modelled discharges at the key gauging stations. This provides further confidence that the model is replicating current catchment conditions.


A comparison of recorded and modelled peak discharges at key gauging stations for the January 1974 event are shown in Table 20. The hydrograph at Clearview is displayed in Figure 15, with all other hydrographs at key gauging stations for the January 1974 event provided in Appendix E (Section 0).

Table 20 Recorded and Modelled Peak Discharges at Key Gauging Stations, January 1974 Flood Event

Peak Discharge


Gauging Station No

Stream Name Recorded (m3/s) Modelled (m3/s)

Whipbird TM 146011a Nerang River 717.5 745.58

4.0km (Nerang) 146009a Little Nerang

Creek 403.4 350.3


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Peak Discharge


Gauging Station No


Clearview 146905 Nerang River 1460.0 1478.90

Figure 15 Jan 1974 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the January 1974 verification:

The model calibration for this event is good, with the predicted hydrographs at Whipbird, Little Nerang Dam and Clearview gauges all reproducing recorded peak discharges, flood volumes and flood timing well.

There were no recorded or modelled discharges (outflows) from Hinze Dam for this event as the dam was constructed after this flood.

7.7.3 March 2004 Event

A comparison of recorded and modelled peak discharges at key gauging stations for the March 2004 event are shown in Table 21. The calibration hydrograph at Clearview is displayed in Figure 16, with all other key gauging stations for the March 2004 event provided in Appendix E (Section 0


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Table 21 Recorded and Modelled Peak Discharges at Key Gauging Stations (March 2004 Flood)

Peak Discharge


Gauging Station No


Little Nerang Dam ALERT

146907 Little Nerang

Creek 129.0 162.2

Hinze Dam ALERT 146906 Nerang River 0 0

Clearview ALERT 146905 Nerang River 75.8 46.5

Mudgeeraba TM 146020 Mudgeeraba

Creek 118.2 126.6

Mudgeeraba ALERT 146912 Mudgeeraba

Creek 230.0 274

Boobegan ALERT 146801 Boobegan

Creek 492.0 332.4

Figure 16 March 2004 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the March 2004 calibration:


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The calibration is reasonably good at the Little Nerang Dam gauge with respect to the timing and shape of the hydrograph; however the modelled peak discharge is a little higher than the recorded peak.

There were no recorded or modelled discharges (outflows) from Hinze Dam for this event as the dam was not spilling.

The calibration is good at the Clearview gauge with respect to the timing and shape of the hydrograph; however the modelled peak discharge is a little lower than the recorded peak. It is worthwhile to note that the recorded discharge is only 70 m3/s.

The calibration is reasonably good at the Mudgeeraba ALERT and Mudgeeraba TM gauge with respect to the peak discharge, timing and shape of the hydrograph.

7.7.4 November 2004 Event

A comparison of recorded and modelled peak discharges at key gauging stations for the November 2004 event are shown in Table 22. The calibration hydrograph for Clearview is shown in Figure 17, with all other calibration hydrographs at all key gauging stations for the November 2004 event provided in Appendix E (Section 0

Table 22 Recorded and Modelled Peak Discharges at Key Gauging Stations, November 2004 Flood Event

Peak Discharge


Gauging Station No




Creek 0 0

Hinze Dam ALERT 146906 Nerang River 0 0

Clearview ALERT 146905 Nerang River 118.1 182


Creek 63.4 148.3


Creek 192 376.2


Creek 484.0 414.9


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Figure 17 November 2004 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the November 2004 calibration:

There were no recorded or modelled discharges (outflows) from Little Nerang Dam for this event.

There were no recorded or modelled discharges (outflows) from Hinze Dam for this event.

The calibration is quite good at the Clearview, Mudgeeraba TM and Mudgeeraba ALERT station with respect to the timing and shape of the hydrograph. However, for all gauges, the modelled peak discharge is a little higher than the recorded.

7.7.5 June 2005

A comparison of recorded and modelled peak discharges at key gauging stations for the June 2005 event are shown in Table 23. The calibration hydrograph at Clearview is displayed in Figure 18, with all other key gauging stations for the June 2005 event provided in Appendix E (Section 0

Table 23 Recorded and Modelled Peak Discharges at Key Gauging Stations, June 2005 Flood Event

Peak Discharge


Gauging Station No


Little Nerang Dam Alert 146907 Little Nerang

Creek 112.0 200.5

Hinze Dam Alert 146906 Nerang River 0 0


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Peak Discharge


Gauging Station No


Clearview Alert 146905 Nerang River 137.2 173.4


Creek 127.6 307.6

Mudgeeraba Alert 146912 Mudgeeraba

Creek - 971.2


Creek 690.0 1036.8

Figure 18 June 2005 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the June 2005 calibration:

The calibration is reasonably good at the Little Nerang Dam gauge with respect to the timing and shape of the hydrograph, however the modelled peak discharge is a little higher than the recorded.

There were no recorded or modelled discharges (zero outflows from Hinze Dam for this event).


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The calibration is quite good at the Clearview and Mudgeeraba TM gauge with respect to the timing and shape of the hydrograph, however, for both gauges, the modelled peak discharge is a little higher than the recorded.

The Mudgeeraba ALERT gauge may have malfunctioned during this event, as erroneous data was recorded.


A comparison of recorded and modelled peak discharges at key gauging stations for the January 2008 event are shown in Table 24. The calibration hydrograph at Clearview is displayed in Figure 19, with all other key gauging stations for the January 2008 event provided in Appendix E (Section 0


Peak Discharge


Gauging Station No




Creek 513.4 430.4

Hinze Dam ALERT 146906 Nerang River 12.2 0



Creek 183.0 291


Creek 494.0 598.2


Creek 540.0 517.31


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Figure 19 June 2008 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the January 2008 calibration:

The calibration for this event is quite good at the Little Nerang Dam gauge with respect to the timing, shape and peak of the hydrograph..

The calibration for this event is reasonable at the Hinze Dam (outflow) gauge with respect to the peak discharge and shape of the hydrograph. It is of note that only very small outflows were recorded and modelled at this location for the event.

The calibration is quite good at the Clearview, Mudgeeraba TM and Mudgeeraba ALERT gauge with respect to the timing and shape of the hydrograph. However, for all gauges, the modelled peak discharge is a little higher than the recorded.

Verification Results 7.8

7.8.1 March 1999 Event

A comparison of recorded and modelled peak discharges at key gauging stations for the March 1999 event are shown in Table 25. The verification hydrograph at Clearview is displayed in Figure 20, with all other key gauging stations for the March 1999 event provided in Appendix E (Section 0


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Table 25 Recorded and Modelled Peak Discharges at Key Gauging Stations, March 1999 Flood Event

Peak Discharge


Gauging Station No




Creek 79.5 116




Creek - -


Creek - -


Creek - -

Figure 20 March 1999 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the March 1999 verification:


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The model verification is very good at the Little Nerang Dam gauge with respect to the peak discharge, timing and shape of the hydrograph; however, the modelled peak discharge is slightly higher than the recorded peak discharge.

The model verification is quite good for the Hinze Dam gauge with respect to the timing and shape of the hydrograph, except for the peak discharge. It is of note that only very small outflows were recorded and modelled at this location for the event.

The model verification for this event is good at the Clearview gauge with respect to the peak discharge, timing and shape of the hydrograph, except for the tail end of the falling limb.

There are no recordings at Mudgeeraba TM, Mudgeeraba ALERT and Boobegan ALERT.

7.8.2 February 2001 Event

A comparison of recorded and modelled peak discharges at key gauging stations for the February 2001 event are shown in Table 26. The verification hydrograph for Clearview is displayed in Figure 21, with all other key gauging stations for the February 2001 event provided in Appendix E (Section 0

Table 26 Recorded and Modelled Peak Discharges at Key Gauging Stations, February 2001 Flood Event

Peak Discharge


Gauging Station No




Creek 0 0




Creek - 198.3


Creek 148.6 434.1


Creek - 448.4


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Figure 21 February 2001 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the February 2001 verification:

There were no recorded or modelled discharges (outflows) from the Little Nerang Dam for this event.

The model verification for this event is not very good at the Hinze Dam gauge with respect to the shape of the hydrograph and peak discharge. It is of note that these are still low flows over the Dam wall.

The model verification is reasonable at the Clearview gauge with respect to the timing and shape of the hydrograph. The third peak is due to outflows from Hinze Dam. The poor matching of the shape of the recorded hydrograph associated with the third peak follows from the poor matching of the hydrograph shape at the Hinze Dam gauge. However, the difference is only about 60 m3/s.

There is no recording at Mudgeeraba TM.

The model verification is reasonable at the Mudgeeraba ALERT gauge with respect to timing and shape of the hydrograph, however the first modelled peak discharge is significantly higher than the recorded peak discharge.

7.8.3 May 2009 Event

A comparison of recorded and modelled peak discharges at key gauging stations for the May 2009 event are shown in Table 27. The verification hydrograph at Clearview is displayed in Figure 22, with all other key gauging stations for the May 2009 event provided in Appendix E (refer Section 0


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Table 27 Recorded and Modelled Peak Discharges at Key Gauging Stations, May 2009 Flood Event

Peak Discharge


Gauging Station No




Creek 74.0 80.7

Hinze Dam ALERT 146906 Nerang River 114 54.2



Creek - 79.7


Creek 168.0 175.5


Creek 324.0 180.4

Figure 22 May 2009 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the May 2009 verification:


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The model verification is good at the Little Nerang Dam gauge with respect to the timing, shape and peak discharge.

The recorded hydrographs at the Hinze Dam and Clearview gauges for this event are reasonably matched with the predicted hydrographs with respect to the shape and timing, however, the predicted peak discharge is lower than the recorded value at the Hinze Dam but higher than the recorded value at Clearview peak. It appears that the recorded peak discharges at the Hinze Dam and Clearview are not consistent with each other. One possible reason for this inconsistency is the Hinze Dam Stage 3 upgrade works may have affected the recordings or dam outflow rating curve during this event. It is unlikely that the recorded peak discharge at the Dam would be significantly higher than the recorded peak discharge at Clearview.

No recordings available at the Mudgeeraba TM station.

The model verification is reasonable at the Mudgeeraba ALERT gauge with respect to the general shape of the hydrograph and the peak discharge, however, the modelled hydrograph predicts an initial small peak which is not recorded and timing of the peak did not match. This could be due to the adopted initial loss being too low and/or recorded rainfall being unrepresentative of the initial rainfall burst for the Mudgeeraba catchment.


A comparison of recorded and modelled peak discharges at key gauging stations for the January 2013 event are shown in Table 28. The verification hydrograph at Clearview is displayed in Figure 23, with all other key gauging stations for the January event provided in Appendix E.9.


Peak Discharge


Gauging Station No




Creek 395.4 326.8

Hinze Dam ALERT 146906 Nerang River 193.9 185.6



Creek 227.9 269.2


Creek 494.0 516.2


Creek 876.0 611.2


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Peak Discharge


Gauging Station No


Worongary ALERT* 540597 Worongary

Creek 3.7 m -

* Only water level is available for this station (i.e. No rating curves)

Figure 23 January 2013 Modelled (C) and Recorded (R) Flows at Clearview (146905)

The following is of note with regards to the January 2013 verification:

The model verification is good at the Little Nerang Dam gauge with respect to peak discharges, the timing and shape of the hydrograph.

The model verification is very good at the Hinze Dam, Clearview, Mudgeeraba TM and Mudgeeraba ALERT gauge with respect to peak discharge, shape and timing of the hydrograph.

The calibration to the recorded water level at Worongary Creek ALERT is only being undertaken in the hydraulic study (Ref 40).


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8. Design Flood Estimation

Methodology 8.1

The calibrated URBS model was used to estimate design flood discharges throughout the Nerang River catchment based on design rainfall intensity – frequency – duration (IFD) data. The model is then used to estimate the design flood discharge hydrographs for a range of storm durations up to the 120 hour event for the 2, 5, 10, 20, 50, 100, 200, 500, 2000 year ARI events, and up to the 120 hour event for the Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) events for both Stage 2 and Stage 3 of Hinze Dam.

A comprehensive review of available design rainfall data and associated procedures to determine the recommended methodology of the design rainfall inputs (IFD data, temporal patterns, areal reduction factors, rainfall spatial distribution and design rainfall losses) was undertaken in 2008 (Ref 28) for the City of Gold Coast.

A number of minor modifications (Ref 9) were made to the 2008 (Ref 28) recommended methodology for which Table 29 summarises the adopted methodology for this study. The most notable modifications were made to the IFD and temporal pattern sources.

The update analysis revealed some anomalies that arose in the design estimates for ARI’s greater than 100 years. The reason for these anomalies was due to the abrupt change in IFD and temporal pattern source between ARIs and storm durations. These anomalies were removed through the interpolation of intensities and temporal patterns (Figure 24). Table 30 and Table 31 illustrate the adopted IFD and temporal pattern sources employed for this study, with the previous layout displayed in Appendix H.

Figure 24 Anomalies for events > 100 year ARI @ Clearview, Hinze Dam Stage 2 (Ref 9)


Table 29 Summary of Recommended Methodology for Design Event Analysis

Design Flood Parameter

ARI Range (Years)

Available Sources/Methods Comment Recommendation

Rainfall depth

≤ 100

ARR 1987 (Ref 11) Industry standard approach. Not Recommended (Rainfall data till 1986)

AWE 1998 a (Ref 1) or

AWE 1992 (Ref 29)

Uses same methodology as ARR 1987 with additional data. AWE 1998 is recommended for Gold Coast catchments.

AWE 1992 is recommended for Logan River catchment.

Both methods use standard methodology with a longer period of recorded data.

Refer Table 30.Error! Reference source not found.

CRCFORGE (Ref 30) Based on analysis of daily data.

Adopted for Hinze Dam hydrology for events from 10 to 2000

year ARI (Ref 8).

Recommended for storm durations ≥ 96 hours.

Refer Table 30

For Nerang and Logan only.

BOM Pilot Study (Ref 31) Data was provided by BoM for investigation of Hinze Dam hydrology, but it is no longer available.

Not Recommended

BOM 2013 New draft IFD was released by BOM in July 2013. The final IFD is expected to be released in 2015.

Not Recommended (Not finalised)

> 100 to 500

ARR 1987 Industry standard approach. Not Recommended

AWE 1998 a (Ref 1) or

AWE 1992 (Ref 29)

Uses same methodology as ARR 1987 with additional data. AWE 1998 is recommended for Gold Coast catchments.

AWE 1992 is recommended for Logan River catchment.

Refer Table 30

CRCFORGE(Ref 30) Based on analysis of daily data.


year ARI (Ref 8).


Refer Table 30 Error! Reference source not found. For Nerang and Logan only.

> 500 to



year ARI (Ref 8).


Refer Table 30



ARI Range (Years)


<2000 Interpolate between ARI 500 (AWE) and ARI 2000 (CRCFORGE)

Creates a smoother transition between rainfall sources. Recommended for all storm durations, excluding storm durations ≥ 96 hours.

Refer Table 30.

2000


Adopted for Hinze Dam hydrology for events from 10 to 2000 year ARI (Ref 8).

Recommended.

Linearly interpolate where CRCFORGE does not have any IFD data.

Refer Table 30.

2,000 to < PMP

Interpolate between CRCFORGE & PMP methods.

No explicit methodology is available to estimate rainfall depths for events of this magnitude.

Section 3.6.3 of ARR 1999 provides a methodology for interpolation (Ref 12).

Recommended.

PMP

GSDM (≤ 6 hours)

GTSMR (≥ 24 hours)

Industry standard approach.

Linearly Interpolated for durations between 6 and 24 hours.

Recommended.

ReferError! Reference source not found. Table 30.

Areal Reduction Factors

≤2000

ARR 1987 Based on United States data. Not Recommended

CRC ARF (Ref 30 and Ref 32) Derived from regional data for durations ≥ 24 hours. Recommended.

Adopt 24 hour duration ARFs for durations less than 24 hours.

Verify using flood frequency analysis where possible.

>2000 < PMP

Interpolate between CRCFORGE & PMP methods (Ref 30 and Ref 12).

Interpolate as recommended by ARR 1999 Section 3.6 using CRCFORGE and PMP rainfalls which are already factored for catchment area.

Recommended.

PMP GSDM

GTSMR

Industry standard approach. Recommended.

Temporal Pattern

≤ 100

ARR 1987 Industry standard approach. Not Recommended.

AWE 2000 Uses same methodology as ARR 1987 with additional data. Alternative patterns derived for ARI > 30 years (but only recommended for sensitivity analysis).

Not Recommended.

UWS 2006 Uses same methodology as ARR 1987 & AWE 2000 with additional Not Recommended.



ARI Range (Years)


data.

WRM v7 (Ref 35) AWE 2000 patterns have been filtered by WRM to eliminate sub-duration inconsistencies.

Recommended.

Use filtered AWE 2000 patterns for storm durations ≤ 72 hours. (Ref 10).

Refer Table 31.

GTSMR (≥ 96 hours) Industry standard approach. Recommended for storm durations ≥ 96 hours.

Refer Table 31.

> 100 to < PMP

GSDM (≤ 6 hours)

GTSMR (≥ 24 hours)

PMP temporal patterns are recommended by ARR 1999 for this range of event magnitudes (Ref 12).

GTSMR Recommended for storm durations ≥ 96 hours.

Refer Table 31.

Interpolate between ARI 100 (WRM v7) and PMP (GSDM & GTSMR)

Creates a smoother transition between temporal pattern sources.

Recommended.

Refer Table 31.

PMP GSDM (≤ 6 hours)

GTSMR (≥24 hours)

Industry standard approach. Recommended.

Refer Table 31.

Spatial Distribution

≤ 500

AWE 1998 a (Ref 1) Estimate design rainfall at the centroid of each model sub-catchment and apply ARF based on whole catchment, as recommended in ARR 1987 (Ref 11).

Recommended.

2000 CRCFORGE Estimate CRCFORGE rainfall at the centroid of each model sub-catchment.

Recommended.

> 2,000 to PMP

GSDM (≤ 6 hours)

GTSMR (> 6 hours)

Adopt PMP spatial distribution for events greater than 2000 year ARI as recommended by ARR 1999 (Ref 12).

Recommended.

≤ 100

ARR 1987 (Ref 11) Very little Queensland data used in recommended loss values for Queensland.

Suggests Initial losses in the range 15-35mm and a continuing loss rate of 2.5mm/hr.

Recommends adoption of median values from catchment-specific

Not Recommended.



ARI Range (Years)


Rainfall Losses

model calibration.

Ilahee 2005 (Ref 27) Comprehensive study based on data for 48 Queensland catchments.

Estimated the median initial and continuing loss rates for eastern Queensland catchment to be 38mm and 1.52mm/hr respectively.

Not Recommended.

Adjust losses to align peak design discharges with the Flood Frequency Analysis (FFA).

Initial and continuing losses should decline with increasing ARI

Recommended.

> 100 to < PMP

ARR 1999 (Ref 12) Interpolate losses between 100 year ARI and PMP Design Flood using approach recommended by ARR 1999.

