Water Management
Environmental rules for rivers
The environmental rules are generally designed to provide water for the environment across a range of flow events from floods to very low flows. The following 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, protecting 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 five 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
- Protect natural water levels in pools of creeks and rivers and wetlands during periods of no flow
- Protect natural low flows
- Protect or restore a proportion of moderate flows, ‘freshes’ and high flows
- Maintain or restore the natural inundation patterns and distribution of floodwaters supporting natural wetland and floodplain ecosystems
- Mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary waterways
- Maintain or mimic natural flow variability in all rivers
- Maintain rates of rise and fall of river heights within natural bounds
- Maintain groundwaters within natural levels, and variability, critical to surface flows or ecosystems
- Minimise the impact of in-stream structures
- Minimise downstream water quality impacts of storage releases
- Ensure river flow management provides for contingencies
- 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
- reduced frequency of algal blooms
The actual environmental flow rules in the water sharing plans for the regulated rivers 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 set out in the table below:
| 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 reinstated
- 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 of environmental release are as follows:
Gwydir River
- 5,100 megalitres (ML) released during the summer of 2003 which promoted wetland plant diversity.
- 13,400 ML realeased in the summer of 2005 inundated 12 hectares of the Gwydir Wetlands and helped to sustain a major bird breeding event.
- 11,340 ML released in the summer of 2006/07 for the Gwydir wetlands in addition to natural high tributary inflows of 10,020 ML
- 10,000 ML released in November/December 2007 which resulted in the inundation of 3,900 hectares of the Gwydir wetlands and the maintenance of core areas of the wetland communities.
Macquarie River
- environmental flow releases totalling 84,000 ML were made into the Marshes from November 2005 to January 2006 to support water bird breeding.
- The combination of local rainfall, tributary flows (32 GL) and environmental releases (22 GL) resulted in flooding over some 15,000 ha of the Macquarie Marshes in late 2007/early 2008. Environmental releases targeted specific areas to support an egret and cormorant colony containing some 2000 breeding pairs. The colony successfully hatched by late March 2008.
Lachlan River
- 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.
Namoi
- environmental water was released from Keepit Dam to maintain flow levels during June, July and August 2006. This amounted to 4,679 ML.
Murrumbidgee
- an environmental allocation of 14,000 ML 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.
- Concern for the survival of the endangered Southern Bell Frog resulted in 8.3 GL of water being released in November/December 2007 into the Murrumbidgee wetlands to protect drought refuge areas, resulting in a good breeding response.
Murray River
- a combined release of 500,000 ML by the NSW and Victorian Governments from mid October 2005 through to January 2006 resulted in flooding of the Barma-Millewa river red gum forest, the largest such forest in Australia.