Erosion risk mapping of Capakcur stream watershed using geographical information system and remote sensing

Abstract

Capakcur stream watershed located in the southwest of Bingol city, in Turkey, covers a 106 km2 area. The watershed with higher slope degrees faces severe soil erosion due to vegetation destruction, lithological and climate properties, except for a limited area located in the west of the watershed. Settlements in the watershed are usually take place near the valley base due to the rugged surface, which may generate costly land-slide events. To describe the basin with high risks and to create sufficient preventative steps, erosion sensitivity maps were obtained using a statistical analysis by the superposition principle. Digital Elevation Model (DEM) was acquired from the digitization of topographic map of the watershed, then the used for calculations of slope degrees. The erosion risk maps were attained by using the parameters of the slope degree, precipitation, Normalized Difference Vegetation Index (NDVI), stream density and soil texture calculated from soil brightness index (SBI) by applying Tasseled Cap transformation to satellite images. During the calculation of the map risks, each parameter was initially divided into subclasses and given a weight point according to the degree of influence upon the erosion, the sensitivity map was then created by adding each parameter map. Results from the sensitivity map indicate that 50% of the watershed is under high and 15% is under severe erosion risk while only 11% of the watershed is under low or very low erosion risk. The rugged structure of the watershed has necessitated the establishment of the settlement to the valley bed. Materials transported by rivers in the watershed where the erosion is severe, are deposited in the stream bed. The reduction in carrying capacity of streams causes floods affecting settlements. The sensitivity maps clearly indicate that the precautionary steps such as protection of the vegetation cover, plantation or relocating settlements away from the valley base will be immediately undertaken for further soil erosion in the watershed.