What i was hoping for some help with is if someone knows any other way to do this using the DEM?
Another thing i would like to try is to somehow automatically calculate the widths and/or depths of the drainage ditches.
Mark - based on the DEM example you provided, I think the best you'll be able to do is manually measure a few transects across each ditch to sample the ditch at appropriate points -- and you'll have to decide where the appropriate points are. This appears to be a DSM (including trees & vegetation) or if it's a "bare earth" DEM, then the processing and resolution aren't adequate to do what you're seeking. Any hydro tool will show your water flow stopping at the apparent high points in the ditches (where I believe there is vegetation overhanging the ditch, so the water channel doesn't *appear* to be unobstructed).
If you're seeking a tool to automatically estimate the MAXIMUM width and depth as transects across a linear feature representing the ditch (where the first step is to generate that linear feature), that should be possible, but a mapping of the width & depth of the full extent of the ditches won't be possible (my opinion) given the resolution and processing of your current data.
Hello Cody. Thank you for your reply. Yes you are right it is a DSM. I've created a stream network using the hydrology tools in spatial analyst but like you say the flow stops at certain points in ditchs or flows off in another direction. The best I can think to do now is to manually digitise or extensively edit the stream network.
I've had a look at transects as you suggested. I've just been using the 'Interpolate Line' and 'Profile Graph' functions in the 3D analyst toolbar. However I can't really do much with the data from the graph as it appears to only create a graphic file. Are there any other tools you would suggest to use. How would you automatically calculate the maximum width and depth?