Schnabel Engineering’s Mirror Lake Dam reconstruction wins safety award

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North Carolina Construction News staff writer

The City of Fayetteville and Schnabel Engineering have been recognized with the 2023 Southeast Regional Dam Safety Award for work on the Mirror Lake Dam.

“This confirms our public services team is one of the best in the region,” said Director of Public Services Sheila Thomas-Ambat. “We will continue to identify opportunities to keep residents safe, improve city infrastructure and execute the best plans to accomplish those goals.”

Floodwaters from Hurricane Matthew washed away a portion of Mirror Lake Drive, which runs along the crest of its namesake dam, and a portion of the dam along with it. Damages encompassed the downstream and upstream slopes of the embankment, several utilities, and parts of the spillway outlet system. The city of Fayetteville hired Schnabel Engineering to assess the dam’s condition, design repairs, and investigate upgrade options.

“Following the October 2016 hurricane, as part of the FEMA 406 hazard mitigation process, we evaluated the dam and spillway, designed repairs to the dam and road, and developed options to upgrade the facility to meet state dam safety requirements. We based our design on a variety of factors, including an engineering analysis that revealed the dam overtops for storms greater than 10 year/6 hours,” Schnabel sates about the project. “We also considered changes in upstream and downstream flood levels, constructability, and cost.”

Three alternatives were presented: a new concrete riser with larger culverts under the road; a combination of embankment overtopping protection and a new riser and culvert system; and eliminating culverts with an open-channel overflow spillway and a bridge over the spillway to maintain road access. The selected alternative – designed for a 25-year flood and responsive to the dam’s hydraulic conditions – was the combined embankment overtopping protection and new spillway system.

Subconsultant Dewberry Engineers, Inc. designed repairs to Mirror Lake Drive. The improvements elevated the road to match the existing spillway’s low point and location, with guardrails on both sides.

“Mirror Lake Dam continues to meet dam safety standards, while also extending the service life of the dam, reducing risk to downstream owners, and safeguarding access to services for the community residents,” according to the nomination.

The One Regional Dam Safety Award is presented to each of ASDSO’s four regions annually recognizing organizations making exemplary community contributions. Fayetteville officials are invited to Palm Springs, California to receive the award at an ASDSO luncheon on Sept. 18.

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