WSP02036

• File Number: 8220.128.J
• Description: Silt Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1951
• Author: USDOI - BOR
• Title: Silt Project-Colorado - A Supplement to the Colorado River Storage Project Report - Part 1 of 2
• Water Supply Pro - Doc Type: Report/Study

.-I
o
~

CRAP1'ER II

~.

DESIGNS AND ESI'IMAYX;S

spillway and Davie ditch pump and outlet wculd be constructed. The
reservoir outlet tunnel could serve to bypass stream flow during the
construction period and therefore it wOUld be completed before the
dam embankment was placed. Roads and telephone and pcmer lines would
be relocated and the reservoir basin cleared while the dam was under
constructi on.

Grass Valley Canal anI! Davie ditch would also be constructed
while the dam construction was underway. The siphon barrels of Grass
Valley Canal could be con3tructed in the winter and early summer when
the canal would be in use but structures that would interfere with
the canal flow would be constructed during late summer or fall.

Project Works

Rifle Gap Dam and Reservoir

Rifle Gap Dam, details of which are shown in the drawing on the
following page, would contain 770,000 cubic yards of clay, sand, and
gravel rolled fill. It would have a maximum height of l26 feet above
streambed, a crest length of 800 feet, and a crest width of 35 feet.
Other dam and reservoir data are given below.

Crest elevation
1mximum water surface elevation
Normal water surface elevation
Dead storage elevation
Stream bed elevation
Normal storage capa~ity
Original active capacity
laO-year active capacity
Dead stORage c apaci t y
Reservoi I' surface area

5,954 m.s.l.
5,948 m.s.l.
5,94') m.s.l.
5,882 m.s.l.
5,828 m.s.l.
10,')0') acre-feet
9,000 acre-feet
7,0')0 acre-feet
l,OOO acre-feet
300 acre s

Main fill would be composed of ~l impervious center section with
a semipervious cover beneath the riprap and rock fill slopes. Four
shallow cut-off trenches would cross the canyon floor upstream from
and parallel. to the dam axis. Two feet of stripping ovaI' the entire
foundation area would provide a surface of good bond between foundation
and embankment. Tile drains would be placed beneath the spillway and
along the downstream toe of the dam.

Outlet works. A tunnel through the left abutment of the dam,
shown in the drawing on the following page, would be provided for the
outlet works. It would have a capacity of 150 second-feet with the
reservoir surface near dead storage level. Provision would be made
for supplying 18 second-feet to Davie ditch through a riser pipe heading

l3