i'm trying to delineate watersheds for an urban catchments using the ArcHydro Tools. My area of interest covers urban and suburban parts. While the outter part of my catchment is of comparably higher elevation, hence topography driven flow can easily be derived by the classical procedure (flow direction, accumulation, stream definition, segmentation etc.), the core of my study area is flat and the drainage takes place by open-channel flow. In the centre of my catchment is a larger sink everything is draining towards. From there the water flow continues via a canal towards the border.
However, I'm not capable of deriving flow directions which follow the open-channel flow. I'm familiar with the general ArcHydro Tools and procedure for larger, steeper catchments i reach my limits processing this dataset.
What I tried so far is to use DEM reconditioning inserting the polyline representing the open-channel network, but it doesn't solve the problem. The drainage lines i obtain do not match with my drainage network. I'm not sure whether I inserted wrong values for DEM reconditioning or if its generally not suitable for flat terrain?
Some parts of the canals and the major sink in my study area are below sea level and whenever I apply Fill Sinks my elevation range is drastically affected shifting the values to positive range. So I think it might be reasonable to leave out that function.
I've been through most of the discussions here where urban watershed were tackled. I couldn't find a similar topic yet, although I guess I need to burn my streams by DEM reconditioning. Also I read about setting up inner walls hindering the flow at certain points, but I haven't worked that way so far.
Hints and ideas how to overcome this puzzle are highly appreciated.