PROJ00187

• Contract/PO #: C153385
• Contractor Name: North Poudre Irrigation Company
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 82-87
• Loan Projects - Doc Type: Feasibility Study

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in a report prepared February, 1980, by BRUNS Incorporated and
approved by the Colorado State Engineer's Office. The peak
inflow Spillway Design Flood was 80,800 cfs, Reservoir routings
mitigate this flood to an outflow with a peak discharge of
61,907 cfs.

Stability analysis completed on the embankment
configuration used a cohesion of 750 pounds per square foot
and a 0 of fifteen degrees for the existing fill material, and
a cohesion of 200 pounds per square foot and a 0 of ten degrees
for the silty clay foundation material saturated. It is felt
that these numbers are conservative if applied to additional
fill material.

The hydraulic capacity of the outlet works was
calculated to be 250 cfs, maximum discharge at the normal
high water line for the repair of the existing outlet works.
A different arrangement for repair could result in a maximum
discharge of 300 cfs. at the normal high water line. A maximum
discharge of 340 cfs. was calculated if the replacement of the
outlet works with a new 54 inch reinforced concrete pipe was
completed.

d. Structure plans. In the engineering report, which was
submitted under separate cover as "Preliminary Plan of
Rehabilitation of Fossil Creek Dam and Spillway", preliminary
sketches are shown of the structures.

e. Drainage. No significant drainage problems are expected
from the project. A positive cutoff trench is proposed for the
upstream area to shale. Seepage associated with the dam could
be controlled by the installation of toe drains; however, these
are not recommended at this time. It is anticipated that the
positive cutoff will eliminate seepage problems. If areas of
seepage occur in the future after the improvements have been
completed and monitored, drains could be installed at that time
without changes to the current construction program.

f. Sedimentation. Fossil Creek Reservoir has existed on this
site since 1902. It is estimated that in that time sedimentation
has occurred to the depth of approximately six feet immediately
in front of the inlet to the outlet works. The volume represented
by this is approximately fifty acre-feet, which is insignificant
compared to the total volume of the reservoir.

g. Right-of-way. The maps depicted in the report which was
submitted under separate cover as "Preliminary Report of Plan
of Rehabilitation of Fossil Creek Dam and Spillway", show the
existing right-of-way limits which are owned by North Poudre
Irrigation Company. North Poudre is currently in the process
of negotiating for additional right-of-way required for the
construction of the enlargement to the emergency spillway, plus
additional right-of-way directly downstream of the embankment.

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