PROJ00400

• Contract/PO #: C153588
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: SB 89-85
• Loan Projects - Doc Type: Feasibility Study

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acre-ft or 5.5 cfs daily for 120 days duri ng the wi nter. The mi nimum annual
reservoi r content is 72 acre-ft wi th a 25 acre surface area. The maximum
content is equivalent to the reservoir's conservation storage of 1,928
acre-ft, which has an approximate surface area of 102 acres.

5.0 SEDIMENT

Sediment yield in the drainage basin above the reservoir was estimated from a
1974 sediment yield map published by the Colorado Land Use Commission. Much
of the quantitati ve data on the map was based on i nformati on deri ved from
small dry reservoirs with drainage basins of one to five square miles. The
amounts of sediment refl ect the average wei ght and vol ume of sediment as
ordinarily deposited in these reservoirs. The information presented represents
an average yield over a period of time greater than 25 years.

The estimated sediment yield for the drainage basin above Barnes Meadow
Reservoir is shown to be very low compared with other drainages in Colorado,
and averages less than 0.1 acre-foot per square mile per year. The basin is a
hi gh mountai n area, with dense vegetati ve cover, and with resi stant rock
outcrops. Assuming a 100-year project life, the total expected sediment yield
from the watershed is 31 acre-ft.

For most pl anni ng studi es, the 50-year sediment accumulati on is subtracted
from the reservoir storage content for estimating project yields. In this
case, the sediment yield is less than the capacity of the minimum pool in the
reservoir; therefore, the conservation storage space has not been diminished.

The trap effi ci ency of a reservoi r is defi ned as the rati 0 of the quanti ty of
deposited sediment to the total sediment inflow. Gunnar Brune has developed a
set of trap effi ci ency curves for use wi th normal ponded reservoi rs usi ng
their capacity-inflow relationships.

The capacity-inflow ratio for Barnes Meadow Reservoir is 0.54 for the
rehabi1 itated structure. Using the Brune curves gives a trap efficiency of

1231 H

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