Stepwise alterations in tidal hydrodynamics in a highly human-modified estuary: The roles of channel deepening and narrowing

Abstract

With the rapid development of coastal cities, estuarine environments have been drastically changed by human interventions that considerably alter hydrodynamics (e.g., tidal amplitude) and water quality (e.g., salinity intrusion). In this study, we used a well-developed one-dimensional analytical model that accounts for the mutual nonlinear interactions between different tidal constituents to investigate the stepwise alterations in tidal hydrodynamics in Lingdingyang Bay of the Pearl River Estuary during 1965–2016, with a particular focus on the impacts of channel deepening and narrowing. The stepwise alterations in tidal hydrodynamics in Lingdingyang Bay can be divided into three distinct phases: the pre-human period (1965–1989), the transitional period (1990–2007), and the post-human period (2008–2016). It was shown that channel deepening and narrowing exert a dramatic influence on the tidal hydrodynamics in terms of increasing wave celerity, amplifying tidal waves, increasing the velocity amplitude and becoming more standing wave character. Furthermore, analytical results show that the responses of the semi-diurnal constituents (M2 and S2) to morphological changes are much more sensitive than those of the diurnal constituents (K1 and O1). In addition, based on the sensitivity analysis, we show that the effects of channel narrowing on tidal hydrodynamics are stronger than those of channel deepening. These results quantifying the effects of estuarine morphology on tidal hydrodynamics can provide scientific guidelines for sustainable water resources management in Lingdingyang Bay and other tide-dominated estuaries that are subject to intensive human interventions, especially regarding morphological changes.