Where any watercourses under the control of the appropriate agency pass under or interfere with, or with the improvement or alteration of, any river, canal, dock, harbour, basin or other work (including any towing-path adjacent thereto) which belongs to or is under the jurisdiction of any relevant authority, the relevant authority may, at their own expense and on substituting for those watercourses other equally effective watercourses—
If any question arises under this section between the appropriate agency and any relevant authority as to whether any watercourses substituted or proposed to be substituted by the relevant authority for any existing watercourses are as effective as the existing watercourses, that question shall be referred to the arbitration of a single arbitrator appointed by agreement between the parties or, in default of agreement, by the President of the Institution of Civil Engineers on the application of either party.
In this section—
"relevant authority" means any navigation authority, harbour authority or conservancy authority; and
"watercourse" has the same meaning as in Part IV of this Act.