Doing watershed delineation properly using ArcGIS Desktop?

Question

I am using ArcGIS Desktop 10.2.

I have the contours and the stream in AutoCAD Civil, after converting to a shapefile, I exported them in GIS,

after I created the TIN from the contours below:

next I created the raster with the command TIN to raster :

after creating the raster, I started using the arc-hydro tool, with DEM recognition, using the raster and the flowline, but I don't think the result of the AgreeDem is proper:

Continuing with the fill sink option using the AgreeDem

after I did the flow direction part using the fill sink's results:

the next step is flow accumulation using the results from flow direction, but I don't think that the streams should be divided like I have in my results

in stream definition I can obviously see that the results aren't as they should be, because there is no connection between the streams

and if this part isn't proper neither the stream sedimentation nor catchment will be properly done or the catchment polygon which has same strange square shapes in some parts

I have tried several times, but I don't know what to do in order to get the right results.

Answer 1

Watershed delineation is tricky, I usually include a larger area then my study area so I don't have anything weird at the edges. i.e. like the edges are cliffs or walls. With that being said, I also include a background stream layer to check that my calculated stream fits the background stream. This stream layer could be a topo map, just to confirm my data is following nature.

Your process looks good, however you need to overlay your streams over the basin layer. This may show your basin size is too small, you have a basin for every little stream segment. By increasing the basin size you will get a basin for each stream tributary.

Check your data by putting the basins layer over the tin, the polygon boundaries should follow the tin ridges. If it does your process is good. It's just not what you expected to see, which I guess was only a few basins.

It's like your trying to map forest cover but your data is showing every tree.

Answer 2

It looks like your issues may in large part be caused by the large flat in the NE portion of your basin. Different pit filling and flow direction algorithms will handle this area differently, and it looks like the one you are using is forcing the flow out of your basin instead of into your expected network.

First, Bill Chappell's answer provides some good advice about running these algorithms on a DEM that is larger than your basin. This reduces any confusion in ridge cells. If you have the option, buffer your expected watershed and use that mask for selecting your DEM.

To handle this large flat area, you may want to employ a Carving/Breaching algorithm rather than a filling one. ArcGIS does not includes one, but open source tools like Whitebox GIS include lots of good options. Alternatively, if you are confortable with your vector stream data, you could rasterize these lines and then burn them into your DEM by subtracting a nominal value from the DEM in all cells coincident with the stream. This will force flow into those pixels and connect the rest of your DEM to your network.

Answer 3

As noted by Bill Chappell you would likely benefit from getting more DEM coverage. Ideally, I would hope that my resulting watershed boundaries would not intersect the DEM limits. Your data is hitting the NO DATA in the DEM like a wall.