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Hydrodynamics in Estuaries and Coast: Analysis and Modeling

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A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics and Hydrodynamics".

Deadline for manuscript submissions: closed (30 June 2021) | Viewed by 30335

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Prof. Dr. Yakun Guo

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School of Engineering, University of Bradford, Bradford BD7 1DP, UK
Interests: hydraulics; coastal engineering; open-channel flows; buoyancy driven flows; CFD; river dynamics
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Special Issue Information

Dear Colleagues,

Estuarine and coastal regions are heavily populated and well developed areas. Fresh river water carries sediment and deposits it as it enters the estuary, while salt water intrusion into the river mouth may affect the river’s ecology and environment. In coastal environments, tidal flow, current, and waves may cause beach erosion and variation of water quality. The hydrodynamics in estuaries and coasts is very complicated and requires a unique approach combining theoretical analysis, numerical modelling, physical laboratory experimental model study, as well as field observation. This Special Issue is set up to receive research papers investigating the hydrodynamics, sediment transport, and water quality in the region of estuaries and coasts. Topics include: fresh–salt water exchange in estuaries, estuarine and coastal sediment transport, beach erosion and nourishment, and water quality modelling in estuaries and coasts.

Prof. Yakun Guo
Guest Editor

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Keywords

fresh–salt water exchange in estuaries
estuarine and coastal sediment transport
beach erosion and nourishment
water quality modelling in estuaries and coasts
theoretical analysis
numerical modelling
physical laboratory experimental model study
field observation

Published Papers (10 papers)

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Editorial

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2 pages, 159 KiB

Open AccessEditorial

Hydrodynamics in Estuaries and Coast: Analysis and Modeling

by Yakun Guo

Water 2022, 14(9), 1478; https://doi.org/10.3390/w14091478 - 5 May 2022

Cited by 4 | Viewed by 1822

Abstract

Estuarine and coastal regions are heavily populated and well-developed areas [...] Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

Research

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19 pages, 5312 KiB

Open AccessArticle

Tidal Oscillation and Resonance in Semi-Closed Estuaries—Empirical Analyses from the Elbe Estuary, North Sea

by Sebastian S. V. Hein, Vanessa Sohrt, Edgar Nehlsen, Thomas Strotmann and Peter Fröhle

Water 2021, 13(6), 848; https://doi.org/10.3390/w13060848 - 19 Mar 2021

Cited by 7 | Viewed by 3652

Abstract

Many tidal influenced estuaries and coastal basins feature tidal amplification because of, e.g., convergence and reflection. Increasing amplification rates were observed in the Elbe estuary, with consequences for construction measures, nautical manoeuvring, flood protection, riverbed morphology and ecosystems. Although many studies were conducted investigating the tidal wave transformation in estuaries, studies based on spatially well-distributed empirical data covering periods over more than a year are rare. To fill this gap, a self-developed adapted harmonic analysis method of least squares was applied to hydrographs from 25 gauges, distributed over the tidal influenced estuary from the river mouth to the tidal border which is given by the weir 160 km upstream of the river mouth. The investigation period for the harmonic analyses covers a whole nodal cycle of 18.613 a beginning in the year 2000. The tidal constituents’ oscillatory behaviour including the appearance of compound tides, generated by nonlinear shallow water processes, and the formation of reflection induced partially standing waves are determined. The tidal constituents show shared frequency-group specific partial clapotis, but also have significant differences in amplification within those groups. The latter fact contributes to the detected inverse proportionality of tidal range amplification inside the estuary to incoming tidal wave height. As reflection can cause resonance in tidal influenced rivers, tests are developed to analyse whether criteria for resonance are met. To determine the system’s specific resonance frequency, a new method was introduced with the three-parameter Lorentzian curve-fitting. As the detected resonance frequency is not close to tidal frequencies, full-established resonance of the tidal wave and of the tidal constituents is not observed in the Elbe estuary. Migrating nodes of the partially standing tidal wave hint at increasing latent resonance. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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18 pages, 3031 KiB

Open AccessArticle

Model Based Assessment of the Reflection Behavior of Tidal Waves at Bathymetric Changes in Estuaries

by Vanessa Sohrt, Sebastian S.V. Hein, Edgar Nehlsen, Thomas Strotmann and Peter Fröhle

