8. If by reason of the construction of any specified work, or of the failure of any such work, or of the Promoter to maintain it, the efficiency of any drainage work for flood defence purposes is impaired, or that work is otherwise damaged, such impairment or damage shall be made good by the Promoter to the reasonable satisfaction of the Agency and if the Promoter fails to do so within such reasonable period as the Agency may require by notice in writing to the Promoter, the Agency may make good the same and recover from the Promoter the expense reasonably incurred by it in so doing.