Levee certification for FEMA's flood maps
William B. Meyer, CFM, Technical Director, AMEC Earth & Environmental, Inc., Lakewood, Colorado, and Brett A. Howey, P.E., Unit Manager - Geotechnical Services, AMEC Earth & Environmental, Inc., Tempe, Arizona
Humans have long settled beside river banks to sustain the basic needs of agriculture, transportation and drinking water. To enjoy these benefits, they have endured devastating floods which have cost lives, ruined economies and threatened whole societies. This paradox is heightened when the enormous costs of flood prevention are weighed against the consequences of inaction.
America's levees, in particular, which are vital for the delivery of fresh water and flood protection, are badly in need of inspection and repair as demonstrated by recent events in California and, of course, along the Gulf Coast. In Sacramento, the California Department of Water Resources has billion-dollar initiatives to investigate and improve their levees that not only protect communities from flooding but provide fresh drinking water (a rare and valuable resource in the West). Levee breaches along the Mississippi River, as demonstrated in the past, could cause catastrophic flooding in huge areas and impact shipping deliveries across the country and abroad.
Today, the challenges to protect our communities and maintain our river systems are exacerbated by highly developed watersheds, upstream and downstream conflicting demands, and competition for limited public and private budgets. The consequences of failure are high, but the magnitude of effort required to maintain these systems is daunting. The Federal Emergency Management Agency (FEMA) estimates that there are more than 15,000 miles of levees spread out amongst one-third of all U.S. counties.
The levee failures during Hurricane Katrina in New Orleans brought the need to inspect and improve our nation's levees to top priority of elected officials and federal and local emergency managers. The responsibility of documenting flood risks, including levees, falls to FEMA's National Flood Insurance Program (NFIP). The NFIP initiated the aggressive Map Modernization effort to update the entire country's flood insurance rate maps (FIRM). Key goals of the program include timeliness and accuracy. Reconciling these two has proven challenging, because it is difficult to timely map communities behind levees of unknown structural integrity and/or insufficient levels of flood protection.
Metro Center Levee, Nashville, Tennessee
Both FEMA and the U.S. Army Corps of Engineers (USACE) have undertaken initiatives to provide our communities with better flood risk information and ultimately with higher levels of flood protection. FEMA, for example, has reevaluated how levees are depicted on maps and has developed criteria that now require communities and levee owners to prove integrity and protection from the base flood. This is a significant development for communities behind levees that were mapped out of the flood zone in the past but, because of certification requirements, may now find themselves in the base-flood zone and subject to flood insurance requirements.
To provide guidance to communities with levees, FEMA authored Procedure Memorandum 34—Interim Guidance for Studies Including Levees. This memo established the requirement communities and levee owners have to comply with Title 44 of the Code of Federal Regulations, Section 65.10 (44 CFR 65.10) in order for FEMA to "recognize a levee as providing protection from the 1-percent-annual-chance flood (base-flood) on the FIRM." Not long after the memo was released, FEMA revised the requirements through Procedure Memorandum 43—Guidelines for Identifying Provisionally Accredited Levees. This memo acknowledged how difficult it is to document that a levee met the requirements of 44 CFR 65.10 and the hardship associated with a change in zone designation. A revised approach allows areas behind levees to be mapped as providing protection while allowing communities up to two years to provide the required certification. The areas in question would be mapped with the following note:
WARNING: This levee, dike, or other structure has been provisionally accredited and mapped as providing protection from the 1-percent-annual-chance flood. To maintain accreditation, the levee owner or community is required to submit documentation necessary to comply with 44 CFR Section 65.10 by (date, year). Because the risk of overtopping or failure of the structure, communities should take proper precautions to protect lives and minimize damages in these areas such as issuing an evacuation plan and encouraging property owners to purchase flood insurance.
44 CFR 65.10 specifically requires owners to demonstrate adequate structural design and that operation and maintenance (O&M) systems are in place that provide reasonable assurance that the levee offers protection up to a base-flood event. The USACE has taken this a step further with the development of the draft Engineer Technical Letter (ETL) No. 1110-2-570, the final version of which is anticipated in early 2008. As detailed in the draft ETL its application is to all USACE riverine, lake, and coastal levee and floodwall systems certification determinations. Content includes a comprehensive assemblage of existing policy, procedural, and technical clarifications and an overview of documentation requirements, independent technical review requirements, and authority and funding mechanisms.
FEMA Certification Requirements
Communities or levee owners are required to seek accreditation (certification) of their levee by providing FEMA the documentation and data as outlined in 44 CFR 65.10. To be clear, FEMA does not certify levees. All levees must be certified by a registered professional engineer or a federal agency responsible for levee design. FEMA, for the purposes of the NFIP, will only recognize in its flood hazard and risk mapping efforts those levees that meet, and continue to meet, minimum design, operation, and maintenance standards that are consistent with providing protection from the base-flood.
