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Murrumbidgee River Catchment
The Murrumbidgee River originates on the edge of the Great Dividing Range in the Kosciusko National Park, south-east of Tumut. The river system drains 84,000 square kilometres and is a major tributary of the Murray-Darling River system. The mainstream is 900 kilometres long. Burrinjuck Reservoir divides the upper and lower catchments where the river flows through a narrow gorge. The valley begins to widen from near Gundagai into alluvial plains and continues westward to its junction with the Murray and Lachlan Rivers. Yanco Creek is a major effluent stream which joins Billabong Creek.
The geology of the catchment is characterised by meta-sediments (slate, phyllite, schist, quartzite, greywacke and limestone) and granitic rocks intruded into the meta-sediments. These intrusions are widespread in the higher country of the Great Dividing Range, the Brindabella and Tinderry Ranges. Yellow and red texture-contrast soils are dominant in the tableland areas.
Land & Water Use
The Murrumbidgee River supports large irrigated agricultural and irrigated pastoral developments in the western part of the catchment and includes the Murrumbidgee and Coleambally Irrigation Areas. Together these account for approximately 3,500 land holdings and consume 1.2 million megalitres of water per year (DWR 1994c). There are 14 major dams, 8 large weirs and over 10,000 km of irrigation canals. There are high demands on surface water and ground water resources in terms of quality and quantity; and irrigation agriculture is expanding. There are several new intensive livestock and feedlot developments. Viticulture is a growth industry in the Yass, Griffith and Balranald areas and the numbers of agricultural processing industries (e.g. wool scouring and beef abattoirs) are increasing within the catchment.
On the Great Dividing Ranges between 1,100-1,400m, the vegetation is dominated by snow gum forests and woodlands. Wet sclerophyll forest is dominated by Eucalyptus delagetensis and E. dalrympleana, or E. viminalis on the cool, moist upper slopes. The drier plateaus and ridges support E. rubida and E. radiata. Logging has occurred in this area since European settlement, but significant areas are now protected as National Parks, Nature Reserves and Wilderness Areas.
Land use has a major influence on the quality of the water and ecosystems of the rivers, streams, lakes and wetlands. The availability of large natural areas interconnected by natural corridors (riparian corridors in particular) can help to maintain biodiversity, and good land and water quality. Additionally, the aesthetics of the landscape can be enhanced for recreational uses.
Poor land management practices have resulted in loss of vegetation, land degradation and erosion, soil structural decline, dryland and irrigation salinity, increasing soil acidity and the invasion of pest plants and animals. Increasing urban development in the catchment has also resulted in soil erosion, sedimentation of rivers and aquatic ecosystems, weed invasion, and the build-up of waste matter and other pollutants in natural areas. Of particular concern is the increase in urban development in the Upper Murrumbidgee catchment.
Vegetation in the Murrumbidgee catchment has been subject to excessive clearing, loss of species diversity, excessive grazing pressures, weed invasion and insect predation (MCMC 1994). As a result, species diversity has declined and wildlife habitat has been lost; there has also been soil erosion, and the development of an inappropriate balance between natural areas and agricultural land. Areas of remnant vegetation and priority areas for revegetation are shown in map 6.
Improved catchment management since the 1950s and a decline in the rabbit population has reduced hill slope and gully erosion to relatively stable conditions (DLWC 1995). In the upper catchment, however, large areas are affected to some degree by sheet, rill, gully or wind erosion (map 7). Additionally, soil structural decline resulting from inappropriate agricultural land management practices affects much of the mid-catchment area.
Dryland salinity develops when salts occurring naturally in the ground rise to the surface via a rising watertable. This happens when native deep-rooted vegetation is removed and replaced with annual shallow-rooted pastures or crops which use less water. Large areas of the catchment are moderately to severely affected by dryland salinity (MCMC 1994).
Irrigation salinity, which also results from rising watertables bringing high concentrations of salts to the soil surface, is caused by the combined effects of over-clearing, over-irrigation, channel seepage and inadequate drainage in irrigation areas. Irrigation salinity is an increasing problem in the Murrumbidgee catchment and affects large areas of the Murrumbidgee Irrigation Area and Coleambally Irrigation Area (MCMC 1994).
