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Utilizing a Basinwide Approach for the North Carolina Flood Mapping
ProgramJohn Dorman, Program Director,NC CTS Flood Mapping Program
Gib Jones, P.E., Dewberry & Davis LLC
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Background
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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
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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
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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)
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Mapping Products High-resolution topographic data
and 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
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Basinwide Approach to Floodplain Mapping
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Three Phases to Mapping Project
Phase I—bluePhase II—gold
Phase III—green
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Phase I — Eastern Six River Basins
Addressing eastern six basins first Basins most affected by
Hurricane Floyd Comprise approximately half
of State
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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
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Project “Scoping”
Meetings held with every community in 6 eastern basins
Their needs synthesized into basinwide objectives
Basinwide work plans developed
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Flood Map Production Process
Topographic Data Collection and DEM Creation
Hydrologic & Hydraulic (H&H) Analyses
DFIRM Production Community Review and Due
Process
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Two Study Contractors
Each to perform Topographic data collection
and DEM production H&H Analyses DFIRM production
Work broken out by basin
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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
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Topographic Data Collectionand DEM Creation
Example: Status of Bare Earth DEM
Creation
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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
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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
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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
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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
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Multi-Basin Counties
Neuse Basin
Tar-Pamlico Basin
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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
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Preliminary Map for Multi-Basin County
BLADEN COUNTYAND INCORPORATED AREAS
LumberRiver Basin
Cape Fear River Basin
“Preliminary revised flood hazard information not yet available for Cape Fear Basin. Please
refer to effective FIRM.”FIRM panel neatlines
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Timeline for Multi-Basin County
FinalMeeting(Lumber)
End ofAppeal Period
(Lumber)
FinalMeeting
(Cape Fear)
End ofAppeal Period
(Cape Fear)
FinalElevationDetermin.
6 month compliance period
90-day appeal
period (Lumber)
90-day appeal
period (Cape Fear)
1stPublicNotice
2ndPublicNotice
1stPublicNotice
2ndPublicNotice
9-28-01 10-5-01 10-12-01 10-26-01 1-10-02 8-28-02 9-6-02 4-25-032-28-0312-26-0212-12-029-27-029-13-02
Eff
ecti
ve
Cou
nty
wid
e F
IRM
PreliminaryIssued
(Lumber)
Preliminary Issued
(Cape Fear)
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Utilizing a Basinwide Approach for the North Carolina Flood Mapping
Program
QUESTIONS? ? ? ? ?