Water Corporation has started work on upgrading the Vasse Diversion Drain to improve flood protection for the popular holiday destination of Busselton, located in the South West of Western Australia (WA).
The coastal town has been developed on a narrow, low-lying dunal formation between Geographe Bay and the Vasse Estuary. Due to this geography, its tranquil, protected bay makes a perfect launchpad for water lovers in summer and a flood zone during heavy rainfall.
From the 1880s through to the 1920s, a series of river modifications was undertaken in Busselton to mitigate flooding. One such modification was the diversion of the Vasse River to the west of the town. This involved building a diversion dam on the river and a six kilometre drain through to Geographe Bay, with dumped spoil from the excavation forming ‘levee banks’. This structure is now known as the Vasse Diversion Drain.
The current upgrade of the Vasse Diversion includes reconstructing the diversion dam, widening of the channel and reconstructing levee banks. This scope will assist with management of water quality, allow floods to be safely conveyed into the Vasse River, and increase the capacity of the drain to manage a 1-in-100-year rainfall event. A popular pedestrian bridge over the drain will also be extended by 11.5 metres as part of the project, due to the widening of the channel. The 35-tonne bridge was recently lifted off the levee banks by a crane to allow for work on the banks.
Temporary cofferdams have been constructed at either end of the drain, to stop the flow of water into the construction area. Water within the construction area has been pumped out, so the channel can be accessed as a transport route for construction machinery. Once the upgrade has been completed, there will be greater control of the flows between the two waterways, protecting residential properties and the surrounding environment from the risk of flooding.
Vasse Joint Venture, an arrangement between Westforce Construction and JWI Contractors, will undertake the work on behalf of Water Corporation. It is expected to create more than 70 local jobs during the project and employ two Aboriginal subcontracting firms in the South West.
Several specialists, including world-renowned restoration ecologist Professor Kingsley Dixon, Tranen Revegetation and local environmental groups, have assisted in the preparation of an extensive revegetation plan due the area being a unique biodiversity hotspot.
Home to the largest population of western ringtail possums in the state, part of the plan involves providing these animals with safe passage during construction and for years to come. With help from Doctors Mike and Mandy Bamford, who are WA fauna specialists, more than 88 fauna shelters and 15 possum rope bridges have been installed in adjacent bushland.
WA’s only freshwater mussel species also resides in the Vasse Diversion Drain. The Carter’s freshwater mussel is described as “the lungs of WA’s waterways” due to its vital role as a natural water filter in the freshwater ecosystem. Aquatic ecology specialists IndoPacific, supported by OzFish volunteers, successfully relocated more than 35,000 mussels upstream in the Vasse River. Once construction has finished, the drain will be naturally repopulated when the mussels spawn and move downstream.
After extensive community engagement, construction commenced in October 2020 and will continue for a period of around eight months. Over the next three years, more than 130,000 seedlings will be planted across 15 hectares of the surrounding area to improve diversity in the local ecosystem and aid ecological restoration of surrounding bushland.
For more information visit yoursay.watercorporation.com.au/VasseDrainUpgrade
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