4001

• UCREFRP Catalog Number: 4001
• Author: U.S. Bureau of Reclamation.
• Title: Colorado River System Consumptive Uses and Losses Report 1976-1980.
• USFW Year: 1981.
• USFW - Doc Type: Washington, D.C.
• Copyright Material: NO

Methodology and data Adequacy
This report is based almost entirely
on data obtained from ongoing programs
and current reports. `Quantitative
measurements of water use-were used
wherever available, but the majority of
the basin water use was theoretically
calculated. The following sections
describe- these calculations .for both
the Lower Colorado River Mainstream and
the Upper and Lower Colorado River
Basin tributaries.
Colorado River Basin Tributaries
In the tributary areas of the basin,
records of diversions and return flows
are not complete enough to allow direct
calculation of consumptive water use,
Theoretical and indirect methods of
estimating consumptive use must. then be
relied upon. In the New Mexico portion
of the Gila River Basin, the annual
consumptive use of water is reported by
the New Mexico Interstate Stream
Commission, pursuant to article VII of
the March 9, 1964, decree of the United
States Supreme Court in Arizona v.
California, et al.
Agriculture: About 85 percent of the
consumptive use in the areas tribu-
tary to the Colorado River mainstream
is for irrigated agriculture. The
annual irrigated acreage of most
crops grown within each reporting area
was estimated from information pub-
lished in the yearly State Agriculture
Statistics. Irrigated pasture and
same minor crops not reported by the
State statistics were estimated from
information in the 1978 National Census
of Agriculture with supporting informa-
tion from the comprehensive framework
study and various other local reports.
The total irrigated acreage values for
the Upper and Lower Basins are shown in
tables UC-7 and LC-9, respectively.
Since most of these data were
presented on a county basis, it was
necessary to separate them into smaller
reporting areas: for computational
purposes. This was accomplished using
land inventory maps and. relationships
developed for the comprehensive frame-
work study.
These -sub-basins generally follow
tributary stream .basin and State
boundaries. A representative climatic
station was selected for each sub-
basin. Using historical records of
temperature, precipitation, and frost
dates, a consumptive use rate was com-
puted for each major crop in each of
the reporting years. For- the purpose
of this report, the consumptive use
rates were computed using the modified
Blaney-Criddle evapotranspiration
f`brmula in the version described in the
Soil Conservation Service Technical
Rel`~ase No. 21, "Irrigation Water
Requ'irements," revised September 1970.
Irrigation consumptive rates were
determined by subtracting the effective
precipitation from the consumptive use
rates. Effective precipitation was
computed using criteria described in
the U.S. Department of Agriculture,
Agricultural Research Service, Techni-
cal Bulletin No. 1275. The values of
irrigation consumptive use rates were
applied to the estimates of irrigated
acreage to yield the final values. of
irrigation consumptive use.
An exception to this procedure
occurred in the Lower Basin in the "low
desert" regions of Arizona and Nevada
where the Blaney-Criddle formula was
used to estimate the crop consumptive
use. This departure was based on
the research results of Leonard Erie,,
et. al. Seasonal crop consumptive use
factors ("K") for the lower elevation
desert areas were selected from Conser-
vation Research Report Number 29,
"Consumptive Use of Water by Major
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