wbw

Trouble Getting Flow Direction on Fairly Flat Land

Discussion created by wbw on Jan 24, 2013
Latest reply on Jan 16, 2015 by mlago16
I'm trying to use ArcHydro to find watersheds and flow patterns in an urban area within a river's floodplain.  Within the district scale site there is a large, flat area where water collects (this urban district is surrounded by levees, so water flows and collects in this specific area).  This is my specific area of study. 

When I use the Fill Sink tool, it makes the entire area one color as if there is no elevation change.  When I use the Flow Direction tool on the incorrect Fill Sink raster, the Flow Direction output has the proper color directions (1,2,4,8,16,32,64,128) but still shows the area as completely flat.

If I run the Fill Sink tool on the DEM again, but this time with a Threshold value of 1, the output Fill Sink shows true elevation differences within the area.  However, when I use the correct-looking Fill Sink raster in a Flow Direction tool, a correct-LOOKING Flow Direction raster appears but with values 1-255.  I cannot move forward with this correct-looking data with the wrong values. 

Does anyone know how to get to Flow Direction to output the correct elevation differences?

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