Abstract
To estimate the volumes of forest road runoff, we measured the infil-tration capacity of forest road surface using in-situ rainfall simulator (1 × 1 m) and monitored forest road runoff including overland flow (OF) and road intercepted flow (RIF) in forest road plots (5 × 15 m). Three plots with different topographic conditions such as plainer, concave, and convex were installed for measurement OF and RIF separately. The results by a rainfall simulator showed that the mean infiltration capacity of forest road surfaces was 33.3 mm/h (SD = 8.8 mm/h) with no relationship between vegetation ground cover and soil physical properties. Runoff coefficients of OF from forest road plots were from 14 to 21％ with 85 to 89％ of contribution to total runoff. The estimated infiltration capacities based on OF values of forest road plots were less than 5.0 mm/h and smaller than values estimated from the in-situ rainfall simulation. This results suggested that continuity of overland flow pathways due to the track length on forest road plots induced greater amount of OF. Contribution of RIF to total road runoff was less than 10％. Antecedent precipitation index was a controlling factor for RIF only in the plot with small areas of bedrock outcrop. Conditions of forest road (track length) and cut-bank (location of bedrock outcrop and fault) can be important factors for controlling the amount of forest road runoff and its pathways．
