Investigation of lateral erosion of Qaleh Rudkhan river in Guilan using streambank erosion potential index

River canal changes are natural river processes and part of the systematic functioning of rivers that cause the destruction of agricultural land around the river and damage to human facilities and roads. The purpose of this study is to investigate riverbank erosion using Oklahoma Ozark streambank erosion potential index (OSEP). Qaleh Rudkhan watershed is located in the west of Gilan province in Fooman city. This river originates from the northern slopes of the Talesh Mountains and after leaving the mountains in the Fooman region, enters the Gilan Plain and finally flows into the Caspian Sea. In order to investigate the erosion of the river bank, a part of the river with an approximate length of 5 km near Fooman was identified and in 8 reaches, the parameters in the Oklahoma Ozark streambank erosion potential index (OSEP) were examined. In this method, eight factors of bank height, bank angle, percentage of bank height with a bank angle greater than 80 degrees, evidence of recent mass wasting, unconsolidated material, streambank protection, riparian woody-vegetation cover and stream curvature are scored. According to the results of relative score, streambank Protection and Riparian Woody-Vegetation Cover have been the most effective factors in the instability of the left and right shores in Qaleh Rudkhan river. In general, it can be said that instability has prevailed in the banks of Qaleh Rudkhan river, which is due to human intrusion and occupation in this part of the river.