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Water for the environment

Environmental rules for rivers

The following diagram illustrates the importance of different flow ranges to a river's environment.

This diagram illustrates the importance of different flow ranges to a river's environment

In addition to the cap on extractions in the Murray-Darling Basin, NSW has embarked on a process of allocating water to the environment. The economic and social development of NSW relies on the assured water supplies that are provided by our water storages. It is therefore not possible to return our rivers to their natural condition. However, in NSW we have now prepared statutory water sharing plans for most of the major river systems that protect both the total volume of water for the environment and the natural variability in flows that is the low flows, moderate flows, freshes and floods. The environmental rules in the water sharing plans are designed to:

limit extractions so that the major share of water is protected – between 56% and 80% of the average annual water in the regulated river systems will be retained in the river – amounting to over 5 million megalitres (a megalitre is a million litres) in the inland systems.
replicate natural flow patterns or events so as to provide water when and where it will best meet environmental needs - on average the rules for the regulated rivers will return an additional 220,000 megalitres of water to the environment over and above that required under the Murray Darling Basin cap.

The environmental flow rules are based on the following broad river flow objectives that set out 12 aspects of flow considered to be critical for the protection or restoration of river health, ecology and biodiversity. The objectives were subject to extensive public consultation and endorsed by the NSW government in 1999.

River Flow Objectives
Objective 1	protect natural water levels in pools of creeks and rivers and wetlands during periods of no flow
Objective 2	protect natural low flows
Objective 3	protect or restore a proportion of moderate flows, “freshes” and high flows
Objective 4	maintain or restore the natural inundation patterns and distribution of floodwaters supporting natural wetland and floodplain ecosystems
Objective 5	mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary waterways
Objective 6	maintain or mimic natural flow variability in all rivers
Objective 7	maintain rates of rise and fall of river heights within natural bounds
Objective 8	maintain groundwaters within natural levels, and variability, critical to surface flows or ecosystems
Objective 9	minimise the impact of in-stream structures
Objective 10	minimise downstream water quality impacts of storage releases
Objective 11	ensure river flow management provides for contingencies
Objective 12	maintain or rehabilitate estuarine processes and habitats

The purpose of the River Flow Objectives is to produce specific environmental benefits such as:

improved survival of ecosystems and aquatic biodiversity;
improved water quality;
healthier wetlands.
improved habitat quality and increased variability of habitat for native fish, frogs, waterbirds and other native fauna, including invertebrates;
more successful breeding of native birds, fish and other native fauna, which only breed in response to specific environmental triggers, for example, rising or falling water levels in the natural seasons;
more natural inundation of flood plains and wetlands, leading to better health and productivity (such as grazing), protection of endangered species, biodiversity and water quality;
discouragement of alien pest species, such as carp, which favour regulated conditions;
improved health of in-stream and riparian vegetation, leading to greater bank stability, improved efficiency of buffer strips in protecting water quality, and reduced erosion and turbidity; and
reduced frequency of algal blooms.

The actual environmental flow rules in the water sharing plans vary from valley to valley, depending on which of the above objectives were considered most important for that valley. The range of rules which apply are:

Environmental flow rules in the regulated rivers	Purpose	Valleys where rule applies
Extraction limit	sets a limit on the long term average annual volume of water that can extracted, thus protecting the major share of water for the environment	All regulated rivers
End-of-system flow	requires a flow to be retained at the end of the river system. This ensures that flow is maintained below the areas of major extraction.	Namoi Murrumbidgee Hunter
Transparent dam release	requires all dam inflows occurring at certain times to be passed immediately downstream, as though no dam was present. This maintains natural flow variability for that part of the year (usually the winter months) when dam releases would otherwise be minimal.	Murrumbidgee
Translucent dam release	requires a proportion of dam inflows occurring at certain times to be passed immediately downstream. This restores the natural flow variability associated with specific flow ranges usually freshes and minor floods.	Lachlan Macquarie
Limits on taking high flows	limits pumping when the dam spills or high flows enter the regulated river from unregulated tributaries. This protects either some or all of these naturally occurring high flows which are important for flooding of wetland areas.	Lachlan Namoi Gwydir Hunter
Limits on taking low flows	limits pumping from lower flows that enter the regulated river from unregulated tributaries. This ensures that sufficient water is retained in the river for the environment.	Gwydir
Environmental water allowances or releases	creates a ‘bank' or volume of water stored in the dam which can be released for specific environmental purposes, such as flushing blue-green algal blooms, reducing salinity or supporting bird-breeding or fish spawning events.	Gwydir Macquarie Lachlan Murray Murrumbidgee Hunter

The management rules in regulated river systems have a lot more flexibility because of the ability of the major storages to provide for environmental flow management. In contrast, the flows in unregulated rivers can only be protected through controls on extraction. In most unregulated rivers, it is during drier periods when flows are naturally low that there is generally greatest concern for the health of the river. This is when pools contract, water quality deteriorates rapidly, algal blooms occur, oxygen levels decline and fauna compete for the reducing food supplies. The water sharing plans for the unregulated rivers therefore require licence holders to stop pumping when the river flow falls below a certain level. In addition many of the plans set limits on how much water can be taken from different flow ranges or classes.

What outcomes have we achieved from the environmental flow rules?

In the long-term, the rules will make significant progress towards restoring important aspects of the natural flow regime. For example:

in the Namoi River 75% of the natural frequency of the mid-river beneficial flooding will be re–instated
in the Lachlan River, the frequency of significant floods will be returned to 65% of natural
the Gwydir wetlands will now receive 85% of natural overbank flow.

The release of water stored in the dam for the environment is designed to support natural flows. In the Murrumbidgee Valley, environmental releases in 2000 from Blowering and Burrinjuck Dams successfully "piggy backed" onto a natural river fresh to produce the most significant filling of billabongs along the Murrumbidgee River since 1996.

Since 2000, drought conditions in all valleys have limited the opportunities for environmental releases. However the releases that have occurred have provided some positive environmental outcomes. Examples include:

In the Gwydir Valley, environmental releases were made during the summer of 2003 (a total of 5,100 megalitres) which promoted wetland plant diversity. A further release occurred in summer of 2005 (a total of 13,400 megalitres) inundating 12 hectares of the Gwydir Wetlands and helping to sustain a major bird breeding event. In 2006/2007 releases were made in December and January and again in March to provide water for the Gwydir wetlands. This delivered 11,340 ML to the wetlands in addition to natural high tributary inflows of 10,020 ML
In the Macquarie, environmental flow releases totalling 84,000 megalitres were made into the Marshes from November 2005 to January 2006 to support water bird breeding.
In the Lachlan Valley, a release of water from the wildlife allocation into Merrowie Creek was made in December 2005 following good catchment rains and a replenishment flow provided along the Creek for landholders. This resulted in the first major water–bird breeding event on the Lower Lachlan for five years with 8,000 to 10,000 pairs of straw-necked ibis present.
Environmental water was released from Keepit Dam to maintain flow levels during June, July and August 2006. This amounted to 4, 679 ML.
In the Murrumbidgee Valley, an environmental allocation of 14,000 megalitres was released in December 2005. The water inundated up to 10,000 hectares of wetlands, triggering successful breeding events for water–birds and other threatened species.
In the Murray Valley, a combined release of 500,000 megalitres by the NSW and Victorian Governments from mid October 2005 through to January 2006 resulted in promising recovery of the Barma-Millewa river red gum forest, the largest such forest in Australia.

In a number of the valleys committees have been established to advise on the environmental flow rules. For information on the Gwydir Environmental Contingency Allowance Operations Advisory Committee.