Evaluation of landslides on sediment yield of Balekhlou-Cahy basin in Ardabil Province

Landslides are the major causes of erosion and sediment yield in the sloping and mountainous basins. However, evidence suggests that the amount of sediment to the river of the mountainous regions in Ardabil province due to landslides is significant, but in quantitative terms it has not been provided the certain value based on scientific research for it. In this study, the subject was evaluated in the Balekhlou-Chay catchment of Ardabil province using data extracted from the aerial photographs, field investigations and the sediment discharge measured data at Pole-Almas hydrometric station. Sediment volume in the sediment measurement stations associated with the catchment was estimated by determining the relationship between flow rate and it′s corresponding sediment discharge. It was attempted to compare the estimated amount of sediment at different time periods with its amount in the periods of activity of landslides and to determine the possible effects of the landslides in increasing erosion and sediment yield in the catchment. The noted large landslides have caused a significant increase in the sediment load of the available rivers. The effects of these slides can be observed in the suspended load passing through Pol-e-Almas station. The mean of the suspended sediment concentration of Balekhlou-Chay catchment has been estimated about 46566.30 tons per year based on sediment discharge values from field data during 40 years (from 1972 to 2001), however the mean of the suspended sediment concentration is 30831 tons per year based on sediment discharge values from field data during 36 years, which means with the elimination of the data related to landslide years (from 1980 to 1983). In conclusion, according to the calculated sediment carried by the Balekhlou-Chay river after the occurrence of the Sarighaye and Ilanjigh landslides during the period of 4 years (from 1980 to 1983) has been increased rapidly.