Relationship between the Slope Position and Land use in Hill Slopes Whit Mudflow Erosion to Soil Activity Coefficient and Atterberg Limits

Mudflow erosion is a pervasive problem with adverse consequences for natural ecosystems in most parts of the world. The main factors creating Mudflow erosion are heavy rains, snow and ice melts and flooding rivers. In this study, the effects of slope position and land use type on Mudflow erosion at hill slopes with three different land uses were investigated. For this purpose, three hill slopes with the same conditions were selected in the land uses. Thereafter, three profiles were drilled at the shoulder (the highest erosion), backslope (average erosion) and footslope (lowest erosion), respectively. After studying and determining the soil layers in each profile, soil samples were obtained from two layers of surface and subsurface. Some soil physical, mechanical and chemical properties were then determined in each sample with three replicates. The results showed that the greatest LL value in the forest land use was observed in the middle slope which was 28.64 and 25.90 in the two investigated layers, respectively. However, in the pasture, the highest LL values were 37.07 and 33.94, respectively. Furthermore, the land use type had a significant relationship (P<0.01) with OM, CCE, clay, SM, LL, PL and PI. The sand, soil activity index, cation exchange capacity (CEC) and the ratio OM/Clay had significant (P<0.05) relationships with land use type while the silt and CEC/Clay parameters had no significant relationship. Forest with an average OM of 1.149 percent had the greatest organic matter content and the degraded pasture had the lowest value (0.47 %). Also the degraded pasture with an average clay content of 16.6 % and silt content of 47.37 % had the highest clay and silt values. The soil activity index in this land use type was 0.36. Liquid and plastic limits in the degraded pasture were higher than the pasture, and the pasture was greater than the forest. The results of this study reveal that the degraded land uses have more potential for the occurrence of this type of erosion due to the high fine materials and saturation moisture percent and also poor soil surface cover.