NSF Award Abstract - #0000546

FLAWS008

Hydrologic Change in Mountainous Tropical Watersheds: The Roles of Roads and
Deforested Land Surfaces in Altering Watershed Function and Accelerating Soil
Erosion

Abstract

0000546 Giambelluca

The expansion of rural road networks and the intensification of cultivation on steeply sloped lands contributes significantly to hydrologic change and sedimentation in major river systems of mainland southeast Asia. Domestic and international conservation projects conducted in highland watersheds of this region have historically focused on the agricultural practices of ethnic minority (hill tribe) groups. While improper cultivation techniques on steep slopes are certainly responsible for serious downstream effects in some areas, expansion of the rural road network may be equally or more important. To advance scientific understanding of the impacts of roads on regional hydrology, they must be studied at the watershed scale, within the context of other hydrologically important land-cover changes. This is true for all regions of the world, temperate or frigid.

The objective of the proposed study is to investigate the roles of, and the interaction between, roads and nonroad land surfaces in altering watershed functions and accelerating soil erosion in areas undergoing tropical deforestation. We propose to (1) validate the Distributed Hydrology-Soil-Vegetation Model (DHSVM) with field data collected during a prior NSF-supported project investigating road impacts in the 93.7-ha. Pang Khum Experiment Watershed (PKEW) in northern Thailand, (2) continue field measurement of soil-vegetation-atmosphere-transfer (SVAT) processes and road-related hydrologic/erosion variables in PKEW, (3) investigate the frequency of runoff generation on roads by subsurface flow processes (i.e., interception of subsurface flow by the road prism), and (4) identify indices that will allow us to extend our methodologies to larger catchments. To study the hydrologic and sediment fluxes measured in PKEW, we will couple sediment detachment and routing equations with equations describing surface flow in DHSVM. The adapted model will help us to determine the sources of overland flow and transported sediment, and to study where these fluxes are redistributed with PKEW, or transported from the basin. We will finally use the model to quantify watershed impacts resulting from the emergence of roads and the expansion of agriculture on steeply sloping lands within PKEW over the last 50 years.

The project unites two groups of researchers who have been studying road-related impacts: one group has been working in the tropics; the other in the U.S. Pacific northwest. Although set in Thailand, this research will directly contribute to the study of road-related impacts in all mountainous areas of the United States undergoing land conversion.