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The present work is related to the study of a water intake projected into a dam reservoir, located in northern Morocco. The object sought is to examine the natural conditions surrounding a water intake and their possible repercussions on its operation. Thus, a two-dimensional numerical model is developed to simulate the sediment transport in a reservoir dam. The developed model consists of hydrodynamic module based on the Saint–Venant equations and sediment transport module based on the mass-balance equation, where there are resolved by a MacCormack numerical scheme and upwind scheme, respectively. The analysis using the numerical model has made it possible to predict the shutdown periods of the drinking water production station with respect to the rate of suspended solids (SS) for extreme rainfall events.

In this work, the mechanism of sediment transport in a U-shaped channel with a lateral intake is investigated experimentally and numerically, together with the processes of sediment entry into the intake itself and formation of bed topography.

Dry sediment is injected into a steady flow in a rigid channel with a bend and sediment particles are traced in time. In order to validate the numerical model, the three components of the flow velocity, as well as the sediment path in time and the diverted sediment ratios, are measured experimentally. A numerical Discrete Phase Model (DPM) is then applied to study the effect of the intake position and diversion angle on the sediment transport mechanism in the bend. The DPM has, in fact, the capability of specifying for each particle its position relative to a reference time and space and, thereby, it is used in this study to analyze the phenomenon evolution and determine the sediment particles diverted into the intake.

The comparison between the experimental data and the DPM numerical results shows a good agreement. In order to investigate the mechanism of sediment transport and to evaluate the percentage of the diverted sediments, a parametric study is then conducted through the numerical model, with different positions of the outer bend of the channel, diversion angles of the lateral intake and diversion discharge ratios.

The results show that the mechanism of sediment entry into the lateral intake is affected by the diversion discharge ratio. For low discharge ratios, the mechanism of sediment entry to the lateral intake only consists of continuous entrance from the upstream edge of the intake. With the increase of the discharge ratio, it consists of a continuous entrance from the downstream edge and a periodic entrance from the upstream edge of the intake.

The DPM results show that, for all diversion discharge ratios, the minimum percentage of sediment entered into the lateral intake corresponds to the position of 120^∘ and diversion angle equal to 50^∘.

The simulation of the variation of the erosion or sedimentation and the sediment-carrying capability of the water on the river segments, as it changes from the lower-water season to the higher-water season, is performed by a dynamical model of the sediment transport on a river network. The model is constructed by considering that the sediment-carrying capability of the water in one segment is modulated by the undergone state of it and that of its neighbor segments. The calculated results can simulate the relative variations occuring in the natural river when the water seasons alternate.

A sediment transport dynamic model, based on the consideration of streams confluence and/or diversion, is proposed to investigate the influence of water diversion on the mainstream. The simulated results accord qualitatively with the observed or experimental phenomenon in the Yellow River, that is, sedimentation will get more in the main channel as the water is diverted. Some interesting scaling laws describing the behavior of the erosion–sedimentation state in the process of sediment transport are observed, which may help us to get some understandings of sediment transport dynamics in a river network.

In order to model nonlinear breaking waves with moving boundary and coastal sandbar migration; we presented a morphodynamic model, where hydrodynamic equations (free surface flows) and sediment transport equation are solved in a coupled manner. The originality lies in the development of an innovative approach, in which, we project the horizontal velocity onto a basis functions depending only on the variable z and we calculate analytically the vertical velocity and the nonhydrostatic pressure. The choice of basis depends on the problem under consideration. This model is numerically stable because there is no mesh in the vertical direction. This model is accurate because we can directly introduce functions that best fits the physical nature of the flow. Our model is validated through laboratory measurements carried out by Dingemans [1994, J. Comput. Phys. 231, 328–344], Cox and Kobayashi [2000, J. Geophys. Res. 105(c6), 223–236. and Dette et al. [2002, Coast. Eng.47, 137–177].

The present analysis, as a kind of case study, deals with the experimental research at two different coast sites of the South Baltic. The analysis of the driving forces caused by wave fields and so on, and the responses, like current circulations, sediment transport and morphological coastal changes, gave rise to the attempt of empirical description of environmental site-specific coastal features and their large-scale interactions. In the present study, the name "large-scale" refers to the processes having the longshore scale of the order of kilometres and the cross-shore scale of hundreds of metres. Time scales lie in the range from months, seasons up to a few or dozen or so years at most. The above investigations provide an insight into the specific hydro- and morphodynamical processes occurring in coastal zones of the Baltic Sea. These processes can be regarded as representative for other small seas.

