The effect of mass movements on the development of the Botan Stream Valley (Siirt) between Kayaboğaz east and Sağlarca

The study area located in the south of Siirt city center covers an area of 55.60 km2. The elevation of the area varies between 449-1294 meters. There are many reasons for the mass movements occurring in the study area. These are geologic, geomorphologic, climatic, fluvial features, vegetation and human activities. When the geological characteristics of the site are evaluated; landslides and landslides are generally experienced on the slopes with lithologically terrestrial crumbs. On travertine slopes, falls and overturns occur in the form of mass movements. In the southwest of the site, southwest of the Ilısu Dam, two faults pass over the north and south. Steepness is sharper in these areas where the faults pass. The areas where the slope varies between 23° and 73° are considered as landslide susceptible areas. When the aspect factor is evaluated, erosion is higher on the slopes with more sunshine duration, since physical fragmentation is more severe. The most important factor that triggers mass movements in the field is undoubtedly the climate factor. In the field where semi-arid climatic conditions are predominant, the physical fragmentation that occurs due to seasonal and daily temperature differences accelerates the transportation of the eroded material. The eroded materials are rapidly transported in the area with high precipitation conditions due to the effect of flooding. The fact that the vegetation cover is quite sparse in the area accelerates erosion. Another condition that causes mass movements is the fluvial erosion processes and curvature values. The masses carved from the bottom with the effect of lateral and retrogressive erosion cause overturning and rock falls after a while with the effect of gravity. In the study area, parallel slope regression and corniced valleys are frequently observed in accordance with the lithology. The effects of mass movements are also evident on the concave slopes. The neritic travertine has an effect on the formation of steep slopes in the field, especially in the Rasıl Hacar (Delikli Taş) region. Overturns and rock falls are observed in this region due to the effect of lateral erosion. Physical fragmentation has a great effect on the formation of different transverse valley profiles especially on the slopes.