Rivers, streams, and their wetlands and floodplains are vital components of ecosystems. They support a high diversity of organisms and play an essential role in many physical, chemical, and biological processes.
Australian plants and animals are adapted to high levels of natural variability within rivers, streams, floodplains, and wetlands.
Impacts of altering watercourses
Altering the natural flow of watercourses can:
- impact crucial stages in the lifecycle of many organisms, such as reproduction, recruitment, or migration patterns
- reduce habitat for native plants and animals by changing the extent, frequency, and duration of flooding of floodplains and wetlands
- increase water flows to certain areas, including permanently flooding some wetlands
- degrade the riparian zone (riverbanks)
- provide more habitat for invasive species that prefer deeper, more permanent, and disturbed habitats
- cause the loss or disruption of ecological functions.
Case Study: Lower Murrumbidgee Floodplain
The Murrumbidgee River is 1,690 km long. It flows west from the Snowy Mountains to join the Murray River near Balranald, on the New South Wales-Victoria border. Its most extensive wetland area is the Lower Murrumbidgee floodplain, which stretches west from around Hay.
The native plants and animals on the floodplain, and the migratory waterbirds that visit during wet periods, depend on natural cycles of flood and drought. However, these have been disrupted by water resource development, such as dams, levee banks, and other irrigation devices.
Historical changes
From 1855 to 1998, water resource development shows that over 140 years:
- around 58% of the floodplain wetlands have been lost, with much of this damage occurring between 1975 and 1998
- of the wetlands that remain, 44% are degraded, and the floodplain vegetation has little chance of returning to health
- waterbird numbers have dropped by more than 80% since 1983, indicating great declines in the invertebrates, fish, frogs, and water plants the birds feed on.