Field measurements are important for understanding coastal processes, verifying and calibrating numerical and physical models, and as direct input to coastal designs. Many aspects of coastal engineering are hampered by the lack of high quality field data particularly during storms. This paper introduces the Sensor Insertion System (SIS), which uses a somewhat different approach for measurements that has proven useful at the US Army Corps of Engineers Field Research Facility (FRF). The SIS is a pier-mounted diverless instrument deployment and retrieval system that can be used to make measurements under calm or storm conditions anywhere across the surf zone. The SIS can operate in wave heights up to 5.6 m, with 20 m/s winds, and 2 m/s currents. The mobility of the SIS permits measurements to evolve with the morphology, thus avoiding many of the problems of traditional stationary instrument installations. The SIS approach is to use a single instrument array and reduce the cost and logistics of instrumenting the surf zone so that a long-term measurement capability can be maintained. This approach has helped overcome many of the obstacles of directly measuring storm longshore sediment transport processes at the FRF during the past six years. The utility of the SIS is demonstrated in this paper through examples of it's application for a variety of coastal science investigations.

The effects on the sediment transport rate due to inclusion of seepage process in the mass of the beach sand in the swash zone are investigated numerically. A higher order Boussinesq model for breaking and non-breaking waves is extended in the swash zone and is coupled with a porous flow model which is based on the shallow water equations. To take into account of the infliltration-exfiltration processes in the sediment transport, a modified Shields parameter is used to account the effects of stabilization or destabilization of the surface layers and boundary layer thickening or thinning. The numerical results indicated that for fine sediments, the time-averaged onshore transport is decreased, while the offshore transport is increased. For coarser sediments the time-averaged onshore transport is increased, while the offshore transport is decreased. The above results are in agreement with field measurements as well as with experimental data. The exact value of the critical grain size changeover point is no straightforward to estimate. Present numerical experiments indicate that the value of the critical grain size changeover point appears to lie somewhere between 0.4 and 0.6 mm. Relatively small changes in the estimation of the friction factor might change the direction of the apparent influence of infiltration-exfiltration.

A horizontal two-dimensional finite element model is developed in order to estimate the process of scour around a large-scale cylinder due to waves. The present model differs from previous models in the sense that the wave model is based on an elliptic mild slope equation and the sediment transport induced by the steady streaming is considered. The current induced by the gradient of radiation stress is considered and calculated using a depth integrated shallow water equation. The contributions of the Lagrangian drift velocity to the scour is also considered in this model. The model is validated against a few cases where experimental data are available. The comparison of the calculation results with the experimental data indicates that the present numerical model predicts the scour around a large cylinder reasonably well. The effects of Keulegan–Capenter (KC) number, the grain size of sediments and the model scale on scour around a large cylinder are also investigated.

Most of the existing sediment transport models are not synchronously driven by both the wave field and the flow field. This paper describes a 3D sediment transport model with waves and currents directly coupled within the model to continuously account for different-scale activities especially those that have significant contribution to local sediment transport processes such as formation of sediment plumes and turbidity maxima. A practical issue in modeling coastal sediment transport, besides the concern of model accuracy, is the efficiency of the model. In the present model, the wave action equation, instead of the computational demanding elliptic mild-slope equation, is used to calculate the wave parameters. The wave action equations take into account wave refraction and diffraction as well as the tidal hydrodynamic modification. The calculation of the wave and current forcing is coupled during the time marching process so that the effects due to short-term activities can be considered. The model has been verified against laboratory measurements and has also been applied to simulate actual sediment transport situations in the Pearl River Estuary (PRE), China. It has been quantitatively shown that the suspended sediment concentration in the PRE increases significantly when waves are present. Sediment deposition occurs at the upstream region of the PRE while erosion takes place mostly at the down-estuary region due to exposure to wave actions.

Artificial submerged sand bars have been used as an alternative soft engineering structure for shore protection. To successfully implement the sand bar in an economically beneficial manner, more knowledge is required concerning the evolution of a sand bar under different conditions. A series of experiments is presented to quantify the sediment transport that is induced by artificial submerged sand bars in a wave-driven beach environment. Artificial movable sand bars of various initial geometries were tested on various fixed, inclined bottom slopes by using different incoming regular wave conditions. A new, beneficial parameter, the cumulative transport rate, is defined by integrating the time-dependent cross-shore sediment transport rate from an initial deposition to a quasi-equilibrium state of a sand bar migration. From many tests and analyses, it has been found that the cumulative transport rate of the sand bar is highly dependent on the local Shields number being related to the bed-load transport. Additionally, the Shields-dependent relation is compared to previous field sand bar evolution projects to determine if the sand bar actively migrates onshore or remains stable. An optimal initial bar geometry is suggested to pursue an efficient onshore sediment transport. The effects of the bottom slope on the cumulative transport rate are also discussed.