Water 2021, 13(4), 489; https://doi.org/10.3390/w13040489 - 13 Feb 2021

Cited by 12 | Viewed by 3870

Abstract

Estuaries are often modified by human activities. Adjustments in the morphology of an estuary have a potential impact on the hydrodynamics and on the reflection behavior of the tide. The influence of such system changes on the complex tidal regime with a large number of superimposed tidal constituents is not fully understood yet. The reflection properties of estuaries that are characterized by abrupt changes in geometry are systematically investigated on the basis of simplified estuary model approaches to improve the understanding of the oscillation and reflection behavior of tidal waves in estuaries. The reflection coefficients at abrupt cross-sectional changes are determined by two different methods, i.e., an analytical energy-based approach and a hydrodynamic numerical (HN) model. Comparisons indicate a high agreement of the results of the different methods when evaluating the reflection coefficient. The tidal constituents are reflected at partial and total reflectors and amplified by shoaling depending on the water depths, the height of the bottom step and the horizontal constriction. A harmonic analysis of simulated water level data partly shows the formation and amplification of higher harmonic components as a result of shallow water effects. The interaction with reflectors results in an increasing amplification of the tidal constituents and the tide. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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23 pages, 8580 KiB

Open AccessArticle

The Response of Turbidity Maximum to Peak River Discharge in a Macrotidal Estuary

by Yuhan Yan, Dehai Song, Xianwen Bao and Nan Wang

Water 2021, 13(1), 106; https://doi.org/10.3390/w13010106 - 5 Jan 2021

Cited by 5 | Viewed by 2545

Abstract

The Ou River, a medium-sized river in the southeastern China, is examined to study the estuarine turbidity maximum (ETM) response to rapidly varied river discharge, i.e., peak river discharge (PRD). This study analyzes the difference in ETM and sediment transport mechanisms between low-discharge and PRD during neap and spring tides by using the Finite-Volume Community Ocean Model. The three-dimensional model is validated by in-situ measurements from 23 April to 22 May 2007. In the Ou River Estuary (ORE), ETM is generally induced by the convergence between river runoff and density-driven flow. The position of ETM for neap and spring tides is similar, but the suspended sediment concentration during spring tide is stronger than that during neap tide. The sediment source of ETM is mainly derived from the resuspension of the seabed. PRD, compared with low-discharge, can dilute the ETM, but cause more sediment to be resuspended from the seabed. The ETM is more seaward during PRD. After PRD, the larger the peak discharge, the longer the recovery time will be. Moreover, the river sediment supply helps shorten ETM recovery time. Mechanisms for this ETM during a PRD can contribute to studies of morphological evolution and pollutant flushing. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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20 pages, 5062 KiB

Open AccessArticle

The Response of Lateral Flow to Peak River Discharge in a Macrotidal Estuary

by Yuhan Yan, Dehai Song, Xianwen Bao and Yang Ding

Water 2020, 12(12), 3571; https://doi.org/10.3390/w12123571 - 19 Dec 2020

Cited by 4 | Viewed by 2895

Abstract

The Ou River, a medium-sized river in southeastern China, is selected to study the lateral flow response to rapidly varied river discharge, i.e., peak river discharge (PRD). A three-dimensional model based on the Finite-Volume Community Ocean Model is validated by in situ measurements from 15 June to 16 July 2005. PRD, which considers the extra buoyancy and longitudinal momentum in a short time, rebuilds the stratification and lateral flow. PRD, compared with low-discharge, generally makes stratification stronger and lateral flow weaker. PRD mainly rebuilds lateral flow by changing lateral advection, lateral Coriolis, and lateral-barotropic pressure gradient terms. After PRD, the salinity recovery time is longer than that of the flow because the impact on buoyancy lasts longer than that on longitudinal flow. Longitudinal flow is mostly affected by the momentum transferred during PRD; therefore, the recovery time is close to the flooding duration. However, the lateral flow is affected by the buoyancy, and its recovery time is generally longer than the flooding duration. The lateral flow recovery time depends on transect width, flow velocity and the variation caused by PRD. PRD occurs widely in global small-/medium-sized river estuaries, and the result of this work can be extended to other estuaries. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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18 pages, 5741 KiB

