Research on the engineering geomorphological investigation methods for planning countermeasures against sediment-related disasters in the Nepal Himalaya

本研究旨在通过对尼泊尔-喜马拉雅地区地貌过程的分析，提出针对侵蚀和沉积灾害的对策规划的工程地貌调查点。通过对10年的沟沟侵蚀、地表侵蚀和植被恢复速率和过程的监测，对采取的各种对策进行评价。在此基础上，提出了通过调查沟沟发育阶段选择治理侵蚀措施的基本概念。2)通过监测坡面/河岸侵蚀、径流过程和地貌演化过程，研究了亚喜马拉雅地区（Siwalik Hills）河道加宽的原因。由于脆弱和年轻的地质地层造成了密集的排水系统网络，导致了径流浓度短调的极端山洪的发生。据估计，斜坡和河岸产生的大量泥沙相当于每年至少5毫米的深度剥蚀速率。它们是河道变宽的主要原因。流域土地覆盖的变化也可能是原因之一。3)利用航拍解译技术编制了下喜马拉雅地区和部分亚喜马拉雅地区的深部滑坡分布图。通过统计分析，提出了岩性、构造等地质特征与边坡角度相结合的滑坡危险边坡检测方法。4)通过统计分析滑坡发生与地形属性的关系，提出了基于gis的滑坡灾害区划方法。

This study aims to propose engineering geomorphological investigation points for countermeasure planning against erosion and sedimentation disasters through analysis of present and past geomorphic processes in the Nepal Himalaya1)By monitoring rate and processes of gully erosion, surface erosion and vegetation recovery for ten years, we evaluated the various adopted countermeasures. Based on it, selecting methods of erosion control measures by investigating stages of gully and rill development is basically conceptualized.2)Causes of river course widening in the Sub-Himalaya(Siwalik Hills) have been studied through monitoring both erosion of slopes/stream banks and run-off processes as well as geomorphological evolution processes. Extreme flash floods with short tune of run-off concentration have occurred due to dense network of drainage systems due to weak and young geological strata. Huge sediment production from slopes and banks equivalent to the denudation rate of at least 5mm/year in depth is estimated. They are the main causes of river course widening. Land coverage change in a watershed may also be the cause of it.3)Deep-seated landslide distribution maps have been prepared by aerial photo interpretation in the Lower Himalaya and partly in Sub-Himalaya. It is proposed through the statistical analysis that landslide hazardous slopes can be detected by combination of geology such as lithology and structure and slope angle.4)A GIS-based landslide hazard zonation method is also proposed from the statistical analysis on the relation between landslide occurrences and then* physiographical attributes.