At 14:46 JST on March 11, 2011 a magnitude 9.0 earthquake (2011 Tohoku Earthquake and Tsunami) occurred off the Pacific Coast of Miyagi Prefecture. This study investigated the extensive changes in beach morphology due to the earthquake and tsunami along the 15 km Northern Sendai Coast using remotely sensed data. The remote sensing analysis on the beach topography and coastal forest demonstrated the following notable characteristics of beach morphological change: erosion of the northern barrier at the mouths of the Nanakitagawa and Natorigawa Rivers; erosion at an old river channel; scour landward of the seawalls in the longshore direction; erosion and deposition in beach areas with detached breakwaters; and deposition in coastal forest areas. Linkage of the deposition in the forest areas with the damage type of coastal forests was observed. The impact of the earthquake and tsunami on the beach morphology was serious; roughly 60% of the study area was degraded by 0.2–0.5 m in elevation mainly due to land subsidence, and a total of 0.4 km² of beach area was eroded mainly due to erosion of the northern barrier at the mouths of the Nanakitagawa and Natorigawa Rivers. This study explores the geographical changes brought on by a tremendous earthquake and tsunami, which will help to elucidate the mechanisms of coastal forest destruction, beach erosion, and their interaction during tsunami events.

In this study, a simplified multicomponent technique for modeling the 2D sediment transport in the vicinity of navigation channels to harbors is formulated. The main simplification assumes that longshore current is the only factor transporting sediments to the offshore navigation channel. The technique requires the application of three numerical models: NMLONG model (1D depth averaged finite difference wave model), RMA2 (2D depth averaged finite element hydrodynamic model) and SED2D (2D depth averaged finite element sediment transport model). RMA2 is forced at the inflow boundary using longshore velocity profiles generated by the incoming waves via the application of NMLONG model. Output of NMLONG provides also the boundary condition of SED2D which takes a velocity field input from RMA2. A variable manning coefficient is used inside RMA2 domain to account for wave roughness. Data collected in the period from 1989 to 1997 in the vicinity of the navigation channel of Damietta Harbor (Egypt) is used to calibrate the multicomponent technique. The results show that the technique explains well the observed spatial variation of bed change in the navigation channel.

The calibrated technique is then applied to study different solutions to reduce sedimentation in Damietta Harbor navigation channel. The results showed that the optimum solution found can significantly reduce the amount of sedimentation. For sedimentation caused by west-to-east longshore current, the reduction amount range is 62–74% (i.e. only 26–38% of the current sedimentation shall occur). For sedimentation caused by east-to-west longshore current, the reduction percentage reaches 60–70%.

A numerical sediment transport model (STM) was used to investigate coastal geomorphic changes that resulted from the 2011 Tohoku earthquake tsunami in Rikuzentakata City and Hirota Bay on the southern Sanriku Coast of Japan. The simulation was verified using observed inundation processes and heights, measured topographic changes and sediment deposition. Aerial video footage recorded by the Iwate Prefectural Police was also used. The results show that the numerical model was able to predict the spatial distribution and volume of erosion and deposition in Hirota Bay, as well as sediment transport processes. The effects of sediment transport on tsunami inundation were also investigated. Numerical results revealed that the majority of the sand dunes were eroded by the first wave, especially during the strong return flow of the receding wave. Large flows and sand dune erosions can occur elsewhere if tsunamis inundate a plain with a limited shore-normal width. These events could cause large-scale morphological changes comparable to those that occurred in Rikuzentakata City.

This study investigates the changes in coastal topography of the Rikuzen-Takata Coast in Iwate Prefecture, Japan before and after the 2011 off the Pacific coast of Tohoku Earthquake Tsunami and the effects of coastal structures on these changes. The changes in coastal topography were analyzed using bathymetry data and aerial photographs before and after the tsunami in addition to aerial video during the tsunami. The bathymetry data were obtained from 1989 to 2002 during the construction of three submerged breakwaters and from after the 2011 tsunami until 2013. The aerial photographs were acquired from 1947 to 2015, and the aerial videos were acquired during the tsunami run-up and backwash. The results demonstrated that the coast was eroded mainly due to the tsunami backwash, and the submerged breakwaters trapped the seaward transport of sediment from the coast. Erosion was partly prevented in locations where the seawall was not washed away. The coastal structures had significant effects on the behavior of the coastal tsunami and on sediment transport. We also found that the coast did not recover naturally at the desired speed after the tsunami because the coast had been stable before the tsunami. Coastal restoration five years after the 2011 tsunami are also summarized in the Appendix to illustrate the future reconstruction plan for the study coast.

A detailed laboratory study of swash zone sediment transport under dam-break waves on a fine sandy slope was carried out. A newly developed sediment transport measurement system was applied for simultaneous measurement of sediment concentration and transport velocity with a vertical resolution of 0.53 mm based on particle image velocimetry (PIV) and a light extinction method, respectively. Concentration data were combined with velocity data to produce sediment flux and were used to investigate the characteristics of sediment transport in the swash zone under dam-break waves. It was found that sand particles followed the flow well in the experiment. Phase difference between the maximum velocity and maximum concentration in the initial uprush was obvious. The maximum concentration varied significantly between different elevations. The onshore flux was much larger than the offshore flux, and the flux near the bed was much larger than that at the higher elevations. The net transport was offshore close to the bed, onshore in the middle layer, and almost zero in the upper layer. The measurement error between the mass change calculated from bed form evolution and the net sediment transport obtained from the measurement system was smaller than 20%.

