Annual River Flow Patterns
It’s not simply the amount of water flowing in a river that is important: The timing, volume and quality of environmental flows are all critical aspects too and, like the natural flow of rivers, different combinations will provide a different range of benefits for each ecosystem.
Freshes through summer, for instance, help to maintain or improve water quality, while spring flooding replenishes a river channel and provides soil and nutrients for floodplains, as well as being vital for the breeding success of water birds and native fish.
Flow components describe the different parts of a flow regime relevant to an ecosystem. They are characterised by season and duration.
|
Flow component |
Definition |
|---|---|
|
Cease to flow |
The period of no discernible flow in a river. |
|
Low flows |
The low flow that generally provides a continuous flow through the channel. |
|
Freshes |
Small or short duration peak flow events. These are flows that exceed the base flow and last for at least several days. |
|
High flows |
Persistent increases in the seasonal base flow that remain within the channel. |
|
Bankfull flows |
Flows of sufficient size to reach bankfull condition with little flow spilling onto the floodplain. |
|
Overbank flows |
Flows greater than ’bankfull‘, resulting in inundation of the adjacent floodplain habitats. |
Regulated rivers - those in which water is stored in dams and diverted for irrigation and urban water supply – can have flow patterns opposite to those which would naturally occur. This is because water is stored in dams in winter (when river flows would naturally be high) and then released to irrigators in summer (when rivers would naturally be drier).
When the Government puts ‘environmental water’ into a river to protect or improve its health, it is the natural flow components it is aiming to emulate.