Forest roads are constructed to access forest interior, wood extraction, conservation, afforestation and recreation. In forest road construction project, the trees and vegetation cover are removed and the soil structures are damaged. So, this causes to increase sediment production in forest roads. Increasing of the yield of sediment to river can damage water quality and aquatic ecosystem. Nowadays, there are different models for prediction of sediment yield and this can be helpful for researchers to predict amount of sediment production in forest roads. In this research, SEDMODL was used to estimate mean of annual production of sediment in forest roads. A road with a length of 2260 meter which is located in compartments of 26, 27 and 32 of Darabkola forests was selected. Then, the road length, road width, production rate of sediment with considering geology condition, road surface factor, traffic factor, longitudinal slope, rainfall and sediment delivery factor were calculated using GIS maps, forest management plan handbook and field survey. Results showed that the production rate of sediment in roads was 77.514 ton per year and of this value, 13.175 ton per year is imported to stream canals and rivers. Besides, the slope, distance of road to stream canals and cut slope height were the most important factors in sediment production and delivery to stream canals.

In this study, the sediment yield of forest roads of Darabkola watershed was investigated and estimated using WARSEM and SEDMODEL. Rainfall simulator was applied to measure the sediment of abovementioned roads directly. In order to apply WARSEM and SEDMODEL models, field operations for measurement of different parameters including road length and width, height and coverage of road cut-slope, road longitudinal slope, shape and configuration of the road, road surface, and etc. were carried out in 63 different segments of the path of forest roads in the study area as 11979 meters long. Then sediment yield of roads was measured by rainfall simulator with nozzle of 3 meters high and plot of 2 square meters. Results of the WARSEM and SEDMODL models and rainfall simulation showed that sediment yield of forest roads are equal to 9.918, 5.109, and 4.141 kg/m2/year, respectively. Results also showed that there was no significant difference between sediment yield of rainfall simulation and SEDMODEL at significance level of %95. It was also revealed that SEDMODL is more suitable for estimating sediment yield of forest road with values of RD, MD, BIAS, RE and RMSE equal to 21.42, 4.54, 0.04, 17.59 and 0.71, respectively.