11The nominated undertaker shall not, except for the purpose of constructing a tidal work or any connected works, remove any gravel, soil or other materials from the bed, shores or banks of the river without the previous consent of the port authority signified in writing under the hand of its secretary (such consent not to be unreasonably withheld), but nothing in this paragraph shall prevent the use by the nominated undertaker of any gravel, soil or other material so removed for the purposes of the construction of other tidal works or any connected works.