33 U.S.C. § 2318: Flood plain management

any new or substantially improved structure (other than a structure necessary for conducting a water-dependent activity) built in the 100-year flood plain with a first floor elevation less than the 100-year flood elevation after July 1, 1991 ; or in the case of a county substantially located within the 100-year flood plain, any new or substantially improved structure (other than a structure necessary for conducting a water-dependent activity) built in the 10-year flood plain after July 1, 1991 ; and any structure which becomes located in the 100-year flood plain with a first floor elevation less than the 100-year flood elevation or in the 10-year flood plain, as the case may be, by virtue of constrictions placed in the flood plain after July 1, 1991 . In calculating the benefits of a proposed project for nonstructural flood damage reduction, the Secretary shall calculate the benefits of the nonstructural project using methods similar to those used for calculating the benefits of structural projects, including similar treatment in calculating the benefits from losses avoided. In carrying out paragraph (1), the Secretary should avoid double counting of benefits. if the county is comprised of lands of which 50 percent or more are located in the 100-year flood plain; and if the Secretary determines that application of the requirement contained in subsection (a)(1)(A) with respect to the county would unreasonably restrain continued economic development or unreasonably limit the availability of needed flood control measures. Not later than January 1, 1992 , the Secretary shall transmit to Congress a report on the feasibility and advisability of increasing the non-Federal share of costs for new projects in areas where new or substantially improved structures and other constrictions are built or placed in the 100-year flood plain or the 10-year flood plain, as the case may be, after the initial date of the affected governmental unit’s entry into the regular program of the national flood insurance program of the National Flood Insurance Act of 1968 [ 42 U.S.C. 4001 et seq.]. Not later than 6 months after the date on which a report is transmitted to Congress under subsection (c), the Secretary, in consultation with the Director of the Federal Emergency Management Agency, shall issue regulations to implement subsection (a). Such regulations shall define key terms, such as new or substantially improved structure, constriction, 10-year flood plain, and 100-year flood plain. The provisions of this section shall not apply to any project, or separable element thereof, for which a final report of the Chief of Engineers has been forwarded to the Secretary before the last day of the 6-month period beginning on the date on which regulations are issued pursuant to subsection (a) but not later than July 1, 1993 .