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Tsunamis continue to pose an existential threat to life and infrastructure in many coastal areas around the world. One of the risks associated with tsunamis is the formation of deep scour holes around critical infrastructure and other coastal buildings, compromising their structural integrity and stability. Despite its importance, tsunami-induced scour is still given limited and simplified consideration in design guidelines for coastal structures. To further improve the understanding of tsunami-induced scour processes, and thus provide the basis for safer design of coastal structures, novel large-scale laboratory experiments have been conducted. The experiments featured a unique combination of boundary conditions, including a square coastal structure on a sloping and dry sandy beach. Single broken solitary waves were used to simulate tsunami bores. The spatiotemporal scour development directly at the square column was monitored by a high-resolution camera system, allowing a detailed description of the highly dynamic flow and scour process. Differences in the scour process between the wave runup and drawdown phases are described, and maximum and final scour depths are given as a function of inundation depth, wave height, and distance of the column from the shoreline. The scour process is characterized by several distinct phases of varying intensity and scour rate, the sequence of which varies depending on the location on the sides of the column. It is shown that the drawdown phase has a large influence on the overall scour development, adding up to 58% to the scour depth obtained during the wave runup phase. As a result of significant sediment infilling during the drawdown phase, the maximum scour depths achieved during the drawdown phase are up to twice the final scour depths at the end of a test. This discrepancy between final and maximum scour depths is greater than in previous studies using a flat sediment bed. The results of this study therefore help to interpret scour depths measured during field investigations after a tsunami event and provide a basis for extending design guidelines for coastal structures. [ABSTRACT FROM AUTHOR]

Barrier islands span 10% of the world's coastlines and dominate along the Atlantic and Gulf of Mexico coasts in the USA routinely exposed to storm surge. These islands serve as buffers between the open coast and the mainland, and protect the mainland from storm damage. During storms, significant morphological change can occur, including substantial erosion of the islands' vegetated dunes. In this study, the focus is on the influence of belowground biomass – namely dune plant roots – and dune topographic characteristics on barrier-island erosion during storms. The numerical model XBeach was employed to simulate storm-induced sediment transport. A parameter study was conducted by varying distance from the shoreline to the dune, dune shape, sediment grain size, and sediment mobility as an analogue for biomass. The influence of individual parameters and the collective impact of parameters were analyzed. The results help improve our knowledge of barrier island dynamics and lay a solid groundwork for future investigations. [ABSTRACT FROM AUTHOR]

The concession of the Peruvian Amazon Waterway (PAW) project seeks to strengthen commercial transport between Brazil and Peru by using four rivers: Amazon, Ucayali, Marañón, and Huallaga, in which the Peruvian Ministry of Transportation and Communications (MTC) was in charge of developing the Terms of Reference (TOR). At the end, the TOR did not specify the methodology for the hydrogeomorphic characterization of rivers. The PAW project was designed to meet specific geometric characteristics to ensure navigable conditions: minimum water depth of 2.44 m (8 ft) and channel width ranging from 44 to 56 m, approximately. The zones where the river bottom limits the layout and dimensions of the navigation channel are called shallow zones (SZs). Based on the PAW project's TOR, the EIA-d (Detailed Environmental Impact Assessment) study was carried out using 14 SZs that required dredging 3.87 million m3 of sediments. In 2019, the EDI (Definitive Engineering Study) described 24 SZs with a total dredging volume of 4.39 million m3 of sediments. The number and locations of SZs and the volume of required dredging changed significantly, revealing a lack of understanding of meandering (i.e., Ucayali and Huallaga) and anabranching (i.e., Marañón and Amazon) river processes. This study presents an integral methodology for the hydrogeomorphic characterization of the meandering Huallaga River (the river with 56% of the total estimated volume to dredge) by using remote sensing and field measurements (hydrodynamic, sediment transport, and bathymetry). Geological confinement of river dynamics, together with the presence of anabranching structures, promote stable SZs. In regions where meandering rivers tend to develop ancient and modern geomorphic structures, SZs are temporarily and highly dependent of river dynamics. The present hydrogeomorphic characterization of the Huallaga River will support the Peruvian government to inform their technical guidelines (TOR), especially for infrastructure projects (e.g., PAW) in Amazonian rivers. Several river-related engineering projects lack a broad and comprehensive view to understand a river's spatial and temporal dynamics. One of these projects is the Amazon Waterway (Hidrovía Amazónica in Spanish) which sought to strengthen commercial transport between Brazil and Peru using four rivers: Amazon, Ucayali, Marañón, and Huallaga. The Terms of Reference (TOR) for the Environmental Impact Study (EIA) did not specify the methodology for understanding river dynamics; however, the focus was mainly concentrated on the need to develop dredging activities. During the EIA evaluation stage, more than 400 technical observations were presented, several related to fluvial geomorphology. This article presents a synthesis of how proper river studies should be carried out and how river dynamics is related to aquatic biodiversity, highlighting the importance of understanding rivers before developing infrastructure projects. [ABSTRACT FROM AUTHOR]

