AUSTRALIAN RAINFALL AND RUNOFF 2016

Introduction and Purpose

• My views

• Approach from viewpoint of Practitioner not a scientist- How do we apply this thing?

• How do we now model Urban Areas, particularly when Book 9 is not finished and one of the supporting projects not loaded?

• Form of Workshop:oNEEDS TO BE INTERACTIVE (PLEASE)

o Share experiences to date and discuss implementation in future

o Too much to discuss in detail

Previous Editions

Version 1: 1958

Version 2: 1977

Version3: 1987

Version?: 1997

Projects Leading to ARR 2016

ARR 2016 Release

Book 1- Introduction to ARR 2016

Revised Terminology1- Clarity of Meaning

• ‘the terms "recurrence interval" and "return period" has [sic] been criticised as leading to confusion in the minds of some decisionmakers and members of the public.’

• ‘Although the terms are simple superficially, they are misinterpreted regularly as implying that the associated event magnitude is onlyexceeded at regular intervals’

Revised Terminology2- Technical Correctness

• ‘The two approaches used when describing probabilities of flood events in previous editions of Australian Rainfall and Runoff were:

oAnnual Exceedance Probability (AEP). The probability of an event being equalled or exceeded within a year. Typically the AEP is estimated by extracting the annual maximum in each year to produce an Annual Maxima Series (AMS); and

oAverage Recurrence Interval (ARI).

The average time period between occurrences equalling or exceeding a given value. Usually the ARI is derived from a peak over threshold series (POTS) where every value over a chosen threshold is extracted from the period of record.

Revised Terminology3- Practicability and Acceptability

• ‘while the terminology adopted must be technically correctit must also be relatively simple and suitable for

use in practice.’

• ‘terminology involving annual percentage probability bestconveys the likelihood of flooding and is less open to misinterpretation by the public.’

Revised TerminologyAdopted Terminology

• Langbein’s 1949 formula relates hydrological recurrence intervals from an annual maximum series and from a partial-duration series.

• Ta = 1

1−𝑒 1−𝑇𝑝

• AEP (1 in x) equivalent to ARI for events >10% AEP

Uncertainty• Greater focus on the uncertainty of design flood estimation

o ‘Aleatory (or inherent) Uncertainty refers to uncertainty that arises through natural randomness or natural variability that we observe in nature; and

o Epistemic (or knowledge-based) Uncertaintyrefers to uncertainty that is associatedwith the state of knowledge of aphysical system (our estimation ofreality), our ability to measure it and theinaccuracies in our predictions of thephysical system.’

UncertaintySources of Uncertainty:

• Data Uncertainty (data limited/incomplete/inaccurate)

• Parametric Uncertainty (parameters based on limited data sets)

• Structural Uncertainty (models partially reflect actual conditions)

• Regionalisation Uncertainty (moving parameters from other areas)

• Deep Uncertainty (Donald Rumsfeld) (climate change)

Uncertainty

Risk Based Design

• Risk expressed in terms of likelihood and consequences

• Range of Guidelines, including:oNational Emergency Risk Assessment

Guidelines, Handbook 10 (Australian Government Attorney General’s Department, 2015)

oManaging the Floodplain, A Guide to Best Practice in Flood Risk Management in Australia, Handbook 7 (Australian Emergency Management Institute, 2013)

Risk Based Design- Likelihood

Aust. Govt 2015, Table 10

Risk Based Design- Consequences

a) People b) Economy and Assets

(Aust. Govt 2015)(Aust. Govt 2015)

Risk Based Design- Consequences

c) Environment

(Aust. Govt 2015)

Risk Based Design- Consequences

d) Public Administration e) Social

(Aust. Govt 2015)

(Aust. Govt 2015)

Risk Analysis• Assess Risk• Consider types and severity of flooding• Flood hazard in area of interest• Warning times• Develop Risk Matrices:

(Aust. Govt 2015) (AEMI 2013)

Risk Management• Management by limiting likelihood and consequences

• Design Flood Standards:oAEP (eg level of service of roads)o Service Life Exceedance Probability (design of bridges)

• Critical community infrastructure

• Hazardous materials

• Level of immunity (to limit risk exposure)

• Flood free access

• Ability to evacuate- options for late evacuation by car or on foot, or shelter in place

Risk Management• Effective Service Life (not design service life)

• Non-Stationary Risk Assessment:

• Assess cost and intergenerational equity (current generation incurring costs that only next generation will benefit from).

