Currimundi lake is an important coastal asset for both the community and the local wildlife. The dynamic nature of the mouth and lack of hard structures; such as training walls, means active management of the entrance is unavoidable to avoid flooding impacts upstream and to protect public assets that are on the southern side of the entrance to the lake.
One management technique that council uses is a sand ‘berm’ at the lake mouth. This has proven effective in directing the outflow to the ocean to be maintained generally to the central and northern sections of the lake mouth and protects the southern hard public assets, i.e. roads, parks and buildings, from migration of the mouth and subsequent erosion.
Due to erosion events such as storms this berm can be depleted of sand. When this occurs, officers from the environmental operations branch organise the reconstruction of the berm. This is usually with large machinery such as 25 tonne excavators, articulated dump trucks and dozers. To reconstruct the berm we must take sand from the sand plug at the entrance to the berm around 200m away, place the sand along the berm length then smooth out the surface with the dozers. The constructed berm runs parallel to the shoreline and tries to mimic the naturally built dunes adjacent to the lake in terms of height and seaward extent to ensure natural sediment processes long the open beach are maintained.
From time to time during periods of low rainfall and the right prevailing conditions out to sea can cause the lake to naturally close to the ocean. This is a natural process that occurs in many systems along the east coast of Australia. Currimundi lake is connected to Lake Kawana via the Wurtulla canal system. It receives inflows each day via the mechanical pumping system at the northern tip of Lake Kawana. When the system is closed the lake’s water level can rise and may overtop revetment walls upstream.
If the lake closes naturally council may decide to turn off the pumping system in Lake Kawana. This keeps the lake’s water level high to manage midge numbers (a proven management technique). If council believes there is either a risk of flooding or for the lake to be impacted by water quality issues, we will open the lake to the ocean using large machinery.
Council may decide to manually close the lake to the ocean to control midge numbers. These works have been completed on an as needs basis since 2005, with the last mechanical closure occurring in 2016. The work to manually close the lake to the ocean is a similar process as reconstructing the sand berm and requires large machinery.
Council has recently started a regular dredging campaign upstream of the sand plug. This is to replenish estuarine beaches that erode during storm events. The dredging occurs on an as needed basis, around every two years, and assists in managing the size and scale of the sand plug.
All works described above occur under our new whole of system permit for Currimundi lake. This was approved by state authorities in 2018 (EA0001226) and is consistent with the lake Currimundi dynamics study and ICOLL (intermittently closed and open Lakes and lagoons) entrance management documentation. This whole of system permit combines many different permits into a ‘one stop shop’ for Currimundi lake works. Many stakeholders were involved in these works and council's coastal team ensured all recreational, environmental, and structural objectives were followed. We have received very positive feedback.