Modeling The Process Of Runoff And Sediment Yield On Slopeland Based On ARCGIS

This study aims at establishing the spatial modeling system of runoff yield and sediment yield on the slopeland based on Geography Information System (GIS) and Remote Sensing (RS).Seldom work has been done in this field in Southwest of China. It is emergent to find out new technology to model runoff and sediment yield in Chongqing. Taking Bishan County as an example, this study focused on settling this problem, seeking support for the policy of water and soil conservation in the Southwest.This study first focused on applying the extraction method for automated watershed delineation to the study area. DEM is utilized as basic data to produce new data; with the help of GIS and RS, spatial database of USLE is set up, therefore, spatial distribution of erosion is calculated; having analyzing the sediment delivery ratio, we get the spatial distribution of sediment yield.With the fast growing progress of computer technologies, instead of manual operation, there is a trend of applying Digital Elevation Model (DEM) in automated watershed delineating and drainage network design. With the help of hydrologic modeling system in ARCGIS8.3, several kinds of maps are produced, including Flow direction map, Flow accumulation map, and in the end the map of three main watersheds of Bishan County.Taking four storms or big storms in 2002 as an example, the amount of runoff in single storm has been calculated through runoff model, which is the method of Runoff Curve Number from Department of Agriculture Soil Conservation Service. Having been set up through data of field exploring, sectional limitations is inevitable in the SCS model. Therefore, to apply this model in the studying area, the values of CN should be defined. In this study, values of CN under different kinds of land use and management are figured out. According to this result, the amount of runoff in single storm has been calculated through this model.Soil erosion and sediment yield appraisal system is set up based on the results of watershed delineating, the concept of sediment yield ratio and the Universal Soil Loss Equation(USLE). Based on the spatial analysis and statistic ability of GIS, information about spatial distribution of the amount of runoff and sediment yield can be rapidly gained by administrators or supervisors of soil and water conservation.Having analyzed and classified the main factors of the Universal Soil Loss Equation (USLE), soil erosion database is set up with ARCGIS8.3. With the function of Raster Calculating, Grades of soil erosion intensity in study area are classified.Calculation of each factor in USLE is key to the accuracy of the result. Different from theoretical models, the definition of the value of each factor requires quantities of field exploring data. That is difficult for vast areas especially those with little data. So when using this model, each coefficient should be rectified to meet the natural environment Making use of both DEM and Remote Sensing TM image, database of erosion factors is set up with the help of GIS and RS technology. In this database, first the rainfall and runoff erodibility factor R value is calculated. Soil erodibility factor K value is calculated using the method in EPIC model set up by Williams. Slope steepness and slope length are evaluated through spatial analysis module in ARCGIS8.3 to make out the topographic factor. And further study on cover management factor C value has been made. In this section, the relationship between C factor and NDVI , which has been delineated through Remote Sensing image processing system, is set up. Thus, the calculation of C factor is connected with NDVI of studying area, so that a more scientific way of the calculating of C value is provided.The acquirement of NDVI is by way of remote sensing image interpretation in ERDAS8.5 software. It's a best approach first to get NDVI through RS image and then to acquire C value by building up the relationship between C and NDVI value. Generally speaking, the higher the NDVI value is, the higher the degree of vegetation cover, and adversely the lower the C value is. Based on this relationship, a formula is set up.This study mainly deals with the rectification of the value of coefficient a . Compared with the field exploring data of Wischmeier and C values under different land use by Cai Chongfa, the value of coefficient α is defined as 2 (1+NDVI) . In turn, the spatial distribution map of C value is delineated.The map of soil erosion is acquired by multiplying all the factors in USLE using the command of Raster Calculation. According to the standard of classification of soil...