PROJ00504

• Contract/PO #: C153334
• Contractor Name: Henry Waneka Mutual Reservoir Company c/o City of
• Contract Type: Loan
• Water District: 6
• County: Boulder
• Bill Number: FSA
• Loan Projects - Doc Type: Feasibility Study

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seepage, and drawdown from spillway elevation are stated ln Reference-
7 as 1.3, and 1.2, respectively. If an earthquake value of 0.1 g is
used, then the minimum factor of safety is 1.0, except for the drawdown
condition which shows that the existing embankment does not meet sug-
gested safety factors (i.e., 1.43 less than 1.50 without earthquake).

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B. Seepage Analysis
Some amount of seepage will occur through essentially all earth dams.
The problems arise when the amount of seepage affects the stability of
the dam and/or the quantity of seepage is excessive from the water value
standpoint. The potential seepage problem, with respect to stability,
was identified by the SED during several inspections. The .effect of the
seepage on the stability at the existing embankment was investigated ln
the previous section of this report, by varying those stability
parameters affected by permeability (i.e., cohesian, and 0 angle).
During the investigation of alternative improvements (Section V-C),
the design of the improvements included the effect of the existing
seepage conditions and other factors.

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Due to the value of the water, however, the magnitude of the
seepage is an important consideration. If the quantity is sufficient
to justify the expense of reducing the amount, then the alternative
improvements should include provisions for minimizing the quantity.
There are several ways of estimating seepage quantities, including
energy or mass balance techniques, flow-net approximations, or direct
measurements. The energy and mass balance techniques require extensive
amounts of field data over a long period of time, and therefore were not
within the scope-of-work of this analysis. Direct measurements were not
practical due to the site constraints and physical limitations (i.e.,
the seepage was not confined as to the source or to the discharge loca-
tion). Therefore, the flow-net approximation was selected due to the
simplicity of the method.

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