(a) Where the administrator has not provided an FHBM or FIRM or a flood insurance study designating flood hazard area boundaries and/or base flood elevations for a particular location, any State agency proposing a project at such location shall determine, in cooperation with the department, the boundaries of flood hazard areas and base flood elevations on the basis of all pertinent information available from Federal, State or other sources.

(b) Where the administrator has provided an FHBM or FIRM and/or flood insurance studies designating flood hazard area boundaries and/or base flood elevations for a particular location, flood hazard area boundaries and base flood elevations shall be as designated by the administrator. Provided, such boundaries or elevations as designated by the administrator shall be modified in such a manner as to be consistent with all pertinent additional information available from any Federal, State or other source, but any boundaries or elevations determined on the basis of such additional information shall not be smaller in area or lower in elevation than the boundaries or elevations designated by the administrator.