The river known as the Blackwood receives its name at the confluence or conflux of the Arthur and Balgarup Rivers, 40 kilometres north-east of the township of Boyup Brook.
However, its hydrological source is a further 140 river kilometres to the north-east. It is clear to anyone who wants to look that the Arthur River and the Blackwood River are the same. The application of the name ‘Blackwood’ from the point where the Balgarup River joins the Arthur River is a simple arbitrary selection of a convenient converging watercourse.
The Arthur River commences in the Arthur River Nature Reserve about 30 kilometres northward of Wagin and flows about 140 kilometres generally south-west to its junction with the Balgarup River about 11 kilometres south-south-west of Moodiarrup. A number of watercourses flow into the Arthur River Nature Reserve, including the Yilminning River. This extends the watercourse a further 10 kilometres to the north-east.
With a mean annual average flow of about 660 million cubic metres per year the Blackwood is the biggest river in Western Australia’s south west. This flow compares with a figure of 320 million cubic metres for the Avon River (measured at Walyunga National Park) and 12,500 million cubic metres for the Ord River (greatest flow of any river in Australia – the peak flow of the Ord is enough to fill Mundaring Weir from empty to full in 38 minutes).
Measured at Winnejup Falls, about 18 kilometres upstream from Bridgetown, the average annual flow of the Blackwood River is 300 million cubic metres. So it can be seen that the Blackwood picks up as much water after Winnejup as before.
The river experienced its biggest recorded flood in January 1982. Extraordinary volumes of water flowed through the Blackwood River Valley during this freak summer flood. At Winnejup Falls, the flow was recorded at 1310 cubic metres per second (the peak for the Ord River is 33,000 cubic metres per second).
The Blackwood River was discovered on 6 May 1830 by Lieutenant Governor James Stirling, who led a party of settlers to found the town of Augusta. The exploration of the river on which this town was sited commenced the next day. Stirling, accompanied by Captains Currie and Molloy, James Woodward Turner, John Bussell and others ascended the river for a day and a half.
On Stirling’s return to Perth from Augusta, the Surveyor General of the fledging Swan River Colony, J.S. Roe, issued a Government Notice to advise prospective settlers of the area’s potential. The notice stated:
“The Inlet is of considerable extent and leads to a River named the Blackwood which was to the north about fifteen miles, and then ten miles to the East before it ceases to be navigable for boats.”
Stirling named it after either Vice Admiral Sir Henry Blackwood or Captain Blackwood, later of the Fly and the Bramble.
The Arthur River was named by Governor James Stirling on 30 October 1835 during the Great Southern Expedition. It was named after Mr Arthur Trimmer, a member of the expedition.
The name for the Yilminning River is of aboriginal derivation and was recorded by surveyor J.O. Oxley in August 1892.
Roe, J.S., Fieldbook 10, SROWA, Series 2217, Cons 3401, Item ROEJ/10.
The Colony of Western Australia from the surveys of J.S. Roe, etc. John Ainsworth, London, 1839. Copy of Exploration Plan 124A, SROWA, Series 50, Cons 3423, Item 202.
Shoobert, (ed.), Western Australian Exploration Volume One December 1826−December 1835: The Letters, Reports & Journals of Exploration and Discovery in Western Australia, Hesperian Press, Carlisle, Western Australia, 2005, pp. 159-60, 468.
Genoma (data set of Geographic Place Names), WA Department of Land Information, Midland, undated, c. 1997.