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2 COMMITTEE APPROACH TO LEVEE POLICY In approaching the assignment of formulating recommendations to FEMA on when and how to recognize levees in the National Flood Insurance Program (NFIP), the committee quickly concluded that different answers would be needed for the various measures used by FEMA to reduce flood damages. The process required defining the program components, establishing a levee recognition policy for each one, and justifying the resulting recommendations. DIMENSIONS OF LEVEE RECOGNITION Flood loss mitigation is promoted through the following six basic measures or dimensions that are either direct requirements of or closely associated with the NFIP: 1. Provision of flood insurance at rates guided by actuarial risk 2. Land development and building construction regulation 3. Mandating the purchase of flood insurance in high risk areas 4. Regulation restricting the placement of critical facilities in hazardous locations 5. Notification of flood hazard to occupants of property at risk 6. Contingency planning, including warning and evacuation during floods While all six measures apply in mitigating flood losses to properties in the 100-year floodplain, none pertain to areas outside the 500-year floodplain. Recognition of a levee by the NFIP is recommended when the levee reduces flood risk to properties behind it to the extent where one or more of these measures would no longer be used. The applicability of the several measures logically varies with level of protection provided by a levee, the structural integrity of the levee, and the property elevation. For example, the recognition of a levee by the NFIP for purposes of reducing insurance rates (from what they would be without levee protection) is logical, but it certainly does not appear advisable to abandon warning and evacuation programs for major floods in levee-protected areas. Once the principle of recognizing a levee for purposes of individually -5-
modifying NFIP activities is established, multiple dimensions of levee recognition are created. Any levee runs the risk of overtopping and structural failure during floods. Accordingly (based on a reasonable risk before requiring a given activity), a levee may be recognized with respect to none, all, or only selected ones of the above listed measures. The risk of levee failure varies with many characteristics, but the primary variable for purposes of levee recognition must be the flood frequency associated with overtopping. Other levee properties can logically be specified as minimum requirements for reducing structural levee failure to acceptably low levels. Given overtopping frequency as the primary variable, the frequency to which a levee reduces flooding must be determined before that levee is recognized. Once it has been determined that the levee achieves a minimum required level of protection and should in fact be recognized to some extent, then each of the dimensions can be addressed. The committee concludes that: 1. The dimension in which a levee would logically first be recognized would be that of reducing insurance rates. In selecting the minimum acceptable overtopping exceedance frequency for this purpose, it can be argued that even small levees reduce actuarial risk. At some point, the reduction in actuarial risk becomes large enough to make rate reduction worthwhile. 2. The dimension of land development and building construction regulation should logically be continued to a rarer overtopping frequency. Areas defined by the 100-year floodplain are subject to these regulations where no levees exist. It would be hard to justify dropping this requirement for lands in the 100-year floodplain where they receive a lesser level of protection from levees. One could more logically argue for a rarer frequency criteria behind levees, since levee failures often cause greater damage than equivalent-frequency floods cause to property on the floodplain fringe (where levees don't exist). 3. The dimension of mandatory insurance purchase may logically be continued to an even rarer overtopping frequency (than the annual 1 percent chance flood), because the risk of flooding over a typical home mortgage period (25 to 30 years) can be significant and there is the threat to public funds of having to rescue and financially assist property owners heavily damaged by levee failure. 4. The dimension of prohibiting location of critical facilities may be tied to a still rarer overtopping frequency due to the consequence of disruptions and risks to the community from flooding of these facilities. However, many communities have no reasonable alternate site for the location of such facilities and require provision for exceptions. 5. The dimensions of notification of hazard and of warning-evacuation programs can logically be argued to be continued behind all levees, however rare their overtopping frequency. These minimal cost programs can achieve major benefits by increasing flood hazard awarenessâan important NFIP objective. -6-
Based on the above considerations, level of protection criteria need to be set at equal or progressively higher minimum levee sizes for: 1. Reducing insurance rates 2. Dropping land development and building construction regulations 3. Removing mandatory insurance purchase 4. Permitting critical facilities 5. Dropping hazard notification 6. Warning and evacuation planning Some of the latter dimensions may be desirable behind all levees regardless of size. Engineering criteria need to ensure structural integrity sufficient to keep failure risks other than by overtopping to an acceptably low level. RECOGNITION BY PROGRAM DIMENSION The committee recommendations on level of protection for levee recognition by program dimension are summarized on Table 1 for convenient reference. This tabulation facilitates comparison among the recommendations and assessment of their impact as a whole. Explanations of the recommendations and their justifications are presented in subsequent chapters. On Table l, the committee recommendations vary according to the level of protection provided by the levee and frequency of flooding that the land behind the levee would experience without the levee. Recommendations are specified for each element of the NFIP and associated with flood hazard mapping designations. For example, a 25-year levee is required before protected property becomes eligible for reduced insurance rates, whereas a 100-year levee is recognized as sufficient to lift requirements for elevation of residential structures and flood proofing of industrial and commercial structures. A levee must be designed to contain the 500-year flood to remove requirements for flood insurance purchase in the natural 100âyear floodplain. Critical facilities should not be allowed in areas behind any levees without demonstrating that there is no practical alternate location. All occupants of levee protected areas are to be notified of their hazard should the levee fail. Contingency planning, including warning and evacuation, should even consider those outside the natural 500-year floodplain but subject to flooding or isolation by levee failure. The plans should cover warning of impending failure and directing evacuees to safe areas that are not on islands. TECHNICAL GUIDANCE FOR SETTING LEVEE POLICY This report integrates technical considerations with economic and administrative factors in recommending a practical levee-recognition -7-
TABLE 1 DIMENSIONS OF LEVEE RECOGNITIONâSUMMARY Levee protection level 0-24 year 25-99 year11 100-500 year** 500 year** Ground elevation compared to < 100 year <100 year < 100 year > 100 year < 100 year >100 year flood level Zone Designation A1-A30 AL ALP BLP BLP BLP NFIP Action 1 Insurance rates Yes No No No No N/A disregard levee 2 New buildings elevated or Yes Yes No N/A No N/A floodproofed to 100-year flood level 3 Insurance pur- Yes Yes Yes No No No chase required 4 Critical facil- - Yes Yes Yes Yes Yes ities regulated 5 Notify - Yes Yes Yes Yes Yes residents 6 Emergency management mea- - Yes Yes Yes Yes Yes sures required *New levees constructed to less than the 100-year flood level should not be recognized in the NFIP. Therefore these required/allowed actions are not applicable to new levees. **0r Standard Project Flood (SPF); a levee designed to pass either the 500-year flood or SPF reflects a conservative design standard. For purposes of this report, no distinction is made. -8-
policy to FEMA. Administrative factors favor the convenience of having very few differentiations by degree of hazard. Economic factors suggest a variation in optimal programs that would require a large number of differentiations according to site hazard characteristics. Technical factors help define a middle ground. It is technical differences in the degree of flood risk which determine whether lumping areas of differing hazard for administrative convenience violates concepts of equity. It is the degree of reliability in technical estimation that determines whether differences along the hazard continuum are significant before applying economic principles to formulate different policies. The goals in the recommendations in this report are to propose policy distinctions when hazard differences can be defended technically but not to encumber the FEMA program with an unwieldy number of different policies that are not based on real technical differences in hazard. -9-
