Study On The Non-point Source Pollution Of Zhuganhe Watershed

Non-point source pollution is defined to be the runoff transport of dissolved orsolid constituents from diffuse sources on the land to streams. This thesis is focusedon studying the non-point source pollution of Zhuganhe watershed. In order toanalyse the non-point source pollution characteristics of mountainous area of HuaiheRiver Basin, Zhuganhe watershed is selected as a representative mountainouswatershed for the study. This study is an important part of the Non-point SourcePollution Estimation of the Huaihe River Basin Project. Zhuganhe River is anupstream of Huaihe River, and located in Hubei and Henan provinces. The study areaof the watershed is 1672 km2.SWAT model developed by USDA Agricultural Research Service (ARS) is usedto estimate the non-point source pollution. It is a continuous and distributed model.And it can predict the impact of land management practices on water, sediment andagricultural chemical yields in large complex watersheds with varying soils, land useand management conditions. Maps, weather, properties of soils and land managementdata were collected for model applying. At first, the map data must be projected to thesame coordinate system by GIS software. Weather and other data also need betransformed to meet the need of the model. Then, DEM data of the watershed wereused to define the stream network and discretize the subbasins by the SWATpretreatment tool TOPAZ (Topographic Parameterization). Topographic parameters ofthe stream network and subbasins were also derived from the DEM. The hydrologicresponse units (HRUs) -the smallest computing unit of SWAT model- were defined byoverlaying the land use map and soil map.Monthly flow and sediment data series of 1996 were used to calibrate correlativeparameters. In addition, daily observed nutrient loadings of one storm event of June,2004 were used to calibrate the correlative parameters of nutrient matters. And themeasured monthly data series of 1998 and yearly data series of 1991-2000 were usedto validate the model. According to the coefficient for judging the adaptability of themodel, such as Nash-Sutcliffe coefficient and Relative Error, the precision of theSWAT model is fairly good.The data series of 1991-2000 were simulated by using the validated model. Thetime and space distributions of the sediment and nutrients were analyzed. Theinfluence on sediment and nutrients of varying land use, soils and fertilization werediscussed. And the relationships of concentration processes of different nutrients andthe flow process of continuous storm events were glanced. At the end, themeasurements for preventing non-point pollution are presented according to themodel results and the experiences of other areas.