Catchment and flow

Close up of tea tree

The Derwent estuary catchment covers an area of approximately 8,900 km2 - approximately one fifth of Tasmania's landmass.

Land cover is made up of:

  • Forests and other native vegetation (69%)
  • Agriculture (27%)
  • Water storages (3%)
  • Urban and industrial lands (<1%)

Agriculture, forestry, hydropower generation and fish hatcheries dominate catchment land use. The Derwent is also an important source of water for irrigation and water supply.

Most of Hobart's water supply is taken from the lower Derwent River.

There are 10 dams and over 20 man-made lakes within the Derwent catchment. Operation of these structures significantly modifies natural river flow and blocks the passage of migratory fish, eels and lamprey.

Changes in land and water use have affected the total yield of water, nutrients and sediments from the catchment to the estuary. Since the 1920s there has been a 30% decline in the flow of the Derwent, due to a combination of water transfers for hydro electricity and a climatic dry period.

The Derwent Estuary Program tracks activities within the catchment that may impact on the estuary. Water quality is also monitored. The Program has recently funded a review of flow-related values, knowledge gaps and objectives, with support from the Australian Government Coastal Catchment Initiative.

Seal pup

Restoring and promoting the Derwent estuary