Multi-Hazard Mitigation Plan: 10. Floods

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Chapter 10:Hazard Analysis—Floods Limitations of the study being addressed prior to FIRM adoption: • Modifications to the Flood Maps to include tsunami inundation as a factor in zoning and construction requirements. • Phase I: The first step presently underway is comparing the differences between the existing and new FIRM maps to determine where historic or the recently modeled tsunami hazard is greater. • Phase II: UHM SOEST mapping (by the Kwok Fai Cheung Group) could produce 100-year and 500-year probabilistic tsunami hazard maps to provide future local modifications to the DFIRMs. 10.4.1.4 Adequacy of Managing Existing Flood Problems and New Development with Watershed Planning and Drainage Standards The current comprehensive drainage plan for the County is the"Drainage Master Plan for the County of Hawaii" prepared over 30 years ago in 1971. This plan needs to be updated to incorporate new studies and to provide a watershed perspective in managing floods using both structural and non-structural methods. This plan would be the basis to prioritize CIP projects and to initiate regulatory changes. FEMA has funded an Area Development Plan for Existing and Future Development project to investigate: County regulations and policies for new development to provide community outreach in regards to protection/precaution measures. Floodplain management and land use regulatory integration scope of work includes examining regulatory integration of grading ordinance (HCC chapter 10), flood control code (chapter 27), subdivision code(chapter 23), and zoning code (chapter 25): Reduction of flood hazards through regulary measures(recommended revisions to hcc chapters 10,23,25& 27) DESCRIPTION: This project will recommend new regulatory measures to the Hawaii County Code that would reduce flood hazards, including hazards caused by dams and levees within the County of Hawaii. Proposed regulatory measures will focus on Chapter 10, Erosion & Sedimentation, Chapter 27, Flood Plain Management, Chapter 23. Subdivisions and Chapter 25, Zoning. Recommendations to other Chapters of the Hawaii County Code may be made as may be appropriate. We are focusing on the four chapters for the following: Chapter 10, Erosion & Sedimentation Control: Any land disturbance activity has the potential of causing flood hazards or aggravating existing flood hazards to surrounding properties and the environment. There is a need to improve enforcement as well as to increase the use of mitigating measures and/or best management practices that would minimize erosion, sedimentation impacts during land disturbance activities that would create flood hazards. Major recommendations are anticipated as this Chapter has not had any major changes since its adoption in November 1975. 10-35 Hawaii County Multi-Hazard Mitigation Plan