Climate Change

• Recommends 5% increase in rainfall per oC of local warming• Assuming 2oC by 2050 and 4oC by 2100 for Queensland, obtain 10% and

20% increases in rainfall intensity that we have been assuming in recent years.

Representative Concentration Pathways for greenhouse gas and aerosol concentrations:RCP’s are 2.6, 4.5, 6.0 and 8.5 (low to high)RCP 4.5 and RCP 8.5 recommended5% per oC is effectively RCP 8.5

Climate Change- Interim Guideline

Step 1- Effective Service Life/ Planning Horizon

(<20 Y from 2015)

Step 2- Design Standard

Step 3- Purpose and Consequences of Failure

Step 4- Climate Change Screening Analysis

Screening Analysis: Consider Impacts of Next 2 Larger Events

FRDR= Flood related design requirementsCOF= Consequences of failureCOR= Costs of retrofitting

1% AEP or more frequent events

Step 5- Consider Climate Change Projections (RCP4.5, possibly RCP8.5)

Step 6- Statutory Req.

Climate Change- GCM Consensus

NRM Region 2050 2090

East Coast North 5 12

Central Slopes 5 12

Rangelands 12 12

Wet Tropics 5 5

Monsoonal North 5 12

General Recommended 10 20 (2100)

Predictions to 2050 and 2090

Book 2- Rainfall and Temporal Patterns

Design RainfallsTerminology

Improvement in Data from 1987

Over 8,000 daily read gaugesOver 2,280 continuous rain gauges (even then majority < 40 years and high proportion < 10 years)

Daily

Continuous

Design RainfallsApproach for frequent and infrequent:• Generalised Extreme Value (GEV)

distribution fitted using L-moments• Extension of sub-daily data by Bayesian

Generalised Least Squares Regression• Regionalisation• Gridding- IFD

Very Frequent

Extension of Daily Data (Unrestricted Depth)

Frequent and Infrequent

Rare

Design Rainfalls from BOM accessed from ARR site

Can pick non-standard durations but not non-standard temporal patterns

‘Missing’ 20 min, 25 min, 45 min, 90 min, 4.5 hour, 9 hour, 18 hour, 30 hour and 36 hour from 1987 ARR

IFD CHARTS- 1987 to 20161987 2016

Relates to bursts of rainfall rather than complete storms.

1 minute to 7 days compared to 5 minutes to 3 days in 1987

What does this mean for the design standard for stormwater drainage?

IFD CHARTS- ComparisonLocation ARR 63.2% AEP 10% AEP 1% AEP

Bundaberg 1987 46 65 99

2016 47 77 113

Hervey Bay 1987 46 65 97

2016 40 71 107

Maryborough 1987 45 65 98

2016 38 69 105

Mt Isa 1987 26 51 78

2016 29 57 87

Longreach 1987 28 55 84

2016 26 53 80

Brisbane 1987 36 70 110

2016 35 64 98

Mackay 1987 42.0 79.6 123

2016 44.6 78.6 114

Rainfall Intensity (mm/h) or Depth (mm), 1 Hour Storm Duration

Areal Reduction FactorsIn 1987 ARR factors were from America

We now have our own factorsMap shows ARF Regions (which do not match temporal pattern regions)

Areal Reduction Factors• The bad news- ARF = 1 only for areas < 1km2

• Also note that the procedure in ARR16 references the WRONG interpolation formulae• Core equations for areas between 1 and 1,000 km2:• A) Duration <12 hours

• B) Duration >24 hours (ARR data hub for

• Interpolation by catchment area if area less than 10 km2 (all durations)

• Interpolation by duration if duration between 12 and 24 hours? How do we use ARF if we are interested in peak flows at a range of locations?

