Sediment Disasters, Their Types and Classification Principles in Drainage System
流域系统的泥沙灾害类型及其划分原则

The sediment disaster is defined as phenomena of erosion, transportation and accumulation of material on land surface, which gradually advances or surpasses threshold so as to cause casualties and economic loss. It belongs to an independent natural hazard system. The sediment disaster appears when the productivity reaches to a certain level and possesses special attributes in natural, sociology and disaster science, hi accordance with dynamics, geomorphologic location, behavior and particular, it can be divided into two subsystems: natural dynamic and man-induced ones. Then a subsystem is heartily typed as the drainage network, slope and gully, channel and plain-estuary-coastline and classified into 5 patterns, i. e. erosion, transportation, accumulation, complexity and cascading, including 49 and 54 kinds for each subsystem. It is a kind of more comprehensive principle and more systematic classification of sediment disaster up to now. Based on fluvial geomorphology, sediment mechanics and disaster science, the sediment disaster is characterized by: 1) geographic-horizontal zoning, 2) vertical zoning, 3) occurring in group, 4) inherit and period, 5) gradually and sharply changing with human environment vibration, and 6) complexity and non-linear figure, etc. Further study and in-depth analysis should be conducted on real characteristics of various high-concentrated sediment disaster, their processes and mechanism, the coupling relationships among various sediment disasters and quantitative relations between the two subsystems of sediment disaster.