Pattern changes in tidal channel morphodynamics under human interventions: a case of Shiziyang tidal channel in the Pearl River Delta, China

The morphodynamics of tidal channels can be considerably altered by intensive human activities, such as the land reclamation and channel dredging. Morphological alterations of Lingdingyang Bay (LDB) in the Pearl River Delta (RPD) have received great attention, while the changes in Shiziyang (SZY) tidal channel connecting LDB with Humen Outlet is less known. In this study, bathymetric maps of the Shiziyang tidal channel in the PRD at different periods were collected to investigate the geomorphologic pattern by means of a digital elevation model (DEM). It was shown that the water depth increased with the decreasing width convergence length, indicating intensified channel deepening and narrowing, while tidal channel bed was drastically cut down due to port construction and channel dredging in 1959, 1975 and 2004, respectively. Consequently, the SZY eroded at a rate of 0.164 m/yr during the study period, with a new pattern of eastward-erosion and westward-deposition. In addition, erosion in the downstream reach (0.271 m/yr) was significantly faster than that in the upstream reach (0.006 m/yr). The EOF results showed that the impact of natural factor, channel dredging and land reclamation on bathymetric changes accounted for 48.48%, 20.54% and 11.57%, respectively. Furthermore, the spring-neap variability of tidal wave celerity and tidal amplification in SZY both increased after human interventions and there is a clear transition pattern and stronger tidal hydrodynamics according to the results of 1D analytical hydrodynamics model. Based on the model results, the decadal evolution of SZY morphology can be well reproduced by the observing water levels. The results obtained from this study can be particularly helpful for quantifying the potential impacts due to human interventions, which is useful for setting future conservation planning strategies in estuarine zones.