Areal Reduction Factors1% AEP Duration (h)

Area (km2) 0.99 1 1.4 1.8 2 2.4 3 3.4 4.4 6 12 24

2 0.98 0.98 - - 0.98 - 0.98 - - 0.99 0.99 0.99

5 - 0.94 0.94 - 0.94 - 0.95 - - 0.97 0.98 0.98

10 - 0.9 - 0.91 0.91 - 0.91 - - 0.95 0.97 0.97

20 - 0.87 - - 0.88 0.88 0.89 - - 0.93 0.96 0.96

50 - 0.82 - - 0.84 - 0.85 0.85 - 0.9 0.94 0.95

100 - 0.77 - - 0.8 - 0.81 - 0.84 0.88 0.92 0.94

10% AEP Duration (h)

Area (km2) 0.99 1 1.4 1.8 2 2.4 3 3.4 4.4 6 12 24

2 0.98 0.98 - - 0.99 - 0.99 - - 0.99 1 1

5 - 0.95 0.96 - 0.96 - 0.97 - - 0.98 0.99 0.99

10 - 0.92 - 0.93 0.93 - 0.94 - - 0.96 0.98 0.98

20 - 0.89 - - 0.91 0.92 0.92 - - 0.95 0.97 0.98

50 - 0.85 - - 0.88 - 0.89 0.89 - 0.93 0.95 0.96

100 - 0.81 - - 0.84 - 0.86 - 0.88 0.9 0.93 0.95

Temporal Patterns• 1987 ARR Temporal Patterns defined by zones• Common patterns for durations <1 hour• 20 durations• Temporal patterns for <30 years and >30 years• One temporal pattern per duration

Temporal Patterns- Less than 75 km2

Developed Ensembles:• 10 temporal patterns for

each duration• 24 durations ranging from 10

minutes to 7 days (note more than text indicates)

• 12 regions• ‘Very Rare’ Missing

Temporal Patterns- Greater than 75 km2

Developed Ensembles based on aerial rainfall bursts:• 10 temporal patterns for each range• Ranges (9) of 100, 200, 500, 1000, 2500, 5000, 10000, 20000, 40000 km2

• 10 durations ranging from 12 hours to 7 days (note more than text indicates)• 12 regions

Pre- Burst Rainfall

ARR Data Hub will provide:• Storm Losses- Initial and Continuing• Pre Burst DepthsCan determine design storm IL

Temporal Patterns- ResultsEnd up with Box Plots• Take average of the 10

runs• Why not median?-

would need 11 patterns to facilitate this

• Adopt temporal pattern that gives flow closest to average flow.

Spatial Variation More bad news if catchment > 20 km2- need to consider spatial variation

Idea is to estimate using the spatial pattern derived from design rainfall grid for 1% AEP event and for a duration that is likely to correspond with critical duration at point of interest.

Continuous Simulation Models

Used predominantly for very frequent events and are poor at representing peak conditions.

Book 3- Peak Flow SimulationTwo key approaches:• Annual Maximum Series• Peak-Over-Threshold Series

ARR Recommends• If AEP <10%, then annual maximum series• If EY of interest is >0.2 events per year,

then peak over threshold

Acknowledgement that rating curves at gauges can be approximate

Detailed description of flood frequency and confidence interval calculations, GEV, Bayesian

Regional Flood Frequency EstimationRFFE Model 2015- for ungauged catchmentsBased on• 853 gauged catchments• Natural neighbour interpolation method (up to 15 catchments

in 300 km radius)• Includes baseflow

Accuracy ± 50% but can be out by a factor of 2

Assumptions:• <10% urbanisation• No dams/ storages• No mines or intensive agriculture• No significant floodplain storage

