Lake Ilo Revival: A Story of Dam Rehabilitation

Lake Ilo Dam is a high hazard-potential dam located on the Lake Ilo National Wildlife Refuge north of the Town of Dickinson, North Dakota. Since 2006, intermittent seepage in the right abutment of Lake Ilo Dam has been observed during dam safety inspections. A Quantitative Risk Analysis (QRA) was performed as part of a Comprehensive Review conducted by W. W. Wheeler and Associates, Inc. (Wheeler) [1]. The findings of the QRA determined that the potential failure mode of contact erosion along coal seams at the right abutment embankment contact was a significant risk. In April 2023, seepage was observed to be increasing, which prompted lowering the reservoir to Elevation 2185 feet, at which point the seepage ceased. This paper discusses the dam performance history, innovative design of a sand filter wall to intersect the existing coal seams in the right abutment, construction, and performance.