Levee Evaluation and Certification under the National Flood Insurance Program (NFIP)

Abstract

Hurricane Katrina raised public awareness of the vulnerability of our nation's levees to failure, due either to deficiencies or an event exceeding design capacity. Prior to Katrina, however, the Federal Emergency Management Agency (FEMA) formulated a program to better understand the location and condition of levee systems currently accredited as providing protection on the Flood Insurance Rate Maps (FIRMs). Following the formation of a Levee Coordination Committee, FEMA issued Procedure Memorandum 34 (PM 34) on August 22, 2005, just prior to Katrina (August 29, 2005), as an interim guidance on the levee policy. PM 34 established guidance for inventorying levee systems and establishing levee review protocol. As part of the levee review protocol, FEMA would provide an inventory of the levee systems. However, the owning agency requesting accreditation of the levee on the FEMA flood maps would be responsible for providing the levee certification and supporting analyses. In September 2007, the United States Army Corps of Engineers (USACE) released a draft Engineering Technical Letter (ETL) 1110-2-570, Certification of Levee Systems for the National Flood Insurance Program (NFIP) (USACE, 2007) , which provides technical procedures for levee certification under the National Flood Insurance Program (NFIP). In September 2008, ETL 1110-2-570 was superseded by EC 1110-2-6067 (USACE, 2008) . To allow more time for the agency to complete levee certifications, FEMA issued PM 43 on September 25, 2006 allowing for the establishment of Provisionally Accredited Levees (PALs) whereby additional time is given to submit certification information. During that time, the levee can be shown on the FEMA flood maps as providing protection on a provisional basis. All existing levees accredited by FEMA as providing protection against a flood having a 1% chance of being equaled or exceeded in any given year (i.e. 1% annual chance, 100-year, or Base flood) must be certified or loose accreditation. Certifying the flood protection system requires conformance to 44 CFR 65.10 of the NFIP Regulations, Mapping of Areas Protected by Levee Systems (CFR 65.10, 1986) , and involves the evaluation of several major components, including: (1) Freeboard; (2) Closures; (3) Embankment Protection; (4) Embankment and Foundation Stability (Stability and Seepage); (5) Settlement; (6) Interior Drainage; and (7) Operations and Maintenance. Failure to submit requested documentation in the required timeframe, 2-years from the date of the PAL agreement, or studies indicate the system does not meet the requirements of CFR 65.10 results in previously protected areas being shown within the 100-year floodplain on FEMA's FIRMs. Refer to Figure 1 and Figure 2 for example FIRMs with and without accreditation, respectively. The same CFR 65.10 requirements apply to floodwalls. This paper addresses an overview of the hydrologic/hydraulic requirements for certification, including freeboard, uncertainty, and interior drainage .