Project 3: Flood Insurance Rate Maps

Kim Rohrs

 

Introduction

The Flood Insurance Rate Map (FIRM) is a map product created and maintained by the Federal Emergency Management Agency (FEMA) to delineate flood zones and hazards.  FEMA, formerly an independent agency, was declared part of the Department of Homeland Security in 2003 and is tasked with responding, preventing, planning for, and mitigating disasters.  FEMA began the flood mapping program to produce the FIRMs as a result of the U.S. Congress establishing a National Flood Insurance Program (NFIP) with the passage of the National Flood Insurance Act of 1968 .

 

Flood Insurance Rate Map

The FIRM is a hardcopy map product that depicts flood information.  This information includes 100 year and 500 year floodplains, flood elevations, floodway and risk premium zones. The FIRMs for Monroe County, Florida are based on the UTM projection, Zone 17, NAD 1927.  The vertical datum referenced for the flood elevation based on the National Geodetic Vertical Datum of 1929.   

FIRMs assist insurance agents, private citizens, and real estate brokers in locating property and corresponding flood risk potential.  Lending agencies use the FIRMs to determine whether flood insurance is required for the property or building they are funding.  In the Florida Keys, where flooding is a risk, almost every homeowner is required to have flood insurance, without it, lending agencies will not process home or business loans.  The FIRMs are also used by State and Local government agencies participating in the National Flood Insurance Program  (NFIP).  The NFIP is a voluntary Federal insurance program to assist homeowners, renters, and business owners in flood prone areas with insurance.  In order to participate in the program, local communities must agree to adopt and enforce a floodplain management program to reduce future flood damage.  This includes adopting flood management ordinances, preparing emergency plans, and inducing preventative and corrective measures to mitigate flood hazards in the future. An estimated 20,000 communities in the United States participate in the NFIP (FEMA 2005).

 

FIRM Metadata for Monroe County, Florida:

 

Base Map:  U.S. Geological Survey Digital Line Graph at 1:24,000 scale.

 

Projection:  UTM Zone 17

 

Horizontal Datum:  NAD 27 , Clarke 1886 Spheriod

 

Vertical Datum:  National Geodetic Vertical Datum of 1929

 


 

Digital Flood Insurance Rate Map

Beginning in 1992, as part of the Flood Hazard Mapping Program, FEMA has created a new mapping product called the Digital Insurance Rate Map (DFIRM) (Figure 1).  The DFIRM is a digital version of the hardcopy FIRM for use with digital mapping software, specifically GIS.  The DFIRMs are comprised of all digital data required to create hardcopy FIRMs; users can determine flood zone, base flood elevation, floodway status.  Also, the DFIRMs include base map information, graphics, text, and shading. The DFIRMs can essentially be compared to a scanned version of the actual FIRMs, except in many cases the DFIRM uses digital orthophotos as a base map (Figure 2).  The majority of DFIRMs are produced in countywide format.  As a means to transfer flood data depicted on the FIRMs to GIS, FEMA created the Digital Insurance Rate Map - Digital Line Graph (DFIRM-DLG).  The DFIRM-DLG is digitized from the hardcopy DFIRMs and includes hydrography, flood hazard zones, and elevation. The DFIRMs for Monroe County, Florida are based on the UTM projection, Zone 17, NAD 1983.  The vertical datum referenced for the flood elevation based on the National Geodetic Vertical Datum of 1929 and and North American Vertical Datum of 1988.     

DFIRMs are created by using base map data provided by local and federal sources.  In the event that a community has current base map information that meets or exceeds FEMA standards, FEMA will use the community's data.  If current data do not exist, FEMA will use the U.S. Geological Survey (USGS) Digital Orthophoto Quarter Quandrangle (DOQs) for the base map.  Road names will be derived from communities or from current FIRM panels or from the U.S. Bureau of the Census Topologically Integrated Geographic Encoding and Referencing System (TIGER) files (FEMA, 2004).

DFIRM Metadata for Monroe County, Florida:

Base Map:  U.S. Geological Survey Digital Orthophoto Quandrangle at 1:12,000 scale and dated from 1994 to 1999.  If Orthophotos were not available, U.S. Geological Survey Digital Line Graphs were used.

 

Projection:  UTM Zone 17

 

Horizontal Datum:  NAD 83 , GRS 80 Spheriod

 

Vertical Datum:  National Geodetic Vertical Datum of 1929 and North American Vertical Datum of 1988

 


 
 

Figure 1:  DFIRM of Plantation Key located in the Florida Keys. DFIRMs are available online and can be searched using location address (FEMA 2006).

 

Figure 2:  DFIRMs contain the same information as the hardcopy FIRMs.  Projection information for this panel is UTM Zone 17 NAD 83 (FEMA 2006).

 


 
Q3 Flood Data
FEMA developed a digital product named Q3 Flood Data to support disaster recovery operations while in the process of producing DFIRMs.  The DFIRMs are intensive to create in both time and resources, and as a result, FEMA decided to create a product that could be useful in the interim.  The Q3 Flood Data only includes certain features from the FIRMs and were created by scanning existing black a white hardcopy FIRMs producing a raster data set.  This scanned document was then vectorized to produce vector data including:  100 year and 500 year floodplains, Coastal Barrier Resources Act areas, politictal areas, FIRM panel areas, 7.5 minute quadrangle areas, and mapaple Letters of Map Change (FEMA 1996).  The Q3 Flood Data does not provide base map data, base flood elevations, cross sections, elevation marks or floodways if not shown on the orginal FIRM (Figure 4).  Q3 Flood Data cannot be used to create a hardcopy FIRM, unlike the DFIRM data.   

Figure 3:  Availability of digital Q3 data (FEMA 2005).

 


 

Figure 4:  Sample of digital Q3 data of Walton County, Florida (FEMA 2005).

 

Data Availability for Monroe County, Florida
The digital Q3 data, hardcopy FIRMs, and hardcopy DFIRMs are available for incorporated and unincorporated Monroe County, FL.  The County is in the process of obtaining the digital DFIRMs and should receive them next week. 
 

Figure 5:  Florida Keys Hurricane Wilma Damage Photographs taken by the Floodplain Administrator on October 25, 2005.  Courtesy of Monroe County, Growth Management.

 
 

 

Roosevelt Blvd. Key West
 

 
Sources
FEMA DFIRMs-Specifications and Procedures (2004) http://fema.gov/fhm/mm_wip5g.shtm Accessed 5 March 2006
FEMA Map Service Center. (2005) http://www.fema.gov/msc/ Accessed 10 March 2006
FEMA Map Viewer.  https://hazards.fema.gov Accessed 10 March 2006.
FEMA Mitigation Division. (2005)  http://fema.gov/fima/nfip.shtm Access 5 March 2006
FEMA (1996) Q3 Flood Data Users Guide.
 

This document is published in fulfillment of an assignment by a student enrolled in an educational offering of The Pennsylvania State University. The student, named above, retains all rights to the document and responsibility for its accuracy and originality.