Namoi

The Namoi River catchment in northern New South Wales stretches westward from the Great Dividing Range to the floodplains of northern New South Wales. The catchment is diverse in climate and landscape, ranging from cool, high rainfall areas in the rugged terrain in the east, to semi-arid, low rainfall areas on extensive riverine plains in the west.

Groundwater extraction in the Namoi is one of the highest for any Basin catchment. Surface water and groundwater are equally important sources of water for towns, stock, domestic use and irrigation. Agriculture is diverse and productive throughout the catchment, which takes in the Liverpool Plains and large cotton-producing areas on the western plains.

The catchment supports a wide range of aquatic habitats including large areas of anabranch and billabong wetlands downstream of Narrabri. Unlike other catchments in the northern Basin, there are few lakes or expansive wetlands in the Namoi Valley.

Snapshot

Catchment area	4% of the Murray–Darling Basin
Contribution to Basin water	3.2%
Annual stream flow	696 GL (Gunnedah)
River length	700 km
Major tributaries	Macdonald, Manilla, Peel, Mooki and Cockburn rivers, Coxs, Baradine and Bohena creeks
Major distributaries	Narrabri, Pian and Gunidgera creeks
Towns include	Tamworth, Gunnedah, Narrabri
Major water storages	Keepit Dam (426 GL), Split Rock Dam (397 GL), Chaffey Dam (101 GL)
Key water users	Irrigated agriculture, urban water supply, stock and domestic, mining

The landscape and its water

The upper part of the Namoi catchment is bordered by the steep ranges and elevated tablelands of the Great Dividing Range. The Namoi River (the McDonald River becomes the Namoi north east of Manilla) and several of its main tributaries have their headwaters in the range, in country that is 1,500 metres above sea level and where annual rainfall averages 800–1,000 mm.

Many of the Namoi's tributaries meet the river in the foothills of the ranges, including the Peel River, which is a regulated tributary running through the city of Tamworth and accounts for 11% of the Namoi catchment area. Beyond the town of Gunnedah, the Namoi River is the main waterway that runs west through undulating country. The catchment is bounded by the Nandewar Ranges and Mount Kaputar in the north and the Liverpool and Warrumbungle ranges in the south.

Downstream of Narrabri, the catchment is flat floodplain country – around 100 metres above sea level and with annual rainfall as low as 400 mm. The Namoi continues its journey west across the floodplain along a primary channel (up to 50 metres wide and 6 metres deep) with a network of anabranches and tributaries. About a quarter of the floodplain is prone to frequent flooding. At the western end of the valley (near Walgett), a number of flood runners (small anabranches) break away from the river and carry water through to the Barwon River during high flows.

High-yield aquifers exist along the Namoi and Peel rivers and are important water resources for stock and domestic purposes. In the lower part of the catchment (west of Narrabri) water is easily accessed from the Great Artesian Basin.

People, industry and water use

The Namoi and Peel river catchments are within the traditional lands of the Gomeroi/Kamilaroi people. The Gomeroi is a large nation which extends from around Singleton in the Hunter Valley through to the Warrumbungle Mountains in the west, and up through the Namoi and Gwydir valleys to just over the Queensland border.

European settlement of the region commenced in the 1830s as far west as Wee Waa, with a focus on sheep and cattle grazing as well as wool production. Land was cleared and dryland cropping developed on the rich soils of the Liverpool Plains and the alluvial plains to the west. Dams were built in the catchment in the 1960s, primarily to secure water for Tamworth but also to enable irrigation. As a result, cotton production and ginning was quickly established on the western plains. Coal has been mined in the catchment since its discovery in the 1870s.

The city of Tamworth is the largest centre in the catchment with a population of 42,000 (ABS 2016), and provides employment across a wide range of sectors. Smaller towns such as Gunnedah (9,700 people) and Narrabri (7,600 people) provide services to the agricultural sector. Agriculture is a significant employer in the rural areas of the catchment, especially in the cotton-growing areas.

Cattle and sheep grazing is the dominant land use in the catchment. The region is a significant producer of grain crops, both dryland and irrigated. While irrigation occupies a small area of the catchment (about 3%) it contributes significantly to the regional economy. Grain crops, cereals, oilseed and legumes are grown under irrigation in rotation with cotton. Lucerne production for hay is significant in the valley, especially around Tamworth. Historically, forestry and mining are also important industries in the region and the development of coal seam gas production is significant. As of 2008, the Commonwealth Scientific and Industrial Research Organisation (CSIRO) reported about 37% of available surface water in the catchment is used for urban water supply, stock, domestic use and irrigation. Generally, about 60% of the water used in the catchment is surface water, however in dry years groundwater usage may account for up to 75% of the water used.

Groundwater is used for town water supplies, stock, domestic supplies, irrigation and industry. At Narrabri and in the catchment's west, water is sourced from the Great Artesian Basin for town and rural domestic supplies, however artesian water is not suitable for irrigation due to high sodium levels.

Regulation of water in the catchment

There are several major water storages in the upper Namoi catchment that were constructed to provide water to cities and and communitiess as well as to supply irrigation water to farms on the plains.

Keepit Dam, on the Namoi River just upstream of Gunnedah, was completed in 1960 as a major irrigation storage (426 gigalitres (GL)). The dam is also the designated water supply for Walgett (over 300 km downstream) and provides for flood mitigation in the valley – it also generates hydropower through a 6 megawatt hydropower station.

Split Rock Dam (397 GL) on the Manilla River was completed in 1987 to augment the supply from Keepit Dam, as well as to supply local irrigators on the river.

Chaffey Dam (62 101 GL – the dam is currently being upgraded which will increase its capacity to 100 GL) on the Peel River south-east of Tamworth was constructed to regulate river flows and augment town water supplies for Tamworth. Dungowan storage on the Dungowan Creek delivers water to Tamworth through a pipeline.

Several weirs were constructed on the Namoi River and its tributaries and distributaries downstream of Narrabri, to regulate flows and deliver water to downstream users with more precision.

Environmental importance

The Namoi catchment is an important water supply for downstream environments in the Barwon and Darling rivers, as there are few wetlands in the valley to capture flows. West of Wee Waa, the lower Namoi River is characterised by a primary channel with a network of anabranches, small tributaries, lagoons and wetlands across the floodplain. The floodplain contains wetlands that require periodic flooding to maintain good condition. Other important ecosystems in the catchment include the Pilliga Scrub (the largest dry sclerophyll forest west of the Great Dividing Range in New South Wales) and Lake Goran, south of Gunnedah, which is independent of the river system. It is the largest wetland in the catchment and a wetland of national significance. The Sustainable Rivers Audit 2 (released in 2012) reported the overall ecosystem health of the Namoi River valley was poor. The health of the fish community was rated very poor, with fewer than expected native species present and a large presence of alien species. The macroinvertebrate community was rated in moderate condition overall, although the lowland zone was rated as poor. Riverine vegetation was rated in poor condition throughout the valley, with vegetation in the lowland zone rating higher than in other zones. The physical form of the river system was rated as moderate, with notable effects of elevated sediment loads in the river. Flow seasonality and variability was rated as good throughout the valley.

Water recovery

The Basin Plan sets Sustainable Diversion Limits, which is how much water can be used in the Murray–Darling Basin, while leaving enough water for the environment. 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.

The use of environmental water in a specific catchment or region will vary from year-to-year. The Murray–Darling Basin Authority (MDBA) has 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 Holder or the state government environmental water manager.

More information

Water management

The management of 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 ensure 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 four states and one territory, are managed cohesively and in the best interests of all water users of the Basin.

Rural water authority