Indicators of Catchment Condition in the Intensive Land Use Zone of Australia – Rivers through forests

It should be noted that this data is now somwhat dated!

Rivers through forests a Length of river within forests per total length of river in the catchment. Riparian vegetation acts as a buffer between the land component of the catchment and the stream or river.

Forests are a sub-set of riparian vegetation that is quantifiable from imagery. Rivers passing through forested areas is a surrogate for the condition of the riparian zone. The length of watercourses draining through forested areas gives a general indication of water quality and quantity maintenance and improvement, through filtering, shading and cooling, and by improved aquatic biota condition. Included in this definition of forest are shrub, scrub and woodlands.

The most detailed river dataset available is the Topo250K dataset from AUSLIG (2000). This scale is appropriate to catchment scale analyses and has been used for this indicator.

Tree cover was defined from the Australian Land Cover Change (ALCC) dataset (2000), which is also at 1:250K. cell is defined as aforesta if it has greater than 20% tree foliage cover and greater than 2 m tall. Topo250K rivers are industry-accepted data with a satisfactory data collection methodology.

The positional and attribute accuracy of the original data are sufficiently reliable for this analysis. The ALCC (2000) data has several gaps in the ILZ, notably in southern Victoria and near the boundary with the ELZ in many areas. These gaps have been filled using Atlas of Australian Vegetation (Carnahan, 1990) data at 1:5M scale. Reliability is good, except where Carnahan data has been stitched in.

Based on this indicator, relatively good riparian/catchment condition corresponds with most coastal catchments, the higher rainfall areas of North Queensland and the forested inland areas of West Australia. Relatively poor conditions are indicated for coastal and near-coastal catchments in southwestern Victoria and southeastern South Australia, and most particularly, the Wakefield, Brighton, Mambray Coast, Willochra Creek, Spencer Gulf and Eyre Peninsula (SA) Broken, Campaspe, Loddon, Avoca, Wimmera-Avon, Hopkins and Lake Corangamite in Victoria. In Western Australia, the Avon River features most poorly. For NSW, the Lachlan, Lake George, Murrumbidgee and Murray-Riverina a southern parts of the Murray-Darling Basin are indicated as having relatively poor condition. In Queensland the condition based on this indicator is generally good. Other catchments with an indicated relatively poor condition occur in drier inland areas where vegetation is generally much less dense (that is it is not naturally forested).

Data are available as:

• continental maps at 5km (0.05 deg) cell resolution for the ILZ;
• spatial averages over CRES defined catchments (CRES, 2000) in the ILZ;
• spatial averages over the AWRC river basins in the ILZ.

See further metadata for more detail.