Level 1, 50 Subiaco Square Road Subiaco WA 6008 PO Box 243 Subiaco WA 6904

Phone (08) 9380 3100 Fax (08) 9380 4606

177 Spencer Street Bunbury WA 6230 PO Box 287 Bunbury WA 6231

Phone (08) 9792 4797 Fax (08) 9792 4708

COL18312.02 M003 RevB

4-Feb-19 1

To: Mark Giles Date: 4 February 2019

Company: Collie Water Project No: COL18312.02

Fax/email: mg@pendulumgroup.com.au Inquiries: Heath Morgan

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

This memorandum presents a water balance of the effects of the proposed Myalup-Wellington Project (‘the

Proposal’) on the Collie River pool located along Collie townsite upstream of the Venn Street weir. This

pool is referred to as the ‘Venn Street Weir Pool’ to distinguish it from ‘Town Pool’1

located on Collie River

South Branch. The Proposal includes extraction of saline river water from the Collie River East Branch

(CREB) at Buckingham, upstream of Collie townsite.

Figure 1 presents the location and depth of the Venn Street Weir Pool.

The water balance has been undertaken to simulate the potential effects of the Proposal saline water

extraction on the Venn Street Weir Pool, to inform community consultation and referral of the Proposal to

the Environmental Protection Authority (EPA) under Section 38 of the Environmental Protection Act 1986

(EP Act).

Water balance development

The water balance was developed as an Excel spreadsheet model using a daily timestep for the following

equation:

𝑉𝑖+1 = 𝑉𝑖 + 𝑄𝑅,𝑖 − 𝐸 𝑖 − 𝑆 𝑖 − 𝐼𝑖 − 𝑄𝑊,𝑖

Where:

V i+1 = pool volume (ML) the day after day ‘i’

V i = pool volume (ML) at day ‘i’

Q R, i = river inflow (ML/d) to pool on day ‘i’

E i = evaporative loss (ML/d) from pool surface on day ‘i’

S i = seepage loss (ML/d) from pool bed on day ‘i‘

I i = irrigation draw (ML/d) from pool on day ‘i’

Q W, i = weir overflow (ML/d) from pool on day ‘i’.

Below is a discussion on the derivation of each equation term.

1

Also referred to as ‘Cardiff Pool’.

Figure 1: Venn Street Weir Pool – Area and Depth Relationship

Coordinate System: GDA 1994 MGA Zone 50

Date: 21/01/2019

info@strategen.com.au | www.strategen.com.au

Analysis area

Suburb boundary

Major RoadMinor RoadTracks

Collie Town Pool extent0.5m Weir height

0.75m Weir height

1m Weir height

1.5m Weir height

2m Weir height

2.5m Weir height

SOLDIERS PARKSOLDIERS PARK

COLLIECOLLIE

PALMERPALMER

VENN ST WEIRVENN ST WEIR

COOMBES ST

GIBBS RD

DEAKIN ST

STEERE ST NORTH

RO

WE

ST

RIVER AV

BUCKTIN S

T

PRINSEP S

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MARY ST

PALMER RD

PAR

K S

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SWANSTONE ST

EVANS ST

WITTENOOM ST

MCVEE RD

OGDEN ST

COLLIEESP

PAU

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T

LANE ST

THROSSELL ST

PRESTO

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D

JONES ST

LYNN ST

CHRISTIE ST

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WA

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ELOUERA ST

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ROBERTS ST

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JOHNSTON ST

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VINCENT ST

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WALLSEND ST

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SWAN AV

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421500

421500

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422000

422500

422500

423000

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423500

423500

6307

500

6307

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6308

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6308

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6308

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6308

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6309

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6309

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6309

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6310

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6310

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Q:\Consult\2018\COL\COL18312\01_GIS_documents\ArcMap_documents\COL18312_G025_RevA.mxd

© 2018. Whilst every care has been taken to prepare this map, Strategen & Collie Water makes no representations or warranties about its accuracy, reliability, completeness or suitability for any particular purpose and cannot accept liabilityand responsibility of any kind (whether in contract, tort or otherwise) for any expenses, losses, damages and/or costs (including indirect or consequential damage) which are or may be incurred by any party as a result of the map being inaccurate,incomplete or unsuitable in any way and for any reason.

