Error delineating large watersheds

michaeldurand[CodePlex]
It seems there's a built-in limit to the watershed size I can delineate, of about 1000 km2. While that is totally fine, maybe the software should produce an error or message stating that the watershed was not delineated correctly. It could easily be misleading,
as is.

To reproduce: try delineating the Olentangy River (in HUC 0506) at the confluence with the Scioto River, near Columbus. The watershed returned shows a watershed boundary that crosses right across the Olentangy River itself. The watershed area is about 1000
km2... should be 1400 km2 or so.

Start by reproducing watershed delineation for the Olentangy River at its confluence with the Scioto River near Columbus, using HUC 0506, and inspect the delineation entry point. Confirm the approximately 1000 km2 limit and make sure an incorrect or incomplete delineation produces a clear error or warning rather than a misleading boundary.

Written by the indexing model from the issue text.