Document Type : Research Paper

Authors

• Majid Mohammady ¹
• Mojtaba Amiri ²

¹ Semnan University

² Department of Environment, Faculty of Natural Resources, Semnan Universiy, Semnan, Iran

Abstract

Erosion is often capable of causing several on-site and off-site impacts. Erosion is common in hilly areas, but their severity will vary depending on the geoenvironmental factors including, Steep sloping, geological characteristics, vegetation and climatic factors making it more vulnerable to erosion. Firozkuh watershed was selected as study area because in this watershed, badlands are the most important contributors to soil erosion because of the condition of climatic, hydrologic, topographic, and reduced vegetation conditions, and as well as presence of susceptible soil and geology formations in this region. The first step in this research is to prepare distribution map of the badlands and determine their location on the map. The maps of condiioning factors were prepared and entered into the GIS environment. After classifying conditioning factors maps, the weight of each map was calculated using the frequency ration model. In the next step, by combining the weights, the final badland erosion susceptibility map was prepared. The ROC curve and the area under the curve were used to assess the accuracy of the frequency ratio models. The results showed that the highest weight of the frequency ratio is related to the elevation class of 1710 to 2286 meters, rainfall 400 to 550, slope more than 35, northwest aspect, distance less than 1150 meters from drainage network, marl, limestone and shale formations, ranglands, Convex and concave slopes, clay 25 to 33%, silt 27 to 35%, hydrological group C, soil depth 57 to 120 cm, pH 7.6 to 1.8, TWI class 6 to 11. The area under the ROC curve was 0.71 that showed frequency ratio model is acceptable for badland erosion susceptibility mapping in the Firozkuh watershed. Despite its simplicity, the freqency ratio model provides acceptable results due to the creation of a logical connection between the badlands and conditioning factors.

Keywords

• Firozkuh watershed
• Badland erosion
• ROC curve
• susceptibility map
• Freqency ratio