The ship-generated waves in restricted waterways can influence the behavior of sediment resuspension and bank erosion. This paper explores the case study considering the effect of ship-generated waves in restricted channels. A fully nonlinear Boussinesq model (FUNWAVE-TVD) is used to simulate the ship-generated waves. The sediment transport model adopted in FUNWAVE has been changed to incorporate the modified diffusion coefficients, deposition flux, and an explicit equation for settling velocity and critical shield parameter. The sediment transport model was validated against the experimental results of solitary waves in a wave tank, and model performance in shoreline geometry was reported. The implementation of the moving vessel in the numerical model and its impact on suspended sediment concentration were evaluated against the field measurements in the Falta stretch of the Hooghly river in Indian National Waterway 1. The error value in predicting the depth-averaged suspended sediment concentration by the FUNWAVE module was 97.6%, which has been significantly reduced to 16.3% based on the present modification. The parametric study of the ship waves in a typical restricted waterway of India revealed that the concentration of the sediments gradually decreases from the navigation channel to the river banks due to dissipation in the ship waves. The change in wave height and depth-averaged sediment concentration increases with the increasing depth Froude number. Finally, the impact on sediment transport due to different scenarios, such as the movement of two vessels in close proximity, the passage of vehicles coming from the opposite direction on the navigation channel, the influence of small draft vessels, and the bed morphology changes due to the multiple vessel movements are analyzed and reported. [ABSTRACT FROM AUTHOR]

The bed level change in rivers and estuaries due to several dynamic parameters such as tide, waves, river discharge, and wind is a common problem. The current practice is to predict the changes through numerical modeling and compare it through field measurements. The empirical relations to be adopted for the sediment transport estimation form an integral part of morphodynamic models. In this study, five different total sediment transport formulae have been incorporated in the morphodynamic routine of a circulation model. The hydrodynamic model accounts for tide-induced flows, tide being the dominant forcing in the estuaries considered for the study. The preceding sediment transport formulae for predicting bed level changes (erosion and accretion) are subjected to an assessment, through statistical approaches, to find the most suitable formula for different hydrodynamic settings of a macrotidal estuary (Hooghly) and a microtidal estuary (Cochin). The results are validated with the field measurements and finally the appropriate empirical formula is designated based on a detailed analysis. The AW model outscores in the Brier skill score (BSS) analysis and thus qualifies to be most suited sediment transport model for the macrotidal estuarine dynamics with a score of 0.55, and the AW model is followed by the VR model with a score of 0.52. As per BSS, the EH model falls under the Good model category with a score of 0.48, for the microtidal estuary and thus qualifies to be the better suited sediment transport model among the models considered. [ABSTRACT FROM AUTHOR]

Colocated sediment pore pressures at depths of approximately 0.02 and 0.22 m below the sand surface and near-bed water velocities were measured for approximately 2 weeks in approximately 1 m mean water depth on an ocean beach near Duck, North Carolina. These measurements suggest that storm wave-driven liquefaction processes may enhance local shoreward sediment transport. During the passage of tropical storm Melissa, wave heights in 26-m water depth (NDBC 44100) were 1–4 m, and storm surge (approximately 1 m) and wave-induced setup increased the water depth on the beach. Upward vertical gradients in pressure heads between the sensors increased with the storm approach, with the largest values observed before the maxima in local wave heights, wave periods, and water depths. The large gradients in pore pressure exceeded several liquefaction criteria and usually occurred when near-bed velocities were upward- and shoreward-directed. Observations on an ocean beach show that during storms the water pressure below the sand surface can be greater than the pressure near the sand surface. When that difference in pressure (called a pressure gradient) becomes large, the sediments fluidize, that is, they act like a fluid in a process called liquefaction. Unlike dry or partially wet sediments, the fluidized sand is moved easily by currents. During tropical storm Melissa, large upward-directed pressure gradients fluidized the sediment, usually as the crest of an ocean wave passed over the surface. Therefore, the sediments possibly became free to move as a liquid when the currents from waves were directed both upward and toward the shore. The liquified sediments could be transported shoreward, leading to changes to the sand surface (accretion and erosion). This phenomenon is important to understand because it contributes to how, where, and when sediment might be transported on an ocean beach. [ABSTRACT FROM AUTHOR]

Process-based models are suitable tools for reproducing storm-driven erosion. However, their performance has been mainly examined on mild-slope sandy beaches and their use on steep beaches still represents a challenge. Here, open-source process-based model XBeach experiments were combined with topographical measurements collected for two storms (16- and 5-year return period) to obtain a reliable model. The model parameters "facua" (parameterized wave asymmetry and skewness sediment transport component), "bermslope" (upslope transport term for semireflective beaches), and "wetslope" (critical avalanching submerged slope) were utilized for calibration and validation. The 16-year storm simulations on an exposed beach revealed that whether bermslope increased and "facua" must be reduced, and vice versa, to properly simulate erosion. Adding bermslope provided excellent results for these storms when using facua and wetslope values close to the recommended values. In a groin-protected site, XBeach was successfully calibrated and validated for the tested storms using these parameters, although with different values. These experiments demonstrated that the appropriate use of these parameters can satisfactorily simulate morphological changes on steep beaches for different hydrodynamic conditions and coastal settings (exposed and groin protected). [ABSTRACT FROM AUTHOR]