Not Recommended.

Assign same losses as 100 year ARI

Rainfall losses were applied based on aligning design discharges with Flood Frequency Analysis for events below 100 year ARI and therefore similar losses were maintained for large and extreme flood events.

Recommended

PMP ARR 1999 (Ref 12) Adopt minimum values from catchment-specific model calibration, as recommended by ARR 1999.

Recommended.

a Includes IEAust 1987 Skewness


Table 30 Adopted Rainfall Depth (IFD) Source for the Nerang Catchment

Storm Duration

(hour)

ARI (Years)

1 2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GSDM

1 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GSDM

1.5 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT GSDM




9 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT INT

12 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC INT

18 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC INT

24 INT AWE AWE AWE AWE AWE AWE AWE AWE INT CRC GTSMR

36 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT GTSMR



96* INT INT CRC CRC CRC CRC CRC CRC CRC CRC CRC GTSMR

120* INT INT CRC CRC CRC CRC CRC CRC CRC CRC CRC GTSMR

INT denotes Interpolated

AWE denotes AWE (Ref 1)

CRC denotes CRC Forge (Ref 31)

* denotes Nerang and Logan River Catchment only


Table 31 Adopted Temporal Pattern Source for the Nerang Catchment

INT denotes Interpolated

GSDM denotes Generalised Short Duration Method (Ref 34)

GTSMR denotes Generalised Tropical Storm Method (Ref 33)

* denotes Nerang and Logan River Catchments only

Storm Duration

(hour)

ARI (Years)

1 2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GSDM

1 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GSDM





9 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT INT



24 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 INT INT INT INT GTSMR




96* GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR

120* GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR


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Rainfall Depth Estimation 8.2

The adopted design rainfall depths for the Nerang River catchment is summarised in Table 30.

8.2.1 Frequent to Large Design Events (up to and including 100 years ARI flood)

Design rainfall intensities for storms of varying durations (up to 120 hours) for all ARI’s up to and including the 100 Year ARI event were determined at the centroid of each model sub-catchment using City of Gold Coast’s Intensity Frequency Duration utility program (Ref 36 and Ref 39). The rainfall intensities for each duration and ARI were then converted to rainfall depths.

For durations up to, and including the 72 hours, the rainfall depth is derived from the AWE 98 study (Ref 1), for durations above 72 hours up to 120 hours the rainfall depth is derived from the CRCForge method (Ref 30).

The AWE IFD calculation parameters were originally based on the 1998 ‘Review of Gold Coast Rainfall Data’ (Ref 1). The AWE study produced a revised set of design rainfall intensity maps and F2 and F50 factor maps for the GCCC area. These maps replaced Maps 1.5, 6.5 and Map 8 and 9, Volume 2 of 1999 AR&R (Ref 12) for the Gold Coast area.

Other than the hyetograph changes, the 1998 AWE (Ref 1) study adopted a zero skew coefficient for Gold Coast catchments. During this study, the skew coefficient was reintroduced as per section 1, book II volume 1 of 1999 AR&R (Ref 12).

8.2.2 Rare to Extreme Design Events (200 to 2000 year ARI flood)

Design rainfall depths for the 200, 500, 1000 and 2000 Year ARI events were estimated as follows:

Design rainfall depths for durations between 10 minutes and 72 hours for the 200 and 500 Year ARI events were estimated at the centroids of each subcatchment using the AWE Study (Ref 1).

Design rainfall depths for durations from 96 hours to 120 hours for the 200 and 500 year ARI events were estimated at the centroids of each subcatchment using the CRCForge application (Ref 30).

Design rainfall depths for all durations for the 2000 Year ARI event was estimated at each centroid using the CRCForge (Ref 30) rainfall application.

Design rainfall depths for all durations for the 1000 Year ARI event was estimated at each centroid by interpolating between the 500 year ARI (AWE (Ref 1)) and 2000 year ARI (CRCForge data, (Ref 30)).

The adopted design rainfall depths for the Nerang River catchment is summarised in Table 30.


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8.2.3 Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) Design

Events

PMP rainfall depths for durations from 24 hours to 120 hours were estimated using the standard methodology given in the Generalised Tropical Storm Method (GTSMR) – Revised Edition (Ref 33), based on the total catchment area of the Nerang River. The Topographic Adjustment Factor at the centroid of each model sub-catchment was used to obtain the individual sub-catchment PMP estimates from the overall catchment PMP estimate.

PMP rainfall depth estimates for shorter durations were obtained using the methodology given in The Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method (GSDM) for durations from 30 minutes to 6 hours (Ref 34). For 9, 12 and 18 hours, the rainfall is linearly interpolated between 6 and 24 hours.

PMP estimation for the Nerang River catchment is presented in Appendix D (Refer Section 0).

For PMF, the individual estimates for each duration of the PMF were derived using PMP rainfall depth.

It is worthwhile to point out that the notional AEP of the estimated PMP design flood is estimated as 1 in 2,000,000 years (Ref 33).

Probable Maximum Flood note:

In order to define the Probable Maximum Flood, it is first necessary to introduce and distinguish two concepts (Ref 8):

• Probable Maximum Flood (PMF) – the limiting value of flood that can be reasonably expected to occur.

• Probable Maximum Precipitation Design Flood (PMPDF) – the flood derived from the PMP under ‘AEP neutral’ assumptions; that is, under assumptions that aim to ensure that the AEP of the flood is the same as the rainfall that caused it.

Temporal Patterns 8.3

Table 31 shows the adopted temporal pattern sources for the Nerang River catchment.


Temporal patterns for design storm events for durations from 30 minutes to 72 hours for design events up to, and including, 100 Years ARI were adopted from filtered 1998 AWE Temporal Patterns as outlined in WRM report (Ref 35).

For 96 to 120 hour durations, the temporal pattern is sourced from the CRCForge study (Ref 30).


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Temporal patterns for the 200, 500, 1000 and 2000 Year ARI design storms for durations from 30 minutes to 72 hours were linearly interpolated between the 100 year ARI temporal pattern and the PMP temporal pattern.

For 96 to 120 hour durations, the temporal pattern is sourced from the CRCForge study (Ref 30).


Events

Temporal patterns for the PMP design storms were obtained as follows:

Temporal patterns for the PMP event for durations from 24 hours to 120 hours were obtained from the Coastal AVM storms from the Generalised Tropical Storm Method (GTSMR) – Revised Edition (Ref 33).

The temporal pattern for PMP event durations between 30 minutes and 6 hours was obtained from The Estimation of Probable Maximum Precipitation in Australia: Generalised Short Duration Method (GSDM) (Ref 34).

For 9, 12 and 18 hours, the rainfall is linearly interpolated between 6 and 24 hours.

Temporal patterns for the PMF design storms were obtained as follows:

For each duration, individual estimates of the PMF were derived using temporal pattern from the top 10 individual storm temporal patterns from the GTSMR, as shown in the following table

Table 32 10 Historical Storm Temporal Patterns used for PMF

24 hours 36 hours 48 hours 72 hours 96 hours 120 hours

PMP01 1893FEB03-1 1893FEB03-2 1893FEB03-2

PMP02 1898APR03-2 1898APR03-2

PMP03 1989MAR14-1

PMP04 1918JAN24-3 1918JAN24-3 1918JAN24-3 1918JAN25-5 1918JAN25-5

PMP05 1954FEB21-1 1954FEB21-2

PMP06 1955FEB25-2 1955FEB25-2

PMP07 1956JAN22-2

PMP08 1963APR16-4 1963APR16-4

PMP09 1970JAN19-1

PMP10 1972JAN12-5 1972JAN12-5 1972JAN12-5 1972JAN12-5

PMP11 1974JAN09-3

PMP12 1974JAN23-6 1974JAN23-6 1974JAN23-6


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24 hours 36 hours 48 hours 72 hours 96 hours 120 hours

PMP13 1974JAN27-2 1974JAN27-2 1974JAN27-2 1974JAN28-4 1974JAN28-4 1974JAN27-9

PMP14 1974MAR13-4 1974MAR13-4 1974MAR13-4

PMP15 1975FEB25-6 1975FEB25-6

PMP16 1975DEC10-2

PMP17 1979JAN06-4 1979JAN06-4 1979JAN06-4 1979JAN06-4 1979JAN06-5

PMP18 1981JAN13-7 1981JAN13-7

PMP19 1982JAN22-2

PMP20 1989MAR14-2 1991JAN01-7 1991JAN01-7

PMP21 1995FEB28-4 1995FEB28-4

PMP22 1997MAR06-7 1997MAR06-7

PMP23 1998JAN29-4

PMP24 1998MAR05-7 1998MAR05-7 1998MAR05-7

PMP25 1998DEC10-2

PMP26 1999FEB13-2

Appendix C (refer Section 0) shows the adopted temporal patterns used for all ARI’s up to, and including, the 100 year and the GSDM and GTSMR temporal patterns for all durations.


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Areal Reduction Factors 8.4


The point design rainfall estimates at the centroids of each sub-area of the Nerang River catchment were converted to values for the complete sub-area using areal reduction factors (ARFs). The Queensland Extreme Rainfall Estimation Project (Ref 30) developed the following relationship between ARF, catchment area and storm duration for Queensland catchments:

ARF = 1 – 0.226 x (Area 0.1685 – 0.8306 x log(Duration)) x Duration -0.3994

Where ARF = Aerial Reduction Factor; Area = Catchment Area in km2; and Duration = Storm Duration in Hours

A review of the ARF, as part of the AR&R review project, also uses a similar equation (Ref 32).

Table 33 shows the adopted ARFs for design rainfalls for all durations and design events. ARFs are calculated based on the total Nerang River catchment area for 24, 30, 36, 48 and 72 hour storm durations which were applied to design rainfall depths for all ARI’s for the estimation of design discharges for the lower Nerang River. The 24 hour ARF was applied for all durations shorter than 24 hours, as recommended in Table 29.

It is noted, however, to reconcile the URBS model design event results with FFA discharge estimates, it was necessary to revise the approach to assigning ARFs. ARFs calculated based on the specific catchment area to both the Clearview and Neranwood gauges were used for design rainfalls used in the URBS design discharge estimates for reconciliation with FFA results at the two gauges. The 24 hour ARF was also applied for all durations less than 24 hours.

Table 33 Adopted Areal Reduction Factors

Areal Reduction Factor for Varying Storm Durations

Catchment to Area (km 2)

24 hrs or less

36 hr 48 hr 72 hr 96 hr 120 hr

Entire Nerang River Catchment

492 0.89 0.92 0.93 0.95 0.96 0.96

Clearview Gauge 250 0.91 0.93 0.95 0.96 0.97 0.97

Neranwood Gauge 40 0.95 0.97 0.98 0.99 0.99 1


Areal reduction factors were applied to the 200, 500 and 2000 Year ARI design rainfalls as shown in Table 33.


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Events

Areal reduction factors are already incorporated in the BOM’s PMP rainfall estimation methodology (Ref 33 and 34), and as such, no ARFs were applied to the rainfalls estimated for the catchment using this method.

Rainfall Losses 8.5


The initial loss (IL) / continuing loss (CL) method of accounting for rainfall losses was adopted for this study. The URBS model design event ILs and CLs were adjusted to align the design output discharges with the Flood Frequency Analysis (FFA) discharges. Table 34 shows the final ILs and CLs for the Nerang River catchment for all ARIs up to, and including, the 100 year ARI event.

Table 34 Adopted Initial and Continuing Loss Values, 2 year to 100 year ARI Events

ARI (Year)

Initial Loss (mm)

Continuing Loss

(mm/hr)

2 80 4 5 60 2

10 40 1 20 20 0.5 50 10 0.1

100 0 0.1


Table 29 gives the recommended procedure for estimating rainfall losses for the 200, 500, 1000 and 2000 Year ARI events. The adopted IL and CL rates for the 200, 500, 1000 and 2000 Year ARI events are given in Table 35. Due to the 0.0mm IL adopted for the 100 Year ARI event, it was considered acceptable (and consistent) to adopt a 0.0mm IL for all events greater than 100 Years ARI, up to the PMP and PMF events. For similar reasons, the adopted CL rate of 0.1mm/hour for the 100 Year ARI event was also adopted for all events greater than 100 Years ARI.

Table 35 Adopted Initial Losses and Continuing Loss Rates, 200, 500, 1000 and 2000 Year ARI Events

ARI (Year) Adopted Initial Loss (mm) Adopted Continuing Loss

Loss (mm/hr)

200 0.0 0.1

500 0.0 0.1

1000 0.0 0.1

2000 0.0 0.1


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Events

Table 29 gives the recommended procedure for estimating rainfall losses for the PMP and PMF events. The adopted ILs and CL rates for the PMP and PMF events are given in Table 36. Due to the 0.0mm IL adopted for the 100 Year ARI event (Refer Section 8.2.5) it was considered acceptable (and consistent) to adopt a 0.0mm IL for all events greater than 100 Years ARI, up to the PMP and PMF events. For similar reasons, the adopted CL rate given in Section 8.2.5 of 0.1mm/hour for the 100 Year ARI event was also adopted for all events greater than 100 Years ARI.

Table 36 Adopted Initial Losses and Continuing Loss Rates, PMP and PMF Events

ARI (Year) Adopted Initial Loss (mm) Adopted Continuing Loss

Loss (mm/hr)

PMP & PMF 0.0 0.1

Spatial Distribution 8.6


As mentioned in Table 29, the spatial distribution is estimates of AWE rainfall at the centroid of each model sub-catchment whilst applying ARF based on the whole catchment, as recommended in ARR 1987 (Ref 11).


The spatial distribution is estimates of rainfall (AWE and CRCForge) at the centroid of each model sub-catchment (Table 29).


Events

Spatial distribution of rainfall is accounted for in the Generalised Tropical Storm Method – Revised Edition rainfall depth estimation methodology (Ref 33).

Initial Water Level for Dams 8.7

The 2007 HDA study analysed recorded and synthetically generated Hinze Dam monthly storage data and daily rainfall data to assess the correlation between the magnitude of the dam inflows and the initial reservoir level (Ref 8). These analyses showed that:

Based on a limited (16 year) data set, there does not appear to be any relationship between dam inflows and initial reservoir levels for more frequent events (up to 10 year ARI).

There is no evidence for the antecedent rainfall (and hence initial reservoir level) to increase with increasing severity of storm events. It is noted, however, the impact of the initial reservoir level on peak outflows from the dam becomes less significant for more extreme events.


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A conservative approach to the assumption regarding the initial water levels in dams was undertaken in this study. Hinze and Little Nerang Dams were assumed to be full at the commencement of design storm events for all storm durations and ARIs. Accordingly, the URBS ‘VBF’ parameter was set to zero for all design event runs.

Modelled Design Discharges for Hinze Dam Stage 2 8.8

The following subsections summarise the modelled design events for Hinze Dam Stage 2 scenario.


Table 37 and Table 38 show the URBS model predicted design peak discharges and critical storm durations for the 2, 5, 10, 20, 50 and 100 Year ARI events at key locations throughout the Nerang River catchment for Hinze Dam Stage 2. Design event hydrographs (for the critical storm duration) at key gauging locations are given in Appendix E (Section 0).

It is worthwhile to note that the design discharges shown in Table 37 are based on total catchment ARF values. Therefore, upper catchment design discharges would be higher than the values shown if ARFs appropriate to upper catchment locations are used (for FFA reconciliation).

Table 37 Nerang River URBS Model (Hinze Dam Stage 2) Design Discharges, 2 year to 100 year ARI Events


Stream Name

Peak URBS Model Design Discharge (m3/s)

2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Whipbird Nerang River

221.9 499.7 668.0 919.3 1165.7 1362.0

Little Nerang Dam (Outflow)

Little Nerang Creek 97.1 180.8 254.8 336.9 422.9 493.1

4.0km Little Nerang Creek

120.7 243.8 342.1 457.4 575.6 669.0

Hinze Dam Inflow

Nerang River

378.2 836.5 1119.0 1529.9 1941.0 2263.1

Hinze Dam (Outflow)

Nerang River

124.5 221.2 389.0 582.4 797.6 964.1

Clearview Nerang River

134.4 237.1 419.5 625.0 866.2 1045.4

Carrara Nerang River

145.5 256.5 450.9 673.2 929.0 1117.6

Mudgeeraba TM

Mudgeeraba Creek

80.5 165.9 238.3 313.6 382.9 438.8


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Stream Name


2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Mudgeeraba Mudgeeraba Creek

167.4 349.6 510.0 673.2 818.9 934.8

Boobegan Creek Lock

Boobegan Creek

198.4 433.8 597.7 798.9 982.7 1120.7

Worongary (Sub 27)

Worongary Creek

31.2 81.0 118.0 158.4 199 252.1

Broadwater (Nerang River Mouth)

Nerang River

364.9 790.3 1055.8 1368.0 1799.4 2111.5

Table 38 Nerang River URBS Model (Hinze Dam Stage 2) Critical Storm Durations, 2 year to 100 year ARI Events


Stream Name

URBS Critical Storm Durations (hours)

2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Whipbird Nerang River 72 72 12 12 9 9

Little Nerang Dam

Little Nerang Creek 72 48 12 12 9 9

4.0km Little Nerang Creek 72 48 12 12 9 9

Hinze Dam Inflow

Nerang River 72 72 12 12 9 9

Hinze Dam (Outflow)

Nerang River 120 48 48 72 48 48

Clearview Nerang River 120 48 48 48 48 48

Carrara Nerang River 120 48 48 48 48 48

Mudgeeraba TM

Mudgeerba Creek 72 12 9 9 9 9


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Stream Name


2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Mudgeeraba Mudgeeraba Creek 72 12 9 9 9 9

Boobegan Creek Lock

Boobegan Creek 36 24 9 9 9 9

Worongary (Sub 27)

Worongary Creek

48 9 4.5 4.5 1.5 1


Nerang River

36 36 36 36 36 36


Table 39 and Table 40 show the URBS model predicted design peak discharges and critical storm durations for the 200, 500, 1000 and 2000 Year ARI events at key locations throughout the Nerang River catchment for Hinze Dam Stage 2. Design event hydrographs (for the critical storm duration) at key gauging locations are given in Appendix E (Section 0).


