When, in the construction or repair of any State highway, a third less may be expended by the State, in conjunction with other funds herein provided for, for the approach to or the crossing of any waterway, creek or river, through the building of a dam, levee or other facility for controlling water, constructing ditches or waterways or doing some other thing to control water, the Department, in its discretion, may estimate the cost of the repair or the construction of the necessary bridge, viaduct or other approach, together with that part of the highway immediately affected thereby, such estimate to be based upon the cost without such water-controlling device, and the Department may allot to or reimburse, or enter into contracts looking to that end, as provided in the law of this State, on account of the building of such highway immediately affected by such approach and the approach and the construction of such water-controlling device as the Department may plan, such reimbursement, reimbursement agreement or allotment to be made to any county, municipality or other agency in the sum of two thirds of the estimated costs of the structure and the highway immediately affected thereby without such water-controlling device, upon such county, municipality or other agency entering into such bond as the Department may consider as surety for the completion of the whole project as planned by the Department. The word "agency" shall mean any person complying with the terms of this section.