PUB00047

• Year: 2000
• Title: SECWD/Arkansas Basin Preferred Storage Options Plan Final Draft Report
• Author: GEI Consultants, Inc
• Description: SECWD/Arkansas Basin Preferred Storage Options Plan Final Draft Report
• Publications - Doc Type: Water Resource Studies

Final Draft - Preferred Storage Options Plan
Southeastern Colorado Water Conservancy District
June 8, 2000

were reviewed by B&V. Raising SugarloafDam to enlarge Turquoise Lake was studied
by B&V. Their findings will be reviewed by the USSR.

Pueblo Reservoir Enlargement

Technical Issues. Three enlargements of Pueblo Reservoir were evaluated - 25,000,
60,000, and 75,000 af as indicated below:

Capacity Increase (at)
Existing
Reservoir 25,000 60,000 75,000
Top of Active Storage (ft) 4880.5 4885.8 4892.7 4895.5
Top of Joint Use Pool (ft) 4893.8 4898.4 4904.2 4906.7
Spillway Crest Elevation (ft) 4898.7 4903.0 4908.6 4910.9
Top of Dam (ft) 4925.0 4925.0 4927.0 4929.0

For the 25,000 af option, the spillway crest would be raised 4.3 feet and the dam crest
would remain at its present elevation. At 60,000 and 75,000 af enlargements, the
spiUway crests would be raised by 9.9 and 12.2 feet, respectively, while the dam crest
would be raised by 2 feet and 4 feet, respectively, using a parapet wall. The spillway
crest would be raised using conventional concrete to reshape the spil!way ogee to a
higher elevation. Although a gated spillway option was studied by the USBR, they
concluded (and B&V concurred) that an ungated spillway would be preferred for cost,
technical, and operational reasons. In addition to modifying the spillway crest and dam
crest, a variety of other measures will need to be implemented to maintain a safe, reliable
dam structure. These include: rock bolts to increase spillway stability; additional
drainage measures to control uplift pressures; post-tensioned tendons to reduce tensile
stresses at the heel of the concrete dam under higher reservoir levels; and a stability berm
extension along the left embankment portion of the dam. The USSR is in the process of
further evaluating the flood hydrology at Pueblo Reservoir. This work could affect the
risk analysis for the dam, which is the basis for the current enlargement concepts.

Environmental and Permitting Issues. Pueblo Reservoir enlargement will involve a
major Federal action requiring permitting and intensive review under the guidelines of
the National Environmental Policy Act (NEPA) and preparation of an Environmental
Impact Statement (EIS). Effects to wetlands, the 'Wildlife inhabiting those wetlands, and
bald eagles will be significant issues. Wetland permitting and mitigation likely will be
challenging but feasible. A variety of institutional issues will need to be addressed
between the USSR, the District, and entities participating in the Project.

m GEl Consultants, Inc.

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