The impact of rain forest disturbance upon near-surface groundwater flow: modelling of hillslope flow experiments

Rain forest disturbance within Sabah, Malaysian Borneo and within other areas of South East Asia has been shown to promote accelerated soil and nutrient losses from upstream catchments. In July 1990 a small hillslope plot, situated within an undisturbed section of the Baru Catchment, Danum Valley, Sabah, was instrumented and monitored during a number of water tracing experiments. The aims of the field experiments were twofold. First, to provide information on the dominant flow processes within a typical hillslope section of the catchment and second, to create a controlled hydrological environment that would allow detailed modelling of the internal state of the system. The results of such monitoring and modelling studies should then allow preliminary investigations of the hydrological effects resulting from changes in canopy processes due to selective logging and changes in soil properties due to compaction by logging vehicles. Utlimately, the model should also provide a tool to examine the influence of forest management practices on other processes such as sediment delivery and nutrient transport. We report here on details of the field experiments, initial modelling results using a detailed finite element solution of the Richards equation, and an outline of proposed modelling studies