Feedback between channel resilience and tidal dynamics in an intensively dredged tidal river

Abstract

Tidal rivers are a complex fluvial-estuarine nexus where intensively anthropogenic interferences emerge. Understanding the morphodynamic response to river training in tidal river systems is a contemporary challenge. Here we explore the process of channel infilling and the evolution of tidal characteristics after significant dredging activities in the Shenzhen River (SZR) based on field observed data, in order to reveal feedback mechanisms between tidal dynamic and morphology. The results found that the SZR experienced rapid sediment accretion on interannual and seasonal scales since the channel was remarkably deepened before 2008. In a very short timeframe, the excavated part of channel was almost filled in 2012, and after that the SZR performed switch between erosion at wet season and deposition at dry season, indicating a dynamic equilibrium state was obtained. The tidal skewness of three primary combinations of tidal constituents, M2/M4, M2/S2/MS4 and K1/O1/M2, was calculated from the tidal level of 1998, 2007, 2012 and 2016 at SZHK (river mouth) and LH (upstream) stations. During the period of 1998 and 2012, the total tidal skewness significantly rose by 109.25% and 31.26% at SZHK and LH, respectively, while it remained roughly constant from 2012 to 2016, which is concurrent well with the temporal variation of channel deposition. Similarly, tidal range amplification between LH and SZHK (TRLH/TRSZHK) decreased by 9.0% from 1998 and 2012 while much less decline rate was found after 2012, indicating that the tidal attenuation was probably induced by the channel infilling. Furthermore, the impact of tidal characteristics evolution on suspended sediment transport was discussed, eventually unraveling the feedback mechanism between morphology, tidal regime, sediment transport and trapping in the heavily trained SZR.