Appendix B

Corps–FEMA Levee Certification Documentation



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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Appendix B Corps–FEMA Levee Certification Documentation

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES DEPARTMENT OF THE ARMY U.S. Army Corps of Engineers WASHINGTON, D.C. 20314-1000 Policy and Planning Division 3 AUG 1992 Mr. John L. Matticks Assistant Administrator Office of Risk Assessment Federal Energency Management Agency 500 C Street, SW. Washington, DC 20472 Dear Mr. Matticks: The Army Corps of Engineers has developed new guidance titled: “Risk Analysis Framework For Evaluation of Hydrology/Hydraulics and Economic In Flood Damage Reduction Studies.” Once adopted, the procedure outlined in that document will be used in the Corps flood damage reduction studies. This recently completed effort, in the form of an Engineering Circular, has been transmitted to our field offices for their final review and comment. As you recall, this effort began as a result of discussions at the August 1991 Hydrology and Hydraulics Workshop in Riverwood, Minnesota. Your participation in that workshop was extremely beneficial and provided a much needed FEMA perspective. Because of the Corps extensive involvement in and support of the National Flood Insurance Program, and the potential significiant impact of this new guidance on Corps methods for hydrologic and hydraulic analyses, your review of this document is important to us. I have enclosed copies for your use and would appreciate any comments you may have. Mr. Jerry Peterson of my staff will contact you in the near future regarding the need for a meeting to discuss the new guidance in future detail. Feel free to contact Mr. Peterson if you have any question in the interim. Sincerely, Jimmy F. Bates Chief, Policy and Planning Division Directorate of Civil Works Enclosures

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Federal Emergency Management Agency Washington, D.C. 20472 APR 23 1993 CERTIFIED MAIL RETURN RECEIPT REQUESTED Mr. Jimmy F. Bates Chief, Policy and Planning Division Directorate of civil work Department of the Army U.S. Army Corps of EngineersWashington, DC 20314-1000 Dear Mr. Bates: This is in response to your letter dated August 3, 1992, regarding new guidance and procedures outlined in your draft circular entitled, “Risk Analysis Framework for Evaluation of Hydrology / Hydraulic and Economic in Flood Damage Reduction Studies,” dated June 30, 1992. Thank you for allowing us to review information presentation conducted by the U.S. Army Corps of Engineers (ACE) at our offices on March 2, 1993. By having the opportunity to ask questions, Federal Insurance Administration personnel gained a better understanding of the new procedures. Please relay our thanks to Messrs. Jerome Peterson, Earl Eiker, Bob Daniel, and Ken Zwickl of your staff. We recognize that the new procedures contained in this circular are designed to account for the uncertainties inherent in hydrologic and hydraulic analyses when determining risk of failure of a flood control structure. As you know, our particular interest is whether we should recognize, on our maps, that a flood control structure provides protection from the base flood. Our regulations define the base flood as the condition of inundation having a one-percent chance of being equalled or exceeded during any given year. We have enclosed copies of the pertinent portion of our regulations for your convenience. Our policy has been to recognize on our maps that a levee provides protection from the base flood if the ACE certifies that the levee provides that level of protection, It has been suggested that implementing the new procedures would restrict future certifications by the ACE by qualifying the level of protection in terms of reliability. For example, the ACE could determine that a levee will safely convey the 100-year discharge with 90-percent reliability. Contrary to

