33 U.S.C. § 701b–11

(a) General considerations; nonstructural alternatives In the survey, planning, or design by any Federal agency of any project involving flood protection, consideration shall be given to nonstructural alternatives to prevent or reduce flood damages, with a view toward formulating the most economically, socially, and environmentally acceptable means of reducing or preventing flood damage, including— (1) floodproofing of structures, including through elevation; (2) floodplain regulation; (3) acquisition of floodplain land for recreational, fish and wildlife, and other public purposes; (4) relocation; and (5) the use of a feature described in section 2289a(a) of this title . (b) Non-Federal participation through nonstructural alternatives; limitation Where a nonstructural alternative is recommended, non-Federal participation shall be comparable to the value of lands, easements, and rights-of-way which would have been required of non-Federal interests under section 701c of this title , for structural protection measures, but in no event shall exceed 20 per centum of the project costs.