The Namoi River catchment is in north-eastern New South Wales, and is based around the Namoi, Manilla and Peel rivers. It is bounded to the east by the Great Dividing Range, the north by the Gwydir, the south by the Macquarie-Castlereagh region and the west by the Barwon-Darling region. The Namoi River and its main tributary, the Peel River, rise in the Great Dividing Range at elevations over 1000 m, falling to 250 m where the two rivers meet near Gunnedah. The river then flows through sedimentary slopes to the open floodplains in the west. Nearly two-thirds of the region is comparatively flat.
This catchment covers an area of 41,856km2 or 4 per cent of the MDB. Other major tributaries of the Namoi River include the Manilla and McDonald rivers, Coxs Creek and the Mooki and Cockburn rivers, all of which join the Namoi upstream of Boggabri. The Namoi River then flows westerly across the western plains and joins the Barwon River near Walgett. Regulation in the catchment includes Keepit Dam (capacity 426 GL), Chaffey Dam (capacity around 63 GL), Split Rock Dam (capacity 397 GL) and a number of weirs.
The Namoi catchment is an ecologically significant area because it includes:
- a wide range of aquatic habitats of ecological importance, including large areas of anabranch and billabong wetlands downstream of Narrabri
- endangered ecological communities
- species protected under state legislation, including silver perch, Australasian bittern, Australian bustard, black-tailed godwit, Bell's turtle and brolga
- a variety of flora including coolabah, river red gum and river cooba, and six vegetation communities including Carbeen Open Forest and bimble box woodland
The only wetland of national importance in the Namoi region is Lake Goran, adjacent to the Liverpool Plains. This lake is situated at the end of an internal drainage basin that does not connect to the Namoi River. Due to this lack of connection it cannot be watered using Commonwealth environmental water.
Lake Goran, is the largest wetland complex in the Namoi catchment, covering more than 60 square kilometres, south of Gunnedah. The lake is an independent drainage basin, disconnected from rivers and creeks. Although it rarely fills, Lake Goran is nationally significant and provides habitat for large numbers of migratory waterbirds, when it fills, which is rare.
Another important ecological site is Gulligal Lagoon, near Gunnedah – a semi permanent wetland that is connected to the Namoi River, filling during flood events and from surface flows. The lagoon provides important habitat for native fish species including olive perchlet. This lagoon acts as a drought refuge in the mid-Namoi region and was restocked with breeding pairs of purple spotted gudgeon in late 2009 as part of the Namoi Demonstration Reach project.