The lake at Lumbee Tribe of North Carolina’s Cultural Center is an integral part of the property and provides multiple recreation opportunities. The dam system for this 90-acre lake consists of a roughly 6,000-foot-long earth embankment with three outlets: a primary riser/barrel outlet at the south end, a secondary riser/barrel outlet about 800 feet from the north end, and a concrete overflow spillway at the north end. All three outlets flow to the Lumber River and are affected by the backwater of the river during significant rain events. During Hurricane Matthew in 2016, the dam was overtopped and experienced damage from the overtopping, as well as from the extended period of high-water levels in the lake and the Lumber River.
LJB provided a dam evaluation and preliminary cost estimate to the Tribe and FEMA to acquire FEMA Hurricane Matthew recovery funding.
During Hurricane Florence in 2018, the dam overtopped again, bringing significant additional damage and requiring design revisions and additional funding. Dam Safety required a Jurisdictional Determination/Hazard Classification to determine the appropriate hazard classification and design storm. LJB’s team performed a Breach Analysis detailing the inundation areas for various breach scenarios during various storm events to provide an incremental risk assessment. Although the analysis determined that the dam should be classified as High Hazard, the downstream impacts of the 1/2 PMP are not expected to be significantly higher than the 1/3 PMP. LJB’s team recommended that the dam be listed as High Hazard with a design storm of 1/3 PMP.
The proposed dam repairs include raising the elevation of the embankment to a consistent elevation of 169.5 feet, replacing damaged slide gates and trash racks at the primary spillway, removing the damaged portion of the concrete spillway and replacing it with a gabion structure, stabilizing a significant headcut/eroded channel with gabions, and replacing the secondary riser/barrel with a 125-linear-foot emergency spillway. LJB prepared plans and received permits/approvals from the Army Corps of Engineers, NC DEQ Division of Water Resources, NC Floodplain Management, and NC Dam Safety.