Study on modeling of pollutant runoff processes and purification processes

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This research was conducted for the following objectives, based on measurements of discharge and water quality of a small urbanized stream :(1) To clarify the characteristics of pollutant runoff for non-rain periods,(2) To analyze the input-output balance of pollutant in the catchment,(3) To model the pollutant runoff processes for rainfall periods.With respect to the pollutant runoff characteristics, it was found that the change in COD load along with the stream flow direction is corresponding to the pollutant inflow from the area having no sewage treatment and to the channel properties such as vegetation and shapes. As for the pollutant balance, about 15% of COD effluent to the catchment was estimated to be deposited in the channel for non-rain periods.For modeling pollutant runoff processes, a new model combining a rainfall-runoff model and load runoff formulas was developed. Since deposit and runoff processes of pollutant take place on the catchment surface and in the channel, the proposed model was designed to handle the processes in the catchment surface and those in the channel separately. For the base rainfall-runoff model, the Sugawara Tank Model (for runoff on the catchment surface) and the kinematic wave channel flow model were applied jointly. Then different pollutant runoff formulas were applied to the catchment surface runoff and the channel flow respectively. Application of the model to EC load showed good agreements between observed and calculated values of both discharge and load.