In any development involving the lesser of either five or more acres or fifty or more building lots:
(a) Where no official base flood level has been determined;
(b) Which are a part of an unnumbered A zone on the Flood Insurance Rate Map; And
(c) Where no other official existing study is available;
the developer, in such case, shall have the base flood water surface elevation calculated by a qualified professional engineer, registered by the State of Ohio, and such base flood water surface elevation shall be shown on the Site Plan and drawing.