Service Layer Credits: Source: Esri, DigitalGlobe, GeoEye, Earthstar Geographics, CNES/Airbus DS, USDA, USGS, AeroGRID, IGN, and the GIS User Community Client: Collie Water. Created by: c.thatcher

0 100 200m

�Scale 1:9,500 at A3

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 3

Pool volume, area and depth (V, A, h)

A volume-area-depth relationship was developed for the Venn Street Weir Pool, to translate the simulated

pool volume to estimated pool area extent and depth across Collie town. The volume-area-depth

relationship was developed based on LiDAR data provided by DWER for Collie townsite (December 2018).

The volume-area-depth relationship is presented in Figure 1, Figure 2 and Table 1. The Venn Street weir

has a current height of 2.2 m above bed (GFG Consulting 2018) which suggests that the Venn Street Weir

Pool has a maximum capacity of approximately 142 ML over 12.8 ha, with an average water depth of

1.1 m. Inflows above this volume will result in an overflow of the weir into the Collie River downstream.

Figure 2: Venn Street Weir Pool – volume-area-depth curves

Table 1: Venn Street Weir Pool – volume-area-depth estimates

Water depth at Venn Street Weir (m)

Pool volume (ML)

Pool area (ha)

Average water depth of pool (m)

0 0 0.0 0.00

0.5 0 0.1 0.30

0.75 1 3.1 0.04

1 16 7.5 0.21

1.5 61 10.2 0.59

2 116 12.1 0.96

2.2 (full capacity) 142 12.8 1.10

2.5 (weir overflow) 180 13.9 1.30

River flow (QR)

Estimates of river flow into Venn Street Weir Pool were taken from Department of Water and

Environmental Regulation (DWER) modelling of Collie River flows and salt loads using the LUCICAT

model (DoW 2017, DWER 2018). The modelling was undertaken for the purposes of assessing water

allocation and the Proposal saline water extraction under the Rights in Water and Irrigation Act 1914 (RIWI

Act).

0

2

4

6

8

10

12

14

16

0

20

40

60

80

100

120

140

160

180

200

0 0.5 1 1.5 2 2.5

Pool

are

a (h

a)

Pool

vol

ume

(ML)

Water depth at Venn Street weir (m)

Pool volume (ML)

Pool area (ha)

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 4

The LUCICAT modelling predicted average river flows (megalitres per day or ML/d) at Collie town site over

the period of 2011-2015, as presented in Figure 3. DWER selected the low flow period of 2011-2015 as

indicative of future river flows under the effects of a drying climate (DWER 2018). The river flows were

modelled at the Preston Road crossing, approximately 1.4 km downstream of the Venn Street Weir

(Cresswell A. 2018, Senior NRM Officer, DWER, pers. comm., 4 December), and are considered

representative of the surface water flows entering upstream of and along the length of the pool.

Figure 3: Monthly average flow (ML/day) at Collie town site

Source: DWER (2018).

The LUCICAT modelling estimated flows as follows:

1. Historic river flows, including mine dewater.

2. Mine dewater contribution.

3. Future river flows, excluding mine dewater.

4. Future river flows, excluding mine dewater and including the Proposal saline extraction.

DWER (2018) note the following with respect to mine dewater disposal into the Collie River:

“Since 2010, a significant component of surface water flow in the Collie River has been provided

from the disposal of surplus mine dewater to the Collie River East branch. This masked the

stream flow declines resulting from reduced rainfall. It is expected that this surplus dewater will

be redirected for power generation use in mid-2018, consistent with the Collie Coal State

Agreement Acts and the Upper Collie plan.”

To simulate the potential effects of the Proposal this water balance adopts the future river flows modelled

by DWER (2018), excluding the mine dewater contribution consistent with the expected discontinuation of

mine dewater disposal to the Collie River. Table 2 presents the data for future river flows (Scenario 1) and

future river flows with the Proposal saline extraction (Scenario 2) incorporated in the water balance.