Regional Flood Frequency Estimation

Humid Coastal:Cut off gauges with 19 years of data (from 1,200 to 798)- median 37 yearsAreas from 0.5 to 4,325 km2 (median 178 km2)Queensland: 196 stations with areas from 7 to 963 km2 (median 227 km2)

20-102 years of data (median 42 years)

7 Zones (5 Humid, 2 Arid/ Semi Arid)

1

2

3

4

5

67

Zones (humid)1- East Coast2- Tasmania3- Humid SA4- Top End NT, Kimberley5- South West WAZones (arid/semi arid)6- Pilbera7- Central AustraliaFringe zones (400-500 mm of annual rainfall)

Regional Flood Frequency EstimationArid/ Semi Arid:55 catchments used to represent 5,000,000 km2

Relaxed to stations with more than 10 years of recordResulted in gauge data Relaxed to areas up to 6,000 km2

Simpler methodology

Accuracy Checks- Leave one out methodology

Regional Flood Frequency Estimation

RFFE- McCoys Creek (14.9km2)

156 (30%)

182 (40%)

Report

RFFE- Eli Creek (Hervey Bay) (3.6km2)

54 (2005)- 93.6 (2008)

Eli Creek Study

RFFE- Lockyer Creek at Helidon (377km2)

73

230 (13%)

400

590 (6%)

800

960 (13%)

BRCFS Hydrology Report

RFFE- Ithaca Creek at Simpsons Rd(5.7km2)

58

79 (129%)

91

103 (42%)

130

157 (12%)

Breakfast Creek Flood Study

Book 4- Catchment Simulation

Book 4- Catchment SimulationVery much an overview book- could have made the introductory chapters of Book 5

Runoff and Baseflow Introduction

When calibrating: Subtract baseflow, calibrate model, then add back

Representation of Spatial Processes

Event Based Approaches

Event Based Approaches- Continued

Joint ProbabilityVery technical discussion of simulation techniques- no real-world guidanceExample not very realistic

Book 5: Flood Hydrograph Estimation

Types of Model• Lumped Models:

o Do not allow spatial variation of runoff or routing characteristics (single catchment

o Examples include time area method, unit hydrograph method• Semi-Distributed Models:

o Effectively the standard for hydrological modelling (RORB, URBS, RAFTS, WBNM)

o Catchment divided into a number of sub-catchments to allow modelling of runoff and then routing and combination with other catchments

• Grid-based (Distributed) Models:o Good for flat areas as do not need to know catchment boundarieso Representation of runoff from ground areas (particularly for shallow flow) is

difficult

Losses• Loss is the rainfall that does not appear as direct runoff due to:

o Interception by vegetationo Infiltrationo Depression storageo Transmission loss (stream bed and banks)

• Used to be thought of as only surface runoff when rainfall intensity exceeds infiltration capacity

• Now thought of as saturated overland flow plus throughflow (moving through cracks etc in temporary saturated zone

• Three types of loss model:o Empiricalo Simpleo Process

Losses• Empirical Loss- focusses on effect on flow• Options include:

o Initial Loss followed by Continuing Loss (favoured as most suitable for design events)o Initial Loss followed by Proportional Losso Variable Continuing Losso SCS Curve Number (from US) based on soil type

Losses• Simple Model- attempt to account for infiltration- mostly too difficult to apply

• Options include:o Horton model (diminishing continuing loss as soil becomes saturated)o Green-Ampto Australian Representative Basin Model (series of buckets)

• Process Methods- Continuous simulation

• Improving, more for flood forecasting

Selecting Losses• Design rainfall burst v complete storms- repeat of Book 4, noting design values

in Book 5 relate to complete storm rather than design storm burst.

• If possible, derive own loss values:o At site event datao Regional Datao Independent FFA

Effective Impervious Area• Recognition of four types of surfaces that affect runoff:

o Directly connected impervious areas (roofs etc directly connected to drainage system)o Impervious indirectly connected areas which flow over pervious areas before entering

the drainage system (eg roof discharging to a lawn)o Pervious areas that interact with indirectly connected areas (eg nature strips)o Pervious areas that do not interact with impervious areas (eg parklands)

• Thinking about Effective Impervious Area (EIA) rather than Total Impervious Area (TIA)• Although can complete detailed GIS studies or gauge analysis, at present can say EIA roughly

55 to 65 percent of TIA• Better appreciation of benefits of WSUD and the reduction in peak flow/ timing gained by

the disconnection of impervious surfaces

• (Good, but then does not go anywhere).

