Numerical Simulation of Debris Flow Affected Area Caused by Different Precipitations

Typhoon Morakot struck south Taiwan in 2009, and caused severe debris flow hazards damaging resident houses and infrastructures in the downstream affected area. In order to understand the affected area of the debris flow caused by different rainfall, field investigation of the debris flow affected area was conducted for five debris torrents that were triggered by both Typhoon Morakot in 2009 and Typhoon Kalmaegi in 2008. The debris flow affected area and depth of sediment on debris flow sediment fan were traced and measured after Typhoon Morakot. Numerical simulation was conducted using FLO-2D to understand the affected area, velocity of debris flow and depth of sediment by typhoons Morakot and Kalmaegi. The simulation results suggested that the higher accumulated rainfall leads to larger sediment volume, higher flow velocity, and larger affected area. However, the ranges of debris deposition were affected by the terrain and rainfall pattern. The simulation results provide good references the mitigation of the debris flow hazards.