WSP07709

• File Number: 8281.300
• Description: Colorado River Studies and Investigations -- Colorado River Consumptive Uses and Losses Reports
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1977
• Title: Colorado River System Consumptive Uses and Losses Report -- 1971-1975
• Water Supply Pro - Doc Type: Report/Study

OPPER COLORADO RIVER

Irrigation Consum~tive Use: The determination'
of annual irrigate4 acreage and crop distribu-
tion during the reporting period was made
using the 1969 N~tional Census of Agricul-
ture, annual StatelAgricultural Statistics Re-
ports, Bureau of R~c/amation Crop Inventory
Reports, and vario~s inventory and planning
reports issued by the Upper Basin States.
. Since most of thes~ data were presented on a
county basis, it wa~ necessary to separate
them into reportingiareas and smaller sub-
basins for computa~ional purposes. This was
accomplished by uSIng land inventory maps
and relationships d~veloped for the com-
prehensive framewotk study.
For purposes of computing irrigation con-
.
sumptive use, the Upper Colorado River
Basin was divided into 58 sub-basins to ac-
,
count for local const\mptive use require-
ments. These sub-basins generally follow
tributary stream basib and State boundaries. A
representative climatic station was selected
for each sub-basin. U,sing historical records of
temperature, precipit~tion, and frost dates,
a consumptive use rat.e was computed for
each major crop in ea~h of the reporting
years. For the purpose\of this report, the con-
sumptive use rates wete computed using the
modified Blaney-Criddle evapotranspiration
formula in the version l:iescribed in the Soil
Conservation Service Tbchnical Release No.
21, "Irrigation Water ~equirements," re-
vised September 1970; Irrigation consump-
tive use rates were determined by subtracting
the effective precipitati!ln from the consump-
tive use rates. Effectiveiprecipitation was
computed using criterialdescribed in the U.S.
Department of Agricultu~e, Agricultural Re-
search Service. Technic~1 Bulletin No. 1275.
The values of irrigation cpnsumptive use rates
were applied against the\estimates of irri-
gated acreage to yield tha final values of irriga-
tion consumptive use. '
The theoretical consumptive use determina-
tions are based on the as~umption of full
water supply during the c~op growing season.
However, it is estimated that in an average
year about 37 percent of the irrigated lands

in the Upper Basin receive less than a full sup-
ply of water, either due to lack of distribution
facilities or inferior water rights. The degree to
which these lands suffer shortages varies
widely from year to year, depending in large
part on the magnitude of runoff. For this
study, an estimate of the short supply service
lands was made for each sub-basin. primarily
on the basis of reports and investigations col- -
lected for the framework study. A streamflow
gaging station was selected within each
sub-basin and the magnitUde of the reces-
sional portion of the hydrograph was used as
an index to select the date at which con-
sumptive use calculations should be termi-
nated for the short supply lands.
Comprehensive framework studies of the in-
cidental consumptive use of water as-
sociated with irrigation indicated that this
use amounted to a magnitude ranging from 5
to 28 percent of the irrigation consumptive
use depending upon location of the study area
within the Upper Basin. lacking an up-to-date
inventory of incidental use lands, these per-
centage adjustments were retained for use in
this study and applied against the annual es-
timates of irrigation consumptive uses. The
total irrigation consumptive use and inci-
dental consumptive use associated with irriga-
tion are reported in tables UC-3 to UC-7.

Reservoir Evaporation: A comprehensive listing
of all reservoirs and stockponds in the Upper
Basin was developed. This listing included
information about major reservoir use, loca-
tion, elevation, total capacity, and surface
area at total capacity. The listing was brought
up to date and is now kept current.
Monthly content records were obtained for
those reservoirs for which records are avail-
able. The average annual water-surface area
was determined for each year of the reporting
period. For those reservoirs lacking records, a
"fullness factor" was estimated on the basis of
reservoir use and historical hydrologic condi-
tions. These "fullness factors" were then used
to obtain estimates of average annual water-
surface area for the unreported reservoirs.
Regression equations relating gross annual
reservoir evaporation to elevation, latitude.

11

o
C)
~
(;::;
....
CJl

;.o.~"''\''"
""',;
I~"!"
., ,,::< .~,
Wi>,

i*:;;
.e'-':
t~;
~~

t ,'"
I,;
i~~
r,',.',',',-,

f'
....