The kanamaluka/Tamar Estuary is a drowned river valley. This type of estuary forms when rising sea levels flood an existing river valley. At nearly 70 km long, it is the longest estuary of its kind in Australia. Key tributaries include the North Esk, South Esk, Macquarie, Meander, Brumbys and Lake Rivers.
Estuaries are strongly influenced by the tides, which push saltwater into the estuary twice a day. These large tidal movements, along with the inflows from the South and North Esk Rivers, affect how kanamaluka/Tamar Estuary works.
Rainfall from the south-east of Ben Lomond flows into the South Esk River and takes about three days to get to the kanamaluka/Tamar estuary as it flows through towns like Evandale, Perth, Longford, Hadspen and finally down through the Cataract Gorge.
The north-east rainfall, near Ben Nevis, flows into the North Esk River and takes about a day to reach the estuary. Rainfall in the urban areas flows immediately into the estuary as stormwater.
Strong tides from Bass Strait flow upstream twice a day bringing saltwater to meet the fresh water near Legana. Water from the two rivers brings sediment into the upper estuary, and tides bring sediment from downstream. When the fresh water meets the saltwater the sediment clumps together and settles to the bottom of the estuary.
As sediment accumulates on the shoals, flows are concentrated into the channel. Large floods move sediment downstream and out of the estuary, while smaller peak flows don’t move sediment from the upper estuary. Pollutants are slow to move out of the estuary due to the strong incoming tide.
Learn more about the mudflats.
You can learn more about how the estuary works by watching the short video below.