FEMA releases revised analysis and mapping procedures for non-accredited levees; public comments due by January 30, 2012

Kaskaskia Island 1993 flooding

On December 15, 2011, FEMA released its proposed solution for Revised Analysis and Mapping Procedures for Non-Accredited Levees. The proposed procedures will replace the “without levee analysis” FEMA employed in its Flood Insurance Rate Maps, which FEMA Administrator Craig Fugate suspended in March 2011 as a result of Congressional pressure. The new mapping procedures will significantly affect areas protected by levees and their participation in the National Flood Insurance Program.  

Public comments are due by January 30, 2012 and can be made at the Federal Rulemaking Portal and the National Flood Insurance Program Levees Comment website. The following is a brief summary of the suite of procedures proposed under the new mapping procedure.

FIRMs identify areas that are prone to a 100-year or base flood.  Generally, if a levee is recognized as accredited by FEMA under 44 CFR 65.10 [PDF], then the area protected by the levee is not shown as a “Special Flood Hazard Area,” i.e. an area in which there is a risk of a base flood occurring. In the wake of Hurricane Katrina, FEMA has stepped up its efforts to inspect and de-accredit levee systems across the country that do not meet 44 CFR 65.10′s standards. As a result, in FEMA’s subsequent re-mapping projects, areas protected by de-accredited levees would be subject to the “without levee analysis,” meaning that for the purposes of a FIRM a de-accredited levee would be treated as if it did not exist. The “without levee analysis” has been harshly criticized as a one-size fits all approach to mapping areas protected by levee systems that does not account for the protection, albeit diminished, that a de-accredited levee provides against a base flood.

In response to a letter from Congress in February 2011, FEMA Administrator Fugate suspended re-mapping programs for areas protected by de-accredited levee systems in March 2011 to give the agency time to develop a “suite of procedures” that would replace the “without levee analysis.”  FEMA has proposed the following procedures be adopted to map areas protected by de-certified levee systems:

1. Sound Reach Procedure - For individual sections or “reaches” of a levee system that have been designed, constructed, and maintained to withstand a base flood, FEMA will show a system-wide Zone D area.  The single reach must meet the standard of 44 CFR 65.10 and be shown to be a fully functioning, hydraulically independent levee system in accordance with 44 CFR 59.1 [PDF].
2. Freeboard Deficient Procedure - Freeboard refers to the vertical distance between the top of a levee and the water level that can be expected during a base flood. 44 CFR 65.10 generally requires a minimum of 3 feet of freeboard for an accredited levee. In cases where a levee is structurally sound but does not have and adequate amount of freeboard, FEMA will map the affected area as Zone D based on a the Natural Valley Procedure (as discussed below) and may depict interior drainage areas as well.
3. Overtopping Procedure - Overtopping refers to when water elevation exceeds the height of the levee but does not affect the structural integrity of the levee itself (i.e., water will flow over the levee without washing it away). For systems that can adequately show that levee overtopping will not result in structure failure of the levee, the levee will be analyzed as a “lateral weir,” meaning that some portion of the floodwaters flow over the top of the levee crest. FEMA will measure the overtopping volume of the flooding on the land-side of the levee as a SFHA and may depict interior drainage.
4. Structural-Based Inundation Procedure - Some levee systems are not accredited due to structural integrity issues or where structural integrity is unknown, thus increasing the likelihood of levee failure.  For these areas, FEMA will map the landward area as a SFHA assuming the levee will fail considering possible locations of system breaches, modes of failure, geometry, failure triggers, and failure duration.
5. Natural Valley Procedure - This procedure is essentially the “without levee analysis” and is used when a levee system would not obstruct the river from flowing within the entire natural valley of the floodplain. FEMA will use this procedure when (i) levees do not significantly obstruct the the riverflow (i.e. its a 10 year levee), (ii) there is a “low hazard potential” in the area landward of the levee as defined by the Corps National Committee on Levee Safety, (iii) data necessary for more complex methods are not available, or (iv) the community provides feedback that it is an acceptable procedure to use.

It is important to note that these proposed procedures do not affect the requirements for levee accreditation under 44 CFR 65.10, requirements for new construction progress that have made adequate progress under 44 CFR 61.12 [PDF], requirements for de-accredited levee systems that are being restored provided in 44 CFR 65.14 [PDF], or the standards for Provisionally Accredited Levee systems.

More importantly, these mapping procedures do not currently alter the process for local communities to give information to FEMA.  Many if not most of the procedures described above will require vigorous advocacy on the part of communities being re-mapped by FEMA and coordination with the Corps regarding the status of certain levee systems.

These procedures are an important step in the right direction toward creating FIRMs that better approximate the flood risk associated with land protected by a levee system.  We are in the process of reviewing the new levee mapping procedures in detail and would appreciate any of your thoughts and comments.