Good question! I knew in general terms that it would include the three rivers and any creeks and streams which flowed into them, but just how far did that extend? So I thought I'd have a bit of a look an see what maps and diagrams were available that would provide a visual image.
On the Australian National Library's website I soon found several historical maps which outlined the area including the following map published in the 1950s:
|Map of the Barwon watershed. Image produced by the Victorian State|
Rivers and Water Supply Commission, 1954 and held by the State Library
of Victoria (Click to enlarge)
For administrative purposes, the Barwon catchment area falls within the boundaries Corangamite Catchment Management Authority (CCMA). The Corangamite Catchment is responsible for some 13,340 square kilometres from Ballarat to Geelong and the Bellarine Peninsula and along the coast to the town of Peterborough which lies about 50km east of Warrnambool. It is one of ten such authorities which cover Victoria.
|Map of the Victorian catchment management authorities taken from the |
Department of Environment and Primary Industries website
But this still doesn't exactly answer the question: what is the combined catchment area of the three rivers - Barwon, Moorabool and Leigh/Yarrowee?
|Another 1950s depiction of the Barwon watershed, titled Catchments|
of Barwon River and inland Basins, created by the Victorian State Rivers
and Water Supply Commission and held by the Victorian State Library
(click to enlarge)
The City of Great Geelong website indicates that the Barwon's catchment extends to 3,700 square kilometres. Given the area covered I believe this refers only to water flowing directly into the Barwon however the wording is ambiguous. Assuming that my interpretation is correct, then the combined catchment area of the three rivers is in the region of 7,790 square kilometres or more than three quarters of a million hectares - but less than the 8,590 square kilometres suggested by Wikipedia.
So, in short, I'm not precisely sure, however if anyone can provide a figure, I would be pleased to add it to this post.
NOTE: subsequent to publishing this post, the CCMA inform me that "Corangamite CMA's GIS (Geographic Information System) figure is 495,480 ha for the entire basin including Upper Barwon, Barwon, Murdeduke, Leigh, Moorabool" which converts to the much smaller figure of 4,955 square kilometres for the Barwon watershed plus the Murdeduke Basin.