Multi-Hazard Mitigation Plan: 11. DamFailures

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Chapter 11:Hazard Analysis—Dam Failures The dam inspections consisted of the visual only examination or condition survey of the regulated dam structures, including abutments, spillways, outlet facilities, and reservoir. The visual assessments yielded conditions ratings that ranged according to the following: • Satisfactory: Dam is expected to fulfill its intended function. • Fair: Dam is expected to fulfill its intended function but maintenance is recommended. • Poor: Dam may not fulfill its intended function and maintenance/repairs are necessary. • Unsatisfactory: Dam is not expected to fulfill its intended function and repair, replacement, of modification is necessary. • Unknown: Dam is not visible, not accessible, not inspected, or unable to determine the condition rating based on the observation taken. Besides the rating, the report includes recommendations for each facility if any. Typical recommendations vary from the removal of vegetation to facilitate future inspections to the requirement of owners to make immediate repair actions to restore the integrity of the facility. A total of thirteen dams were inspected in the County of Hawaii. Full summary reports of these inspections can be found at http://www6.hawaii.)4ov/dlnr/reports/dam-inspections/. 11.5.2.2 Pacific Disaster Center Dam Failure Inundation Map Project In 2009, the State of Hawaii DLNR and the Pacific Disaster Center (PDC) engaged in an effort to generate Dam Failure Inundation Maps for all one-hundred-thirty-five (135) registered dams in the State of Hawaii. Besides the inundation maps, the project aims at providing basic damage assessment and social-economical vulnerability assessment. The inundation maps for this project were produced using MIKE software—one of the industry standards for simulating flow and water level,water quality and sediment transport in rivers, floodplains, irrigation canals,reservoirs, and other inland bodies of water. All three available modules of the MIKE Modeling Suite were used to substantiate the results of the analyses: MIKE 11 for one-dimensional dynamic modeling of river, channel, and reservoir hydraulics; MIKE 21 for two-dimensional free surface flow models; and MIKE FLOOD for the integration of a series of dams within one single model. For illustration purposes, inundation maps for the same dam based on the two- and three-dimensional modeling capabilities of MIKE 1 1 and MIKE 21 are shown in Figure 1 1-7. Similarly, Figure 1 1- illustrates a single model of a series of dams using MIKE FLOOD. The following failure scenarios and assumptions were use to assure conservatism in the preparation of the maps: 11-10 Hawaii County Multi-Hazard Mitigation Plan