Landslide risk assessment and management in Shahroud watershed of Qazvin province

Landslide risk assessment is essential for all landslide damage mitigation plans. The purpose of this research is to assess the risk of landslides in the Shahrood watershed of Qazvin province. First, the landslide susceptibility map was prepared using fuzzy operators. the landslide distribution map and also 11 effective factor layers including slope, slope direction, altitude, land use, lithology, distance to road, distance to stream, distance to fault, earthquake acceleration, precipitation, and maximum daily precipitation were first prepared. After determining the frequency ratio and fuzzy membership values for the map classes of different factors, the landslide susceptibility map was prepared using different gamma values. Then, after preparing the fuzzy map of vulnerability for different land use units, the amount of landslide risk was determined from the product of two maps of landslide susceptibility and vulnerability. In general, 104 landslides with a total area of 1401 hectares were recorded in this region, 70% of which were used for modeling (73 landslides with an area of 982 hectares) and the remaining 30% (31 landslides with an area of 418 hectares) were used to assess the accuracy. The evaluation results showed that the highest value of Qs index (equal to 1.34) belongs to the gamma equal to 0.93 and therefore this model has higher accuracy than other gamma values. The importance of features at risk ranges from 0.05 (no coverage) to 1 (residential and industrial areas). To deal with landslide damages, three general policies including suitable for development, prevention, and treatment were proposed, which should be applied based on the two factors of risk and vulnerability for different areas of landslide risk. Finally, in order to reduce landslide damages, suitable land uses for high-risk regions were introduced.