Rural Catchment Loss Prediction• Work by CSIRO and BOM to identify loss rates

Region 1

Region 2

Rural Catchment Loss Prediction

• ARR Data Hub gives ILs and CL Estimates (RURAL)

Initial Loss

Continuing Loss

ARR Recommends keeping IL and CL the same for AEPs unless catchment conditions suggest otherwise

Note CL based on figures for 1 hour-beware if timestep is less than this

CL could reduce over time but realistically difference in flow will be slight

Brisbane

IL 14

CL 1.7

Urban Catchment Loss Prediction• Effective Impervious Areas

o IL 1-2 mmo CL zero

• Indirectly Connected Areas (impervious and pervious)o IL 60-80% of rural value, trending to 100% as impervious area reduceso CL 1-4 mm

• Urban Pervious Areaso As per rural areas

Note CL values based on 5 minute timestep

Baseflow• Concept introduced in Book 4• Traditionally ignored unless have a big

catchment• For a 10% AEP, about 2/3 of Australian

catchments have baseflow contributions between 5 and 30% of peak flow (decreasing for more severe events)

• Although best to use gauged data, ARR presents method for ungauged catchments:

o Baseflow Peak Factor- Applied to 10% AEP peak surface flow to give peak base flow for 10% AEP event

o Baseflow Volume Factor- Applied to surface runoff volume to give baseflow for 10% AEP event

o Baseflow Under Peak Factor- Factor to derive baseflow at time of surface peak = 0.7 x Baseflow Peak Factor

Baseflow• ARR Data Hub for Factors

• Multiply factors for a 10% AEP event to obtain factors for other AEP

Peak Factor

Volume Factor

Time of Peak Baseflow

Hydrology- Flood Routing• Overview discussion of basic storage equations• Overview discussion of routing options for routing through reaches

Hydrology- Flood Hydrograph Modelling• Time Area Method• Unit hydrograph Approach• Runoff Routing:

o Lumpedo Semi-distributed (simple and node-link)

• Overland Flow• Rainfall on grid (good overview):

o Issues with topography and depression storageo Sensitive to roughness parameters (usually apply depth varying roughness parameter)o ‘it is considered premature to recommend the general use of rainfall-on-grid- models’

Book 6: Flood Hydraulics

Book 6: Early Chapters• Chapters 1 to 4 provide a general overview of flood modelling• Should it be in ARR or a supporting background text?• Chapter 2 talks about general hydraulics/ provides general concepts:• Velocity profile not uniform• Compound channels• Mannings n values• Basic assumptions (flow incompressible, hydrostatic)• Basic equations for steady, unsteady, 2D and 3D modelling presented• Also presents basic description of physical modelling and curious

statement: ‘with the advent of widespread, powerful and cheap computing facilities, numerical modelling has advanced significantly. Physical modelling, however, is by no means obsolete. Indeed, as discussed by Martins (xxxx), the development of physical modelling has kept pace with numerical modelling.’

Book 6: Early Chapters• Chapter 2 also mentions bed shear stress but stops there• No mention of geomorphologic impacts• No mention of superelevation at bends

• Chapter 3 discusses hydraulic structures:o Weirs, flumes, spillways (but only overview of stilling basins), culvertso Could have included more recent work on outletso Bridge waterways (losses by 2 bridges can be between 1.3 and 2

times the loss caused by 1 bridge)o Introduction to basic considerations with respect to bridge scour and

methods for protection – refers to Qld Main Roads publication

Book 6: Early Chapters• Chapter 4 provides a solid overview of numerical models:

o Steady and unsteady modelso 1D modelso 2D modelso Coupled 1D/2D modelso 3D modelso CFD

