Hydrological and Erosional Impacts of Road and Land-Cover Change in Small Mountainous Watershed in Northern Thailand

Abstract

Through fieldwork in northern Thailand, a realistic assessment of hydrological and geomorphological impacts of roads in mountainous tropical watersheds was carried out. Findings from field rainfall simulations, surveys of road and traffic phenomena, and computer simulations are presented. Because roads generate Horton overland flow (HOF) during most rain events, they transport sediment into the stream system throughout the rainy season. Linkage of road sections via rut and gully systems allow them to transport runoff generated in one basin into adjacent basins, where it may contribute to hydrological and erosional impacts. Footpaths, like roads, accelerate runoff, and may enhance field erosion by acting as source areas for surface runoff. Vehicle detachment and maintenance activities during interstorm periods increase the volume of loose material that can be removed by overland flow during subsequent rainstorms. Road sediment transport is simulated best when the surface layer of loose sediment is explicitly modeled. This research serves as a foundation for future work aimed at quantifying road and agricultural contributions to cumulative watershed effects in South East Asia.