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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Samples were taken and laboratory classifications of the soil, natural den-

sity and moisture content, Atterberg limits, and unconfined compressive

shear strength tests were made. The location of the borings is shown on

Figure-II and a profile of the borings is shown on Figure-III (page 54).

A copy of the laboratory tests on the selected samples is shown in Appendix-D.

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The results of the geologic investigation show that the embankment

was not adequately compacted and the consistency varied from soft to

firm. A very soft to soft zone, just above the bedrock, was identified

in the southeast portion of the embankment from about stations 14+00 to

19+00 (see Figure-III). The exact origin of the soft layer was not iden-

tified. Due to the period of dam construction (earlier 1900's) the most

probable source of the soft zone is considered to be improper foundation

preparation. Since the area is the natural low spot, the saturated soil

was probably not removed prior to embankment construction.

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In addition to the test borings, the surface geological conditions
were defined using the Reference-2 report. A geological fault, potential
subsidence areas, and mine shafts were identified and are shown on Figure-II.
The impacts of these conditions on the dam are addressed in subsequent sec-
tions of this report.

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3 - Hydrologic Investigations
A hydrological analysis was undertaken by WRC (Reference-3) to define the
design flood and evaluate the existing spillway for Waneka Dam. A summary of
the results is presented in Table-4 (page 42). The highest peak inflow occurs
for the thunderstorm event, but the maximum spillway discharge occurs for
the general type storm event. The actual reservoir routing will change,
however, when the final spillway configuration is selected. The Reference-
3 analysis does show that the existing spillway is adequate from the capacity
viewpoint, although the configuration does not meet current State design
standards.

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