Rivers and wetlands in Australia and their dependent native plants and animals have evolved around the variability and seasonality of rainfall runoff.
The regulation of many river systems through the development of major instream dams and the extraction of large volumes of water for irrigation has altered natural river flows.
Environmental water or flows is a way of returning water to river systems to reinstate some of the triggers for fish, bird and vegetation recruitment and to improve water quality. The crashing populations of native fish, water birds and River Red Gums can only be reversed by putting water back into the rivers to assist with breeding and regeneration events. The increasing levels of salt can be diluted and flushed out with more water in the rivers.
Environmental water in NSW comes in a number of different forms. Under Water Sharing Plans there is:
- planned environmental water: water not allocated for extraction under the plan
- environmental water allowance: additional water available for release from storages when needed to support river, floodplain and wetland health
- held environmental water: water licences purchased by state and federal governments to be used for supporting native fish, waterbird and vegetation populations.
The Murray-Darling Basin Plan was established to determine how much water needed to be returned to river systems to maintain and improve their health.
The final bipartisan agreement in 2012 was that the equivalent of 3200 GL (gigalitre = 1 billion litres) must be returned to the Basin over a 10 year plan by 2024.
Environmental water must be protected from extraction across the Basin through specific rules in Water Sharing Plans.
What does water for the environment do?
Water for the environment has helped to restore, maintain and improve river and wetland sites across NSW over the past 20 years.
Water releases trigger a surge in the number of insects and micro-organisms within a wetland. Frogs emerge to feed and become food for waterbirds, fish, turtles and other reptiles.
Plants reproduce and set seed, providing food, shelter and nesting materials for animals. Wetland plants also filter the water, capturing sediment and returning it to the floodplain floor ready to feed the next generation of wetland plants.
Native fish respond to the conditions and begin to breed. Fish are an essential part of a healthy river. Supporting native fish supports the recreational fishing and tourism industries.
Specific sites are targeted to support waterbird and woodland bird breeding events. Birds play an important role in the riverine environment, controlling pest insects and helping pollination. Bird-watching and bushwalking support tourism in local communities.
During dry times, water for the environment is used strategically to provide refuge sites for key plant and animal species ensuring their survival in the longer term.
Environmental flows help to recharge ground water systems. Rivers and wetlands also cool the land around them. They help to slow fast-flowing flood waters and filter the water running through them. Flows spread out onto the floodplain, depositing sediments which in turn enrich the soil and increase productivity for agriculture.