Hydrological response to bauxite mining and rehabilitation in the jarrah forest in south west Australia

- Streamflow response to bauxite mining peaked at 225 mm (18% of rainfall), returning to pre-mining levels after 11 years.
- The response was closely associated with changes in a groundwater discharge area in the valley floor.
- Shallow subsurface flow, considered to dominate streamflow generation, is unlikely to extend far beyond the valley floor.
- The response to mining could not be distinguished from other land use changes.

Study regionJarrah forest in south west Australia.Study focusThe hydrological response to bauxite mining in the jarrah forest could differ from other land uses such as timber harvesting or clearing for agriculture, since mining involves excavation of the upper regolith in addition to changes in forest cover due to clearing and subsequent rehabilitation. Three catchments, one subject to mining, a second subject to an intensive forest thinning treatment and an untreated control were monitored for streamflow, rainfall, groundwater and leaf area index over a 36-year period.New hydrological insights for the regionMining caused a peak streamflow response of 225 mm or 18% of rainfall, before returning to pre-disturbance levels 11 years after mining commenced. Streamflow changes were closely associated with changes in a groundwater discharge area in the valley floor. Changes in groundwater level, in turn, were related to rainfall and leaf area index, and these effects did not differ between mine rehabilitation and unmined catchment areas. The streamflow response to mining could not be distinguished from the intensive thinning treatment in this study, or from clearfelling or clearing for agriculture reported elsewhere in the jarrah forest. The results indicate that shallow subsurface flow processes, considered to dominate streamflow generation in jarrah forest catchments, do not extend beyond the valley floor and immediately adjacent slopes which were not disturbed by mining.