Once the tunnel system has been brought into operation, the Concessionaires shall, in accordance with a scheme agreed with the county planning authority or, in default of agreement or on notice being given by the Secretary of State to the authority and the Concessionaires, settled by him, put so much of the area on the landward side of the sea wall as consists of land reclaimed by the deposit of spoil and is not required for or in connection with the operation of the tunnel system into such a condition as the scheme may provide.