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Water planned and delivered to benefit the environment
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Water used to improve or maintain the health of rivers and wetlands
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Water held in entitlements for the environment

What is environmental water?

Though environmental water can mean any water in a river or wetland that benefits the environment, when we talk about 'environmental water' we are referring to water that's set aside in storages such as reservoirs and dams which is managed for plants and animals.   

Many of Victoria's river systems have been modified as the state has prospered and population grown, to provide water important for towns, industry and food production.

Instead of water flowing naturally through the landscape, water is now captured in dams and weirs, and then delivered via pipes and man-made channels.

As a result, some of our rivers give up more than a third – and sometimes half – of the water that would have naturally flowed in them throughout each year.

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Stimulates animals like native fish to feed and breed (for example, cod and yellowbelly fish need to be able to move on to floodplains to feed)
triggers plants to seed or germinate (for example, river red gums need flooding for seeds to germinate)
Triggers plants to seed or germinate (for example, river red gums need flooding for seeds to germinate)
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Moves carbon between rivers, floodplains and estuaries, an important process for food chains
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Allows fish and plants to move about rivers and colonise new areas
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Helps restore groundwater
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Stabilises river banks through better plant growth, reducing erosion into the river
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Flushes out salt along river banks and floodplains

Changing flows

Instead of flowing naturally, with high flows in winter and low flows in the hotter months of summer, rivers now run higher when water needs to be delivered for farming and urban use.  These changes have interrupted many of the natural river and wetland processes needed by native plants and animals to survive, feed and breed.

Environmental water is released into some of these rivers and wetlands to improve their health and protect environmental values.

In rivers, environmental water can be delivered to mimic some of the flows that would have occurred naturally before rivers were modified.

Environmental water does not try to return rivers and wetlands to their pre-European condition. Many rivers and wetlands are so modified that this is not feasible; however environmental watering can help to minimise some of the impacts of these modifications on rivers and wetlands.

Environmental water managers generally focus on returning some of the small and medium-sized river flows important in the life cycles of native plants and animals.

In wetlands, environmental water is focused on mimicking some of the natural wetting and drying cycles which plants and animals depend on for their diversity and long-term resilience.

Types of flows

It's not simply the amount of water flowing in a river that's important.

It's the entire environmental flow regime that matters, including the volume, timing, duration, frequency and quality of flows that are provided. Like the natural flow of rivers, different combinations of these provide a range of benefits for ecosystems.

Releasing small amounts of water, called 'freshes', through summer helps to maintain or improve water quality. Flooding in spring replenishes a river channel and provides soil and nutrients for floodplains, as well as being vital for water birds and native fish to breed.

Types of flows

Flows are characterised by their size, frequency, timing and duration.

Type of flow

Description

Benefits

Cease to flow

No discernible flow in a river.Total or partial drying of the river channel.

Drying is important for some ecological processes. It can also reduce exotic pests such as European carp.

Low flows, also called base flows 

Low flows generally provide a continuous flow through the channel. This may  maintain the flow above a cease to flow, or provide habitat as a change from high flows.

Connects in-stream habitats and can benefit other river users, such as providing water for livestock.

Freshes

Small pulses of water. These flows exceed the low flow and last for at least several days.

Freshes are a key contributor to the variability of flows.

Helps maintain or improve water quality and prevents algal blooms.

High flows

Persistent increases in the seasonal base flows that remain within the channel.

High flows do not fill the channel to 'bankfull'.

Allows for fish migration and enhances recreational fishing opportunities.

Bankfull flows

Flows that reach the top of the river bank with little flow spilling onto the floodplain.

An important trigger for fish breeding. Helps move sediment and maintain banks.

Overbank flows

Flows greater than bankfull, inundating adjacent floodplains.

Environmental water is not released for overbank flows on private land without permission from landholders.

Maintains floodplain and wetland connectivity, stimulates fish and bird breeding and enhances recreational opportunities

Overbank flows are critical for a range of ecological factors, including floodplain productivity.

A typical natural flow pattern of a victorian river, before the construction of dams, weirs and channels
Modified from a graphic that originally featured in Why rivers need water, Department of Sustainability and Environment 2007