Interaction of Coastal and Catchment Flooding• Addresses concerns in relation to flooding in waterways and coincidence

of high levels in coastal areas

• Complex joint probability modelling undertaken

Interaction of Coastal and Catchment Flooding• Program has been developed (accessed via ARR website)• Input table with levels for a range of combinations of flooding and storm

tide (i.e. many runs)

• Program advises level estimates• Use for tributary problem?• Not working at the moment

Blockage of Hydraulic Structures

• Limited to blockage of bridges and culverts (noting that blockage can occur in other parts of the drainage system)

• Blockage is a genuine concern that is now being addressed• Largely qualitative, based on catchment conditions, but reasonable approach

given random nature of blockage• Although random, blockage potential increased by services on upstream side of

bridges and culverts, as well as other design features (multiple small openings, fauna passage works)

• Site visit recommended if blockage critical

Blockage of Hydraulic Structures• Types of Debris: Floating, Non-floating, urban• Floating (noting small pieces of debris pass through until larger pieces start

blockage)o Small (<150mm-small branches, leaves, refuse, vegetation)o Medium (150mm to 3m- branches)o Large

• Non-floating (typically sediment)o Fine (silt and sand- 0.004 to 2mm)o Gravels (2 to 63mm) and cobbles (63 to 200mm)o Boulders (>200mm)

• Urban (floating and non-floating)o Fence palings, building materials, vehicleso Garbage bins, shopping trolleys

Assessment Procedure• Assign High, Medium, or Low debris availability, mobility, transportability• Debris Availability• From creek and banks in small events, floodplain in large events• Availability will depend on:

o Potential for soil erosion (erodibility, rainfall, slope)

o Local geology and area available for supply of debris

o Vegetation cover, land clearing, urbanisation

o Preceding rainfall

Assessment Procedure (contd)• Debris Mobility• To describe the mobilisation of debris• Mobility will depend on:

o Intensity and duration of rainfall and soil erosivityo Catchment slope and vegetation cover

Assessment Procedure (contd)• Debris Transportability• Ability of debris to be transported will depend on:

o Flow velocity and deptho Width of channel

Assessment Procedure (contd)• Debris Potential• If more than 1 potential source of debris consider each in turn• Combine availability, mobility and transportability to obtain debris potential for

1% AEP Event

• Adjust classification according to AEP of interest (NEED TO CHANGE PER RUN)

Assessment Procedure (contd)• Design Blockage Level• Defined based on L10 which represents the average length of longest 10% of the debris

reaching the site• A) Inlet Blockage

(BDES %) Floating ornon-floatingW is width

• B) Barrel Blockage- Non-floating (sediment deposition)o Consider likelihood of sedimentation in barrel and then adjust by debris potential

• Take higher value

Assessment Procedure (contd)• Other notes• For low height culverts (H<1/3 W), consider potential for vertical blockage- take

L10 vertical >= ½ L10 calculated previously• For multiple spans, could have lower blockage overall:

o If stream is narrow adopt BDES for those culverts in stream and half BDES for rest

o If stream is wide, adopt BDES for all • To assess sensitivity and to avoid blockage upstream lowering levels

downstream, suggested to complete ‘all clear’ run and ‘blocked to design’ runs and other runs depending on sensitivity to blockage.

Assessment Procedure (contd)• Hydraulic Analysis• Types of blockage

o Top downo Bottom upo Porous plug

• Correlation between debris type and type of blockage

Management of Blockage• Presents options to minimise potential for blockage:

o Separating barrelso Adding deflectorso Adding sills

Safety Design Criteria• Presents updated data on stability of people and vehicles to allow new flood

hazard standard• 1,859 flood fatalities between 1900 and 2015• Higher death toll in flash floods compared to river floods• 1/3 of Australian flash flood depths were inside vehicles• People more likely to be killed outside home- need to be sure evacuation is the

correct course of action (correlation with bushfire?)• Flood hazard depends on:

o Velocityo Deptho Combined hazard expressed as depth x velocity (dv)o Isolationo Effective warning time/ rate of rise of water

