Macquarie–Castlereagh

Snapshot

Summary

In central-western New South Wales, 3 major river networks flow north-west to the Barwon River: the Castlereagh, the Macquarie and the Bogan. The rivers of these catchments are an important water source for urban water supply and irrigated agriculture, however groundwater is equally important as a water source in the region.

The catchment covers about 7% of the Basin and provides 8.4% of inflow of surface water for the Basin. The catchment uses about 4% of all surface water diverted and 11% of groundwater used in the Basin (excluding the confined aquifers of the Great Artesian Basin).

The catchments are ecologically important as their waters feed the Macquarie Marshes which are Ramsar-listed and nationally important wetlands, and one of the largest freshwater wetlands in the Basin.

The Macquarie–Castlereagh catchment is home to about 9% of the population of the Basin, and the large service centres at Orange, Dubbo and Bathurst are regional hubs for health, education and business services. Agriculture in the catchment is diverse from horticulture in the east, dryland grazing and cropping on the slopes, to irrigated cropping and extensive grazing in the west.

Photo by Denise Fowler (2015)

Taking the dogs for a walk along the Macquarie River at Bathurst, New South Wales.

The landscape and its water

The Castlereagh River rises in the volcanic remnants that shape the Warrumbungle Ranges, west of Coonabarabran in northern New South Wales. After winding through hilly country, the river then flows north-west across alluvial plains, past Gulargambone and Coonamble. The Castlereagh meets the Macquarie River a little upstream of where the Macquarie meets the Barwon River.

The Macquarie River rises in the Great Dividing Range near Bathurst and flows north-west through foothills and slopes past Wellington and towards Dubbo. After Dubbo, the river crosses alluvial plains, passing Narromine and Warren to meet the Barwon River, upstream of Brewarrina.

The Bogan River rises in the Harvey Ranges near Parkes, in central-west New South Wales, and flows north-west past Nyngan to meet the Barwon River upstream of Bourke.

The 3 rivers run more or less parallel as they cross the plains, where creeks and streams break away from the main rivers, making connections between the Macquarie and the Bogan, the Macquarie and the Barwon, and the Castlereagh and the Barwon. As the waterways approach the Barwon River, the interconnected streams, as well as lagoons and channels, support extensive flood-dependent woodlands and grasslands.

The Castlereagh and Macquarie catchments are typical of most Basin catchments, rising in or near the Great Dividing Range where most of the streamflow originates at high altitude (up to 1,300 m in the Macquarie catchment) and annual average rainfall is above 600 mm. After running through foothills and slopes, the rivers emerge onto expansive plains where rainfall is lower, the climate is warmer and elevations are less than 300 m.

Groundwater is found in alluvial sediments on the plains in the lower catchment and is generally associated with the ancient channels of the rivers. The highest yielding aquifers are located north-west of Narromine. Much of the upper Macquarie catchment and the Bogan catchment is underlain by fractured rock which yields very little groundwater. The Great Artesian Basin underlies the northern part of the Macquarie catchment downstream of Warren.

People, industry and water use

The First Nations people of the upper and middle Macquarie catchment are the Wiradjuri, whose nation is the largest of the First Nations in New South Wales. On the plains, the Bogan River formed the boundary between the Ngemba and Ngiyampaa Nations to the west and the Wailwan Nation in the east. The country of the Wailwan people takes in most of the Castlereagh catchment. The north-east corner of the Castlereagh catchment, around the Wurrumbungles is the traditional land of the Gamilaroi.

In 1814, the Macquarie River was the first river of the Basin to be discovered by Europeans. The Castlereagh, Gwydir, Namoi and Barwon river systems were subsequently explored and by 1834 the colony was divided into 19 counties which started a land rush by people keen to settle new areas and benefit from the rich soil and open plains. Gold was first discovered in the Basin at Bathurst in 1851, which led to another period of population expansion, and the establishment of towns such as Bathurst, Sofala, Hill End and Peak Hill.

The Macquarie–Castlereagh catchment has about 9% of the Basin population. It has 3 large regional cities – Dubbo, Orange and Bathurst – all with populations of 38,000 to 42,000 (ABS 2016). The catchment supports a diverse range of industry including agriculture, agribusiness, tourism, mining and viticulture. Extensive livestock grazing accounts for 70–80% of the land area in the catchment. The largest agricultural use of water in the valley is for cotton, downstream of Dubbo. Other significant irrigated crops in the region include lucerne, cereals, oilseed, wheat, vegetables and fruit. Irrigated agriculture accounts for less than 5% of land use in the catchment but makes up about 25% of production.

The rivers in the catchment are an important source of water for most cities and towns, and water storages are critical to ensure supply throughout the year. Lithgow, to the east of the catchment and outside the Basin, also receives water for town water supply.

As of 2008, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) reported on average 24% of available surface water was used annually, which is moderately high compared with other catchments in the Basin. Water in the catchment is diverted from the river system for irrigation, stock, domestic and urban use. Groundwater is important in the Macquarie valley for stock, domestic, irrigation and town water supplies. Together with the adjacent Castlereagh valley, groundwater on average accounts for 33% of total water use in the region.

