Watershed area calculation

Thomas Adams adams at ohrfc.noaa.gov
Tue Jan 27 07:00:00 EST 1998

I'm getting discrepencies (which are expected) between various methods
of determining/calculating watershed areas. These are my 'methods':

(1) look them up based on USGS streamgage locations;
(2) use the GRASS 4.1 program v.area, applied to vector boundaries
determined elsewhere.
(3) approximate the area calc. using the count from r.stats, following
use of v.to.rast to get a raster mask area for each basin & multiply by
the *approximate* pixel area (3 arc-sec grid, ~90x90 m^2 between lats 38
to 40 deg. N)

My 'errors' are ranging 5-10%; I do need to be consistent, and
(obviously) would prefer what's best & what makes the most sense.

The vector boundaries in Method-2, above, appear reasonable when
compared to the underlying (3 arc-sec) terrain; so, my guess is that
this will provide the most consistent & reproducible areas.

All comments are appreciated...

Tom Adams                              adams at ohrfc.noaa.gov
Development & Operations Hydrologist   NWS-Ohio River Forecast Center
1901 S. State Route 134                Wilmington, OH 45177
(937) 383-0527 (VOICE)                 (937) 383-0033 (FAX)

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