Abstract
A small (300 ha) experimental catchment in a high salt storage landscape in southwest Western Australia was subject to several different clearing treatments to determine their respective impacts on groundwater levels.
Within subcatchments that were 60–70% cleared, groundwater level rises were observed of 7.8–10.2 m compared with a 5.8 m rise with 32% clearing and a 2.3 m fall in a native forest control, from 1977 to 1989. Under parkland clearing (leaving wide-spaced trees), the rate of groundwater level rise has declined in recent years in response to increasing crown leaf areas, and in contrast to other treatments (strips and block clearing) where groundwater rise has accelerated. The presence of a bedrock high at the valley invert within one subcatchment has led to substantial groundwater rises in recent years which could intercept the surface in the next 5 years if the current rates of rise are maintained.
The combination of clearing treatments affecting 38% of the catchment has resulted in a modest (13 mm) increase in catchment streamflow. This was over double the average forested streamflow. Stream salinity has remained low. Stream yield, stream salt load and stream salinity appear to be at an equilibrium. However, as a result of considerable expanses of clearing located close to or on the streamline or valley invert, there is a significant risk of salt discharge to the stream in the future.
