Flood Forecast Mapping, Tar River Basin, North Carolina

Project Overview

Hurricane Floyd (1999), the fourth hurricane to impact the State of North Carolina since 1996, produced devastating flooding across eastern North Carolina. Over 4,000 homes and businesses were destroyed and, as a result, the governor requested a program to address flood-mapping deficiencies. In 2000, the National Oceanic and Atmospheric Administration (NOAA) formally agreed to participate in the North Carolina Flood Mapping Project by proposing enhancements to National Weather Service (NWS) flood predictions. Enhancements include flood forecast maps. A demonstration project under the NWS Advanced Hydrologic Prediction Service (AHPS) has been organized for the Tar River Basin in eastern North Carolina.

Objectives

This project was created to display flood forecast information disseminated by the National Weather Service in a graphical, easy-to-read format that will enable emergency managers and disaster planners to better prepare for potential flood conditions. It will improve the delivery of graphical flood information through visualization products and steer the development of future flood forecast mapping tools.

Intended Audience

The intended audience for this project is the National Weather Service and its customers, especially emergency managers, disaster planners, state transportation officials, town managers, and commercial and residential property owners.

Collaboration

Southeast River Forecast Center (SERFC)

The NWS Southeast River Forecast Center will provide enhanced flood forecasts in the Tar Basin through the addition of modeling segments, calibration, and Internet-based graphical representations of flood hydrographs, as well as through Ensemble Streamflow Prediction (ESP) and probabilistic forecasts. In addition, an unsteady flow dynamic hydraulic model is being developed for the Tar River using information provided by new FEMA flood insurance studies. This model accurately predicts flood stages at all points on the river through time, and not only enables prediction of peak flooding, but also transgression and recession of flood waters.

NOAA Coastal Services Center/National Weather Service Partnership

A new partnership with the NOAA Coastal Services Center brings geographic information system (GIS) and modeling expertise to this project. This partnership will enable the development of a flood inundation mapping capability that is incorporated into SERFC's operational forecasts. These flood maps provide a graphical aerial depiction of the forecasted inundation areas and supplement the traditional text and hydrograph forecast products. Using Light Detection and Ranging (LIDAR)-derived elevation data collected by the State of North Carolina, SERFC and the State of North Carolina's Flood Mapping Information System will provide accurate flood forecast inundation maps via the Internet. This presentation highlights the methodologies in flood forecast mapping, GIS products that will be made available as NWS forecast products via the Internet, and new partnerships between federal, state, and local governments. The successful demonstration of this project in the Tar River Basin and several other basins in North Carolina will lead to nationwide implementation.

North Carolina Floodplain Mapping Program

The State of North Carolina, through the Federal Emergency Management Agency's (FEMA) Cooperating Technical Community partnership initiative, has been designated as the first Cooperating Technical State (CTS). As a CTS, the State will assume primary ownership and responsibility of the Flood Insurance Rate Maps (FIRMs) for all North Carolina communities as part of the National Flood Insurance Program (NFIP). This project will include conducting flood hazard analyses and producing updated, digital FIRMs (DFIRMs).

What this project entails

Acquisition of high-resolution topographic data and development of accurate Digital Elevation Models (DEMs).
Use of the DEMs to perform engineering studies to develop up-to-date, accurate flood hazard data and floodplain mapping.
Use of the updated flood hazard data and floodplain mapping to produce seamless DFIRM coverage statewide.
Production of DFIRMs on a countywide basis where the county and its incorporated municipalities are shown on the same set of maps.
Production of Digital Orthophoto Quadrangles in partnership with the State of North Carolina and the U.S. Geological Survey will be used as the primary base map. In areas where there is a locally produced base map that is more current or accurate than the Digital Orthophoto Quadrangle, the locally developed map may be used as the base.
Conversion of FIRMs to the North American Vertical Datum of 1988 (NAVD 88).
Implementation of a state-of-the-art, dynamic Information Technology (IT) infrastructure to analyze, maintain, and archive maps and associated flood hazard data. This system will also distribute the mapping data and associated reports to the public via the Internet.
Development of flood forecasting and inundation mapping capability.

The National Weather Service (NWS) will work with the state to develop and implement a flood forecasting and inundation mapping component as part of its program. LIDAR data of the North Carolina coast, developed by the NOAA Coastal Services Center, will be used to analyze and map coastal flood hazards. Both NWS and the Center will assist the state in completing its requirement analysis for the on-line Information Management System. The Center will also assist the state in defining technology and data standards for its digital mapping products.

Partners

This project is a collaborative effort of the National Weather Service (NWS), the U.S. Geological Survey (USGS), the Federal Emergency Management Agency (FEMA), the NOAA Coastal Services Center, and the North Carolina Floodplain Mapping Program.

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