The main purpose of this paper is to undertake the relationships between the occurrence’s mechanism of debris flow and the geologic, topographic , hydrologic characteristics and the hu- man activities are reviewed in order to discuss the active counter measure.

Using mass conservation law of debris flow which passing through a slit dam and laboratory experiments, this paper has established three primary efficiency parameters: the sediment flow out ratio, sediment concentration ratio, and sediment storage rate behind the slit dam.

This paper introduced the debris-flow monitoring and warning system in Taiwan.