Forensic engineering field surveys conducted in the aftermath of large-scale tsunamis documented the presence of deep local scour holes around structures caused by extreme inundation occurring during such events. The mechanisms leading to scour in extreme flows are still not well understood, as several physical phenomena influencing the spatiotemporal extent of scour have not been adequately investigated. The authors have conducted an experimental test program that has employed a large square column in the Large Wave Flume of the Coastal Research Center, Germany, while they also used a state-of-the-art numerical model (FLOW-3D) to numerically reproduce the experimental results. An investigation of the turbulent flow structures observed around the impacted structure showed that these flow structures are largely responsible for the sediment transport during the runup phase, but the turbulent energy was far less intense during the drawdown phase. The weakness of the turbulent structures observed during drawdown indicates that a different physical phenomenon than the one corresponding to the inflow phase is responsible for the sediment transport experienced during inundation drawdown. Due to the rapid lowering of the flow depth during the drawdown phase of tsunami inundations, a loss of excess pressure occurs because of the upward pressure gradient forming within the soil. However, the pore pressure measurements taken inside the soil in the physical experiment indicate no sign of upward pressure gradient on the inshore side of the column, which is an observation that is incongruent with previous similar studies and previous theoretical concepts. This difference was explained by a layer of soil that remained with a low water content throughout the test because the column was installed on dry sand with low permeability, a condition never tested before for pore pressure change caused by tsunami-like waves. [ABSTRACT FROM AUTHOR]

In this paper, we present a simple theoretical method of determining the optimal groin length on a sandy multibar shore of a nontidal sea. Example computations for the seashore of the Hel Peninsula (Poland, south Baltic Sea) are provided. The proposed unsophisticated method, which consumes little time and is thus innovative, is based on calculations of the mean annual sediment transport rate and a determination of the width of the surf zone. The reliability of the theoretical modeling results was demonstrated, as well as their compatibility with the features of the groin system designed and constructed along this stretch of the shore a few decades ago. Long-term field observations in the village of Kuźnica have shown that such a system effectively supports and supplements the artificial shore nourishment in the considered region. The method can be applied to other sandy and multibar shores of nontidal seas. [ABSTRACT FROM AUTHOR]

The mechanisms controlling sediment transport at river mouths and estuaries nearby ports are complicated interactions among waves, tidal currents, and river flows over complex bathymetry. Episodic river discharge triggered by large rainfall may contribute to significant sediment into the ocean. Over the last decade, the exposed riverine sediment from the Zhuoshui River, north of Mailiao Port, is one of the major sources of sediment supply in this region. Previous field observations shortly after the passage of a typhoon suggested fine-grained sediments settled rapidly near the river mouth, and tidal currents and strong wind-driven waves during winter were the mechanisms that transported sediment toward the navigational channel. Numerical simulations provide insights into the patterns of residual circulations for a range of spring-neap tidal forces and wave conditions. Model results show that extending North Jetty could be one of the engineering countermeasures to modify the circulation system between the port and the river mouth to mitigate the siltation problem. [ABSTRACT FROM AUTHOR]

A comprehensive case study of the coastal processes for Fortescue Inlet (New Jersey, USA) is presented with the objective of minimizing maintenance dredging of the navigational channel. This study compares the effectiveness of both traditional sedimentation control structures and modified dredging templates, including construction of a new jetty, modification of the length and orientation of an existing jetty, and the use of upland and offshore deposition basins. The alternatives were analyzed using Deflt3D Flexible Mesh. The results indicate that sediment transport near Fortescue Inlet is dominated by wave action with pronounced seasonal variations in wave direction. The site exhibits relatively shallow depths above the depth of closure and pronounced offshore bars. Consequently, much of the sediment transport occurs well offshore (approximately 300 m offshore) and beyond the existing jetty. The results indicate that structural modifications (i.e., relocation or lengthening) of the existing jetty do not improve the sedimentation rate within the channel. Instead, use of offshore deposition basins delivers the most promising improvement, with potential cost savings over 10% over existing strategies. [ABSTRACT FROM AUTHOR]

This paper studies the effect of the wave front-current angle on the scour around a circular pile. An experimental study was carried out in the Coastal, Ocean and Sediment Transport (COAST) laboratory at the University of Plymouth (UK) using a single monopile of 0.125 m in diameter and an 8 m long by 1.5 m wide by 0.2 m high sand pit. The results obtained during the test campaign show the influence of the angle between waves and currents on both the maximum scour depth and the time scale of the process. Wave fronts partially aligned with current (65°) produce deeper scour holes than perpendicular forcing conditions (90°). Wave fronts partially against the current (115°) produce less scour than any of the two previous scenarios. The addition of waves reduced the maximum scour depth, compared with the current-only case. The development of the scour hole was found to be more rapid when waves are added to the current, with 50% of the final scour achieved in half the time. The results show that wave direction relative to the current is an important component in scour prediction. [ABSTRACT FROM AUTHOR]

Along sandy coastlines, submerged, shore-parallel sandbars play an essential role in shoreline morphology by dissipating wave energy through depth-induced wave breaking. While wave breaking and sediment transport around sandbars are complex three-dimensional (3D) processes, shoreline morphology is typically simulated with depth-averaged models that feature lower computational demand than do 3D models. In this context, this study examines the implications of depth-averaging the flow field and approximating the breaking process in nonhydrostatic models (e.g., XBeach nonhydrostatic) for the hydro- and morphodynamic processes around sandbars. The implications are drawn based on reproducing large-scale experiments of a barred beach profile using the single-layer (XBNH) and the reduced two-layer (XBNH+) modes of XBeach. While hydrodynamic processes were predicted with high accuracy on the sandbar's seaward side, wave heights were overpredicted on the bar's landward side. The overestimation was due to the simplified reproduction of the complex breaking process near the sandbar's peak, particularly in terms of the generated turbulence in the water column. Moreover, the velocity profile with a strong undertow could only be represented in a simplified way even using the two-layer mode XBNH+, thus resulting in inaccurate predictions of sediment loads around the sandbar. A parametric study is performed, and it revealed which model parameters control the simulation of the wave-breaking process. Thus, wave height predictions could be improved by tuning the energy-dissipation parameters. However, flow velocities and morphodynamic predictions could not be improved accordingly. Thus, this study identifies possible hydrodynamic model improvements, such as incorporating a roller dissipation model. Moreover, it improves understanding of key drivers and processes that should be included in nonhydrostatic depth-averaged models to simulate morphological changes around sandbars more efficiently. [ABSTRACT FROM AUTHOR]

