Impacts of human activities on tidal dynamics in a sexta-diurnal tidal resonant bay

Abstract

Using numerical modelling, we study changes in tidal dynamics in Daya Bay (DYB) between 1989 and 2014. During this period, a total water area of 30 km2 was reclaimed and the average water depth increased by 38 cm. As DYB is a sexta-diurnal tidal resonant bay, the sexta-diurnal tides respond differently to the coastline and bathymetry changes than other tides. Taking K1, M2, M4, and M6 as examples, model results show a decrease in tidal elevation amplitude, tidal current magnitude, and tidal energy flux for K1, M2, and M4 tides. For the M6 tide, however, the model predicted an increase in tidal elevation amplitude, tidal current magnitude in some parts of the bay, and the tidal energy flowing into the bay. Land reclamation leads to the enhancement of sexta-diurnal tidal resonance and thus the magnitude of the M6 tide. Furthermore, due to the magnification of M6, tidal duration asymmetry in DYB changed from ebb-dominance to flood-dominance, and water exchange became much more active. Therefore, owing to the sexta-diurnal tidal resonance, the impact of human activities on tidal dynamics in DYB is different from that in previously reported semi-enclosed bays where large-scale land reclamation has been carried out.