Opening General Session: ASDSO Welcome & Rapidan Dam Spillway Blockage & Abutment Breach, Inter-Agency Independent Forensics Team Evaluation

Abstract Description: In May and June of 2024, the Rapidan Dam drainage basin in south central Minnesota experienced precipitation resulting in the fifth wettest month on record and the second largest flooding event in the hydropower project's 114 years of operation. The flooding mobilized an accumulation of interlocked woody debris masses that broke loose from the upstream boater safety cable and highway bridge piers that blocked spillway bays reducing discharge capacity. The blockage caused rising reservoir water to overtop the crest and flow around low areas at the left abutment. These flanking flows concentrated around obstructions and knick-points increasing the localized hydraulic energy and turbulence causing scour of weak fill and geologic materials composing the abutment leading to uncontrolled release of the reservoir and accumulated sediment. The breach enlarged vertically and laterally, fully capturing the Blue Earth River and bypassing around the left side of the still standing and intact concrete Ambursen slab and buttress dam. During the flooding and dam breach the project owner and operator implemented the project Emergency Action Plan (EAP). Fortunately, the failure did not result in any loss of life. However, consequences incurred included: o Undermining and loss of a residential structure o Demolition of the historic Rapidan Dam general store o Loss of transformers, substation, and County maintenance storage shed o Damaged the stepped concrete overtopping protection just downstream of the powerhouse o Loss of functionality and benefits of the dam (i.e. hydropower, recreation) o Erosion and transport of impounded reservoir sediment flushed through the breach and deposited along the downstream riparian corridor o Regressive scour caused undermining and destabilization of the upstream bridge piers jeopardizing its structural integrity ultimately resulting in closure, demolition, and replacement of the structure o Post-failure mitigation and restoration of the river system Following the failure the Federal Energy Regulatory Commission assembled a technical Independent Forensic Team (IFT) composed of dam safety professionals from the Army Corps of Engineers and Bureau of Reclamation. The mission of the IFT was to evaluate the project background, site conditions, operations, performance, past dam safety evaluations and modifications; evaluate the sequence, physics, and root cause(s) of the failure; assess the decisions made and actions taken by responsible parties; and develop lessons learned from the failure to inform the dam safety community and improve the FERC dam safety program. This presentation summarizes the IFT review findings and lessons learned related to debris management, planning, or system changes; early failure mode development recognition; intervention methodologies and preparation; operational communication during ownership transfer; and importance of experience with dam management responsibilities, safety incidents, and emergency response. IFT Report: https://www.ferc.gov/dam-safety-and-inspections

John Roche

Chief, Dam Safety Permits

Maryland Department of the Environment

John Roche, P.E. serves as the Chief of the Maryland Department of the Environment, Dam Safety Permits Division and is the primary point of contact for geotechnical engineering, policy, and regulatory matters. John also has experience with facilitating dam removal projects, emergency response and preparedness activities, and process improvement. Prior to joining the Dam Safety program in 2015, John spent nearly 10 years as a geotechnical engineering consultant in the Mid-Atlantic and New England states serving as a project manager for a wide array of geotechnical, environmental, and geothermal projects. He maintains active professional registration in three states and serves on the Executive Board and multiple committees for the Association of State Dam Safety Officials.

Greg Paxson, P.E.

Principal, Schnabel

Schnabel Engineering, LLC.

Greg has over 25 years of experience with dam safety projects, ranging from inspections and evaluations to design and construction of dam safety modifications. This includes spillway upgrades, stabilization of gravity dams, and seepage remediation projects for embankment dams. He serves as chair of the Technical Journal Committee for ASDSO and chair of the USSD Hydraulics and Hydrology Committee. He also led an ASDSO Task Force charge with evaluating the design review process for dam safety projects, which included co-facilitating several soapbox and town hall sessions at ASDSO national conferences.
Greg has undergraduate and graduate degrees in civil engineering from University of Delaware and Villanova University, respectively.

Todd Loar, P.G., CEG

Senior Geological Engineer

US Army Corps of Engineers

Todd Loar is a Senior Geological Engineer at the US Army Corps of Engineers, Risk Management Center in Lakewood, Colorado.

