In February 2006, the Hawaiian Islands experienced unusually severe rain showers that caused severe flooding throughout the state. The resulting heavy rainfall resulted in the failure of privately-owned Kaloko Dam on the Northeast side of the island of Kaua‘i. The dam failure sent a floodwave of water and debris downstream that overtopped the Morita Dam, damaged Kuhio Highway, and swept away homes resulting in 7 fatalities. This disaster resulted in a Federal Assistance program with the Department of Land and Natural Resources (DLNR) to re-evaluate the condition and awareness of the highest hazard dams throughout the state. In 2008, Oceanit analyzed dam break scenarios for those high-hazard dams- Nu‘uanu Reservoir near Honolulu and Wahiawā (Wilson) Dam in the Kaukonahua Watershed of central Oahu. Analyses were required to evaluate the likely downstream inundation area in the case of a dam failure.
This project required:
- Acquisition of accurate topographic data and information, over a larger watershed area, for the development of baseline information to assess existing dam status and project area characterics.
- Performance of complex evaluations of various inflow scenarios, various dam failure scenarios, and mapping for resulting downstream inundation area hazards.
- Coordination with the U.S. Army Corps of Engineers, the DLNR Dam Safety Office, and the City and County of Honolulu.
- Provided hydrological and hydraulic analyses for Probable Maximum Flood (PMF) events for a range of possible dam break scenarios.
- Developed a computer model of the areas’ hydrology with each areas’ geometry to simulate a PMF flood event flooding.
- Utilized both 2D & 3D hydraulic models to best stimulate and verfiy hydrologic results to model hydraulic conditions caused by a reservoir breach.
- Calibrated and optimized model performance to produce stable accurate results by adjusting land roughness values, uneven stream profiles, and other model parameters. These set paramaters allowed for a sensitivity analysis to determine the most conservative estimate on the potential effects of a dam breach
- Mapped the floodwave and debris flooding downstream from the dam breach with computer model results, which displayed the inundation harzard zones.
- Given the hazard innundation areas resulting from possible dam failure scenarios, informed future mitigation plans could now be formulated.