If any question arises under this Act—
whether any work is a drainage work in connection with a main river; or
whether any proposed work will, if constructed, be such a drainage work,
the question shall be referred to one of the Ministers for decision or, if either of the parties so requires, to arbitration.
Where any question is required under subsection (1) above to be referred to arbitration it 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.