16.—(1) Work Nos. 31 and 31A must not commence until, for that numbered work, a written surface and foul water drainage plan (including details of any watercourse crossings and proposals for management and maintenance) has, following consultation with Natural Resources Wales, been submitted to and approved by the relevant planning authority. The surface and foul water drainage plan must be substantially in accordance with the principles set out in the outline drainage strategy.
(2) The surface and foul water drainage plan must be implemented in accordance with the approved details, prior to final commissioning of Work No. 31A.