The Urubamba River exercise, additionally, illustrates the burning-in streams process used to improve the stream delineation. When using DEM's, it is often the case that the relief is not accurate enough to delineate the stream networks in flat areas. Burning streams is a very useful technique for identifying stream locations in flat areas where high resolution DEMs are not available, but this technique should be used with caution. Filling pits is typically the first processing step taken after a DEM is projected into the chosen map projection. Pits are cells or groups of cells which are completely surrounded by cells of higher elevations.
Some pits are artificial while others represent real inland drainage basins.
It is sometimes difficult to distinguish between real pits and artificial pits automatically by using the DEM alone. Two criteria that are useful for identifying real pits are the pit depth and area. Starting with a DEM and a SCS curve number grid, CRWR-PrePro delineates streams and watersheds, calculates parameters for each of them, determines their interconnectivity, and prepares an input file for HMS that includes the computed hydrologic parameters. The first attempt to connect GIS data layers with HEC's HMS was developed by F. Hellweger and D. Maidment. Graphics depicting some Exciting Success Stories illustrate the application of CRWR-PrePro to basins of the City of Austin in Texas, of the Upper Mississippi and Missouri Rivers, and of the Niger River in West Africa.