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES that suggestion, we belive the circular allows the ACE to be quite explict. The new procedure determine the value that fills the blank in the following statement: The levee has a ___ percent chance of being overtopped in any given year. If the value is equal to or greater than 1.0 then we do not credit the levee on our maps; if it is less than 1.0 then we do credit the levee on our maps. Traditionally, the term base flood hass been synonymous with 100-year discharge. Because the methods used to define the base flood elevations essentially are one-to-one relationships between the discharge and elevation, no distinction was necessary between the base flood and the 100-year discharge. However, accounting for the uncertainties inherent in hydrologic and hydraulic analysis as described in the draft circular eliminates that convenient relationship. That is, a distinction must be made between the base flood and the 100-year discharge. Because our definition of a base flood does not depend on a particular discharge, we belive that the ACE can certify that a levee has been adequately designed and constructed to provide protection from the base flood without the aforementioned qualification. The basis of such a certification would be a determination that the levee is structurally sound and everywhere higher than the elevations determine to have a one-percent chance of being equally or exceeded in any given year. That would be the elevation corresponding to a simulation exceedance (true) probablity of 0.01 in Table 3 of Appendix B to the draft circular. In addition to the Federal Emergency Management Agency (FEMA), other programs, particular at the State and local levels, will be affected by your proposed procedures. At the annual meeting of the Association of State Floodplain Managers(ASFPM) in Atlanta, Georgia, in March 1993, many officers of the ASFPM expressed a concern about the ACE 's new riskbased analysis for levee certification. Additionally, several other members of the ASFPM with responsibility for floodplain management activities at the State and local shared similar concerns with members of my staff. It was explained that many of the states have adopted legislation or regulations that require the State and local bodies of goverment to assure that a specific number of feet of freeboard exist before a levee can be accredited. These ASFPM officers and members were very concerned that the new ACE procedures would put them in conflict with their own State and local statutes. I would urge you to obtain public comments on the ACE procedures before you finalize this engineering circular. Perhaps a briefing of the ASFPM comparable to that which you conducted in our offices would be of great benefit. Or, you may want to consider proposed and final rule-making with a public comment period to adopt the circular as ACE regulations. Otherwise, I fear you may be a target for some undesired congressional intercession. We trust that this letter clarifies how your new procedures fit into the National Flood Insurance Program and, in particular, that the ACE can still certify levees for flood insurance purposes

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES without qualifying that certification. Again, thank you for the opportunity to review and comment on this draft circular. Mr. William R. Locke of my staff will serve as liaison during the implementation phase of these new procedures outlined in the draft circular. If you have any questions, you may contact him either by telephone at (202) 646-2754 or by facsimile at (202) 646-3445. Sincerely, John L. Matticks Assistant Administrator Office of Risk Assessment Federal Insurance Administration   Enclosure cc: Mr. Jerome Peterson Chief, Floodplain Management Services and Coastal Resources Branch U.S. Army Corps of Engineers

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES Federal Emergency Management Agency Washington, D.C. MAR 21 1996 Major General Stanley G. Genega Director of Civil Works Department of the Army U.S. Army Corps of Engineers Washington, DC 20314-1000 Dear This is regarding our letter to the U.S. Army Corps of Engineers (USACE) dated April 23, 1993, concerning our comments on your draft circular entitled Risk Analysis Framework for Evaluation of Hydrology/Hydraulics and Economics in Flood Damage Reduction Studies, dated June 30, 1992. We had the opportunity to meet with USACE staff on September 13, 1995, to discuss the Federal Emergency Management Agency's (FEMA's) re-evaluation on Risk-Based Analysis with respect to FEMA's current levee certification policy. It has come to my attention that the USACE has adopted a new levee design policy predicated on a risk-based approach. This risk-based analysis no longer incorporates freeboard as a design parameter. In May 1995, we sent you a letter stating we were reviewing our position on Risk-Based Analysis as it pertains to our current levee certification policy and the comments in our April 1993 letter. As part of this ongoing review, a member of our staff attended a week-long training course in Risk-Based Analysis procedure. In addition, we reviewed the final results of analyses for 12 USACE projects provided to us by your staff. Based on this initial review, it became apparent that the criteria discussed in our April 1993 letter may not, in themselves, be the most appropriate standard for use by the USACE when certifying to FEMA that a levee may be credited for the purposes of removing the Special Flood Hazard Area (SFHA) designation from areas protected by that levee. Our April 1993 letter pointed out that when using the Risk-Based Analysis procedures, the USACE could certify to FEMA that a levee provides protection from a base (1-percent) or less frequent flood without the use of a percent reliability That letter was not intended to indicate that the USACE must certify levees to

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES FEMA if the simulation exceedance (true) probability was 0.01 or less. For the 12 USACE projects, the simulation exceedance (true) probability standard of 0.01 referenced in our April 1993 letter produced levee designs with only 0.1 to 1.5 feet of freeboard and contained the FEMA base flood with a reliability of between only 50 and 75 percent. I am concerned that there may be a potential for conflict between levee projects designed by the USACE and by other Federal Agencies and Private Engineering firms. It is conceivable that levee designs (especially levee heights) would differ significantly between the USACE and others, although both would be designed to provide protection against the one-percent chance event. At this point, we are asking that the USACE continue to use the engineering and judgment expertise you are known for when certifying levees to FEMA, and not rely merely on the simulation exceedance probability if that, in the opinion of the USACE, results in unacceptable freeboard height. Although we are rescinding the April 1993 letter and restoring the previous certification criteria, I believe that would be in the best interests of FEMA and the National Flood Insurance Program to continue dialoguing on this issue. Until such time as detailed criteria can be developed (which may include the concepts of annual exceedance probability and reliability), FEMA will continue to accept letters of certification from the USACE stating that a particular levee has been adequately designed and constructed to provide protection against the FEMA base flood as a means of removing the SFHA designation from areas behind the levee. I look forward to discussions with you on this matter and other issues of mutual interest. Sincerely, Richard W. Krimm Acting Associate Director Mitigation Directorate cc: Jerome Peterson, USACE