Regulation of water in the catchment

The Castlereagh is an unregulated river that has no major water storages. Consequently, streamflows are highly variable and the river bed is often dry.

The rivers of the Macquarie catchment are highly regulated, with many smaller dams built on the tributaries of the Macquarie in the 1940s through to the 1960s, to secure town water supplies. Burrendong Dam, near Wellington, is the largest storage in the catchment and was constructed in 1967 to provide storage for irrigation, town water, stock and domestic requirements. The dam also serves to provide flood mitigation and stores water for environmental purposes, in particular for watering of the Macquarie Marshes.

There are many weirs in the lower reaches of the Macquarie and Bogan rivers, constructed to manage water for irrigation diversion and to supply creeks and canals that service off-river irrigation areas.

Environmental importance

The catchments of the Castlereagh and Macquarie rivers support a diverse range of ecosystems, from forest, woodlands, and wetlands to grasslands, in temperate and semi-arid environments. Important wetland environments in the catchment include the Macquarie Marshes which are home to many threatened species. The Macquarie Marshes and the privately owned Wilgara Wetland and Mole Creek are Ramsar-listed sites. These wetlands support large numbers of waterbirds, up to 500,000 when flooded. Once one of the biggest bird-breeding sites in Australia, the Macquarie Marshes have shrunk by 40% as a result of river regulation and consumptive uses of water upstream.

The Sustainable Rivers Audit 2 (released in 2012) reported overall ecosystem health of the Macquarie River valley was very poor. The health of the fish community was rated extremely poor, and the macroinvertebrate community was rated in moderate condition. Riverine vegetation was rated in moderate condition throughout the valley. The physical form of the river system was rated moderate. Overall the hydrology of the system was rated moderate but the lowland and slopes zones were rated poor, reflecting the regulation of the river.

The audit also reported that the overall ecosystem health of the Castlereagh River valley was poor. The health of the fish community was rated as very poor condition, and the macroinvertebrate community in moderate condition. Riverine vegetation was rated in good condition throughout the valley. The physical form of the river system was rated good. Overall the hydrology of the system was rated good, reflecting the low levels of regulation of the river.

Water recovery

The Basin Plan specifies how much water is required to satisfactorily manage environmental sites and functions in the Murray–Darling Basin. A sustainable diversion limit (SDL) was established for each catchment (or group of catchments) and the reduction in diversions required to achieve the SDL was identified.

For the Macquarie–Castlereagh catchment, the baseline diversion level of surface water determined by the Basin Plan is 734 gigalitres (GL) per year. The required local reduction in take, to achieve an environmentally sustainable level of diversion is 65 GL per year. In addition to the 'local reduction', a further 143 GL per year is to be recovered from all northern Basin catchments (the northern zone 'shared reduction') to meet the needs of the Barwon–Darling system.

Groundwater extractions and/or entitlements determined by the Basin Plan mostly matched the SDL set for the groundwater units in the south-east of the catchment, and therefore there were not required reductions in groundwater extraction. Much of the northern catchment is underlain by the New South Wales Great Artesian Basin Shallow groundwater unit, where groundwater extractions and/or entitlements were considerably less than the SDL set for the unit.

Further information on water recovery in the Murray–Darling Basin, which includes an interactive map with catchment-specific information, is available at water recovery progress.

The Basin Plan allows for adjustments to SDLs if new works or changes in river operation and management rules increase the quantity of water available to be extracted; or efficiency measures through infrastructure works and upgrades reduce the quantity of water required in a delivery system.

The use of environmental water in a specific catchment or region will vary from year-to-year. The Murray–Darling Basin Authority (MDBA) has produced a Basin-wide environmental watering strategy to guide the use of environmental water across the Murray–Darling Basin to help achieve the best possible results over the long term. Environmental water managers make the day-to-day decisions on what to water and when, in line with the strategy and taking into account seasonal conditions, priorities and the availability of environmental water. Watering decisions are made in consultation with various waterway managers and local landholders.

Catchment or regionally-specific details about environmental water use in the catchment including watering actions, portfolio details and planning, and monitoring of environmental watering, can be found through the Commonwealth Environmental Water Office or the state government environmental water manager (see table below).

Water management

The management of the water resources is the responsibility of local, regional, state and Australian governments.

Delivery to households, industry and farms is managed by local councils or regional water authorities.

State government departments for water ensures the network of authorities manages water responsibly and fairly, that catchment and waterway health is maintained or improved through catchment management authorities, and that water saving, re-use and flood management projects are implemented. State governments must manage their state's water resources according to state and commonwealth water legislation.

In addition to directing operations of the regulated River Murray system, the MDBA implements a number of plans and programs to ensure the waters of the Basin, which flow through 4 states and 1 territory, are managed cohesively and in the best interests of all water users of the Basin. Such programs include:

• the Basin Plan, to guide sustainable extraction of water from the Basin
• the Basin-wide environmental watering strategy, to guide the use of environmental water across the Murray–Darling Basin to help achieve the best possible results over the long term
• the Basin salinity management strategy, to manage salinity of river water and riverine environments
• the water quality program, to monitor water quality and plan quality management actions.

Useful links