Floodplains are generally flat areas next to a stream that are covered by flood waters when the stream overflows. Centennial and Arapahoe County regulate the 100-year floodplain. 

• Provide floodplain maps to the public
• Complete evaluations and comment on whether property and structures are floodprone (a referral to FEMA may be required for an official determination)
• Review elevation certificates for insurable structures within the floodplain
• Provide general information on flood insurance and the National Flood Insurance Program (NFIP)
• Review land development plans for floodplain impacts and compliance with local, state, and federal regulations
• Review and issue Floodplain Development Permits for improvements within or adjacent to regulatory floodplains

Floodplains are generally defined by the Special Flood Hazard Area (SFHA) shown on Flood Insurance Rate Maps (FIRMs) published by the Federal Emergency Management Agency (FEMA), by the 100-year floodplain limits shown on Flood Hazard Area Delineation (FHAD) studies, and by other local floodplain maps.

• For newly purchased homes, real estate professionals are required to disclose if a building is in a SFHA at the time of a property sale.
• For newly purchased homes with federally backed mortgages, lenders will notify borrowers if their property is in a SFHA and if flood insurance is required as a condition of the mortgage loan (National Flood Insurance Reform Act of 1994). 
• Request a floodplain map for a property within Centennial or unincorporated Arapahoe from SEMSWA. 

Flood Insurance Rate Map (FIRM) 

A Flood Insurance Rate Map (FIRM) is the official FEMA flood hazard map. FIRM maps are split into panels that are numbered with a letter suffix. The letter suffix is the version of the FIRM panel. If a FIRM panel is updated, it keeps the panel number and gets the next letter in the alphabet as its suffix.  

Special Flood Hazard Areas (SFHAs)

SFHAs have the highest risk for flooding, shown on FIRMs as Zones A or V. Over a 30-year mortgage, homes in Zones A or V have a 26-percent chance of being flooded. 

Flood Hazard Area Delineation (FHAD)

A FHAD is a local flood study prepared on a watershed basis. In the Denver Metro, these are completed by the Mile High Flood District (MHFD). FHADs are adopted by the State and affected communities. 

How are floodplain maps updated? 

Floodplain maps can be updated multiple ways. Note, a FEMA process must be followed to change a FEMA map.  

SEMSWA has an ongoing partnership with MHFD to update flood maps by producing FHADs. You can see upcoming studies and learn more at MHFD’s website. FHADs that are submitted to FEMA as Physical Map Revisions (PMRs, see below) become part of the next update to affected FEMA FIRM panels. 

FEMA maps are updated for several reasons including: newer topography data, new man-made structures (such as a dam or pond, bridge or culvert, channel improvements), new land development, climate change, reconfiguration of the floodplain (filling, grading, mining, etc.), and newer modeling techniques and software.

FEMA has different processes to follow depending on the reason for the map change. Their process includes forms that must be filled out by the applicant and a professional engineer or surveyor. 

CLOMR (Conditional Letter of Map Revision) is FEMA’s comment on a proposed project that will impact the SFHA. Impacts to the SFHA can be a modification of the footprint of the regulatory floodway, increase in the flood elevations, or the footprint of the Special Flood Hazard Area (SFHA).

The letter does not revise an effective FIRM map or its SFHA, and a CLOMR is not a permit. An approved CLOMR indicates how FEMA would recognize the impacts of the proposed project. 

Note: the project must be built to the proposed project specifications for the CLOMR to be valid. 

Once a project is completed, the community must request a LOMR to revise the effective FEMA map.

LOMC (Letter of Map Change) is a general term used to refer to the several types of changes to FEMA maps that can be accomplished by a letter. See types below:

A LOMA (Letter of Map Amendment) is a letter from FEMA officially amending the effective FIRM, which establishes that a property or structure is not located in a FEMA SFHA (Special Flood Hazard Area). A LOMA does not mean the structure or lot is safe from all flooding; it means that the risk of flooding is not as high as it is in the SFHA. 

A LOMR (Letter of Map Revision) is a letter from FEMA officially revising the effective FIRM to show changes in zones, delineation, and flood elevation of floodplains and floodways.

Note: In some circumstances, a LOMA or LOMR-F has already been completed for the property in question. By logging into FEMA’s Mapping Information Platform and reviewing the previously completed LOMAs and LOMR-Fs for the community, SEMSWA can determine if one was submitted. In addition, FEMA’s Map Service Center website contains digital copies of completed LOMA and LOMR-F determination documents.

PMR (Physical Map Revision) – A PMR is an action where one or more FIRM panels are revised and republished (with a new lettered suffix). A PMR changes flood risk zones, floodplain and/or floodway delineations or footprints, base flood elevations (BFEs), and/or other map features. PMR procedures include a community comment period where affected residents can provide input as well as a 6-month compliance period for the community to update ordinances while the new maps are printed and distributed. A PMR can take a few years to complete because of the large amount of flood hazard information incorporated into the maps and the number of people that will be affected.