9614259 Giambelluca Unpaved roads play a significant role in altering near-surface hydrologic response and subsequently accelerating soil erosion in temperate drainage basins. Road-related impacts are also of particular concern in tropical areas where agriculture practices are most often blamed for erosion and sedimentation problems. The focus of this study is to show how an expanding road network changes the hydrological and erosion processes of a mountainous tropical watershed in northern Thailand. The major objective are to (1) determine the degree to which hydrologic processes in tropical watersheds are disrupted by roads--this information can later be compared with what is known about road disruption in temperate watershed; (2) establish the importance of roads in relation to agricultural areas in initiating hydrologic change and contributing to accelerated erosion; and in so doing, obtain a detailed understanding of erosion processes operating on and adjacent to road surfaces; and (3) evaluate the conservation value of several road management-related what if scenarios. The proposed research strategy can be represented by four components: (1) a comprehensive field study to build a database of hydrological, erosional, and soil-vegetation-atmosphere-transfer (SVAT) information; (2) in-depth analysis of changes in hydrologic and erosion processes due to land-cover change, especially changes due to road expansion; (3) determination of the important road-related runoff processes in order to select the appropriate model or models to simulate hydrologic change and erosion resulting from the expansion of road networks; and (4) use of model(s) to simulate the effects of several management scenarios. This research will improve our knowledge of hydrologic and geomorphic processes operating in tropical watersheds undergoing dramatic landuse changes; help determine the importance of roads, as compared with agricultural practices, in contributing to cumulative watershed impacts; aid in the fut ure management of tropical mountainous watersheds; and provide insight into improving the design, routing, maintenance, and usage of rural roads.
