| Digital Mapping: FEMA DIgital Flood Mapping Program
The Federal Emergency Management Agency converts flood insurance rate maps to digital format, anticipating shorter production time and decrease cost.
By Stan Grzeda Introduction
While the most recent flooding throughout the U.S. regions has brought these hazards into daily public attention, the U.S. Congress passed the National Flood Insurance Act in 1968 and further expanded it through the Flood Disaster Protection Act of 1973. The 1968 act established the Federal Emergency Management Agency (FEMA) as the administrator of the National Flood Insurance Program (NFIP) whereby flood insurance became available to communities adopting floodplain managment programs mitigating future flood losses. The act also provided for required identification of all U.S. floodplain areas along with their respective flood-risk zones.
Flood Insurance Studies (FISs) are utilized by FEMA to acquire flood risk data through hydrologic and hydralic studies. Currently, FISs have been completed for virtually all of the 21,400 nationwide communities with flood risks. The results of each Flood Insurance Study are utilized by FEMA's Technical Evaluation Contractors to prepare the Flood Insurance Rate Map (FIRM). These maps depict the spatial extent of Special Flood Hazard Areas, areas subject to inundation by the 100 year flood (> 1 percent annual probability) and other thematic features. The FIRM is the basis for floodplain management, mitigation and insurance activities of the NFIP being utilized as the basis for establishing flood coverage premium rates. Over 80,000 different FIRM panels have been published with 6 to 8 million copies distributed annually. Digital Flood Mapping Program
FEMA investigated the feasibility of NFIP mapping and engineering automation as a result of the rapid implementation of computer based technologies to cartography and the subsequent development of geographic information systems (GIS). A series of technological assessments and pilot projects provided the confidence that conversion to automated methodologies was feasible. A plan was implemented in Fiscal Year 1992 to automate, beginning with the conversion of FIRMs to a digital format.
The conversion of FIRMs to a digital format (DFIRMs) is anticipated to shorten production time and decrease costs associated with the preparation of new and revised FIRMs as well as providing the database for automating the massive FIRM storage, retrieval, and distribution system. In addition to these internal benefits, FEMA also expects FIRM end users, especially at state and local government levels, to benefit from the increased capability to perform analytical and administrative tasks required under the NFIP. FEMA has established a crediting plan for local government use of GIS technology and DFIRMs as an element of the Community Rating System to encourage the use of digital FIRMs.
Since Hurricane Hugo, the Federal Insurance Administration (FIA) has attempted to support disaster relief operations with digital Flood Insurance Rate Maps (DFIRMs) in order to provide speedier relief to flooding victims. The use of digital flood data has provided significant time savings and more effective map use in performing the required flood hazard assessments for disaster loan closings by the Small Business Administration (SBA), Temporary Housing, Individual Assistance and Family Grant Programs, and Temporary Housing Programs. Recent funding increases for post-disaster mitigation activities have also lead to extensive geographic information systems (GIS) and digital FIRM use for planning activities. Applications include selection of sites for relocation, prioritizing eligibility for home buyout programs, and identifying repeatedly damaged properties in Special Flood Hazard Areas.
To support disaster operations, FEMA's Risk Assessment Branch developed specifications for a digital "Emergency FIRM," or Quality Level 3 DFIRM (Q3) that can be created rapidly and at minimal costs. This product has the advantage of being far less costly, in time and resources to produce than the Quality Level 1 engineered Digital Flood Insurance Rate Map (DFIRM) product, or the complete Quality Level 2 thematic flood risk overlay created from existing paper FIRMs, the DFIRM-Digital Line Graph (DFIRM-DLG) data. The Q3 flood data product is designed to serve the needs of FEMA for both response and recovery activities, as well as NFIP flood insurance policy marketing initiatives. This product is designed to allow rapid access to and distribution of digital FIRM data, while maintaining compatibility with all current and developmental flood data efforts.