Open AccessArticle

Reconstruction of River Topography for 3D Hydrodynamic Modelling Using Surveyed Cross-Sections: An Improved Algorithm

by Yunhao Song, Jinfeng Huang, Erik Toorman and Guolu Yang

Water 2020, 12(12), 3539; https://doi.org/10.3390/w12123539 - 16 Dec 2020

Cited by 4 | Viewed by 2689

Abstract

Multidimensional hydrodynamic modelling becomes tricky when lacking the bathymetric data representing the continuous underwater riverbed surface. Light detection and ranging (LiDAR)-based and radar-based digital elevation models (DEMs) are often used to build the high-accuracy floodplain topography, while in most cases the submerged riverbed could not be detected because both radar and LiDAR operate at wavelengths that cannot penetrate the water. Data from other sources is therefore required to establish the riverbed topography. The inundated river channel is often surveyed with an echo sounder to obtain discrete cross-section data. In this context, an improved algorithm based on the classic flow-oriented coordinates transformation is proposed to generate the riverbed topography using surveyed cross-sections. The dimensionless channel width (DCW) processing method is developed within the algorithm to largely increase the prediction accuracy, especially for the meandering reaches. The generated riverbed topography can be merged with the floodplain DEM to create an integrated DEM for 2D and 3D hydrodynamic simulations. Two case studies are carried out: a benchmark test in the Baxter River, United States, with carefully surveyed channel–floodplain topographic data to validate the algorithm, and a 3D hydrodynamic modelling-based application in Three Gorges Reservoir (TGR) area, China. Results from the benchmark case demonstrate very good consistency between the created topography and the surveyed data with root mean square error (RMSE) = 0.17 m and the interpolation accuracy was increased by 55% compared to the traditional method without DCW processing. 3D hydrodynamic modelling results match the observed field data well, indicating that the generated DEM of the TGR area was good enough not only to predict water depths along the tributary, but also to allow the hydrodynamic model to capture the typical features of the complex density currents caused by both the topography of the tributary estuary and the operation rules of TGR. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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22 pages, 5524 KiB

Open AccessEditor’s ChoiceArticle

Investigating an Innovative Sea-Based Strategy to Mitigate Coastal City Flood Disasters and Its Feasibility Study for Brisbane, Australia

by Usman Khalil, Shu-Qing Yang, Muttucumaru Sivakumar, Keith Enever, Mariam Sajid and Muhammad Zain Bin Riaz

Water 2020, 12(10), 2744; https://doi.org/10.3390/w12102744 - 30 Sep 2020

Cited by 6 | Viewed by 3259

Abstract

This study examines an innovative Coastal Reservoir (CR) technique as a feasible solution for flood adaptation and mitigation in the Brisbane River Estuary (BRE), Australia, which is vulnerable to coastal flooding. The study analysed the operation of a CR by using the MIKE 21 hydrodynamic modelling package. The 2D hydrodynamic model was calibrated and validated for the 2013 and 2011 flood events respectively, with a Nash-Sutcliffe coefficient (E_ns) between 0.87 to 0.97 at all gauges. River right branch widening and dredging produced a 0.16 m reduction in water level at the Brisbane city gauge. The results show that by suitable gate operation of CR, the 2011 flood normal observed level of 4.46 m, with reference to the Australian Height Datum (AHD) at Brisbane city, could have been reduced to 3.88 m AHD, while under the improved management operation of the Wivenhoe Dam, the flood level could be lowered to 4 m AHD at Brisbane city, which could have been reduced with CR to 2.87 m AHD with an overall water level reduction below the maximum flood level. The results demonstrated that the innovative use of a CR could considerably decrease the overall flood peak and lessen flood severity in the coastal city of Brisbane. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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16 pages, 4794 KiB

Open AccessArticle

Numeric Study on the Influence of Sluice-Gate Operation on Salinity, Nutrients and Organisms in the Jiaojiang River Estuary, China

