Abstract: It is an important key and foundation to set up a database of spatial water cycle based on GIS technology for developing water cycle information system. In order to match the observation data, the structure of database will be organized according to drainages. So automated extraction of the flow network and drainages is a premise of all other works. This paper puts forward a method that automatically extracts drainages in China from DEM data. This method used DEM data of 1∶250,000 scale, and firstly divided the DEM of whole country into 14 parts based on the drainages extracted from 1 km DEM data; secondly filled sinks and removed peaks in each part; thirdly identified the flow direction of each cell using flowdirection () function; fourthly calculated the flow accumulation of each cell according to flow direction and identified the flow network by setting the threshold value; finally used the watershed() function to find out all the subdrainages based on the flow networks and the watershed outlet. On the other hand, this article listed the AML code for automated extraction drainages from DEM data. Finally the authors checked the result of automated extraction using some surveyed data in Haihe drainage area. Through analysis on the comparison between the flow networks and drainage area that extracted using this method and surveyed data, it is concluded that this method is effective and efficient.

Key words: hydrology, drainage, Digital Elevation Model (DEM), Geographical Information System (GIS), automated extraction