PROJ00235

• Contract/PO #: C153633
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 3
• County: Larimer
• Bill Number: HB 91-1006
• Loan Projects - Doc Type: Feasibility Study

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duplication of effort ~ addnlonal dam safety features are required or ~ the City wishes to use Hourglass
Reservoir as a long-term storage facility. If Option 1 Is built first as expected, the construction cost of
Option 2 Is reduced to $924,000.

The present administration of the Poudre River aIk7Ns Greeley and other storage facilnles to offset
seepage losses wnh Inflow to .hold point" at the storage level diverted while in priority, After inflows
diminish in late summer or fall, Hourglass Reservoir does sustain actual reservoir losses due to seepage.
Current operation has been to fill Hourglass Reservoir wnh native inflow and discharges from Comanche
Reservoir through the feeder canal in the spring and to release the water downstream as needed before
seepage losses occur In the fall,

Hourglass Reservoir has high seepage losses, based on the single simplified seepage loss investigation,
Apparent losses at elevation 9356,8 feet (24,0 gage) appear to be In the order of seven acre-feet per
day, or 200 acre-feet per month. Losses will be greater at higher reservoir levels. Very little of the
reservoir seepage loss returns to the stream channel above the measuring flume,

Hi(;'h s€'"pge iosses through the fall and wir,Ier amit the :"1i1~y d [he reservoir for :,,~g-!al m water
storage, especially at higher reservoir levels. The reservoir could continue to be used as n is now,
following construction of Option 1, as seasonal storage to offset peak demands or to facilnate
exchanges.

The altematives for rehabilitation recommended In this report are:

Option 1 . Downstream Drainage Construction, bmgIng the dam up to present safety stability standards
is recommended for flnal design and constructlon at a feasibility level construction cost of 328,075
thousand dollars. This is the minimum rehabilitation to adequately Improve dam safety, Seepage losses
will not be reduced, but wRI be controlled, to enhance dam stability.

Option 2 . Partial Depth Slurry Wall Includes a partial slurry well seepage cutoff in addnion to the safety
Improvements Included In Plan " The estimated cost of construction Is 1,346,975 dollars. Such cost
for a potential savings of a few hundred acre-feet of water per year is not considered to be
economically attractive at present. If the cost at water does rise to justify a partial cutoff, n can be
placed at any lime after completion of Option 1 lor 995,500 dollars,