Debris-flow simulations for Tsing Shan in Hong Kong

Debris flow is a dangerous form of natural landslides because of its unpredictable nature of occurrence. Recently, the risk of debris flow in Hong Kong increases tremendously because of the rapid development of rural areas next to steep terrains. For example, the largest reported debris flow occurred on September 11, 1990 and located at the Eastern flank of Tsing Shan (or Green Mountain) next to a construction site. The objective of this paper is to conduct a back analysis for the 1990 Tsing Shan debris flow. Both the extent and depth of the debris are simulated using a computer model developed by Takahashi et al. (1992). Typical debris flow parameters for Hong Kong are calibrated by comparing the deposition fan with the field observation. The histrograph of discharge for the simulation is set-up by referring to the record of the debris flow resulted from the Mount St. Helens eruption. The original model by Takahashi et al. (1992) is found not resulting in satisfactory shape and runout of the deposition fan, thus a new erosion criterion has been adopted by using the minimum streampower concept. The results of the current approach did give a better comparison with the actual field observations. Further simulations and parametric studies are still required before a robust model can be used for debris flow hazard estimation for other areas of Hong Kong.