《国际泥沙研究》2021年第六期

Papers Published in the International Journal of Sediment Research

Volume 36, No.6, 2021

Pages 687-769 ( December 2021)

1. Use of Large-Eddy Simulation for the bed shear stress estimation over a dune
Adrien Bourgoin, Sylvain S. Guillou, Jér?me Thiébot, Riadh Ata
Pages 687-695

6. Key drivers of changes in the sediment loads of Chinese rivers discharging to the oceans
Cheng Liu, Yun He, Zhongwu Li, Jia Chen, Zhijing Li
Pages 747-755

7. Modeling of climate change impacts on Lake Burullus, coastal lagoon (Egypt)
A. Shalby, M. Elshemy, B.A. Zeidan
Pages 756-769

1. Use of Large-Eddy Simulation for the bed shear stress estimation over a dune
Adrien Bourgoin, Sylvain S. Guillou, Jér?me Thiébot, Riadh Ata
Pages 687-695
https://www.sciencedirect.com/science/article/abs/pii/S1001627919300654
https://doi.org/10.1016/j.ijsrc.2019.10.002
Abstract: Environmental flows are generally characterized by complex bed morphology and high current speeds. Such configurations favor the formation of vortex structures that strongly affect hydrodynamics and sediment transport. Large-Eddy Simulation (LES) enables investigation of the dynamics of the largest turbulence scales and, thanks to enhanced calculation resources, has now become applicable for simulating environmental flows. In this paper, a LES approach is developed in a CFD code (TELEMAC-3D), which was originally developed to simulate free surface flows using RANS methods. The present developments involve implementing sub-grid models, boundary conditions and numerical schemes suitable for LES. The LES version of TELEMAC-3D was validated by comparing results on the model with experimental data for flow past a cylinder. Then, the model was applied to a test case representing flow over dunes. After validating the hydrodynamics, the model was used to assess the bottom shear stress, using both a RANS and a LES approach. Comparison highlighted the potential contribution of LES to investigating the hydrodynamic forces acting on the bottom.

Keywords: Turbulence; Environmental flows; Large eddy simulations; Bed shear stress

2. Impact of the blockage ratio on the transport of sediment in the presence of a hydrokinetic turbine: Numerical modeling of the interaction sediment and turbine
Fatima Khaled, Sylvain Guillou, Yann Méar, Ferhat Hadri
Pages 696-710
https://www.sciencedirect.com/science/article/abs/pii/S1001627921000056
https://doi.org/10.1016/j.ijsrc.2021.02.003
Abstract: Interactions between hydrokinetic turbines and near scale and far scale bed sediment particles are considered a critical area of assessment; however, a limited number of research studies have been published to address this issue. The current paper explores the influence of the blockage ratio on the morphology evolution downstream from a hydrokinetic turbine. A modeling framework is derived to predict the significant transport induced by a turbine installed on the erodible fluvial sandy bed surface, such as the Eulerian multi-phase model for the sediment and the Blade Element Momentum Theory (BEMT) for the turbine, using the open source platform Open FOAM. Two configurations of different blockage ratios are considered. The configurations show differences in the bed morphology and the sediment transport. It has been shown for both configurations that the scour capabilities are enhanced below the turbine due to the acceleration of the flow and increasing local shear stress on the sediment.

Keywords: Environmental impact; Blockage effects; Euler-Euler multiphase; Hydrokinetic turbine; Numerical simulations; Open FOAM

3. 3D numerical simulation of seagrass movement under waves and currents with GPUSPH
Anne-Eléonore Paquier, Thibault Oudart, Caroline Le Bouteiller, Samuel Meulé, Philippe Larroudé, Robert A. Dalrymple
Pages 711-722
https://www.sciencedirect.com/science/article/abs/pii/S1001627920300925
https://doi.org/10.1016/j.ijsrc.2020.08.003
Abstract: The current study tries a new approach to simulating interactions between waves and seagrass through Smoothed Particle Hydrodynamics (SPH). In this model, the plants are defined as a solid that respects Hooke's law, and are assumed to have direct interaction with the fluid. Given the characteristics of the SPH method, especially in terms of computational time, the dimensions of the simulations were limited. The first goal of the current study was to optimize the approach to avoid reaching certain limits such as the rupture of the simulated plant. Plant movements under waves and/or currents have been studied by several authors in various in-situ, physical, and numerical experiments concerning various vegetation species, thus proving that plant movements can be successfully reproduced by SPH 2D/3D. Manning's roughness coefficient, n, was calculated to confirm that the results were in accordance with what had been measured in flume studies. Even though there is still room for improvement, it is shown that this method can be used to estimate Manning's coefficient for coastal vegetation (seagrass and saltmarsh vegetation) and to greatly improve the modeling and forecasting of coastal erosion and storm surge risks by including the effects of vegetation in integrated models.
Keywords: Numerical seagrass movement; GPUSPH; Fluid structure interaction; Waves; Current

