Small catchment are basic management units in the flash flood disaster control planning(FFDCP) in China. This paper discusses a method for extracting small catchments units by using lots of available data sets in FFDCP, including DEM and data related to streams, climates, relief, lithology, etc., on the basis of stream system and catchment units extracted for surface runoff simulation and analysis. Division of fundamental geographic units and grouping of environmental factors are firstly conducted, then on this basis, stream systems and small catchment units are extracted by dividing a provincial planning unit into several different geographical subregions with different contributing area thresholds respectively. Derived small catchment units are further subdivided and merged to meet the requirements of FFDCP.
flash flood disaster
small catchment extraction
geographical unit division
contributing area threshold for a stream