PROJ00077

• Contract/PO #: FS0008X
• Contractor Name: Longmont, City of
• Contract Type: Loan
• Water District: 0
• County: Boulder
• Loan Projects - Doc Type: Feasibility Study

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More recently, the Colorado Geological Survey (Kirkham and Rogers 1982)
published the ~ost complete document on Colorano Seismicity currently available.
They recommend Colorado he upgraded to Zone 2 of the Uniform Building Code and
that a value of O.lg he considered a minimum design value for structures in
r.olorarlo.
The U.S. Bureau of Reclamation performed a thorough site specific study
for their SEED Report on Bluebird Dam. They used two commonly accepted methods
for evaluating probahle earthquake accelerations, the Deterministic Method
(fault-proximity evaluation) and the Probabilistic Method (historical-statistical
evaluation). They concluded that horizontal accelerations at the site were
0.32g for the maximum credible earthquake as estimated using the Deterministic
Method (a M=7.0 quake on the Laramie River fault) ann the 10,000 year event pro-
duced loaoing of 0.16g as estimated using the Probabilistic Method. They also
rated the potential for movement on the Laramie River fault as low. In accor-
dance with the USBR recommendations that "for the purposes of safety analysis of
existing dams, a prohability of occurrence or exceedence of 1 in 10,000 per
annum is recommended for selection of parameters for use in seismic stability
considerations~, a value of 0.16g horizontal acceleration was used in our
pseudo-static earthquake analysis.
VI. CONCRETE PROPERTIES
Visual Inspection
The dam displays significant physical deterioration over much of its
exposed surface. The surface deterioration appears to be a result of freeze-
thaw action and poor construction procedures. Much of the dam has lost several
inches of surface concrete and locally there are holes up to two feet deep.
Figures 7 and 8 are maps of surface deterioration of the upstream and downstream

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