Table 39 Nerang River URBS Model (Hinze Dam Stage 2) Design Discharges, 200, 500, 1000 and 2000 year ARI Events


Stream Name


200 year ARI 500 year ARI 1000 year ARI 2000 year ARI

Whipbird Nerang River 1541.5 1782.8 1857.4 1995.1

Little Nerang Dam

(Outflow)

Little Nerang Creek 556.2 622.8 634.8 672.5

4.0km Little Nerang Creek 754.1 844.0 869.6 940.8

Hinze Dam Inflow

Nerang River 2547.6 2917.3 3041.4 3314.9


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Stream Name



Hinze Dam (Outflow)

Nerang River 1141.8 1429.8 1546.6 1666.4

Clearview Nerang River 1236.0 1540.0 1671.9 1807.4

Carrara Nerang River 1316.7 1627.7 1785.7 1964.9

Mudgeeraba TM

Mudgeeraba Creek 489.0 554.4 626.2 740.3

Mudgeeraba Mudgeeraba Creek 1040.5 1189.8 1370.3 1624.7

Boobegan Creek Lock

Boobegan Creek 1240.4 1401.9 1537.5 1737.5

Worongary (Sub 27)

Worongary Creek

278.8 314.7 416.1 550.4


Nerang River

2407.5 2827.1 3181.2 3599.4

Table 40 Nerang River URBS Model (Hinze Dam Stage 2) Critical Storm Durations, 200, 500, 1000 and 2000 year ARI Events


Stream Name

URBS Critical Storm Duration (hours)


Whipbird Nerang River 9 9 9 4.5

Little Nerang Dam

(Outflow)

Little Nerang Creek 9 9 9 3

4.0km Little Nerang Creek 9 9 9 4.5

Hinze Dam Inflow

Nerang River 9 9 9 4.5


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Stream Name



Hinze Dam (Outflow)

Nerang River 48 48 48 48

Clearview Nerang River 48 48 48 48

Carrara Nerang River 48 48 48 48

Mudgeeraba TM

Mudgeeraba Creek 9 9 3 3

Mudgeeraba Mudgeeraba Creek 9 6 3 3

Boobegan Creek Lock

Boobegan Creek 9 9 6 6

Worongary (Sub 27)

Worongary Creek

1 1 1 1

Broadwater (Nerang

River Mouth)

Nerang River 36 36 36 36


Events

Table 41 and Table 42 show the URBS model predicted peak PMP Design Flood (PMPDF) and PMF discharges and critical durations at key locations throughout the Nerang River catchment for Hinze Dam Stage 2 respectively. PMP and PMF event hydrographs at key gauging locations are given in Appendix E (Section 0).

It is worthwhile to note that the PMF events were only run for the 24, 36, 48, 72, 96 and 120 hour durations.


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Table 41 Nerang River URBS Model (Hinze Dam Stage 2) Discharges and Critical Durations, PMPDF Event


Stream Name


PMPDF (mᶟ/s) PMPDF Critical Storm Duration

(hours)

Whipbird Nerang River 4472.22 12


Little Nerang Creek

1397.21 12

4.0km Little Nerang

Creek 2061.07 12

Hinze Dam Inflow Nerang River 7389.09 12

Hinze Dam (Outflow)

Nerang River 3979.24 36

Clearview Nerang River 4344.89 36

Carrara Nerang River 4593.95 36

Mudgeeraba TM Mudgeeraba

Creek 1751.66 2.5

Mudgeeraba Mudgeeraba 3579.9 2.5

Boobegan Creek Lock

Boobegan Creek 4046.99 12

Worongary (Sub 27)

Worongary Creek 1222.35 1.5

Broadwater (Nerang River

Mouth) Nerang River 7939.92 36

Table 42 Nerang River URBS Model (Hinze Dam Stage 2) Discharges and Critical Durations, PMF Event


Stream Name


PMF

(m3/s)

PMF Critical Storm Duration (hours)

Critical PMF Storm Temporal Pattern

Whipbird Nerang River 5013.64 36 21 Feb 1954

Little Nerang Dam

Little Nerang 1654.53 96 13 Jan 1981


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Stream Name


PMF

(m3/s)

PMF Critical Storm Duration (hours)


(Outflow) Creek

4.0km Little Nerang

Creek 2410.71 36 21 Feb 1954

Hinze Dam Inflow

Nerang River 8514.69 36 21 Feb 1954

Hinze Dam (Outflow)

Nerang River 4546.25 36 21 Feb 1954

Clearview Nerang River 4882.25 36 21 Feb 1954

Carrara Nerang River 5065.84 36 21 Feb 1954

Mudgeeraba Mudgeeraba

Creek 1703.38 96 13 Jan 1981

Boobegan Creek Lock

Boobegan Creek 3644.37 96 13 Jan 1981

Broadwater (Nerang

River Mouth) Nerang River 3989.16 20 27 Jan 1974

8.8.4 Comparison with Previous Studies

A number of previous studies have been undertaken in the Nerang River Catchment as described in Section 2.5

Table 43 compares the peak design discharge estimates at Hinze Dam and Clearview from this study with the peak design discharges reported in the 1999 GHD (Ref 5), 2001 GCCC (Ref 7) and 2010 WRM (Ref 3) studies for Hinze Dam Stage 2. The following is of note:

The results are compared only for the lower catchment because this study applied an ARF based on the entire catchment area and, as a result, discharge estimates at locations in the upper catchment (with small contributing catchments) are not comparable.

Both GHD and GCCC studies are based on previous unfiltered 1998 AWE (Ref 10) temporal patterns and without the use of ARFs for design rainfalls.


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Table 43 Comparison of Peak Design Discharges Estimated in Different Studies for Nerang River Catchment, Hinze Dam Stage 2

ARI (Years) Estimated Peak Discharge (m3/s)

Hinze Dam Outflow Clearview

GHD GCCC WRM This Study

GHD GCCC WRM This Study

5 328 425 313 221 346 455 330 237

10 468 618 470 389 485 663 496 420

20 664 776 595 582 709 833 628 625

50 775 928 772 798 834 998 814 866

100 938 1119 919 964 1007 1201 968 1045

200 1143 1278 934 1142 1218 1369 988 1236

500 1478 1487 1132 1430 1576 1596 1194 1540

Table 44 compares the estimated Hinze Dam peak design outflows from this study with the peak design outflows reported in the 2009 HDA (Ref 8) for Hinze Dam Stage 2. The following is of note:

The HDA study used the Monte-Carlo (i.e. joint probability) modelling approach to estimate design discharges. This approach did not assume that the Hinze Dam is full at the commencement of design storm events.

HDA noted that their 100 year ARI peak design outflow estimate for Hinze Dam Stage 2 would increase to 870 m3/s if the dam is assumed full at the commencement of design storm events.

Table 44 Comparison of Estimated Hinze Dam Stage 2 Design Outflows with 2007 HDA Results (Ref 8) and WRM Results (Ref 3)

ARI (Years) Estimated Peak Outflow (m3/s)

HDA This Study

10 370 389

20 460 582

50 600 798

100 740 964

200 900 1142

500 1140 1430

1000 1350 1547


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HDA This Study

2000 1590 1666

Table 45 compares the estimated Hinze Dam peak design outflows from this study with the peak design outflows reported in the 2005 GHD (Ref 18) and 2010 WRM (Ref 3) for Hinze Dam Stage 2. The following is of note:

The current study estimated peak design outflows from the Hinze Dam for Hinze Dam Stage 2 are also lower than the estimates given by the GHD study for the PMPDF and PMF events. The lower estimates from this study are attributed to the method used to calculate PMP rainfall depths. This study calculated PMP rainfall depths based on the entire Nerang River catchment area and then applied topographical adjustment factors (TAFs) at the URBS model subcatchment centroids. The GHD study calculated PMP rainfall depths based on the catchment upstream of Hinze Dam and does not appear to have used TAFs at model subcatchment centroids as done in the current study.

Table 45 Comparison of Estimated Hinze Dam Stage 2 Design Outflows with GHD (Ref 18) and WRM Results (Ref 3)


GHD WRM This Study

1000 1310 1325 1547

PMPDF 4260 3799 3979

PMF 4570 4210 4546

Modelled Design Discharges for Hinze Dam Stage 3 8.9

Design discharges along the Nerang River were also estimated for Hinze Dam Stage 3 conditions. Results in this section are presented only for locations downstream of the Hinze Dam which are affected by the Hinze Dam upgrade.


Table 46 and Table 47 show the URBS model predicted design peak discharges and critical storm durations for the 2, 5, 10, 20, 50 and 100 Year ARI events at key locations downstream of the Hinze Dam in the Nerang river catchment for Dam Stage 3 conditions. Design event hydrographs (for the critical storm duration) at a key gauging location are given in Appendix F (Section 0). The following is of note:



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Table 46 Nerang River URBS Model (Hinze Dam Stage 3) Design Discharges, 2 year to 100 year ARI Events


Stream Name


2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Hinze Dam (Outflow)

Nerang River

62.8 114.8 164.8 244.2 375.8 528.8


76.5 137.9 193.2 273.1 413.0 575.0


91.4 177.7 257.9 358.0 480.8 624.4


Nerang River

360.2 764.2 1022.7 1316.1 1638.8 1881.7

Table 47 Nerang River URBS Model (Hinze Dam Stage 3) Critical Storm Durations, 2 year to 100 year ARI Events


Stream Name


2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

Hinze Dam (Outflow)

Nerang River

120 120 120 72 72 48


120 120 120 72 72 48


120 36 72 72 72 72


Nerang River

36 36 24 12 12 12


Table 48 and Table 49 show the URBS model predicted design peak discharges and critical durations for the 200, 500, 1000 and 2000 Year ARI events at key locations downstream of the Hinze Dam in the Nerang river catchment for Hinze Dam Stage 3 conditions. Design event hydrographs (for the critical storm duration) at key gauging locations are given in Appendix F (Section 0).


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Table 48 Nerang River URBS Model (Hinze Dam Stage 3) Design Discharges, 200, 500, 1000 and 2000 year ARI Events


Stream Name



Hinze Dam (Outflow)

Nerang River

709.8 981.6 1106.9 1244.7


767.7 1056.2 1194.3 1351.6


825.3 1127.7 1280.3 1452.1


Nerang River

2099.8 2408.0 2743.3 3139.3

Table 49 Nerang River URBS Model (Hinze Dam Stage 3) Critical Storm Durations, 200, 500, 1000 and 2000 year ARI Events


Stream Name



Hinze Dam (Outflow)

Nerang River

48 48 48 48


48 48 48 48


48 48 48 48


Nerang River

12 36 36 36


Events

Table 50 and Table 51 show the URBS model predicted peak PMP Design Flood (PMPDF) and PMF discharges and critical durations at key locations downstream of the Hinze Dam in the Nerang river catchment for Hinze Dam Stage. PMP and PMF event hydrographs at key gauging location are given in Appendix F (Section 0).


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It is worthwhile to note that the PMF events were only run for the 24, 36, 48, 72, 96 and 120 hour durations.

Table 50 Nerang River URBS Model (Hinze Dam Stage 3) Discharges and Critical Durations, PMPDF Event

Gauging Station Name Stream Name


PMPDF (mᶟ/s) PMPDF Critical Storm

Duration (hours)

Hinze Dam (Outflow) Nerang River 3405.79 36

Clearview Nerang River 3690.97 36

Carrara Nerang River 3963.57 36


Nerang River 7095.73 12

Table 51 Nerang River URBS Model (Hinze Dam Stage 3) Discharges and Critical Durations, PMF Event


Stream Name


PMF (m3/s) PMF Critical Storm Duration (hours)


Hinze Dam (Outflow)

Nerang River

4061.53 120 25 Feb 1975


4284.82 120 25 Feb 1975


4421.35 120 25 Feb 1975

Broadwater (Nerang

River Mouth)

Nerang River 8284.83 120 25 Feb 1975

8.9.4 Comparison with Previous Studies

Table 52 compares the estimated peak design outflows from this study with the peak design outflows reported in the 2007 HDA (Ref 8) and 2010 WRM (Ref 3) study for Hinze Dam Stage 3. The following is of note:

The HDA (2009) study used the Monte-Carlo (i.e. joint probability) modelling approach to estimate design discharges for all design events up to 2000 year ARI. This approach did not assume that the Hinze Dam is full at the commencement of design storm events.


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Table 52 Comparison of Estimated Hinze Dam Stage 3 Design Outflows with 2007 HDA Results (Ref 8) and WRM Results (Ref 3)


HDA WRM This Study

10 130 244 165

20 180 316 244

50 230 415 376

100 290 497 529

200 430 606 710

500 700 812 982

1000 980 982 1107

2000 1210 1181 1245

PMPDF 3720 3127 3406

PMF 4060 3615 4062

Climate Change (10% increase in rainfall intensity) 8.10

The effects of climate change have been considered by increasing rainfall intensity by 10% for the

year 2100 for all ARIs, Q2 to Q2000. This is achieved by setting the “FAF” factor within the URBS

Control Centre to 1.1 (See Appendix H.9). There is no increase in rainfall intensity for PMF and

PMPDF.

8.10.1 Modelled Design Discharges for Hinze Dam Stage 2 with Climate Change

Table 53 and Table 54 show the URBS model predicted design peak discharges and critical storm durations for the 2 to 2000 Year ARI events at key locations throughout the Nerang River catchment for Hinze Dam Stage 2 with the additional 10% increase in rainfall intensity.

Table 53 Nerang River URBS Model (HD 2) Design Discharges with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events



2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Whipbird 273.6 561.8 760.9 1026.5 1295.5 1512.4 1710.1 1975.3 2056.9 2215.9


115 203.9 288.2 375.1 470.3 547 602.2 684.9 699.1 743.6

4.0km 145 275.5 388.5 510.5 639.2 741.1 819 925.4 954.7 1037


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2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Hinze Dam Inflow

464.1 939.2 1269.7 1708.5 2157.6 2507.7 2810.4 3219.6 3357.8 3673.2

Hinze Dam (Outflow)

155.8 272.9 456.7 658 895.7 1094.2 1311.2 1638 1730 1857.4

Clearview 170 293 493.4 706.4 972.8 1186.1 1414.8 1747.9 1869 2021.1

Carrara 184.3 315.5 529.8 760.4 1043.2 1263.6 1496.6 1850.6 2015.6 2205.3

Mudgeeraba TM

94.4 193.5 269.8 348.5 423.8 484.9 540.1 611.9 693.8 820.9

Mudgeeraba 196.7 409.7 577.7 747.9 905.2 1032.8 1149 1316 1517.7 1798.4

Boobegan Creek Lock

237.8 493.4 677.2 887.6 1085.6 1236.3 1368.4 1545.9 1699.6 1919.9

Worongary (Sub 27)

40 96.3 135.9 176.4 224.7 280.8 310.3 350 463.2 612.1


445.9 892 1179.8 1528.1 2003.5 2346 2673.8 3141.9 3533.7 3996.4

Table 54 Nerang River URBS Model (HD 2) Critical Storm Durations with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events



2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Whipbird 72 72 12 12 9 9 9 9 9 4.5


72 48 12 12 9 9 9 9 9 3

4.0km 72 48 12 9 9 9 9 9 9 4.5

Hinze Dam Inflow

72 72 12 12 9 9 9 9 9 4.5

Hinze Dam (Outflow)

120 48 48 72 48 48 48 36 36 48

Clearview 120 48 48 72 48 48 48 36 48 48

Carrara 120 48 48 48 48 48 48 48 48 48

Mudgeeraba TM

72 12 9 9 9 9 9 9 3 3

Mudgeeraba 72 12 9 9 9 9 9 6 3 3

Boobegan Creek Lock

36 24 9 9 9 9 9 9 6 6


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2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Worongary (Sub 27)

48 9 4.5 4.5 1 1 1 1 1 1


36 36 36 72 36 36 36 36 36 36

8.10.2 Modelled Design Discharges for Hinze Dam Stage 3 with Climate Change

Table 55 and Table 56 show the URBS model predicted design peak discharges and critical storm durations for the 2 to 2000 Year ARI events at key locations throughout the Nerang River catchment for Hinze Dam Stage 3 with the additional 10% increase in rainfall intensity.

Table 55 Nerang River URBS Model (HD 3) Design Discharges with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events



2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Whipbird 273.6 561.8 760.9 1026.5 1295.5 1512.4 1710.1 1975.3 2056.9 2215.9


115 203.9 288.2 375.1 470.3 547 602.2 684.9 699.1 743.6

4.0km 145 275.5 388.5 510.5 639.2 741.1 819 925.4 954.7 1037

Hinze Dam Inflow

464.1 939.2 1269.7 1708.5 2157.6 2507.7 2810.4 3219.6 3357.8 3673.2

Hinze Dam (Outflow)

80.5 135.8 191.8 278.7 457.5 658.4 864.3 1174.1 1311.1 1466.5

Clearview 97.1 162.4 223.7 309.8 500 713 931.3 1264.9 1418.8 1595.4

Carrara 114.5 203.1 292.5 402.5 547.2 768.2 997.4 1342.2 1511.2 1705.8

Mudgeeraba TM

94.4 193.5 269.8 348.5 423.8 484.9 540.1 611.9 693.8 820.9

Mudgeeraba 196.7 409.7 577.7 747.9 905.2 1032.8 1149 1316 1517.7 1798.4

Boobegan Creek Lock

237.8 493.4 677.2 887.6 1085.6 1236.3 1368.4 1545.9 1699.6 1919.9

Worongary (Sub 27)

40 96.3 135.9 176.4 224.7 280.8 310.3 350 463.2 612.1


439.5 859.4 1141.5 1461.7 1810.5 2075.1 2315.6 2663.6 3035.6 3474.2


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Table 56 Nerang River URBS Model (HD 3) Critical Storm Durations with 10% increase in Rainfall Intensity, 2 year to 2000 year ARI Events



2 year ARI

5 year ARI

10 year ARI

20 year ARI

50 year ARI

100 year ARI

200 year ARI

500 year ARI

1000 year ARI

2000 year ARI

Whipbird 72 72 12 12 9 9 9 9 9 4.5


72 48 12 12 9 9 9 9 9 3

4.0km 72 48 12 9 9 9 9 9 9 4.5

Hinze Dam Inflow

72 72 12 12 9 9 9 9 9 4.5

Hinze Dam (Outflow)

120 120 120 72 48 48 48 48 48 48

Clearview 120 120 120 72 48 48 48 48 48 48

Carrara 120 36 72 72 72 48 48 48 48 48

Mudgeeraba TM

72 12 9 9 9 9 9 9 3 3

Mudgeeraba 72 12 9 9 9 9 9 6 3 3

Boobegan Creek Lock

36 24 9 9 9 9 9 9 6 6

Worongary (Sub 27)

48 9 4.5 4.5 1 1 1 1 1 1


36 36 24 12 12 12 12 36 36 36


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9. Flood Frequency Analysis

Method of Analysis 9.1

The methodology recommended in Australian Rainfall and Runoff (Ref 11) was used to fit a Log-Pearson Type III distribution to an annual series of recorded peak flood rated discharges and was then compared against the URBS peak modelled discharges.

Design Flood discharges were estimated by Flood Frequency Analysis (FFA) using all available height data and the adopted rating curves (Refer Section 5). The following gauges were selected for FFA due to their length of historical record:

Nerang River at Clearview (146002A &146002B) – 55 years (1919-1975) of data before construction of Hinze Dam;

Little Nerang Creek at Neranwood (146004A) – 34 years (1928-1961) of data before construction of Hinze Dam.

Analysis and Results 9.2

9.2.1 Clearview (Pre-Hinze Dam)

Figure 25 and Table 57 shows the plot of the fitted flood frequency distribution and the FFA

estimated design peak discharges respectively at Clearview (Pre-Hinze Dam). The following is

of note with regards to the FFA results for Clearview (Pre-Hinze Dam Stage 1): Seventeen low

flows were omitted from the analysis.

