This study compares a biophysical index of catchment salinity status based on readily available indicators with field measures of stream salinity. It also looks at the time required to compile a data set from readily available data, and whether meaningful results can be obtained from averaged data for third-order catchments. The catchments studied form the entire Upper Murrumbidgee catchment (approximately 12,000 km²).

The study outlines a systematic approach to selecting relevant, appropriate and readily available indicators. The indicators selected were per cent forest cover, forested areas greater than 50 ha, road density per unit area, per cent agriculture on slopes greater than 5%, number of roads crossing streams/rivers per unit area and the hypsometric integral per catchment. The indicators were compiled and collated in 10 days. The field data comprised stream salt concentration, salt load and two measures of macroinvertebrate group richness — the number of families of macroinvertebrates and the number of families observed compared to the number expected (O/E). The field work required nine months to complete. The biophysical and field indexes were calculated using a simple additive model. The data were placed in three classes using threshold values equivalent to best, intermediate and worst, weighted as 3, 2 and 1 respectively.

Significant relationships were detected between stream salinity and the biophysical index, and between the biophysical and field indexes. A lesser but significant relationship was detected between O/E biota and the biophysical index. These relationships suggest that the readily available data ranked the salinity status of the catchment in a credible way. We suggest that coarse-scale data are grossly undervalued in developing comparative scenarios; indicators carefully selected from readily available data can be used to quickly derive big picture scenarios.