A Levee Policy for the National Flood Insurance Program (1982) / Chapter Skim
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'ENGINEERING CRITERIA FOR LEVEE RECOGNITION'
'ENGINEERING CRITERIA FOR LEVEE RECOGNITION'
Pages 10-17
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From page 10... ...
Major among the engineering factors were: level of protection and the hydrologic and hydraulic analyses required to support this level, embankment geometry, seepage control, slope protection, freeboard, closure devices, and interior drainage facilities. Additionally, the committee recognized that a number of institutional and social realities need to be considered in setting levee criteria.
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From page 11... ...
RECOGNITION OF LEVEES IN THE NATIONAL FLOOD INSURANCE PROGRAM Prior to developing design criteria, one very basic issue had to be addressed by the committee: what levees, if any, should be recognized for purposes of modifying NFIP requirements currently applied to the area protected or to be protected by the levee. Existing Levees Many existing levees have, for a great number of years, provided varying degrees of protection to the occupants of the floodplains behind them.
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From page 12... ...
Recognition of new levees provides consistency with this key tenet of the NFIP and permits growth behind appropriately constructed levees. The 100-year flood has become a widely accepted, applied, and institutionalized standard, and the establishment of the 100-year minimum degree of protection as a standard for new levees would be consistent with the base flood level of the National Flood Insurance Program guidelines.
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From page 13... ...
Evaluations of the suitability of the engineering of a specific levee must be based on sound technical analyses made by professional engineers skilled in structural, geotechnical, hydrologic, and hydraulic engineering, with specific experience in levee design. Exceptions to the general design criteria discussed below should be permitted only when information presented by professional engineers shows that the risk of flooding will not increase as a result of the exceptions.
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From page 14... ...
Freeboard requirements should apply equally to floodwalls and levees, since the lack of precision associated with flow line calculations pertains to both floodwalls and levees. Both existing and new levees and floodwalls must have a freeboard of 3 feet, or 1 foot plus wave height plus runup, whichever is greater.
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From page 15... ...
The interior drainage system may include storage areas, gravity outlets, pumping plants, or combinations thereof. These provisions are necessary in view of the high potential for damage created by flooding behind levees during periods when the river stages do not permit gravity flow and the flow into the leveed area exceed what can be discharged through pumps.
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From page 16... ...
Further, where circumstances dictate, regional hydraulic analyses of the cumulative effects of construction of several levees on flood flows and stages should be required in order to determine the impacts of the total system of existing levees and/or proposed new levees on levee flow lines. In cases where the 10-, 50-, 100-, and 500-year flood levels have already been determined in the NFIP study for communities, where levees already exist, the committee suggests that FEMA recognize a practical and economical alternative method of determining the level of protection.
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From page 17... ...
Such surveillance can be accomplished as part of FEMA's periodic restudy process, as part of a national monitoring program, perhaps using advanced remote sensing systems, or through reports from federal, state, or local agencies and NFIF participants. EXCEPTIONS In the application of the principles presented in this report, levee proponents may, because of unusual circumstances or advances in technologies or construction techniques, request exceptions to the criteria and guidelines.
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