Study on modeling of pollutant runoff processes and purification processes

本研究以一条城市小溪的径流和水质实测资料为基础，分析了非降雨时段污染物径流的特征，分析了流域内污染物的输入输出平衡，建立了降雨时段污染物径流过程的数学模型，发现污染物径流负荷沿河流流向的变化与未经污水处理的区域的污染物入流量以及河道的植被、形态等特征相对应。在污染物平衡方面，在非雨季，汇流到该流域的COD约有15%沉积在河道中，为了模拟污染物径流过程，建立了降雨径流模型和负荷径流公式相结合的模型。由于污染物的沉积和径流过程发生在汇流面和渠道中，因此该模型被设计为分别处理汇流面和渠道中的过程。对于基本降雨-径流模型，采用了杉原水槽模型(用于集水面上的径流)和运动波槽流模型。在此基础上，将不同的污染物径流计算公式分别应用于集水面流和渠道流。将该模型应用于EC负荷，流量和负荷的实测值与计算值吻合较好。

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.