为了从数字高程数据中自动提取区域水资源信息，以提高基于GIS的区域水资源勘查评价工作的效率，提出了一种从DEM中自动提取自然水系的实用方法，该方法通过DEM数据预处理，首先将其中的洼地和小平原改造成斜坡；然后依据水总是沿斜坡最陡方向流动的原理，确定DEM中每一个栅格点的水流方向，再根据各点的水流方向数据，计算出每一个栅格点的上游给水区；接着，根据栅格点上游给水区数值，用阈值法确定水系栅格点，并对水系栅格点进行筛选；最后，根据水系栅格点的水流方向，将整个水系追索出来，另外，还用该方法对试验区的DEM数据进行了自动提取自然水系的试验，其结果与用手工方法提取的水系基本一致，证明该方法是有效的。

Automatic extraction of regional water resource information from digital elevation data can promote the efficiency of regional water resource prospecting and assessment in GIS. Therefore, a practical method for automatic extraction of natural river system from DEM is introduced in this paper. The method, first, needs to pre process DEM data in order to transform depressions and flat areas in the DEM into extended parts of the corresponding slopes. And then the flow direction of every grid point in the DEM is determined according to the theory of which water always flow along the steepest down slope direction. Third, the upstream catchment's area of every grid point can be calculated on the basis of the data of grid point flow direction. Forth, giving a threshlod value of upstream catchment's area picks out the grid points in river lines. Finally, the river system is pursued from DEM according to the flow direction data of grid points in river lines. The method has been applied to extracting the natural river system automatically from the DEM of a testing area. The natural river system extracted automatically with the method is basically consistent with that drew manually based on the corresponding topographical map. This experimental result has proved that the automatic extracting method is effective.