Analysis of rainfall induced landslides using hydrological model

Landslides are a major type of geological disaster, commonly triggered by heavy or prolonged rainfall that increases the water content of slopes, leading to instability and movement of soil and rock. India is a country which has witnessed the deleterious effect of many disastrous landslides. North eastern parts (Himalayan Region) and Western Ghats of India are more prone to landslides every year mainly due to heavy rainfall and thus resulting in large casualties and huge economic loss. Therefore there is a need to precisely assess and manage these landslide hazards. In the present study, a methodology has been implemented to analyze rain induced slope failures by taking a landslide prone area in Wayanad, Kerala as a case study. Many previous landslides are reported in this region due to heavy rainfall during monsoon and steep slopes of the area. A hydrological model has been set up to evaluate rain induced slope failures in a deterministic framework using Microsoft Excel. Rainfall data, hydrologic properties and geotechnical properties of the study area are collected. Rainfall data and the infiltration capacity at the site is an important input to the model. Initial moisture content distribution, saturated moisture content, residual moisture content and saturated conductivity of the soil deposits are used to obtain soil water characteristic curves (SWCC).Pore water pressure and hydraulic conductivity of soil is estimated from SWCC for the initial state of stability. An implicit finite difference backward solution is used to solve partial differential equations for variably saturated flow and change in pore water pressure and moisture content as a result of a rainfall event is obtained. Thus change in pore water pressure (negative and positive) with respect to time and depth is obtained and this results from the hydrological model.