18.—(1) For the purpose of carrying out the works the Commissioners may irrespective of anything in any enactment—
(a)temporarily close the area of works to vessels by means of one or more coffer dams at such places within the harbour as the Commissioners shall think appropriate;
(b)dry out the area of works by pumping or otherwise and carry out all such measures and construct or install all such valves, sluices, gates, pipes, channels, aqueducts, pumps and similar works of a temporary nature as may be necessary to convey water entering the area of works into tidal waters.
(2) Irrespective of anything contained in this Order, the area of works shall not be closed to vessels for a period continuous or discontinuous longer than two years.