Murchison River (Western Australia)
|Mouth||Indian Ocean, at Kalbarri|
|Length||820 kilometres (510 mi)|
|Source elevation||521 metres (1,709 ft)|
|Avg. discharge||217,100 Ml/year |
|Basin area||82,000 square kilometres (31,660 sq mi)|
The Murchison River is the second longest river in Western Australia. It flows for about 820 km (510 mi) from the southern edge of the Robinson Ranges to the Indian Ocean at Kalbarri. It has a mean annual flow of 217 Gigalitres, although in 2006, the peak year on record, flow was 1806 Gigalitres.
The Murchison River basin covers an area of about 82,000 square kilometres (31,660 sq mi) in the Mid West region of Western Australia. It extends about 550 km (340 mi) inland from the Indian Ocean, onto the Yilgarn Plateau. Rain generally only falls in the upper basin during summer cyclones, so for much of the year the Murchison River does not flow, having dry sandy river beds with occasional permanent pools.
The eastern reaches of the basin contain large chains of salt lakes, which flow only following rainfall. The drainage lines from these lakes merge to form the Murchison River about 90 km (56 mi) north north east of Meekatharra, near Peak Hill. From here the river flows west, then south west, then west to the Indian Ocean.
The Murchison River rises on the southern slopes of the Robinson Ranges, about 75 kilometres north of Meekatharra in central Western Australia. From there it flows in a westerly direction for about 130 kilometres to its juncture with the Yalgar River, then west for another 100 kilometres before turning south-south-west for 120 kilometres, at which point it is joined by the Roderick River, about 30 kilometres east of the Murchison Settlement. Another 70 kilometres to the south-south-west it meets its other important tributary, the Sanford River. Over the next 100 kilometres it makes a number of sharp turns, taking it about 70 kilometres to the west. It then flows to the south-west, passing under the North West Coastal Highway at the Galena Bridge. Entering the Kalbarri National Park, it flows first to the north-west and then to the north, flowing through the Murchison Gorge, and passing through a number of tight bends known as the Z Bend and The Loop respectively. It eventually turns to the south-west, passing through one more dogleg before disgorging itself into the Indian Ocean at Kalbarri, the only settlement at any point along the river.
Murchison Gorge is a deep gorge in near pristine condition. It is popular with tourists, and there are a number of tourist lookouts. It is also of geological interest, as it exposes an excellent section through the Tumblagooda Sandstone, a geological sequence rich in Ordovician trace fossils.
The final 18 kilometres (11 mi) of the Murchison River, from the Murchison House Ford to the mouth, are estuarine, and consist of a sequence of long sandbars and shallow pools mostly less than a metre deep. The estuary is permanently open to the sea, so is constantly affected by tides and the inflow of saline sea water. When river flow is low, the estuary accumulates sediment from the ocean, narrowing the river channel; this sediment is evacuated to the ocean during periods of high flow, but high flow also brings sediment into the estuary from upriver. Because of the high sediment load, and continual stirring by wind and river flow, the water is turbid.
The mouth of the estuary is a small delta, closed by a sandbar except for a narrow channel. Although this channel is permanently open, it is usually very narrow and shallow, and so is now dredged every year to allow passage by western rock lobster fishing boats.
The Murchison River was named by the explorer George Grey, whose boats were wrecked at its mouth on 1 April 1839, during his second disastrous exploratory expedition; the name honours the Scottish geologist Sir Roderick Murchison. Murchison's advocacy had been essential in securing official support for Grey's Western Australian expeditions.
In 1951 the town of Kalbarri was gazetted at the river mouth, and by the end of the 1990s the population was about 2,000. In 1963 the Kalbarri National Park was gazetted, formally protecting the lower reaches of the river, including the gorge.
The river was once again flooded in 1900 following heavy rains with the river estimated to be running 8 miles (13 km) wide, road to Cue and Peak Hill were submurged under 10 feet (3 m) of water. Roads were cut for up to a fortnight resulting in food shortages in many isolated towns. Ernest Lee Steere of Belele Station reported that over 5in. of rain fell in less than a fortnight. Further downstream the river was reported to be running 15 miles (24 km) wide and at depths of up to 70 feet (21 m), despite the damage pastoralists were jubilant at how quickly the grasses were growing.
Flooding again occurred in 1939 and once more following another significant rain event in February 1945 resulted in flooding and the old Galena Bridge being swept away, effectively stranding the citizens of Carnarvon. A ferry service was established using a fishing boat. Bananas were the main item that urgently needed to be sent across for transport to market.
Following Cyclone Emma in 2006 much of the catchment area received 100 millimetres (4 in) of rainfall. The river swelled to having a width of over 20 kilometres (12 mi) in places and Kalbarri had to be sandbagged to protect it from foodwaters.
- "Interesting facts about Western Australia". Landgate. Western Australian Land Information Authority. Retrieved 6 May 2012.
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- "702 - Murchison River Basin". Water Resources Data - Streamflow Sites. Government of Western Australia Department of Water. 2 Jul 2012. Retrieved 3 July 2012.
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- Grey, George (1841). Journals of two expeditions of discovery in North-West and Western Australia, during the years 1837, 38, and 39, describing many newly discovered, important, and fertile districts, with observations on the moral and physical condition of the aboriginal inhabitants, etc. etc. 2. London: T. and W. Boone. p. 3. Retrieved 17 March 2012.
- Stafford, Robert A. (1989). Scientist of Empire: Sir Roderick Murchison, scientific exploration and Victorian imperialism. Cambridge: Cambridge University Press. p. 41. ISBN 0 521 33537 X.
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- "Pastoralists jubilant". Western Mail (Perth, WA: National Library of Australia). 5 May 1900. p. 23. Retrieved 24 June 2012.
- "Flood waters in the Murchison.". Sunday Times (Perth, Western Australia: National Library of Australia). 12 June 1927. p. 24. Retrieved 24 June 2012.
- "Miners marooned.". The Brisbane Courier (Queensland.: National Library of Australia). 26 March 1926. p. 7. Retrieved 24 June 2012.
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- "WA rivermouth closed after waters rise". Australian Broadcasting Corporation. 14 March 2006. Retrieved 17 February 2013.
- Curry, P.J. et al. (1994) An inventory and condition survey of the Murchison River catchment and surrounds, Western Australia. Department of Agriculture, Western Australia: Technical Bulletin Number 84. ISBN 0-7309-5998-8
- Western Australia. Dept. of Land Administration. Cartographic Services Branch.(1991) Land systems of the Murchison River catchment and surrounds : map series to accompany W.A. Department of Agriculture technical bulletin no. 84 Map Data: Scale 1:250,000 (E 115o10'--E 118o45'/S 25o—S 28o10').Notes: Land systems of the Murchison River catchment and surrounds by K.A. Leighton ... [et al.]. Date of survey: 1986-1988. Location maps:Belele, Byro, Cue, Glenburgh, Murgoo, Robinson Range.