The Vasse Diversion Drain catchment is one of the largest of the Geographe sub-catchments. Waterways in the catchment include the upper Sabina River, the Sabina Diversion Drain, the upper Vasse River and the Vasse Diversion Drain. The headwaters of the Sabina River are located in the Whicher Range National Park, an area known for its unique environmental features and floristic diversity.
The Vasse River is known to support several species of freshwater fish and is culturally and historically significant as a site of camping and foraging by the Wardandi people and an area of early european settlement for the Molloy and Bussell families. A River Action Plan developed by GeoCatch in 2002 outlines the characteristics, values, condition and management issues of the Vasse River system.
Land use is varied in the Vasse Diversion Drain catchment. The catchment supports a thriving agricultural industry dominated by beef and dairy grazing, with pockets of timber plantations, horticulture and vineyards. Ten dairies are located in the catchment, which constitute over a quarter of all dairies in the Geographe catchment. A large area of native vegetation (Whicher Range National Park and state forest) occurs in the south-eastern section of the catchment. Urban residential and lifestyle lots of west Busselton occur closer to the coast.
Image: The catchment has a diversity of land uses. The centre of the catchment is dominated by beef and dairy grazing.
The headwaters of the Sabina and Vasse Rivers are located in the Whicher Range. The upper Vasse and upper Sabina River were diverted in the 1920s to prevent flooding of the Busselton township. The upper Sabina River flows into the Sabina Diversion Drain before connecting with the Vasse Diversion Drain downstream. The Vasse Diversion Drain receives water from approximately 60% of the Sabina River catchment and 90% of the Vasse River catchment, diverting flow away from the Vasse-Wonnerup Wetlands and directly into Geographe Bay. Since 2000, the mean annual flow for the Vasse Diversion Drain is 23GL/yr of a total of 203 GL/yr for the waterways of the Geographe catchment.
The Vasse Diversion Drain flowing into Geographe Bay
The nutrient sources in the Vasse Diversion Drain catchment are from a diversity of land uses. Primary sources include beef and dairy grazing, dairy sheds (ten in total), the Busselton wastewater treatment plant (WWTP) and urban residential land use.
Image: Nutrients in the Vasse Diversion Drain catchment are primarily sourced from dairy and beef grazing, with smaller quantities from point sources (such as dairy sheds and the Busselton WWTP) and urban diffuse sources.
The Department of Water and Environmental Regulation has been monitoring the water quality of the Vasse Diversion Drain fortnightly since 2006. Data from 2008-2016 is presented in the table below (as data from 2008 represents data from 2006-2008). The data shows total nitrogen concentrations to be consistently two to three times above water quality targets since 2009.
The Vasse Diversion Drain catchment is categorised as a ‘recovery’ catchment as this waterway does not meet the nitrogen or phosphorus target established in the Water Quality Improvement Plan.
Trends in nutrient concentrations of the Vasse Diversion Drain
Phosphorus concentrations were below water quality targets until 2013. There is a weak significant increasing trend in total phosphorus concentration from 2006 to 2016. No statistical trend in total nitrogen concentration was observed in the data.
Since 2009 on-ground works led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the waterway. These programs included working with farmers to reduce fertiliser use, managing dairy effluent and carrying out fencing and re-vegetation in the riparian zone. Key achievements between 2009 and 2015 include:
Thirty-two landholders completed soil testing and nutrient mapping to inform fertiliser decisions, assisting farmers to use only the phosphorous needed for the pasture growth required.
Two dairy effluent management plans were developed and implemented in the catchment supporting farmers in the re-use of dairy effluent on farms with the aim to reduce nutrients entering the waterways.
Thirty-three landholders completed 29.78 km of riparian fencing and 27.5ha of re-vegetation to improve the riparian zone with the aim to protect and restore riparian vegetation, increasing the absorption of nutrients and reducing the sedimentation and pollution of the waterways.
For the next three years management programs will continue to focus on reducing nutrients entering the waterways of the catchment under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management and dairy effluent management are key goals for this ‘recovery’ catchment.
At least two effluent upgrades are proposed in the catchment, at farms in Yoongarillup and Kalgup and a soil amendment trial is being carried out at the Vasse Sports Oval. Farmers will be supported in the implementation of best practice fertiliser management programs through the ‘Smart Soils’ project where soil testing, whole farm nutrient mapping, agronomic advice and workshops will be carried out on at least five farms in the catchment.
The option for reconnecting flows from the upper catchment of the Sabina and Vasse Rivers have been investigated using hydrodynamic modelling in the Reconnecting Rivers Program. The lower end of the Vasse Diversion Drain will be converted to a living stream to improve nutrient attenuation and ecological health in the Vasse Diversion Drain Enhancement Project. These projects will contribute to a review of the drainage network in the catchment in the Optimising Drainage project.
Monitoring the water quality of the Vasse Diversion Drain will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated.
Actions to reduce nutrients entering the waterways of the Vasse Diversion Drain catchment will continue as part of Revitalising Geographe Waterways program.