Sediment Transport In Coastal Waters Research Articles

Study on the Impact of Typhoon Maria (2018) on Suspended Sediment in Hangzhou Bay, China

Sediment transport in coastal waters has an important impact on the siltation of port channels and changes in the estuary ecological environment. The southeast coast of China is often hit by typhoons, which can affect the suspended sediment concentration (SSC) in coastal waters. In this study, we used Geostationary Ocean Color Imager (GOCI) data to analyze SSC variations in Hangzhou Bay during Typhoon Maria (2018), and the influencing factors were also analyzed. The results showed that: (1) During the typhoon’s transit, the SSC in Hangzhou Bay (HZB) increased by 200–800 mg/L, which was one-fold higher than the day before the typhoon. The variation of SSC on the south bank was noticeable, and the typhoon effect on SSC lasted for 2–3 days; (2) The wind speed and significant wave height (SWH) increased during the typhoon. In general, in the early stage of the typhoon, the SSC in HZB was affected by the wind, and in the interim and late period, SSC was influenced by the effect of wind and wave height; (3) Typhoon “Maria” accelerated the transport of sediment and land-based pollutants from land to sea; the effect of residual current and wind stress are the driving mechanisms for seaward sediment transport. However, mechanisms and driving factors of sediment transport in coast water are complex and diverse. The results of this study can help to understand the processes of riverbed erosion and deposition in Hangzhou Bay and adjacent waters. They are also significant for the study of nearshore hydrodynamic characteristics of typhoons and channel engineering.

A 3-D finite volume model for sediment transport in coastal waters

A 3-D model has been developed to simulate sediment transport and bed change induced by currents and waves in coastal waters. The currents are calculated with the 3-D phase-averaged shallow water flow equations, the wave characteristics are determined with a horizontal 2-D wave spectral transformation model, and multiple-sized non-cohesive suspended load and bed load are simulated using a non-equilibrium transport model. The classical mixing length model is modified to determine the horizontal and vertical eddy viscosity considering the effects of current, waves, and wave breaking. A new approach is proposed in the present 3-D model framework to calculate the bed grain shear stress, which is applied to determine the equilibrium bed-load transport rate and near-bed suspended-load concentration. The flow and sediment transport equations are numerically solved using an implicit finite volume method on a hexahedral mesh constructed with horizontal telescoping (quadtree) rectangular cells and vertical sigma coordinate. The difference in the near-bed cells for flow and suspended load calculations is avoided by adding the bed load to the suspended load in the first flow cell above the bed. The developed model has been tested in four laboratory and field cases. It reasonably well reproduces the measured water levels, flow velocities, sediment concentrations, and bed changes.

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

Scientific research on sediment dynamics in the coastal zone and along the littoral zone has evolved considerably over the last four decades. It benefits from a technological revolution that provides the community with cheaper or free tools for in situ study (e.g., sensors, gliders), remote sensing (satellite data, video cameras, drones) or modelling (open source models). These changes favour the transfer of developed methods to monitoring and management services. On the other hand, scientific research is increasingly targeted by public authorities towards finalized studies in relation to societal issues. Shoreline vulnerability is an object of concern that grows after each marine submersion or intense erosion event. Thus, during the last four decades, the production of knowledge on coastal sediment dynamics has evolved considerably, and is in tune with the needs of society. This editorial aims at synthesizing the current revolution in the scientific research related to coastal and littoral hydrosedimentary dynamics, putting into perspective connections between coasts and other geomorphological entities concerned by sediment transport, showing the links between many fragmented approaches of the topic, and introducing the papers published in the special issue of Water on “Sediment transport in coastal waters”.

A depth-averaged 2-D model of flow and sediment transport in coastal waters

A depth-averaged 2-D model has been developed to simulate unsteady flow and nonuniform sediment transport in coastal waters. The current motion is computed by solving the phase-averaged 2-D shallow water flow equations reformulated in terms of total-flux velocity, accounting for the effects of wave radiation stresses and general diffusion or mixing induced by current, waves, and wave breaking. The cross-shore boundary conditions are specified by assuming fully developed longshore current and wave setup that are determined using the reduced 1-D momentum equations. A 2-D wave spectral transformation model is used to calculate the wave height, period, direction, and radiation stresses, and a surface wave roller model is adopted to consider the effects of surface roller on the nearshore currents. The nonequilibrium transport of nonuniform total-load sediment is simulated, considering sediment entrainment by current and waves, the lag of sediment transport relative to the flow, and the hiding and exposure effect of nonuniform bed material. The flow and sediment transport equations are solved using an implicit finite volume method on a variety of meshes including nonuniform rectangular, telescoping (quadtree) rectangular, and hybrid triangular/quadrilateral meshes. The flow and wave models are integrated through a carefully designed steering process. The model has been tested in three field cases, showing generally good performance.