Thus, the Digital Flood Mapping Program has two current objectives of: rapidly developing the digital flood data product (Q3) from effective Flood Insurance Rate Maps (FIRMs); and phased conversion of existing Flood Insurance Rate Maps (FIRMs) into the Digital Flood Insurance Rate Map format (DFIRM). Short term goals seek the creation of digital flood data product (Q3) covering over 880 priority counties within a one year production program (1996) and subsequent ongoing biannual product maintenance. Long term goals intend the creation of Digital Flood Insurance Rate Maps (DFIRM) on a countywide basis through a multi-year ongoing production and maintenance program. FEMA Digital Flood Data Users
Digital flood data is utilized at all government and public/commercial levels. FEMA utilizes the data to support several levels of effort. This data supports Disaster Field Offices and the Disaster Assistance Center in response and recovery activities, while the Mitigation Directorate utilizes the data in flood insurance studies, repetitive losses investigations, elevation certification and natural hazards assessments. The Federal Insurance Administration also incorporates data usage to maintain flood insurance policy database currency, policy misrating evaluations and as marketing support information. State, regional, county and community agencies use digital flood data for floodplain management, planning, zoning and permitting activities. The commercial sector utilizes this data to perform flood insurance studies, map revisions, disaster response along with map determinations by or for lenders, insurance agents and realtors. Value added vendors have begun to use the data incorporating it into a variety of applications.
Computer system hardware requirements to utilize flood data effectively include: 386 or higher PC; CDROM drive (optional); 3.5" drive; 8mm tape drive (optional); and a VGA monitor. While DFIRM data are provided in DLG format on 8mm tape in UNIX TAR protocol, Q3 flood data is available in DLG, ARC/INFO and MapInfo formats on CDROM or through the Internet. The Q3 data may be used directly with DLG, ARC/INFO, ArcView, MapInfo, ArcCad and GenaSys application software. With file conversion the data may also be utilized with MicroStation (DGN), AutoCad (DXF) and AtlasGIS (DLG) software. DFIRM Data
The Digital Flood Insurance Rate Map (DFIRM) depicts the spatial extent of Special Flood Hazard Areas in relation to other thematic features for flood-risk assessment. The DFIRM product is intended to convey all thematic information required to implement the mandate of the NFIP and as a result automated cartographic techniques are utilized to replicate manually produced FIRMs. Specifications for the digitization of FIRMs to create the DLG-3 thematic flood risk overlay are generally consistent with those required for mapping at a scale of 1:24,000. As such, DFIRM data is optimized for USGS 7.5-minute topographic quadrangle map overlay. Increasingly, highly detailed large scale digital mapping is becoming available and such data is becoming readily available from state and local governments, as well as private sector firms. DFIRMs are intended for use in combination with such data.
Respective DFIRM feature data includes all floodplain boundaries and zone designations, base flood elevations (BFEs), cross sections with letter identifiers, political boundaries, Federal Information Processing Standards (FIPS) and Community ID (CID) codes, FIRM panel outlines and associated panel numbers. Official change information to the effective NFIP map, Letter of Map Change (LOMC) information is also incorporated into DFIRM data as is metadata. Thus, each DFIRM reflects its associated effective FIRM along with LOMC information in a DLG format. DFIRMs provide: hardcopy maps for all respective needs served by FIRMs; rapid support for disaster response requirements; provision of community CRS credits; support in community planning and zoning applications; assistance for floodplain management activities, enabling more effective map determinations; and support to the development of value added products.
Regardless of the base map source and scale of digital data used in conjunction with DFIRMs, users should bear in mind that the DFIRM is foremost the result of hydrologic and hydraulic engineering processes, not a cartographic process. Inherent in these engineering processes are many uncertainties of both data and methodology. The resulting regulatory Base Flood Elevations (BFEs) and the Special Flood Hazard Area (SFHA) delineations are also impacted by tolerances and specifications used in the development of hardcopy FIRM maps. Recognizing these issues, FEMA has consistently noted that the FIRM should be used as guide to the spatial extent of flood hazards within a community. Sound judgement must be used, particularly when analyses performed involve areas located within tens-of-feet of SFHA boundary areas. FEMA guidance has been that in such circumstances comparison of the topographic data relative to the site or structure, and to the BFE as determined from the flood profile in the FIS study text, is the best means to resolve issues related to floodplain location for floodplain management and insurance purposes. Q3 Flood Data
The Q3 flood data is intended to depict all Flood Insurance Rate Map (FIRM) information in a raster form, while including horizontally controlled select features in a vector form. This data has been developed to satisfy the need for digital data that can support computer based activities in mitigation, disaster response, flood insurance policy marketing, community CRS credits, planning and zoning, in/out determinations and value added product development as well as support the needs of a publish-on-demand system.
