To improve navigation, the deep waterway project (DWP) was implemented in the North Passage of the Changjiang Estuary in 1998, which includes a deep channel and two dikes protecting it. By altering estuarine morphology, the DWP can affect saltwater intrusion and mixing, with implications for drinking water intake and supply. In this study, we employ a numerical model to study the influence of dikes of the DWP on saltwater intrusion in the estuary under the climatic and persistent strong northerly wind conditions that occurred in February 2014. The model results show that the dikes prevent the southward transport of relatively low‐salinity water at the mouth of the North Channel (NC) under climatic wind conditions, resulting in the weakening of saltwater intrusion and mixing in this channel. Under persistent strong northerly wind conditions, relatively high‐salinity water is transported southward to the mouth of NC and blocked by the dikes causing a water level rise at the mouth of the NC. As a result, a large amount of high‐salinity water advected into the NC and then out to the sea from the South Chanel, forming a counterclockwise horizontal circulation. The salinity increases abnormally, but mixing decreases in the NC for no more salinity variance input with the implementation of the DWP. Overall, the DWP favors water intake for the reservoir in NC under climatic wind conditions and is unfavorable to water intake under persistent strong northerly winds (>9 m/s), which can lead to extremely severe saltwater intrusion.
In estuaries and tidal rivers, the landward amplification or attenuation of tidal range depends on the competing effects of friction and convergence. In funnel-shaped estuaries, the tendency for amplification is a consequence of mass conservation: the landward decrease in cross-sectional area requires an increment in water elevation or velocity for volume to be conserved. This response to funneling can be attenuated by friction as the tide propagates over the relatively shallow topography. The observable responses of tidal range (amplification, damping, or no change) can be used to classify an estuary as "hypersynchronous," "hyposynchronous," or "synchronous," respectively (de Miranda et al., 2017). One of the main factors that determine the extent of synchronicity is then local topography, which largely modulates frictional effects. Changes in bed morphology can occur naturally over relatively long geological time scales (Hall et al., 2013), but humans have deepened estuarine channels over the last century, in some cases doubling the natural thalweg depth (Ralston et al., 2019). In the late 1800s, river engineers sought to ensure navigability through dredging, so technical guidelines focused on sediment management rather than the impact of dredging on tides (Brooks, 1841). The role of channel deepening in sea level became a topic of interest when historical records revealed that tidal amplitudes worldwide have changed at rates not explained by astronomical forcing (see Haigh et al., 2020; Talke & Jay 2020, for a detailed review). Assessing the effect of channel deepening on tides is key to evaluate shifts in sediment concentration and turbidity (Dijkstra et al., 2019; Winterwerp & Wang, 2013), which play a role in estuarine ecology and water quality (McSweeney et al., 2017).
High tide floods (HTFs)-defined as non-threatening, minor floods that occur primarily through the action of tides-are increasing in frequency around the world (Hague et al., 2019;Moftakhari et al., 2018;Sweet et al., 2020). Although HTFs are not individually destructive, they may cause large cumulative impacts on infrastructure, transportation networks, and society in general through the persistent disruption of economic activities (Moftakhari et al., 2018). The primary driver of HTFs is relative Sea-Level Rise (SLR), such that the tidal elevation exceeds a minor flood datum more often today than under lower sea-levels (Sweet et al., 2020). Factors that drive variations in HTFs may include sea-level variability caused by the El Niño Southern Oscillation (Long
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