Latest Contributions by MarkBoucher

Fernando, I think you are not following the proper order of the steps. Doing it they way you are explaining does not make sense to me. It helps me to think of the DEM as a physical model I need to manipulate a little before the water will shed off it "correctly". Think of the grids in he DEM as tiles with different elevations. The DEM usually includes grids that are not a the flowline of the creek (bridges/culverst) or poorly defined watersheds such as areas in the flat lands. So, I have to lower the grid in some places and raise it in others in order to make the water flow where is should. Then there are all the minor imperfections in the DEM of small local sinks that need to be filled so the water will flow in the right direction. Once I'm done filling the sinks, I want to have a "hydrologically correct" DEM. Once I have a good filled DEM, the rest should be correct also. With the filled DEM (fil), the flow direction will be "correct" and then the flow accumulation will also be correct. If I find later that an important stream is in the wrong place or an important watershed boundary is incorrect, then I have to go back and correct the fil DEM. If you have Arc Hydro installed, the order of steps in the Terrain Processing in generally the same order as the functions are listed in the Terrain processing menus. You probably don't need to use all of them. My steps using Arc Hydro are as follows: (You can follow these in general with in the Spatial Analyst Tool>Hydrology, but there are not parallel tools there to all the Arc Hydro tools.) 1) Terrain Processing>DEM Manipulation>DEM Reconditioning. Use a polyline layer for the streams to "burn" in the streams where they should be. This lowers the DEM in the vicinity of the stream features.  Many times the DEM will not provide enough definition for the subsequent processes to define streams. It can be helpful to put a short line just a bridges or culverts to "breach" them and avoid fill behind them and flow directions around them. You may need to put in polylines for the streams and major drainage systems in some places. 2) Terrain Processing>DEM Manipulation>Build Walls. Only do this if you need to define a watershed "ridge" in a flat area of the DEM. 3) Terrain Processing>DEM Manipulation>Fill Sinks 4) Terrain Processing>Flow Direction 5) Terrain Processing>Flow Accumulation 6) Terrain Processing>Stream Definition 7) Terrain Processing>Stream Segmentation 😎 Terrain Processing>Catchment Grid Delineation 9) Terrain Processing>Catchment Polygon Processing 10) Terrain Processing>Drainage Line Processing 11) Terrain Processing>Adjoint Catchment Processing 12) Terrain Processing>Drainage Point Processing The above steps assume a simple dendritic system.  If you compare the steps to the Arc Hydro menus you will see that there are a lot of functions that I don't typically use. I recently posted here about Terrain Processing (http://forums.arcgis.com/threads/52110-Terrain-Processing-Steps.?p=178459#post178459). This may also be of help. ... View more