The flood frequency distribution at Clearview is based on 56 years and, as such, the results for

ARIs of up to 50 years can be considered acceptable; however, the 100 year ARI discharge

estimate contains a significant level of uncertainty.


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Figure 25 Comparison of URBS Model Design Discharges and Flood Frequency Distribution, Nerang River at Clearview (146002 A & B) - Pre-Hinze Dam, 1920-1975

Table 57 FFA Results, Nerang River at Clearview (146002A & B) - Pre- Hinze Dam

Estimated Peak Discharge (m3/s)

ARI (Years) 95% Confidence Limit Adopted Value 5% Confidence Limit

2 333 389 454

5 712 828 962

10 970 1148 1358

20 1210 1482 1815

50 1492 1953 2556

100 1680 2335 3246

9.2.2 Neranwood

Figure 26 and

0

500

1000

1500

2000

2500

3000

3500

1 10 100

Discharge (m

ᶟ/s)

ARI

Peak Annual Flood Series

URBS Design Outputs

CL Upper

CL Lower

LP3 Distribution




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Table 58 show the plot of the fitted flood frequency distribution and the FFA estimated design peak discharges respectively at Neranwood. The following is of note with regards to the FFA results for Neranwood:

4 low flow were omitted from the analysis.

The flood frequency distribution at Neranwood is based on 34 years and, as such, discharge estimates up to about 20 year ARI can be considered reliable. There is a higher degree of uncertainty for discharge estimates for ARIs greater than 20 years.

Figure 26 Comparison of URBS Model Design Discharges and Flood Frequency Distribution, Little Nerang Creek at Neranwood (146004A)

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 10 100

Discharge

(mᶟ/s)

ARI

Peak Annual Flood Series

URBS Design Outputs

CL Upper

CL Lower

LP3 Distribution

2 86 127 186

5 201 290 418

10 284 423 629

20 351 565 910

50 406 767 1448

100 425 929 2029



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Table 58 FFA Results, Little Nerang Creek at Neranwood (146004A) - Pre-Dams.


2 86 127 186

5 201 290 418

10 284 423 629

20 351 565 910

50 406 767 1448

100 425 929 2029


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Comparison with Previous FFA Studies 9.3

The 1999 GHD (Ref 5), 2000 GCCC (Ref 7), 2009 Hinze Dam Alliance (Ref 8), 2010 WRM (Ref 3) studies undertook FFAs at Clearview as part of their design flow estimations. The Hinze Dam Alliance Study (2007) used a Generalised Extreme Variable (GEV) distribution to fit the data and included only a flood frequency curve plot in the report. The results were not tabulated and, as a result, no accurate estimates from the study were available for comparison. All other mentioned studies fitted a Log Pearson Type III distribution to the annual peak discharge series data.

Clearview FFA (Pre-Hinze Dam)

Table 59 compares the estimates of the GHD, GCCC and WRM studies with the results of the current

study. When comparing these results the following should be noted:

The GHD and GCCC studies do not appear to have omitted low flows from their analyses. The skew coefficient of the GHD and GCCC fitted distributions is not known. The WRM study omitted 4 low flows. It is noted that this study omitted 17 low flows.

The GHD and GCCC study FFA results are similar for all ARIs.

The 10 year ARI discharge estimates from all four studies are similar. The 5 year ARI discharge estimates from this, and the WRM study, are lower than the equivalent GHD and GCCC estimates. The 50 and 100 Year ARI event estimates are similar to the GHD and GCCC study, but slightly lower than WRM estimates.

Table 59 FFA Comparison, Nerang River at Clearview (146002 A & B) - Pre-Hinze Dam


ARI (Years) GHD 1999 (Ref 5) GCCC 2000 (Ref 7) WRM 2010 ( Ref 3) Current Study

5 920 965 808 828

10 1163 1212 1192 1148

50 1833 1885 2237 1953

100 2182 2232 2754 2335


ARI (Years) GHD 1999 (Ref 5) GCCC 2000 (Ref 7) WRM 2010 ( Ref 3) Current Study

5 920 965 808 828

10 1163 1212 1192 1148

50 1833 1885 2237 1953

100 2182 2232 2754 2335


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9.3.1 Neranwood

Only the 2010 WRM study (Ref 3) performed a FFA at the Neranwood gauging station, with its results compared to the current study in Table 60. When comparing these results the following should be noted:

The WRM study (Ref 3) omitted only 1 low flow, whereby the current study omitted 4 low flows.

The 5 and 10 year ARI discharges are similar. The current study’s 50 and 100 year ARI is slightly lower than the WRM study (Ref 3). As there is only 34 years of data available at the Neranwood gauging station, any estimate above approximately the 20 year ARI becomes uncertain.

Table 60 FFA Comparison, Little Nerang Creek at Neranwood (146004A)


ARI (Years) WRM 2010 ( Ref 3) Current Study

5 280 290

10 425 423

50 844 767

100 1061 929

Comparison with URBS Results 9.4

Clearview (Pre-Hinze Dam) Table 61 compares the URBS model estimated peak design discharges at Clearview with the peak

discharge estimates obtained from the FFA. Figure 25 shows the URBS model peak design

discharges plotted against the fitted flood frequency distribution curves and recorded peak series data

at Clearview. The following is of note:

The design peak discharges estimated by the URBS model for the Nerang River at Clearview

for the pre-dam scenario correspond well to the FFA estimates for all ARIs, with the URBS

design model outputs producing slightly higher discharges, but well within the confidence limits

of the FFA.

The FFA results for the pre-dam scenario are based on 55 years of data and have a reasonable degree of uncertainty for discharge estimates for ARIs greater than 50 years.

Table 61 Comparison of URBS model and FFA Estimated Peak Design Discharges, Clearview

Estimated Peak Discharge

(m3/s)

ARI (Years) FFA URBS


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(m3/s)


2 389 390

5 828 868

10 1148 1195

20 1482 1612

50 1953 2061

100 2335 2399

Neranwood (Pre-Hinze Dam)

Table 62 compares the URBS model estimated peak design discharges at Neranwood with the peak

discharge estimates obtained from the FFA. Figure 26 shows the URBS model peak design

discharges plotted against the fitted flood frequency distribution curve and recorded peak series data

at Neranwood. The following is of note:

The design peak discharges estimated by the URBS model for Little Nerang Creek at

Neranwood correspond well to the flood frequency discharge estimates for the 2 and 5 year

ARIs. For ARIs 10 years and greater, the URBS model discharge estimates are lower than

those predicted by the FFA; it is noted that the flood frequency estimates for the higher ARIs

have a high degree of uncertainty due to the relatively short peak annual data series (34

years). However, it is noted that the URBS model discharge estimates are within the fitted

flood frequency curve confidence limits.

Table 62 Comparison of URBS model and FFA Estimated Peak Design Discharges, Neranwood


(m3/s)


2 127 110

5 290 209

10 423 303

20 565 398

50 767 502

100 929 584


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10. Joint Probability Approach (Monte Carlo Simulation)

The “design event approach” is the current practice for design flood estimation which uses all model inputs as single fixed values, with the exception of rainfall. A lot of effort has been made to ensure that the adopted parameters result in a flood with an annual exceedance probability that is similar to the rainfall that caused the flood (Figure 27).

Figure 27 Schematic Illustration of Design Event Approach

However, this approach has its limitations. For example, a 1 in 100 AEP flood could result in a 1 in 50 AEP rainfall on a dry catchment. Joint probability approaches (Monte Carlo) attempt to mimic “mother


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nature” in that the influence of the most important flood producing factors are treated as variables, thereby providing a more realistic representation of the flood generation processes (Figure 28). Joint probability techniques offer an alternative to the design event method (Ref 41, 42 and 43).

Figure 28 Schematic Illustration of Joint Probability Approach

There are currently two Monte Carlo techniques available: the Total Probability Theorem approach (TPT) (Ref 41); and the Cooperative Research Centre – Catchment Hydrology approach (CRC-CH) approach (Ref 38). The TPT approach builds on the current critical storm duration approach whereas the CRC-CH generates design storms of variable duration. The CRC-CH approach requires event based IFD tables whereas the TPT approach uses burst IFD tables as issued by the BoM.

To generate the CRC-CH event based IFD tables, a relationship was developed during Don Carroll’s Review and Update of GCCC’s Hydrological Models (Ref 9) between complete storm IFD tables and burst IFD tables for the Gold Coast Region. This was done by obtaining raw pluviograph data from the BoMto derive complete IFD tables and comparing these tables to their burst table equivalents. The relationship between these tables (Ref 9) was assumed to be:

Where p, q and r are constants, D is the Duration (hours), T is the ARI in years, I is the intensity. b=burst, e = event.


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For the Gold Coast area it was found that p = 0.1 x I2D24 - 0.25, q = 0.6 x (1 - p) and r= -0.025. The mean duration was found to be approximated by 0.9 x I2D241.56 where I2D24 is the 2 year 24 hour burst intensity.

In the application of the JPA, a beta distribution was assumed for the initial loss whose parameters were sourced from Ilahee (2005) and from the historical calibration events. Temporal patterns were randomly selected based on the multiplicative cascade model (CRC-CH, 2001) and parameterized according to Carroll (Ref 42), with filtering for patterns used for the TPT burst events to ensure that the generated patterns did not contain sub-bursts. It was assumed Hinze dam was full according to best floodplain management practice. Both continuous losses and variability were assumed to be constant.

Don Carroll (Ref 9) notes that both approaches suffer from limitations. The TPT approach has been developed for large to extreme floods and its application here for the more frequent ARI’s is questionable. The CRC-CH approach, while often applied to derive design flow estimates up to and including large floods, is not robust in the estimation of rare and extreme floods when compared to the TPT approach. Other limitations are: (i) the assumption that the loss distribution applied is consistent across the entire frequency range – generally higher losses are experienced with the more frequent ARI events; (ii) convective storms are typically front loaded whereas frontal storms are end loaded, which is not accounted for; (iii) storm patterns are likely to be less variable with increasing ARI; and (iv) how El Nino/La Nina cycles impact antecedent conditions. It is obvious that further research work is required to apply these technologies over the entire frequency spectrum, but as applied, it is likely there will be over-estimation of peak flows for the more frequent design events.

The use of Monte Carlo simulations within this study is for comparative purposes only with the URBS Design Event Approach (DEA).

The URBS Control Centre includes the functionality for estimation of design floods using both forms of Monte-Carlo simulation.

Monte Carlo Results 10.1

Overall it was found that the TPT approach had a slighter better fit to the DEA compared to the CRC-CH approach (Figure 29 & Figure 30). For the more frequent ARIs, the Monte Carlo approaches produced higher peak discharges which could be attributed to the DEA approach using high loss values for more frequent flooding events, whereas the Monte Carlo approach assumes that the loss distribution applied is consistent across the entire frequency range.

The Monte Carlo approach supports the DEA estimates providing further support for use as inputs to Council’s hydraulic models.

See Table and Table in Appendix I for exact values from the Monte Carlo runs.

It is of note that both approaches have some limitations. The TPT is developed for large to extreme floods and its applications for more frequent events are questionable. The CRC-CH is often applied in the derivation of design flow estimates up to large floods (~200 year ARI) so this approach is not robust in the estimation of rare and extreme floods. Hence, the following figures show CRC-CH is only


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up to 200 year ARI. In this study the TPT and CRC-CH Monte Carlo simulations are undertaken only to verify the results of Design Event Approach.

Figure 29 Comparison of Peak Discharges for Hinze Dam stage 2 at Clearview

Figure 30 Comparison of Peak Discharges for Hinze Dam stage 3 at Clearview


0

500

1000

1500

2000

2500

1 10 100 1000 10000

ARI

Dis

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arg

e (

m3

/s)


TPT Approach

CRC-CH Approach


0

200

400

600

800

1000

1200

1400

1600

1 10 100 1000 10000

ARI

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TPT

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11. Conclusions

Overview 11.1

A URBS model of the Nerang River catchment has been satisfactorily calibrated and verified against available data, and then the calibrated model has been used to estimate design flood discharges at key locations in the catchment for design events ranging from 2 year ARI to PMF. Design event runs have been undertaken for both Stages 2 and 3 of the Hinze Dam. In addition, the URBS model design discharge estimates have been reconciled with FFA estimates of design discharges at Clearview and Neranwood gauging stations within the catchment. Monte Carlo simulations have also been undertaken, which gave further support of the discharges produced in the design event approach. All analyses in this study have been undertaken using an approach and methodology consistent with the hydrologic modelling currently been undertaken for other catchments in the Gold Coast. In addition, the methodology and results of this study have been fully documented to a consistent standard.

Model Calibration and Verification 11.2

The Nerang URBS model has been calibrated against five historical flood events (January 1974, March 2004, November 2004, June 2005 and January 2008) and then verified against another four historical flood events (March 1999, February 2001, May 2009 and January 2013). The selected calibration and verification events cover a wide range of discharges across the catchment.

The emphasis of the model calibration was to achieve the best possible fit between the predicted and recorded (or rated) discharge hydrographs at key stations in the Nerang River catchment for the selected calibration events A single set of model parameters were adopted for the model and maintained for all calibration and verification events. The model parameters were adjusted to achieve the best calibration across all events, resulting in a compromise between model accuracy and model simplicity.

Uniform initial and continuing losses were applied across all sub-catchments. Rainfall losses were adjusted to achieve the best possible hydrograph shapes and flood volumes for each historical flood event.

A good calibration and verification was achieved throughout the catchment, with the URBS model generally reproducing recorded flood discharges satisfactorily for all calibration and verification events.

The model calibration is considered generally good, considering that a single set of global parameters was adopted. Gauges upstream of the Clearview gauge and Hinze Dam are well calibrated. The calibration results for gauging stations downstream of Clearview are uncertain because of the unavailability of well rated gauging stations. The gauges downstream of Clearview are affected by downstream water levels. In addition, the affects and operation of the Boobegan lock during the historical events are unknown to adequately calibrate the model to flows at this location.


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Design Flood Discharges 11.3

The calibrated URBS model was used to estimate design flood discharges throughout the Nerang River catchment based on design rainfall intensity – frequency – duration (IFD) data from a number of sources. Design flood discharge hydrographs were estimated for a range of storm durations up to the 120 hour event for the 2, 5, 10, 20, 50, 100, 200, 500, 2000 year ARI events, and for the Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) events. The design rainfall data and associated procedures and input data (including IFD data, temporal patterns, areal reduction factors, rainfall spatial distribution and design rainfall losses) adopted in the study are based on a comprehensive review of the latest available data and information.

The peak design discharges estimated in this study were compared with the peak design discharges reported in four previous studies (WRM 2010 (Ref 3), GHD 1999 (Ref 5), GCCC 2001 (Ref 6), and HDA 2009 (Ref 8)). The GHD (Ref 5) and GCCC (Ref 6) studies reported results only for Stage 2 of Hinze Dam. WRM (Ref 3) and HDA (Ref 8) reported results for both Stage 2 and Stage 3 of Hinze Dam. The current study results produced discharges similar to the previous studies.

The effects of climate change have been considered by increasing rainfall intensity by 10% for the year 2100 for all ARIs, Q2 to Q2000.

Flood Frequency Analysis 11.4

Flood frequency analyses (FFA) was undertaken using the methodology recommended in Australian Rainfall and Runoff (Ref 11) by fitting a Log-Pearson Type III distributions to annual series of recorded peak flood discharges at Clearview and Neranwood gauging stations. These were the only two gauging stations with a sufficiently long record to undertake a useful FFA. The URBS model estimated peak design discharges at the above stations and were compared with the peak discharge estimates obtained from the FFA to assess the consistency between the two sets of discharge estimates and reconcile any differences between estimates from the two methods. The results were also compared with FFA results from the WRM 2010 (Ref 3), GHD 1999 (Ref 5) and GCCC (Ref 7) studies.

The design peak discharges estimated by the URBS model for the Nerang River at Clearview for the pre-dam scenario correspond well to the FFA estimates for all ARIs up to 100 years.

Monte Carlo Simulations 11.5

Monte Carlo simulations were undertaken using the Total Probability Theorem approach (TPT) and Cooperative Research Centre – Catchment Hydrology approach (CRC-CH). These techniques offered an alternative to the design event approach in estimating peak discharges for various ARI events. The results of the Monte Carlo simulations gave further support of the discharges obtained from the Design Event Approach, which are used as inputs into Council’s hydraulic models.

Spreadsheets 11.6

All Excel spreadsheets showing adopted design rainfalls for all model sub-catchments for all ARIs and durations and PMP Calculation Spreadsheet are located:

W:\Work_in_Progress\Hydrology Review Update\Catchments\Nerang


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12. Recommendations

The hydrological modelling undertaken in this study has revealed several issues that should be addressed in any future studies to improve the quality of design discharge estimates in the Nerang River catchment:

Quality of the model calibration for the Nerang River catchment downstream of Clearview is not as good for the catchment upstream of Clearview. This is because the gauging stations in the lower river reach (at Carrara and Evandale) are affected by downstream tailwater levels. These stations are BOM flood forecasting stations and not EHP (DERM) stream gauging stations. As such, these stations have not been rated accurately. The rating curves available for these stations have been developed by BOM by correlating the recorded water levels with URBS model predicted discharges. There is significant room for improving the calibration for the Lower Nerang River. It is recommended that a joint calibration between the URBS and Council’s hydraulic models be undertaken to improve the model calibration and hence the design discharge estimates for the lower reaches of the Nerang River.

Investigate the possibility of undertaking a FFA using peak annual 1-day, 2-day and 3-day flood volumes at the Mudgeeraba TM station, using the most up to date information.


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13. Reference

1. AWE. Review of Gold Coast Rainfall Data - Volume 1. Final Report. May 1998.

2. WRM Water & Environment. Hydrological Modelling Studies for Gold Coast Catchments. Summary Report. April 2010.

3. WRM Water & Environment. Nerang River Flood Study Hydrological Modelling. Final Report. April 2010.

4. GCCC. Nerang Hydrology Addendum Report. November 2011.

5. GHD. Final Report, Nerang River Hydrological Model. December 1999.

6. GCCC. Nerang River Flood Mitigation Investigation Project – Review of Nerang River Catchment Hydrology. Addendum Report. May 2001.

7. GCCC. Nerang River Flood Mitigation Investigation Project – Review of Nerang River Catchment Hydrology. December 2000.

8. Hinze Dam Alliance. Hinze Dam - Flood Hydrology for Stage 3 Design. Report Version 6. February 2009.

9. Don Carroll. Review and Update of GCCC’s Hydrological Models. April 2013.

10. AWE. Review of Gold Coast Rainfall Data - Volume 3 (Temporal Patterns). Final Report. October 2000.

11. IEAust. Australian Rainfall and Runoff. A Guide to Flood Estimation. 1987.

12. IEAust. Australian Rainfall and Runoff. A Guide to Flood Estimation. Revised Edition. 1999.

13. IEAust. Australian Rainfall and Runoff. Flood Analysis and Design. 1977.

14. Kinhill Cameron McNamara. Nerang River Hydrology Studies. February 1992.

15. BOM. Nerang River URBS Flood Forecasting Model. June 1998.

16. GHD. Hinze Dam Design Rainfall Estimate. 2005.

17. GHD. Hinze Dam Probable Maximum Flood Review. 2005.

18. GHD. Hydrologic Assessment of Augmentation Options for Raising Hinze Dam. 2005.

19. GCCC. Mudgeeraba Creek Catchment Hydrological Study. August 2009.

20. GCCC. Worongary Creek Catchment Hydrological Study. 2009.


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21. GCCC. Mudgeeraba & Worongary Creeks Hydrology Study Report. June 2004.

