WSP03306

• File Number: 8281.300
• Description: Colorado River Studies and Investigations - Colorado River Consumptive Uses and Losses Report
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1984
• Title: Colorado River System Consumptive Uses and Losses Report 1976 - 1980
• Water Supply Pro - Doc Type: Report/Study

:-:'~~t
1
J
,
j'

t
I
I
I

c

Crops in the Southwestern United
States," issued. May 1982 by the United
States Depart~ent of Agriculture.
Effective precipitation was derived
from criteria developed for the area by
Wayne D. Criddle, former Utah State
Engineer.
These theoretical consumptive use
calculations were based on the assump-
tion of full water supply during the
crop 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 supply of water, either due to
lack of distribution facilities or
junior water rights. The degree ~o
which these Hinds suffer shortages
varies widely from year to year,
depending in large part on the magni-
tude of runoff. For this study, an
estimate of the short suppl-y 'service
lands was made for each sub-basin,
primarily on the basis of reports and
inves t igat ion's co llec ted for the
comprehensive' framework study. A
stream-flow gaging stat~on was selected
within each sub~basin and the magnitude
of the recessional portion of the
annual hydrograph was used as an index
to select the date at which consumptive
use calc'ulations should be terminated
for the short supply lands.
Comprehensive framework studies of
the incidental consumptive use of water
associated witn irrigation indicated
that this use varied between' 5 and 28
percent of the irrigation consumptive
use depending upon the location of the
study area within the Colorado Basin.
These percentages were used in the
Upper Basin and an average value of l5
percent was used in the Lower Basin to
adjuat the calculated consumptive
use.
The agricultural data is generally
adequate for use in this report. With
the exception of Utah, each state
pre pared annu'al coun t y i rr igat ed
acreage estima'tes of the harvested
crops during the reporting period.
These statistics are assumed to be
reliable. The irrigated pasture values
were based largely on the 1978 National
Census of Agriculture since the State
statistics do not include pastureland.

w
~
lA.
~

Due to the length of time between
reporting dates, this item needs to be
considerably strengthened. In this
regard, Wyoming and New Mexico have
initiated aerial photographic' mapping
of their State's irrigated acreage to
verify the annual statistical sampling.
Other areas of agricultural data
collection Which need to be updated and
verified are 0) 'the consumptive water,
use of lands which receive less than a
full seasonal supply of irrigation
water and the areal extent of these
lands, and (2) the,amount of incidental
seepage and phreatophytic losses
associated with irrigation.

Reservoir Evaporation: A comprehen-
s.ive listing was developed ,of all
reservoirs in the Colorado River Basin
which included the_ latitude, elevation,
and surface area at total capacity for
each reservoir.
Monthly content records were ob-
tained for those, reservoirs for Which
records are available. The average
annual water-surface area was deter-
mined for each year of the reporting
period. For those reservoirs lacking
records, a "fu lines s tac.tor" was
estimated on the basis of reservoir use
and historical hydrologic 'conditions.
These "fullness factors" were then used
to obtain es timates of average annual,
water-surface area for the unreported
reservoirs.
For tha ~ajority of the basin,
historical evaporation rates were used
to determine reservoir evaporation.
In the Upper Basin, regression
equations relating gross annual evap-
oration to elevation, latitude, and
climatic subarea were developed for
each of the reporting years. In the
Lower Basin, evaporation values were
calculated for each climatic subarea.
Account was taken of precipitation and
runoff salvage to determine net evapor-
ation rates. The net evaporation rates
were applied to the estimates of
average annual water-surface area to
yield the values of annual reservoir
evaporation.
An exception to this procedure was
the determination of evaporation from
the main stem reservoirs shown in

13