People Stability• People lose stability by moment instability and/or friction instability• Human stability expressed in terms of H.M (height x mass)• Classifications:

o Adult- H.M >50 mkgo Child- 25<H.M<50 mkgo Infants/very young children- H.M<25 mkg

Vehicle Stability• Vehicles lose stability by buoyancy and/or friction instability

Building Stability• Buildings subject to flow forces (which can be increased by debris)• Due to number of building construction materials, building stability curves are

variable.

General Flood Hazard Curves• Due to similarities between depth and velocity curves, combined curve has

been developed

Other Flood Hazard Issues• In addition to flood hazard, other factors affect overall hazard:

o Isolationo Effective warning timeo Rate of Rise of flood waterso Time of Day

Book 7- Application of Catchment Modelling System

Catchment Modelling Overview• General

o Need to know what the model is to be used for (eg flood forecasting, development assessment)

o Caution if adapting an existing model- need to know its basis for creation• Hydrologic Model

o Repetition of options for lumped models, Semi-distributed models, and Distributed models

• Hydraulic Modelo General advice regarding making model extend sufficiently downstream and

upstream and to minimise dry areaso Boundary conditions (avoid double routing of flow from hydrologic model)

• Validation and Sensitivity Modellingo Good to assess performance of model on non-calibration eventso Sensitivity modelling (n values, lag, blockages) to give idea of potential

variation associated with assumed values

Model Parameters• Calibration

o Available data will range from nil to some to extensiveo Data will be from a range of sources eg gauges, debris marks, anecdotal,

timing of peakso Good to consider a range of flood events if possibleo Suggests hydrologic component is more critical for calibration as errors in

hydrologic model transfer to hydraulic model.o Warns of potential concern in relation to Joint Calibration.o My warning- watch sub-catchments

• Data Issueso Datums (particularly ALS and detailed survey)o Changes in stream profileo Changes to catchment over time (new roads etc)

Model Parameters (contd)• Acceptance of Calibration

o Proximity to data will depend on reliability of data (eg gauge vs debris)o Timing and magnitude (and volume)o Acceptance will need to consider representativeness of eventso Level of calibration required for purpose of modelo (my view)- close calibration may not be possible with reasonable parameters

• Ungauged Catchments (Normal Situation)o General guidance for parameterso Regional relationships (eg Weeks’ kc equation)o Transfer from neighbouring catchments (typically perilous)o No mention of RFFE or Rational Method

Regional Relationships• Details relationships for RORB and WBNM (notes relationships for others are

elsewhere but this is not the case)• Notes regional relationships will contain ‘some scatter’• RORB

o Kc will increase for larger floods when floodplain activatedo Recommends use of Weeks’ equation for Qld (kc=0.88 A 0.53)o No mention of McMahon and Muller (kc=1.2 dav) or work by Greer

• WBNMo For Qld- lag parameter C=1.47 (my experience is between 1.2 and 2)

• URBAN Catchmentso Suggest adjusting storage by (1+U)2 (or other exponent between 1.7 and 2.7)

Uncertainty and DocumentationUncertainty• Book 1 introduced concepts of aleatory uncertainty (uncertainty due to variation

in natural conditions) and epistemic uncertainty (uncertainty due to our representation of natural processes)

• Chapter 9 of Book 7 looks at epistemic uncertainty• Looks at sensitivity based on model parameters• Considers Monte Carlo simulations- would need about 100 x the runs to quantify

epistemic uncertainty• Considers some examples but does not give confidence to practitioners, with one

example noting ‘the relative errors…are assumed to be 10% and 20%’• Are we giving ourselves a false sense of confidence?Documentation• Consider your audience, noting for members of the public reports need to be

written ‘in plain English’