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES DEPARTMENT OF THE ARMY U.S. Army Corps of Engineers WASHINGTON. D.C. 20314-1000 05 DEC 1996 Planning Division Flood Plain Management Services and Coastal Resources Branch Mr. Richard W. Krimm Associate Director Mitigation Directorate Federal Emergency Management Agency Washington, DC 20472 Dear Mr. Krimm: This concerns your letter of March 21, 1996, and our recent discussions regarding the use of risk-based analyses in flood damage reduction project planning and levee certification for National Flood Insurance Program (NFIP) purposes. I strongly believe that the risk-based approach to project formulation provides important information on potential levee performance that should be utilized in levee certification decisions. As we have discussed, our desire to introduce these concepts into levee certification decisions must be tempered with your need to maintain consisteacy with existing regulations. With that in mind, we have developed specific guidanc to ensure application of engineering principles and judgement when the U.S. Army Corps of provides levee certification information to your agency in support of the I would appreciate your commems on the enclosed guidance. It is our intent to provide the guidance to our districts and divisions as soon as possible to eliminate any confusion that may exist on this issue. Sincerely, John P. D'Aniello, P.E. Deputy Director of Civil Works Enclosure

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES DEPARTMENT OF THE ARMY U.S. Army Corps of Engineers WASHINGTON. D.C. 20314-1000 10 APR 1997 CECW-P/CECW-E MEMORANDUM FOR ALL MAJOR SUBORDINATE COMMANDS SUBJECT: Guidance on Levee Certification for the National Flood Insurance Program Use of risk-based analysis by the U.S. Army Corps of Engineers in flood damage reduction project formulation studies has created a disconnect between the Corps analysis and the Federal Emergency Management Agency's (FEMA) levee certification policy. FEMA's policy requires that levees be structurally sound, properly maintained, and have at least three feet of freeboard above the 100-year flood profile elevations before FEMA will recognize that the levees provide protection. The Corps risk-based analysis eliminates the concept of arbitary freeboard by incorporating risk and uncertainty throughout the formulation process. To ensure that levee certification to FEMA is performed by the Corps in a consistent manner, the enclosed guidance has been developed for use by all Major Subordinate Commands (MSC). This guidance has been reviewed and accepted by FEMA, and establishes Corps-wide standard procedures applicable to all future levee certification decisions. It is recognized that levee certification commitments based on existing FEMA regulations have been made to non-Federal sponsors for some projects in progress. Exceptions to the new guidance will be considered for uncertified projects for which levee certification commitments already have been made. Each MSC should submit a list of projects that fall into this category, along with a justification for the exception, to CECW-EH by NLT 30 April 1997. Points of contact for this guidance are Mr. Earl Eiker, telephone (202) 761-8500, or Mr. Ken Zwickl, telephone (202) 761-1855. FOR THE COMMANDER: RUSSELL L. FUHRMAN Major General USA Director of Civil Works   Encl DISTRIBUTION: See next page.

