The role of river flow and tidal asymmetry on 1‐D estuarine morphodynamics

Abstract

Numerous research efforts have been devoted to understanding estuarine morphodynamics under tidal forcing. However, the impact of river discharge on estuarine morphodynamics is insufficiently examined. Inspired by the Yangtze Estuary, this work explores the morphodynamic impact of river discharge in a 560 km long tidal basin based on a 1-D model (Delft3D). The model considers total load sediment transport and employs a morphodynamic updating scheme to achieve long-term morphodynamic evolution. We analyze the role of Stokes drift, tidal asymmetry, and river discharge in generating tidal residual sediment transport. Model results suggest that morphodynamic equilibrium is approached within millennia by vanishing spatial gradients of tidal residual sediment transport. We find that the interaction between ebb-directed Stokes return flow/river flow with tides is an important mechanism that flushes river-supplied sediment seaward. Increasing river discharge does not induce continuously eroded or accreted equilibrium bed profiles because of the balance between riverine sediment supply and sediment flushing to the sea. An intermediate threshold river discharge can be defined which leads to a deepest equilibrium bed profile. As a result, the shape (concavity or convexity) of the equilibrium bed profiles will adapt with the magnitude of river discharge. Overall, this study reveals the significant role of river discharge in controlling estuarine morphodynamics by supplying sediment and reinforcing ebb-directed residual sediment transport.

Suspended sediment dynamics in a tidal channel network under peak river flow

“…Although numerical models, because of the recent increase in computational power, now can consider more processes, longer time frames, and larger spatial scales, many studies seek to simplify the problem in order to understand the inherent estuarine processes (Ganju and Schoellhamer 2009;Guo et al 2014;Townend 2012). Simplifications such as estuarine numbers, non-dimensional numbers, and 1D models allow for a quick assessment of a study area without requiring high computational power.…”

“…In addition, in estuaries, residual flow is caused by river discharge, tidal asymmetry, Stokes' drift, horizontal circulation, winds, and channel geometry (Aubrey 2013;Dronkers 1986;Friedrichs and Aubrey 1988;Guo et al 2014;Hoitink et al 2003;Rijn 2011;van der Wegen and Roelvink 2012;van der Wegen et al 2008). …”

Analysis on residual coarse sediment transport in estuaries

“…Ranasinghe and Pattiaratchi (2000) and Woodworth et al (2005) investigate the tidal asymmetry in diurnal tidal regions. Guo et al (2014) study the role of river discharge and tidal asymmetry on morphodynamic in the Yangtze Estuary based on a 1D model. Song et al (2011) propose a general formula to calculate tidal sediment transport.…”

The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China

“…We consider the resultant hydrodynamic forcing 68 using the total BSS, as the combined effect of currents due to tide, river and waves. In recent 69 decades, there has been an increasing interest in the use of BSS to examine morphological 70 change in estuarine environments, through both numerical modeling (Bolla Pittaluga et al, 2015; 71 Guo et al, 2014;Lanzoni and Seminara, 2002)and laboratory experiments (Vlaswinkel and 72 Cantelli, 2011). However, such studies tend to highlight the dominance of tidal BSS in controlling 73 the estuary morphology because their focus is within the estuary.…”

“…Guo et al (2014) temperate latitudes, where calmer, warm summers and windy, cold winters tend to result in a 107…”