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: [email protected] 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
[email protected] | 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
T NORTH
MARY ST
PALMER RD
PAR
K S
T
SWANSTONE ST
EVANS ST
WITTENOOM ST
MCVEE RD
OGDEN ST
COLLIEESP
PAU
LL S
T
LANE ST
THROSSELL ST
PRESTO
N R
D
JONES ST
LYNN ST
CHRISTIE ST
VIE
W S
T
SIMPSON ST
WA
LSH
ST
RO
BB
ST
ELOUERA ST
AR
CH
ER
ST
DENTON STB
RIG
GS
ST
RAYMOND ST
WYL
AM RD
PITT ST
MEDIC ST
ROBERTS ST
SA
UN
DE
RS
ST
CAMERON RD
JOHNSTON ST
SP
ICE
R S
T
LAURIE STS
TEE
RE
ST
SO
UTH
DAV
IS S
T
BOYSON ST
VINCENT ST
REGENT ST
HU
NTE
R S
T
PATT
ER
SO
N S
T
VENN ST EAST
WALLSEND ST
WE
LLS
ST
LEF
RO
Y S
T
CARMA AV
BULLFINCH RD
SWAN AV
BE
VAN
WA
Y
DE
RB
Y R
D
BL
AY
DO
NR
D
DU
KE
ST
CH
APM
AN
ST
GLAD STONECR
FOSTER ST
BR
IDG
E S
T
BLA
IR S
T
LO
WR
Y C
T
LEE
SO
NST
BEN
WEL
L PL
GIBBS RD
FOSTER ST
421500
421500
422000
422000
422500
422500
423000
423000
423500
423500
6307
500
6307
500
6308
000
6308
000
6308
500
6308
500
6309
000
6309
000
6309
500
6309
500
6310
000
6310
000
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.