Watershed analysis is very important for water resource management, since it is the basis for hydrologic modeling. It is therefore important to precisely delineate watersheds in order to define catchment areas. Though watershed delineation by manually digitizing on a map is widely used, it is at the same time a very time consuming and possibly error-prone method.
ArcHydro, a tool in ESRI® ArcGIS 9.x, has been developed especially for dealing with water resource modeling. To faciliate the most basic use of this software, which is watershed delineation and defining catchment areas, Digital Elevation Models (DEMs) have to be used. Based on this three-dimensional terrain information ArcHydro is able to automatically calculate watersheds and catchment areas.
DEMs can be derived from any kind of elevation data such as contour lines or elevation point data and this elevation data can also be derived directly from satellite data. This article will demonstrate how watersheds are delineated using elevation data from satellite radar imagery (Satellite Radar Thematic Mapping (SRTM)).