0

50

100

150

200

250

300

350

400

450

500

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Ave

rage

dai

ly fl

ow

(M

L/d

)

Historic river flows (including mine dewater)

Mine dewater contribution

Future river flows (excluding mine dewater)

Future river flows with saline extraction

Reduction in flow

due to Proposal saline extraction

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 5

Table 2: Adopted river flow, evaporation and irrigation data

Month

Scenario 1: Future river flows

Scenario 2: Future river flows with Proposal Reduction in

river flows due to extraction

Pan evaporation Irrigation draw

ML/day ML/mth ML/day ML/mth mm/mth mm/day ML/mth

January 4.7 146.3 4.6 141.5 3.3% 264.2 8.52 22.0

February 1.8 51.5 1.8 51.2 0.4% 228.9 8.18 12.2

March 2.2 67.1 2.2 67.0 0.2% 168.6 5.44 14.1

April 5.6 167.2 5.6 167.2 0.0% 105.9 3.53 15.0

May 26.6 823.2 24.1 747.4 9.2% 55.6 1.79 10.7

June 50.5 1514.7 42.0 1261.0 16.7% 49.0 1.63 0.6

July 116.9 3624.0 92.3 2859.8 21.1% 48.0 1.55 0.2

August 248.0 7687.6 193.1 5987.1 22.1% 63.9 2.06 0.2

September 425.9 12777.0 331.1 9933.5 22.3% 96.5 3.22 0.2

October 106.9 3315.1 78.0 2416.9 27.1% 151.3 4.88 2.0

November 48.4 1452.7 32.1 962.4 33.8% 231.5 7.72 7.9

December 52.1 1616.2 42.5 1318.2 18.4% 269.7 8.70 11.7

Annual total 33242.4 25913.2 22.0% 1732.9 96.6

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 6

Pool evaporation losses (E)

Pool evaporative losses were calculated as:

𝐸𝑖 =𝐸𝑝𝑎𝑛,𝑖 𝑥 𝐴 𝑖𝑥 𝑃𝐹

100

Where:

E i = evaporative loss (ML/d) from pool surface on day ‘i’

E Pan, i = average pan evaporation (mm) for day ‘i’

A i = pool area (ha) at the start of day ‘i’

PF = pan factor.

Pan evaporation data was taken from the nearest meteorological station, being the McAlinden station

operated by Department of Primary Industries and Regional Development (DPIRD)2

. Average monthly

data was derived from the 2013-2015 period and converted to daily values, as presented in Table 2.

The pool surface area was determined based on the pool volume and interpolated from the volume-area

data presented in Figure 2 and Table 1. An average pan factor of 0.9 was used based on regional data for

farm dams presented in Luke et al (1988).

Pool seepage losses (S)

The Venn Street Weir Pool lies over the north-western extent of the Collie Basin, which comprises up to

5 m thickness of Nakina Formation (sandstone, mudstone) over a subcrop of sandstone, shale and coal

seams (Varma 2002). Seepage losses will occur when the pool water level is higher than the adjacent

groundwater table, and seepage gains will occur when the pool water level is lower than the adjacent

groundwater table.

Pool seepage losses were calculated based on Varma (2002):

𝑆𝑖 = (ℎ 𝑖 − ℎ′𝑖) 𝑥 𝐴 𝑖𝑥 𝑐 𝑥 10

Where:

S i = seepage loss (ML/d) from pool bed on day ‘i‘

h i = average depth of pool (m) at start of day ‘i’

h’ i = average depth of groundwater table below pool bed (m) on day ‘i’

A i = pool area (ha) at start of day ‘i’

c = average riverbed conductance (m2/day/m2).

The pool surface area was determined based on the pool volume and interpolated from the volume-area

data presented in Figure 2 and Table 1. The average depth of pool was calculated as the pool volume

divided by the pool surface area.

2

Data accessed from: https://www.agric.wa.gov.au/climate-weather/legacy-weather-stations-and-radar

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 7

Groundwater levels are not currently monitored in the vicinity of the Venn Street Weir Pool, with monitoring

focussed on abstraction areas further to the east (Cresswell A. 2018, Senior NRM Officer, DWER, pers.

comm., 5 December). SKM (2010) indicated the Collie River through Collie town was historically gaining

water from seepage (i.e. the groundwater table was above the river water level). However, groundwater

levels across Collie town may fall in the future in response to falling rainfall / recharge as well as

propagation of drawdown originating from dewatering / abstraction to the east. Accordingly, the water

balance considered a range of scenarios for depth of groundwater (h’) that could affect seepage (see

Table 3).

Riverbed conductance has not been determined for the Venn Street Weir Pool, and will depend on the

thickness and permeability of the sediments that have accumulated in the riverbed upstream of the weir.

