C150122 Feasibility Study

• Contract/PO #: C150122
• Contractor Name: Central Weld County Water District
• Contract Type: Loan
• Water District: 4
• County: Larimer
• Bill Number: SB 03-110
• Loan Projects - Doc Type: Feasibility Study

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and it does not appear that the site contains sufficient resources to be mined
economically.

Hydrologic Evaluation

Hydrologic analysis for the basin was conducted to estimate the size of spillway
needed to pass the 100% PMP design storm. A runoff coefficient of 0.04 was
assumed for the basin based on topographic and land-use conditions. A uniform
infiltration rate of 0.1 in/hr was selected based on soil conditions in the basin as
determined from Soil Conservation Service Maps. HEC-HMS was used to model
storm flow in the basin. A spillway length of approximately 350 feet is necessary
to pass the design storm. Results of the hydrologic study are in Appendix E.

Outlet Works

A 48-inch diameter outlet pipe is necessary to meet the State Engineer's
requirement of lowering the reservoir five feet from full capacity in five days. An
outlet profile is shown in Figure 6. In order to provide a good conduit for
pressure flow and for connections to the pump station, a ductile iron pipe
encased in concrete is recommended for the outlet pipe. A gate on the upstream
end of the pipe will be required for control of the outlet. Additionally, a gate tower
within the dam is recommended in order to facilitate operation and maintenance
of the outlet works.

Raw Water Transmission System

Pipeline

Water will be obtained from the St. Vrain Supply Canal through the influent line to
the Carter Lake Filter Plant. It is proposed to utilize an existing 20-inch treated
water transmission line owned by the CWCWD for carrying water between the
plant and the reservoir. The pipeline runs from the existing storage tanks at the
Carter Lake South Water Treatment Plant (WTP) and passes through the
reservoir site. In addition to the existing 20-inch CWCWD line, L TWD owns an
18-inch line that could be converted if additional capacity is required. In order to
utilize the existing 20-inch line some additional piping will be installed between
the influent line at the South WTP and the 20-inch line at the storage tank site
and from the reservoir outlet to the northwest side of the reservoir to replace
some of the 20-inch line that will be located in the reservoir site. Figure 3
included previously shows the current location of the existing 20-inch line owned
by the CWCWD. Figure 7 shows details for the proposed connection to the
existing 20-inch line at the Carter Lake Filter Plant.

Dry Creek Reservoir Feasibility Study

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