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

[0000546 . giambelluca]农村公路网的扩大和陡坡土地耕作的加强对东南亚大陆主要河流水系的水文变化和沉积有重要影响。在该地区高原流域开展的国内外保护项目历来侧重于少数民族（山地部落）群体的农业实践。在某些地区，陡峭山坡上不恰当的耕作技术无疑是造成严重下游影响的原因，而农村道路网络的扩展可能同样重要，甚至更重要。为了促进对道路对区域水文影响的科学认识，必须在流域尺度上，在其他水文上重要的土地覆盖变化的背景下进行研究。世界上所有地区都是如此，无论是温带还是寒冷。该研究的目的是调查道路和非道路地表在改变流域功能和加速热带森林砍伐地区土壤侵蚀中的作用及其相互作用。我们建议(1)利用先前nsf支持的93.7 ha道路影响调查项目收集的现场数据验证分布式水文-土壤-植被模型（DHSVM）。泰国北部的Pang kum实验流域（PKEW），(2)继续实地测量土壤-植被-大气转移（SVAT）过程和PKEW中与道路相关的水文/侵蚀变量，(3)调查地下流过程（即道路棱镜拦截地下流）在道路上产生径流的频率，以及(4)确定指数，使我们能够将我们的方法扩展到更大的流域。为了研究PKEW测量的水文和泥沙通量，我们将在DHSVM中将泥沙分离和路径方程与描述地表水流的方程耦合起来。调整后的模型将帮助我们确定陆地流和输运泥沙的来源，并研究这些通量在PKEW的重新分配或从盆地输运的位置。最后，我们将使用该模型来量化过去50年来PKEW内陡坡土地上道路的出现和农业扩张对流域的影响。该项目联合了两组研究人员，他们一直在研究道路相关的影响：一组在热带地区工作；另一个位于美国太平洋西北部。虽然以泰国为背景，但这项研究将直接有助于研究美国所有正在进行土地转换的山区的道路相关影响。

0000546GiambellucaThe 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.