Development and Application of Water Quality Mathematical Model for Small Watershed in River Network Region Based on DEM Raster

Abstract:

Due to the abundant rainfall in river network region， the river water quality shows a temporal-spatial dynamic change affected by the point pollution and precipitation-runoff nonpoint pollution discharge. In order to assess the attainment of river water quality in small watershed， a nonpoint pollution model based on digital elevation model （DEM） raster was developed. Coupled with the hydrodynamic and water quality model， the dynamic river water quality response to point pollution and nonpoint pollution discharge was established. The modeling system was calibrated and the main water quality parameters were determined in the small watershed of Wujing River catchment in Changzhou， Jiangsu province. The modeling system developed is able to perform dynamic simulation of water quality in river network on daily scale， and realize an elaborate analysis from annual average attainment to daily attainment. According to the characteristics of regional pollution sources in the site studied， different pollutant load reduction schemes were simulated and evaluated. Under the optimal conditions， throughout the whole year， the frequency of attaining Grade III of surface water quality standard at lake inflow station would increase from 23.0%， 0， 16.4% to 71.8%， 66.3%， 75.9% for COD_Mn， NH₃-N， and total phosphorus （TP） respectively.