Sandy beaches generally are influenced by various coastal dynamic processes and undergo constant changes. The present study is an attempt to understand the hydromorphodynamic characteristics of a sandy pocket beach situated along the central west coast of India through field observation and numerical modeling. Multiple oceanographic instruments are deployed to capture the actual nearshore hydrodynamics, and sediment transport is measured using the streamer trap method suggested earlier during the premonsoon season. The observed vertical distribution of sediment fluxes showed a typical upward decrease from the seabed to the water surface. It is also noted that nearly 75% of the trap measurements showed that near-bed transport is higher than the depth-integrated values, confirming that the maximum sand remobilization is in the vicinity of the seabed rather than in suspension. The beach profiles of selected transects were measured during the pre- and postmonsoon seasons to understand the bed evolution. A one-dimensional numerical model, developed using XBeach and validated with field-observed values, demonstratively captured the effect of monsoon hydrodynamics on the beach profiles with fair accuracy. The various significant numerical parameters that govern the morphodynamics in the sandy beach are evaluated through a comprehensive analysis. In the end, the simulated beach profile that captures the effect of monsoon and storm are in good agreement with that obtained from field observations, with Brier Skill Scores (BSSs) of 0.69, 0.76, and 0.74 for Profiles 1, 2, and 3, respectively. [ABSTRACT FROM AUTHOR]

Dredged sediment is commonly placed as a submerged nearshore berm to nourish the beach or to dissipate high-energy waves, but the lifespan of such features is not easily predicted by existing methods. This paper presents a simple technique for generating order-of-magnitude estimates of the sediment transport rate of nearshore berms using offshore hindcast wave characteristics transformed to the nearshore. Total longshore transport for the entire nearshore region is calculated using eight published longshore transport equations (e.g., CERC equation and Kamphuis equation), which were evaluated for their relative performance. Because nearshore placements occupy only a portion of the cross-shore profile, the total longshore transport rate is scaled by an empirically-based fraction between 0 and 1, which is determined by the nearshore berm's position in nondimensional space. The cross-shore transport rate is calculated independently using the near-bed orbital velocity from stream-function wave theory. The longshore and cross-shore transport rates are then superimposed to generate a total transport rate for the nearshore berm's constructed footprint. The total transport rates were calculated at 11 historical nearshore berms and evaluated based on accuracy, inclusion of relevant coastal processes, and sensitivity to input parameters. The recommended total transport rate technique resulted in an average percent error magnitude of 72% and a maximum percent error magnitude of 167% at the historical placement locations. This technique is recommended for generating rapid, order-of-magnitude estimates of nearshore berm deflation rates for project design, particularly in scenarios when application of a full numerical model is prohibitive. [ABSTRACT FROM AUTHOR]

Driven by waves, water surface elevation, and wind conditions, a coupled wave, hydrodynamic, and sediment transport modeling system was developed to investigate the transport of placed dredged material in the surf and nearshore zones of southern Lake Michigan. With the measured bathymetric data and the implementation of a cross-shore transport routine, the modeling study focused on nearshore sediment migration, bed volume change, and subaqueous profile change due to wave action. The field datasets validated the model's capability in properly reproducing longshore and cross-shore current and wave processes that govern nearshore sediment transport. The analysis on survey data and simulation results indicates that time-averaged longshore current dominates the redistribution of sediment. Although the cross-shore transport is an order of magnitude smaller than the longshore transport, including the surf zone cross-shore process in the model contributes to net bed and subaqueous profile changes, and greatly improves the model performance. [ABSTRACT FROM AUTHOR]

This paper presents a proof of concept that acoustic velocity and backscatter intensity measurements can provide essential information on ship wave–induced sediment transport processes in the littoral zone of a large river. Through a case study in the Hungarian section of Danube River, a combined application of an acoustic Doppler velocimeter (ADV) and a formerly calibrated acoustic backscatter sensor (ABS) is introduced for parallel measurements of 3D flow velocities and suspended sediment concentration (SSC) in a characteristic point of the near-bank zone. SSC times series detected by the ABS supported the calibration of the ADV backscatter, which eventually enabled the analysis of the temporal behavior of flow velocity and SSC conditions altered by ship waves. A suitable method for the separation of primary and secondary waves provided essential information on the turbulence intensities and sediment fluxes, and was found that the low-frequency primary waves are rather responsible for the lateral sediment transport instead of the dynamic secondary waves. The introduced data processing techniques and the main findings of the paper mean an important step toward the better understanding of the impacts of ship waves on the riverbanks, inherently playing a crucial role in the hydro-morphological and habitat conditions of river systems. [ABSTRACT FROM AUTHOR]

