More than 40 community members attended a meeting in Busselton last week about the proposed changes to improve water quality – which include opening the Wonnerup Inlet sandbar and Vasse surge barrier gates in early December, to allow seawater into the estuary during summer months to maintain slightly higher water levels.
Department of Water and Environmental Regulation (DWER) lead scientist Linda Kalnejais said four years of seawater trials conducted with the Vasse Wonnerup Partnership and researchers had shown that introducing seawater into the estuary reduced algal blooms and improved conditions for fish.
“The trials showed that we can use seawater inflows to reduce harmful algal blooms, if we introduce seawater quickly into the Vasse Estuary channel and maintain the channel salinity levels in line with seawater,” said Dr Kalnejais.
Dr Kalnejais said the cutting-edge science supporting the new management approach included DWER’s development of a hydrodynamic model for the Vasse-Wonnerup system. “The model allowed us to look at different ways of opening the surge barrier for a range of water levels and salinity in the estuary, to achieve the best water quality outcome,” she said.
Community members at last week’s meeting were also informed about ongoing monitoring by Murdoch University and the Department of Biodiversity, Conservation and Attractions, of aquatic plants, macroinvertebrates, fish and water birds under changed conditions in the estuary, which has adapted ecologically to the historical management regime.
Dr Kalnejais said further monitoring would assess how making the estuary salty earlier in summer impacts the ecology of the wetlands system in the longer term.
“With reduced rainfall and river flows across the South West from climate change, we are trying to manage a unique system with competing objectives – so having the ability to review our management and science on a yearly basis is important to assess if we are getting the balance right,” said Dr Kalnejais.
The science and monitoring supporting the updated surge barrier management is an initiative of the State Government’s award-winning Revitalising Geographe Waterways project to improve water quality, waterway health and management. For more information on Revitalising Geographe Waterways, visit https://rgw.dwer.wa.gov.au/.
