Subtidal variability of exchange flows produced by river pulses, wind stress and fortnightly tides in a subtropical stratified estuary

Valle‐Levinson, Arnoldo; Schettini, Carlos Augusto França; Truccolo, Eliane Cristina

doi:10.1016/j.ecss.2019.03.022

Cited by 13 publications

(5 citation statements)

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“…In order to investigate the mechanisms driving SWI in the Po Delta, the numerical results were processed to estimate the along‐channel salt fluxes for Pila, Gnocca, and Goro branches at sections located approximately at 7–8 km from the mouth (light blue lines in Figure 1). The aim is to take advantage of the temporal and spatial coverage of modeling results to identify the relative contribution of advection and diffusion in determining the salt transport along the river branches (Valle‐Levinson et al., 2019). The salt flux is decomposed into an advective term associated with the river flow, a steady shear dispersion associated with the estuarine exchange flow, and a tidal oscillatory salt flux (Lerczak et al., 2006).…”

Section: Resultsmentioning

confidence: 99%

Saltwater Intrusion in a Mediterranean Delta Under a Changing Climate

et al. 2021

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Coastal zones are dynamic and sensitive to changing forcing conditions related to climate variability, such as flooding and droughts, storm surges, and sea-level changes. Among coastal systems, deltas and estuaries are characterized by complex dynamics between fresh water of continental origin and salt waters (Horner-Devine et al., 2015; Valle-Levinson, 2010). Moreover, deltas are impacted by human activities and in some cases the anthropic control on the natural environment can override the climatic signal, forcing deltas toward a man-made river-dominated system (Maselli & Trincardi, 2013). One of the major problems affecting deltas and estuaries, especially during drought conditions, is the upstream extent of the mixing zone between freshwater and saltwater. This would lead to a consequent increase of the salt content in aquifers and surface waters. Saltwater intrusion (SWI) in rivers can hinder the use of surface water for irrigation or drinking purposes and can threaten the livelihood of coastal communities that rely on fresh water supplies for their livelihood. Furthermore, when there is contact between the channel bed and the underlying coastal aquifer, saltwater can intrude and lead to salinization of soils (Werner et al., 2013; White & Kaplan, 2017). A variety of factors drives SWI on different spatial and temporal scales. These can be natural (sea level, storm surges, hurricanes, climate fluctuations, and subsidence) or anthropogenic (land drainage, exploitation of coastal aquifers, reduction in freshwater discharge from hydropower production and irrigation, interbasin diversions and other hydraulic infrastructures, changes in land-use within the drainage basin and channel deepening), as well as combinations of both (White & Kaplan, 2017). Therefore, understanding the processes controlling SWI and their effects under climate change is crucial for defining proper coastal mitigation and management strategies.

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Section: Resultsmentioning

confidence: 99%

Saltwater Intrusion in a Mediterranean Delta Under a Changing Climate

et al. 2021

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“…Tidally dominated areas are similar to the sea, commonly wide and flat. For tidal dominated areas in alluvial systems at geomorphic equilibrium, the width converges landward forming a trumpet shape and the shallowest region is a bar at the mouth (Figure 1a ; Dronkers, 2017 ; Friedrichs & Aubrey, 1994 ; Kästner et al., 2017 ; Valle‐Levinson et al., 2019 ). These reaches can be open bays, divided into multiple deltaic distributaries, or a combination of both (e.g., bayhead delta; Dalrymple & Choi, 2007 ).…”

Section: Introductionmentioning

confidence: 99%

The Role of River Discharge and Geometric Structure on Diurnal Tidal Dynamics, Alabama, USA

2022

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As tides propagate inland, they become distorted by channel geometry and river discharge. Tidal dynamics in fluvial‐marine transitions are commonly observed in high‐energy tidal environments with relatively steady river conditions, leaving the effects of variable river discharge on tides and longitudinal changes poorly understood. To study the effects of variable river discharge on tide‐river interactions, we studied a low‐energy tidal environment where river discharge ranges several orders of magnitude, the diurnal microtidal Tombigbee River‐Mobile Bay fluvial‐marine transition, using water level and velocity observations from 21 stations. Results showed that diurnal tidal attenuation was reduced by the width convergence in seaward reaches and height convergence of the landward backwater reaches, with the channel convergence change location ∼40–50 km inland of the bayhead and seaward of the largest bifurcation. River events amplified tides in seaward regions and attenuated tides in landward regions. This created a region of river‐induced peak amplitude seaward of the flood limit (i.e., bidirectional‐unidirectional current transition), allowing more tidal energy to propagate inland. Tidal currents were attenuated and delayed more by river discharge than water levels, making the phase lag dynamic. The river impacts on the tides were delineated longitudinally and shifted seaward as river discharge increased, ranging up to ∼180 km. Results indicated the longitudinal shifts of river impacts on tides in alluvial systems can be estimated analytically using the ratio of river discharge to tidal discharge and the geometric convergence of the system. Our simple analytical theory provides a pathway for understanding the tide‐river‐geomorphic equilibrium along increasingly dynamic coasts.

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“…Our study covers transient river and ocean forcings by considering a realistic numerical simulation covering a full year and thus including strong seasonal monsoonal variability. Even though wind and atmospheric forcing is known to impact salt transport and intrusion (e.g., Li & Li, 2012;Scully et al, 2005;S.-N. Chen & Sanford, 2009;Valle-Levinson et al, 2019;Xie & Li, 2018), ocean and Q r remain the dominant drivers, particularly so for the Modaomen estuary where tidal range and Q r have the largest effect on the the intraseasonal variability (Lin et al, 2019). We therefore focus on ocean and river forcing and neglect atmospheric forcing.…”

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Multiscale Temporal Response of Salt Intrusion to Transient River and Ocean Forcing

et al. 2022

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Salt intrusion in surface waters endangers freshwater availability, influences water quality, and affects estuarine ecosystem services with high economic and social values. Salt transport and the resulting salinity distributions result from the non‐linear interactions between salt and water dynamics. Estuaries are often considered under (quasi)‐steady assumption or by focusing on specific timescales. Our understanding of their temporal multiscale response to transient forcing is limited, which hinders the implementation of effective mitigation strategies. We apply wavelet analyses to quantify the variability of salt intrusion from hourly to seasonal timescales and unravel the temporal variability of its response across scales. We focus on an estuary that undergoes significant transient forcing, the Modaomen estuary in the Pearl River Delta, and apply the wavelet analyses to year‐long data generated by a coastal ocean numerical model. Our results show that this estuary responds to changes in tidal and riverine forcing throughout the year over interwoven timescales. Our results highlight the temporal variability of the salt intrusion response time both within a given regime and for the transition between regimes. They also suggest that tides control the response time more strongly than river discharge, even though river discharge determines the magnitude of the salt intrusion, and thus modulates the evolution of the salt intrusion response time. We propose a broadly applicable framework to calculate response times with simple data. These results can provide a first‐order guidance for design and implementation of estuarine management strategies and mitigation measures that ensure water access and facilitate sustainable development.

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Subtidal variability of exchange flows produced by river pulses, wind stress and fortnightly tides in a subtropical stratified estuary

Cited by 13 publications

References 20 publications

Saltwater Intrusion in a Mediterranean Delta Under a Changing Climate

Saltwater Intrusion in a Mediterranean Delta Under a Changing Climate

The Role of River Discharge and Geometric Structure on Diurnal Tidal Dynamics, Alabama, USA

Multiscale Temporal Response of Salt Intrusion to Transient River and Ocean Forcing

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