NavTEL is a new decision support tool for the short-term (36 h) planning of ship routes and the management of underkeel clearance in estuarine navigation channels. NavTEL uses a deterministic method and is coupled with the TELEMAC-MASCARET system for numerical modeling of hydrodynamic and sediment transport in the estuary with a two-dimensional approach. In its present version, NavTEL allows (i) daily simulations to be automatically prepared and launched; and (ii) simulation outputs to be postprocessed to find the safest ship route and to predict underkeel clearances at specified locations. As the reliability of the results relies on the accuracy of water-level predictions, numerical simulations were performed with measured river discharges, storm surge forecasts, and time-varying friction coefficients for bed roughness. Even though NavTEL was initially developed for the Atlantic Port of Bordeaux located in the Gironde Estuary, its kernel has a modular structure allowing the tool to be adjusted to different port configurations and types of water bodies. Finally, examples of graphical outputs and reports generated by NavTEL are shown for an application of a container ship coming into the port of Bordeaux. [ABSTRACT FROM AUTHOR]

This study develops a site-specific analysis of sediment transport for the in-the-wet construction of Olmsted Locks and Dam on the Ohio River using the HEC-RAS model. Results from the analysis are used to assess the frequency of need for dredging. Toffaleti's sediment transport function is used herein and is calibrated to the United States Army Corps of Engineers (USACE), Louisville District measurements of sediment concentrations. We apply the calibrated model to historical river flow along the excavated portion of the streambed, during dam construction. We make predictions over a simulation period for deposition in the excavated area without considering the shell placements that are actually made or any dredging to remove deposited sediment. One notable trend on sediment deposition in the excavated area is that approximately half of the long-term predicted deposition occurs within the first six months. Our results show that trapping efficiency of the transported sediment load follow a similar trend starting at less than 10% and dropping to 1% within a half a year. The results of this analysis are useful for other planning dredging operations where in-the-wet construction will be performed. [ABSTRACT FROM AUTHOR]

Aggregation state significantly influences the size, density, and transport characteristics of fine sediment. Understanding sediment transport and deposition processes in the nation's navigable waterways is a primary mission for the US Army Corps of Engineers (USACE), particularly when it comes to infilling of navigation channels. In this study, a newly developed camera system was used to evaluate the aggregation state of eroded sediment from cores collected in the tidal James River, VA. Results showed that bed sediments were composed mostly of mud, but that erosion predominately occurred in the form of aggregates with median sizes 50–270 times larger than the disaggregated sediment. Aggregate size weakly correlated to shear stress at levels <2 Pa, as well as sand content and bed density. A numerical simulation demonstrated that mud aggregates were predicted to transport in incipient suspension or bedload, while disaggregated fines were predominately maintained in full suspension. This difference in transport mode has significant implication for channel infilling and sediment transport within the system. [ABSTRACT FROM AUTHOR]

The coastal stretch between Vagueira and Praia de Mira, northern Portugal, is subject to high-energy wave conditions. At the same time, the shoreline is a main contributor to the local economy, extensively due to tourism. Despite the shoreline being currently protected by groynes, a better understanding of the hydrodynamics and the morphodynamics in the area is crucial for coastal managers and planners. In this work, it is intended to use a process-based model, COAST2D, to predict the beach morphological changes of the said sandy beach as the study site. The model is applied to simulate the morphological changes over a 4-month period between October 2013 and February 2014 to the study site, during which a series of high-intensity storm events occurred along the west coasts of Europe. Model results are compared with the measurements from topobathymetric fieldwork campaigns. The model results show the effect of the groynes on the nearshore coastal processes under the combined wave and tide conditions. The predicted morphological changes agree well with the field measurements. The model results also show the shoreline sensibility at the study site to high-energy waves during storms, where the shoreline changed its slope to adapt to the more energetic conditions. The results clearly demonstrate the capability of COAST2D in modeling the complex hydrodynamics and morphodynamics at the study site in a seasonal scale. [ABSTRACT FROM AUTHOR]

In this study, the dynamic behavior of bed-load sediments under unsteady flow conditions is experimentally investigated and discussed. A series of experiments were conducted in a 6-m-long laboratory flume with naturally shaped hydrographs, and a video technique was applied to simultaneously monitor the bed-load motion and variations in the water level. Analysis of the experimental results demonstrated that the flow unsteadiness contributes to easier entrainment of the bed load, and the effect on the bed-load behavior decreases with an increase in the hydrograph duration. A further analysis revealed that the time lag between the occurrence of the peak discharge and that of the peak sediment transport rate is related to the base flow, and the bed-shear-stress peak triggers the bed-load transport peak. An unsteadiness parameter is proposed to account for the influence of the bed-load incipient. The regression analysis indicates a strong linear relationship between the bed-load transport and the unsteadiness parameters, which can be used for the estimation of the bed-load motion in the unsteady flow. [ABSTRACT FROM AUTHOR]

Longshore sediment transport (LST) prediction is still a challenging task in coastal engineering, due to complexity in affecting physical processes. There have been studies to develop tools to predict the LST rate, but there is still room to revisit methods and data previously collected to achieve a more robust formula. In this study, an extensive sediment data set including sand, gravel, and shingle was collected and used to evaluate the performance of existing LST volumetric rate prediction formulas and to derive two new formulas (based on dimensional and nondimensional approaches). Both formulas are based on commonly available parameters, that is, significant wave height at breaker point (Hsb), peak wave period (TP), wave angle at breaker point (αb), and sediment size (D50). The benefits of the formulas are: (1) minimum required input parameters; (2) easy to comprehend, physically justifiable functional forms, free from making any assumptions or using any other equation; and (3) a wide range of applicability. Eventually, the formula derived based on nondimensional parameters is suggested, owing to its homogeneity and accuracy using an independent field data set. [ABSTRACT FROM AUTHOR]

