Anthropogenic Influences on the Tidal Prism and Water Exchanges in Jiaozhou Bay, Qingdao, China

Abstract

The tidal-driven flow field and average residence time for water in Jiaozhou Bay in the years 1966, 1988, 2000, and 2008 were investigated using the EFDC (Environmental Fluid Dynamics Code) with a coupled dye module. Jiaozhou Bay (JZB) in northeastern China is a semi-enclosed shallow bay that has undergone large-scale land reclamation over the last four decades, especially over the extensive intertidal flats. Data from field observations were used to calibrate and verify the EFDC model for JZB. The verified JZB model was used to study spatial variations of flow field and water exchanges from 1966 to 2008. The overwhelming influence of human activities, especially land reclamation, is the main cause of the significant changes in hydrodynamic conditions and water exchange in JZB. The human-induced changes of the coastline position-configuration and nearshore bathymetry have resulted in substantial changes in the residual current patterns, especially in Qianwan Bay, Haixi Bay, and northeastern Jiaozhou Bay. The overall tidal prim of JZB has been reduced by 26% as compared to that in 1928. This is considerably less than the 35% reduction obtained by other studies. The decreasing water-exchange ability corresponds to an increasing average residence time (ART) over the past several decades, particularly after the 1980s. In addition, the influences of the return flow of the bay water from the open sea back into the estuary were quantified by determining the return flow factor for each year. An existing tidal prism model was revised by introducing a mixing factor κ, and a simplified formula was developed for JZB. The revised tidal prism model suggests continued deterioration in water quality and exchange ability of Jiaozhou Bay in the near future.