Western Prescribed Water Resources Area

2016 Surface water status report

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This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

© Crown in right of the State of , through the Department of Environment, Water and Natural Resources 2017

ISBN 978-1-925668-05-06

This document is available online at www.waterconnect.sa.gov.au/Systems/GSR/Pages.

To view the Western Mount Lofty Ranges PWRA Surface water status report 2012–13, which includes background information on rainfall, streamflow, salinity, water use and water dependent ecosystems, please visit the Water Resource Assessments page on WaterConnect.

For further details about the Western Mount Lofty Ranges PWRA, please see the Water Allocation Plan for the Western Mount Lofty Ranges PWRA on the Natural Resources Adelaide and Mount Lofty Ranges website.

Gridded rainfall data was sourced from the Bureau of Meteorology (BoM). Station rainfall data was sourced from the Scientific Information for Land Owners database (SILO) and is Patched Point Data. Further information on SILO climate data is available at: http://www.longpaddock.qld.gov.au/silo/index.html.

Streamflow and salinity data are available via WaterConnect: http://www.waterconnect.sa.gov.au. SA Water are data custodians of the Kersbrook Creek (A5040525) and (A5020502) gauging stations.

To view descriptions for all status symbols, please visit WaterConnect.

WESTERN MOUNT LOFTY RANGES PWRA

The Western Mount Lofty Ranges (WMLR) Prescribed Water Resources Area (WMLR PWRA) is located 10 km east of Adelaide. Surface water, watercourses, and groundwater resources in the WMLR PWRA have been prescribed under South Australia’s Natural Resources Management Act 2004. A Water Allocation Plan (WAP) developed by the Adelaide and Mount Lofty Ranges Natural Resources Management Board and adopted in 2013, seeks to provide for sustainable management of water resources.

The eastern regions of the PWRA include the highest hills in the area and form the upland eastern extent of the Mount Lofty Ranges watershed. Several important watercourses drain the northern and central parts of the PWRA, flowing west through metropolitan Adelaide and its surrounding suburbs before entering , including: the South Para, Little Para, Torrens, Onkaparinga and Myponga Rivers. The south western parts of the PWRA includes the , which is characterised by smaller, coastal catchments, draining a central plateau. The Fleurieu Peninsula contains numerous wetlands including Environment Protection and Biodiversity Conservation Act 1999 (EPBC) listed Fleurieu Swamps. The most south-westerly parts of the PWRA comprise the Hindmarsh and Inman Rivers which drain the Fleurieu towards the south east.

Surface water resources are highly dependent on rainfall, with trends in streamflow and salinity primarily climate driven, i.e. below-average winter rainfall results in a reduction in annual streamflow volumes. Below-average summer rainfall can also result in increased irrigation extractions, and these two elements can cause salinities to increase by reducing the amount of streamflow available to dilute salts. Conversely, increased rainfall results in increased streamflow volumes, decreased irrigation extractions and salinities may stabilise or decline.

2016 Western Mount Lofty Ranges PWRA Surface water status report 1

2016 Status

Torrens & The Torrens River and catchments are assigned a red surface water status for 2016 based Onkaparinga on the combined streamflow recorded at the Torrens and Onkaparinga River gauging stations: 2016 ‘Total annual streamflow was below the 25th percentile of the period of record’

The Fleurieu Peninsula catchments are assigned a red surface water status for 2016 based on the combined Fleurieu streamflow recorded at the Myponga, Inman and Yankalilla Rivers gauging stations: 2016 ‘Total annual streamflow was below the 25th percentile of the period of record’

This status report does not seek to evaluate the sustainable limits of the resource, nor does it make any recommendations on management or monitoring of the resource. These actions are important, but occur through separate processes such as prescription and water allocation planning.

Rainfall

Annual rainfall for the 2015/16 period was slightly above the long-term average for the PWRA, as indicated in Figure 1, Mt Bold rainfall station, which is representative of the region. The spring months of 2015 recorded well below average rainfall, while higher than average rainfall was experienced the following May and June in 2016, accounting for approximately 38% of the total rainfall for the 2015/2016 period. These trends were consistent with data from Cudlee Creek (M023731), Mount Pleasant (M023737), Yankalilla (M023754) and Port Elliot (M023734) rainfall stations.

The 5-year average annual rainfall distribution across the PWRA (Figure 5-2) shows rainfall conditions to be typically drier across the whole WMLR PWRA, when compared to the long-term data (Figure 5-1). This is particularly evident in the hills surrounding the township of Stirling, and the region between Willunga and Middleton, where there is a clear reduction in the proportion of region receiving more than 900 mm of annual rainfall. Drier conditions were also experienced on the plains west of Willunga and the northern extent of the PWRA. The spatial distribution of rainfall during 2015/16 (Figure 5-3) is more consistent with the 5-year average than with the long-term average. Streamflow

Streamflow data was analysed from eight gauging stations located in the Torrens River, Onkaparinga River and Fleurieu Peninsula catchments. The Mount Pleasant, Sixth Creek and Kersbrook Creek gauging stations are located in the Torrens River catchment, and the Scott Creek and Bakers Gully gauging stations are located in the Onkaparinga River catchment (Figure 6). The Fleurieu Peninsula analysis sites include the Myponga River, and Yankalilla River gauging stations (Figure 6). All gauging stations within the PWRA recorded streamflow below the long-term average during the 2015/16 period (Table 1). All catchments in the WMLR are ranked below the 25th percentile (%ile) for streamflow, with the exception of the Kersbrook Creek and Bakers Gully gauging stations which ranked at the 26th and 53rd percentiles, when compared to their respective long-term streamflow records.

