Runout modeling and calibration of friction parameters of Kurichermala debris flow, India
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Minu Treesa Abraham I Neelima Satyam I Sai Kumar Peddholla Reddy I Biswajeet Pradhan
Runout modeling and calibration of friction parameters of Kurichermala debris flow, India
Abstract Debris flows account for a substantial economy and property loss in Western Ghats of Kerala, India, especially during monsoon seasons. Wayanad district is an active erosion zone in the plateau margins of Western Ghats, and there is a remarkable rise in the number of debris flows since 2018, due to very highintensity rainfalls in this region. This study comprises geotechnical investigation, runout modeling, and calibration of friction parameters of Kurichermala debris flow, one of the devastating debris flow events that happened in Wayanad, during the 2018 monsoon. The detailed investigation and back analysis of such events are substantial in calibrating the flow parameters for the region. These parameters can be used for predicting the flow paths of possible debris flows and quantitative risk assessment in the future. The geotechnical investigation provided vital information regarding the soil type and shear strength parameters of the debris flow and has helped in understanding the flow behavior. A dynamic numerical model, rapid mass movements (RAMMS), was used for the back analysis of the debris flow, using the shape information of the flow. For precise calibration using statistical comparison, an image processing tool has been developed, to compare the structural similarity of simulated results with the original shape of debris flow. The dry-Coulomb friction coefficient (μ) was calibrated as 0.01 and turbulent friction coefficient (ξ) as 100 m/s2 for the event, using Voellmy-Salm rheology. The shape predicted by the model had a similarity index of 0.626 with the actual shape of debris flow. The results were found to be in accordance with the field and geotechnical observations. Hence, the results can be used to predict the shape of possible debris flows in the study area. The study is the first of its kind for the region and has significant influence in risk assessment for this highly susceptible landslide zone. Keywords Debris flows . RAMMS . Runout modeling . Rheology . Image processing . Wayanad Introduction Debris flows are characterized as rapid flow-like landslides, traveling vast distances and causing severe damages (Varnes 1978). Due to higher saturation, the failed mass on the steep slope rapidly propagates downward in a flow-like manner. Among all the landslide types, debris flows and avalanches are the most damaging category, and their destruction potential are practically difficult to control. Numerical modeling is thereby critical in estimating the flow parameters of possible debris flows. The flow parameters can be used to estimate the flow path and runout distance and can help in evaluating the risk associated with debris flows. Rainfallinduced landslides and debris flows are among the major natural disasters in Indian terrain (Soja and Starkel 2007; Dikshit and Satyam 2018, 2019; Dikshit et al. 2018, 2019; Teja et a
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