He has over 30 years experience in private and public sectors for projects involving applied geological, geotechnical, foundation design and engineering, and site characterization assessments for dams; tunnels; mining infrastructure and tailing dams; hydrogeologic assessments; and water resources projects within the US and internationally.

For the past 11 years he has served as USACE senior technical advisor, subject matter expert (SME), and instructor for the national dam and levee safety program, applying a risk informed decision making process to characterize and prioritize the USACE inventory and support engineering analysis, modifications, and construction for infrastructure improvements and risk reduction. In addition, Todd serves in a technical advisory and SME roll for projects within and external to the USACE enterprise addressing civil engineering challenges with domestic and international partners, and for emergency response or after-action forensic assessment.

Todd in a registered professional geologist (PG) and certified engineering geologist (CEG), has degrees in geology and geological engineering from University of California, Santa Cruz (BA), and the Colorado School of Mines (MS), respectively, and is an adjunct professor at CSM and CU Boulder.

Kent Walker, P.E.

Dam Safety Program Manager

Bureau of Reclamation

Kent Walker is Reclamation’s Dam Safety Program Manager for the Missouri Basin, and Arkansas Rio Grande Texas Gulf Region and is the Hydraulics and Hydrology specialist for the Dam Safety office. He completed his Master of Civil Engineering at Colorado State University’s hydraulics laboratory in 2008 and has 22 years of experience with hydraulic engineering and dam and levee safety with both Bureau of Reclamation and the US Army Corps of Engineers. While working at Reclamation’s hydraulics laboratory, he thoroughly studied dam safety risk with reservoir debris obstructing spillway capacity, work which he continues in his role in the Dam Safety Office. Kent lives in Breckenridge, Colorado and is an avid skier and open water swimmer.

Josh Cackley, P.E.

Dam Safety Program Manager

US Army Corps of Engineers

Josh Cackley is the Dam Safety Program Manager for the Rock Island District, managing the routine dam safety program for an inventory of 26 dams that includes 18 navigation locks and dams and 8 flood-risk management dams. In this role, he leads multi-disciplinary teams performing routine dam safety activities to include inspections, risk assessments, emergency action planning, dam safety exercises, instrumentation, and performance monitoring. His additional roles within the agency include the US Army Corps of Engineers (USACE) Emergency Action Planning Subject Matter Expert Working Group Team Lead and the USACE representative on several federal inter-agency emergency action planning working groups.

Josh has 23 years of experience with the Rock Island District, 12 years as a structural engineer before becoming the dam safety program manager in 2015. He earned his B.S. in civil engineering from Purdue University, is a registered Professional Engineer in the State of Iowa, and a Certified Floodplain Manager in Illinois.

Outside of work, Josh enjoys spending time with his family, attending his children’s activities and sporting events, helping on the family farm, chasing muskies, and riding snowmobiles.

Eric Gross

Senior Civil Engineer

Federal Energy Regulatory Commission

Mr. Gross is a senior civil engineer who has been with the Federal Energy Regulatory Commission for 20 years. He joined the Division of Dam Safety and Inspections’ Risk Informed Decision Making (RIDM) group in 2011, which later became the current RIDM branch in 2016. Mr. Gross has a Master’s of Civil Engineering – Water Resources from University of Maryland College Park, a Bachelor’s of Environmental Science – Geophysics from Rensselaer Polytechnic Institute, and is a licensed professional engineer in Maryland

Melissa Shinbein, P.E.

Hydraulic Engineer

Bureau of Reclamation

Melissa Shinbein is a hydraulic engineer with 8 years of experience at the Bureau of Reclamation’s Hydraulics Laboratory in Denver, Colorado. Melissa primarily works on physical modeling and hydraulic analysis in dam safety, debris, fish passage, and river restoration. Additionally, she is working on developing a standard of practice for terrestrial-LiDAR systems acquired by Reclamation in the last year. Previously, she worked for the Pennsylvania Department of Environmental Protection and the City of Philadelphia as a regulator of stormwater management and waterways. She is a registered Professional Engineer in the states of Colorado and Pennsylvania with a Master of Engineering and a B.S. in Civil Engineering from Cornell University.