WSP08519

• File Number: 8281.300
• Description: Colorado River Studies and Investigations - Colorado River Consumptive Uses and Losses Report
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 6/1/1991
• Title: Colorado River System Consumptive Uses and Losses Report 1981 - 1985
• Water Supply Pro - Doc Type: Report/Study

Consumptive Uses and Losses 11
0 acreage estimates of the harvested crops
\...:) during the reporting period, These basin, historical evaporation rates were
~ statistics ~ assumed to be reliable. used to determine reservoir evaporation.
N
0 The irrigated pasture values were based
Q largely on the 1978 and 1983 National In the Upper Basin, a multiple
Census of Agriculture since the State regression equation relating gross
statistics do not include pastureland. annual evaporation to elevation and
Because or the length of time between latitude was developed. Adjustments to
reporting dates, this item needs to be computed evaporation were made based
considerah~y strengthened. In this on climatic subareas. In the Lower
regard, Wyoming and New Mexico have Basin, evaporation values were
initiated a~rial photographic mapping of calculated for each climatic subarea. An
their State,'s irrigated acreage to verify account was taken of precipitation and
the annual statistical sampling. Other runoff salvage to determine net
areas ofagricultural data collection that evaporation rates, The net evaporation
need to be updated and verified are rates were applied to the estimates of
(1) the con$umptive water use of lands average annual water.surface area ,to
that receive less than a full seasonal yield the values of annual reservoir
supply of irrigation water and the areal evaporation.
extent ofthese lands, and (2) the
amount of incidental seepage and An exception to this procedure was the ":~
phreatoph1tic losses associated with determination of evaporation from, what ,iJ
irrigation. are called the main stem reservoirs
shown in table UC-l. Predetermined
ReservoIr Evaporation average evaporation rates were applied
to historical surface areas to yield values
of evaporation on a monthly basis.
A comprehensive listing was developed
of all reservoirs in the Colorado River
Basin which included the latitude, Ground Water
elevation, and surface area at total
capacity for each reservoir. Currently, all ground-water pumpage is
counted as consumptive use charged
Monthly content records were obtained against the Colorado River Basin.
for those reservoirs for which records Obviously, this is not necessarily true.
are available. The average annual Depending on the location and depth of
water-surface area was determined for the well and what types of soils are
each year of the reporting period, For present in the area, it is possible that
those reservoirs lacking records, a little or none of the water pumped would
"fullness fa~tor" was estimated on the have contributed to the Colorado River
basis of reservoir use and historical System for hundreds or even thousands
hydrologic conditions. These "fullness of years. It has recently been proposed
factors" were then used to obtain that an interagency study team be put
estimates of average annual water- together consisting of personnel from
surface area for the unreported various State Engineers Offices, Bureau
reservoirs. . For the majority of the