WSP11664

• File Number: 8220.128.J
• Description: Silt Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 8/1/1961
• Title: Report of the Reappraisal of Direct Agricultural Benefits and Project Impacts - Silt Project-Colorado - Part 1 of 2
• Water Supply Pro - Doc Type: Report/Study

N
C)
M Adequacy of Water Supply

Irrigation water for the Silt project is now supplied by direct diversion
of the natural flows of East Rifle Creek, supplemented by releases from
the existing Harvey Gap Reservoir. This reservoir is filled during the
winter and spring months when stream flows exceed the needs of downstreu.
users. Lands in the Dry Elk Valley are upstream from the Harvey Gap Reser-
voir and hence receive water only by direct diversions from East Rifle Creek.
During the spring snowoo1llelt period, the flow in the creek is usually greatly
in excess of the irrigation requirements for all lands which use it. both
project and non-project. By early summer, however, the flow dim inishes
rapidly and is insufficient to meet the irrigation demands, As a result,
the Dry Elk Valley lands with their junior water rights are unable to
obtain irrigation water subsequent to midsummer, and crop yields are
adversely affected. Bureau of Reclamation operations studies indicate
that the total historical supply avall~~le to the presently cultivated land
in Dry Elk Valley has amounted only to about 35 percent of seasonal require-
ments on an ideal demand basis for a normal rotation cropping pattern.

Lands on Davie Mesa have previously been subjugated and placed under irriga-
tion. Irrigation water was diverted directly from Rifle Creek near the
Rifle Gap Reservoir site. The available water rights were of such low
priority, however, that insufficient irrigation water was available and
the supply was undependable. Natural precipitation is inadequate for dry
farming, hence successful farmIng is not possible without an adequate supply
of irrigation water, and these lands were abandoned.

Lands on Harvey Mesa cOOlprise the greater part of the project, some 4,680
out of the total of 6,597 acres. These lands are supplied by direct diver-
sions during the early part of the irrigation season when the flow of East
Rifle Creek is adequate, and by releases of stored water from Harvey Gap
Reservoir during the latter part of the season when their natural flow
rights are junior to those of downstream users on Rifle Creek. Total
seasDnal water supplies available to these lli.Rds have averaged substantially
less than requirements. Most severe shortages have occurred during July
and August, and in a number of years the water available during these moaths
has been less than 20 percent of requirementso Bureau of Reclamation opera-
tions studies indicate that the average seasonal water supply available to
lands under the Harvey Gap Reservoir has been about 69 percent of estimated
requirements. There have been few years during which all water requirements
hive been completely satisfied. In the 24-year study period, only four years
,
had seasonal water supplies greater than 90 percent of ideal requirements,
while in 12 years the supply was less than 60 percent of requirements.

In recent years, some 326 acres of land on the lower part of Harvey Mesa,
including 7 acres of non-project land, have been irrigated by pumping from
the adjacent Cactus Valley Canal, which originates by direct diversion from
the Colorado River. These lands have had essentially a full water supply
and, accordingly, have been analyzed separately in the economic studies.
Under project operations, they would receive their water supply from project
sources.

- 17 -