WSP07539

• File Number: 8281.300
• Description: Colorado River Studies and Investigations - Colorado River Consumptive Uses and Losses Report
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 10/1/1991
• Title: Consumptive Uses and Losses in the Arizona Portion of the Upper Colorado River Basin for the Water Year 1990
• Water Supply Pro - Doc Type: Report/Study

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Consumptive Uses and Losses

14

These values are found in table 5. The percentage of crop water requirement
met was multiplied by the total net crop water requirement to come up with
the amount of crop consumptive use. Incidental irrigation losses, evaporation,
and phreatophyte consumptive use along supply canals are estimated to be
5 percent of the consumptive use of the irrigated area and are added to
the crop consumptive use value to develop a total consumptive use value.

If a full supply of water was assumed for all the irrigation projects in
table 5, the total consumptive use of water by the crops would be about
6,710 acre-feet for 1990.

In addition to those lands associated with developed irrigation projects, a
number of small irrigated plots of about 1 to 2 acres each are found in Canyon
de Chelly and Canyon del Muerto. In 1985, this land comprised less than
100 acres. There are also small plots of land located in Piute Canyon which is
on the northern border of Arizona, east of the city of Page. These irrigated
plots typically lie on small benches a few feet above the level of the stream and
are irrigated by constructing small earth and brush dams to divert the
upstream flow. Farming in these canyons has been carried out in this manner
for hundreds of years. It has been mentioned that this land is mostly dry land
farmed at the present time, since the diversion dams have been damaged and
the canals are no longer in use. The crops grown consist mainly of corn and
small vegetables, and consumptive use on these small canyon plots was
estimated using the same method as the project irrigation lands. Total
acreages have not been confirmed, and it is suggested that for future studies
further investigation of productive acreages be completed. As a result, "plot"
irrigated acreages inventoried for previous reports were used for this report and
are included in table 4 and table 5 as Nonproject Irrigation.

Not all of the water used for irrigation at these sites should be considered a
depletion to the Colorado River. Some of the water now diverted to irrigated
crops and not consumptively used would likely have evaporated or been
consumed by phreatophytes before returning to the Colorado River -since
evaporation rates in the area are high and the nature of most of the drainages
enhances evapotranspiration. A good example of such a drainage is Chinle
Wash which, after it leaves Canyon de Chelly, becomes wide and sandy and is
lined with willows, cottonwoods, and other phreatophytes.

The uncertainties in the irrigation consumptive use values displayed in table 5
are very large and are estimated as 40 percent, resulting in an uncertainty of
(:1:1,380) acre-feet. This estimate of possible error only reflects the uncertainty
of consumptive use and does not account for any possible errors in the acreage
estimates. The effective consumptive use for irrigation for 1990 was estimated
to equal 3,450 acre-feet. With the 5 percent for incidental losses, the irrigation
related consumptive use is 3,620 (:1:1,450) acre-feet.