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Compute Basin Data


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I have a question about watershed delineation:

I'm using a shapefile polygon to map new drainage boundaries. I am getting these errors when trying to Compute Basin Data: 

"Basin edges were encountered while computing the maximum flow distance for the following basin(s): 1"

"Basin edges were encountered while computing the maximum basin length for the following basin(s): 1"

My new drainage values are still generated and I can successfully continue my GSSHA model and generate a hydrograph. I'm just wondering what these errors means and how I can avoid them. Thanks


The process I'm following is this:

1. Add DEM data

2. Add outlet and Delineate Watershed

3. Map Shapefile polygon to the same drainage coverage 

4. Delete Drainage delineated by DEM

5. Select new polygon and change it to Drainage Polygon Type

6. In Drainage Module, DEM, I click in Polygon Basin IDs->DEM

7. In Drainage Module, DEM, I click in Polygon Basin IDs->Compute Basin Data

Errors appear after this.








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Those 2 messages are normal if you have modified the WMS-computed basin boundaries.  They show up because WMS follows the flow directions on your DEM to compute the maximum flow distance and the maximum basin length.  If basin edges are encountered while following the flow directions, you get this error because the flow directions will usually intersect the basin boundary if you have modified the basin boundaries from the boundaries WMS-computed boundaries (WMS uses the original flow directions and accumulations to compute the boundary to begin with, so if you change the boundaries, you'll almost always get this error message).  It's probably not a big issue for what you're doing since WMS should still be able to find an approximate flow distance and max basin length if you need those values for computing the Time of Concentration or another watershed parameter.  You might want to keep an eye on these parameters that WMS computes though to see that the values look reasonable.

Hope this helps,


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