4. Numerical modeling of bedload and suspended load contributions to morphological evolution of the Seine Estuary (France)
Baptiste Mengual, Pierre Le Hir, Aurélie Rivier, Matthieu Caillaud, Florent Grasso
Pages 723-735
https://www.sciencedirect.com/science/article/abs/pii/S1001627920300755
https://doi.org/10.1016/j.ijsrc.2020.07.003
Abstract: This numerical modeling study (i) assesses the influence of the sediment erosion process on the sediment dynamics and subsequent morphological changes of a mixed-sediment environment, the macrotidal Seine estuary, when non-cohesive particles are dominant within bed mixtures (non-cohesive regime), and (ii) investigates respective contributions of bedload and suspended load in these dynamics. A three dimensional (3D) process-based morphodynamic model was set up and run under realistic forcings (including tide, waves, wind, and river discharge) during a 1-year period. Applying erosion homogeneously to bed sediment in the non-cohesive regime, i.e., average erosion parameters in the erosion law (especially the erodibility parameter, E0), leads to higher resuspension of fine sediment due to the presence of coarser fractions within mixtures, compared to the case of an independent treatment of erosion for each sediment class. This results in more pronounced horizontal sediment flux (two-fold increase for sand, +30% for mud) and erosion/deposition patterns (up to a two-fold increase in erosion over shoals, generally associated with some coarsening of bed sediment). Compared to observed bathymetric changes, more relevant erosion/deposition patterns are derived from the model when independent resuspension fluxes are considered in the non-cohesive regime. These results suggest that this kind of approach may be more relevant when local grain-size distributions become heterogeneous and multimodal for non-cohesive particles. Bedload transport appears to be a non-dominant but significant contributor to the sediment dynamics of the Seine Estuary mouth. The residual bedload flux represents, on average, between 17 and 38% of the suspended sand flux, its contribution generally increasing when bed sediment becomes coarser (can become dominant at specific locations). The average orientation of residual fluxes and erosion/deposition patterns caused by bedload generally follow those resulting from suspended sediment dynamics. Sediment mass budgets cumulated over the simulated year reveal a relative contribution of bedload to total mass budgets around 25% over large erosion areas of shoals, which can even become higher in sedimentation zones. However, bedload-induced dynamics can locally differ from the dynamics related to suspended load, resulting in specific residual transport, erosion/deposition patterns, and changes in seabed nature.

Keywords: Non-cohesive sand-mud mixtures; Erosion; Suspended sediment transport; Bedload transport; Morphodynamics; Seine Estuary

5. Two-dimensional modeling of fine sediment transport with mixed sediment and consolidation: Application to the Gironde Estuary, France
Sylvain Orseau, Nicolas Huybrechts, Pablo Tassi, Damien Pham Van Bang, Fabrice Klein
Pages 736-746
https://www.sciencedirect.com/science/article/abs/pii/S1001627919303075
https://doi.org/10.1016/j.ijsrc.2019.12.005
Abstract: In order to optimize ship navigation in the macrotidal Gironde Estuary, a recent project funded by the port of Bordeaux aims at better understand and forecast hydrodynamic and fine sediment transport within the estuary. In the framework of this project, a two-dimensional hydro-sedimentary model is built. The model includes hydrodynamic forcings, mixed-sediment transport, and consolidation processes. The harmonic analysis of the astronomical tides reveals a strong distortion of the tidal wave inducing the growth of overtide constituents and the non-significant effect of tide-surge interactions in annual-scale prediction. Depending on hydrological conditions, river discharge can considerably alter the model accuracy due to the migration of the turbidity maximum zone modifying the bottom roughness. Comparison with measurements shows the ability of the model to reproduce suspended-sediment concentrations in the central Estuary. Sensitivity of the model to sediment features has also been discussed in regard of suspended-sediment concentrations and fluid mud deposits. The model will be further coupled with ship squat predictions and a morphodynamic model.
Keywords: Sediment transport; Numerical modeling; Mixed sediment; Gironde Estuary; Opentelemac