In this paper, we propose a model for the simulation of the bed evolution dynamics in coastal regions characterized by articulated morphologies. An integral form of the fully nonlinear Boussinesq equations in contravariant formulation, in which Christoffel symbols are absent, is proposed in order to simulate hydrodynamic fields from deep water up to just seaward of the surf zones. Breaking wave propagation in the surf zone is simulated by integrating the nonlinear shallow water equations with a high-order shock-capturing scheme. The near-bed instantaneous flow velocity and the intra-wave hydrodynamic quantities are calculated by the momentum equation integrated over the turbulent boundary layer. The bed evolution dynamics is calculated starting from the contravariant formulation of the advection–diffusion equation for the suspended sediment concentration in which the advective sediment transport terms are formulated according to a quasi-three-dimensional approach, and taking into account the contribution given by the spatial variation of the bed load transport. The model is validated against several tests by comparing numerical results with experimental data. The ability of the proposed model to represent the sediment transport phenomena in a morphologically articulated coastal region is verified by numerically simulating the long-term bed evolution in the coastal region opposite Pescara harbor (in Italy) and comparing numerical results with the field data.

Shore protection projects require the prediction of coastal storm damage and economic loss but the damage processes are not well understood. An exploratory experiment consisting of 11 tests was conducted in a wave flume with a sand beach to examine the movement of 10 wooden blocks (floatable objects) placed on the foreshore and berm as well as on short and long pilings. The still water level was varied to create accretional and erosional profile changes. The cross-shore wave transformation on the beach and the wave overtopping and overwash of the berm were measured in 101 runs of irregular waves where each run lasted 400s. The initial block elevation above the sand surface had little effect on the hydrodynamics, sediment transport, and profile evolution in this experiment with widely-spaced blocks. The block floating and sliding on the sand surface and the block falling from the pilings depended on the swash hydrodynamics and block clearance above the foreshore and berm whose profile varied during each test. A simple probabilistic model is developed to estimate the immersion, sliding, and floating probabilities for the blocks in the swash zone. The predicted probabilities are compared with the observed cross-shore variation of the block response on or above the accretional and erosional beach profiles. The accurate prediction of the block response is shown to require the accurate prediction of the beach profile change.

This paper presents an experimental investigation of local scour beneath two identical pipelines placed in a tandem arrangement. Changes in the equilibrium scour depth and time scale of scour due to steady currents are explored for different spacing between the pipelines (defined in terms of a gap ratio $G/D)$ under both live bed and clear water conditions. It is found that the smaller the gap ratio, the larger the interaction between the two tandem pipelines. More specifically, when $G/D<3$ it is found that (i) the equilibrium scour depth beneath the downstream pipeline is larger than that below the upstream pipe, and (ii) the equilibrium scour depth for both pipelines is larger than for a single pipeline in isolation. Alternatively for $G/D>3$ it is found that the equilibrium scour depth beneath the upstream pipeline can be deeper than the downstream pipeline, however both pipelines have a depth that is not significantly different to the equilibrium depth for an isolated pipeline. In terms of the time scale of scour it is observed that the downstream pipeline has a similar or larger time scale than the upstream pipeline over all gap ratios analyzed. In comparison to an isolated pipeline the time scale for both tandem pipelines is larger when $G/D<3$, whilst for $G/D>3$ and $G/D>6$, respectively, the upstream and downstream pipelines have a similar time scale to an isolated pipeline. The trends in the experimental results are shown to agree well with recent numerical results in the literature. Empirical formulas for predicting the time development of scour beneath two tandem pipelines are proposed.

A two horizontal dimensional compound model is developed to simulate coastal sediment transport and bed morphology evolution due to wave action. The wave module is a higher-order Boussinesq-type model. The bed load in the surf zone is computed from an advanced semi-empirical formula while the suspended load can be calculated through the solution of the advection-diffusion equation for the sediment or alternatively from a simplified formula. The estimation of the sediment transport in the swash zone is based on the ballistic theory. The unified sediment transport module is valid under combined waves and currents including the wave asymmetry and phase-lag effects. The bathymetry is updated through the sediment conservation equation and the morphological accelerator factor technique accounts for extended simulation time. The model is validated against a number of short-term tests in one horizontal dimension. The response is generally good with most of the morphological features being reproduced in the cross-shore direction. A comparison between various sediment transport formulae and a sensitivity analysis are also performed illustrating the need for inclusion of the phase-lag effects.