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  • Floodplain Map
  • Creeks of Boulder
  • Floodplain Development
  • Be Prepared
  • Community Resilience

Maps of Floodplains

Maps of Floodplains

Floodplain maps provide the basis for floodplain management, regulation, and insurance requirements by identifying flood-prone areas that may threaten life and property. They also guide flood management programs, including floodplain regulation, safety, preservation, preparation and mitigation. Floodplain maps are reviewed and approved by FEMA for flood insurance purposes .

Use the Map of Floodplains (Interactive) to see if a property is located in a floodplain.

To have city staff look up floodplain information for a property, apply online through the Customer Self-Service Portal.

The FEMA Map Service Center provides access to a Public Flood Map or a Flood Insurance Rate Map.


Floodplain maps are periodically updated and revised to reflect changing conditions, such as impacts of flooding, new topography, land development, updated mapping studies, and construction of floodplain improvements.

Floodplain map changes can take several forms:

  • Local map changes;
  • Flood Insurance Rate Maps (FIRMs) or Digital Flood Insurance Rate Maps (DFRIMs);
  • Letters of Map Change (LOMCs); and
  • Conditional Letters of Map Amendment (CLOMAs):

The Flood Insurance Rate Map (FIRM) identifies areas in a community that are subject to flooding and shows the associated risks. One of the areas shown on a FIRM is a Special Flood Hazard Area (SFHA), or the 100-year floodplain. This area has a 1% or greater chance of flooding in any given year.

FEMA uses the most accurate flood hazard information available and applies rigorous standards while developing FIRMs. But, because of limitations of scale or topographic definition on the source maps, there may be elevated areas or "islands" that are not actually in the new regulatory floodplain shown on the maps. These island areas may appear relatively small on the FIRM and are sometimes included in the 100-year floodplain by nationwide floodplain map determination companies that prepare floodplain designations on behalf of the mortgage industry. Such cases are referred to as "inadvertent inclusions."

The City of Boulder will try to identify any inadvertent inclusions and let the property owners know of the Letter of Map Amendment (LOMA) processes and the "grandfather" provisions of the NFIP that may apply to them.

A Letter of Map Amendment (LOMA) or a Letter of Map Revision Based on Fill (LOMR-F) is needed to change the designation of an inadvertent inclusion and avoid the federal flood insurance requirements for properties located in the 100-year floodplain. In most cases, a licensed land surveyor or registered professional engineer will need to prepare an Elevation Certificate for the property. FEMA will normally complete its review and issue a decision in four to six weeks.

The granting of a LOMA or LOMR-F removes the federal flood insurance requirement as a condition of federal or federally-backed financing. Mortgage lenders can still require flood insurance as a condition of providing financing, regardless of the location of a structure.

Buying a flood insurance policy is wise even for properties located outside of the 100-year floodplain. More than 25% of claims are made by property owners located outside of the 100-year floodplain.

LOMA and LOMR-F determinations cannot be made by FEMA until after a flood mapping study is officially adopted. Property owners who think they qualify for a LOMA or LOMR-F determination, may want to confirm this by contacting a licensed land surveyor or registered professional engineer today.

Homes that were previously considered outside of the 100-year floodplain and constructed without flood protection measures may be eligible for reduced insurance rates.

The NFIP offers Grandfather Provisions for structures built in compliance with the Flood Insurance Rate Map (FIRM) that was in effect at the time of construction, as well as structures built before a rate map was in place.

If a  building was constructed  before July 17, 1978  (Pre-FIRM construction), it is eligible to maintain the prior flood zone and base flood elevation as long as continuous coverage is maintained and  the policy is bought before the revised FIRM goes into effect. The flood policy can also be assigned to a new owner at the option of the policyholder. Owners who do not get a policy for a Pre-FIRM building before the effective date of the FIRM change are eligible to receive the Pre-FIRM (subsidized) rates based on the new flood zone rather than the actual elevation-based rates.

If a building was constructed  after July 17, 1978  (Post-FIRM construction), it is eligible to maintain the prior flood zone and base flood elevation as long as continuous coverage is maintained and  the policy is bought before the revised FIRM goes into effect. The flood policy can also be assigned to a new owner at the option of the policyholder. If the building was constructed in compliance with a specific FIRM, it is eligible for a policy using the flood zone and base flood elevation from the FIRM that was in place at the time of construction. Proof of the compliant construction and FIRM in place at the time of construction must be submitted to the insurance company as part of getting a policy. Continuous flood insurance coverage is not required to remain eligible for this rating.

  1. Preferred Risk Policies offer low-cost flood coverage to owners and tenants of eligible buildings. Buildings written on Preferred Risk Policies are required to be located in zones of moderate risk of flood, or zones B, C, or X on the FIRM in effect on the date of application and on the date of each subsequent renewal.
  2. A building that becomes ineligible for a Preferred Risk Policy due to a map change to a special flood hazard area (100-year floodplain) can be rewritten on a standard rated policy using zones B, C, or X.