22. GCCC. Mudgeeraba Creek Hydrological Model Update 2007. October 2007.

23. IPWEA. Queensland Urban Drainage Manual. Third Edition – Provisional. 2013.

24. Cardno MBK. Hinze Dam – Little Nerang Dam Consolidated Report on Yield Reassessment Studies No 2. July 2004.

25. Don Carroll. URBS 2002 – A Rainfall Runoff Routing Model for Flood Forecasting and Design Version 5.000 Manual. 2012.

26. WRM. Summary Findings of the Review of Hydrological Models for the Gold Coast City Catchments. Report No 0451-01-G. March 2008

27. Mahbub Ilahee. Modelling losses in Flood Estimation. PhD Thesis. Queensland University of Technology. 2005

28. WRM. Hydrological Modelling Studies for Gold Coast Catchments, Summary Report, prepared. April 2010.

29. AWE. Logan River Floodplain Filling Study. November 1992.

30. Hargraves, G. Extreme Rainfall Estimation Project, CRCFORGE and (CRC) ARF Techniques, Queensland and Border Locations, Development and Application. 2004.

31. BOM. A Pilot Study to Explore Methods for Deriving Design Rainfalls for Australia. 2005.

32. IEAust. Spatial Patterns of Design Rainfall. Collation and Review of Areal Reduction Factors from Applications of the CRC-Forge Method in Australia.

33. BOM. Guide to the Estimation of Probable Maximum Precipitation: Generalised Tropical Storm Method. November 2003.

34. BOM. The Estimation of Probable Maximum Precipitation in Australia: Generalised Short-Duration Method. June 2003.

35. WRM. Revision of Design Rainfall Temporal Patterns for Gold Coast Catchments. October 2008.

36. WRM. GCCC IFD Utility Modifications, Report (No 0451-07-A). July 2008.

37. GCCC. Hydrology Review – Desi9gn Model Inputs. 2013.

38. Rahman, A. et al. Monte Carlo Simulation of Flood Frequency Curves from Rainfall. Cooperative Research Centre for Catchment Hydrology. Technical Report 01/04. March 2001.


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39. City of Gold Coast. IFD Utility Manual. April 2013.

40. City of Gold Coast. Nerang River Catchment Hydraulic Study. June 2014.

41. Weinman, PE et al. Use of a Monte-Carlo Framework to Characterise Hydrologic Risk. ANCOLD conference on dams. Adelaide. 2002

42. Carroll D.G. Investigation of sub-tropical rainfall characteristics for use in the joint probability approach to Design Flood Estimation. HIC, Koyoto. 2004.

43. Carroll D.G & Rahman A (2004), “Investigation of sub-tropical rainfall characteristics for use in the joint probability approach to Design Flood Estimation” HIC, Kyoto, 2004..

44. CCS. CatchmentSim User Manual. Version 3.

45. GCCC. Mudgeeraba Creek Hydrological Study. Addendum Report. October 2010.

46. GCCC. Worongary Creek Hydrological Study. Addendum Report. October 2010.


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14. APPENDICES

Appendix A - URBS Model Sub-Catchment Areas and Land Uses

Table A-1 Nerang URBS Model Sub-Catchment Areas and Land Uses Sub-Catchment

ID Area (km2) UL (%) UM (%) UH (%) UR (%) UF (%)

1 10.67 0.00 0.00 0.00 0.53 0.47 2 7.76 0.00 0.00 0.00 0.17 0.83 3 9.40 0.00 0.00 0.00 0.21 0.79 4 18.75 0.00 0.00 0.00 0.40 0.60 5 15.27 0.00 0.00 0.00 0.04 0.96 6 9.00 0.00 0.00 0.00 0.55 0.45 7 16.38 0.00 0.00 0.00 0.30 0.70 8 16.36 0.00 0.00 0.00 0.03 0.97 9 7.49 0.00 0.00 0.00 0.00 1.00 10 6.80 0.00 0.00 0.01 0.00 0.99 11 12.76 0.00 0.00 0.10 0.00 0.90 12 12.85 0.00 0.00 0.16 0.10 0.74 13 8.83 0.00 0.00 0.24 0.15 0.61 14 9.97 0.03 0.00 0.00 0.26 0.71 15 7.62 0.00 0.00 0.01 0.00 0.99 16 11.20 0.04 0.00 0.00 0.27 0.68 17 6.41 0.00 0.00 0.08 0.11 0.81 18 4.84 0.00 0.00 0.00 0.01 0.99 19 7.13 0.00 0.00 0.05 0.00 0.95 20 7.33 0.00 0.00 0.32 0.00 0.68 21 5.73 0.00 0.00 0.34 0.00 0.66 22 8.01 0.00 0.00 0.00 0.84 0.16 23 15.25 0.00 0.00 0.00 0.88 0.12 24 3.48 0.43 0.00 0.00 0.47 0.10 25 2.50 0.22 0.38 0.00 0.36 0.04 26 10.50 0.04 0.00 0.00 0.66 0.30 27 5.95 0.14 0.13 0.04 0.31 0.38 28 15.14 0.07 0.29 0.19 0.32 0.13 29 3.60 0.07 0.79 0.00 0.13 0.00 30 4.67 0.17 0.18 0.30 0.35 0.00 31 3.10 0.00 0.13 0.38 0.49 0.00 32 8.81 0.00 0.16 0.00 0.44 0.40 33 7.08 0.00 0.30 0.08 0.62 0.00 34 1.61 0.00 0.59 0.00 0.41 0.00 35 3.71 0.00 0.17 0.14 0.69 0.00 36 3.18 0.00 0.17 0.11 0.72 0.00 37 4.34 0.00 0.12 0.11 0.77 0.00 38 2.12 0.00 0.41 0.46 0.13 0.00 39 8.36 0.03 0.26 0.52 0.20 0.00 40 4.51 0.06 0.39 0.12 0.43 0.00 41 7.81 0.09 0.13 0.36 0.34 0.07 42 3.79 0.00 0.13 0.66 0.00 0.21 43 3.26 0.00 0.14 0.52 0.16 0.18 44 3.09 0.00 0.24 0.74 0.00 0.03 45 2.84 0.00 0.44 0.49 0.08 0.00 46 3.77 0.00 0.12 0.88 0.00 0.00


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Sub-Catchment ID

Area (km2) UL (%) UM (%) UH (%) UR (%) UF (%)

47 3.10 0.00 0.58 0.16 0.26 0.00 48 1.35 0.00 0.15 0.24 0.61 0.00 49 7.83 0.00 0.00 0.90 0.10 0.00 50 4.30 0.00 0.20 0.80 0.00 0.00 51 12.68 0.00 0.15 0.79 0.06 0.00 52 9.03 0.00 0.29 0.66 0.06 0.00

101 0.37 0.00 0.00 0.07 0.93 0.00 102 0.44 0.00 0.00 0.05 0.95 0.00 103 0.60 0.02 0.00 0.11 0.87 0.00 104 0.33 0.00 0.00 0.09 0.91 0.00 105 0.27 0.00 0.00 0.07 0.93 0.00 106 0.57 0.00 0.00 0.01 0.79 0.21 107 1.23 0.00 0.00 0.05 0.81 0.14 108 0.36 0.00 0.00 0.07 0.91 0.02 109 1.20 0.01 0.00 0.06 0.76 0.17 110 0.48 0.02 0.00 0.09 0.80 0.09 111 0.68 0.00 0.00 0.06 0.77 0.16 112 0.79 0.00 0.00 0.13 0.87 0.00 113 0.60 0.00 0.00 0.09 0.89 0.02 114 0.55 0.00 0.00 0.03 0.88 0.09 115 0.35 0.03 0.00 0.11 0.20 0.67 116 0.54 0.01 0.00 0.06 0.83 0.09 117 0.35 0.00 0.00 0.12 0.88 0.01 118 0.60 0.00 0.00 0.09 0.91 0.00 119 0.60 0.00 0.00 0.07 0.93 0.00 120 0.27 0.00 0.00 0.11 0.89 0.00 121 0.36 0.00 0.00 0.04 0.96 0.00 122 0.65 0.00 0.00 0.07 0.93 0.00 123 0.39 0.00 0.00 0.08 0.92 0.00 124 0.28 0.00 0.00 0.11 0.89 0.00 125 0.55 0.00 0.00 0.10 0.90 0.00 126 0.28 0.00 0.00 0.20 0.80 0.00 127 0.44 0.05 0.00 0.26 0.60 0.10 128 0.46 0.00 0.00 0.09 0.91 0.00 129 0.61 0.05 0.16 0.34 0.46 0.00 130 0.24 0.00 0.00 0.28 0.72 0.00 131 0.52 0.00 0.00 0.19 0.81 0.00 132 0.25 0.00 0.00 0.17 0.83 0.00 133 0.42 0.00 0.17 0.23 0.59 0.01 201 6.54 0.00 0.00 0.00 0.20 0.79 202 5.35 0.00 0.00 0.05 0.31 0.65 203 8.00 0.00 0.00 0.04 0.87 0.08 204 4.65 0.00 0.00 0.09 0.82 0.09 205 5.43 0.00 0.00 0.06 0.93 0.00 206 4.42 0.01 0.00 0.11 0.78 0.11 207 2.83 0.01 0.05 0.11 0.83 0.01 208 0.84 0.01 0.06 0.20 0.73 0.01 209 6.50 0.00 0.00 0.02 0.65 0.33 210 7.23 0.09 0.00 0.06 0.55 0.30 211 5.02 0.04 0.00 0.06 0.74 0.16 212 5.85 0.00 0.00 0.04 0.53 0.43


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Sub-Catchment ID

Area (km2) UL (%) UM (%) UH (%) UR (%) UF (%)

213 4.73 0.00 0.00 0.08 0.79 0.12 214 3.48 0.00 0.00 0.05 0.42 0.53 215 2.60 0.00 0.00 0.10 0.84 0.06 216 4.54 0.00 0.00 0.04 0.94 0.03 217 2.70 0.01 0.02 0.13 0.84 0.00 218 1.75 0.03 0.40 0.21 0.36 0.00 219 1.57 0.00 0.17 0.24 0.59 0.01

Appendix B - URBS Catchment Definition File (Design Event)

Nerang River URBS model (URBS model created by (WRM) 20/06/2008)_CONTAINS DAMS MODEL: SPLIT USES: L,F*0.5,U,IF DEFAULT PARAMETERS: alpha=0.10 m=0.70 beta=1.5 n=1.0 DEFAULT PARAMETERS: IF = 200 CATCHMENT DATA FILE = Nerang_all.csv {NERANG RIVER} RAIN #1 L=3.54 {001d002} STORE. {STORE DAVES CK} RAIN #2 L=2.11 {002w002} GET. {GET DAVES CK} ROUTE THRU #2 L=1.50 {002d004} STORE. {STORE NATURAL BRIDGE} RAIN #3 L=3.74 {003d004} GET. {GET NATUAL BRIDGE} ROUTE THRU #4 L=2.99 {004u002} ADD RAIN #4 L=4.17 {004d006} STORE. {STORE NIXON CK} RAIN #5 L=4.44 {005d006} GET. {GET NIXON CK} ROUTE THRU #6 L=1.53 {006u004} ADD RAIN #6 L=1.92 {006d007} ROUTE THRU #7 L=3.32 {007u006} STORE. {STORE TONYS CK} RAIN #7 L=2.48 {007w007} GET. {GET TONYS CK} ROUTE THRU #7 L=1.55 {007d010} ROUTE THRU #10 L=0.88 {010u007} STORE. {STORE PINDARI} RAIN #10 L=1.72 {010w010} GET. {GET PINDARI} ROUTE THRU #10 L=0.31 {010d008} STORE. {STORE WATERFALL CK} RAIN #8 L=7.38 {008d010} GET. {GET WATERFALL CK} ROUTE THRU #10 L=0.81 {010u008} STORE. {STORE PINE CREEK} RAIN #9 L=2.51 {009d010} ROUTE THRU #10 L=0.25 {010u009} GET. {GET PINE CREEK} ROUTE THRU #10 L=0.60 {010d011 - START OF LEFT SIDE HINZE DAM} FACTOR = 0.1 {FACTOR FOR HINZE DAM} ROUTE THRU #11 L=1.75 {011u010 - IN HINZE DAM} ADD RAIN #11 L=1.50 {011d012 - IN HINZE DAM} PRINT. NER_WHIP {STREAMGAUGE WHIPBIRD(DNR)} ROUTE THRU #12 L=1.14 {012u011 - IN HINZE DAM} ADD RAIN #12 L=1.44 {012d013 - IN HINZE DAM} ROUTE THRU #13 L=0.79 {013u012 - IN HINZE DAM} STORE. {STORE BACK CREEK - IN HINZE DAM} RAIN #13 L=1.74 {013w013 - IN HINZE DAM} GET. {GET BACK CREEK} ROUTE THRU #13 L=1.42 {013d022 - IN HINZE DAM} STORE. {STORE HINZE DAM WALL} FACTOR = 1.0 {FACTOR FOR NON-HINZE DAM} RAIN #14 L=2.53 {014d015} ROUTE THRU #15 L=2.25 {015u014}


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ADD RAIN #15 L=2.88 {015d017 - START OF RIGHT SIDE LITTLE NERANG DAM} ROUTE THRU #17 L=0.33 {017u015 - IN LITTLE NERANG DAM} STORE. {STORE LITTLE NERANG DAM} RAIN #16 L=3.74 {016d017} FACTOR = 0.1 {FACTOR FOR LITTLE NERANG DAM} ROUTE THRU #17 L=0.78 {017u016 - START OF LEFT SIDE LITTLE NERANG DAM} GET. {GET LITTLE NERANG DAM} ROUTE THRU #17 L=0.59 {017w017 - IN LITTLE NERANG DAM} ADD RAIN #17 L=1.16 {017d018 - LITTLE NERANG DAM WALL} DAM ROUTE VBF=0 FILE = LNERANG.SQ {LITTLE NERANG DAM WALL} PRINT. LITTLE_N {STREAMGAUGE LITTLE NERANG DAM ALERT} FACTOR = 1.0 {FACTOR FOR NON-LIT NER DAM} ROUTE THRU #18 L=1.85 {018u017} ADD RAIN #18 L=1.41 {018d019} ROUTE THRU #19 L=2.78 {019u018} FACTOR = 0.1 {FACTOR FOR HINZE DAM} ADD RAIN #19 L=2.12 {019d020 - START OF RIGHT SIDE HINZE DAM} ROUTE THRU #20 L=2.14 {020u019 - IN HINZE DAM} ADD RAIN #20 L=2.11 {020d021 - IN HINZE DAM} PRINT. LT_NER_4K {STREAMGAUGE 4.0KM} ROUTE THRU #21 L=0.76 {021u020 - IN HINZE DAM} ADD RAIN #21 L=1.85 {021d022 - IN HINZE DAM} GET. {GET HINZE DAM WALL} PRINT. HINZE_INFLOW {PRINT INFLOW FOR HINZE DAM} DAM ROUTE VBF=0 FILE = HINZEST2.SQ {HINZE DAM WALL} PRINT. HINZE_DA {STREAMGAUGE HINZE DAM ALERT, HINZE DAM DOWN, HINZR DAM UPPER INTAKE} FACTOR = 1.0 {FACTOR FOR NON-HINZE DAM} ROUTE THRU #22 L=0.93 {022u013} STORE. RAIN #22 L = 0 PRINT. LH_SC22 GET. ROUTE THRU #22 L=1.35 {022d023} ROUTE THRU #23 L=4.61 {023u022} STORE. RAIN #23 L=0 PRINT. LH_SC23 GET. ROUTE THRU #23 L=4.10 {023d024} ROUTE THRU #24 L=0.89 {024u023} STORE. RAIN #24 L=0 PRINT. LH_SC24 GET. ROUTE THRU #24 L=1.32 {024d025} PRINT. CLEARVIE {STREAMGAUGE CLEARVIEW ALERT, GLENHURST, NERANG} FACTOR = 4.0 {FACTOR FOR NERANG RIVER} ROUTE THRU #25 L=1.26 {025u024} STORE. {STORE NERANG} RAIN #25 L=0 ROUTE THRU #25 L=1.09 {025w025} PRINT. LH_SC25 GET. {GET NERANG} ROUTE THRU #25 L=0.16 {025d027} STORE. RAIN #26 L=0 PRINT. LH_SC26 {STORE CRANE CK} ROUTE THRU #26 L=3.94 {026d027} GET. {GET CRANE CK} ROUTE THRU #27 L=1.96 {027u025} STORE. RAIN #27 L=0 PRINT. LH_SC27 {STORE MOOYUMBIN CK} ROUTE THRU #27 L=2.40 {027d028} GET. {GET MOOYUMBIN CK} ROUTE THRU #28 L=2.76 {028u027} STORE. {STORE PRINT #28} RAIN #28 L=0.00 {LOCAL #28} PRINT. SC28_LH {#28 A=15.14 X=535297.71 Y=6903541.93} GET. {GET PRINT #28} ROUTE THRU #28 L=3.77 {028d051} PRINT. CARRARA {STREAMGAUGE CARRARA ALERT} ROUTE THRU #51 L=0.99 {051u028} STORE. {STORE BENOWA} FACTOR = 1.0 {FACTOR FOR NON NERANG RIVER} RAIN #29 L=0.00 {LOCAL #29}


