9. The Agency must pay to A.B. Ports the reasonable costs of such alterations to the marking and lighting of the navigational channel of the river as may be necessary during or within five years of the completion of and in consequence of the construction of a tidal work and afford to A.B. Ports such facilities as it may reasonably require for the placing and maintenance on any tidal work of signals, tide-boards, tide-gauges or other apparatus for the safety or benefit of navigation.