Tidal regime shift in Lingdingyang Bay, the Pearl River Delta: An identification and assessment of driving factors

Abstract

Both natural changes (e.g., tidal forcing from the ocean and global sea level rise) and human‐induced changes (e.g., dredging for navigation, sand excavation, and land reclamation) exert considerable influences on the long‐term evolution of tidal regimes in estuaries. Evaluating the impacts of these factors on tidal‐regime shifts is particularly important for the protection and management of estuarine environments. In this study, an analytical approach is developed to investigate the impacts of estuarine morphological alterations (mean water depth and width convergence length) on tidal hydrodynamics in Lingdingyang Bay, Southeast China. Based on the observed tidal levels from two tidal gauging stations along the channel, tidal wave celerity and tidal damping/amplification rate of different tidal constituents are computed using tidal amplitude and phase of tidal constituents extracted from a standard harmonic analysis. We show that the minimum mean water depth for the whole estuary occurred in 2006, whereas a shift in tidal wave celerity for the M2 tide component occurred in 2009. As such, the study period (1990–2016) could be separated into pre‐human (1990–2009) and post‐human (2010–2016) phases. Our results show that the damping/amplification rate and celerity of the M2 tide have increased by 31% (from 7 to 9.2 m−1) and 28% (from 7 to 9 m·s−1) respectively, as a consequence of the substantial impacts of human interventions. The proposed analytical method is subsequently applied to analyse the historical development of tidal hydrodynamics and regime shifts induced by human interventions, thus linking the evolution of estuarine morphology to the dominant tidal hydrodynamics along the channel. The observed tidal regime shift is primarily caused by channel deepening, which substantially enlarged the estuary and reduced effective bottom friction resulting in faster celerity and stronger wave amplification. Our proposed method for quantifying the impacts of human interventions on tidal regime shifts can inform evidence‐based guidelines for evaluating hydraulic responses to future engineering activities.

Responses of tidal duration asymmetry to morphological changes in Lingding Bay of the Pearl River Estuary

“…The average tidal range is between approximately 1.0 m (Lantau Island) and 1.7 m (Humen outlet) (Zhang et al, 2019), indicating a microtidal character in LDB. As the tidal wave propagates upstream, the tidal energies converge owing to the effect of the convergent funnel-shaped shorelines overwhelming the frictional dissipation, which amplifies the tidal ranges (Wang et al, 2020;Zhang et al, 2021a).…”

“…Owing to economic development, many estuaries have been intensely modified by anthropogenic activities worldwide (e.g., land reclamation, channel dredging, and sand excavations), causing irreversible and remarkable changes in estuarine morphology . The morphological changes caused by human activities can drastically change the processes of tidal propagation and distortion in estuaries, leading to modifications in tidal properties such as tidal amplitudes and phases, wave celerity, tidal attenuation/amplification, and tidal asymmetry (Wang et al, 2020;Zhu et al, 2021;Zhang et al, 2021a). These modifications of tidal properties, especially tidal asymmetry, impact large-scale morphological evolution and water quality in tide-dominated estuaries because of their important role in the import-export process of sediments and waterborne pollutants (Hoitink et al, 2003;Chernetsky et al, 2010;Winterwerp, 2011;Maren and Gerritsen, 2012;Guo et al, 2018).…”

“…Moreover, owing to channel dredging and sand mining, together with a sharp decrease in the amount of sediment debouching into estuaries, the underwater geomorphology of estuaries has also changed significantly (Wu et al, 2014;Wu et al, 2016;Yang et al, 2019;Chen et al, 2020). Previous studies have revealed the impacts of human-intervened topographic changes on estuarine hydrodynamics by observations or numerical modeling, including tidal dynamics (Zhang et al, 2010;Cai et al, 2018a;Lin et al, 2021;Chu et al, 2022), water level dynamics (Zhang et al, 2017;Cai et al, 2018b;Cao et al, 2020;Luo et al, 2020;Yang et al, 2020), and the main astronomical tides and tidal regime shifts (Wang et al, 2020;Zhang et al, 2021a;Zhang et al, 2021b). Few studies have focused on the TDA in the PRE, even though it is strongly linked to large-scale morphological evolution.…”

Assessment of Empirical Algorithms for Shallow Water Bathymetry Using Multi-Spectral Imagery of Pearl River Delta Coast, China

“…In recent years, intensive human activities, such as aquaculture and human-induced land use and land cover change, have dramatically changed the morphology and altered the hydrodynamics [39]. For example, the average water depth increased from 4.2 to 4.6 m between 1980 to 2010 due to decreasing sediment input from dam construction in the Lingding Bay, and the mean tidal range is amplified from 1.1 m near the mouth to 3.7 m near the top of the bay [38].…”

“…In this study, we incorporated multi-spectral information from L8 and S2 data to derive bathymetry in a large coastal region of the Pearl River Delta (PRD), China from 2019 to 2020 with Google Earth Engine (GEE). Four widely used empirical models, namely the linear band model [36], the log-transformed band ratio model [23], the support vector regression model [37] and the random forest regression model [38] were adopted. To evaluate model performance with areal spectral features, all models were applied both with and without area segmentation.…”