I am performing watershed analysis using Archydro tools in ArcGIS10. After calculating all flow direction, accumulation, drainage network when I perform watershed delineation, it gives me the same boundaries of watershed as of adjoint catchment.

So my question is: can I use the adjoint catchment grid as basin boundaries? Plus, these boundaries don't cover the entire area to be mapped (shown in attached picture). Editing the polygons will change the basin area. What can I do to form a continuous map of river basins in my area of interest? Sample snapshot of my work is attached for further clarification.


1 Answer 1


Can I clarify, did you extract the basin for a specific point that you digitized? If so, did you use the Snap Pour Point tool to reposition your digitized point onto the 'digital' stream (i.e. the path of high flow accumulation derived from the DEM) as per the instructions given by ESRI? If so, this is likely your problem. The extraction of a watershed (or basin, or catchment area, depending on your terminology and location) is highly sensitive to the positioning of outlet points. We use tools like Snap Pour Points so that we don't get 'stub watersheds' (much smaller watersheds than expected) when our outlet point falls off the digital stream. Moving that point by even a single grid cell can result in the mapping of a completely different watershed than the intended. Unfortunately, when the outlet point is positioned near a confluence in the river network, application of Snap Pour Points is very likely to result in a repositioning that will yield a completely incorrect watershed. I talk about this phenomenon in my answer here and a blog here. Ultimately, however, I recommend not using Snap Pour Points and instead use an alternative algorithm developed by Jenson to reposition outlets. Hopefully this is of help for you.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.