I would like to do some watershed delineation research/development (at the County level) with our LIDAR generated DEM, after it is corrected, but am wondering what, if any, differences might result from using the hydrology toolbox to generate watersheds or the ArcHydro suite of tools? I will probably try both toolboxs but am curious if anyone has done anything similar? The tools and workflow between both seem similar, at first blush, so I am wondering what the differences would be between the tools...algorithms? Am using ArcInfo 10.0.
I found an answer to this on the ArcGIS Discussion Forums where Crystal Dorn back in 2007 says more or less the same as @GetSpatial:
The core Hydrology tools serve as a foundation for the ArcHydro extension.
The ArcHydro extension helps with the overall workflow of building a hydrologically correct elevation surface amongst other things. It has nice menus organized in order of how most hydrology projects would start to finish, so it helps you keep track of the processing flow.
A great example, the core Hydrology tools include a "Fill" function, but that only does one iteration of filling sinks -- the next step is often run 'Sink' again to find if there are still sinks to Fill and so on and so on. Fill often requires iterative processing until all sinks are filled and the ArcHydro tools are a big help here b/c you just run it and let it finish and it will figure out the iterations for you.
But there are many more custom written tools that are on the ArcHydro toolbar to help in analysis and hydrology dataset building. I've found them to be a big time saver.
ArcHydro also includes a data model you may find useful for modeling your resulting hydrology datasets in the Geodatabase.