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 l NC vulnerability to hurricanes and flooding 4 14 federally declared disasters since Hurricane Floyd damages = $3.5 billion 4 4,117 uninsured/under-insured homes destroyed as result of Hurricane Floyd l Accurate, up-to-date flood hazard information crucial to protect NC lives and properties

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

North Carolina CTS Flood Mapping Program l Cooperating Technical State (CTS) partnership with Federal Emergency Management Agency (FEMA) l State ownership and responsibility for Flood Insurance Rate Maps (FIRMs)

Mapping Products l High-resolution topographic data and accurate Digital Elevation Models (DEMs) l Engineering studies l Countywide digital FIRMs l State-of-the-art, dynamic Information Technology (IT) infrastructure l Real-time flood forecasting and inundation mapping capability

Basinwide Approach to Floodplain Mapping

Three Phases to Mapping Project Phase I—blue Phase II—gold Phase III—green

Phase I — Eastern Six River Basins l Addressing eastern six basins first l Basins most affected by Hurricane Floyd l Comprise approximately half of State

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

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

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

Two Study Contractors l Each to perform 4 Topographic data collection and DEM production 4 H&H Analyses 4 DFIRM production l Work broken out by basin

Topographic Data Collection and DEM Creation l Includes 4 LIDAR surveys 4 Field surveys of structures and channels 4 Automated and manual post-processing 4 DEM creation l Conducted on a basinwide approach 4 Efficiency of scale realized in surveying large geographic areas

Topographic Data Collection and DEM Creation Example: Status of Bare Earth DEM Creation

Engineering Analyses l Hydrology and stream hydraulics do not follow corporate boundaries l Set up H&H models using basinwide approach 4 Allows large areas to be study contiguously 4 Minimizes discontinuities and mismatches

Digital FIRM Production l “Carve” up data into countywide maps 4 Countywide maps more user friendly 4 Corresponds to community-based approach to floodplain management l Merge data for counties in more than one basin

Community Review and Due Process l Community meetings held on county or basinwide basis l Due Process 4 90-day appeal period 4 Evaluate and resolve community comments and concerns 4 Update community ordinances l Printing and distribution of maps

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

Multi-Basin Counties Neuse Basin Tar-Pamlico Basin

Processing Multi-Basin Counties l Process different portions of county separately 4 Produce separate preliminary maps 4 Separate due process l Merge different portions after all portions have gone through due process l Prioritize multi-basin counties

Preliminary Map for Multi-Basin County BLADEN COUNTY AND INCORPORATED AREAS Lumber River 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

Timeline for Multi-Basin County Final Meeting (Lumber) End of Appeal Period (Lumber) Final Meeting (Cape Fear) End of Appeal Period (Cape Fear) Final Elevation Determin. 6 month compliance period 90-day appeal period (Lumber) 90-day appeal period (Cape Fear) 1st Public Notice 2nd Public Notice 1st Public Notice 2nd Public Notice Effective Countywide FIRM Preliminary Issued (Lumber) Preliminary Issued (Cape Fear)

Utilizing a Basinwide Approach for the North Carolina Flood Mapping Program Q UESTIONS ? ? ? ? ?