For riverine levees, a minimum three feet of freeboard above the base-flood water-surface elevation must be provided. Coastal levee freeboard requirements are established through consideration of the larger of maximum wave run-up or the height of the one percent occurrence wave. An exception to the minimum requirements may be requested through the use of appropriate engineering analysis for demonstration of adequate protection, but under no circumstances will FEMA accept freeboard of less than two feet.
In addition to freeboard requirements, engineering analysis must demonstrate that during a base-flood event the levee would meet the following criteria:
Lastly, for FEMA to recognize a levee as certified, compliance with an O&M plan is necessary. All mechanical systems and closure devices for internal drainage must be operated in accordance with an officially adopted operation manual and periodic maintenance occurs to maintain the as-designed condition of the levee. All O&M activities must be performed under the jurisdiction of a federal or state agency, an agency created by federal or state law, or an agency of a community participating in the NFIP.
Content of USACE Draft ETL No. 1110-2-570
The USACE has been given certain authorities for its role in levee certification. Federal Publication Authority and Funding Guidance for USACE Levee Certification Activities (August 15, 2006), details the USACE's authorities and its relationship to supporting and/or performing levee certifications. In short, the USACE does not have the authority to perform levee certifications for nonfederal projects that are not within a USACE program or part of an ongoing USACE study project. Nevertheless, levee owners should consult the guidance publication or a USACE district office for more details.
Since the mid-1990s, the USACE has issued several guidance letters on the subject of certification for NFIP purposes. Through the evolution of the guidance letters, the USACE has adopted a statistically-based performance target for the hydrologic adequacy of levees. This is because of stream profile variability and uncertainty, which call for a more risk-based analysis. Conversely, the geotechnical analysis of levees remains deterministically-based; however, in the future, a more probabilistic geotechnical assessment approach will likely be adopted.
The draft ETL describes the role of the USACE in levee certification and the basic certification process. A flow chart guides local sponsors through the process of requesting assistance from the USACE. Once assistance is granted, the USACE initiates a series of actions to ensure the most efficient and effective use of time and resources. Many factors play into the scope of the investigation and evaluation needs. The process will begin with compilation of existing data and, depending on the level of supporting information, may call for detailed engineering evaluation of hydrologic, hydraulic, geotechnical, structural, electrical, and mechanical conditions and components. Finally, the draft ETL provides references, template draft letters, an example certification project, and lessons learned from the Interagency Performance Evaluation Team's report on New Orleans and Southeast Louisiana Hurricane Protection System.
For levees outside the authorities of the USACE, both probabilistic and deterministic approaches have been employed by professional engineers to evaluate levees for FEMA certification. The most widely used, and usually the most economical, approach has been the deterministic approach, which is frequently conducted in phases.
The initial phase includes compilation and review of all available data, such as design investigations, design engineering analysis, as-builts, original construction records, historic records, inspection reports, maintenance records, and any other data that could help assess the adequacy of a structure to meet 44 CFR 65.10 requirements. If the information is deemed sufficient to support certification, the process is complete and certification is provided to FEMA. Should insufficient documentation exist, additional effort is required.
The second phase includes acquisition of additional data through engineering investigations and analysis, such as geotechnical and geologic field investigations, laboratory soil testing, and geotechnical analysis. Updates or documentation of hydrology and hydraulic adequacy and assessment of scour potential, and structural, mechanical, and electrical sufficiency and reliability may be required. Should the additional engineering analysis identify deficiencies, then repairs, remediation and/or mitigation would be necessary.
The final phase includes an analysis of remediation alternatives to determine which method best meets project and benefit-cost goals followed by a detailed design and subsequent design implementation. Possible alternatives include levee improvements, removal of the levee, provisions for flood insurance, and other flood control measures.
Levees that have too many deficiencies or that are deficient in the required engineering and operation documentation would not meet the requirements of 44 CFR 65.10 and would not be certifiable in their existing condition. If a community or owner lacks resources required for certification, the impacts to the once-protected areas could be substantial. A community behind one of these levees once shown on the FIRM as being protected from the base-flood will be shown through redelineation as a special flood hazard area on the new FIRM. Such a designation will affect the type and cost of required insurance for landowners within the flood zones and may impact future improvements and further development potential unless special procedures are employed.
As communities build new levees and continue to develop behind existing levees, certification and levee safety will only increase in significance. As responsible engineers, planners and public servants we must not only work to assure all levees meet current standards, but push for higher standards to further protect our communities from catastrophic levee failure.
William B. Meyer has worked for over 12 years in the field of floodplain management and emergency response. He serves AMEC as Technical Director of Floodplain Management, with program responsibilities for the western U.S. He can be reached at (303) 935-6505 or email@example.com.
Brett A. Howey is an Arizona registered civil engineer with 16 years of experience in the construction and civil engineering fields. He currently holds the position of Unit Manager with AMEC responsible for overseeing the Tempe, Arizona geotechnical practice. He can be reached at (480) 940-2320 or firstname.lastname@example.org.