I'm trying to delineate a watershed in an area where many open regional drainage ditches exist. The problem I'm running into is that the DEM from USGS doesn't account for culverts so when a roadway crosses over one of these ditches, it shows up as a break when I run the Flow Accumulation tool. The result is areas that should be part of a watershed not getting included.
The (possibly) good news is that I have a shapefile of the major, county maintained ditches. Even they have breaks where major roads cross over them, but that can be easily edited. Is it possible and/or correct to incorporate these into the flow accumulation raster? My thought was to convert the flowacc raster to a vector, merge the drainage system shapefile to it, and then convert it back to a raster. One potential issue I foresee is that the system shapefile doesn't exactly align with the flowacc raster. Perhaps there is a better or more correct way. I hope there's some guidance out there.