Ocean colour opportunities from Meteosat Second and Third Generation geostationary platforms

Abstract. Ocean colour applications from medium-resolution polar-orbiting satellite sensors have now matured and evolved into operational services. These applications are enabled by the Sentinel-3 OLCI space sensors of the European Earth Observation Copernicus programme and the VIIRS sensors of the US Joint Polar Satellite System programme. Key drivers for the Copernicus ocean colour services are the national obligations of the EU member states to report on the quality of marine, coastal and inland waters for the EU Water Framework Directive and Marine Strategy Framework Directive. Further applications include CO2 sequestration, carbon cycle and climate, fisheries and aquaculture management, near-real-time alerting to harmful algae blooms, environmental monitoring and forecasting, and assessment of sediment transport in coastal waters. Ocean colour data from polar-orbiting satellite platforms, however, suffer from fractional coverage, primarily due to clouds, and inadequate resolution of quickly varying processes. Ocean colour remote sensing from geostationary platforms can provide significant improvements in coverage and sampling frequency and support new applications and services. EUMETSAT's SEVIRI instrument on the geostationary Meteosat Second Generation platforms (MSG) is not designed to meet ocean colour mission requirements, however, it has been demonstrated to provide valuable contribution, particularly in combination with dedicated ocean colour polar observations. This paper describes the ongoing effort to develop operational ocean colour water turbidity and related products and user services from SEVIRI. SEVIRI's multi-temporal capabilities can benefit users requiring improved local-area coverage and frequent diurnal observations. A survey of user requirements and a study of technical capabilities and limitations of the SEVIRI instruments are the basis for this development and are described in this paper. The products will support monitoring of sediment transport, water clarity, and tidal dynamics by providing hourly coverage and long-term time series of the diurnal observations. Further products and services are anticipated from EUMETSAT's FCI instruments on Meteosat Third Generation satellites (MTG), including potential chlorophyll a products.

Numerical model of wave-current interaction based on unstructured quadtree grid for nearshore coastal waters

According to the characteristics of complex topography, hydrology, sediment transport in coastal waters, the aim of this paper is to develop an implicit, depth-averaged 2-D numerical mode of coupling current and wave for coastal area. The hydrodynamic model is the two dimensional depth averaged non-linear shallow water equations with an unstructured non-staggered and multiple-level quadtree rectangular mesh with local refinement for important region. In this non-staggered system, primary variables u -, v -velocity, and water level are stored on the same set of grid points in order to simplify the program code, and fluxes at cell faces are determined using the Rhie and Chow’s momentum interpolation method to avoid spurious checkerboard oscillations. The discretized algebraic equations are solved iteratively using the GMRES method with ILUT preconditioning for speeding the computation. The Wave model is a two-dimensional spectral wave action model of taking into account the effect of wave breaking, shoaling, refraction, diffraction, wave-current interaction, bottom friction. The wave model readily provides the radiation stresses for the hydrodynamic model. The coupling model has been tested against measurement data for steady flow around a spur-dyke in a laboratory flume and tidal flows in Gironde Estuary, France and Grays Harbor, USA. The model reasonably well reproduces the temporal and spatial variations of water level, current speed and wave height observed in the measurements. It shows that the coupling current and wave model can simulate accurately the questions of tide and wave for complex domain, the modeling approach presented herein should be useful in engineering application and environmental protection for coastal area.

AN IMPLICIT 2-D DEPTH-AVERAGED FINITE-VOLUME MODEL OF FLOW AND SEDIMENT TRANSPORT IN COASTAL WATERS

An implicit depth-averaged 2-D finite volume model has been developed to simulate sediment transport and bed morphological changes under actions of currents and waves near coastal inlets. The model computes the depth-averaged 2-D shallow water flow and non-equilibrium transport of total-load sediment, accounting for the effects of wave radiation stresses and turbulent diffusion induced by currents, waves and wave breaking. The model uses a quadtree rectangular mesh to locally refine the mesh around structures of interest or where the topography and/or flow properties change rapidly. The grid nodes are numbered by means of an unstructured index system for more flexibility of mesh generation. The SIMPLEC algorithm is used to handle the coupling of water level and velocity and the Rhie and Chow's (1983) momentum interpolation method is adopted to determine the intercell fluxes on non-staggered grid. Well-developed longshore current and wave setup determined with the reduced 1-D momentum equations are used as the cross-shore boundary conditions. The model has been tested in several laboratory and field cases, showing good performance. In particular, it can use a long time step and is efficient in computation on a PC platform. It has a potential for simulation of long-term coastal morphodynamic processes.

Bedload sediment transport in coastal waters

Formulae for bedload transport of sediments in conditions characteristic of coastal waters are developed from principles of physics. They cover driving forces of: current alone, current plus symmetrical waves, current plus asymmetrical waves, asymmetrical waves alone, and integrated longshore transport. In each case the transport is given as one or more analytical functions of the basic input variables. The formulae are tested against laboratory and field data, and give predictions that lie within a factor of 2 of the measured values for between 47% and 91% of the data, depending on the driving force. The formulae are suited to practical application in coastal waters, especially for transport of coarse materials such as shingle, and also for the bedload component of transport of sand.