Waterways, floodplains, wetlands and groundwater aquifers are an integral part of the Catchment, providing many environmental, social and economic values. They underpin livelihoods, supporting agriculture and urban centres, contain significant flora and fauna habitat, have high recreational and aesthetic values, and are central to the culture of Traditional Owners.
The Goulburn River Basin is Victoria’s largest, covering 1.6 million hectares or 7.1 per cent of Victoria. The Goulburn River is 570 kilometres long, flowing from the Great Dividing Range upstream of Woods Point to the Murray River east of Echuca. Streamflow along the Goulburn River has been modified by two major features, Lake Eildon and the Goulburn Weir, which regulate river flow and supply water for irrigation, urban and environmental purposes. Along its course, users of the Goulburn River have adapted to the altered state or modified flow regime introduced by regulation. The lower reaches of the Goulburn River are bordered by the Lower Goulburn National Park. The National Park is a linear park protecting the lower Goulburn River from Shepparton to its junction with the Murray River near Echuca and is home to an array of aquatic-dependent native plant and animal communities (GB CMA 2002b).
The Broken River Basin is 772,386 hectares or 3.4 per cent of Victoria’s total area. The Broken River is a tributary of the Goulburn River. The basin also includes the catchment of the Broken Creek, which diverges from the Broken River west of Winton Wetlands and flows north-west to the Murray River. Flow in the Broken River is extremely variable between seasons and years. Two major storages were constructed within the basin, Lake Nillahcootie and Lake Mokoan. Lake Nillahcootie is in the Broken River’s upper catchment and stores flows to provide water for irrigation, urban, stock and domestic use. Lake Mokoan was constructed in 1971, but was decommissioned as an active reservoir in 2010. Its natural wetland habitat is being restored (GB CMA 2002b) and is now known as Winton Wetland.
Wetlands are also an important feature, with over 2,000 wetlands mapped and classified covering approximately 86,000 hectares of the Catchment. These wetlands include large permanent lakes, floodplain billabongs, small spring soaks, alpine bogs and shallow freshwater depressions. Most wetlands are on private land on the Catchment’s floodplains, hold water for short periods of time and cover less than 10 hectares (GB CMA 2002b).
Natural floodplains across the Catchment have an important ecological function with floods supporting vegetation and wetlands on the floodplain as well as the river channel ecology. Floodplains have been highly modified with built infrastructure to support and protect urban centres and agricultural production from flooding impacts. River regulation has altered flood frequency and patterns. Across the Catchment, some 5,800 square kilometres of floodplain have been mapped up to the extent of the 100-year Average Recurrence Interval (ARI) flood.
Groundwater is found in aquifers, which are layers of underground sediments or fractured rock (DSE 2009). The significant deep and shallow groundwater aquifer systems across the Catchment vary in character and connectivity. Fresh groundwater is extracted for domestic and stock use as well as irrigation and urban supply. Some shallow and saline aquifers across the floodplains are managed as a threat to productivity and natural assets. Several groundwater systems are important elements of the river and wetland ecosystems.