The Hydrological Effects of the January 94 Bush Fires on the Royal National Park

Abstract

Previous research into the hydrological effects of fire have found that runoff increases immediately after the fire. This was attributed to the removal of vegetation and a decrease in the initial losses associated with rainfall. Another possible cause for the increase in runoff is heat treating of. the soil as the fire scorches the soil and there is a resultant decrease in the ability of the water to infiltrate. After this initial period of increased runoff, the conversion of rainfall to runoff has been reported to decrease. This decrease in runoff has been attributed to increases in the evapo-transpiration losses of the forest. In January 1994, Sydney was surrounded by a number of wild fires. The Royal National Park which is located to the south of Sydney is one of the areas burnt by these bush fires. For a number of years, SCEE UNSW has operated and maintained a network of pluviometers and stream flow gauges within the Upper Hacking Catchment, which lies within the Royal National Park. During the January 1994 bush fires approx 30% - 40% of the monitored catchment was burnt. Analysis of pre and post fire daily totals was undertaken for the catchment to assess the impact of the fire. Excessive change in the rainfall-runoff relationship of the catchment determined through the lnltlal.analysls lead to the investigation of other parameters affecting the hydrology. It was shown that changes in the rainfall-runoff relationships due to the fire are interrelated to the changes in the rainfall-runoff relationship due to the onset of drought. Furthermore, it was shown through investigation of two catchments that changes in the rainfall-runoff relationships in both catchments were similar. Consequently, it was concluded that for the Royal National Park, the impacts of bush fires on the rainfall-runoff relationship are interrelated to the impacts of the drought on the rainfall-runoff relationship.