by Xi Weng, Cuiling Jiang, Manxue Zhang, Menglin Yuan and Tianshan Zeng

Water 2020, 12(7), 2026; https://doi.org/10.3390/w12072026 - 16 Jul 2020

Cited by 11 | Viewed by 2558

Abstract

The estuary—located in the joint zone between river and ocean—has created unique ecosystems and rich biodiversity due to its complex habitat conditions. As the critical period for the growth and reproduction of estuarine organisms, the flood season is also crucial for estuary sluice to play a role in flood control and drainage. This study aims at proposing an ecological scheduling scheme that comprehensively considers the adverse factors brought by draining of the estuarine sluice to maintain different ecological functions of the Jiaojiang River estuary. A two-dimensional mathematical model in MIKE 21 was used to ascertain the change of salinity and nutrients in the study area, and results were analyzed to understand the impact of draining on estuarine organisms. Based on an analysis of the change and redistribution of salinity and nutrients, the sea area could be divided into three parts during the operation of the estuarine sluice: nearshore area with low-salt and high eutrophication, medium mixed salinity under nitrogen limitation area and high-salt under phosphorus limitation area. The aquaculture area was alternately situated in the mesohaline (>5.0‰–18.0‰) and polyhaline (>18.0‰) zones. The after-effects of salinity change—including the lowest value and the sharp change of salinity, especially the sharp change of salinity (11.8‰–12‰) caused by large-volume discharge—would affect the growth of organisms to a certain extent, but would not be lethal. Moreover, a high-incidence red tide area was determined to be formed within 8–14 km away from the estuarine sluice after the sluice opening, and the area of this zone was firmly related to the opening schemes. The study suggested that the proposed sluice should choose the mode of draining frequent with the small flow at neap tide in order to reduce the stress of sluice construction and operation on mariculture organisms and phytoplankton in Jiaojiang River estuary on the strength of the ecological restoration measures for estuary and riparian zones. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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28 pages, 11729 KiB

Open AccessEditor’s ChoiceArticle

Response of Salt Transport and Residence Time to Geomorphologic Changes in an Estuarine System

by Wen-Cheng Liu, Min-Hsin Ke and Hong-Ming Liu

Water 2020, 12(4), 1091; https://doi.org/10.3390/w12041091 - 12 Apr 2020

Cited by 9 | Viewed by 2542

Abstract

Anthropogenic changes in tidal estuaries have significantly altered bathymetry and topography over the past half century. The geomorphic-driven changes in estuarine hydrodynamics and salt transport remain unclear. To explore this issue, a SELFE (Semi-implicit Eulaerian-Lagrangian Finite Element) -based model was developed and utilized in a case study in the Danshui River, Taiwan. The model was calibrated and validated using observed water level, current, and salinity data from 2015, 2016, and 2017. The performance of the SELFE model corresponded well to the measured data. Furthermore, the validated model was utilized to analyze the hydrodynamics, residual current, limit of salt intrusion, and residence time under the predevelopment (1981) and present (2015) conditions. The predicted results revealed that the time lag of water surface elevation at both high tide and low tide under the present condition was approximately 0.5–2 h shorter under the predevelopment condition. The residual circulation under the predevelopment condition was stronger than under the present condition for low flow, causing the limit of salt intrusion to extend further upstream under the predevelopment condition compared to the limit of salt intrusion under the present condition. The calculated residence time under the predevelopment condition was longer than the residence time under the present condition. The freshwater discharge input is a dominating factor affecting the salt intrusion and residence time in a tidal estuary. A regression correlation between the maximum distance of salt intrusion and freshwater discharge and a correlation between residence time and freshwater discharge were established to predict the limit of salt intrusion and residence time under the predevelopment and present conditions with different scenarios of freshwater discharge input. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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13 pages, 1924 KiB

Open AccessBrief Report

Variability of Currents and Water Column Structure in a Temperate Estuarine System (Sado Estuary, Portugal)

by Beatriz Biguino, Fátima Sousa and Ana C. Brito

Water 2021, 13(2), 187; https://doi.org/10.3390/w13020187 - 14 Jan 2021

Cited by 16 | Viewed by 2586

Abstract

The circulation in estuaries promotes the transport of organisms, nutrients, oxygen and sediments. Simultaneously, the mixture of fresh and salt water leads to variations of the physicochemical and biological components of the region. Therefore, it is important to further understand the hydrodynamic patterns of an estuary as one of the bases to understand the whole dynamic of these systems, ecologically important regions that must be preserved. However, little is known about the hydrodynamics of some estuarine systems. In order to bridge the knowledge gap about the Sado estuary, sampling was conducted with the purpose of evaluating some circulation patterns of the estuary and classifying it according to the stratification of the water column. The campaigns were conducted to collect monthly data on the intensity and direction of the currents, and on the temperature and salinity of the water column, between September 2018 and September 2019. The data indicated that water circulation in the Sado estuary, occurred through the two main navigation channels (North and South), according to the tidal regime. Both the temperature and the salinity were homogeneous along the water column, revealing little stratification. The analysis suggests possible hydrodynamic changes of the estuary in the past years. Full article

(This article belongs to the Special Issue Hydrodynamics in Estuaries and Coast: Analysis and Modeling)

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