Nutrient run-off from urban areas in the Geographe catchment accounts for around 8% of phosphorous and 5% of nitrogen entering Geographe Bay. Although currently a relatively small contributor, urban expansion is predicted to be the main source of large increases in both nitrogen and phosphorus in the future. In the more urbanised catchments such as the Lower Vasse River and Toby Inlet, nutrient inputs from urban areas contribute substantially to current total nutrient loads.
Minimising nutrient runoff from existing and new urban areas by working with home gardeners, urban developers, and local government and industry groups is a key priority of Revitalising Geographe Waterways.
Stormwater runoff from businesses and industries in urban areas transport pollutants and nutrients into local wetlands, waterways and Geographe Bay. Over the last 15 years GeoCatch, the Department of Water and Environmental Regulation, the City of Busselton and the Shire of Capel have been working together to retrofit urban stormwater systems to reduce nutrients entering waterways. Under Revitalising Geographe Waterways the City of Busselton has installed rain gardens in the new City of Busselton Administration building carpark and within residential areas. Raingardens capture stormwater allowing it to settle on the garden surface before soaking through the plants and filter media, taking up nutrients before they enter waterways. The City is also reviewing stormwater infrastructure to inform future retrofitting projects for water quality improvement.
Soil amendments are products that bind with phosphorus, keeping it within the soil available for plant growth rather than washing into waterways. The City of Busselton has partnered with the Department of Water and Environmental Regulation and Iluka Resources to establish a trial at the new Vasse Sporting Complex that will assess the effectiveness of the soil amendment Iron Man Gypsum (IMG) in an urban setting.
This project provided deep sewage connections to 206 dwellings in the Quindalup area between Toby Inlet and Geographe Bay. The importance of connecting areas serviced by septic tanks to in fill sewerage connection is considered a critical action to reduce both environmental and human health risk. This is particularly important near Toby Inlet and Geographe Bay where nutrient reduction from this project is estimated to be 1860 kilograms of nitrogen and 372 kilograms of phosphorus per year and will also reduce pathogens and improve odours in the area.
Septic systems were identified in the Water Quality Improvement Plan (2010) as a significant source of nitrogen and phosphorous in the Toby Inlet. The project will also include monitoring before and after connections to measure reductions achieved in nutrients. The Water Corporation led this project.
