C153301 Feasibility Study

• Contract/PO #: C153301
• Contractor Name: Cache La Poudre Reservoir Company
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 77-35
• Loan Projects - Doc Type: Feasibility Study

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clay layer, a special relief drainage system at
the downstream toe \vould be cons .:ructed in order
to provide a means of reducing possible hydraulic
uplift from seepage through the lower sand and
sandy, silt layer under the darn. The combination
of toe drains and relief drains will provide a
system of maintaining a high stability with the
downstream slope and still not completely reduce
the seepage through the lowest strata. It should
be noticed that this repair controls seepage through
the existing embankment and organic subsoils, but
is not designed to reduce the seepage through the
sand and sandy silt under the dam.

c. Construction of i service spillway and outlet works
combination. The existing outlet works would be
completely removed from the dam by excavating through
the center of the dam. Where possible, the remains of
the new outlet will be broken up in size,so as to be
used as riprap on the new dam face. The new outlet
,structure shall consist of a 60" I.D. upstream conduit.,.
"and a 48" I.D, downstream conduit.' The entire condui.t
,_shall be lowexed approximately 8 feet to establi sh the
outlet foundation on more suitable bearing materials.
By lowering the, outlet, the outlet capacity is increased
for lower water surface elevations in the reservoir,
and the hydraulic problems of constructing a high
capacity spillway through the outlet is solved. Due
to the hydraulics and the uncertain condition of the
stone outlet tunnel, it was determined that the entire
outlet should be replaced rather than saving only a
small portion of the structure. The outlet shall be
controlled by two gates. First, a slope face gate,
shall be installed on the face of the dam. This gate
shall be enclosed in a trash rack structure and shall
permit closing of the outlet for repairs and the winter
storage months. A second gate shall be installed in
a vertical well and shall be designed to control the
normal discharge demands. A morning glory spillway
shall be constructed in the well capable of by-passi~g
an excess of 200 cfs during rainstorm and runoff peri-
ods when the reservoir is full. The downstream end
, of the outlet shall' contain a stilling structure and
diversion structure providing normal operation of the
reservoir as required by the outlet demands and lake
canal demands. It may be desired to reconstruct the
measuring flumes if inaccuracies exist. This item
shall be the same for Alternates 2A and 2B.

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