12.—F30[Subject to section 12A, whenever] in the course of the carrying out of a drainage scheme it becomes necessary, in the opinion of the Commissioners, to acquire compulsorily or interfere substantially with any lands not mentioned in that behalf in the drainage scheme or to acquire, restrict, terminate, or otherwise interfere with compulsorily any easement, fishery, water-right, navigation-right, or other right similarly not mentioned or to divert, remove or otherwise interfere with any road or bridge (whether public or private) similarly not mentioned, the following provisions shall apply and have effect, that is to say:—

(a) it shall be lawful for the Commissioners, with the sanction of the Minister, so to amend provisionally the said drainage scheme as to include therein the compulsory acquisition, restriction, termination, diversion, removal, or interference so found necessary;

(b) the provisions of this Act in relation to sending copies of a drainage scheme to councils of counties, serving notice on reputed proprietors, owners, occupiers and local authorities, enabling such councils, proprietors, owners, occupiers, and local authorities to send observations to the Commissioners, and requiring the Commissioners to consider such observations shall apply and have effect in relation to every such provisional amendment of the said drainage scheme in like manner as they applied to the scheme itself, subject to the modification that the time within which observations may be sent to the Commissioners shall in every case be twenty-one days;

(c) the Commissioners shall consider every such observation sent to them within the time appropriate thereto and shall, when all such times have expired, confirm such amendment either (as they shall think proper) without alteration or with such alterations as they shall think proper;

(d) when such amendment has been so confirmed, the said drainage scheme shall have effect and be deemed always to have had effect with and subject to such amendment, and accordingly references in this Act to a drainage scheme shall, in relation to the said drainage scheme, be construed and have effect (wherever the context so permits) as referring to the said drainage scheme as so amended;

(e) while any such amendment is a provisional amendment it shall be lawful for the Commissioners to act on such amendment as if it had been confirmed, subject to the Commissioners making such restitution or restoration (if any) or paying such compensation (if any) as may be just and equitable in consequence of such amendment being confirmed with alterations;

(f) every dispute as to the need for any such restitution, restoration, or compensation or as to the nature, extent, or amount thereof shall be decided by an arbitrator nominated by the Reference Committee from the Panel of Drainage Arbitrators whose decision thereon shall be final and conclusive.