This page provides an overview of the outcomes of the Wivenhoe and Somerset Dam Optimisation Study (WSDOS), an investigation of alternative strategies for operating Wivenhoe and Somerset dams during floods. WSDOS was completed in response to recommendations of the Queensland Floods Commission of Inquiry.
After seeking community feedback on the options in the WSDOS report, the option known as Alternative Urban 3 was selected as the optimised operational strategy for the dams during floods.
Alternative Urban 3 was incorporated into Revision 12 of the Manual of Operational Procedures for Flood Mitigation at Wivenhoe Dam and Somerset Dam in November 2014.
Alternative Urban 3 changes how the flood mitigation compartment of Wivenhoe Dam is used, placing a lower priority on the protection on rural crossings and allocating more space to protecting houses and buildings from damage during a large floods.
This operational strategy potentially delivers a 5 to 10 per cent reduction in flooding during a major flood, resulting in significantly fewer houses being inundated in these floods.
The Wivenhoe and Somerset dams are dual purpose water supply and flood mitigation dams. They are key infrastructure for our water supply and provide flood mitigation to communities downstream including Brisbane and Ipswich.
Wivenhoe Dam is one of the largest storages in Queensland. The dam catchment receives, on average, 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 1,835,000 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.
The Brisbane River catchment has an area of about 14,000 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. Flooding in the Brisbane River catchment can originate from any of the major sub-catchments.