Any reasonable and proper additional expenses not otherwise provided for in this Part of this Schedule which the GYPA may incur in maintaining the river under any powers existing at the making of this Order by reason of the existence of a specified work must, be repaid by the undertaker to the GYPA (but subject to the submission to the undertaker, to its reasonable satisfaction, of demonstrable evidence that the additional expenses are a direct result of the construction of the specified work) so as to ensure that the GYPA has been reimbursed for all and any greater maintenance liability it incurs by reason of the existence of a specified work (on the proviso that there will be no double recovery).