Horton overland flow contribution to runoff on unpaved mountain roads: A case study in northern Thailand

Abstract

AbstractTwo indirect methods are used to detect evidence of intercepted subsurface flow (ISSF) by the road prism in the Pang Khum Experimental Watershed (PKEW) in northern Thailand. During the 12‐month study period we failed to observe a soil moisture change that corresponds with ISSF being generated by the water table rising above the road surface. In support of the soil moisture data, δ18O signatures of rain water, road runoff, and stream water (a proxy for soil water) suggest Horton overland flow (HOF) generated on the road surface, not ISSF, is the dominant source of observed road runoff during typical rainfall events in the study area. This finding, which is contrary to the ISSF‐dominant road runoff regime found typically on unpaved mountain roads in the US Pacific NW, suggests that the use of a HOF‐based model to simulate runoff and sediment transport on unpaved roads in PKEW provides not only lower bound estimates of these processes, but realistic approximations for typical events. Copyright © 2001 John Wiley & Sons, Ltd.