Hydrodynamic and transport responses to land reclamation in different areas of semi-enclosed subtropical bay

Abstract

Many coastal areas worldwide have been reclaimed to meet the increasing land demand. Understanding the effects of land reclamation on the hydrodynamics and transport processes of a semi-enclosed bay is therefore of significance. From a case study of Deep Bay (DB) in China and referring to idealized bay models, the effects of two types of land reclamation, one that narrows the bay mouth and another that reduces the water area inside the bay, were examined in this study. Simulation results of idealized models show that the current velocity at the bay mouth and the incoming tidal energy flux are negatively correlated with the width of bay mouth, as the tidal prism remains almost constant when the bay mouth width reduces. The bay mouth width reduction would also increase the tidal energy dissipation inside of the bay due to friction increase. In DB, a 30% reduction in the mouth width increased the bay mouth current velocity by up to 5% and the total incoming energy flux by 18%. The narrowed bay mouth also substantially changed the bay's vertical structure of salinity, increasing the stratification strength by 1.7×10−4s−2. For reductions in the water surface area in the head of the bay, results from idealized bay simulations show that the current velocity throughout the bay, the incoming tidal energy flux, and salinity at the inner bay all decrease with water area reduction. Reclaiming 14% of area in DB, the current velocity reduced by 9% at the bay mouth, but increased in the middle and inner parts. The incoming tidal energy flux also increased as the coastline became more streamlined after reclamation, and the salinity at inner bay decreased. Both reclamation types have substantially altered the water and salt transport processes and increased the water exchange ability of the bay with the adjacent sea.