Surface water is found on the surface of land, such as in a stream, river, lake or wetland. Surface water is replenished by rain and when groundwater seeps to the surface. It is lost through evaporation, seepage into the ground, use by plants and animals, runoff into the ocean and use by humans for living, agriculture and industry.
Surface water is a highly valued asset in the Adelaide and Mount Lofty Ranges region. There are over 5,500 square kilometres of surface water catchments and over 10,000 kilometres of watercourses in the region. The largest watercourses in the region include the Gawler, South Para, North Para, Torrens, Onkaparinga and Inman rivers. The region’s surface water systems are mainly seasonal, flowing in response to rainfall events, and drain into Gulf St Vincent. Modelling indicates that flows through watercourses in the region exceed 345,000 mega litres per year.
Why surface water is important
Surface water is essential to life and livelihoods in the region. It provides important water sources for natural ecosystems and for human consumption, agriculture and industries. It is also important for aesthetic, recreational and cultural reasons.
Use of surface water
The main uses of surface water in the region are for domestic consumption and agriculture. In a median year the greater Adelaide area sources an average of 60 per cent of its 200 gigalitres of domestic water from the Mount Lofty Ranges area, called the ‘watershed’. The remainder is sourced from the Murray River and is stored in 10 reservoirs in the watershed area, with total capacity of 198,000 mega litres. There is also over 15,300 farm dams in the region, storing over 39,700 mega litres and capturing an average of 10 per cent of the annual surface water flow, with up to 70 per cent in some catchments.
To ensure surface water is used sustainably, some resources are protected by prescription and a water allocation plan that details how the resources can be used. These plans are developed by the Adelaide and Mount Lofty Ranges Natural Resources Management Board together with the local community.
Managing surface water
Ensuring the quality of surface water in the Mount Lofty Ranges watershed is challenging. Over 90 per cent of the land in the watershed is privately owned, compared to just 10 percent in Melbourne and 20 percent in Sydney. This high level of private ownership increases the demand of catchment surface water sources and greatly increases risks to water quality, resulting in extensive and costly water treatment as part of the mains water supply system. More information on the management of surface water in the region can be found in the Adelaide and Mount Lofty Ranges Natural Resources Management Plan.