<p>I would recommend looking at automatic stream network delineation and/or known stream locations features, and overlaying those as a check on the final watersheds created through whatever procedure you have. Watersheds can be merged or lumped together, which is fine, you just want to make sure it is consistent with the other information you have and what your goal is. There will always be some variation in the exact extents of the watersheds depending on what algorithm you use, but you should definitely make sure the general areas and drainage patterns are consistent with what you expect. Beyond that, I am not sure there is a correct answer.</p>

CC BY-SA 4.0
2018-06-28T17:09:14.130Z
2018-06-28T17:09:14.130Z
Rob
<p>When I use one DEM in my study area to delineate watersheds, the results are different from when I mosaic 4 DEM layers adjacent to each other. 
After the mosaic process, 3 of the basins were merged in one large basin, and 2 other basins got larger extent.</p>

CC BY-SA 4.0
2018-05-27T23:25:23.440Z
This is a better fit for [GIS Stack Exchange](http://gis.stackexchange.com).
Spencer
CC BY-SA 4.0
2018-05-28T13:24:16.337Z
@Spencer I agree that it would probably get better answers there, but I think it's still on topic here as well. Spirit Garden might want to request a transfer to GIS.SE if they don't get answers here in a few days.
Semidiurnal Simon
CC BY-SA 4.0
2018-05-28T14:19:24.043Z
What meters do you have in these 4 DEMS ?
PROBERT
CC BY-SA 4.0
2018-06-02T14:52:12.873Z
the maximum elevation reaches around 235 meters, I noticed that the presence of the sea water body alters the results, but when clipping the mosaic and removing the water body, the basins are back to what they were.
Spirit Garden
CC BY-SA 4.0
2018-06-29T01:03:34.643Z
I'm not clear why this is surprising. You will get edge effects if the basins are truncated by splitting the landscape into separate layers.
haresfur
<hydrology><gis><watershed>
how to know the correct results in watershed delineation in ArcGIS?
Spirit Garden
# how to know the correct results in watershed delineation in ArcGIS?

(Asked by: username_0 on 2018-05-27)

When I use one DEM in my study area to delineate watersheds, the results are different from when I mosaic 4 DEM layers adjacent to each other.
After the mosaic process, 3 of the basins were merged in one large basin, and 2 other basins got larger extent.

**Tags:** hydrology, gis, watershed

> **Comments:**
> **username_1**: This is a better fit for [GIS Stack Exchange](http://gis.stackexchange.com).  
> **username_2**: @username_1 I agree that it would probably get better answers there, but I think it's still on topic here as well. username_0 username_0 might want to request a transfer to GIS.SE if they don't get answers here in a few days.  
> **username_3**: What meters do you have in these 4 DEMS ?  
> **username_0**: the maximum elevation reaches around 235 meters, I noticed that the presence of the sea water body alters the results, but when clipping the mosaic and removing the water body, the basins are back to what they were.  
> **username_4**: I'm not clear why this is surprising. You will get edge effects if the basins are truncated by splitting the landscape into separate layers.  

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## 1 answers

### Answer by username_5 on 2018-06-28. Score: 1

I would recommend looking at automatic stream network delineation and/or known stream locations features, and overlaying those as a check on the final watersheds created through whatever procedure you have. Watersheds can be merged or lumped together, which is fine, you just want to make sure it is consistent with the other information you have and what your goal is. There will always be some variation in the exact extents of the watersheds depending on what algorithm you use, but you should definitely make sure the general areas and drainage patterns are consistent with what you expect. Beyond that, I am not sure there is a correct answer.


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