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Curve Number Estimation for Watershed using Digital Image of IRS-1D LISS-III
Soils
The soil map of 1:25000 scale was traced, scanned and exported to ERDAS IMAGINE. Image to image registration was performed using the registered topographic maps. The scanned map was loaded in ARC/INFO and boundaries of different soil textures were digitized carefully and the polygons representing various soils were assigned and flood filled with different colors for identification (Fig. 3). Different gray level values were assigned to different soil texture while preparing the maps. Four hydrologic soil groups, A, B, C, and D, were considered for the basic classification of soils of the watershed. The soils of group A are of low runoff potential, high infiltration rate, high rate of water transmission, the soils of group B are of moderate infiltration rate, moderately well drained to well drained, the soils of group C are of moderately fine to moderately coarse textures, moderate rate of water transmission and the soils of group D are of slow infiltration and high runoff potential.  Figure 3 Soil map of watershed The AVSWAT (Arc View SWAT) interface model (Neitsch, 2001) that is linked with raster based GIS to facilitate the input of the spatial data such as land use map, soil map and digital elevation model was used for delineation of watershed. The land use /land cover and soil maps were loaded in AVSWAT to clip these layers. The area of the map grids that falls outside the watershed boundary was removed and map grids were reclassified and resampled at the DEM map grid resolution. Finally areas of different land use class and soil combinations were obtained for individual watershed. |