WSP06255

• File Number: 8240.200.47.G
• Description: Silt Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1997
• Author: USDOI/BOR
• Title: Silt Project - Final Appraisal Report
• Water Supply Pro - Doc Type: Publication

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Chapter 1 - Introduction

Agriculture is an important activity in this area. Several thousand acres of
rangeland and National Forest reserves surround the cultivated areas and are used
for summer grazing. Most irrigated farmland is devoted to the production of
alfalfa, grain, and native hay for livestock feed; a small acreage is used for
production of fruit and truck crops.

3. Investigations and Project Authorization

Investigations of the Silt Project by the Reclamation began in 1936. A report
concerning the Colorado River dated March 1946 briefly described a project plan
that was similar to the final plan. The plan was described in greater detail in a
January 1951 report on the Silt Project, which served as a supplement to the
1950 report on the Colorado River Storage Project and participating projects. The
1950 report was amended in 1953 and was the basis for authorization of the Silt
Project. A December 1961 definite plan report presented the results of studies
which generally confirmed the 1951 feasibility plan.

The project is one of the 16 participating projects authorized under the CRSP Act
of April 11, 1956 (70 Stat.1 05) for the purpose of developing Colorado's Colorado
River Compact apportionment. The act also directed that power sales from Glen
Canyon Dam, Flaming Gorge Dam & the Curecanti Unit (Blue Mesa, Crystal and
Morrow Point Reservoirs) be used to repay for costs of the Nparticipating
projects" (including the Silt Project! that were beyond the benefited irrigators
ability to pay.

4. Project Features

Project storage is in Rifle Gap Reservoir, formed by Rifle Gap Dam. The dam is
located on Rifle Creek about 5.5 miles north of Rifle, Colorado, at a point where
the creek cuts through the Grand Hogback. The dam is a zoned earthfill structure
with a height of 157 feet, a crest length of 1,450 feet, and a volume of
1,768,000 cubic yards.

The spillway consists of a short approach channel, concrete inlet walls, concrete
crest structure, and concrete chute and stilling basin. The outlet works consists
of a concrete intake structure, a 6-foot diameter upstream tunnel at the gate
chamber with two 2.25-foot-square high-pressure gates. The river outlet diverts
to a downstream 6-foot-diameter flat-bottom free-flow tunnel, which discharges
into the spillway stilling basin. A 7-foot-diameter horseshoe tunnel branches from
the gate chamber and contains a 3D-inch steel pipe that conveys water to a
concrete pipe that in turn discharges into Davie Ditch. Rifle Gap Reservoir has a
total capacity of 13,602 acre-feet and an active capacity of 12,168 acre-feet,

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