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

Abstract

Tidal asymmetry is one of the main factors for generating net transport for waterborne materials in tidal estuaries, and thus, this phenomenon has significant influences on controlling morphological development and the ecological environment. Tidal propagation is sensitive to changes in the coastline and geometry of estuarine regions. Moreover, tidal waveforms vary with various factors, such as coastline changes and bathymetry evolution due to local anthropogenic activities. The topography of Lingding Bay (LDB) of the Pearl River Estuary (PRE) has greatly changed since the 1960s because of human interventions, but the response of tidal duration asymmetry (TDA) to morphological changes is still poorly understood. Utilizing the two-dimensional Delft-3D flexible mesh numerical model, the spatial pattern of TDA and its primary contributors in LDB of the PRE were reproduced for 1964, 1989, and 2016, accounting for the changes in both shoreline and bathymetry owing to human interventions. The results reveal that as the tidal wave propagates upstream, the tidal skewness increases from negative values to positive values longitudinally, indicating the transition from a shorter ebb-duration state to a shorter flood-duration state. Additionally, a prominent shift in TDA and its primary contributors takes place approximately in the period of 1989. In 1964-1989, the tidal skewness increased by at least 0.1 throughout the LDB, indicating that the flood duration of the entire bay was shortened significantly. However, in 1989-2016, the tidal skewness decreased by at most 0.15 throughout the LDB, representing a longer flood duration in the entire LDB. The scenario simulations reveal that reclamation-induced shoreline changes control the increase in TDA and its primary contributors by enhancing width convergence of estuary in the period of 1964-1989. Conversely, the increase in water depth plays a vital role in the decrease of TDA in the period of 1989-2016. The results obtained from this study are particularly useful for understanding the controlled factors contributing to net sediment transport and the associated long-term morphological evolution in estuaries heavily impacted by human interventions.

Physical mechanisms, dynamics and interconnections of multiple estuarine turbidity maximum in the Pearl River estuary

“…The time series observation of SPM on 25-26 August 2018 at a site on the west shoal (Zhang et al, 2020) was used to calibrate the sediment model. The available data for the validation of the location of ETMs were obtained from a number of sources (Yang and Liu, 2015a;Liu et al, 2016;Cui et al, 2022). The distribution of SPM and salinity of a transect was utilized to validate the model result, which was derived from Cui et al (2022).…”

Imbalance of sediment transport in a meso-tidal bay: effect of tidal pumping and residual circulation

“…where m 3 , s, u b , and N are the third moment of the mean, standard deviation, near-bed velocity, and total number of near-bed velocity samples, respectively (Nidzieko, 2010;Nidzieko and Ralston, 2012). In this study, a running discrete lunar-day window of approximately 24.84 h, equivalent to approximately 300 samples, was used to perform low-pass filtering on the time series of the tidal asymmetry index (Seo et al, 2022;Yang et al, 2022). Water elevation variations during the rising and falling periods cause velocity distortions.…”

Analysis of the Invasion of Acetes into the Water Intake of the Daya Bay Nuclear Power Base

“…The inflow period was around 10 days and the outflow period was 6 days in all cases. This result may be due to a combination of astronomical tides and tidal waves in the marginal seas, which were influenced by topography and water depth [31]. (Condition 1: the moment when the rising tide flows fastest; Condition 2: the moment when the falling tide flows fastest; Condition 3: the moment when the tide is at its lowest and the water level is stable; Condition 4: the moment when the tide is at its highest and the water level is stable).…”