Plant growth and yields decline as soil becomes more acid due to increased levels of aluminium and manganese. Soil pH tends to decline naturally, particularly in the high rainfall areas because of the leaching process (MCMC 1994). Farming systems involving annual shallow rooting legume pastures, hay production and the use of ammonium based fertilisers cause the greatest soil acidity problems. Soil pH levels of less than 5 affect plant growth and may lead to lower crop and pasture yields as well as affecting the regeneration of native vegetation. Large areas of the Murrumbidgee catchment are affected or susceptible to high surface soil acidity with pH levels of less than 5. Increasing subsoil acidity has been noted in recent years, but its extent is unknown (MCMC 1994).
Pest and weed invasion affects all areas of the catchment including agricultural land, national parks, state forests, and native bushland (MCMC 1994). Additionally, feral, introduced and domestic animals have had a substantial impact on agricultural and natural ecosystems (MCMC 1994). The impacts from all these pressures on catchment ecosystems include land degradation and loss of native species diversity.
The riparian zone is the zone of interaction between land and water. Water and waste water enter the waterways via a variety of pathways across the zone, and floodwaters cross the zone to replenish soils and wetlands. The riparian vegetation provides a range of essential functions including the filtering of pollutants, stream bank stabilisation and providing habitat for terrestrial and aquatic fauna. The zone is also used for agriculture and urban development and must be crossed by recreational users of the waterways. The riparian zone and adjacent land therefore require special management to ensure that water is as clean as possible before crossing the zone and entering the stream. This includes water flowing through pipes, across the land surface and through the ground water system. The riparian zone should also be managed to support both the natural and human uses of the waterway. This involves:
Since 1991, there has been extensive community-driven action to address stream bank erosion in the upper Murrumbidgee catchment. In the mid catchment, with the exception of small urban programs in Wagga Wagga and Junee, there are no plans covering riparian zone or floodplain management for specific reaches of Murrumbidgee waterways (DLWC 1995).
Stream bank erosion has been identified as a major problem acrossthe catchment. Virtually all rivers and creeks are affected to some degree, in particular the Bredbo, Numeralla, Molonglo, Yass, Tumut and Murrumbidgee rivers (MCMC 1994). Jerrabomberra, Burra and other creeks in the Googong Dam and Lake Burley Griffin sub-catchments are actively eroding and remain largely untreated (DLWC 1995).
Changes in land use and land management practices within the Murrumbidgee catchment have resulted in increased turbidity, nutrient levels, bacterial pollution and pesticide levels in the rivers and ground water (MCMC 1994). In the Murrumbidgee, the five most significant types of water quality problems are salinity, nutrients and associated algal blooms, turbidity and pesticides. Levels of pollutants such as salinity and nutrients tend to increase downstream, while some areas of ground water are also highly saline (MCMC 1994). The three main human influences on water quality in the Murrumbidgee catchment are agriculture, pastoralism and urban development.
During 1993-94 the EPA conducted a water quality investigation of the Murrumbidgee River and its tributaries involving four sampling events at 61 sites downstream of Burrinjuck Dam. Intensive sampling was conducted in the vicinity of Wagga Wagga to determine the impacts of sewage effluent and stormwater discharge on water quality downstream of the town. The DLWC routinely monitors 7 key sites in the catchment and 2 of these sites are sampled by ACT Electricity and Water. Further information on the Murrumbidgee catchment water quality can be found in Rivers, Estuaries, Lakes & Wetlands.
Natural variations in ground water quality and volume can be affected by human activities such as water extraction and pollution. Licensed bore users report extraction volumes, while ground water storage variations are inferred from water level measurements taken periodically in a valley-wide network of piezometers (DWR 1995). Estimated ground water storage in the Murrumbidgee basin is about 1,000,000 gigalitres, of which over 98% is in alluvial deposits. The extent to which ground water can be exploited is related to the natural recharge rate of an aquifer system and the size of the ground water storage - estimated at 1,600,000 megalitres per year for 1995.
