JWSS - Journal of Water and Soil Science

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Forest roads must be constructed according to technical standards and guidelines which have been published by the scientific and operational organizations. Recently, hydraulic excavators have been used beside the bulldozer for excavating the forest roads. Thus, it is necessary that their ability in construct of standard cross sections be compared. This study was conducted in Lattalar forest which is located south of Sari city (Mazandaran Province). 60 cross section samples were randomly selected for each machine in slope classes of 30-40, 40-50, 50-60 and 60-70%. Then, cross sections were taken by niveau and clinometer. The results in different slope classes showed that the hydraulic excavator and bulldozer had no significant effect on cut and fill slopes length and gradient. Roadbed width in bulldozer construction area was more than the hydraulic excavator at probability level of 1%. Also, there was a significant difference between the hydraulic excavator and bulldozer earthworking width in slope classes of 30-40 and 40-50% at probability level of 5 and 1%, respectively, whereas this difference was not significant in other slope classes. Finally, the average standard cross sections for hydraulic excavator and bulldozer were 89.96 and 84.81%, respectively.

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In this research, sediment production and delivery amount by Darabkola forest roads was estimated using the SEDMODL model. To evaluate the model results, the sedimentation rate in the above roads was directly measured using rainfall simulator. Also, the paired t-test, BIAS, RE and RMSE were used to assess the results. The analysis showed that the rate of sediment production from study roads' surface using the SEDMODL model and direct measurement under the rainfall simulation were 420.97 and 341.19 tons per year, respectively, and rate of sediment delivered to the stream with sediment delivery ratios of 42% and 51%, respectively, was about 177.58 and 174.02 tons per year. Also, results of the statistical methods of BIAS, RE and RMSE for the aforesaid model were 0.04, 17.59 and 0.71, respectively, and at 95% confidence level, no significant difference was obtained between the observed and estimated data. Therefore, the aforesaid model has the appropriate accuracy and efficiency to estimate the sedimentation rate of the Darabkola forest roads. It was also found that from among the input parameters of model, longitudinal slope of road, precipitation and sediment delivery factors were the most influential factors in the sediment production and transport, respectively.