Altered flow regimes
The flow regime of a river is the quantity, duration and seasonal pattern of flows - see diagram below. The flow regime of a river system influences the flora and fauna present in a river ecosystem - some species require permanent water and some are naturally adapted to periods without flow. It also influences the lifecycle activities of fauna such as spawning and the survival of larvae and juveniles.
Human activities such as abstraction of water, disposal of excess water, irrigation and clearing of vegetation can change the natural flow regime. These activities can lead to either an increase or a decrease in quantity of flow as well as changing the timing, duration and seasonal pattern of ecologically important flow events.
Climate change is also contributing to changed flow regimes such as the reduction in flow seen in parts of south-west Western Australia.
Changes to a river's flow regime can influence the fauna community present, including the fish and crayfish and macroinvertebrates. It can also impact the river ecosystem by causing changes in aquatic and riparian vegetation, aquatic connectivity, water quality and erosion and sedimentation processes.
The Department of Water determines and manages the flow regimes necessary to maintain or enhance the ecological values of rivers through the water allocation planning process.
The flow regime of a waterway is an important indicator of its health and forms part of the assessment of waterways in the South West Index of River Condition.
Representative hydrograph showing different components of the flow regime. Source:
Source: Green, A, Donohue, R, Storey, A, Lynas, J & Pauli, N 2010, Ecological water requirements of the Margaret River, Environmental water report series, Report no. 11, Department of Water, Western Australia.