What options were considered about the proposal to increase the capacity of Suma Park Dam?
The proposal is to raise the wall of Suma Park Dam by one metre, which will increase the amount of water it can hold. The Council investigated this proposal and the impacts and issues associated with it.
Currently Suma Park dam has a capacity of 17,290 megalitres. A raising of the dam wall by 1 metre would increase the capacity to 18,970 megalitres.
An initial report on raising the wall went to the Council in November 2011. Included in this report was a structural assessment of design works associated with dam safety during extreme flooding
This assessment found that from a structural point viewpoint the spillway could not be raised more than 1 metre.
Would there be enough water to fill a bigger dam?
The Suma Park Dam catchment is only 179km2, which is extremely small compared with the 960km2 catchment of Bathurst’s Chifley Dam.
Climate change modelling conducted by the NSW Government is forecasting an average drop of 2% in rainfall onto the Suma Park Dam catchment. It is also expected the median annual stream flow will decrease by 15% as only a limited amount of rainfall runs off the catchment.
The natural catchment that includes Suma Park Dam, urban run-off and the creeks the stormwater harvesting infrastructure is built on, is limited and other communities and people rely on this water downstream. This means there is a limited supply from this catchment available to the Orange City community.
An assessment of more than 100 years of data has found that even if Suma Park Dam was bigger, for the majority of time it would not be full. However, if another source of water were used to supplement the water from the existing catchment, such as from the Macquarie Pipeline project, the project of raising the wall becomes more feasible.
What environmental impact will the raising of the dam wall have?
Orange City Council has examined the environmental impact on Summer Hill Creek as part of the environmental impact statement for the raising of Suma Park Dam. This assessment considered the size of additional environmental flows to be released as part of raising the dam wall.