Table 1: WMLR PWRA streamflow statistics

Onkaparinga River Catchment Fleurieu Peninsula Catchment Mount Kersbrook Bakers Myponga Inman Yankalilla Sixth Creek Scott Creek Pleasant Creek Gully River River River (A5040523) (A5030502) (A5040512) (A5040525) (A5030503) (A5020502) (A5010503) (A5011006) 2015/16 streamflow 266 2671 2058 1604 4269 4995 2870 2567 (ML) Long-term average 2047 6972 2754 3382 4451 7358 7775 6015 streamflow (ML) Percentile Rank (%ile) 21st 9th 26th 15th 53rd 24th 9th 18th

2016 Western Mount Lofty Ranges PWRA Surface water status report 2

Water use

Water use in the WMLR, described at a whole PWRA scale, includes allocated volumes for licensed extractions from dams and watercourses, SA Water licensed extractions for public water supply, estimated demand from non-licensed activities (generally stock and domestic) and forestry. Total water use for the WMLR PWRA in 2015/16 was estimated to be 63,647 ML, approximately half the previous year’s total of 120,249 ML. Water use from licensed surface water sources (based on allocation data in the absence of total actual usage data) totalled 19,870 ML while SA Water extracted 21,108 ML (78,200 ML in 2014/15).

Non-licensed water demand is sourced from the WMLR Water Allocation Plan (WAP) and is estimated to be 4956 ML, equating to approximately 30% of the existing stock and domestic dam capacity. Estimated use for forestry is also taken from the WMLR WAP and totals 17,413 ML for the 2015/16 period. Salinity

The seasonal pattern of regional variation in salinity is shown in Figures 4. Salinity increases during sustained summer events, while decreasing throughout the winter months as a result of higher diluting flow levels. In the Onkaparinga River, 98% of salinity data is less than 1000 mg/L, while 96% is less than 1000 mg/L in the Torrens River.

Background information

The spatial variability in hydrological behaviour of the surface water catchments within the WMLR makes it challenging to assign a single water resource status for the PWRA. Therefore streamflow gauging stations used for analysis were chosen to be representative of the central, and southern portions of the WMLR PWRA. The Torrens River and Onkaparinga River catchments represent the central part, while the southern part of the region is represented by streamflow gauging stations located on the Fleurieu Peninsula.

Annual streamflow records from the Torrens River and Onkaparinga River gauging stations were combined each year for the common period 1973-74 to 2015-16 to represent total streamflow for the central part of the PWRA. A similar exercise was undertaken with the gauging stations located on the Fleurieu Peninsula. The total annual streamflow data for each area was than ranked to derive the relative rank of each year’s streamflow in comparison to the annual stream flows for the entire period of record. The total 2015/16 streamflow for the central WMLR was 9,868 ML, and it represents the 24th percentile over the period of record, i.e. only 23% of the long-term historic annual streamflow totals were less than the streamflow in 2015/16. Similarly, the 2015/16 streamflow from the southern part of the WMLR PWRA (10,432 ML) represents the 19th percentile. Streamflow percentiles of individual gauges are shown in Figure 6.

Further information may be found among the Frequently Asked Questions on the Water Resource Assessments page of www.waterconnect.sa.gov.au.

1200 Annual Rainfall Long-term Average 1100 5-Year Trend Long-term Trend 1000 900 800 700 600

Annual rainfall (mm) rainfall Annual 500 400 300 200

Figure 1. Annual rainfall (mm) for the 1973/74 to 2015/16 water-use years (July–June) at Mount Bold rainfall station (M023734)

2016 Western Mount Lofty Ranges PWRA Surface water status report 3

9000 Annual Streamflow Long-term Average (1973-2015) 8000 5-Year Trend Long-term Trend 7000 6000 5000 4000 3000

2000 Annual Streamflow (ML) Streamflow Annual 1000 0

Figure 2. Annual streamflow (ML) for the 1973/74 to 2015/16 water-use years (July–June) at Mount Pleasant gauging station (A5040512)

20000 Annual Streamflow Long-term Average (1995-2015) 18000 16000 5-Year Trend Long-term Trend 14000 12000 10000 8000 6000

Annual Streamflow (ML) StreamflowAnnual 4000 2000 0

Figure 3. Annual streamflow (ML) for the 1995/96 to 2015/16 water-use years (July–June) at the Inman River gauging station (A5010503) 1600 Onkaparinga River u/s Hahndorf Dissipator 1400 Torrens River d/s Hollands Ck 1200

1000

800

600

Total Dissolved Solids (mg/L) Solids Dissolved Total 400

200

0

Figure 4. Salinity data (TDS mg/L) for the 2002/03 to 2015/16 water use years at Onkaparinga River u/s Hahndorf Dissipater (A5031001) gauging station, and the 2007/08 to 2015/16 water use years at Torrens River d/s Hollands Creek (A5041003) gauging station

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Figure 5. (1) Long-term and (2) five-year average annual rainfall and (3) annual rainfall for the 2015/16 water-use year in the Western Mount Lofty Ranges PWR

2016 Western Mount Lofty Ranges PWRA Surface water status report 5

Figure 6. Surface water gauging stations and streamflow percentiles in the Western Mount Lofty Ranges PWRA

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2016 Western Mount Lofty Ranges PWRA Surface water status report 7 2017 © Department of Environment, Water and Natural Resources Published 2017 | FIS 94502 www.environment.sa.gov.au