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: +1 = + , − − − − , 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’.
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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
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
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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.
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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