Altered river flow regimes

The flow regime of a waterway is critical to its ecosystems and health.
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Image of Wellington Dam

What is a flow regime?

The flow regime of a river encompasses the quantity, duration, and seasonal pattern of flows.

This is illustrated in the representative hydrograph showing different components of the flow regime below.

Representative hydrograph showing different components of the flow regime

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

Impacts of changes to flow regimes

Even small differences in the flow regimes between rivers can have marked effects on the aquatic and riparian vegetation and the fauna (fish and crayfish and aquatic macroinvertebrates) present.

Some species require permanent water, some are naturally adapted to periods without flow, and all are reliant on aspects of the flow regime to support their life histories. For example, flows are known to trigger migrations for reproduction, can provide the cues for spawning, and are essential to the survival of larvae and juveniles through inundating nursery habitats.

What alters the flow regime of rivers?

Human activities such as creation of dams and weirs, water abstraction, disposal of excess water, irrigation and clearing of vegetation can change the natural flow regime of rivers. These activities can lead to increases or decreases in the quantity of flow as well as changing the seasonal pattern of ecologically important flow events.

Climate change is also influencing flow regimes such as the reduction in flows seen across much of south-west Western Australia.

In addition to the influence of flows on the community of flora and fauna species present in a river, changes to flow regimes can impact the river ecosystem through changes in aquatic connectivity, water quality and erosion and sedimentation processes.

What we do

The Department of Water and Environmental Regulation determines and manages the flow regimes necessary to maintain or enhance the ecological values of specific rivers (environmental water requirements) through the water allocation planning process.

The flow regime of a waterway is an important indicator of its health. It is one component in the South West Index of River Condition that we use to assess waterway condition at a range of sites across the south west.

For more information about flow and ecology see ecological water requirements on our Healthy Rivers website.