Landslide-induced debris flows and its investigation using r.avaflow: A case study from Kotrupi, India

This paper focuses on the Kotrupi landslide-triggered debris flow event in Himachal Pradesh, India, on March 13, 2017, leading to significant human and property losses. The study, situated in Kotrupi village of Mandi district, addresses three major landslide-triggered debris flows occurring between 1977 and 2017, each with a 20-yr return period. Ongoing erosion in the adjacent area underscores the imperative for a comprehensive investigation into debris flow events in the region. Employing the r.avaflow simulation tool, this study numerically models the slope, reconstructing the runout from the initial landslide to debris flow initiation. Calibration of friction parameters yielded optimized values of δ = 22° and Φ_B = 9°. The debris flow, measuring 1044 m in total length, exhibited channelization with predetermined event volume and depth. Key characteristics included a peak velocity of 18.7 m/s, a maximum height of 7.34 m, and a kinetic energy of 375 MJ. Our findings underscore the significance of factors such as material availability, maximum velocity, release height, and proximity to streams in determining debris flow susceptibility, with peak velocity emerging as a primary factor. The r.avaflow simulation accurately reproduced debris flow metrics, indicating the potential for another event of similar or greater intensity due to the unstable slope condition. The research advocates for additional debris flow modelling to uncover novel parameters for predictive simulations. Furthermore, it sheds light on the limitations of debris flow investigations in the western Himalayan region.