Several factors are involved in the destruction of forest roads, and most of them are generated as a result of rainfall runoff which directly threatens the surface of forest roads. To minimize this damage, a well-designed drainage system in accordance with the situation in the region is needed, for which the optimal number and diameter of pipes must be calculated. Mixed broadleaf high-elevation forests in northern Iran. In this study, by employing hydrological models, geographic information systems (GIS), and field survey, we divided the area to 42 sub-areas. We then considered the factors such as hydrologic soil groups, hydrology situation, curve number (CN), and time of concentration, to calculate runoff and peak flow moments. The proper diameter and the number of transversal drainage pipes were then determined. The results showed that the existing cross-drains and their diameter are not sufficient, and are therefore not suitable for the high volume of water in this area. Our findings showed that all of the pipes that have been used in this region have a 60 cm diameter, although, while considering all the relevant factors, it should be at least 80 cm. The results showed that the changing land use and deforestation are the main causes of high rate of runoff in the study areas. Improper maintenance of roads has caused widespread destruction along the road, thereby affecting all the drainage channels and blocking all connections between them.
Cite this article as: Naghdi, R., Ghajar, I., Nikooy, M., Moradi, M., & Tavankar, F. (2021). Determining the best dimension of transversal drainage for a forest road network by employing hydrological models. Forestist, 72(2), 129-136.