Book 9- Runoff in Urban Areas

Book 9- Runoff in Urban Areas

• First of four mentions of the Rational Method (in all cases only in passing)• No consideration of natural channel design• No real consideration of effective and total impervious area and desire to

use swales and other WSUD measures• No consideration of outlet protection• No consideration of safety in terms of grates or use of measures (eg

detention basins) for multiple uses

Chapter 2- Aspects of Urban Hydrology• Overview of urban water balance• Development results in more runoff sooner and more often• Volume of stormwater runoff apparently exceeds demand for water

Chapter 3- Philosophy for Management• First mention of Rational Method (90% of the way through the document)

with sense of where things were rather than where they are• Notes shift towards Integrated Water Cycle Management• ‘The intellectuals have gradually realised that this issue can be solved by

viewing urban stormwater as an opportunity to supplementurban water supplies and enhance the amenity of urban areas’

• Major and Minor system introduced (no reference to Argue)• Brief discussion of 2D modelling of urban areas and need for care in

mapping due to potential impact of obstructions, lack of survey, and inability to calibrate models

Chapter 4- Stormwater Volume Management• Objectives:

o Control peak dischargeso Harvest/ infiltrate stormwatero Improve water quality

• Research shows multiple small volumes can provide catchment scale reductions (in Queensland even rainwater tanks are optional)

• ‘Detailed Design’ Considerations:o Broad overview, with freeboard for detention basins taken from QUDMo No mention of safety considerations, maximum depths, batters for

escapeo OSD overview (not really for Qld apart from townhouses and larger

developments)

Chapter 4- Stormwater Volume Management (Continued)• Rainwater harvesting- refers to rainwater tanks Bioretention (only with reference to

water quality and vague reference to infiltration to groundwater- no mention of benefit of disconnecting drainage system)- simply refers to other guidelines

• Wetlands (again only with reference to water quality)- simply refers to other guidelines and specifically says not for harvesting

• Aquifer recharge – mainly Melbourne and WA (where they have sand) guidelines • Mention of stormwater harvesting but level of detail (for example treatment) is

extremely basic

Downstream Embankment Guideline:• Summary of infiltration

systems:o Basins/ wellso Permeable pavemento Infiltration swales

Chapter 5- Stormwater Conveyance• Very broad and overly simplistic- similar to a text for someone completing a stormwater

elective for a different degree• One reference to standard for minor drainage being 150 mm below surface• Lists steps in the ‘conveyance design process’, including:

o Hydrology by design storm temporal patterns/ ensembles- typically some form of computer model (with reference back to Book 5 and Book 7)

o ‘Calibrate or validate the hydrology and hydraulics of the existing catchment to any gauged data or nearby flood frequency information or accepted parameters for the area’

• Above ‘parameters’ apparently do not include the Rational Method as there ‘is significant ongoing concern about the reliable characterisation of the parameters (such as runoff coefficient and time of concentration) underpinning the Rational Method due to insufficient rainfall runoff observations in urban areas.’

• So, what do we use instead? People in charge of writing this section do not have an urban drainage design background (one is a continuous simulation modeller)

Stormwater Conveyance (contd)• Gully Pits:

o Section on inlet structures which includes formulas for inlets but no discussion of inlet blockage factors

o All formulas- no mention of physical testing that occurs to confirm capacities• Pit Losses:

o Overview of pit loss forms and difference between HGL and EGLo Notes Missouri Charts/ Hare Charts and simplistic K values proposed by Argue

• Modelling:o ‘some designers of conveyance networks are still using simple, steady flow procedures’o Modelling using unsteady flow procedures.

• Overland Flow:o Basic discussion of depth limitations to avoid property flooding and appropriate dv

productso Izzard’s equation (nice throwback to 1987)

Stormwater Conveyance (contd)• Flows through conveyance network:

o Losses and an example from Hydraulics 101 (discharge from a reservoir through a pipe)o Repeat of HGL/EGL and part full/ full flow

• Culverts and floodways:o Discussion of inlet and outlet controlo Weir equation for floodways- no mention of drowning (although there is elsewhere in

ARR)

Chapter 6 and Projects