The Lower Vasse River flows through the centre of Busselton into the internationally significant Vasse-Wonnerup wetland system. The river is highly valued by the community and has long been an iconic town feature and focal point for recreational and social events. Riparian vegetation provides habitat for a diversity of waterbirds and the river’s aquatic habitat supports macroinvertebrates, freshwater mussels and several species of native fish.
In recent decades frequent algal blooms and poor water quality that have sparked a number of science initiatives including the Lower Vasse River Clean-up Program and control of feral goldfish. The Lower Vasse River Action Plan developed by GeoCatch in 2000 outlines the values, condition and management priorities of the river system (from the Whicher Scarp to Fairlawn road).
The Lower Vasse River catchment supports urban residential, industrial and commercial land uses with large areas of parkland and golf courses. Land-use in the upper catchment is primary beef grazing with pockets of horticulture. Residential land-use is growing in the lower catchment with the expansion of the City of Busselton. The Vasse-Wonnerup wetlands take up much of the catchment area and are surrounded by areas of native vegetation and larger rural residential blocks.
Image: The lower catchment is dominated by urban residential land-use. Land-use in the upper catchment is primarily beef grazing.
The Lower Vasse River flows through the centre of Busselton, and extends from the Vasse Diversion Drain at its headwaters, to the Vasse Delta Wetlands at the downstream boundary. The Lower Vasse River is regulated to protect Busselton from floods in the winter months and maintain water levels in summer months (for aesthetic reasons).
The Lower Vasse River receives regulated upstream flows from the Vasse Diversion Drain, through a 900mm culvert at the headwater of the Lower Vasse River (below right).
The mean annual flow to the Vasse Wetlands (post-2000) is approximately 9GL/yr, the majority of which originates in the Vasse Diversion Drain and flows through the culvert. The downstream boundary is partially regulated by weir boards at the Old Butter Factory (left), which are operated to assist in retaining water in the Lower Vasse River during summer, as the main body of the estuary downstream dries. The weir boards are inserted to a height of 0.4mAHD late in the flow season and are removed at the beginning of the flow season the following year.
The nutrient loads in the Lower Vasse River are derived from both the Vasse Diversion Drain catchment (flow coming in through the off-take pipe) and the Lower Vasse River catchment.
Fertiliser from dairy grazing in the Vasse Diversion Drain catchment is a major source of nitrogen, with smaller contributions from beef grazing, point sources, septic and urban areas from both catchments. Dairy grazing and point sources in the Vasse Diversion Drain catchment contribute a significant proportion of the phosphorus load with smaller contributions from urban diffuse and septic sources in the local catchment.
Image: Nutrient loads in the Lower Vasse River are derived from both the Vasse Diversion Drain catchment and the Lower Vasse River catchment
In recent decades poor water quality has negatively affected the Lower Vasse River and has included annual blue-green algal blooms. The blooms reduce the amenity of the Lower Vasse River and often result in offensive odours.
The Department of Water and Environmental Regulation has been monitoring the water quality of the Lower Vasse River fortnightly since 2006. Data from 2008-2016 is presented in the table below (as data from 2008 represents data from 2006-2008) and shows total nitrogen and total phosphorus concentrations to be consistently above water quality targets.
Image: Trends in nutrient concentrations of the Lower Vasse River
No statistical trend in nutrient concentration was observed in the data.
Significant works have been carried out in the Lower Vasse River to improve water quality including the Lower Vasse River Clean-up Program, completed in 2005.
Since 2009 programs led by GeoCatch and partners have focussed on reducing nitrogen and phosphorus entering the waterway. These programs included completing fencing and re-vegetation in the riparian zone, stormwater upgrades and working with local businesses. Key achievements between 2009 and 2015 include:
For the next three years management programs will continue to focus on reducing nutrients entering the Lower Vasse River under the Revitalising Geographe Waterways program. As residential urban areas expand in the lower catchment managing nutrient loads from new urban developments and the incorporation of water sensitive urban design are a priority for this ‘recovery’ catchment.
Implementation of best practice agricultural management and targeted riparian management are also key priorities. Effluent upgrades and best practice fertiliser management through the Smart Soils project are being implemented at several farms within the Vasse Diversion Drain catchment, a contributor to nutrient loads in the Lower Vasse River Catchment.
The extent and likely impact of water lilies on water quality and ecology of the river will be investigated and new water quality treatments such as algae flocculants and new generation phosphorus binding clays will be investigated as part of the Water Quality Treatment Trials program. A River Health Assessment will also be conducted to measure and report on the ecological health of the Lower Vasse River.
Monitoring the water quality of the Lower Vasse River will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated. The option for increasing flows from the upper catchment of the Vasse River as a means of improving water quality will be investigated using hydrodynamic modelling in the Reconnecting Rivers Program.
Actions to reduce nutrients entering the Lower Vasse River will continue as part of Revitalising Geographe Waterways.