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PRINT. SC29_LH {#29 A=3.60 X=533879.47 Y=6901278.23} ROUTE THRU #29 L=2.12 {029d031} ROUTE THRU #31 L=0.39 {031u029} STORE. {STORE CARRARA} RAIN #30 L=0.00 {LOCAL #30} PRINT. SC30_LH {#30 A=4.67 X=534288.48 Y=6902381.83} ROUTE THRU #30 L=2.74 {030d031} ROUTE THRU #31 L=0.27 {031u030} GET. {GET CARRARA} ROUTE THRU #31 L=0.85 {031w031} STORE. {STORE PRINT #31} RAIN #31 L=0.00 {LOCAL #31} PRINT. SC31_LH {#31 A=3.10 X=536622.19 Y=6900573.02} GET. {GET PRINT #31} ROUTE THRU #31 L=1.30 {031d051} ROUTE THRU #51 L=0.37 {051u031} STORE. {STORE EMERALD LAKES} RAIN #32 L=0.00 {LOCAL #32} PRINT. SC32_LH {#32 A=8.81 X=533084.12 Y=6899169.38} ROUTE THRU #32 L=1.82 {032d033} ROUTE THRU #33 L=2.12 {033u032} STORE. {STORE PRINT #33} RAIN #33 L=0.00 {LOCAL #33} PRINT. SC33_LH {#33 A=7.08 X=536243.65 Y=6898930.01} GET. {GET PRINT #33} ROUTE THRU #33 L=2.10 {033d051} ROUTE THRU #51 L=0.65 {051u033} GET. {GET EMERALD LAKES} GET. {GET BENOWA} FACTOR = 4.0 {FACTOR FOR NERANG RIVER} ROUTE THRU #51 L=2.04 {051d039} STORE. {STORE CYPRESS GARDENS} FACTOR = 1.0 {FACTOR FOR NON NERANG RIVER} Rain #101 L = 0.46 Store. Rain #102 L = 0.49 Get. PRINT. TH_SC102 Route Thru #103 L = 0.54 Store. RAIN #103 L = 0 PRINT. LH_SC103 GET. ROUTE THRU #103 L = 0.54 Store. RAIN #104 L = 0.61 PRINT. LH_SC104 Get. Route Thru #105 L = 0.23 STORE. Rain #105 L=0 PRINT. LH_SC105 Get. ROUTE THRU #105 L = 0.23 Store. Rain #106 L = 0.57 PRINT. LH_SC106 Get. Route Thru #107 L = 0.09 Store. Rain #107 L = 0.84 PRINT. LH_SC107 Get. Route Thru #108 L = 0.59 Store. Rain. #108 L=0 PRINT. LH_SC108 GET. ROUTE THRU #108 L = 0.62 Store. Rain #109 L = 0.68 Route Thru #110 L = 0.31 Add Rain #110 L = 0.36 PRINT. TH_SC110


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Get. Route Thru #111 L = 0.64 STORE. RAIN. #111 L=0 PRINT. LH_SC111 GET. ROUTE THRU #111 L = 0.43 Store. RAIN. #112 L=0.8 PRINT. LH_SC112 GET. Print. TH_SC112 {X = 533210.13, Y = 6896651.52} {Contribution from SC101 to SC112} Route Thru #113 L = 0.54 Store. Rain #113 L = 0 Print. LH_SC113 {X = , Y = } Get. Route Thru #113 L = 0.53 Store. Rain #114 L = 0 Route thru #114 L = 0.53 Store. Rain #115 L = 0 Route Thru #115 L = 0.39 Get. Print. TH_SC115 Route Thru #116 L = 0.29 Store. Rain #116 L = 0 Print. LH_SC116 Get. Route Thru #116 L = 0.30 Route Thru #117 L = 0.49 Store. Rain #117 L = 0 Print. LH_SC117 Get. Route Thru #117 L = 0.48 Store. Rain #118 L = 0 Route Thru #118 L = 0.74 Print. LH_SC118 Get. Route Thru #119 L = 0.63 Store. Rain #119 L = 0. Print. LH_SC119 Get. Route Thru #119 L = 0.64 Store. Rain #120 L = 0 Route Thru #120 L = 0.46 Print. LH_SC120 Get. Route Thru #121 L = 0.16 Store. Rain #121 L = 0 Route Thru #121 L = 0.59 Print. LHSC121 Get. Store. Rain #122 L = 0 Route Thru #122 L = 0.92 Print. LH_SC122 Get. Route Thru #123 L = 0.39 Store. Rain #123 L = 0 Print. LH_SC123 Get. Print. TH_SC123 Route Thru #123 L = 0.30 Get. Route Thru #124 L = 0.45 Store.


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Rain #124 L = 0 Print. LH_SC124 {X = , Y = } Get. Route Thru #124 L = 0.50 Store. Rain #125 L = 0 Print. LH_SC125 {X = , Y = } Route Thru #125 L = 0.64 Get. Route Thru #126 L = 0.29 Store. Rain #126 L = 0 Print. LH_SC126 {X = , Y = } Get. Route Thru #126 L = 0.31 Store. Rain #127 L = 0 Print. LH_SC127 {X = , Y = } Route Thru #127 L = 0.77 Get. Route Thru #127 L = 0.39 {PRINT. WORONGARY127*} {Print. TH_SC127} {X = 535434.11, Y = 6895611.73} {INPUT.WORONGARY127:A=14.1} {****INPUT FROM WORONGARY SUB #27****} PRINT. WORON127 {****INPUT FROM WORONGARY SUB #27****} ROUTE THRU #34 L=0.65 {034uW27} STORE. {STORE PRINT #34} RAIN #34 L=0.00 {LOCAL #34} PRINT. SC34_LH {#34 A=1.61 X=535906.55 Y=6895888.11} GET. {GET PRINT #34} ROUTE THRU #34 L=0.57 {034d035} ROUTE THRU #35 L=1.55 {035u034} STORE. {STORE PRINT #35} RAIN #35 L=0.00 {LOCAL #35} PRINT. SC35_LH {#35 A=3.71 X=537298.01 Y=6897491.03} GET. {GET PRINT #35} ROUTE THRU #35 L=1.32 {035d039} ROUTE THRU #39 L=0.11 {039u035} STORE. {STORE MERRIMAC} Factor = 1 Rain #201 L = 2.25 Route Thru #202 L = 1.28 Add Rain #202 L = 1.21 Route Thru #203 L = 1.96 Add Rain #203 L = 0.00 Print. TH_SC203 Route Thru #203 L = 1.84 Route Thru #204 L = 1.37 Store. Rain #204 L = 0.00 Print. LH_SC204 Get. Route Thru #204 L = 1.39 Route Thru #205 L = 1.47 Store. Rain #205 L = 0.00 Print. LH_SC205 Get. Route Thru #205 L = 1.31 Route Thru #206 L = 1.56 Store. Rain #206 L = 0.00 Print. LH_SC206 Get. Print. TH_SC206 Route Thru #206 L = 1.56 Route Thru #207 L = 0.82 Route Thru #207 L = 0.89 Store. Rain #207 L = 0.89 Print. LH_SC207 {X = , Y = } Get. Print. mudge_tm {X =534668.42 , Y =6893224.09} {Contribution from SC201 to SC207} Factor = 2.4 {********************************}


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Route Thru #208 L = 1.03 Store. Rain #208 L = 0 Print. LH_SC208 {X = , Y = } Get. Route Thru #208 L = 1.05 Store. Factor = 1.0 {********************************} Rain #209 L = 0.00 Print. LH_SC209 Route Thru #209 L = 2.14 Route Thru #210 L = 1.51 Store. Rain #210 L = 0.00 Print. LH_SC210 Get. Route Thru #210 L = 1.53 Route Thru #211 L = 1.16 Store. Rain #211 L = 0.00 Print. LH_SC211 Get. Route Thru #211 L = 1.08 Store. Rain #212 L = 2.53 Print. LH_SC212 Get. Route Thru #213 L = 1.96 Store. Rain #213 L = 0.00 Print. LH_SC213 Route Thru #213 L = 2.25 Get. Store. Rain #214 L = 1.89 Print. LH_SC214 Get. Factor = 2.4 {********************************} Route Thru #215 L = 0.75 Store. Rain #215 L = 0 Print. LH_SC215 Get. Route thru #215 L = 0.74 Get. Route Thru #219 L = 0.94 Store. Rain #216 L = 0 Print. LH_SC216 Factor = 1.0 {********************************} Route Thru #216 L 1.72 Route Thru #217 L = 1.41 Store. Factor = 2.4 {************************} Rain #217 L = 0 Print. LH_SC217 Get. Print. TH_SC217 {X = , Y = } Route Thru #217 L = 1.42 Route Thru #219 L = 0.18 Get. Store. Rain #219 L = 0 Print. LH_SC219 {X = , Y = } Get. Route Thru #219 L = 0.7 Store. Rain #218 L = 0 Print. LH_SC218 {X = , Y = } Route Thru #218 L = 1.22 Route Thru #219 L = 1.27 get. Print. Mudgeeraba* {X = , Y = } {INPUT.MUDGEERABA:A=84.0 } {****INPUT FROM MUDEGEERABA****} FACTOR = 4.0 {FACTOR FOR ROBINA-CANALS}


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ROUTE THRU #36 L=1.15 {036uMud} STORE. {STORE PRINT #36} RAIN #36 L=0.00 {LOCAL #36} PRINT. SC36_LH {#36 A=3.18 X=536626.62 Y=6894669.43} GET. {GET PRINT #36} ROUTE THRU #36 L=0.84 {036d037} STORE. {STORE SKILLED PARK} FACTOR = 1.0 {FACTOR FOR NON ROBINA-CANALS} Rain #128 L = 0 Print. LH_SC128 {X = , Y = } Route Thru #128 L = 0.39 Route Thru #129 L = 0.36 Store. Rain #129 L = 0 Print. LH_SC129 {X = , Y = } Get. Route Thru #129 L = 0.37 Route Thru #130 L = 0.27 Store. Rain #130 L = 0 Print. LH_SC130 {X = , Y = } Get. Route Thru #130 L = 0.28 Store. Rain #131 L = 0 Print. LH_SC131 {X = , Y = } Route Thru #131 L = 0.48 Get. Route Thru #132 L = 0.29 Store. Rain #132 L = 0 Print. LH_SC132 {X = , Y = } Get. Route Thru #132 L =0.10 Store. Rain #133 L = 0 Print. LH_SC133 {X = , Y = } Route Thru #133 L = 0.62 Get. PRINT. WORONGARY132* Print. TH_SC132 {X = 535530.14 , Y = 6895366.71} {INPUT.WORONGARY32:A=2.5} {****INPUT FROM WORONGARY SUB #32****} ROUTE THRU #36 L=1.7 {036uW32} GET. {GET SKILLED PARK} FACTOR = 4.0 {FACTOR FOR ROBINA-CANALS} ROUTE THRU #37 L=1.11 {037u036} STORE. {STORE ROBINA} RAIN #38 L=0.00 {LOCAL #38} PRINT. SC38_LH {#38 A=2.12 X=537584.06 Y=6893556.42} ROUTE THRU #38 L=1.92 {038d037} ROUTE THRU #37 L=1.55 {037u038} GET. {GET ROBINA} STORE. {STORE PRINT #37} RAIN #37 L=0.00 {LOCAL #37} PRINT. SC37_LH {#37 A=4.34 X=537751.61 Y=6896165.43} GET. {GET PRINT #37} ROUTE THRU #37 L=1.25 {037d039} ROUTE THRU #39 L=1.22 {039u037} STORE. {STORE CLEAR ISLAND} RAIN #39 L=0.00 {LOCAL #39} PRINT. SC39_LH {#39 A=8.36 X=539243.09 Y=6897880.13} ROUTE THRU #39 L=0.87 {039w039} GET. {GET CLEAR ISLAND} ROUTE THRU #39 L=0.76 {039d035} GET. {GET MERRIMAC} PRINT. BOOBEGAN {STREAMGAUGE BOOBEGAN CREEK LOCK ALERT} ROUTE THRU #39 L=1.24 {039d051} FACTOR = 1.0 {FACTOR FOR NON ROBINA-CANALS} FACTOR = 4.0 {FACTOR FOR NERANG RIVER} ROUTE THRU #51 L=0.62 {051u039} GET. {GET CYPRESS GARDENS} ROUTE THRU #51 L=2.21 {051w051} STORE. {STORE PRINT #51} RAIN #51 L=0.00 {LOCAL #51} PRINT. SC51_LH {#51 A=12.68 X=540193.07 Y=6900844.88}


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GET. {GET PRINT #51} ROUTE THRU #51 L=1.36 {051d050} STORE. {STORE LITTLE TALLEBUDGERA CK} FACTOR = 1.0 {FACTOR FOR NON NERANG RIVER} RAIN #40 L=0.00 {LOCAL #40} PRINT. SC40_LH {#40 A=4.51 X=538649.20 Y=6891773.19} ROUTE THRU #40 L=2.21 {040d046} FACTOR = 4.0 {FACTOR FOR BURLEIGH-CANALS} ROUTE THRU #46 L=0.37 {046u040} STORE. {STORE VARSITY LAKES} RAIN #41 L=0.00 {LOCAL #41} PRINT. SC41_LH {#41 A=7.81 X=539558.77 Y=6890468.69} ROUTE THRU #41 L=2.84 {041d046} ROUTE THRU #46 L=0.38 {046u041} GET. {GET VARSITY LAKES} ROUTE THRU #46 L=0.95 {046w046} STORE. {STORE PRINT #46} RAIN #46 L=0.00 {LOCAL #46} PRINT. SC46_LH {#46 A=3.77 X=540719.66 Y=6893735.93} GET. {GET PRINT #46} ROUTE THRU #46 L=0.44 {046d045} STORE. {STORE BURLEIGH WATERS} FACTOR = 1.0 {FACTOR FOR NON BURLEIGH-CANALS} RAIN #42 L=0.00 {LOCAL #46} PRINT. SC42_LH {#42 A=3.79 X=541485.61 Y=6890492.62} ROUTE THRU #42 L=1.11 {042d043} ROUTE THRU #43 L=0.94 {043u042} STORE. {STORE PRINT #43} RAIN #43 L=0.00 {LOCAL #43} PRINT. SC43_LH {#43 A=3.26 X=542598.63 Y=6891904.84} GET. {GET PRINT #43} ROUTE THRU #43 L=0.91 {043d044} FACTOR = 4.0 {FACTOR FOR BURLEIGH-CANALS} ROUTE THRU #44 L=0.90 {044u043} STORE. {STORE PRINT #44} RAIN #44 L=0.00 {LOCAL #44} PRINT. SC44_LH {#44 A=3.09 X=542909.79 Y=6893293.12} GET. {GET PRINT #44} ROUTE THRU #44 L=0.79 {044d045} ROUTE THRU #45 L=0.52 {045u044} STORE. {STORE PRINT #45} RAIN #45 L=0.00 {LOCAL #45} PRINT. SC45_LH {#45 A=2.84 X=542574.69 Y=6894262.52} GET. {GET PRINT #45} ROUTE THRU #45 L=1.04 {045d046} ROUTE THRU #46 L=0.51 {046u045} GET. {GET BURLEIGH WATERS} ROUTE THRU #46 L=1.21 {046d048} STORE. {STORE BOND} FACTOR = 1.0 {FACTOR FOR NON BURLEIGH-CANALS} RAIN #47 L=0.00 {LOCAL #47} PRINT. SC47_LH {#47 A=3.10 X=539706.3 Y=6894356.39} ROUTE THRU #47 L=2.14 {047d048} GET. {GET BOND} FACTOR = 4.0 {FACTOR FOR BURLEIGH-CANALS} ROUTE THRU #48 L=0.47 {048u046} STORE. {STORE PRINT #48} RAIN #48 L=0.00 {LOCAL #48} PRINT. SC48_LH {#48 A=1.35 X=541425.77 Y=6895447.35} GET. {GET PRINT #48} ROUTE THRU #48 L=0.43 {048d049} ROUTE THRU #49 L=1.39 {049u048} STORE. {STORE PRINT #49} RAIN #49 L=0.00 {LOCAL #49} PRINT. SC49_LH {#49 A=7.83 X=541655.61 Y=6897245.85} GET. {GET PRINT #49} ROUTE THRU #49 L=1.56 {049d050} ROUTE THRU #50 L=1.98 {050u049} STORE. {STORE PRINT #50} RAIN #50 L=0.00 {LOCAL #50} PRINT. SC50_LH {#50 A=4.30 X=541593.32 Y=6900007.13} GET. {GET PRINT #50} ROUTE THRU #50 L=0.95 {050d051} GET. {GET LITTLE TALLEBUDGERA CK} FACTOR = 1.0 {FACTOR FOR NON BURLEIGH-CANALS} FACTOR = 4.0 {FACTOR FOR NERANG RIVER}


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ROUTE THRU #51 L=3.42 {051d052} PRINT. EVANDALE {STREAMGAUGE EVANDALE ALERT} PRINT. COAST {STREAMGAUGE COAST ALERT} ROUTE THRU #52 L=1.42 {052u051} STORE. {STORE PRINT #52} RAIN #52 L=0.00 {LOCAL #52} PRINT. SC52_LH {#52 A=9.03 X=541168.04 Y=69040096.41} GET. {GET PRINT #52} ROUTE THRU #52 L=1.31 {052out} PRINT. NERANG_OUT {ENTER BROADWATER} END OF CATCHMENT DATA. 8 RATING CURVES: LOCATION. NER_WHIP LOCATION. LITTLE_N LOCATION. LT_NER_4K LOCATION. HINZE_DA LOCATION. CLEARVIE LOCATION. BOOBEGAN LOCATION. CARRARA LOCATION. MUDGEERA {LOCATION. EVANDALE/COAST=-0.76 LOCATION. EVANDALE/COAST=-0.25 LOCATION. EVANDALE/COAST=0.70 LOCATION. EVANDALE/COAST=1.50 LOCATION. COAST} END OF RATING CURVE DATA.