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES CECW-P/CECW-E 25 March 1997 GUIDANCE ON LEVEE CERTIFICATION FOR THE NATIONAL FLOOD INSURANCE PROGRAM PURPOSE AND APPLICABILITY: This document provides guidance to be used for certifying levees to the Federal Emergency Management Agency (FEMA) for their administration of the National Flood Insurance Program (NFIP). This guidance does not affect plan formulation and evaluation procedures. It is intended to provide a consistent methodology for levee certification by the Corps of Engineers. This guidance applies to all Corps District and Division offices. Note that levee certifications are provided to FEMA at the District/Division option and within available funds. BACKGROUND: By letter dated 21 March 1996, FEMA requested that the Corps review its criteria for levee certification in order to ensure consistency in administration of the NFIP by FEMA. This concern has arisen as a result of the Corps application, of Risk-Based Analysis (RBA) in flood damage reduction project formulation studies. FEMA's policy requires that levees be structurally sound, properly maintained, and have at least 3 feet of freeboard above the 100-year flood profile elevations before FEMA will recognize that the levees provide protection from the 100-year flood. The FEMA requirements are fully explained in 44 CFR, Chapter 1, Part 65.10 of the Code of Federal Regulations. The FEMA requirements include data and analysis submission requirements for design criteria (freeboard, closures, embankment protection, embankment and foundation stability, settlement, interior drainage), operations plans and maintenance plans. 44 CFR Part 65.10 also states that in lieu of the structural requirements and data and analysis requirements, a Federal agency with responsibility for levee design may certify that a levee has been adequately designed and constructed to provide 100-year protection. Levee certification for NFIP purposes can best be explained as follows. FEMA may request a “levee certification” from the Corps by letter directly to the Corps District office. The letter normally contains language such as: “...Please provide this office with current certification as to whether the design and maintenance of this levee are adequate to credit it with 100-year flood protection. Please note that such a statement does not constitute a warranty of performance, but rather the Corps current position of the levee system's design adequacy...” POLICY: The Corps will continue to work with FEMA to ensure that Risk-Based Analysis provides improved information for levee certification decisions. The following guidance and decision tree should be used until further notice. (Page 1 of 3)

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES CECW-P/CECW-E 25 March 1997 GUIDANCE ON LEVEE CERTIFICATION FOR THE NATIONAL FLOOD INSURANCE PROGRAM Existing Levees, No Risk-Based Analysis Available: For certification purposes, the Corps should evaluate the levees based primarily on FEMA criteria contained in 44 CFR Chapter 1, Part 65.10. Thus, the general rule will be that if a levee will contain the median one percent chance flood, with three feet of freeboard, it should be certified as being capable of passing the FEMA base flood, as long as it is adequate based on a geotechnical and structural evaluation, as described below. Exceptions to the three feet of freeboard requirement may be pursued, based on the FEMA policy of permitting other Federal agencies responsible for levee construction to certify that levees will pass the FEMA base flood. Such exceptions should be based on careful evaluation of the hydrologic, hydraulic, structural and geotechnical uncertainties, and current levee condition as discussed below. Existing and Proposed Levees, Risk Based Analysis Available: In these cases, output on project performance from the Risk-Based Analysis should be used to arrive at a decision regarding levee certification for FEMA. Existing and proposed levees will be certified as capable of passing the FEMA base flood if the levees meet the FEMA criteria of 100-year flood elevation plus three feet of freeboard, with two exceptions, as follows. When the FEMA criteria results in a “Conditional Percent Chance Non-exceedance” (Reliability) of less than 90%, the minimum levee elevation for certification will be that elevation corresponding to a 90% chance of non-exceedance. When the FEMA criteria results in a reliability of greater than 95%, the levee may be certified at the elevation corresponding to a 95% chance of non-exceedance. For existing levees, the certification decision is also contingent upon a structural and geotechnical evaluation, as described below. For proposed levees, the geotechnical and structural issues are assumed to be accounted for during design and construction of the levees. Engineering Evaluation: A geotechnical and structural evaluation will be used to determine the water elevation at which the levee is not likely to fail. In some cases, this water level will be the determining factor in the decision to certify the levee system. The procedures to be used in the evaluation of a levee system for NFIP levee certification should consist of an engineering evaluation to determine if the levee system meets the Corps design, construction, operation and maintenance standards, regardless of levee ownership or responsibility. The District will examine available existing information and data, such as original design, surveys of levee top profile, levee cross-sections, records of modifications and changes, performance during past flood events, and remedial measures. It will also include a field inspection of the levee, structures, closure devices and pumping stations to evaluate the adequacy of maintenance. The engineering analysis should examine the project with respect to embankment stability, underseepage, through seepage, and erosion protection. Existence of closure devices will necessitate a review of the adequacy of flood warning time for the complete operation of all closure structures. (Page 2 of 3)

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RISK ANALYSIS AND UNCERTAINTY IN FLOOD DAMAGE REDUCTION STUDIES LEVEE CERTIFICATION DECISION TREE FEMA Criteria = 1% chance median annual flood event plus three feet of freeboard RELIABILITY = % chance non-exceedance given the 1% chance annual event occurs (Page 3 of 3)