Study And Application Of Non-point Source Pollution Model Of River Network Area Based On Digital Basin System

A typical agricultural watershed and runoff plots in hilly area around Taihu Lake was selected and experiment in situ was conducted. The transporation characteristics of various forms nutrients drived by natural rainfall-runoff were studied by field observations and laboratory testings. Regression relationships between transporation fluxes and runoff fluxes were set up. Temporal variation of agricultural nutrients concentration under storm rainfall condition was analyzed also. Furthermore, different land uses in the watershed were investigated on frequency, temporal and spatial distribution characteristics of nutrients losses in surface runoff. The main reasons about significant difference of temporal and spatial distribution were analyzed and transportation fluxes of nutrients were compared between different land uses.The water-soil coupled nutrient loss model of paddy field had been developed based on the characteristic that paddy field area in plain river network had a large proportion. It can simulate the nutrient transporation and transformation dynamically and adsorption-desorption rate formula of soil colloid was adopted. The parameters of the model were calibrated and verified with field datas, and sensitivity analyses were carried out on critical parameters.Distributed waste load model (DWLM) was derived from waste load model (WLM) developed by Delft Hydraulics Institute, and draw lessons from non-point source pollution model and distributed hydrological model. Research findings of the watershed around Taihu Lake and nutrient loss model of paddy field were introduced into the DWLM. In addition, temporal and spatial distribution method for non-point source pollution of river networks was promoted. The pollution source of DWLM had nine types, such as industries, municipal citizens, town citizens, rural citizens, municipal and town runoff, dryland runoff, paddy field runoff, fish breeding and poultry raising. The waste loads from different pollution source were calculated by using corresponding methods.As channels in river networks area were crisscross and lakes were densely, 0d, 1d and 2d water quality models that had different kinetic reaction items were applied to modeling transportation and transformation of pollutants in medium and small sized lakes, channels and large lake respectively. The basic equations of the different dimensional water quality models were coupled with each other to solving as well as hydrodynamic model. The water quality models were comprised of C, N and P cycling and can simulate 6 water-quality indexes, including COD, BOD₅, TN, TP, NH₃-N and DO.