Varma (2002) estimated conductance for pools along the Upper Collie River at between approximately

0.006 to 0.07 m2/day/m2, with a lower conductance estimated for longer and deeper pools possibly due to

a greater capture of sediment. It is expected that the Venn Street Weir Pool will have accumulated

sediment since the weir has been in place and given the extended length of the pool, which reaches

approximately 4.3 km upstream from the weir.

In the absence of riverbed conductance data for the Venn Street Weir Pool, the water balance has

adopted a high and low range (see Table 3) based on data for other Collie River pools (Varma 2002).

Table 3: Groundwater seepage scenarios

Scenario Average groundwater level across pool

Conductance (m2/day/m2)

A At pool water height – no seepage n/a

B At river bed Low: 0.01

C At river bed High: 0.07

D 1 m below river bed Low 0.01

E 1 m below river bed High: 0.07

Irrigation draw (I)

The Shire of Collie abstracts water from Venn Street Weir Pool to irrigate approximately 14.4 ha of public

open space and sports grounds. Abstraction also occurs downstream of the weir, to irrigate other public

open space and the golf course. The abstraction occurs under Surface Water Licence (SWL) 163197

issued under the RIWI Act.

The water balance incorporated the average abstraction data for 2016-2018, as reported by the Shire to

DWER under SWL 163197 and presented in Table 2. The data indicates that the Shire has abstracted an

average of 96.6 ML/year, which annually comprises 0.3% of the incoming river flows, however the

irrigation peaks during the summer and autumn when it comprises up to 24% of the incoming river flows.

Accordingly, the water balance has incorporated the irrigation water take to simulate the effect on summer

and autumn water levels.

Water balance findings

Table 4 presents a summary of the water balance findings for the ten scenarios modelled. Figure 4 and

Figure 5 present the variation in pool water levels at the weir (i.e. maximum pool depth) during an average

year, for the future river flows and with the Proposal saline extraction, respectively. Figure 4 and Figure 5

denote the approximate water depth at the weir at which the pool is expected to dry out at the key

foreshore locations of Soldiers Park and (further upstream) Collie Esplanade.

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 8

Table 4: Water balance findings – summary

Scenario

Average groundwater level

Conductance River inflow Evaporation Seepage

Irrigation take

Weir overflows

Weir overflows as proportion of river inflows

Minimum water level at weir during the year

Number of days during the year where water level at weir is below the depth:

M2/d/m2 GL/yr GL/yr GL/yr GL/yr GL/yr m

Reduction due to Proposal (m) 2.0 m 1.5 m 1.0 m 0.75 m

1A Pool level n/a 33.2 0.2 0.0 0.1 32.9 99% 2.20 n/a 0 0 0 0

1B At bed 0.01 33.2 0.2 0.5 0.1 32.4 98% 2.01 n/a 0 0 0 0

1C At bed 0.07 33.2 0.2 2.8 0.1 30.2 91% 1.03 n/a 118 88 0 0

1D 1 m below bed 0.01 33.2 0.2 0.9 0.1 32.0 96% 1.58 n/a 64 0 0 0

1E 1 m below bed 0.07 33.2 0.1 5.0 0.1 28.0 84% 0.51 n/a 126 116 105 47

2A Pool level n/a 25.9 0.2 0.0 0.1 25.6 99% 2.20 0.000 0 0 0 0

2B At bed 0.01 25.9 0.2 0.5 0.1 25.1 97% 2.00 0.002 0 0 0 0

2C At bed 0.07 25.9 0.2 2.8 0.1 22.9 88% 1.03 0.004 118 90 0 0

2D 1 m below bed 0.01 25.9 0.2 0.9 0.1 24.7 95% 1.57 0.002 64 0 0 0

2E 1 m below bed 0.07 25.9 0.1 5.0 0.1 20.7 80% 0.50 0.012 127 117 106 53

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 9

Figure 4: Venn Street Weir Pool – depth at weir for future river flows (no mine dewater)

Figure 5: Venn Street Weir Pool – depth at weir for future river flows plus Proposal saline extraction

Drying of Venn Street Weir Pool

As indicated by 1A, 1B and 2B, the Venn Street Pool is expected to experience limited drying (up to 20 cm

or 10% of depth) in the event of high groundwater levels (at bed level or higher) and a low riverbed

conductance (thick/low permeability sediments). This is due to the limited scale of evaporative loss and

irrigation take compared to the summer/autumn river inflows.

