Understanding Your Flood Risk

Patricia Skinner  |  1/17/2007 7:17:43 PM

Our predecessors in Louisiana -- the Indians and the early Europeans -- avoided floods by vacating the floodplains during flood season or by building their homes on the higher ground and, even then, on piers. But we are a less-mobile society and one that has abandoned a certain degree of self-reliance and tradition.

Over the years, we have adopted a slab-on-grade building style that may be inappropriate for this area, and we have altered the landscape to protect our earlier real estate investments.

The concentration of investment in certain areas fairly guarantees that our engineered protection systems will be maintained. But the engineered systems, whether levees or pumps, can provide protection only up to their capacity limit and then only if they are working properly.

Understanding your flood risk means:

  • Recognizing the limitations of engineered systems
  • Realizing that future development within a watershed can alter natural flooding and reduce the effectiveness of existing protection systems.

The National Flood Insurance Program (NFIP) is both an insurance program and a regulatory program. The flood risk determination system used today by insurance agents, floodplain administrators, realtors, bankers and citizens today was developed, and continues to be refined, through the resources of the NFIP. The most-visible component of this system is the Flood Insurance Rate Map (FIRM), which shows areas most likely to flood.

Flood Maps: The Official Source for Risk

Roughly 30% of the Louisiana's land mass lies in Special Flood Hazards Areas (SFHAs). These areas are shown on FIRM maps produced by the Federal Emergency Management Agency (FEMA) or their contractors. The maps are used by insurance agents to rate flood insurance and by parish and local governments in regulating development. Before being adopted for regulatory purposes, the maps are subject to local public review.

The SFHA is an area that will be inundated by the 1% annual chance flood; that is the flood that has a 1% chance of being equaled or exceeded in any year. The 1% annual chance flood is sometimes called the 100-year flood or the base flood. The elevation of the water surface of the base flood is called the Base Flood Elevation (BFE); BFE is an initialism commonly used in the floodplain regulatory and insurance industries.

If your home or office is in the SFHA, has no flood protection and has the lowest floor at the BFE, your risk of having floodwater in the building is 1% a year. If your building is at a lower elevation than the BFE, your probability of flooding is higher than 1% a year.

There is a 26% chance that floodwater will reach the BFE sometime during the life of a 30-year mortgage. This is approximately five times the risk of a house fire over the same time period.

Flood Forecasting Is Not an Exact Science

The boundary between SFHA and not-SFHA is just a line on a map; it’s not a levee. Many communities have experienced events of greater magnitude (less probability) that push floodwaters outside the designated SFHA. In fact, more than 30% of flood insurance claims paid nationally are for properties located outside the SFHA.

Because flood probability forecasting and map-making are both subject to error, some property shown as not in the SFHA may be more at risk of flooding than some property designated as being in the SFHA. If your property is wrongly designated as being in the SFHA, you can have it removed. If you’re shown as "out," but your property is lower than the BFE of the nearest SFHA, your risk is probably higher than the map indicates.

Others Sources of Risk Information

The FIRM is only one tool for determining personal flood risk. Before buying property, building a home or office or planning a flood protection system, talk to the floodplain administrator, permit official, drainage board, parish emergency manager and people who’ve lived in the area a while.


FEMA Flood Insurance Rate Maps - the LSU AgCenter Flood Maps portal.

Find your property on road maps or aerial images, obtain flood zone information, ground elevation data (from the US Geological Survey LIDAR service) and your Basic Wind Speed (part of the building code).

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