The Capel River is located in the eastern Geographe catchment. The Capel River is the largest and only perennial river in the Geographe catchment receiving discharges from the Leederville aquifer year round. Several foreshore reserves of conservation value are situated on the Capel River including Ironstone Gully Falls and the river is of historical and cultural significance to the Wadandi people.
Aquatic fauna surveys in summer 2016 by the Department Water and Environmental Regulation found Carters Freshwater Mussel (currently listed as ‘vulnerable ’ on the 2014 IUCN Redlist of threatened species), Smooth Marron, Gilgie, Freshwater cobbler, Nightfish, Western pygmy perch, Western minnow and Pouched lamprey. A River Action Plan developed by GeoCatch in 1999 outlines the characteristics, values, condition and management issues of the river system. A more recent publication, the Upper Capel River Action Plan, was developed by the Donnybrook Balingup Land Conservation District Committee in 2010 and outlines the results of foreshore assessments on the Upper Capel River.
Land-use of the upper Capel River catchment is predominately native vegetation (state forest) and beef grazing. The lower catchment is dominated by beef and dairy grazing with pockets of native vegetation and horticulture. Urban areas occur at the towns of Capel and Peppermint Grove Beach.
Image:Beef and dairy grazing are the primary land-uses in the catchment.
The Capel River has most of its catchment in the Darling and Whicher Scarp, where it flows through a deeply incised channel across the Swan coastal plain, through the Capel township where it is joined by Gynudup Brook and Tren Creek before discharging into the ocean at Peppermint Grove Beach. The Capel River flows year round, and receives discharges from the underlying Leederville Aquifer. Since 2000, the mean annual flow for the Capel River is 35.5GL/yr of a total of 203 GL/yr for the waterways of the Geographe catchment. The Capel River was diverted in the late 1880s when the River was diverted from the Wonnerup Inlet into Geographe Bay through the Higgins Cut. The downstream end of the river is regulated by a floodgate (right) to prevent salt water from migrating upstream during low flows and affecting grazing land in the lower reaches of the catchment.
Nutrient concentrations are currently acceptable in the Capel River, however nitrogen and phosphorus loads discharging to Geographe Bay are one of the highest of all the reporting catchments due to the large size of the catchment.
The nutrient loads in the Capel River are driven by agricultural land use in the catchment, mostly beef grazing, dairy grazing and horticulture. Three dairy sheds occur in close proximity to the river in the middle catchment. These point sources contribute to both nitrogen and phosphorus loads.
Nutrients in the Capel River are primarily sourced from agricultural land use, with smaller quantities from horticulture and point sources (such as dairy sheds).
The Department of Water and Environmental Regulation has been monitoring the water quality of the Capel River fortnightly since 2006. Data from 2008-2021 is presented in the table below. The data shows total nitrogen and phosphorous concentrations to be consistently below water quality targets. The likely dilution of nutrients from freshwater flows in the upper catchment of the Capel River, as well as by groundwater inflows, has contributed to this system meeting the water quality targets.
The Capel River catchment is categorised as a ‘protection’ catchment as waterways are currently meeting both the nitrogen and phosphorus targets established in the Water Quality Improvement Plan.
Total nitrogen and total phosphorus trends for the Capel River catchment from 2011 to 2021.
Since 2009 on-ground 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, undertaking fencing and revegetation in the riparian zone and stormwater upgrades.
Key achievements between 2009 and 2015 include:
Management programs will continue to focus on maintaining the good water quality of the Capel River catchment waterways under the Revitalising Geographe Waterways program. Reducing nutrient input from urban sources, promoting the practice of best-practice agricultural fertiliser management, best-practice dairy effluent management and raising community awareness to recognise the values of the Capel River are key goals for this ‘protection’ catchment.
Farmers will be supported in the implementation of best practise fertiliser management programs through the Fertiliser Management project where soil testing, whole farm nutrient mapping, agronomic advice and workshops will be undertaken at two farms in the catchment.
Monitoring the water quality of the Capel River will continue in the Catchment Water Quality Monitoring Program and the Water Quality Improvement Plan will be reviewed and updated. GeoCatch will continue to work with community groups and partners to raise community awareness and promote best practice fertiliser and dairy-effluent management.
Image: Actions to reduce nutrients entering the Capel River will continue as part of Revitalising Geographe Waterways program.