Variations in the water quality of a small urban tropical catchment: implications for load estimation and water quality monitoring

This paper presents findings on the quality of runoff draining a small urban tropical catchment in Singapore. Variations in runoff quality were studied by continuous, regular and storm event water sampling over a period of eleven months for suspended sediment, nutrient and inorganic variables. Storm events and anthropogenic activities exerted the most influence on runoff quality. Concentration-discharge rating relationships were derived to assess the rating curve method for calculating load of the variables monitored. The poor rating relationships obtained indicated that the method was not suitable for load estimation in this catchment. Instead, an interpolation method was used to calculate sediment loads. The preliminary results highlighted the importance of conducting small-scale, relatively short-term studies to identify and assess specific water quality problems facing each catchment. Such a sampling strategy might be more useful than either routine or continuous sampling in the context of planning more detailed monitoring strategies and management options suitable for disturbed catchments.