The mechanisms of fluid mud formation and its characteristics are far from clear in the deep-dredged waterway in Xiamen estuarine bay. Some experiments were conducted in the muddy estuarine bay of Xiamen when Super Typhoon Meranti, which was the strongest typhoon to have affected the area over the last 70 years, struck and after it passed. Contrary to expectation, results reveal that typhoon-induced waves are not the main hydrodynamic forcing that transport sediment. The influence of fluvial flooding and ebb tidal flow results in high concentrations (greater than 14 kg/m3) of suspended sediment in a layer near the bed, which may either deposit or be released directly into the waterway to form fluid mud. Further, new indicators are proposed, namely, river discharge and fluvial flood duration, to describe quantitatively the conditions under which fluid mud forms; it is in fact likely to form in the waterway when a discharge greater than 1,000 m3/s lasts for more than one day. The new indicators may be applied as reference by waterway administrators in their operations. [ABSTRACT FROM AUTHOR]

Geotechnical surface sediment properties and behavior contribute to the success of wetland conservation and remediation actions, but the correlation between geotechnical sediment characteristics and active morphodynamics in such areas is still poorly understood. Therefore, a field investigation of surficial sediments was conducted in wetland waterways in the Terrebonne Parish, the St. Bernard Parish, and the Rigolets in coastal Louisiana. In situ tests were conducted at 290 locations using a portable free-fall penetrometer, supported by seven sediment core samples and data available from the literature. The results allowed the authors to map changes in sediment strength and stratification and discuss them with regard to local site characteristics, such as sediment type, abundance of vegetation, and vicinity to human-made structures and engineering activities, and to the local geomorphology. Stiff sediments were observed at submerged banks and bars. Two lakes differed significantly in their sediment-strength profiles, indicating differences in sediment-deposition history. Meandering resulted in an asymmetry of the geotechnical cross-channel profile. In summary, geotechnical sediment characteristics seem to reflect the inferred local sediment dynamics. [ABSTRACT FROM AUTHOR]

This study presents results of the temporal development of propeller scour around a sloping bank. During the scouring process, the centerline scour profile along the propeller axis comprises a toe scour hole, a primary scour hole, or a combination of both. Their formation is dependent on the length of the toe clearances, which is defined as the longitudinal distance between the propeller face and toe of the slope. As a result, the overall maximum scour depth along the centerline profile may occur either in the primary or toe scour hole. The results show that the temporal development of the overall maximum scour depth for all the cases consistently exhibits an exponential form. An empirical method was obtained to estimate the maximum scour depth evolution throughout the scouring process. [ABSTRACT FROM AUTHOR]

Advancement of technology has improved the efficiency of marine trading activities through use of vessels equipped with twin propellers instead of a single propeller. The progression from a single propeller to twin propellers will certainly increase occurrences of scour unless protection measures are studied and designed accordingly. An experiment to model a ship's twin-propeller wash was conducted on a flat noncohesive soil bed for observation of scour. The asymptotic scour profile was defined in the following four stages: (1) initial, (2) developing, (3) merging, and (4) asymptotic. An equation is proposed to relate the densimetric Froude number, clearance ratio, and reference time scale to the predicted maximum scour depth and area. The predicted equations were found to be highly correlated with the observed parameters. [ABSTRACT FROM AUTHOR]

A fully coupled hydrodynamic and morphologic numerical model was utilized for the simulation of wave-plus-current scour beneath submarine pipelines. The model was based on incompressible Reynolds-averaged Navier-Stokes equations, coupled with k-ω turbulence closure, with additional bed and suspended load descriptions forming the basis for seabed morphology. The model was successfully validated against experimental measurements involving scour development and eventual equilibrium in pure-current flows over a range of Shields parameters characteristic of both clear-water and live-bed regimes. This validation complements previously demonstrated accuracy for the same model in simulating pipeline scour processes in pure-wave environments. The model was subsequently utilized to simulate combined wave-plus-current scour over a wide range of combined Keulegan--Carpenter numbers and relative current strengths. The resulting equilibrium scour depths and trends were shown to be in accordance with existing experimentally based expressions from the literature. The variety of scour profile types emerging under various flow conditions is detailed and reconciled with experimental observations. The resulting matrix of scour depth time series was systematically analyzed, resulting in a new generalized expression for the scour time scale in combined waveplus-current flow environments. This expression is fully consistent with existing experimentally based relations at both pure-current and purewave limits and is appropriate for engineering use. [ABSTRACT FROM AUTHOR]

Analysis of velocity and suspended sediment concentration data from field measurements at Pearl Beach in New South Wales, Australia, reveals the existence of onshore currents in the close vicinity of the rippled bed, whereas the velocity is offshore directed farther up in the water column. This might be caused by wave-induced streaming beneath irregular waves over ripples. To test this hypothesis, a simple one-dimensional vertical bottom boundary layer model capable of capturing streaming was applied, yielding a qualitatively fair agreement between the predicted and measured mean velocity and suspended sediment concentration profiles, although the predicted suspended sediment concentration was 1 order of magnitude smaller. Overall, these model results support the hypothesis of the mean near-bed onshore velocity caused by wave-induced streaming over ripples. [ABSTRACT FROM AUTHOR]

