Landslides in the three studied basins of the Siwalik Hills are not random in distribution; they tend to cluster in certain areas implying the control of certain in situ factors or their combination. Landslide controlling in situ factors were reviewed and analyzed from maps, aerial photos and imageries using GIS. Chi square analysis was carried out to test the significance of landslide distribution vis-à-vis in situ factors. Slope gradient and relative relief were consistently significant in landslide distribution. Geology, dip-topography relation, land use and land cover, and vegetation conditions appeared important in landslide occurrence in all three basins either in terms of area or count in any two basins. Slope aspect and altitude tested significant for landslide occurrence in at least two basins. However, upslope flow contributing area, drainage density and distance to lineament were found insignificant in all three basins. In situ factors that tested significant in any two basins were used for landslide susceptibility analysis using a bivariate statistical approach. The distribution of landslides strongly correlates with susceptibility indices. With in situ factors, landslide susceptibility had good correlation with slope gradient and relative relief. Incorporating calculated factor weight values from one basin to the other two basins, proxy susceptibility index maps were also prepared. A moderate to good positive correlation appeared between them implying certain range of confidence for replicating the result for whole of the Siwalik Hills. Slope gradient and relative relief can be used as proxy indicators of landslide susceptible areas in the Siwalik Hills.

Studies assessing the groundwater spring potential in the Himalayan mountain slopes are very important for sustainable water resources management and build climate resilience in mountains, but such studies are few in the Himalayas. Hence, this paper attempts to identify the groundwater spring potential zone in the Central Himalayas of Nepal. About 412 groundwater springs were surveyed, which were mainly originated from the weathered, jointed or fractured rock aquifers in the high-grade metamorphosed rocks. Eleven influencing factors, viz., altitude, slope gradient, slope shape, relative relief, flow accumulation, drainage density, geology, lineament density, land use and vegetation density were considered in assessing the groundwater spring potential using the weight of evidence method. Weight indicating the probability of groundwater spring occurrence on multiple classes of each factor was calculated and finally summed up to determine the groundwater spring potential. Gentle slope, low relative relief, high flow accumulation, north-and east-facing slopes, denser lineament density, altitude class of 1500-2500 m, high vegetation density, and forest demonstrated a higher likelihood of spring occurrence. Validation of the groundwater spring potential map was successful, which implies the method can be replicated in a similar biophysical environment, where the hydrogeological or geophysical surveyed data is not available.

No abstract

No abstract

The tendency of occurrences of slope failures in future in an area is landslides susceptibility. This tendency in eastern hills of Rara Lake was analyzed through mapping process. Bivariate statistical index method was used to produce the susceptibility of landslides. Ninety six slope failures were delineated from Google Earth imagery. The ratio of landslide densities of each individual factor classes to that of whole area gave weight values necessary to produce landslide susceptibility index (LSI). East and South facing slopes, gradients of <30o, elevation of 2000-2800 m, buffers closer to road and streams, grassland and cultivation lands, and lithology of pelitic metamorphic rocks were factor classes with positive weight values. The LSI values ranging from -7.12 to 5.45 were reclassified into five susceptibility classes. Landslide densities of 8.12 and 4.76 per km2 were observed for very high and high susceptible zones. Success rate curve, made from 35 landslides located in the field survey, showed 0.76 portion area under the curve. This gives 76% overall success rate. Higher susceptible areas are cultivated areas and grasslands, where most houses were located. Thus, knowing the landslide susceptibility of areas, necessary preparedness can be done to reduce the impacts.