Inundation Mapping of Dam Breach Conditions

The Hawaiian Islands experienced unusually severe rain showers in February 2006 that caused severe flooding throughout the State. On March 14, 2006, the privately-owned Kaloko Dam on the island of Kauai failed sending a wall of water and debris downstream that overtopped the Morita Dam, damaged Kuhio Highway and swept away homes. As a result of this disaster, and to assure public safety, U.S. Senator Daniel K. Inouye secured $2 million in the FY 06 Emergency Supplemental Appropriation Act (Public Law 109-234) for the conduct of dam break analyses. The State of Hawaii Department of Land and Natural Resources is the non-cost sharing sponsor. The dam break analysis evaluates the extent of inundation for downstream areas that result from several unexpected dam failure scenarios. The analyses does not establish the likelihood of dam failures, but focus primarily on quantifying and mapping flood extents due to potential dam failures in order to prepare appropriate emergency action plans and provide better community awareness of these types of hazards. Eleven dams were studied as part of this State-wide project, including Twin Reservoir, Waita Reservoir, Elua Reservoir, Aepo Reservoir, Puu Lua Reservoir, Halamanu Field 21 Reservoir, and Upper Kapahi Reservoir on the island of Kauai; Reservoir 24 on Maui; Nuuanu Dam and Wahiawa Dam on Oahu; and Kualapuu Reservoir on Molokai. There are four parts to each dam site evaluation study including: hydrology, hydraulic flood wave routing, inundation mapping, and reporting. This paper addresses the development of mapping to depict areas of inundation and flood risks downstream of each dam. The final dam site evaluation studies were completed in early 2008. These studies were performed by an integrated team of experts including local Corps staff, Corps' HEC, and AE firms of Tetra Tech, Oceanit Laboratories, SSFM/West Consultants, and PB Americas/Northwest Hydraulic Consultants.