This work aims to shed some light on longshore sediment transport (LST) in the highly energetic northwest coast of Portugal. Data achieved through a sand-tracer experiment are compared with data obtained from the original and the new re-evaluated longshore sediment transport formulas (US ACE Waterways Experiment Station's Coastal Engineering and Research Center, Kamphuis, and Bayram bulk formulas) to assess their performance. The field experiment with dyed sand was held at Ofir Beach during one tidal cycle under medium wave-energy conditions. Local hydrodynamic conditions and beach topography were recorded. The tracer was driven southward in response to the local swell and wind- and wave-induced currents (Hsb = 0.75 m, Tp = 11:5 s, θb = 8 - 12°). The LST was estimated by using a linear sediment trans-port flux approach. The obtained value (2.3 x 10-3 m³ ⋅ s-1) approached the estimation provided by the original Bayram formula (2.5 x 10-3 m³ ⋅ s-1). The other formulas overestimated the transport, but the estimations resulting from the new re-evaluated formulas also yield approximate results. Therefore, the results of this work indicated that the Bayram formula may give satisfactory results for predicting the longshore sediment transport on Ofir Beach. [ABSTRACT FROM AUTHOR]

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours. [ABSTRACT FROM AUTHOR]

Beach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations. [ABSTRACT FROM AUTHOR]

The response of physical models of beach profiles to random breaking waves was studied to investigate size-selective sediment transport and cross-shore profile evolution. Three types of beach profiles with different sediment mixtures were considered and subjected to waves until profiles reached equilibrium. Size-selective sediment transport was evident in the experiments, with the mean sediment size varying up to 20% along the beach profiles. Consistent coarsening and fining of the surface sediment in the experiments revealed size-selective sediment transport governed by cross-shore variations in energy dissipation, affecting important beach profile features such as sandbar structures and offshore and foreshore slopes. The theoretical basis of the transport phenomenon was described by analyzing the relationship between the transport processes and essential wave and hydrodynamic parameters obtained using a new set of numerical models. The results showed that beach profile changes and associated sediment grain sorting are most sensitive to instantaneous total water velocity and local energy flux under propagating waves. [ABSTRACT FROM AUTHOR]

Interactions among waves, sand dunes, and vertical cylinders are investigated in a laboratory experiment. A cross-shore numerical model is expanded to include the drag force acting on cylinders. The hydrodynamic variables modified by the cylinders are used to predict bed load and suspended sand transport rates. The expanded model is compared with five previous tests. The drag coefficient is calibrated to obtain similar agreement for the dunes with and without the cylinders. Four tests were conducted to examine the placement density and toppling of the cylinders. The effectiveness of the cylinders in reducing dune erosion and overwash decreased significantly with the density decrease and cylinder toppling. The reduced effectiveness is reproduced by the expanded model with the calibrated drag coefficient. However, a simple toppling criterion needs to be adjusted for each test for the reproduction of the observed landward progression of cylinder toppling during the dune profile evolution. Field data will be required to improve the model for real woody plants. [ABSTRACT FROM AUTHOR]

Sediment spillage from hopper overflow constitutes a source for sediment plumes and can also impact the turbidity of aquatic environments. The overflowing mixture is often different from the mixture pumped into the hopper (the inflow), because the mixture undergoes compositional transformation as a result of different timescales in the segregation of the various sediment fractions. The heavier constituents in a mixture will have had time to settle, and overflowing sediments are therefore primarily composed of the finer and lighter constituents, whose concentrations potentially exceed those at the inflow. The hopper constitutes a complex system despite its geometrical regularity; the complexities are largely from the settling processes in concentrated polydisperse mixtures. These settling processes can, however, be captured by employing available settling formulas applicable for multifractional sediment mixtures (i.e., polydispersions). Strictly speaking, these formulas have been validated for homogeneous and unenergetic mixtures only, but the hopper system fulfills these criteria reasonably well. A proper description of the compositional transformation during filling and subsequent overflow stages can be captured using a sediment budget approach, i.e., by using continuity equations for water and sediment phases. In this study, the compositional transformation and the bed height inside the hopper are obtained by solving these equations, considering monodisperse, bidisperse, and polydisperse mixtures, the former analytically. Although assumptions tied to the mathematical model are fulfilled best for hoppers rigged with a multiple-inflow system, the model accurately predicts measured concentrations in the final stage of overflow for single-inflow systems. The model can be used as a preprocessing tool for engineering plume models, providing source specifications for overflow spill and for the subsequent dumping of hopper loads. [ABSTRACT FROM AUTHOR]

This study presents an application of a two-dimensional beach evolution model to a shoreline change problem at the Kızılırmak River mouth, which has been facing severe coastal erosion problems for more than 20 years. The shoreline changes at the Kızılırmak River mouth have been thus far investigated by satellite images, physical model tests, and one-dimensional numerical models. The current study uses a two-dimensional depth-averaged numerical beach evolution model, developed based on existing methodologies. This model is mainly composed of four main submodels: a phase-averaged spectral wave transformation model, a two-dimensional depth-averaged numerical wave-induced circulation model, a sediment transport model, and a bottom evolution model. To validate and verify the numerical model, it is applied to several cases of laboratory experiments. Later, the model is applied to a shoreline change problem at the groin field to the east of the Kızılırmak River mouth at the Bafra alluvial plain. The results of the numerical model agree with the existing laboratory and field measurements. [ABSTRACT FROM AUTHOR]

