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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,'d. Construction of an emergency spillway capable of
meeting 'the State Engineer's requirements. By con-
structing the service spillway in the outlet works
. and providing approximately 2.5 feet of freeboard
between the service spillway flowline and the emer-
gency spillway flowline, a considerable reduction of
'the cost of the emergency spillway can be made. The
2.5 foot storm storage between the service and emer-
gency spiJlways will essentially provide a safe con-
trol and discharge of a "50 year" rainstorm. (Proba-
bility of occurring once in 50 years). The emergency
spillway would thus become an overflow area capable
of meeting the maximum probable flood criteria. Hence,
the spillway may need a control section in excess
of 1000 feet, but it shall be constructed of earth
and sod, with reinforcement by soils cement at the,
, water surface only. ' The spillway could be constructed
at two different sites, from borrow areas used in
construction of the embankment fills. It appears
,evident that additional right-of-way or land shall be
, required for 'expansion of the existing spillway. As
, stated above, ,land used for right-of-way for the spill-
way may also contain soils adequate for the construction
of the embank~ent fills, thus helping to reduce the
cost of excavation and haul. It is estimated that
an additional 15 acres of land may be needed to the
east of the existing spillway. It should be noted
that the spillway can be designed so as to permit
farming in the spillway channel below the overflow
crest. The only time crops would face potential
damage would be during an extremely large rainfall
when the reservoir was full. This ~tem shall be the
same for Alternates 2A and 2B.

Alternate No. 2A (FULL CUTOFF)

Estimated Cost . . . . . .

Repairs:

a. See Alternate 1

b. Construction of an impervious earth fill cutoff along
the face of Dam No.1. This cutoff would be the
same as Alternate No. I, except that at the bottom
of the cutoff trench, sheet piling would be driven
through the sand and sandy silt to bedrock to provide
the complete seepage cutoff. The sheet piling would
eliminate the need for relief drains along the toe
of the dam. It should be noted that the extremely
dense sand layer may make driving sheet piling a
difficult job and additional tests must be performed
before this alternate could be finalized.

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$1,549,525

See Alternate I
See Alternate 1

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