C150163 Feasibility Study

• Contract/PO #: C150163
• Contractor Name: New Cache La Poudre Irrigating Company
• Contract Type: Loan
• Water District: 3
• County: Weld
• Bill Number: 04-1221
• Loan Projects - Doc Type: Feasibility Study

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25 feet and an 18-foot crest width. A cutoff trench will be constructed beneath
the dam to reduce seepage along the foundation. A toe drain and a blanket drain
will be constructed on the downstream side of the dam. Because the dam is
being constructed in a natural depression, the drain outfall pipe will have to
extend approximately 4000 feet toward Barnesville Reservoir in order to allow
gravity flow out of the drains. The reservoir will be designed to store up to 1600
ac-ft of water. Typical details for Cornish Plains Reservoir are shown in Figure 5.

Barnesville Equalizer

Barnesville Equalizer would be located in a natural depression on the south side
of the North Side Extension that will be filled by gravity flow of water diverted
from the ditch. Barnesville Equalizer will require a dam along the south side and
a dam along the west side. The total length of the dams will be approximately
1230 feet and the maximum embankment height will be approximately 5 feet. An
18-foot crest width will be used to allow vehicles to travel easily along the top of
the dam. The reservoir will be designed to store up to 300 ac-ft of water. Inlet
flow to Barnesville Equalizer will be from a ditch diversion structure constructed
in the North Side Extension. The concrete diversion structure will be comprised
of a silt trap, two Obermeyer Gates, and an overflow spillway. The Obermeyer
Gates will be used to check flow in the ditch and to control flow into Barnesville
Equalizer. Both gates will have automatic controls for regulating flow in the ditch
and into the reservoir. The overflow spillway will serve to catch and control
surges in the ditch caused by localized storms. Typical details for the Barnesville
Equalizer are shown in Figure 6. The proposed ditch diversion structure is
shown in Figure 7.

Geotechnical Evaluation

Reservoir Sites

The soils on the site consist of fine sand overburden underlain by a layer of well-
graded sand and gravel. Bedrock at the Barnesville Equalizer site consists of
shale. At the Drury and Cornish Plains sites, the bedrock consists of sandstone.

The soil survey of Weld County by the Soil Conservation Service indicates that
the reservoir basins are dominated by Heldt Clay Loam. Renohill Clay Loam
appears on the north and south abutments with Longmont Clay also in the south
abutment area. Kim Loam emerges on the western edge of the basin.

The soils encountered on the site are predominantly fine sand and sand with
gravel. BH-2/PZ at the Drury Reservoir site showed clay from the surface to
approximately seven feet below grade where the material transitioned to sand
with gravel. In all of the other borings on the proposed sites, overburden sand
and sand with gravel were encountered from the surface to depths ranging from
approximately twenty to thirty-two feet. At the Barnesville Equalizer site, shale

New Cache Feasibility Study

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