Lupo Lake Dam

Lupo Lake Dam carried a high hazard (Class C) classification in the NCDEQ Dam Safety Program inventory, and with it the full weight of North Carolina’s dam safety requirements. The owner needed to understand what compliance would actually cost, and whether the classification driving that cost was correct. Class C is the most consequential class in North Carolina. It drives the largest spillway design storm, the most frequent inspection cycle, an Emergency Action Plan with a maintained inundation map, and a compliance obligation that runs with the property indefinitely. Every obligation in that list scales with the classification, so the class a dam carries determines the cost of compliance as much as the condition of the dam does.

The classification had been assigned without a breach analysis behind it. It reflected an assumption about what failure would do downstream rather than a demonstration of it. The owner was being held to the most demanding standard in the state without anyone having quantified the consequences that standard exists to address. Class C also foreclosed an option. North Carolina exempts dams below its size thresholds from the Dam Safety Law of 1967, but that exemption is unavailable where the Department determines failure could cause loss of life or significant property damage downstream. As long as the dam was classified high hazard, its size was irrelevant.

RiskHydro served as the owner’s single point of coordination across the compliance effort, the field investigations, and the regulatory submittal. The first step was understanding the actual position. RiskHydro reviewed the dam’s compliance status with the NCDEQ Dam Safety Program, visited the site to observe conditions firsthand, and opened direct coordination with the Program on what the path forward would require. Field investigations followed, with subconsultants working under RiskHydro’s direction so the owner dealt with one party rather than several. The analysis that resolved the classification ran the storm twice. Rather than mapping the breach flood alone, RiskHydro modeled the same event with the dam failing and with it holding, and isolated the difference. That difference is the only flooding the dam is responsible for, and it is what the classification criteria are meant to measure. Everything else was going to happen regardless.

Key tasks included:

• Served as owner’s advisor across NCDEQ Dam Safety compliance, field investigation, and regulatory submittal
• Coordinated directly with the NCDEQ Dam Safety Program throughout the engagement
• Conducted multiple site visits to observe and document existing embankment and spillway conditions
• Advised the owner on compliance obligations and their cost implications under the existing classification
• Coordinated stream and wetland delineation through subconsultants
• Oversaw geotechnical field investigation
• Modeled sunny day breach scenarios at normal pool and maximum pool
• Modeled a hydrologic loading breach scenario, with failure at peak reservoir elevation during the spillway design flood (SDF)
• Routed each scenario downstream in two dimensions to capture inundation extent, water surface elevation, and velocity
• Ran a corresponding non-breach SDF scenario and compared it to the breach results to isolate the incremental depth, velocity, and inundation caused by the dam failure itself, separate from the storm event alone
• Evaluated incremental consequences against the Class A, B, and C criteria in 15A NCAC 02K .0105
• Prepared and submitted the Jurisdictional Determination and Hazard Classification (JDHC) request, with follow-on technical correspondence supporting the intermediate classification and the size-based exemption

The incremental damage analysis showed that failure of Lupo Lake Dam does not produce the consequences that define high hazard. The flooding attributable to the dam, as distinct from the storm that would be occurring anyway, was consistent with the intermediate hazard criteria. NCDEQ concurred. Because the dam falls under the size thresholds in the Dam Safety Law of 1967 and is no longer classified high hazard, the reclassification carried it out of Dam Safety Program jurisdiction.

• High hazard reclassified to intermediate, based on measured incremental consequence rather than an assumption about downstream impacts
• Exemption unlocked by the reclassification, since the statutory size exemption is unavailable to dams classified high hazard
• Compliance resolved through analysis rather than capital work, with the classification question answered before the owner committed to construction
• Indefinite compliance program reduced to a one-time effort, removing Class C spillway, inspection, and emergency planning obligations
• One point of coordination for the owner, across the regulator, the field investigations, and the submittal