While a demo CDROM has been released along with associated documentaion, initial Q3 flood data set releases are intended to commence early 1996 and be completed within six months. The production schedule continues to be adjusted to support necessary response to declared disasters. Completed data sets will cover over 880 counties nationwide including 8,800 communities. This data will provide information for 80 percent of the households at risk from flooding. With the initial product release completion anticipated by July 1996, the maintenance phase will commence providing biannual Q3 flood data updates.
Q3 flood data is developed by scanning and digitizing existing hardcopy FIRMs in order to produce both raster data suitable for display or printing and select thematic flood risk vector data. While the Q3 raster data is intended to provide all FIRM data, the vector data will be limited to: 1 percent and .2 percent annual chance floodplain boundaries and zone designations; political boundaries; FIPS and CID codes; FIRM panel neatlines and panel numbers. Associated LOMC and metadata are also included in the data sets. Thus, the Q3 vector flood data provides quick, effective FIRM data in DLG, ARC/INFO and MapInfo formats. These are countywide products, horizontally controlled to 7.5 minute USGS quads, though a 250' buffer is recommended for most applications. DFIRM - Q3 Comparative Features
The DFIRM is comprised of all digital data required to create the hardcopy FIRM. This includes base map information, graphics, text, shading, and other geographic and graphic data required to create the final hardcopy FIRM product to FEMA standards and specifications. This product serves the purpose of the map design and provides the database from which the Digital Line Graph (DLG) thematic product of the flood risks is extracted to create the DFIRM-DLG. The product is generally produced in a countywide format. DFIRMs are subjected to community review and approval and are, therefore, the official basis for implementing the regulations and requirements of the NFIP within the community. Specifications for digitizing DFIRMs are consistent with those required for mapping at a scale of 1:24,000 or larger. The features depicted on a DFIRM include:
• 1 percent and 0.2 percent Annual Chance
• Letters of Map Change (LOMCs) Floodplain Boundaries
• Coastal Barrier Resources Act Boundaries
• Floodways
• Base Flood Elevations (BFEs)
• Gutters (Zone Breaks)
• Cross Sections
• Political Boundaries
• Elevation Reference Marks (ERMs)
• FIRM Neatlines
• Base Map Data (Streets, etc.)
• Quad Neatlines
The Q3 flood data do not replace either existing hardcopy FIRM or DFIRM products. This product has been designed to support planning activities, some Community Rating System (CRS) activities, insurance marketing, and mortgage portfolio review. It does not provide base flood elevation information; thus, it has limited application for engineering analysis, particularly for site design or rating of flood insurance policies for properties located within SFHAs. Q3 flood data are not tied to a base map, are not used to produce a new version of the hardcopy FIRM, and are not subjected to community review. Q3 flood data are intended to provide users with automated flood risk data suitable for determining whether features are within or outside the SFHA.
The Q3 flood data product can be a valuable tool to assist in screening property addresses within a GIS to determine flood risks. However, as the geographic processing performed to develop the Q3 flood data may introduce differences with the source hardcopy FIRMs, user must apply considerable care and judgement in the application of this product. For instance, the Q3 flood data may be overlaid on highly detailed large scale community base mapping data, but, if parcel level determinations are made, they must be prefaced with information about the accuracy of the data from which thay are derived.
The features depicted on a Q3 include:
• 1 percent and 0.2 percent Annual Chance
• LOMCs Floodplain Boundaries
• COBRAs (OuterBoundaries)
• Political Boundaries
• Metadata
• FIRM Neatlines Summary
The FEMA Digital Mapping Program is developing timely and effective digital flood data to serve various levels of user needs. While it is impossible for FEMA to produce data to support all mapping software applications and format requirements, that which is developed should support the majority of users. Primary considerations have been given to: vector data structures compatibility; topological data structure support; data import/export compatibility with user dominant software applications; data compatibility to support future standards (SDTS); thorough documentation; and continued support maintenance by a major public agency. The FEMA Digital Flood Mapping Program continues to support existing and emerging user requirements. About the Author:
Stanislaw Grzeda is the FEMA project computer systems manager at Michael Baker Jr. Inc. in Alexandria, Va. He may be reached at 703-960-8800 (voice), 703-960-9125 (fax) or e-mail: [email protected] Back |
