Home > Water Management > Water for the environment > Wetlands > Wetlands

Wetlands

Lachlan Valley

Introduction
Wetlands of the Lachlan Valley
Environmental Flow Rules

Introduction

Water from the Lachlan River supports a major irrigation industry and provides income and employment for thousands of people. As well as producing food for local consumption, it is also the source of millions of dollars in agricultural exports for Australia. The Lachlan Valley is also noted for its wetlands and waterbirds.

Marool Lake at Cumbung Swamp
Source: DLWC

Wetlands of the Lachlan Valley

Floodplain Wetlands

The Lachlan catchment contains up to 400, 000 ha of floodplain wetlands. A number of these floodplain wetlands have regional, state and national significance.

Tableland Wetlands

Tableland wetlands are common along many of the streams and depressions of the headwaters of the catchment. Many of these wetlands are associated with either springs (groundwater seepage), high water tables or local runoff.

Wetlands of National Importance

The following wetland summary has been adapted from the Directory of Important Wetlands in Australia, 3^rd Edition. More information on these wetlands and the reasons for their inclusion in the Directory of Important Wetlands in Australia can be found on Environment Australia's Website.

Lake Brewster (No. 48 on Map 2)

Aerial view of Lake Brewster
Source: DLWC

Lake Brewster is a large shallow basin, located on the floodplain of the Lachlan River between Lake Cargelligo and Hillston. The lake is an important refuge habitat, supporting large numbers of waterbirds.

Lake Cowal/Wilbertroy Wetlands (No. 40 on Map 2)

Lake Cowal is the largest natural lake in the catchment. It is a terminal drainage lake of Bland Creek, located on the Lachlan River floodplain between Forbes and West Wyalong. The total area of the lake and associated wetlands is approximately 20,500 ha. The wetland is an extensive freshwater lake with a maximum depth of 4.2m. It forms part of a chain of wetlands including Lake Cowal, Nerang Cowal and Bogandillon Swamp.

The lake is fringed, in the shallow northern area, with River Red Gum (Eucalyptus camaldulensis) with a Lignum (Muehlenbeckia florulenta) understorey. A study of the flora of Lake Cowal in 1993, found at total of 411 plant species including 321 native and 90 exotic species (NSR, 1995).

Lake Cowal provides important drought refuge when wetlands in other parts of the state are dry. It is also a major rookery site for ibis and pelicans.

Lachlan Swamp - Part of the mid Lachlan Wetlands. Also known as Waljeers Wetlands (No. 40 on Map 2)

This wetland system occurs on the Lachlan River floodplain downstream of Booligal and includes Lake Waljeers, Peppermint Swamp, Lake Bullogal and Ryans Lake. Lake Waljeers and Ryans Lake are shallow depressions, and Peppermint Lake and Lake Bullogal are shallow depressions with undulating surfaces (DWR, 1988). The floodplain is forested with Black Box (Eucalyptus largiflorens) and River Cooba (Acacia stenophylla), with River Red Gum (Eucalyptus camaldulensis) on the margins. These wetlands are considered to be a good example of River Red Gum / Black Box vegetation association in western NSW. When flooded the area supports large numbers of waterbirds

Lake Merrimajeel / Murrumbidgil Swamp (No. 49 on Map 2)

Murrumbidgil Swamp is a shallow depression with an undulating surface that retains water after Merrimajeel Creek has ceased flowing. It is situated approximately 20km west of Booligal. Murrumbidgil Swamp is known as a major rookery site for ibis, heron and ducks.

Murrumbidgil Swamp is a site of intensive research by National Parks and Wildlife Service and CSIRO Division of Wildlife and Ecology. It was here that the importance of wetting / drying cycles to wetland health were established (Maher, pers. com.).

Booligal Wetlands (No. 43 on Map 2)

The Booligal wetlands consist of low gradient braided channels situated on the Merrimajeel, Merrowie and Muggabah Creeks, which are distributaries of the Lachlan River. The wetlands are rarely to infrequently flooded (approximately every 5 years) from major and minor streams. They are renowned for the large numbers of waterbirds that congregate to breed and forage in the area during and following floods. The Booligal wetlands remain in a relatively natural condition and provide a representative example of inland floodplain wetlands.

The Great Cumbung Swamp (No. 45 on Map 2)

Aerial view of the Great Cumbung Swamp
Source: DLWC

The Great Cumbung Swamp comprises the terminal drainage swamp of the Lachlan River and the surrounding floodplain, including Baconian Swamp, near Oxley. The Great Cumbung Swamp and Baconian Swamp remain in a relatively natural condition, and therefore represent a good example of the terminal reed swamps, and associated floodplain vegetation. As with many other large inland wetlands, this area provides drought refuge when wetlands in other parts of the state are dry. This wetland system supports large numbers of waterbirds, many of which breed in the area.

The Great Cumbung Swamp is listed on the Register of the National Estate.

Cuba Dam (No. 44 on Map 2)

Cuba Dam is located on Merrowie Creek, 37 km, west of Booligal, NSW. The wetland occurs in the middle reaches of Merrowie Creek, which is a distributary of the Lachlan River. Despite slight modifications it is still a good example of a relatively natural wetland. The impoundment of this wetland has actually made it particularly suitable for ibis. The ibis form large colonies in the wetland and are what makes this wetland a site of national significance.