Appendix C- Design Temporal Patterns

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

0.5 hours

ARI <30 13.9 26.6 20.2 15.6 12.4 11.3

ARI >30≤100 13.9 25.6 19.5 17 12 12

GSDM 20.4 23.65 20.45 17.2 12.4 5.9

1 hour

ARI <30 5.5 8.2 9.5 11 10.4 17.8 8 7.3 6.2 5.7 5.5 4.9

ARI >30≤100 5.9 7.5 8.4 11.3 11 17.7 7.9 6.6 6.2 6 5.8 5.7

GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1

1.5 hours

ARI <30 3.4 4.8 6.7 7.3 12.1 8.2 6.1 6 5.7 5.3 4.3 5.2 4.4 4.4 4.2 4.1 4 3.8

ARI >30≤100 4.4 4.7 6.4 6.8 11 8.8 5.6 6.1 6 5.3 4.8 5.3 4.4 4.3 4.2 4.1 4 3.8

GSDM 5.1 6.8 8.5 8.3 7.7 7.6 7.2 6.8 6.5 6.1 5.6 5.5 5 4.2 3.2 2.7 1.9 1.3

3 hours

ARI <30 6.6 12.1 15.8 9.7 7.3 6.8 5.9 7.8 11.1 6.2 5.5 5.2

ARI >30≤100 7.2 11.7 15.8 9.1 7.5 7.1 6.4 7.4 10.5 6.1 5.9 5.3

GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1

4.5 hours

ARI <30 8.8 6.1 4.5 7.1 4.8 5.5 3.5 7.5 11.7 8.6 4.6 3.2 4 3.7 3 4.6 5.2 3.6

ARI >30≤100 7.7 6.6 4.7 7 4.9 5.6 4 6.5 10.9 7.9 4.8 4 3.9 3.7 3.4 4.9 5.6 3.9

GSDM 5.1 6.8 8.5 8.3 7.7 7.6 7.2 6.8 6.5 6.1 5.6 5.5 5 4.2 3.2 2.7 1.9 1.3

6 hours

ARI <30 5.8 6.1 7.3 9.6 17.2 6.6 13.5 7.7 6.4 4.5 9.9 5.4

ARI >30≤100 6.1 6.9 7.4 10.2 15.3 7.2 12.2 8.2 6.8 4.8 9.8 5.1

GSDM 8.1 12.3 12.1 11.55 10.75 9.7 8.8 8.4 7.3 5.1 3.8 2.1

9 hours

ARI <30 3.8 4.3 2.6 3.4 4.9 4.5 6.1 7.1 8.5 7.4 11.7 6.7 5.8 5.2 3.7 2.9 6.9 4.5

ARI >30≤100 3.7 4.4 3 3.8 5.6 4.5 5.8 6.9 8.2 7.2 11.2 6.7 5.7 5.4 4.1 2.9 6.9 4

GSDM GTSMR 6.03 6.03 7.93 7.93 7.28 7.28 7.13 7.13 6.8 6.8 5.63 5.63 4.45 4.45 3.05 3.05 1.73 1.73

12 Hours

ARI <30 3.2 2.5 2.6 2.8 3.1 3.2 3.5 4.4 5.1 4 4.6 7.4 4.7 9.7 5.8 5.3 4.4 3.3 3.7 2.5 3 4.5 3.6 3.1

ARI >30≤100 3.3 2.5 2.8 3.3 3.9 3.5 3.8 4.2 4.7 3.8 4.7 7.2 4.4 9.5 5.5 4.9 4.4 3.8 3.8 2.5 3.1 4.2 3.3 2.9

GSDM GTSMR 4.35 4.35 5.57 5.57 5.53 5.53 5.06 5.06 5.4 5.4 5.88 5.88 4.89 4.89 4.08 4.08 3.35 3.35 2.51 2.51 2.1 2.1 1.29 1.29

18 hours

ARI <30 3.5 2.7 2.3 4.7 4.9 7.1 9 14.4 5 7.8 7 5.7 6.3 5.2 4.2 3.4 3.9 2.9


ARI >30≤100 3.6 2.7 2.2 4.8 5.2 6.8 9.5 14 5 7.6 6.7 4.8 6.5 5.2 4.4 3.7 4.2 3.1

GSDM GTSMR 6.07 6.37 6.68 6.59 6.36 6.13 7.13 8.2 9.27 7.17 6.18 5.2 4.03 3.77 3.5 2.94 2.45 1.96

24 hours

ARI <30 3.3 2 2.5 2 2.4 3.8 4.9 5.4 3.8 5.1 6.1 6.8 11.5 3.1 6.5 7.9 4.2 3.6 2.6 3 2.4 3.4 2 1.7

ARI >30≤100 3.4 1.7 2.5 1.9 2.5 3.6 5.1 5.5 3.4 5.3 6.2 6.9 12.2 3 6.4 7.8 3.7 3.4 2.4 2.9 2.2 3.3 2.5 2.2

GTSMR 4.76 4.76 4.76 4.28 4.28 4.28 3.65 3.65 3.65 7.92 7.92 7.92 5.94 5.94 5.94 2.3 2.3 2.3 2.84 2.84 2.84 1.65 1.65 1.65

36 hours

ARI <30 3.5 2.5 2.8 3.4 3.6 6.9 4 4.7 5.8 3.4 15.2 8.9 7.7 11.8 5.9 3.7 3.4 2.8

ARI >30≤100 3.9 3.1 2.8 3.6 3.2 6.5 3.6 4.3 5.9 3.6 14.3 9.9 8.3 10.9 6.5 3.7 3.2 2.7

GTSMR 2.2 2.62 3.04 3.49 5.02 6.54 4.96 4.26 3.56 7.67 9.74 11.8 8.74 7.41 6.09 3.99 4.29 4.6

48 hours

ARI <30 2.4 2.2 2.3 2.3 3.2 3.4 2.5 3.6 2.7 3.7 3.5 5.5 13.5 8.9 6.2 3.4 5.3 8.7 3.5 4.1 2.8 2.3 2 2

ARI >30≤100 2.8 2.5 2.4 2.1 3 3.2 2.1 3.6 2.7 3.5 3.5 5.8 11.8 9.3 6.7 4.1 5.9 8.6 3.3 4.1 2.5 2.3 2.1 2.1

GTSMR 4.1 3.66 3.22 1.5 2.16 2.81 3.96 3.71 3.47 5.69 5.93 6.17 9.35 7.32 5.29 2.48 4.91 7.33 4.73 3.2 1.67 2.67 3.56 1.11

72 hours

ARI <30 6.3 2.9 4.2 7.3 4.7 3.4 9.2 11.7 16.8 6.1 4.2 3.9 3.9 3.4 3.2 3.1 2.9 2.8

ARI >30≤100 6.5 3.4 4.2 6.7 4.5 3.3 8 11.1 16.9 6.8 4.8 3.9 3.8 3.5 3.4 3.3 3 2.9

GTSMR 5.55 8.68 9.3 5.06 2.33 4.26 12.88 3.99 2.09 2.23 4.03 6.82 4.43 9.76 11.26 3.49 2.45 1.39

96 hours

ARI <30 1.41 3.8 6.25 0.96 3 2.2 5.77 6.85 7.78 4.75 0.45 2.02 2.42 3.49 2.79 1.8 1.04 4.13 9.56 3.19 0.24 1.44 4.47 5.08 2.52 2.61 1.82 1.1 2.39 1.24 1.94 1.49

ARI >30≤100 1.41 3.8 6.25 0.96 3 2.2 5.77 6.85 7.78 4.75 0.45 2.02 2.42 3.49 2.79 1.8 1.04 4.13 9.56 3.19 0.24 1.44 4.47 5.08 2.52 2.61 1.82 1.1 2.39 1.24 1.94 1.49

GTSMR 1.41 3.8 6.25 0.96 3 2.2 5.77 6.85 7.78 4.75 0.45 2.02 2.42 3.49 2.79 1.8 1.04 4.13 9.56 3.19 0.24 1.44 4.47 5.08 2.52 2.61 1.82 1.1 2.39 1.24 1.94 1.49

120 hours

ARI <30 0.45 0.3 0.52 2.1 1.34 1.43 1.67 0.72 1.51 5.14 3.62 1.12 0.64 0.94 3.21 7.88 10.15 5.59 2.5 2.18 6.93 6.16 0.83 0.89 1.06 4.22 1.78 4.64 2.76 1.95 3.03 1.2 2.31 3.92 3.37 0.14 0.37 0.21 0.57 0.66

ARI >30≤100 0.45 0.3 0.52 2.1 1.34 1.43 1.67 0.72 1.51 5.14 3.62 1.12 0.64 0.94 3.21 7.88 10.15 5.59 2.5 2.18 6.93 6.16 0.83 0.89 1.06 4.22 1.78 4.64 2.76 1.95 3.03 1.2 2.31 3.92 3.37 0.14 0.37 0.21 0.57 0.66

GTSMR 0.45 0.3 0.52 2.1 1.34 1.43 1.67 0.72 1.51 5.14 3.62 1.12 0.64 0.94 3.21 7.88 10.15 5.59 2.5 2.18 6.93 6.16 0.83 0.89 1.06 4.22 1.78 4.64 2.76 1.95 3.03 1.2 2.31 3.92 3.37 0.14 0.37 0.21 0.57 0.66


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Appendix D – Probable Maximum Precipitation (PMP) Calculation

The PMP calculations were undertaken based on BOM methodology (Ref 33).

D.1 PMP Method Selection

Worksheet E.1 - PMP method selection, Nerang River catchment

Catchment Name: Nerang Catchment Area: 492 km2

Long Duration PMP

HIGHLIGHT THE ZONE IN WHICH THE CATCHMENT IS LOCATED

GTSMR (Coastal)

GTSMR (Inland)

GTSMR (Coastal

& SWWA)

Coastal Transition - GTSMR Coastal - GSAM Coastal

GSAM (Coastal)

WA Transition - GTSMR Coastal

-GSAM Inland

GSAM (Inland)

WCTas

Short Duration PMP (GSDM)

Short duration PMP estimates can not be calculated for the catchment

PMP estimates for up to 6 hours can be calculated using the GSDM for this catchment

PMP estimates for up to 6 hours can be calculated using the GSDM for this catchment and can include winter estimates

PMP Method Summary

Method Zone Season Duration

GSDM 6 hours Summer 0.5 – 6 hours

GTSMR Coastal Summer 24 – 120 hours

What Next?

GTSMR: Calculate the PMP estimates for the catchment following the procedures in the guidebook

GSDM: Calculate the PMP estimates for up to 6 hours following the GSDM (Bureau of Meteorology, 2003) guidebook (http://www.BOM.gov.au/hydro/has/gsdm_document.shtml)

GSAM: Contact the Hydrometeorological Advisory Service, Bureau of Meteorology

WCTas: Contact the Hydrometeorological Advisory Service, Bureau of Meteorology

West Coast Tasmania Method Zone

Inland Zone

Inland Zone

HOBART

DARWIN

PERTH

Port Hedland

Townsville

BRISBANE

CANBERRACANBERRA

SYDNEYSYDNEYSW WAWinter Zone

Coastal Transition Zone

Coastal Zone

Coastal Zone

ADELAIDE

GTSMR

GSAM

GTSMR

GTSMR

GSAM

GSAM-GTSMR

GSAM-GTSMRWA Transition Zone

Is the catchment less than 1000km2?

Is the catchment less than 500km2 and south of 300 S ?

YES

NO

YES

NO


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D.2 Generalised Short Duration Method (GSDM)

Worksheet E.2 – GSDM PMP calculation sheet, Nerang River catchment

Location Information

Catchment: Nerang Area: 492 km2

State: QLD Duration Limit: 6 hrs

Latitude (dd.dd): -28.1033 S Longitude (dd.dd): 153.3077 E

Proportion of Area Considered

Smooth, S (0.0 - 1.0): 0.0 Rough, R (0.0 - 1.0): 1.0

Elevation Adjustment Factor (EAF)

Mean Elevation: 184m AHD

Adjustment for Elevation (-0.05 per 300m above 1500m)

EAF = 1.00 (0.85- 1.0)

Moisture Adjustment Factor (MAF)

MAF = 0.84 (0.40-1.00)

PMP Values (mm)

Durations (hours) Initial Depth Initial Depth PMP Estimates = Rounded

(hours) - Smooth - Rough (DSxS + DRxR) PMP Estimate

(DS) (DR) x MAF x EAF (nearest 10 mm)

0.25 125 125 105.00 110

0.50 185 185 155.40 160

0.75 235 235 197.40 200

1.0 288 288 241.92 240

1.5 330 380 319.20 320

2.0 380 435 365.40 370

2.5 415 495 415.80 420

3.0 450 530 445.20 450

4.0 510 607 509.88 510

4.5 530 626 525.84 530

5.0 550 645 541.80 540

6.0 590 695 583.80 580

Note: Value of 4.5 hours duration obtained from interpolation between 4 & 5 hour values


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Figure D-1 GSDM design spatial distribution of PMP, Nerang River catchment


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Table D-1 GSDM, mean rainfall depth between ellipses, Nerang River catchment

Ellipse

Mean Rainfall Depth between Ellipses (mm)

Storm Duration (hours)

0.25 0.5 0.75 1 1.5 2 2.5 3 4 5 6

A 195 282 357 414 534 625 690 757 865 953 1008

B-A 167 247 315 370 473 553 610 666 761 836 892

C-B 141 207 263 319 412 473 535 577 650 712 761

D-C 119 175 222 272 353 404 462 500 560 607 645

E-D 102 151 193 235 310 356 406 438 502 530 565

F-E 101 139 181 209 284 316 369 379 434 460 508

G-F 87 138 157 226 279 325 354 409 472 484 526

H-G 19 70 112 122 234 280 330 274 373 371 413

Value for 4.5 hour duration obtained from Interpolating between the 4 and 5 hour values

D.3 Generalised Tropical Storm Method Revised (GTSMR)

Worksheet E.3 – GTSMR PMP calculation sheet, Nerang River catchment

Location Information

Catchment Name: Nerang State: QLD GTSMR zone (s): Coastal

Catchment Factor Topographic Adjustment Factor TAF = 1.8782 (1.0 -2.0) Decay Amplitude Factor DAF = 0.9678 (0.7 -1.0) Annual Moisture Adjustment Factor MAFa = EPWcatchment/120 Extreme Precipitable Water (EPWcatchment): 86.2231 MAFa = 0.718526 (0.4 - 1.1)

PMP Values (mm) - Annual Coastal

Duration (hours) Initial Depth

(Da) PMP Estimate

=DaxTAFxDAFxMAFa

Preliminary PMP Estimate

(nearest 10mm)

Final PMP Estimate

0.5

Calculate GSDM (Bureau of Meteorology, 2003) depths

160 1 240

1.5 320 2 370 3 450 4 510

4.5 530 5 540 6 580


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9 No preliminary estimates available 910 12 No preliminary estimates available 1230 18 No preliminary estimates available 1450

24 1275.05728 1665.32705 1670 1670

36 1531.37104 2000.093373 2000 2000

48 1770.88672 2312.920057 2310 2310

72 2193.08752 2864.348156 2860 2860

96 2462.76592 3216.569771 3220 3220

120 2593.2248 3386.959529 3390 3390

Worksheet E.4 – GTSMR design spatial distribution, Nerang catchment

PMPi = PMPc x Average Ratioi (TAFi) / Average Ratioc (TAFc)

i = individual sub catchment

c = catchment

PMPi = average PMP depth for individual sub catchment

PMPc = average PMP depth over the whole catchment

TAFc = 1.8782

Sub Catchment

TAF of Subcatchment

(1.0‐2.0)

PMP 12hours

PMP 24hours

PMP 36hours

PMP 48hours

PMP 72hours

PMP 96hours

PMP 120hours

Neran01 1.9839 1299.221 1763.983 2112.555 2440.001 3020.953 3401.213 3580.78

Neran02 1.8976 1242.705 1687.249 2020.658 2333.86 2889.541 3253.26 3425.015

Neran03 2 1309.765 1778.298 2129.699 2459.802 3045.469 3428.815 3609.839

Neran04 1.8621 1219.456 1655.685 1982.856 2290.199 2835.484 3192.398 3360.941

Neran05 1.7081 1118.605 1518.756 1818.869 2100.794 2600.983 2928.379 3082.983

Neran06 1.6741 1096.339 1488.525 1782.664 2058.977 2549.21 2870.089 3021.616

Neran07 1.5793 1034.256 1404.233 1681.717 1942.383 2404.855 2707.564 2850.51

Neran08 1.8001 1178.854 1600.557 1916.835 2213.945 2741.074 3086.105 3249.036

Neran09 1.7739 1161.696 1577.262 1888.936 2181.721 2701.179 3041.187 3201.747

Neran10 1.5986 1046.895 1421.394 1702.268 1966.12 2434.243 2740.652 2885.344

Neran11 1.6746 1096.666 1488.969 1783.197 2059.592 2549.971 2870.947 3022.518

Neran12 1.6664 1091.296 1481.678 1774.465 2049.507 2537.485 2856.889 3007.718

Neran13 1.6295 1067.131 1448.869 1735.172 2004.124 2481.296 2793.627 2941.116

Neran14 2 1309.765 1778.298 2129.699 2459.802 3045.469 3428.815 3609.839

Neran15 1.9995 1309.437 1777.854 2129.166 2459.187 3044.708 3427.958 3608.937

Neran16 1.9845 1299.614 1764.517 2113.193 2440.738 3021.867 3402.242 3581.863

Neran17 1.9206 1257.767 1707.7 2045.15 2362.148 2924.564 3292.691 3466.529

Neran18 1.8866 1235.501 1677.469 2008.945 2320.331 2872.791 3234.401 3405.161

Neran19 1.8527 1213.301 1647.327 1972.846 2278.638 2821.17 3176.283 3343.975

Neran20 1.7717 1160.255 1575.306 1886.594 2179.016 2697.829 3037.416 3197.776

Neran21 1.7097 1119.652 1520.178 1820.573 2102.762 2603.419 2931.122 3085.871

Neran22 1.6449 1077.216 1462.561 1751.571 2023.064 2504.746 2820.029 2968.912

Neran23 1.5865 1038.971 1410.635 1689.383 1951.238 2415.818 2719.907 2863.505

Neran24 1.5452 1011.924 1373.913 1645.405 1900.443 2352.929 2649.102 2788.962

Neran25 1.5298 1001.839 1360.22 1629.006 1881.503 2329.479 2622.7 2761.166


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Neran26 1.5293 1001.512 1359.776 1628.474 1880.888 2328.718 2621.843 2760.264

Neran27 1.4863 973.3516 1321.542 1582.686 1828.002 2263.24 2548.124 2682.652

Neran28 1.4455 946.6324 1285.265 1539.24 1777.822 2201.113 2478.176 2609.011

Neran29 1.5239 997.9752 1354.974 1622.724 1874.246 2320.495 2612.585 2750.517

Neran30 1.4931 977.8048 1327.589 1589.927 1836.365 2273.595 2559.782 2694.925

Neran31 1.4914 976.6915 1326.077 1588.116 1834.274 2271.006 2556.867 2691.857

Neran32 1.5943 1044.079 1417.571 1697.689 1960.831 2427.696 2733.28 2877.583

Neran33 1.5414 1009.436 1370.535 1641.359 1895.769 2347.143 2642.588 2782.103

Neran34 1.6341 1070.143 1452.959 1740.07 2009.781 2488.301 2801.513 2949.419

Neran35 1.5461 1012.514 1374.714 1646.364 1901.55 2354.3 2650.645 2790.586

Neran36 1.646 1077.936 1463.54 1752.742 2024.417 2506.421 2821.915 2970.898

Neran37 1.5654 1025.153 1391.874 1666.915 1925.287 2383.689 2683.733 2825.421

Neran38 1.6307 1067.917 1449.936 1736.45 2005.6 2483.123 2795.684 2943.282

Neran39 1.4802 969.3568 1316.119 1576.19 1820.499 2253.952 2537.666 2671.642

Neran40 1.6151 1057.7 1436.065 1719.838 1986.413 2459.369 2768.939 2915.126

Neran41 1.5922 1042.704 1415.703 1695.453 1958.248 2424.498 2729.679 2873.793

Neran42 1.5121 990.2476 1344.482 1610.159 1859.733 2302.527 2592.355 2729.219

Neran43 1.4486 948.6625 1288.022 1542.541 1781.635 2205.833 2483.491 2614.607

Neran44 1.4149 926.593 1258.057 1506.655 1740.187 2154.517 2425.715 2553.781

Neran45 1.4144 926.2656 1257.613 1506.123 1739.572 2153.756 2424.858 2552.878

Neran46 1.4967 980.1624 1330.79 1593.76 1840.793 2279.077 2565.954 2701.423

Neran47 1.5268 999.8743 1357.553 1625.812 1877.813 2324.911 2617.557 2755.751

Neran48 1.4389 942.3102 1279.397 1532.212 1769.705 2191.063 2466.861 2597.099

Neran49 1.3988 916.0494 1243.742 1489.511 1720.385 2130.001 2398.113 2524.722

Neran50 1.3584 889.5922 1207.82 1446.491 1670.697 2068.483 2328.851 2451.803

Neran51 1.3828 905.5713 1229.515 1472.474 1700.707 2105.637 2370.683 2495.843

Neran52 1.3246 867.4571 1177.767 1410.499 1629.127 2017.014 2270.904 2390.797

Mudge01 2 1309.765 1778.298 2129.699 2459.802 3045.469 3428.815 3609.839

Mudge02 1.9937 1305.639 1772.697 2122.99 2452.054 3035.876 3418.014 3598.468

Mudge03 1.9557 1280.753 1738.909 2082.526 2405.317 2978.012 3352.867 3529.881

Mudge04 1.903 1246.241 1692.051 2026.408 2340.502 2897.764 3262.517 3434.762

Mudge05 1.8488 1210.746 1643.859 1968.693 2273.841 2815.232 3169.596 3336.935

Mudge06 1.8168 1189.79 1615.406 1934.618 2234.484 2766.504 3114.735 3279.178

Mudge07 1.7672 1157.308 1571.304 1881.802 2173.481 2690.976 3029.701 3189.654

Mudge08 1.7316 1133.994 1539.651 1843.893 2129.697 2636.767 2968.668 3125.399

Mudge09 1.9846 1299.679 1764.605 2113.3 2440.861 3022.019 3402.413 3582.043

Mudge10 1.9244 1260.256 1711.079 2049.196 2366.821 2930.35 3299.206 3473.387

Mudge11 1.8675 1222.993 1660.486 1988.606 2296.84 2843.707 3201.656 3370.687

Mudge12 1.8315 1199.417 1628.477 1950.272 2252.564 2788.888 3139.937 3305.71

Mudge13 1.7573 1150.825 1562.502 1871.26 2161.305 2675.901 3012.728 3171.785

Mudge14 1.8024 1180.36 1602.602 1919.284 2216.774 2744.577 3090.048 3253.187

Mudge15 1.7219 1127.642 1531.026 1833.564 2117.766 2621.997 2952.038 3107.891

Mudge16 1.7287 1132.095 1537.072 1840.805 2126.13 2632.351 2963.696 3120.165

Mudge17 1.7027 1115.068 1513.954 1813.119 2094.152 2592.76 2919.121 3073.237

Mudge18 1.725 1129.672 1533.782 1836.865 2121.579 2626.717 2957.353 3113.486

Mudge19 1.6859 1104.066 1499.017 1795.229 2073.49 2567.178 2890.319 3042.914


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Woron01 1.6888 1105.965 1501.595 1798.318 2077.057 2571.594 2895.291 3048.148

