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过去和现在的地貌过程的分析，提出防治侵蚀泥沙灾害的工程地貌调查要点。1)通过对尼泊尔喜马拉雅地区近十年来沟谷侵蚀、地表侵蚀和植被恢复的速率和过程的监测，对所采取的各种防治措施进行了评价。在此基础上，初步构想了通过沟谷发育阶段选择侵蚀防治措施的方法。2)通过对坡岸侵蚀、径流过程和地貌演变过程的监测，研究了亚喜马拉雅(锡瓦利克山)河道拓宽的原因。由于地质地层薄弱和年轻，排水系统网络致密，发生了径流集中时间短的极端山洪灾害。据估计，从斜坡和堤岸产生的巨大泥沙相当于至少5毫米/年深的剥蚀率。它们是河道加宽的主要原因。流域的土地覆盖变化也可能是造成滑坡的原因。3)通过航空照片解译，绘制了下喜马拉雅地区和部分次喜马拉雅地区的深层滑坡分布图。通过统计分析，提出了岩性、构造、坡角等地质因素相结合的滑坡危险坡度检测方法。4)通过对滑坡发生与地形属性关系的统计分析，提出了基于地理信息系统的滑坡危险性区划方法。

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.