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Missouri State Emergency Management Agency: Promoting Higher Standards with Freeboard Mapping

Challenge

The Base Flood Elevation (BFE), or how high floodwater is likely to rise during a 1%-annual-chance flood event, is one way to measure flood risk. However, there are many factors that can cause flood waters to rise above the BFE such as debris-blocked bridge and culvert openings, city sewer storm drain blockage and development in the floodplain. Plus, floods can be more severe than the 1%-annual-chance event. To reduce flood risk in areas beyond FEMA regulatory flood zones, communities can benefit from additional information about flooding that exceeds the 1%-annual-chance event.

Solution

When the Missouri State Emergency Management Agency maps flood hazards for the state’s counties, in addition to federal regulatory Flood Insurance Rate Maps (FIRMs), they create maps showing the extent of flooding that is 1, 2, and 3 feet above the BFE.

Freeboard, or an additional amount of flooding above BFE, is a safety factor used in floodplain management. The Freeboard Maps developed by the state help to show where it rains it can flood. Using the information provided on these maps, communities can mitigate this risk in areas beyond the Special Flood Hazard Area, the mapped area of mandatory flood insurance purchase.

Communities can use the freeboard delineation on the map to determine the level to which a structure’s lowest floor should be elevated or floodproofed. By adopting these higher standards, communities can help reduce flood risk to development in, around, and beyond high-risk flood areas.

Outcome/Results

  • Communities understand flooding can extend beyond the mapped Special Flood Hazard Area.
  • Emergency managers know the places most likely to flood when the next large event occurs.
  • Shows when a community adopts a stricter ordinance than the federal minimum standard.
  • Communities can see the reduced risk associated with adopting a stricter ordinance.

Benefit

Mapping and managing flood risk in areas beyond the 1%-annual-chance flood event improve public safety and reduce recovery costs after floods. It also decreases the potential for existing development to experience increased flood risk as upstream development occurs. The freeboard approach shows the impacts of increased risk.

A freeboard requirement adds height above the BFE to provide an extra margin of protection against unknown factors. Additionally, electrical, heating, ventilation, plumbing, air conditioning equipment, and other service facilities (including ductwork) must be elevated or waterproofed to the BFE plus freeboard. This reduces damage and reduces the need for Public Assistance, Individual Assistance, and Hazard Mitigation Grant Program funds.

Communities that adopt higher freeboard ordinances and participate in the National Flood Insurance Program’s Community Rating System can score points leading to reductions in flood insurance costs. Communities with freeboard ordinances may earn discounts of up to 45% on flood insurance policies. Including freeboard into a newly constructed residence adds from 0.25 to 1.5% to the total construction cost. This could mean adding $240 a year to a mortgage but saving more than a $1,000 a year on flood insurance for a building in a Zone AE riverine Many of the areas where Freeboard Maps were created had minimal increases in the horizontal area added to the floodplain because the 1%-annual-chance floodplain extends to the “bluffs”—places where the slope of the land rapidly increases.

Many of the areas where Freeboard Maps were created had minimal increases in the horizontal area added to the floodplain because the 1%-annual-chance floodplain extends to the “bluffs”—places where the slope of the land rapidly increases.
Many of the areas where Freeboard Maps were created had minimal increases in the horizontal area added to the floodplain because the 1%-annual-chance floodplain extends to the “bluffs”—places where the slope of the land rapidly increases.
These areas historically have lower claims on flood insurance as well.

Risk Mapping, Assessment, and Planning Program (Risk MAP) Phases

This project involved the following Risk MAP phases:

  • Data Development and Sharing
  • Risk Awareness and Mitigation Outreach
  • National Flood Insurance Program Map Changes and Impacts
  • Preliminary Map Release and Mitigation
  • Resilience

Risk MAP Goals Advanced

The Risk MAP goals advanced through this project include:

  • Increasing Awareness

National Mitigation Investment Strategy Connections

GOAL 2: Coordinate mitigation investments to reduce risk

  • Recommendation 2.1 – Make risk information more available and easier to use
    • Recommendation 2.2 – Align program requirements and incentives

Recommendation 2.3 –

Lessons Learned

Many of the areas where Freeboard Maps were created had minimal increases in the horizontal area added to the floodplain because the 1%-annual-chance floodplain extends to the “bluffs”—places where the slope of the land rapidly increases.

Resources

Missouri Floodplain Management Program

The 1%-annual-chance floodplain is in the standard blue color. The additional 1-, 2- and 3-foot freeboard delineations are green, yellow, and red. Note: In some reaches there is very little difference between the 1%-annual and the 3-foot freeboard delineations.
The 1%-annual-chance floodplain is in the standard blue color. The additional 1-, 2- and 3-foot freeboard delineations are green, yellow, and red. Note: In some reaches there is very little difference between the 1%-annual and the 3-foot freeboard delineations.

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Last updated May 12, 2021