Woron02 1.695 1110.026 1507.108 1804.92 2084.682 2581.035 2905.921 3059.339

Woron03 1.682 1101.512 1495.549 1791.077 2068.693 2561.239 2883.633 3035.875

Woron04 1.699 1112.645 1510.664 1809.179 2089.602 2587.126 2912.778 3066.558

Woron05 1.7008 1113.824 1512.265 1811.096 2091.816 2589.867 2915.864 3069.807

Woron06 1.7121 1121.224 1522.312 1823.129 2105.713 2607.074 2935.237 3090.203

Woron07 1.7223 1127.904 1531.382 1833.99 2118.258 2622.606 2952.724 3108.613

Woron08 1.6959 1110.615 1507.908 1805.878 2085.789 2582.405 2907.464 3060.963

Woron09 1.6631 1089.135 1478.744 1770.951 2045.448 2532.46 2851.231 3001.762

Woron10 1.6836 1102.56 1496.972 1792.78 2070.661 2563.676 2886.376 3038.763

Woron11 1.6735 1095.946 1487.991 1782.025 2058.239 2548.296 2869.061 3020.533

Woron12 1.6919 1107.995 1504.352 1801.619 2080.869 2576.315 2900.606 3053.743

Woron13 1.6789 1099.482 1492.793 1787.776 2064.881 2556.519 2878.319 3030.28

Woron14 1.7569 1150.563 1562.146 1870.834 2160.813 2675.292 3012.042 3171.063

Woron15 1.7626 1154.296 1567.214 1876.903 2167.823 2683.972 3021.815 3181.351

Woron16 1.7546 1149.057 1560.101 1868.385 2157.984 2671.79 3008.099 3166.912

Woron17 1.7526 1147.747 1558.323 1866.255 2155.524 2668.745 3004.67 3163.302

Woron18 1.7387 1138.644 1545.964 1851.454 2138.429 2647.579 2980.84 3138.214

Woron19 1.7267 1130.785 1535.294 1838.675 2123.67 2629.306 2960.267 3116.555

Woron20 1.7168 1124.302 1526.491 1828.133 2111.494 2614.231 2943.295 3098.686

Woron21 1.7145 1122.796 1524.446 1825.684 2108.665 2610.728 2939.352 3094.535

Woron22 1.7105 1120.176 1520.89 1821.425 2103.746 2604.637 2932.494 3087.315

Woron23 1.6928 1108.585 1505.152 1802.577 2081.976 2577.685 2902.149 3055.368

Woron24 1.6768 1098.107 1490.925 1785.539 2062.298 2553.321 2874.718 3026.489

Woron25 1.6713 1094.505 1486.035 1779.683 2055.533 2544.946 2865.289 3016.562

Woron26 1.6594 1086.712 1475.454 1767.011 2040.898 2526.826 2844.888 2995.084

Woron27 1.6477 1079.05 1465.051 1754.552 2026.508 2509.01 2824.829 2973.966

Woron28 1.7183 1125.284 1527.825 1829.731 2113.339 2616.515 2945.866 3101.393

Woron29 1.6978 1111.859 1509.597 1807.901 2088.126 2585.299 2910.721 3064.393

Woron30 1.6789 1099.482 1492.793 1787.776 2064.881 2556.519 2878.319 3030.28

Woron31 1.6718 1094.832 1486.48 1780.215 2056.148 2545.708 2866.146 3017.465

Woron32 1.6633 1089.266 1478.922 1771.164 2045.694 2532.764 2851.574 3002.123

Woron33 1.6815 1101.185 1495.104 1790.544 2068.078 2560.478 2882.776 3034.972


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Appendix E - Calibration and Verification Hydrographs

E.1 January 1974 Calibration

Figure E-1 Daily Rainfall Stations used (January 1974).


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Figure E-2 Modelled and Recorded Flows in Nerang River at Whipbird (146011A).

Figure E-3 Modelled and Recorded Flows in Little Nerang Creek at 4.0km (146009A).


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FigureE-4 Modelled and Recorded Flows in Nerang River at Clearview (146905).


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E.2 March 2004 Calibration

FigureE-5 Pluviograph and Daily Rainfall Stations used (March 2004)


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Figure E-6 Modelled and Recorded Flows in Little Nerang Creek at Little Nerang Dam (146907)

FigureE-7 Modelled and Recorded Flows in Nerang River at Hinze Dam (146906), March 2004 (Note that there were no spillway flows for Nerang Dam during the event)


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Figure E-8 Modelled and Recorded Flows in Nerang River at Clearview (146905)

Figure E-9 Modelled and Recorded Flows in Mudgeeraba Creek at Mudgeeraba TM (146020)


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Figure E-10 Modelled and Recorded Flows in Mudgeeraba Creek at Mudgeeraba ALERT (146912)


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E.3 November 2004 Calibration

Figure E-11 Pluviograph and Daily Stations used (November 2004)


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Figure E-13 Modelled and Recorded Flows in Nerang River at Hinze Dam (146906) (Note that there were no spillway flows for Hinze Dam during the event)


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FigureE-14 Modelled and Recorded Flows in Nerang River at Clearview (146905)

FigureE-15 Modelled and Recorded Flows in Mudgeeraba Creek at Mudgeeraba TM (146020)


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FigureE-16 Modelled and Recorded Flows in Mudgeeraba Creek at Mudgeeraba (146912)


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E.4 June 2005 Calibration

FigureE-17 Pluviograph and Daily Rainfall Stations used (June 2005)


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FigureE-18 Modelled and Recorded Flows in Little Nerang Creek at Little Nerang Dam (146907)

Figure E-19 Modelled and Recorded Flows in Nerang River at Hinze Dam (146906) (Note that there were no spillway flows for Hinze Dam during the event)


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Figure E-22 Modelled and Recorded Flows in Mudgeeraba Creek at Mudgeeraba (146912)


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E.5 January 2008 Calibration

Figure E-23 Pluviograph and Daily Rainfall Stations used (January 2008)


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Figure E-25 Modelled and Recorded Flows in Nerang River at Hinze Dam (146906)


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E.6 March 1999 Verification

Figure E-29 Pluviograph and Daily Rainfall Stations used (March 1999)


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E.7 February 2001 Verification

Figure E-33 Pluviograph and Daily Rainfall Stations used (February 2001)


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Figure E-34 Modelled and Recorded Flows in Little Nerang Creek at Little Nerang Dam (146907) (Note that there were no spillway flows for Little Nerang Dam during the event)



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E.8 May 2009 Verification

Figure E-39 Pluviograph and Daily Rainfall Stations used (May 2009)


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E.9 January 2013 Verification

Figure E-45 Pluviograph and Daily Rainfall Stations used (January 2013)


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Appendix F - Design Event Discharge Hydrographs (Hinze Dam

Stage 2 Current Climate).

Figure F-1 Frequent to Large Design Event Hydrographs, Nerang River at Clearview

Figure F-2 Extreme Design Event Hydrographs, Nerang River at Clearview

0

200

400

600

800

1000

1200

1/01/2013 0:00 3/01/2013 12:00 6/01/2013 0:00 8/01/2013 12:00

Discharge

(m3/s)

Time

Q2H120

Q5H48

Q10H48

Q20H48

Q50H48

Q100H48

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1/01/2013 0:00 3/01/2013 12:00 6/01/2013 0:00

Discharge

(m3/s)

Time

Q200H48

Q500H48

Q1000H48

Q2000H48


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Figure F-3 PMP and PMF Critical Storm Duration Hydrographs, Nerang River at Clearview

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1/01/2013 0:00 2/01/2013 0:00 3/01/2013 0:00 4/01/2013 0:00

Discharge

(m3/s)

Time

PMP36H

PMF36H05


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Appendix G - Design Event Discharge Hydrographs (Hinze Dam Stage 3

Current Climate).

Figure G-1 Frequent to Large Design Event Hydrographs, Nerang River at Clearview

Figure G-2 Extreme Design Event Hydrographs, Nerang River at Clearview

0

100

200

300

400

500

600

700

1/01/2013 0:00 3/01/2013 12:00 6/01/2013 0:00 8/01/2013 12:00

Discharge

(m3/s)

Time

Q2H120

Q5H120

Q10H120

Q20H72

Q50H72

Q100H48

0

200

400

600

800

1000

1200

1400

1600

1/01/2013 0:00 3/01/2013 12:00 6/01/2013 0:00

Discharge

(m3/s)

Time

Q200H48

Q500H48

Q1000H48

Q2000H48


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Figure G-3 PMP and PMF Critical Storm Duration Hydrographs, Nerang River at Clearview

0

500

1000

1500

2000

2500

3000

3500

4000

4500

1/01/2013 0:00 3/01/2013 0:00 5/01/2013 0:00 7/01/2013 0:00

Discharge

(m3/s)

Time

PMP36H

PMF120H15


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Appendix H – Hydrological Modelling Utilities

H.1 URBS Control Centre

As mentioned in Section 6, the hydrological model is based on the URBS software, specifically urbs32.exe (9/08/2009 3:31 PM) using the URBS Control Centre.

The following figures show the URBS Control Centre setups for calibration event (1974), design event and Monte Carlo (MC CRCCH and TPT).

Figure H-1 Calibration Event using the URBS Control Centre


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Figure H-2 Design Event Approach using the URBS Control Centre

Figure H-3 CRC-CH Approach using the URBS Control Centre


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Figure H-4 TPT Approach using the URBS Control Centre

For PMP and PMF setups, batch files were created to run those events. The following figures show sample of the PMP and PMF batch files.

Figure H-5 Sample of PMP batch file

Figure H-6 Sample of PMF batch file

For more information, please refer the URBS manual (Ref 25).


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H.2 Subrain (Calibration Only)

To create the rainfall files for URBS (.rdf file), URBS’ Subrain utility was used to create a virtual pluviograph for each sub-catchment based on 4 nearest pluviograph stations. This methodology is the same as previously adopted (Ref 3). That is, Inverse Distance Squared. Previous study used RAINAL utility developed by SunWater Queensland.

The only difference between Subrain and RAINAL is the additional functionality of Subrain to export to KML format for visualization. Examples are displayed for each calibration event in Appendix E (Section 0).

The Subrain utility is only used for calibration events. An example batch is shown in the following figure. Basically it requires a rainfall network file (.net); sub-catchment centroid (.sub) and subrain switches.

Figure H-7 Subrain batch for the 1974 calibration event

The rainfall network file (.net) that contains daily manual and pluviograph stations is shown below. This file was subsequently used for the Subrain utility.

The Pluviograph (.r) and the Gauging station (.g) files were obtained from the Bureau of Meteorology for flood events up to 2008. For recent flood events, two utilities (ProcessGroup and ProcessGauges) were used to convert Enviromon (ALERT stations) Group files (rain and level respectively) to individual .r and .g files.


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Figure H-8 Rainfall network file for Nerang River Catchment

Another file that was created for the Subrain utility is the Sub-area file (.sub). It contains centroid of each sub-catchments.

For more information, please refer the URBS manual (Ref 25).

H.3 IFD (Design Event Only)

A IFD tool, developed using ArcGIS Python scripting, was developed to generate Intensity-Frequency-Duration table for design event simulation.

The latest IFD tool version is v3.

For more information, please refer the IFD utility manual (Ref 39).

It is worthwhile to note that the draft Bureau of Meteorology’s IFD was not used in this study. For more information, please refer the following webpage.


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http://www.bom.gov.au/water/designRainfalls/index.shtml

H.4 Combine IFD

Referring to Section 8.2.1 and 8.2.2 , there are two data sources for rainfall depth. That is, 1999 AWE (Ref 1) and 2004 CRCForge (Ref 30).

To enable URBS to simulate events from 2 year ARI to 2000 year ARI, a utility was developed to combined those two rainfall sources.

Figure H-9 IFD table from AWE study

Figure H-10 IFD table from CRCForge study


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Figure H-11 Combined table

It is worthwhile to note that the 1 year ARI was estimated from the 2 year ARI (0.8 ratio based on 1998 AR&R Book II Section 1.3 Step 6). The 1,000,000 year ARI is only meant for Monte Carlo calculation.

H.5 MaxQ

MAXQ is an URBS utility which determines the peak flow rates for the PRINT and/or PLOT

locations listed in the catchment definition file. This is done by accessing ".p" files generated by

URBS for a series of design storms.

It is used to determine peak flow rates for PMP as shown in the following batch file. The data

was further processed using Microsoft Excel.

Figure H-12 Peak PMP discharge extraction using MaxQ

H.6 MaxMaxQ

This utility reads output files generated by the MAXQ utility (".mq" files) to generate a list of peak

flows for a range of ARIs as defined in each ".mq" file. The output file has a default "amq"

extension.


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It is used to determine peak flow rates for PMF as shown in the following batch file. The data

was further processed using Microsoft Excel.

Figure H-13 Peak PMF discharge extraction using MaxMaxQ

H.7 Detain

The DETAIN program or module was written to generate storage discharge files for the URBS

model.

H.8 Convert to dfs0

A utility to convert URBS output (.csv) to MIKE Timeseries file (.dfs0) was developed using

Microsoft Excel. For Nerang River Catchment, it is the “Nerang_DesignURBSCombiner.xlsm”.

H.9 Frequency Adjustment Factor (FAF)

Each rainfall value in the design rainfall files is scaled by the FAF value as highlighted in Figure

H-14.


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Figure H-14 Frequency Adjustment Factor (FAF)

Figure H-15 Dfs0 Converter


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The converter can be found at this location:

W:\Work_in_Progress\Hydrology Review Update\Catchments\Nerang

Appendix I – Previous Hydrology IFD and Temporal Pattern Source

(Ref 2)

Table I-1 Previous Rainfall Depth (IFD) Source for Gold Coast Catchments Storm

Duration (hours)

ARI (Years)

1 2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 INT AWE AWE AWE AWE AWE AWE AWE AWE CRC CRC GSDM

1 INT AWE AWE AWE AWE AWE AWE AWE AWE CRC CRC GSDM





9 INT AWE AWE AWE AWE AWE AWE AWE AWE INT INT INT

12 INT AWE AWE AWE AWE AWE AWE AWE AWE CRC CRC INT

18 INT AWE AWE AWE AWE AWE AWE INT INT CRC CRC INT

24 INT AWE AWE AWE AWE AWE AWE CRC CRC CRC CRC GTSMR

36 INT AWE AWE AWE AWE AWE AWE INT INT INT INT GTSMR



96 INT INT INT INT INT INT INT CRC CRC CRC CRC GTSMR

120 INT INT INT INT INT INT INT CRC CRC CRC CRC GTSMR

Table I-2 Previous Temporal Pattern Source for Gold Coast Catchments Storm

Duration (hours)

ARI (Years)

2 5 10 20 50 100 200 500 1000 2000 PMP

0.5 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 GSDM GSDM GSDM GSDM GSDM

1 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 GSDM GSDM GSDM GSDM GSDM






12 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 WRMv7 GTSMR GTSMR GTSMR GTSMR GTSMR






96 GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR

120 GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR GTSMR


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Appendix J – Monte Carlo Results

Table J-1 Monte Carlo Results @ Clearview, Hinze Dam Stage 2

ARI (Years)

Peak Flow (mᶟ/s) @ Clearview Hinze Dam Stage 2

Design TPT CRC-CH

2 138.4 230.4 226.4

5 246.2 369.9 350

10 431.4 507.5 454.6

20 637.6 641.1 595.2

50 883.2 815.9 765.3

100 1068.1 965.2 901

200 1260.2 1127 1104.2

500 1573.1 1369.3

1000 1705.7 1610.5

2000 1839.5 1923

Note: All values above are calculated using an Areal Reduction Factor (ARF) for the Catchment area upstream of Clearview (250km2). Design run outputs used as inputs in to the Hydraulic model use an ARF calculated for the total catchment area (492km2).

Table J-2 Monte Carlo Results @ Clearview, Hinze Dam Stage 3

ARI (Years)

Peak Flow (mᶟ/s) @ Clearview Hinze Dam Stage 3

Design TPT CRC-CH

2 78.5 136 164.1

5 140.5 199.3 238.3

10 196.4 267.4 300.6

20 277.8 347 379.5

50 423.5 482.7 500.5

100 594.7 643.5 639.6

200 794 805.7 727.8

500 1088.9 1077.1

1000 1230.3 1258.6

2000 1389.2 1495.2 Note: All values above are calculated using an Areal Reduction Factor (ARF) for the Catchment area upstream of Clearview (250km2). Design run outputs used as inputs in to the Hydraulic model use an ARF calculated for the total catchment area (492km2).


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Council of the City of Gold Coast PO Box 5042 GCMC Qld 9729 P 1300 GOLDCOAST E [email protected] W cityofgoldcoast.com.au

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