Sediment and Coastal Water Quality

Australia State of the Environment Report 2001 fact sheet
Department of the Environment and Heritage, February 2002

What is happening overall?

Many coastal areas have excellent water quality but many others do not. Sediments entering coastal waters are a major cause of poor water quality. A number of government programs are in place to minimise sediment loss.

Why is coastal water quality so important?

Good water quality is essential to maintain the plants and animals that live in or near the sea, for industries such as fishing and tourism, and for our recreational pursuits.

How can sediments affect coastal waters?

Sediments can kill fish and shellfish, help create algal blooms, fill shipping channels, clog ports, and smother seagrass habitats for creatures such as the Dugong. Sediment can also make estuaries shallower over time.

What are we doing about it?

Sediments are carried from land into coastal waters by creeks and rivers. Government programs are aimed at stopping erosion from land getting into the rivers.

  • The Natural Heritage Trust Bushcare program which, while aimed at preservation and regeneration of native vegetation, helps address erosion control.
  • The Murray-Darling Basin 2001 Initiative includes erosion control in its programs for the watersheds of the Murray and Darling rivers.
  • The National Rivercare Program promotes the sustainable management of rivers outside the Murray-Darling Basin.

In addition, land management agencies and farmers' groups are improving farm management practices and publicising them.

How much sediment is there?

The figures are huge. Scientists estimate that 11.7 million tonnes of sediment is transported into the waters of the Great Barrier Reef alone each year.

During Cyclone Sadie in 1994, the Herbert River discharged more than 100,000 tonnes of suspended sediment, sourced mainly from grazing lands.

Where does the sediment come from?

The northern regions of Australia are much more vulnerable to widespread erosion than the southern regions. Infrequent but very intense storms are responsible for most erosion and sediment transport off the land. The sediment often shows up as plumes of discoloured water flowing from estuaries weeks after a storm.

The less intensive land uses which cover vast areas of Australia have the largest volume of soil loss but the intensively used cropping lands have the highest rate of soil loss per hectare. An example from North Queensland catchments showed grazing lands are responsible for about 66% of the estimated annual sediment export from North Queensland rivers.