Estuarine and coastal regions are heavily populated and well-developed areas. Rapid population growth and urbanisation in these regions will continure in the future [1] and will significantly affect the environmental and water quality in these regions. Fresh river water flow carries sediment and deposits as it enters into estuaries [2], while salt water intrusion into the river mouth will affect river and estuary ecology and environments [3]. At the coast, tidal flow, current and waves may cause beach erosion and variations in water quality. A better understanding of the hydrodynamics of estuaries and coasts is therefore important in order to accurately monitor the envoronment and water quality in these regions and to predict coastal evolution. The hydrodynamics of estuaries and coasts, affected by many factors, is very complicated, and requires a unique approach combining theoretical analysis and modelling studies. As such, this Special Issue is set to investigate the hydrodynamics, sediment transport and water quality in estuaries and coasts. The primary objectives of this Special Issue were to bring studies investiagting and simulating (1) fresh–salt water exchange in estuaries; (2) estuarine and coastal sediment transport; (3) beach erosion and nourishment and (4) water quality modelling in estuaries and coasts.
In total, nine research papers are published in this Special Issue, covering a broad range of hydrodynamic aspects of esturaries and coasts. Hein et al. [4] investigated tidal oscillation and resonance in semi-closed estuaries in the North Sea. They developed a harmonic analysis method of the least squares to examine the hydrographs collected from 25 spatially distributed guages, covering a broad region of the estuary. Sohrt et al. [5] developed analytical and numerical models to simulate tidal wave oscillations and reflection features in estuaries. They calculated the reflection and transmission coefficients of long regular waves by considering the variation in the bathymetry. Yan et al. [6,7] investigated how the peak river discharge affected lateral flow and turbidity currents in a macrotidal estuary. They applied a three-dimensional (3D) numerical model to predict the variation in estuary turbidity currents and sediment transport with the change in river flow discharge during the neap and spring tides. They also studied the estuary bed’s morphological evolution induced by sediment transport. The paper by Song et al. [8] presented a new method to accurately survey the river bed topography. The method is useful for deep water depths where LiDAR and radar-based DEM cannot be used.
The study by Khalil et al. [9] presented a new approach—a coastal reservoir technique—for mitigating estuary flooding. Brisbane, a coastal flooding-vulnerable city, was taken as a case study. Weng et al. [10] applied the numerical simulation software MIKE 21 to show the effect of building a sluice gate in the river mouth on the salinity, nutrients and organisms in the estuary. The Jiaojiang River Estuary was taken as a case study. Liu et al. [11] developed a semi-implicit Eulaerian–Lagrangian finite-element-based model to investigate the effect of geomorphologic variations on estuarine hydrodynamics. They took the Danshui River estuary as a case study and demonstrated how the constructions of engineering projects affected the hydrodynamics in the estuary. Biguino et al. [12] carried out monthly field observations over a one year period to collect data on current velocity and direction, temperature and salinity in the Sado Estuary, Portugal. From the collected data, they were able to analyse the circulation features and the temerature and salinity distribution through the water column in the estuary.
The papers published in this Special Issue contain theoretical analyses, numercial model simulations and field observations, and investiagte various aspects of the hydrodynamics of estuary and coastal regions. The findings help to improve our understanding of the hydrodynamics of estuaries and coasts. All papers published in this Special Issue have gone through the normal review processes.
Funding
This research received no external funding.
Conflicts of Interest
The author declares no conflict of interest.
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