Fish and turtles in South East Queensland’s Lake Macdonald Dam will be able to just keep swimming, with Seqwater updating the design of a new spillway to better protect aquatic life.
The utility is currently planning the first major safety upgrade to the dam since the walls were raised in 1980. This will involve building a new spillway and embankments to guard against extreme flooding and bring the dam in line with modern engineering standards.
In order to undertake the construction safely, the lake’s water level will be lowered to about 5% to 10% of its full supply level.
Seqwater has conducted a number of studies to assess the potential environmental impacts of the project, including using boats fitted with sonar equipment to identify and count fish species in the water.
As a result of the studies, the utility has updated the initial design of the spillway and pushed the lowering of the lake to 2021 to meet environmental conditions.
“The revised design features what’s known as an ‘ogee’ spillway, which allows fish and turtles in the storage to slide safely into the pooled water below,” Seqwater CEO Neil Brennan said.
“The new timeline for the lake lowering will provide us with more time to finalise our aquatic management plan to allow the safe lowering of the dam and the relocation of aquatic life.
“It also enables us to meet one of the strict conditions of approval for this project: to only lower the lake in a narrow window between March and August, outside the wet season.”
The project will begin next year with a range of construction works including replacing the bridge to the Noosa Water Treatment Plant and relocating existing utilities and services.
Seqwater will also carry out water security projects to improve the South East Queensland Water Grid ahead of the lake lowering. The final timing for this phase of the project is subject to further water supply security assessments in 2020 and early 2021, which will take into account dam storage levels and water consumption in South East Queensland (SEQ).
The Lake Macdonald project is part of Seqwater’s Dam Improvement Program, which will see a series of dam upgrades across SEQ to ensure dams meet national and state safety standards into the future.