City of Duncan

PROJECT PURPOSE

Clear Creek Lake Dam consists of an earthen embankment and uncontrolled concrete overflow spillway. The embankment has a history of seepage at the downstream toe of the embankment and was shown in preliminary studies to be marginally stable with respect to slope stability. A recent dam inspection revealed sink holes on the downstream slope of the embankment with seepage emanating on the slope surface. A current study of slope stability and seepage is in process to develop long term alternatives for long term improvements to address stability and seepage issues, but with the recent observations, that process needs to be accelerated. Indications are that internal backward erosion is occurring (aka Piping) and this is an immediate dam safety concern. If unmitigated, internal erosion can and does usually lead to mass instability of the embankment (i.e. slope failure) but often leads to a breach of the embankment and loss of reservoir. The long-term solution will consist of installing a granular filter layer at the toe and up the downstream slope some pre-determined distance, covered by earth fill to flatten the slope and improve stability. Total project cost (engineering, permitting, construction) is expected to range from $3.5 to $4.5 million.

EVIDENCE

Clear Creek Lake provides substantial quality of life benefits to the residents in and around the City of Duncan. Indications are that internal backward erosion is occurring (aka Piping) and this is an immediate dam safety concern. If unmitigated, internal erosion can and does usually lead to mass instability of the embankment (i.e. slope failure) but often leads to a breach of the embankment and loss of reservoir. The long-term solution will consist of installing a granular filter layer at the toe and up the downstream slope, covered by earth fill to flatten the slope and improve stability.

POPULATION DESCRIPTION

This program would be an incredible benefit to the community and Southwest Oklahoma. Clear Creek Lake is an affordable and easily accessible recreation lake. It is our most popular recreational area in this community. Vulnerable populations are able to enjoy Clear Creek Lake?s recreation services, exercise, and enjoy the health benefits of being in nature. Many families cannot afford to travel due to rising gas costs or loss of income from the COVID pandemic. The lake provides a much needed escape to our community. It is also home to birds, fish, and wildlife.

PERFORMANCE MEASURING

City staff will consult with an engineering firm and OWRB to complete the proposed project. Project performance will be measured by the improvement of the condition rating of the dam, and therefore the reduction of risk to downstream communities and water customers.

ONGOING INVESTMENT AMOUNT

$

ONGOING INVESTMENT DESCRIPTION

None

ONGOING INVESTMENT REQUIRED

One-time project will not need continued funding