The Wivenhoe and Somerset Dams Optimisation Study (WSDOS) will look at options for striking a better balance between dam operations, flood mitigation and water supply security for South East Queensland.
The study is in response to Recommendation 17.3 of the Queensland Flood Commission of Inquiry's final report. The findings of the study will be presented to government in early 2014.
The study will investigate alternative strategies for the operation of Wivenhoe and Somerset dams. These investigations will include seasonal, temporary or permanent alterations to the full supply levels, dam gate operating procedures and the duration of water releases.
It will consider the impact of the dams' operations on the closure of upstream and downstream crossings and bridges.
The study will generally not be considering new infrastructure or the expansion of existing dam infrastructure. The results of this study may however, lead to further investigations of other flood mitigation options (including infrastructure).
The study is being led by the Department of Energy and Water Supply (DEWS) in partnership with other Queensland Government departments, Seqwater, and Brisbane City, Ipswich City, Somerset and Lockyer Valley Regional councils.
DEWS is also leading an optimisation study of the North Pine Dam. The results of the WSDOS and the North Pine Dam Optimisation Study (NPDOS) will feed into the Brisbane River catchment flood study (led by the Department of Natural Resources and Mines) and the development of a Brisbane River catchment floodplain risk management Plan (led by the Department of State Development, Infrastructure and Planning).
The findings of the WSDOS will be reviewed again when the Brisbane River catchment flood study is completed.
The Brisbane River catchment has an area of about 15,000 km2 extending from Moreton Bay to the Great Dividing Range. This catchment includes the major sub-catchments of the Upper Brisbane, Stanley and Bremer rivers and Lockyer Creek. Average annual rainfall ranges from 1,700 mm at Peachester above Somerset Dam to 730 mm at Cooyar near the western boundary.
Wivenhoe Dam accounts for about 50 per cent of the total Brisbane River catchment area and is one of the largest storages in Queensland. The dam catchment receives approximately 1,000 mm of rainfall annually, mostly occurring in summer. It has a full supply volume of 1,165,000 megalitres for urban water use (including drinking water), and an additional temporary flood storage of approximately 1,450,000 megalitres.
Somerset Dam drains into Wivenhoe Dam and is operated concurrently during floods to maximise the flood mitigation benefits downstream of Wivenhoe Dam. Somerset Dam has a full supply volume of 380,000 megalitres for urban water use (including drinking water), and an additional temporary flood storage of approximately 524,000 megalitres.