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In erosion and soil conservation projects, lithological characteristics of drainage basin are very important. Sensitivity of different rocks to erosion is different and some of the geological materials are very sensitive to erosion and sediment yield. Sensitivity of rocks and sediments to weathering and erosion are dependent on different factors, some of which are related to the nature of geological
materials and the others related to the surrounding environment. In small drainage basins, the nature of
geological materials is more important than the factors related to the surrounding environment. Different factors such as geomorphology, climate, vegetation cover, human effect, etc. are effective on erosion. The investigation of all effective factors is difficult and complex. Therefore, the effective factors should be listed according to their (decreasing) importance in erosion, and then the most effective factors should be studied. As a result, the homogeneous land units with the size suitable for investigation will be obtained by crossing these factors, and the relationship between effective factors and sediment yield data will also be reached.
The area studied was Latian Drainage Basin and its sub-catchments. By primary field investigation, it was found that among all effective factors on erosion, geological materials, slope and climate were the most effective ones in the area. Then, the maps of three mentioned factors were prepared and were overlain to obtain land units map of the area. Next, sensitivity of formations and rocks to erosion was obtained in each land unit; for pre-Quaternary consolidated geological materials, Rock Mass Strength Classification of Selby (A.) and for Quaternary sediments and pre-Quaternary unconsolidated geological materials, K factor in USLE model were used for qualitative approach. For quantifying sensitivity of geological materials to erosion, sediment yield data of hydrometric stations in Latian Drainage Basin were used.