Why Your BFE is Wrong

The Base Flood Elevation (BFE) represents the Federal Emergency Management Agency’s (FEMA) 1% Annual Chance Floodplain (aka. 100-year flood). Generally speaking, the nearer the structure’s elevation is to the BFE the greater the risk, and for structure elevations below the BFE, the further the structure’s elevation is to the BFE, the more flood water would be expected to inundate the structure during a flood event causing greater damage, therefore higher insurance premiums.

The BFE is also used by planners so a structure can be built above the 100-year floodplain.  And it is frequently used for other insurance, planning, and flood mitigation activities. So, the BFE is one of, if not the most, critical measurements we can use to evaluate and plan for flood risk. With that level of importance, you would assume there would be clear standards for reporting accurate BFE values and penalties for inaccuracy. Sadly, that does not exist today. Moreover, most stakeholders are generally unaware of how their BFE is measured.

There is a standard method for calculating the BFE used by FEMA when establishing an official BFE for a Letter of Map Amendment (LOMA) application. All staff who process a LOMA on behalf of FEMA are trained to use this process. Additionally, training for this method is adopted and provided by the National Flood Association (NFA) and the Association of State Floodplain Managers (ASFPM) for their eLOMA Certification and Certified Floodplain Manager certifications. The procedure leverages not only the Flood Insurance Rate Map (FIRM) but also the highly accurate floodplain engineering and professional land survey data found in the Flood Insurance Study (FIS). The procedure produces an accurate BFE to 0.1’ (that’s 1.2 inches) for your specific structure, but it can take up to an hour to gather the materials and calculate the BFE.

To calculate a flood insurance premium, FEMA’s Flood Insurance Manual (FIM) says a BFE value from an Elevation Certificate (EC), a flood zone determination, or any other source can be used. There is no requirement to use FEMA’s highly accurate LOMA process, or to take data from the FIS as described above.  Since many professionals don’t have an hour to use FEMA’s accurate method for your BFE, they use simpler and faster methods to approximate it. Property owners would be remiss in believing the BFE on the EC, flood zone determination, or any other source is accurate if the document does not say how the BFE was measured.  Remember, if your BFE is inaccurate, you could be paying a lot more for flood insurance than you should be, or you could be building a structure to the wrong elevation.

FEMA’s Flood Insurance Rate Map provides some BFE values printed on the map which look like squiggly lines crossing the floodplain; those BFEs are rounded to a whole-foot number. The BFE line on the map is squiggly for a reason – it’s an estimation and not accurate to the 0.1’ engineering standard in the FIS. Further, the squiggly line is rarely touching your structure, therefore, it’s not the BFE for the structure but rather it is an estimated rounded-off BFE at some unreported distance from the structure. The fact that the number is estimated and isn’t at your structure is not disclosed on an elevation certificate or a flood zone determination – two of the sources used to set your insurance premium. If you see a problem here, so do we.

For the price of an EC, you would expect to receive the highest level of accuracy, but it often is not done as there is no requirement to do so nor is there consequence for using the estimated value from FEMA’s flood maps. It’s not the land surveyor’s fault because the EC instructions are not clear. And it’s not your insurance agent’s fault for the same reason. It’s simply a lack of standards, awareness, and communication about how the most important number for flood insurance is measured and reported.

Several years ago, some flood zone determination providers began placing a BFE on the Standard Flood Hazard Determination Form as a “value-added” service to their customers. It was incorrectly assumed that, since the BFE was on an official federal form, the BFE was guaranteed to be accurate like the flood zone is on that document. But the BFE is not guaranteed to be accurate by most flood zone determination providers, and as a determination can cost under $10, a provider cannot take an hour to use the FEMA technique for accurately calculating the BFE. Consequently, flood zone determination providers typically use a digital technique to find the nearest squiggly BFE line to the structure and reporting that as the BFE value. This method ignores the highly accurate floodplain engineering work and ignores the professional land surveyed cross sections that may be closer to the structure than the estimated squiggly BFE line on the map. Some determination vendors take extra steps to provide a more accurate BFE value by using the mapped cross sections from FEMA’s flood map which contain the more accurate engineered BFE measured to 0.1’ increments, not 1.0’ increments as on the squiggly BFE lines.  That’s a 10x difference in reported accuracy.

Recent language added to the FEMA’s Flood Insurance Manual states that the BFE should be measured at the structure’s foundation, but as stated above, most flood professionals use the number provided on an elevation certificate or flood zone determination because it printed on a federal form. But those professionals are unaware of the inherent inaccuracies as the method used to measure the BFE is not given to them on those forms. It is now more important than ever to properly identify and rate flood risks, and the BFE is a crucial element to accomplish this.

At MassiveCert, we have a simple proposal for the flood risk industry at large to address this issue. The beauty of this proposal is it significantly mitigates the problem without requiring changes to companies’ existing procedures. Rather, it only requires that they report the measurement method for the BFE when one is provided with their flood certification products. Therefore, you know the accuracy of the BFE you are using and can make a more informed choice about the trust you place in that measurement. We suggest FEMA, and the industry at-large, adopt new terms for any document used to report a BFE. Below are brief descriptions of the proposed terms:

  1. “Structure BFE” would be adopted as the term to signify the full FEMA procedure for LOMAs, as taught by  the National Flood Association and the Association of State Floodplain Managers, was employed to produce the Base Flood Elevation to 0.1’ from the Flood Insurance study at the structure’s foundation. Those procedures may be replicated digitally if technologically feasible. This moniker signifies the highest standard for accuracy was used to calculate the BFE. which provides the greatest level of confidence to the professionals who rely on BFE measurements for critical risk actions and will be directly comparable to FEMA’s LOMA BFE.
  2. “Nearest BFE” would be adopted as the term to signify that the BFE value presented to you is not calculated at the structure’s foundation but is the FEMA report value - including mapped cross sections, squiggly BFE lines, and static BFE values - nearest the structure.  In addition, the distance from the structure location to the feature containing the BFE value should be reported. Providing the distance measurement informs the user as to the potential inaccuracy in the BFE value which can trigger further action by the user of the BFE, such as requesting a Structure BFE for the property.
  3. “Approximated BFE” would be adopted as the term to signify that neither the “Structure BFE” nor the “Nearest BFE” procedures were used. The processes employed are varied and could include glancing at the flood map and stating the nearest BFE squiggly line, or digitally measuring to the nearest BFE squiggly line while ignoring engineered and land survey cross section values, or any other technique that is not “Structure” or “Nearest”. This moniker informs the user that the BFE value may not be created by an independently reproducible method and it is unlikely that the value carries any guarantee for accuracy.

It should be expected, if not required, that Structure BFE is a guaranteed accurate measurement meeting FEMA’s standard procedures. The “Nearest BFE” is also easily guaranteed as the process is common and repeatable within a reasonable margin of error, which is reported as the distance from the structure. By distinguishing the production method and accuracy of a BFE and having consequences associated with failing to meet guaranteed accuracy, the flood risk industry will mitigate the significant problem of inaccurate and misleading information being used to assess risk and issue flood insurance policies.

What do you think?  Crazy idea or necessary change?


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