PROJC01820 ‎(2)‎

• Contract/PO #: C150189
• Contractor Name: Larimer and Weld Irrigation Company, The
• Contract Type: Loan
• Water District: 2
• County: Weld
• Loan Projects - Doc Type: Feasibility Study

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Alternative #3

This alternative consist of a total replacement of the existing structures with new concrete
structures which incorporates energy management features to control downstream erosion;
effective gates for the control of flows; and, measurement capabilities of the flows at Lake Lee
Dam and at the Big Windsor Inlet. Obermeyer gates will be used at the Finley Check and at the
Big Windsor Inlet check. The gates will not be automated, however, as are those previously
installed on the system. The operation of these checks is such that a manual control system is
sufficient. Both the Lake Lee Dam and at the Big Windsor Inlet structure gates will be replaced
with gates that are also manually controlled.

The Finley Check and Big Windsor Inlet Check will have the same configuration as those
previously constructed on the system as shown on Figure B2 in Appendix B of this report. Those
checks have a critical-flow throat in a rectangular constricted section, with upstream stilling wells
and air-operated Obermeyer gates to control the upstream water surface elevation. Gate operation
will be manual with power supplied by an air storage tank: and a portable air compressor. For
hydraulic energy management, the downstream sections of the checks have a plunge pool stilling
basin, with a solid end sill. Water exits the structures in a trapezoidal cross-section that
approximates the downstream ditch cross-section, A downstream riprap apron of approximately
40 feet in length provides downstream erosion protection.

The Finley Check will be 25 feet in width based on the maximum flow rate of 1,000 cfs as
requested by the Larimer and Weld Irrigation Company. The Big Windsor Inlet Check was also
designed for a maximum flow rate of 1,000 cfs and will also be 25 feet in width.

The existing Lake Lee Dam, shown in photographs 3 and in Appendix A, will be completely
removed and a new concrete structure which incorporates a Parshall flume to measure flows will
be constructed. The new structure is anticipated to be 60 foot in width, 125 feet in length, and
approximately 15 feet in depth. The structure will utilize two radial gates to control flows and will
have an overflow spillway set at gage height 10 to pass storm flows. A 25 foot wide Parshall
flume will be incorporated into the structure and will be capable of measuring flows up to 1200
cfs. A bridge structure will cross over the ditch at this location to allow access to the ditch riders
house. The proposed details of the structure are shown on Figure B3 in Appendix B.

The Big Windsor Inlet and Check Structure will also be completely removed and replaced with
a new concrete structure. The new structure is anticipated to be 40 foot in width, 220 feet in
length, with the depth varying from 15 feet to 35 feet below grade. The new structure will include
a check in the main ditch, as described previously, to divert water into the reservoir inlet structure.
The inlet structure will consist of an inlet section containing four control gates; a converging
section with a Parshall flume; a drop structure to affect the .approximately 35 feet in elevation
change from the ditch to the reservoir; and, an outlet to control the energy. The drop structure
and outlet will be connected by approximately 115 feet of reinforced concrete pipe. The hydraulic
design criteria for this structure is to have a capacity of 800 cfs from the ditch to the reservoir.

Larimer & Weld Feasibility Study
Lake Lee & Big Windsor - 03.043

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