Student, Institute of Forestry
Landslide is a natural phenomenon, which is common to Nepal due to its active tectonics and uneven topography. Shallow slope failures are common to Nepal during monsoon. Vegetation plays an important role in stabilizing shallow failures. Phewa Watershed’s lithology is mainly siltstone, sandstones and intensively weathered rocks, highly prone to erosion and shallow landslide; and 47.5 ha of the Phewa lake area has shrunk over period of 1988 to 2012. SINmap stands for Stability Index mapping, and model applies for shallow slope failures. The objective of the study is to access the stability of terrain, to map the landslide hazard and to check stability of terrain under two grass species. Study was conducted in Andheri khola watershed, and soil samples were collected in random distributive manner with sample size of 35. Landslide mapping and soil depth measurement was conducted throughout the basin. Constant head method was conducted to measure transmissivity and triaxial and direct shear test was conducted for cohesion and frictional angle. Analysis was conducted in SINMAP model in Arc GIS. Root cohesion of two grass species Vetiver(Chrysopogon zizanioides) and Amliso (Thysanolaena maxima) was used. When model was run using soil parameters from field without vegetation, it showed that 0.003% of the site is under defended class and 3.35% in upper threshold. As parameter in model was upgraded with grass species cohesion, it showed that there was no region under defended and upper threshold class. In comparison, Vetiver has 54.95% and Amliso 22.31% of Stable zone; which implies that vetiver can be more effective among two species to stabilize the terrain. The site under defended, upper threshold and quasi stable needs immediate intervention measure and anthropogenic activities should be checked to prevent upscaling of the present percent of defended and upper threshold index.
Abstract: During the last decades, damages to houses caused by landslides have been consistently occurring in a residential area in Öschingen/Germany. The residential area is located in ductile Callovian clays (Jurassic). Furthermore, in the back slope of the research area, a large Pleistocene slide mass negatively influences the slope stability. Through an integrative approach, the maximum data available for the study area was compiled in order to create a susceptibility map for landslide hazard. Detailed geomorphological field survey provided a valuable base for the assessment of slope stability using Stability Index Mapping (SINMAP). In the framework of long-term studies, consolidated results concerning mass movements and climatic-driven Pleistocene slope evolution, as well as recent slope dynamics, could be gained. These outcomes are compared to the results provided by slope stability modelling with SINMAP. The calculations outline some parameters responsible for higher risks. In general, the interaction of topography, water balances and substrate at the Schönberger Kapf can be designated to cause instability in wide areas. Hydrological parameters are essential for destabilisation of slope and they cause at least temporally destabilisation along channel structures, which presumably are influenced by seasonally increased spring discharge and a reduction in the underground shear strength. The exceptional dimension of the rotational block in connection with the specific slope hydrologic conditions and the intensive anthropogenic impact in the rear slope of the building area Auchtert in Öschingen has to be termed very problematic on the basis of the studies carried out.
Pub.: 22 Sep '09, Pinned: 29 Jun '17
Abstract: The Shallow Landsliding Stability Model (SHALSTAB) and Stability Index Mapping (SINMAP) models have been applied to various landslide management and research studies. Both models combine a hydrological model with an infinite slope stability model for predicting landslide occurrence. The objectives of the present study were to apply these two models to the Cunha River basin, Santa Catarina State, southern Brazil, where many landslides occurred in November 2008, and perform a comparative analysis of their results.Soil samples were collected to determine the input parameters. The models were calibrated with a landslide scar inventory, and rainfall data were obtained from three rain gauges. A comparison of their results obtained from the models was undertaken with the success and error index.Based on the maps of stability and instability areas for the study basin, the models performed well. Since the initial equations of both models are not particularly different, their results are similar. Locations with steep slopes, as well as areas with concave relief that tend to have larger contribution areas and moisture, have lower stability indexes. SHALSTAB classified only ~13 % of the total area of the Cunha River basin as unstable, while SINMAP classified ~30 % as unstable.The analysis of maps based on the results of the two models shows that if SHALSTAB is correctly calibrated, based on hydrological parameters, its results could be more accurate than SINMAP in the prediction of landslide areas. Although SINMAP showed better calibration of the landslide scars, its classification over the basin results in an overestimation of stability areas. The conclusion is that SHALSTAB is more suitable than SINMAP for the prediction of landslides in the Cunha River basin, Brazil.
Pub.: 18 Mar '14, Pinned: 29 Jun '17
Abstract: The Serra do Mar mountain range is a fault scarp with steep slopes that are often affected by shallow landslides triggered by extreme rainfall. Most of these events result in casualties and economic and environmental damage, especially in areas close to urban centers, major roadways and agricultural areas. The goal of this study was to evaluate the susceptibility to shallow landslides in the Serra do Mar, specifically within a drainage basin affected by such an event in January of 1985. For this purpose, the mathematical modeling technique of SINMAP was used by introducing the topographic values from a digital terrain model as well as geotechnical and hydrological values from previous studies performed in the Serra do Mar. In all, 32 susceptibility scenarios were generated, and three were analyzed for this study. These scenarios were validated using landslide scar maps produced using orthophotography; this technique was also used to analyze the functions of morphological parameters (e.g., slope angle, curvature and hypsometric features). The basin was classified as unstable, with landscape rates above 70 % for all three of the scenarios chosen. A higher landscape frequency was expected on straight slopes with angles between 30° and 50° under unsaturated soil conditions, as evidenced by low moisture rates, especially for N–S-facing slopes. The susceptibility maps generated using this model should prove useful for other critical parts of the Serra do Mar to understand better and, above all, predict these landslides, which annually cause significant damage in Brazil.
Pub.: 17 May '14, Pinned: 29 Jun '17