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Why can't I define a stream network?

Question asked by fernandocabral on Mar 19, 2012
Latest reply on Feb 12, 2014 by MBoucher21
Id appreciate an opinion from an experienced user of ArcGIS and its Hydrologic Functions.
In order to develop an analysis protocol to my research project on roads drainage in forested areas, I created a mask with a very small portion of the area I'm studying, between two arms of a lake (about 300 km2), with the DEM I have to the whole. I tried to run FLOW DIRECTION, SINK, FILL and then the FLOW ACCUMULATION, as indicated in the help file ("Deriving runoff characteristics"). In a first try, based on the functions sintaxe, I used the output of each function as the input of the following. I noticed that the result of the FILL was quite the same layer/attribute table of its input, the result of SINK; and the final result, from FLOW ACCUMULATION, was a layer with no attribute table! (showed in light grey when right clicking the layer). Then I reinterpretated the help flowchart and decided to run the FILL using the exit from FLOW DIRECTION directly as its  input (the same I had used as an input to the the SINK, which showed a high number of sinks). The result was more consistent, a layer visually quite similar to the input one (at the 1:100,000), but with different values to the 255 registers. HOWEVER, using this raster as an input to FLOW ACCUMULATION led to an apparently infinity loop! It has been runing for 6 hours, when it took me only 1 hour to do the whole process (with many further steps) manually, over the 1:100,000 paper chart. The help file actually prevent us that this may happen, but only if we use an input not created with FLOW DIRECTION. My input is a depressionless DEM created with FLOW DIRECTION, followed by the FILL function. If anyone has time and patience to read me, could you be kind enough to let me know your best guess why I'm not successful in defining the stream network? Moreover, would I need ArcHydro and/or HEC-GeoHMS to do that simple analysis of a big area, with thousands of culverts points (plus the delineation and calculation of main attributes of the watersheds at each culvert). Thank you very much for you attention!