Dartford-Thurrock Crossing Act 1988

10 (1) The Secretary of State shall carry out to the reasonable satisfaction of the Port Authority such surveys as may be required to ascertain the condition, before the commencement of the construction of the bridge, of the parts of the river of which the regime may be adversely affected by any tidal work and shall supply the Port Authority with the results of such surveys.

(2) If, while any operations for the construction or improvement of the bridge are being carried out or after they are completed, the Port Authority carry out any other survey which may be reasonably required to ascertain whether the regime of the parts of the river referred to in sub-paragraph (1) above has been adversely affected by any tidal work, the Secretary of State shall pay to the Port Authority any costs reasonably incurred by them in carrying out the survey, not being costs which the Port Authority would have incurred for other reasons.