33 U.S.C. § 701b–15

(a) In general If requested by a non-Federal interest, the Secretary shall carry out a locally preferred plan that provides a higher level of protection than a flood risk management project authorized under this Act if the Secretary determines that— (1) the plan is technically feasible and environmentally acceptable; and (2) the benefits of the plan exceed the costs of the plan. (b) Non-Federal cost share If the Secretary carries out a locally preferred plan under subsection (a), the Federal share of the cost of the project shall be not greater than the share as provided by law for elements of the national economic development plan.