Torbay Inlet

	Torbay Inlet at a glance
	Total catchment area:		330 square kilometres
	Average annual rainfall over catchment:		800 - 1000 millimetres
	Total cleared		55%
	Length of catchment waterways:		244 kilometres

      


The Torbay Inlet and Lake Powell drainage catchment is one of the most severely altered systems on the south coast. Torbay Inlet drains a large area of swampy land that includes Lakes Manarup and Powell and Five and Seven Mile Swamps. Marbellup Brook is the only natural river that flows into Lake Manarup and then Torbay Inlet, with many other agricultural drains. The lagoon is fairly shallow, with less than one square kilometre of open water surrounded by a wide fringe of paperbark trees and sedges. The swamp valley between Torbay Inlet and Princess Royal Harbour has a fertile soil and was developed for agriculture in the late 19th century. Drains were dug to drain a series of swamps to the east of Lake Powell into Lake Manarup, which in turn flows into Torbay Inlet. The unfortunate effect this had on Seven Mile Swamp was that the exposure of the soil to air by drainage and cultivation caused the oxidation of iron pyrite in the soil, which rendered the land acid and infertile.

Much of the land surrounding Torbay Inlet is only one half to one metre above sea level and on occasions throughout the year the land was inundated by saltwater that flooded back up the estuary. A barrage with floodgates was built across the narrow channel linking Torbay Inlet and Lake Manarup in 1912 to unsuccessfully try and prevent the flooding of saltwater back onto farmland. As a result of draining agricultural land the estuary is high in nutrients but not overly eutrophic.

The Watershed Torbay project has been set up to try and prevent any further eutrophication of the system in the future.

In 2005 a project (Our Living Rivers) was set up to collect and analyse data, enabling the Department of Water to monitor the health of the river over time and help determine what systems need better protection. In spring 2006 and 2007 samples were taken from the river system to assess the quality of the water and habitat as well as the presence of fish and macroinvertebrates. Twenty-seven sites were sampled on Marbellup Brook, which feeds into the inlet. In addition, one site was sampled on Seven Mile Creek, which lows to Lake Powell and eventually into the Torbay Inlet.

Further Information:

South Coast Regional Land and Water Care Strategy: The Albany Hinterland Sub-region. Prepared by: the South Coast Regional Assessment Panel and the South Coast Regional Initiative Planning Team: December 1996.