Sediment and nutrient export by water from an agricultural catchment: An analysis of hysteresis patterns in the Upper Relau River, Penang

A small drainage basin (0.5 km2) was selected on the Relau hill to evaluate sediment and nutrient export. Stream flow gauging, water depth and gulp water samples were collected manually on a weekly basis between November 2001 to October 2002 with additional gauging and water samples taken during storm events. The concentrations of sediment and nutrient were analysed to determine the quality of the river water and the health of the catchment. The highest suspended sediment concentrations and nutrients concentration in upper Relau catchment are, in most cases, associated with periods of high discharge during the monitoring period. Hysteresis relationships between SSC, NO3-N, TN, orthophosphate and TP concentration with discharge (Q) shows some form of pattern of variation during the monitoring period. The hysteresis approach was used to identify the sources of SSC, NO3-N and orthophosphate in streams. The findings from this study are common to most drainage systems having seasonal bimodal discharge. We describe the mechanisms of SSC, NO3-N and orthophosphate, TN and TP concentrations generation with discharge magnitudes, highlighting the importance of storm events in the transportation of pollutants from this small hill-land catchment where agriculture is the dominant land use.