Salinity is the most significant factor determining ground water quality. It varies substantially throughout the catchment, from < 400 µS/cm in some areas upstream of Narrandera to values of around 80,000 µS/cm near Balranald. Approximately 270,000 gigalitres of ground water in the Murrumbidgee basin is of low salinity (< 1500 µS/cm), although the distribution of this low salinity ground water throughout the catchment is uneven (DWR 1995).
Stream flow may affect water levels in wetlands, determine how often riparian vegetation is flooded, dilute pollutants, and stimulate some species of fish and waterbirds to breed. Dams and weirs regulate the amount and timing of flows downstream. The more stream flow characteristics change from natural patterns, the greater is the stress on river ecosystems (DLWC 1995).
In the upper catchment, mid catchment tributaries and Billabong Creek, stream flow is largely unregulated and dominated by weather patterns. There are 7 supply storages and 3 recreational storages in the upper catchment. Since the construction of Burrinjuck Dam in 1913, the degree of river regulation and extraction from the river has slowly increased. The major irrigation projects have resulted in reduced winter high flows and increased summer low flows (DLWC 1995).
The regulated mid catchment is now not subject to the same degree of flow variation as would be expected under natural conditions. The flow regime is dominated by summer irrigation demand and curtailment of winter discharge from the upper catchment to fill storages (DLWC 1995).
The main remnant vegetation types in the catchment are stringybark forests, box woodlands, river red gum, black box and lignum, saltbush plains, sandhill vegetation (dispersed throughout the western part of the catchment), gray box woodlands, mallee and grasslands (MCMC 1994).
Rapid development and inappropriate modifications of the natural environment over the last 200 years has resulted in the degradation of many of the natural resources of the Murrumbidgee catchment (MCMC 1994). Some of the most serious natural resource degradation issues identified by the community relate to: land management, land and water salinity management, vegetation management and water management.
The Murrumbidgee Catchment Management Committee's intended strategy for achieving a healthy, sustainable, attractive environment in the catchment includes achieving water quality at a level acceptable to the community, maintaining and enhancing biological diversity and reversing land degradation.
The Natural Resources Management Strategy for the catchment (MCMC 1994) summarises the major land and water management issues and provides guidance on how local communities can work together to create a trend of increasing environmental quality. Refer also to Rivers, Estuaries, Lakes & Wetlands, Land and Agriculture, which summarise the major national and state-wide catchment management initiatives.
The following management plans and reports are either being prepared or implemented in all or parts of the catchment to ensure sustainable use of the land and water resources for all values (DLWC 1995):
Several studies are currently being conducted on macroinvertebrate communities:
In 1992-93, the EPA played a major role in a water quality modelling project using the AQUALM model, which takes rainfall and land use data for a catchment and calculates the water quality and quantity that such rainfall would produce at the bottom of the catchment. This model was useful in predicting water quality for future land uses anticipated for the year 2016. Three parameters were investigated: total phosphorus, suspended solids and nitrate. The full report provides information on current and predicted future water quality for 37 identified sub-catchments in the upper Murrumbidgee area (EPA & ACT Planning Authority 1994).
Results of the modelling indicate that, on the whole, the current water quality of the upper Murrumbidgee catchment is declining and is on the threshold of sustainability. This means that current land use and management practices are contributing pollutants at a rate with which the aquatic ecosystems are unable to cope, and so water and environmental values within the catchment are also being affected.
The modelling of future land uses predicted that pollutant loads to the river system would increase and therefore growth based on current land use management practices would be unsustainable. The study also demonstrated that sustainable water quality for the upper Murrumbidgee catchment can be achieved through best management practices and a holistic planning approach. It is clear from the study that changes in land use need not cause an increase in the pollutant load.
The most effective approach recommended for a specific rural property is the development of a farm management plan which is designed to be used to integrate production and economic issues with land capability, resource management and protection issues.
EPA and ACT Planning Authority 1994, Regional Water Quality Study, Upper Murrumbidgee Catchment, Prepared for the ACT and Sub-region Planning Committee and the Upper Catchment Coordinating Committee, Queanbeyan