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

Wa

ter

he

igh

t at

we

ir (

m)

Scenario 1A Future, no seepage

Scenario 1B Future, GW at bed, low conduct

Scenario 1C Future, GW at bed, high conduct

Scenario 1D Future, GW below bed, low conduct

Scenario 1E Future, GW below bed, high conduct

Drying at Soldiers Park

Drying at Collie Esplanade

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

Wa

ter

he

igh

t at

we

ir (

m)

Scenario 2A Proposal, no seepage

Scenario 2B Proposal, GW at bed, low conduct

Scenario 2C Proposal, GW at bed, high conduct

Scenario 2D Proposal, GW below bed, low conduct

Scenario 2E Proposal, GW below bed, high conduct

Drying at Soldiers Park

Drying at Collie Esplanade

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 10

As indicated by 1C, 1D and 1E, should groundwater levels drop below the riverbed and/or the riverbed has

a high conductance (thin/high permeability sediments) then the Venn Street Pool is expected to dry out

over a portion of its length for the period of January to May. The duration and spatial extent of the drying

will depend on the groundwater levels and the riverbed conductance. The drying is due to the larger scale

of seepage losses that exceed the summer/autumn river inflows and deplete the pool storage.

Effect of Proposal on Venn Street Weir Pool

The water balance findings, as presented in Table 4, Figure 4 and Figure 5, indicate that the Proposal will

result in a very slight additional drying of the Venn Street Weir Pool.

Should groundwater remain at close to the riverbed (Scenarios 1B, 1C, 2B, 2C) then the Proposal is

expected to result in less than 1 cm of additional drying, and extend the period of low water levels in the

pool by up to a few days. Should groundwater levels drop to below the riverbed (Scenarios 1D, 1E, 2D,

2E) then the Proposal is expected to result in approximately 1 cm of additional drying, and extend the

period of low water levels by a few days to a week depending on the riverbed conductance. The very

slight additional depth and duration of drying is presented in Figure 6, for the conservative high

conductance scenarios.

Figure 6: Venn Street Weir Pool – effect of Proposal, high conductance scenarios

The limited effect of the Proposal on the Venn Street Weir Pool is due to the proposed saline extraction

occurring predominantly in winter and spring, with a very limited reduction in river flows (< 3.3%) expected

between January to April when river flows are lowest. The winter and spring river flows, at greater than

50 ML/day, substantially exceed the evaporation and seepage losses and the storage capacity of the Pool,

and are thus mostly (80-99%) lost to weir overflows rather than being retained within the Pool to sustain it

during the summer/autumn period.

The potential for drying of Venn Street Weir Pool is thus predominantly affected by the scale of seepage

losses (in turn dependent on groundwater levels and riverbed conductance) over the summer/autumn

period and how fast these deplete the pool storage volume, and is only slightly affected by the very limited

reduction in river flows due to the Proposal over this period.

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

Wat

er h

eigh

t at

wei

r (m

)

Scenario 1C Future, GW at bed, high conduct

Scenario 2C Proposal, GW at bed, high conduct

Scenario 1E Future, GW below bed, high conduct

Scenario 2E Proposal, GW below bed, high conduct

Drying at Soldiers

Park

Drying at Collie Esplanade

Myalup Wellington Project - Collie River, Venn Street Weir Pool Water Balance

COL18312.02 M003 RevB

4-Feb-19 11

References

Department of Water (DoW) 2017, Upper Collie Model, Hydrological and constituent modelling for

allocation planning and Water for Food, Water Resource Technical Series, May 2017.

Department of Water and Environmental Regulation (DWER) 2018, Upper Collie water allocation plan,

Evaluation statement 2009-2017, Government of Western Australia, September 2018.

GFG Consulting 2018, Draft Collie River Revitalisation Strategy 2018-2022, report prepared for Shire of

Collie, Version G, July 2018.

Luke G. J., Burke K. L. and O’Brien T.M. 1988, Evaporation data for Western Australia, Western Australian

Department of Agriculture and Food, Resource Management Technical Report 65.

SKM 2010, Identification and mapping of groundwater dependent ecosystems associated with the Collie

River, report prepared for Department of Water, Version 2, April 2010.

Varma S. 2002, Hydrogeology and groundwater resources of the Collie Basin, Western Australia, Water

and Rivers Commission hydrogeological record series report HG-5.