Castlereagh River

Castlereagh River
The river seen from the Castlereagh Highway, south of Walgett
Etymology	Lord Castlereagh[1]
Native name	Wallambangle[2]
Location
Country	Australia
State	New South Wales
Region	IBRA: Brigalow Belt South, Darling Riverine Plains
District	Central West, Orana
Municipalities	Warrumbungle, Gilgandra, Coonamble, Walgett
Physical characteristics
Source	Warrumbungles
• location	west of Coonabarabran
• elevation	630 m (2,070 ft)
Mouth	confluence with the Macquarie River
• location	west of Walgett
• elevation	121 m (397 ft)
Length	541 km (336 mi)
[3]

The Castlereagh River is located in the central–western district of New South Wales, Australia. It is part of the Macquarie-Castlereagh catchment within the Murray–Darling basin and is an unregulated river, meaning no dams or storage have been built on it to control flows.^[4] On a map of NSW, the Castlereagh has a distinctive appearance among the north-western rivers for its fish-hook-like shape: from upstream in the north at its confluence with the Macquarie River it extends southwards to a hook-shape, flattened-out at the base, which curves to the right (east and northwards) through to the tip of the hook in the Warrumbungle Mountains at the river's source.

The Castlereagh rises 20 km west of Coonabarabran in the heart of the Warrumbungle mountains^[1] at an elevation of about 850 metres.^[5] From its commencement upstream in the mountains the river initially flows east through the town of Coonabarabran. It then arcs round south and southwesterly to the village of Ulamambri, then south to Binnaway, and SSW to the small town of Mendooran which lies at the eastern side of the river's hook-shape. From here the Castlereagh flows in a westerly direction at the flattened bottom of the hook and then turns north-westerly towards the town of Gilgandra. From Gilgandra it continues to run northwesterly across the plains through Gulargambone and Coonamble, then continuing across expansive plains, with no urban centres, where elevations are less than 200m, until it joins the Macquarie River at its uppermost reaches beyond the Macquarie Marshes. Its confluence with the Macquarie is about 65 km SW of Walgett.^[3] Not far from the Castlereagh/Macquarie confluence the Macquarie itself joins the Barwon River at a place about halfway between Walgett and Brewarrina.^[6][5]

Downstream from Gilgandra, the Castlereagh runs through alluvial plains. These are flat landforms with alluvial soil that has been created from sediments being deposited over a long period of time by one or more rivers flowing down from highland regions.^[7] Groundwater is found in the alluvial sediments on the plains in the lower Castlereagh catchment and is generally associated with the ancient channel of the river.^[8] The Castlereagh has a very sandy bed throughout its course, with especially wide outer banks on the plains. Charles Sturt, after travelling along the Castlereagh in 1828 from Coonamble to its junction with the Macquarie, noted that there was not one pebble or stone to be picked up in its bed, which was dry for the whole length he travelled.^[9]

Further upstream, the Castlereagh, Macquarie and Bogan 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".^[8] In this extreme northern section of the catchment the floodplain between the Barwon and Castlereagh Rivers is intersected by Womat and Wanourie Creeks, which carry flows from the Barwon to the Castlereagh River during major floods.^[10]

Estimates of the length of the course of the Castlereagh River from its commencement to its mouth vary from 541 kilometres (336 mi),^[3] 549 km,^[4] and 566 km.^[1] Over its course it drops over 600 m.