Flood conditions, like those experienced in 2022–23, pose social, economic and environmental challenges. The Department of Climate Change, Energy, the Environment and Water is aware of the difficult situations many people face at these times.
During periods of significant flooding, natural river flows and rainfall are generally sufficient to meet the needs of rivers, wetlands and wildlife without the addition of environmental flows.
When floodwaters recede and drier times return, water for the environment may be used to ensure key habitats remain healthy, rivers and wetlands connect, nutrients are transported throughout the river system, and wildlife has opportunities to breed and feed.
The Department of Climate Change, Energy, the Environment and Water manages the limited volume of water set aside for the environment to ensure essential environmental assets remain viable now and into the future. We devise annual water plans with different scenarios in mind – very dry, dry, moderate, and wet to very wet. As part of this annual planning process, we prioritise certain rivers and wetlands to ensure their water requirements are met in the coming months and years. Our management approach is adaptive. We revisit our priorities as the seasons change from dry times to floods and the scenarios in between.
In dry years, the need to release water into our wetlands and rivers for plants, animals and the environment is clearly visible. However, during wet years, our rivers, wetlands and floodplains may still need water to ensure their health.
The river is flooding, so why do we need water for the environment?
Despite wet conditions, the natural flow cycle of many NSW wetlands, rivers and floodplains remains disrupted by dams and weirs, which affects river and wetland health.
The volume, timing, duration, regularity and range of river flows are all essential for thriving ecosystems. Water for the environment helps to support a more natural flow pattern to rivers, creeks and wetlands affected by river regulation, imitating some of the flows that once occurred naturally. Environmental flows are timed to ensure that the right amount of water is delivered at the right time to support the lifecycle needs of native fish, waterbirds, plants and other wildlife.
We use water for the environment during wet times to enhance restoration of key floodplain and wetland habitats and enhance opportunities for native plants and animals to breed, move and thrive.
When would we use water for the environment?
There are times during or following a flood event when water for the environment might be used to achieve specific ecological outcomes for our rivers and wetlands.
If the recession of a flood peak is rapid and dam releases are reduced very quickly, water for the environment can be used to slow the recession rate.
Why would we want to do this?
- To support wildlife breeding events (especially native fish, waterbirds, macroinvertebrates and amphibians) that higher unregulated flows might have triggered
- To avoid the stranding of native fish and support dispersal through the system
- To avoid abandonment of nests for colonial nesting waterbirds
- To support vegetation lifecycles (complete flowering or setting seeds, avoid rapid desiccation of aquatic plants)
- To minimise bank slumping by allowing riverbanks to drain more slowly and maintain their structural integrity.
If natural flooding is brief, water for the environment might be used to extend the duration of inundation in some areas to support the completion of breeding or provision of foraging habitats.
Water for the environment may also be used to create refuges for aquatic wildlife (mainly native fish) in the event of a low-oxygen (hypoxic) blackwater event. Freshwater plumes attract native fish and allow them to survive until conditions improve.
Can water allocated for the environment be saved for drier times?
In very wet years, it may not be necessary to use all the water allocated for the environment, as widespread natural flooding may be sufficient to support river and wetland health. In some circumstances, it may be ‘carried over’ for future use.
Deciding whether to carry over water, and how much to carry over, is a complex decision that is governed by strict rules and considers longer-term objectives and risks.
Some water may be carried over if forecast conditions are dry and rainfall is likely to be low in order to support multi-year objectives relating to, for example, wetland restoration or the provision of refuge habitat through extended droughts.