Evolution of sedimentary dynamic environment in the western Jiaozhou Bay, Qingdao, China in the last 30 years

Intensive reclamation and cross-sea bridge construction occurred in the Jiaozhou Bay, Qingdao, China in the last 30 years. These changes have not only reduced water volume but also altered sedimentation in the bay. Using the data collected in the 1980s, 2000s and early 2010s, bottom sediment evolution in the last 30 years in the western bay were studied. Furthermore, a numerical model was used to study the hydrodynamic environment change in the surrounding sea areas. The seabed sediment became finer in the northwestern area from the 1980s to 2003, which was mostly influenced by the reduced sediment discharge from the Dagu River. However, from 2003 to July 2014 during which the Jiaozhou Bay Bridge was built, the seabed sediment became coarser on the north side of the bridge, and became finer on the south side; in particular, two coarser sediment belts appeared across the channel bridge. Numerical simulation results indicated increased current velocity on the north side and decreased velocity on the south side of the bridge. The tidal-duration asymmetry was calculated from the tidal harmonic parameters of the model output. In the flood dominated JZB, the larger deceased tidal-duration asymmetry on the north side of the bridge could result in more coarser seabed sediment brought in from the northern bay. These could be the reasons for the coarser seabed sediment on the north side of the bridge and finer sediment on the south side after the bridge construction. Deeper water on the north side and shallower water on the south side of the bridge from 2005 to July 2014 further demonstrated the effect of hydrodynamic change caused by the bridge construction.