6. Key drivers of changes in the sediment loads of Chinese rivers discharging to the oceans
Cheng Liu, Yun He, Zhongwu Li, Jia Chen, Zhijing Li
Pages 747-755
https://www.sciencedirect.com/science/article/abs/pii/S1001627920300561
https://doi.org/10.1016/j.ijsrc.2020.05.005
Abstract: The magnitude and variation of the sediment loads transported by rivers have important implications for the functioning of river systems and changes in the sediment loads of rivers are driven by numerous factors. In this paper, the key drivers of changes in the sediment loads of the major rivers of China are identified by reviewing recent studies of changes in their sediment loads. Except for the Songhua River, which presents no clear tendency of change in runoff or sediment load, nearly all the major rivers of China are characterized by an apparent decline in annual sediment load. The total annual sediment load of major Chinese rivers transported to the coast decreased from 2.03 billion t/yr during the period 1955–1968 to 0.50 billion t/yr during the period 1997–2010. The primary drivers of changes in the sediment loads of the rivers are dam construction, implementation of soil and water conservation measures, catchment disturbance, agricultural practices, sand mining and climate change. Examples drawn from Chinese rivers are used to demonstrate the importance of these drivers. Construction of a large number of reservoirs in the Yangtze River basin represents the primary driver for the reduced sediment load of the Yangtze River. The implementation of soil and water conservation programmes is one of the key drivers for the sharp decline in the sediment load of the Yellow River. Catchment disturbance explains why the reduction of the sediment load of the Lancang-Mekong River at the Chiang Saen gauging station was much less than that at the Gajiu gauging station upstream. A reduction in sediment load resulting from the expansion of agricultural production may be the main driver for the reduced sediment load of the Huaihe River. The decrease in the sediment load of the Pearl River has been influenced by sand mining activities. Climate change is one of the key drivers responsible for the greatly reduced sediment load of the rivers in the Haihe River Basin.

Keywords: Sediment load; Dam construction; Soil and water conservation; Catchment disturbance; Sand mining; Climate change

7. Modeling of climate change impacts on Lake Burullus, coastal lagoon (Egypt)
A. Shalby, M. Elshemy, B.A. Zeidan
Pages 756-769
https://www.sciencedirect.com/science/article/abs/pii/S1001627919303087
https://doi.org/10.1016/j.ijsrc.2019.12.006
Abstract: Coastal lagoons are particularly vulnerable to climate change, in particular, Sea Level Rise (SLR) due to their shallowness. Lake Burullus provides a variety of socio-economic services as the second largest coastal lagoon in Egypt. Recently, it has experienced significant ecological deterioration. Thus, its ecosystem is fragile in the face of anthropogenic induced changes. The main objective of the current study is to investigate the climate change impacts on characteristics of Lake Burullus. A depth averaged hydro-ecological modeling system, MIKE21, was applied to develop an eco - hydrodynamic model for the lake. The developed model was calibrated and verified for two successive years: July 2011–June 2012 and July 2012–June 2013. The model simulations exhibited good agreement with the measurements during the calibration and verification processes. Six different Regional Climate Models (RCMs) were compared, using six different statistical metrics, to determine the most accurate one for the study area. The required meteorological input, including surface air temperature, precipitation, and evaporation were derived from the selected RCM. The meteorological input was extracted for two different years in the 21 st century considering one Representative Concentration Pathways (RCPs) scenario, based on the Intergovernmental Panel on Climate Change (IPCC) 5th Report. Regional SLR projections for the Mediterranean Sea for the selected RCP scenario and the two studied years were obtained. These future climate change estimates were used to modify the validated model of the lake. A sensitivity analysis was applied to assess effect of future climatic conditions and SLR, separately. The results revealed that the lake water depths will increase and it will be warmer and more saline. Significant spatial variability of the studied parameters under climate change forcing is expected. Consequently, climate change is going to restrict the lake's ability to preserve the present-day species. An urgent management plan involving adaptation works, should be implemented to reduce such potential species losses in Egyptian lagoons.

Keywords: Climate change; IPCC; Lake Burullus; MIKE 21; Nile Delta; Water quality model