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A GIS-based method has been applied for the determination of soil erosion and sediment yield in a small watershed in Mun River basin, Thailand. The method involves spatial disintegration of the catchment into homogenous grid cells to capture the catchment heterogeneity. The gross soil erosion in each cell was calculated using Universal Soil Loss Equation (USLE) by carefully determining its various parameters. The concept of sediment delivery ratio is used to route surface erosion from each of the discritized cells to the catchment outlet. The process of sediment delivery from grid cells to the catchment outlet is represented by the topographical characteristics of the cells. The effect of DEM resolution on sediment yield is analyzed using two different resolutions of DEM. The spatial discretization of the catchment and derivation of the physical parameters related to erosion in the cell are performed through GIS techniques.

Abstract:A physically based distributed hydrologic model is developed in this study for¯ood inundation simulation combining newly developed overland and channel network¯ow simulation models with evapotranspiration, unsaturated zone and saturated zone models. The overland¯ow and river¯ow models are validated individually with test data, and then coupled with other models. The model can take ®ne resolution spatial data as input preserving spatial heterogeneity of physical characteristics of a river basin. River embankments play an important role in¯ood prevention. The model can incorporate river embankment data in¯ood inundation simulation. The model is applied in a river catchment in Japan to simulate a¯ood event in 1996. Outputs from the model show good agreements with observed¯ood hydrographs and surveyed¯ood inundation.

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