study of the relation between landuse and slope with sediment yield in the southern watersheds of mahabad river

the mahabad river watershed has been exposed to severe erosion as a result of landuse change. the aim of this study is to quantify the amount of sediment yield and the relationship between land use change and slope. different sources such as geologic and topographic maps, satellite images, hydrometric as well as meteorological data were used to extract and gather the information needed for this research. six factors including altitude, slope, precipitation, rock erodibility, time of concentration and land use were specified as the most effective factors. the overlapping of the six factors maps resulted in the preparation of sediment delivery potential map. the distribution maps prepared on each of these parameters and their overlaps have shown that areas with more severe slopes are categorized as highly susceptible to erosion. however, in areas with resistant rocks, change of land use has been the determining factor. comparison of water and sediment discharge data of 1996-97 with 2001-02(similar annual water volume) showed that the sediment yield has increased. studying land use map prepared using satellite imagery of 1987 and 1998 showed that land use of the area has severely changed from pasture to dryland farming. this factor has also caused the intensification of mass movement recently occurred in the area. landuse is the only parameter modified by human, and it is the only one which can be quickly and effectively changed. hence, it seems that the upstream areas in the south and southwest of the basin with low concentration time, steep slope, high erodibility, high amount of precipitation, and the landuse of forest and pasture mixture as well as alluvial terraces with fine and granular sediments are the most sensitive areas which need protecting and control measures.