Numerical study of water exchange in the Jiaozhou Bay and the tidal residual currents near the bay mouth

A barotropic tidal model covering Jiaozhou Bay (JZB) and Qingdao coastal waters is developed based on Princeton Ocean Model (POM). This numerical model, combined with the field survey currents data obtained from a vessel-mounted Acoustic Doppler Current Profiler (ADCP), is used to investigate the characteristics of the tidal currents near the mouth of JZB. Furthermore, a water quality sub-model is coupled into the tidal model to simulate the water exchange processes in JZB. The tidal model includes six main tidal constituents (M₂, S₂, K₁, O₁, M₄, and MS₄), and reasonably reproduces tidal current field which is consistent with ADCP observation. The tidal current in the bay mouth channel is very strong. The observed peak current speed during spring tide period was 2.01 m/s. A couple of tidal residual eddies are found at both sides of the headland of Tuandao. The residual eddies converge near Tuandao, forming an offshore jet current of 57 cm/s. The modeled mean water residence time (WRT) in JZB is 71 days, and the mean half-life time (HLT) is 25 days. The horizontal distributions of WRT and HLT are quite uneven in space: they increase from the mouth to the top of JZB. The lowest water exchange rates are found in two regions, the west-southwest part and the northeastmost part of JZB, where the WRT is above 80 days with a maximum of 120 days, and HLT mostly exceeds 40 days. Such spatial distribution differences are controlled by the structure of tidal (residual) currents as well as the distance from the bay mouth.