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internetofwater / ref_gages

Reference Stream Gages
https://internetofwater.shinyapps.io/geoconnex-reference-features/
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Basin area discrepancy between NLDI and NHD #27

Open cheginit opened 1 year ago

cheginit commented 1 year ago

I found two USGS stations where the area of the NLDI's delineated basin geometry is way off compared to the total drainage area provided by NHD. The IDs are:

dblodgett-usgs commented 1 year ago

USGS-01446000 has a stated drainage area of 36.7 sqmi in NWIS which matches NHD. image

This looks like it's got the wrong major river.
EDIT: Yeah, I need to see why the reference gage linking logic isn't getting this one right. I have a theory but need to investigate.

USGS-11295230 has a stated drainage area of 29.3 sqmi in NWIS which matches NHD. image

This looks OK to me... not entirely clear what would be wrong in this case.
EDIT: upon closer inspection, this one is actually a diversion that is adding drainage area that is probably not included in the NWIS and NHD estimate because of how drainage area is calculated vs. how drainage basins are delineated. When we add up drainage area, we ignore diversions but when we delineate a basin polygon we include all network connections (diversions included).

@cheginit -- where are you deriving the NHD identifiers that link gages to the network from?

cheginit commented 1 year ago

@dblodgett-usgs I got the associated NHD IDs of the station from the Gage layer of the NHDPlus (MR). From this layer, I extracted the NHD areas and IDs of all CONUS stations and put them in a gist.

When we add up drainage area, we ignore diversions but when we delineate a basin polygon we include all network connections (diversions included).

That's an interesting distinction between the basin polygon and drainage area.