Land reclamation and its impact on tidal dynamics in Jiaozhou Bay, Qingdao, China

Over the past few decades, there has been large-scale land reclamation in Jiaozhou Bay, which inevitably has affected the hydrodynamics and sediment transport in the bay, and thus has consequences for its management. In this study we set up a three-dimensional barotropic hydrodynamic model based on the Finite Volume Coastal Ocean Model to investigate changes in tidal dynamic factors in Jiaozhou Bay from 1935 to 2008. According to the model, the M2 tide has experienced only minor changes over this period. Land reclamation on a large scale took place between 1935 and 1966, leading to significant hydrodynamic changes during this period. Again according to the model, the M4 tidal amplitude rose dramatically, by up to 80% at the northeastern part of Jiaozhou Bay, and this has caused a significant increase in the M2-M4 tidal-duration asymmetry. Concurrently, the M2 tidal-energy fluxes across the entrances to both the inner and outer bay were both reduced by more than 50%. From 1966 to 2008, land reclamation was conducted on a smaller scale. Over this period, the M2 tidal-energy flux continued to decrease but at a relatively smaller rate. Both the M4 tidal amplitude and M2-M4 tidal-duration asymmetry also experienced a gradual decrease during this period, probably due to the reduced M2 tidal energy, in contrast to the increase between 1935 and 1966. The changes in the M2-M4 tidal-duration asymmetry from 1935 to 2008 caused by the land reclamation were reproduced in the model by progressively removing tidal flats from the head of the bay to its mouth. However, the M2-M4 tidal-duration asymmetry showed a different variation when the tidal flats were removed progressively in the opposite direction, from the mouth to the head of the bay. Our study shows that the significant increase in the M2-M4 tidal-duration asymmetry between 1935 and 1966 was a consequence of the change in bottom friction when the tidal flats were land-filled; advection played only a secondary role.