The Impact of Land Reclamation on Tidal Dynamics in the Pearl River Estuary, China

Abstract

Large scale land reclamations have been constructed since the 1950s along the coast of the Pearl River Estuary (PRE) to meet the increasing land demand, which resulted in a reduction in tidal flat area of almost 762 km², comparable to the land area of Singapore. The spatio-temporal tidal dynamics have been distorted by both the artificially simplified coastline and the reduction in tidal flats. A 2D hydrodynamic model covering the entire PRE and its adjacent coastal waters was employed to quantify the impacts of land reclamation on the hydrodynamics and transport processes of the semi-enclosed estuary. After well validated by the observed water levels and current velocities, model sensitivity runs were conducted using the coastline data of the 1970s, the 1990s and 2010. We quantified the effects through different hydrodynamic and transport indicators (e.g., M₂ and M₄ tidal constituents and tidal asymmetry) over the period from the 1970s to 2010. The results indicated that the M₂ amplitude increased generally with a maximum value of 8 cm and the M₂ amplitude decreased in the Jitimen water area due to strait-channel effect. Unlike the the M₂ tide, the M₄ tidal variation in the PRE was more sensitive to the coastline alteration. Thus the tidal asymmetry represented by the amplitude ratio (M₄/M₂) and relative phase (2φ_M2-φ_M4) was complex. In general, the tidal asymmetry enhanced as the coastline advanced seaward. The flood dominance fostered in the Huangmao and Lingding Bays, and the water area in the middle of the Lingding Bay experienced a critical change from ebb to flood dominance. In contrast, the flood dominance attenuated in the Jitimen and Modaomen water areas after the 1990s due to the increased runoff action. Analyses of the above indicators could distinctly deepen our understanding of anthropogenic impacts on estuarine tidal hydrodynamics.