Merrowie Creek Cuba Dam to Chillichil Swamp (No. 51 on Map 2)

Aerial view of the Merrowie Creek Wetlands
Source: DLWC

Merrowie Creek is a distributary of the Lachlan River, leaving the river near Hillston. Beyond Cuba Dam, Merrowie Creek spreads into a series of channels before flowing into several large lake bodies (Tarwong Lakes) some of which are interconnected with Box Creek. Box Creek then continues south to reach Chillichil Swamp. The Tarwong Lakes are a series of shallow depressions off Merrowie Creek which are fringed by River Red Gum (Eucalyptus camaldulensis) and a surrounding understorey of Lignum (Muehlenbeckia florulenta) and Nitre Goosefoot (Chenopodium nitrariaceum). This area is frequently inundated by flood waters and therefore provides excellent waterfowl habitat. The dominant vegetation along Box Creek to Chillichil Swamp is Black Box (Eucalyptus largiflorens) woodland. These wetlands support large numbers of waterbirds which breed at Cuba Dam, Tarwong Lakes and Chillichil swamp.

Environmental Flow Rules

Their Relevance to the Wetlands of the Lachlan Valley

Over the last 100 years the Lachlan River, and its large and very significant areas of wetlands and floodplains have changed significantly from their natural state. In part, this is the result of the growing use of water for agriculture, industry and domestic needs. While this use of water generates significant economic benefits in the Lachlan, there is clear evidence of increasing environmental stress within the river and, in particular, in its important wetland areas.

A River Management Committee was set up in 1997 to recommend environmental flow rules for the Lachlan River. Click here to view a PDF of the River Management Committees Report on Environmental Flow Rules for the Lachlan Valley.

The rules were introduced in the Lachlan Valley in 1998/99. The Committee was then asked to advise on a statutory water sharing plan for the Lachlan Regulated River. This plan commenced on 1 July 2004 and includes the following environmental water provisions:

Reserve all water above the Plan extraction limit for the environment
- This ensures that there is no erosion of the long-term average volume of water available to the environment during the life of the Plan. On a long-term basis, approximately 75% of yearly flows in the river will be protected for the maintenance of environmental health.
Improve lower system flows and winter/spring flow variability
- This involves passing some inflows through Wyangala Dam (called 'translucent' releases) and prohibiting extraction of some tributary inflows or the diversion of flows into Lakes Brewster or Cargelligo.
- The rules apply from mid-May to mid-November at Wyangala and the start of June to the end of November at Lake Brewster.
- The Lake Brewster flow targets vary between 3,500 ML/day and 8,000 ML/day.
- Total volume of translucent and tributary flows provided is up to 350,000 ML/year measured at Brewster Weir.
Provide reserves of water for environmental purposes
- 10,000 ML of water in Wyangala Dam and another 10,000 ML in Lake Brewster are reserved in storage whenever the total volume of water available to general security access licences exceeds 50% of the access licence share volume at the beginning of a water year or reaches 75% during a water year.
- This water is released to support waterbird or fish breeding, wetland watering or increase flow variability.
Provide a reserve of water for water quality management purposes
- Reserve 20,000 ML of water in Wyangala Dam each water year.
- Release this water for purposes to reduce salinity levels or mitigate blue-green algae outbreaks.

What do the current rules address?

The flow rules are designed to:

Protect natural low flows;
Protect and restore a portion of freshes and high flows;
Mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary streams;
Maintain or mimic natural flow variability in all streams;
Minimise the impact of in-stream structures;
Manage contingent environmental and water quality events; and
Improve overall river health.

The Integrated Monitoring of Environmental Flow Rules

In order to adequately assess the response of the riverine ecosystems of Lachlan River to the environmental flow rules, it was seen as essential that a sound scientific assessment of the rules be made.

The NSW Government implemented the Integrated Monitoring of Environmental Flows or IMEF program in 1997. The environmental side of the program involves the collection of biological, physical and/or chemical data from river sites and wetlands within sections of the river that are affected by the flow rules. The program provides not only additional understanding of the flow responses of riverine ecosystems based on sound scientific methods, but also an opportunity to evaluate the environmental performance of the flow rules themselves.

Monitoring is under-way in the Lachlan Valley to assess the response of the river and associated wetlands to the environmental flow rules. Twelve wetlands are monitored for:

Hydrological regimes, inundation timing, volume, surface area, gauge height/depth, number of fillings, connectivity with the river (duration) etc;
Aquatic macroinvertebrates;
Aquatic plants;
Frogs;
Birds; and
Water quality.

Morgan's Billabong - an IMEF wetland
Source: Patrick Driver (DNR)

What have they achieved so far?

There were positive results from the environmental flow rules in the 1998-99 season. Additional water was provided to Lachlan to facilitate the completion of a bird breeding event in the Lower Lachlan and to relieve a severe algal bloom. The successful bird breeding event included the breeding of around 40, 000 pairs of Ibis.

In 1999-2000 there were two periods of translucent releases. These provided inflows to the Great Cumbung Swamp, a significant wetland at the end of 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 for landholders. As a result the first major water bird breeding event on the Lower Lachlan in five years occurred with some 8,000 to 10,000 breeding pairs of straw-necked Ibis present.

Robsar Billabong - an IMEF wetland
Source: Patrick Driver (DNR)