This postcard shows the Swan River in Perth, Western Australia. Its Aboriginal Noongar name is the Derbarl Yerrigan. The Swan River estuary flows through the city of Perth. Its lower reaches are relatively wide and deep, with few constrictions, while the upper reaches are usually quite narrow and shallow.
The Swan River drains the Avon and coastal plain catchments, which have a total area of about 121,000 km2. It has three major tributaries, the Avon River, Canning River and Helena River. The latter two have dams (Canning Dam and Mundaring Weir) which provide a sizeable part of the potable water requirements for Perth and the regions surrounding. The Avon River contributes the majority of the freshwater flow. The climate of the catchment is Mediterranean, with mild wet winters, hot dry summers, and the associated highly seasonal rainfall and flow regime.
The Avon rises near Yealering, 100 km southeast of Perth: it meanders north-northwest to Toodyay about 90 km northeast of Perth, then turns southwest in Walyunga National Park – at the confluence of the Wooroloo Brook, it becomes the Swan River.
The Canning River rises not far from North Bannister, 100 km southeast of Perth and joins the Swan at Applecross, opening into Melville Water. The river then narrows into Blackwall Reach, a narrow and deep stretch leading the river through Fremantle Harbour to the sea.
The Noongar believe that the Darling Scarp is said to represent the body of a Wagyl (also spelt Waugal) – a snakelike being from Dreamtime that meandered over the land creating rivers, waterways and lakes. It is thought that the Wagyl created the Swan River.
The estuary is subject to a microtidal regime, with a maximum tidal amplitude of about one metre, although water levels are also subject to barometric pressure fluctuations. [wikipedia]