23 CFR § 650.111 - Location hydraulic studies.
(a) National Flood Insurance Program (NFIP) maps or information developed by the highway agency, if NFIP maps are not available, shall be used to determine whether a highway location alternative will include an encroachment.
(b) Location studies shall include evaluation and discussion of the practicability of alternatives to any longitudinal encroachments.
(c) Location studies shall include discussion of the following items, commensurate with the significance of the risk or environmental impact, for all alternatives containing encroachments and for those actions which would support base flood-plain development:
(2) The impacts on natural and beneficial flood-plain values,
(3) The support of probable incompatible flood-plain development,
(4) The measures to minimize flood-plain impacts associated with the action, and
(d) Location studies shall include evaluation and discussion of the practicability of alternatives to any significant encroachments or any support of incompatible flood-plain development.
(f) Local, State, and Federal water resources and flood-plain management agencies should be consulted to determine if the proposed highway action is consistent with existing watershed and flood-plain management programs and to obtain current information on development and proposed actions in the affected watersheds.