Abstract
As intercepted subsurface flow can encourage road surface erosion in forests, it is neccessary to predict areas where this could possibly occur and to take some measures to prevent such erosion. The purpose of this study is to test the assumption that such locations can be predicted on the basis of the roadside drainage area. In this study, we recorded locations on four forest roads where road surface flow persisted over 12 h after rain events or where cross drains were added during maintenance activities, which were assumed to be subjected to intercepted subsurface flow. Results showed that the appearance frequencies of locations where there was persistent road surface flow or where cross drains had been added did not significantly differ in relation to the roadside drainage area. Further, these locations were often found near valleys; however, the proportions of the valleys within 20 m of the locations were not significantly different with respect to the drainage area of the valleys. These results suggest that there is no correlation between the roadside drainage area and locations that are subjected to intercepted subsurface flow and that such flow can occur near valleys with large and small drainage areas.
