Estimating the amount of forest road sedimentation employing Washington Surface Erosion Model and evaluating the effect of fillslope variables on it

Abstract

Forest roads are recognized as one of the primary sources of sediment production in mountainous watersheds. Predicting the amount of sediment they produce is crucial for effective management. The WARSEM model, developed in the forests of the United States and used globally, is one of the most efficient models for estimating sediment from forest roads. However, a significant limitation of this model is the lack of fillslope data. Given the unique characteristics of the northern forests of Iran, such as steep slopes, this study investigated the potential impact of this factor on the model's results. The study was conducted in the third district of the Chelavand forestry project, located in the natural resources area of Astara city in Northwestern Iran. The total length of the roads studied was 5.5 km, divided into 48 samples with homogeneous characteristics. Essential information was collected for the implementation of the model. The model estimated the amount of road and cutslope sediment to be 94.786 tons per kilometer per year. After incorporating information about the fillslope area, the model was run again. The predicted amount of sediment from the fillslope area was 3.4 tons/km per year. A t-test analysis revealed that the observed difference between the results was not significant. Therefore, it can be concluded that adding features related to the fillslope area does not significantly affect the final results of the model in the study area. © 2023, Iranian Society of Forestry. All rights reserved.