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Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program

Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program. John Dorman, Program Director, NC CTS Flood Mapping Program Gib Jones, P.E., Dewberry & Davis LLC. Background. Why North Carolina Is Undertaking This Project. NC vulnerability to hurricanes and flooding

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Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program

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  1. Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program John Dorman, Program Director,NC CTS Flood Mapping Program Gib Jones, P.E., Dewberry & Davis LLC

  2. Background

  3. Why North Carolina Is Undertaking This Project • NC vulnerability to hurricanes and flooding • 14 federally declared disasters since 1989 • Hurricane Floyd damages = $3.5 billion • 4,117 uninsured/under-insured homes destroyed as result of Hurricane Floyd • Accurate, up-to-date flood hazard information crucial to protect NC livesand properties

  4. Why North Carolina Is Undertaking This Project (Continued) • Hurricane Floyd revealed flood hazard data and map limitations • Age of North Carolina FIRMS • 55% at least 10 years old • 75% at least 5 years old • FEMA’s mapping budget is finite • NC receives only one updated flood studyfor one county per year • Many counties and communities lack resources to take on this responsibility

  5. North Carolina CTS Flood Mapping Program • Cooperating Technical State (CTS) partnership with Federal Emergency ManagementAgency (FEMA) • State ownership and responsibility for Flood Insurance Rate Maps (FIRMs)

  6. Mapping Products • High-resolution topographic dataand accurate Digital ElevationModels (DEMs) • Engineering studies • Countywide digital FIRMs • State-of-the-art, dynamic Information Technology (IT) infrastructure • Real-time flood forecasting and inundation mapping capability

  7. Basinwide Approach to Floodplain Mapping

  8. Three Phases to Mapping Project Phase I—bluePhase II—goldPhase III—green

  9. Phase I — Eastern Six River Basins • Addressing eastern six basins first • Basins most affected byHurricane Floyd • Comprise approximately halfof State

  10. Phase I — Eastern Six River Basins • Affect 48 counties and 334 incorporated municipalities (in whole or in part) • Encompass approximately 21,200 linear miles of streams and rivers • Flood hazard mapping for remaining 11 basins to be discussed with General Assembly in 2001

  11. Project “Scoping” • Meetings held with every community in 6 eastern basins • Their needs synthesized into basinwide objectives • Basinwide work plans developed

  12. Flood Map Production Process • Topographic Data Collection and DEM Creation • Hydrologic & Hydraulic (H&H) Analyses • DFIRM Production • Community Review and Due Process

  13. Two Study Contractors • Each to perform • Topographic data collectionand DEM production • H&H Analyses • DFIRM production • Work broken out by basin

  14. Topographic Data Collectionand DEM Creation • Includes • LIDAR surveys • Field surveys of structures and channels • Automated and manual post-processing • DEM creation • Conducted on a basinwide approach • Efficiency of scale realized in surveying large geographic areas

  15. Example: Status of Bare Earth DEM Creation Topographic Data Collectionand DEM Creation

  16. Engineering Analyses • Hydrology and stream hydraulicsdo not follow corporate boundaries • Set up H&H models using basinwide approach • Allows large areas to be study contiguously • Minimizes discontinuities and mismatches

  17. Digital FIRM Production • “Carve” up data into countywide maps • Countywide maps more user friendly • Corresponds to community-based approach to floodplain management • Merge data for counties in more than one basin

  18. Community Review andDue Process • Community meetings held oncounty or basinwide basis • Due Process • 90-day appeal period • Evaluate and resolve community comments and concerns • Update community ordinances • Printing and distribution of maps

  19. Multi-Basin Counties • Many counties are in more than one basin • Basins will be completed at different times Insert figure with schedule for different basins

  20. Multi-Basin Counties Tar-Pamlico Basin Neuse Basin

  21. Processing Multi-Basin Counties • Process different portions of county separately • Produce separate preliminary maps • Separate due process • Merge different portions after all portions have gone through due process • Prioritize multi-basin counties

  22. Preliminary Map for Multi-Basin County 657 LumberRiver Basin 658 658 SMITHVILLE ROAD 659 660 BLADEN COUNTYAND INCORPORATED AREAS Basin Divide Cape Fear River Basin “Preliminary revised flood hazard information not yet available for Cape Fear Basin. Please refer to effective FIRM.” FIRM panel neatlines

  23. 6 month compliance period 90-day appealperiod (Cape Fear) 90-day appeal period (Lumber) Effective Countywide FIRM 1stPublicNotice 2ndPublicNotice 1stPublicNotice 2ndPublicNotice PreliminaryIssued(Lumber) FinalMeeting(Lumber) End ofAppeal Period(Lumber) Preliminary Issued(Cape Fear) FinalMeeting(Cape Fear) End ofAppeal Period(Cape Fear) FinalElevationDetermin. 10-12-01 10-26-01 12-12-02 12-26-02 9-28-01 10-5-01 1-10-02 8-28-02 9-6-02 9-13-02 9-27-02 2-28-03 4-25-03 Timeline for Multi-Basin County

  24. Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program QUESTIONS? ? ? ? ?

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