Mechanisms Controlling the Distribution of Net Water Transport in Estuarine Networks. Issue 1 (29th December 2021)

• Record Type: Journal Article
• Authors: Wang, Jinyang; Dijkstra, Yoeri M.; de Swart, Huib E.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 1(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-12-29
• Subjects: net water transport -- Yangtze Estuary -- river‐tide interaction; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2021JC017982
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: Net water transport (NWT) in estuaries is important for, for example, salt intrusion and sediment dynamics. While NWT is only determined by river runoff in single channels, in estuarine networks, it results from a complex interplay between tides and residual flows. This study aims to disentangle the various contributions of these physical drivers to NWT in estuarine networks and investigate the sensitivities of NWT to variable forcing conditions, interventions, and sea level rise (SLR). To this end, a processes‐based perturbative network model is developed, which accounts for the vertical flow structure to resolve density‐driven flow driven by a vertically uniform along‐channel salinity gradient. Other identified drivers are river discharge and three tidal rectification processes: Stokes transport and its return flow, momentum advection, and velocity‐depth asymmetry. The model is applied to the Yangtze Estuary. NWT due to tidal rectifications and density‐driven flow can be comparable to river discharge. Specifically in the North Branch, the direction of NWT may differ from the direction of river discharge. Varying river discharge mainly affects NWT as tide‐river interaction is weak and density‐driven flow is shown to be insensitive to salt intrusion. Conversely, variations in tidal amplitude strongly affect NWT related to tidal rectification and density‐driven flow. The deepening (narrowing) of one channel (Deep Waterway Project), affected the NWT mostly through the density‐driven flow (advection). Furthermore, NWT distribution in the Yangtze is insensitive to SLR up to 2 m because the effects of SLR on transport due to different drivers compensate each other. Plain Language Summary: To complement numerical models, a partly analytical model is used to decompose net water transport in estuarine networks into different components according to their driving physical processes related to river discharge, differences in water density, and tidal rectification. Applying the model to the Yangtze Estuary (China), this study demonstrates the dependence of each component of net water transport on external forcing conditions (river and tide), as well as their sensitivity to local human intervention and sea level rise. Previous understanding of the tidal influence on net water transport is generalized to explain the creation of net water transport by arbitrary physical processes in estuarine networks. Key Points: Using a 2DV exploratory model, net water transport is disentangled into different components and attributed to their driving mechanisms The theory of differential water level setup is extended to explain net water transport due to these various driving mechanisms In the Yangtze Estuary, net water transport due to tidal rectifications and density gradients can be comparable to river water transport