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

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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.