The Lower Sabina River flows through the centre of the Geographe catchment into the Vasse-Wonnerup Estuary, an important habitat for waterbirds. The river is of cultural significance to the Wadandi people and a registered Aboriginal site of significance. Other cultural sites of significance occur within the catchment including a fish trap, campground and two historical missions. A survey in October 2017 by the Department of Water and Environmental Regulation have found several species of native fish and crayfish including the Gilgie, Southwest glass shrimp, Nightfish, Western minnow, Western pygmy perch and the Bluespot goby. A River Action Plan developed by GeoCatch in 2002 outlines the characteristics, values, condition and management issues of the river system.
The Lower Sabina River supports a thriving agricultural industry dominated by beef and dairy grazing. Small urban and rural residential areas occur in the lower reaches. Very little native vegetation remains in the catchment.
The natural hydrology of the Lower Sabina catchment has been significantly altered with approximately 60% of the flows from the upper catchment diverted. The upper Sabina River flows into the Sabina Diversion Drain before connecting with the Vasse Diversion Drain downstream. In addition, numerous artificial drainage channels dissect the lower catchment, constructed to alleviate waterlogged paddocks during winter months. Since 2000, the mean annual flow for the Lower Sabina River is 6GL/yr of a total of 203GL/yr for the waterways of the Geographe catchment.
The Lower Sabina River contributes a disproportionately large nutrient load to the Vasse-Wonnerup Wetlands given its small catchment size. The nutrient loads in the Sabina River are driven by intensive land-uses, particularly dairy, with a high proportion of agricultural grazing in the catchment. Nutrients enter the waterways through vegetation clearing, fertiliser use, discharge of dairy effluent and run-off. The concentrated drainage network of the Lower Sabina catchment accelerates the speed at which nutrients enter the catchment waterways.
Image: Nutrients in the Lower Sabina River are primarily sourced from fertiliser used for dairy and beef grazing, with smaller quantities from point sources (such as dairy sheds).
Nutrients in the Lower Sabina River are primarily sourced from fertiliser used for dairy and beef grazing.
The Department of Water and Environmental Regulation has been monitoring the water quality of the Lower Sabina River fortnightly since 2006. Data from 2008-2017 is presented in the table below. The data shows total nitrogen and phosphorous concentrations to be consistently two to three times above water quality targets.
The Lower Sabina River catchment is categorised as a ‘recovery’ catchment as waterways do not meet the nitrogen or phosphorus target established in the Water Quality Improvement Plan.
There is a significant decreasing trend in total nitrogen concentration in the Sabina catchment from 2011 to 2017.
Significant on-ground works have been carried out in the Lower Sabina catchment as a result of the high nutrient concentrations. Since 2009 programs 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 completing fencing and re-vegetation in the riparian zone. Key achievements between 2009 and 2015 include:
Nineteen landholders completed 3.3km of riparian fencing and 19ha of re -vegetation with the aim to restore and protect riparian vegetation, prevent stock access, increase the absorption of nutrients and to reduce sedimentation and pollution.
Eleven landholders completed soil testing and nutrient mapping to inform fertiliser decisions, assisting farmers to use only the phosphorus needed for pasture growth required.
Three dairy effluent management plans were developed to support the re -use of dairy effluent, reducing nutrients entering the waterways.
Further works in the Lower Sabina catchment are a priority to continue to improve water quality. For the next three years management programs will continue to focus on reducing nutrients entering the Lower Sabina River under the Revitalising Geographe Waterways program. Implementation of best practice agricultural fertiliser management and dairy effluent management are key goals for this ‘recovery’ catchment.
Farmers will be supported in the implementation of best practice fertiliser management programs through the Fertiliser Management project on at least one farm where soil testing, whole farm nutrient mapping, agronomic advice and workshops will be completed. At least one effluent upgrade is proposed in the catchment, at a dairy farm in Ruabon, reducing the dairy industry nutrient footprint. GeoCatch will work with the community to support sustainable behaviours and best management practices in fertiliser and effluent management.
A river health assessment will be conducted to measure and report on the ecological health of the Lower Sabina River. Monitoring the water quality of the Lower Sabina River will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated. The option for reconnecting flows from the upper catchment of the Sabina River will be investigated using hydrodynamic modelling in the Reconnecting Rivers Program.
Image: Actions to reduce nutrients entering the Lower Sabina River will continue as part of Revitalising Geographe Waterways program.