Development of a water quality modeling system for river pollution index and suspended solid loading evaluation

SummaryThe Kaoping River Basin is the largest and most extensively used watershed in Taiwan. In the upper catchment, the non-point source (NPS) pollutants including suspended solid (SS) and ammonia nitrogen (NH3–N) are two major water pollutants causing the deterioration of Kaoping River water quality. Because SS is one of the four parameters involving in the River Pollution Index (RPI) calculation, it needs to be carefully evaluated to obtain the representative water quality index. The main objective of this study was to develop a water quality modeling system to obtain representative SS and RPI values for water quality evaluation. In this study, a direct linkage between the RPI calculation and a water quality model [Water Quality Analysis Simulation Program (WASP)] has been developed. Correlation equations between Kaoping River flow rates and SS concentrations were developed using the field data collected during the high and low flows of the Kaoping River. Investigation results show that the SS concentrations were highly correlated with the flow rates. The obtained SS equation and RPI calculation package were embedded into the WASP model to improve interactive transfers of required data for water quality modeling and RPI calculation. Results indicate that SS played an important role in RPI calculation and SS was a critical factor during the RPI calculation especially for the upper catchment in the wet seasons. This was due to the fact that the soil erosion caused the increase in the SS concentrations after storms. In the wet seasons, higher river flow rates caused the discharges of NPS pollutants (NH3–N and SS) into the upper sections of the river. Results demonstrate that the integral approach could develop a direct linkage among river flow rate, water quality, and pollution index. The introduction of the integrated system showed a significant advance in water quality evaluation and river management strategy development.

► A direct linkage between the RPI calculation, SS estimation, and the WASP model was developed.
► SS equation and RPI package are embedded into WASP model for immediate water quality simulation.
► The integrated modeling system is useful in developing strategies for water quality improvement.