Past, Present and Futures of the Tamar Estuary, Tasmania

The Tamar Estuary is located on the Bass Strait coast of North Tasmania, a drowned river valley of some 71km in length. The vast majority of fluvial flow enters through two rivers that meet at the estuary head, the South and North Esk Rivers with a catchment area comprising over 20% of Tasmania (about 11,000km²). The Tamar valley is a down-faulted graben structure, giving a bedrock-confined long and narrow shape to the majority of the estuary, causing tidal amplification to give the head of the estuary the largest tidal range in Tasmania. At the time of first European discovery in the early 1800s the upper Tamar Estuary was found to feature extensive mud banks, with a channel that was difficult to navigate in the 1.7m draft Lady Nelson. With establishment of the city of Launceston, the channel was dredged starting in the late 1870s until the 1960s allowing ship passage, until the major port was moved to the lower estuary. During this period contamination of the upper estuary increased, from organic and inorganic wastes from industrial, mining and domestic sources, as well as heavy metals from mining industries in the catchments, combined with high sediment yield. The Tamar has a high conservation significance being the only mesotidal drowned river valley in Tasmania, along with recording a large number of species not found elsewhere. There are significant threats to native species habitats from introduced species in the estuary, including Australia’s largest area of introduced Rice grass. This has caused a dramatic change to the physiography of the intertidal zone, with previous beaches or rock shorelines converted to accreting mud banks under Spartina. Sedimentation and water quality issues have long been a concern to the community, and over the last 15 years Natural Resource Management of the estuary and its catchments has greatly improved, including introduction of systematic monitoring. Aspirations for the estuary’s future are based on community consensus to maintain and improve biophysical values of the estuary, although preference remains for an upper estuary that resembles its early twentieth century dredged state rather than how it was first described 200 years ago.