Establishing Soil Moisture and Rainfall Intensity-Duration Thresholds for Initiation of Mass Movements Along the National Higway-58 in the Chamoli District of Uttarakhand

The Rishikesh-Badrinath National Highway 58 (NH-58), in the district of Chamoli, Uttarakhand, India records several incidences of landslides and related casualties every year during intense rainfall periods. Mass movements that occurred along this highway during monsoon, in the period 2015–2019 have been studied to arrive at meaningful rainfall and soil moisture thresholds. Data from the Border Road Organization (BRO) was compiled for 166 mass movement events, including 67 debris slides, 33 rock slides, 24 debris flows and complex movements. The relationship between rainfall maximum intensity (Imax) and total duration (D) was analysed for each site and Imax-D thresholds were derived using Global Precipitation Mission (GPM) half-hourly data. Significant differences were observed between the derived Imax-D thresholds, which are: Imax = 59.06D−1.31 (all mass movements), Imax = 21D−0.96 (debris slides), Imax = 11.55D−0.6 (rock slides) and Imax = 4.45D−0.44 (debris flows). For short-duration rainfall events ( 47 mm) can trigger both landslides and debris flows.