Paragraph 61 I1

during the period from commencement of the works in the river until the date occurring one year after substantial completion of the works surveys are to be carried out 4 times per calendar year at such times within the year as the GYPA reasonably directs;

during the period from the date occurring one year after substantial completion of the works until the date occurring three years after substantial completion of the works surveys are to be carried out 2 times per calendar year at such times within the year as the GYPA reasonably directs;

paragraph (d) is to apply if any of the surveys undertaken under paragraph (b) or other evidence provided by the GYPA to the undertaker shall have demonstrated that the works are creating an adverse effect and that adverse effect has not been mitigated to the reasonable satisfaction of the GYPA by the expiry of the period referred to in paragraph (b);

where this paragraph applies, surveys shall be carried out once per calendar year, at such time as the GYPA reasonably directs, during the period commencing with the date of expiry of the period referred to in paragraph (b) and ending on the seventh anniversary of that date or such date as the adverse effect has been demonstrated to the reasonable satisfaction of the GYPA to have been mitigated (whichever date shall first occur);

should a survey carried out during construction show any discernible change has occurred to the river bed levels, localised sediment sampling will be undertaken in the area of change to determine the composition of the material, hydrodynamic modelling will be undertaken to assess the extent to which the new bridge construction activity may have contributed to the change and a detailed report prepared;

should a survey carried out after construction show either a sudden large change to the river bed level or, over time, that a longer-term trend of change in level pattern has occurred, localised sediment sampling will be undertaken in the affected area to determine the composition of the material, hydrodynamic modelling will be undertaken to assess the extent to which the new bridge construction activity may have contributed to the change and a detailed report prepared;

the extent of the surveys carried out under this paragraph will be 200 metres upstream and downstream of the centre line of the new bridge covering the full width of the river over this length; and

all hydrographic surveys mentioned in this paragraph will be undertaken using a suitable multibeam echo-sounder, in accordance with the International Hydrographic Organization Standards for Hydrographic Surveys 5th Edition (February 2008) to Survey Order 1a.