Recent turbulence-resolving simulations of fine sediment transport in the oscillatory bottom boundary layer (OBBL) revealed the existence of a diverse range of flow regimes over muddy seabeds. Transitions between these flow regimes are caused by different degrees of sediment-induced stable density stratification in the OBBL. These transitions have critical implications for the role of wave resuspension in the delivery of fine sediment and hydrodynamic dissipation over muddy seabeds. This study further investigates the effect of Newtonian rheology, parameterized as a concentration-dependent effective viscosity, on turbulence modulation and the transition from turbulent to laminar states. Assuming small particle Stokes number, the equilibrium approximation is adopted to simplify the Eulerian two-phase flow governing equations. The resulting simplified equations are solved with a high-accuracy hybrid scheme in an idealized OBBL. A sixth-order centered compact finite difference is implemented in the vertical direction to solve the governing equations with a flow-dependent viscosity while the pseudospectral method is retained for two horizontal directions. At Stokes Reynolds number , simulations reveal that when rheology is incorporated, the enhanced effective viscosity can further attenuate the flow turbulence in addition to the well-known sediment-induced stable density stratification. Through the enhanced viscosity, the velocity gradient very near the bed is significantly reduced, which leads to much weaker turbulent production and the onset of laminarization. Although the sediment-induced stable density stratification is known to cause laminarization of bottom boundary layer flows, our preliminary finding that the enhanced viscosity via rheological stresses encourages the flow laminarization may be useful in explaining the field-observed large wave dissipation rate over muddy seabeds during the waning stage of a storm. [ABSTRACT FROM AUTHOR]

Reliable simulation of onshore-offshore sandbar migration under various wave and current conditions has remained a challenging task over the last three decades because wave-undertow interaction in the surf zone has been neglected in the existing numerical models. This paper presents the development of an improved sandbar migration model using a phase- and depth-resolving modeling approach. This new model includes interactions between waves and undertow and an empirical time-dependent turbulent eddy viscosity formulation that accounts for the phase dependency of turbulence on flow velocity and acceleration. The authors demonstrate through extensive model-data comparisons that these enhancements resulted in significant improvements in the predictive capability of the cross-shore sandbar migration beneath moderate and energetic waves. The comparison showed wave-undertow interaction playing a crucial role in cross-shore sediment transport. Waves increased the undertow-induced suspended-load flux during offshore sandbar migration, and a weak undertow suppressed the wave-induced onshore bed-load transport during onshore sandbar migration. The proposed empirical time-dependent turbulent eddy viscosity significantly improved the prediction of onshore-directed bed-load transport during onshore sandbar migration. [ABSTRACT FROM AUTHOR]

Sheet flow sediment concentration profiles were measured in natural conditions for the first time as part of a comprehensive field study on swash-zone hydrodynamics and sediment transport. Three conductivity concentration profilers (CCPs) measured the sediment concentration profile in the sheet flow layer with a 1-mm resolution in the swash zone of a dissipative beach. This paper focuses on sheet flow during quasi-steady backwash events generated by infragravity motion when the effects of phase lags, surface-generated turbulence, and accelerations are small. The sheet flow sediment concentration profile has a linear shape in the lower section of the profile and a power-law shape in the upper section, with the transition occurring at sediment volume fractions of 0.20-0.30. The shape of the concentration profile is self-similar for measured sheet flow layer thicknesses ranging from 6 to 18 mm. Because of the self-similarity, a single concentration profile curve can be used to describe the normalized profile for the entire range of sheet thicknesses, leading to improved estimates of the sheet flow layer thickness in a simple analytical model. The sheet flow layer thickness and sheet load, the sediment mass mobilized in the sheet flow layer, are well correlated with the hydrodynamic forcing represented by the mobility number ( for sheet thickness and for sheet load). [ABSTRACT FROM AUTHOR]

A comprehensive study of swash-zone hydrodynamics and sediment transport was conducted on a macrotidal beach in Perranporth, United Kingdom. The unique study is the first to simultaneously measure suspended sediment and sheet flow sediment concentrations, water depth, near-bed velocity profiles, and high-resolution swash surface and bed-level changes on a natural beach. Data collected during the study are used to quantify the vertical profile of cross-shore and alongshore velocities and the importance of sheet flow sediment processes in the swash zone. The swash-zone boundary layer for cross-shore velocities is observed to generally occur over at least the lower 0.06 m of the water column. Alongshore velocities are often the same order of magnitude as the cross-shore velocities and are dominant near cross-shore flow reversal. Flows are often logarithmic in profile, but the instantaneous nature of the measurements renders application of the logarithmic model difficult. When valid, the logarithmic model enabled cross-shore shear stress estimates of up to with maximum alongshore shear stress estimates of , further highlighting the potential importance of alongshore flows. Friction coefficient estimates, assuming a quadratic drag law, showed no statistical difference between onshore- and offshore-directed motion, with typical values of (). Sheet flow concentrations exceeded the maximum measured suspended sediment concentrations of approximately . Sediment loads in the sheet layer are up to 10 times larger than the sediment loads in the lower suspension layer. Simplified sheet flow sediment transport estimates are 3.6 times larger on average than those in the suspension layer. The latter two findings indicate the importance of sheet flow processes in the swash zone that are generally ignored. [ABSTRACT FROM AUTHOR]

Despite its relatively small amplitude, the nodal tide can play a relevant role in several environmental processes, spanning from ecology to morphodynamics; in particular, field studies and numerical investigations indicate the nodal tide as the dominant factor in long-term and large-scale net sediment transport in some estuaries. Nevertheless, while some important results have been obtained about its morphological effect on estuary channels, the response of tidal flats and salt marshes is still to be investigated. In the present work, a two-dimensional (2D), vertically averaged, long-term morphodynamic model based on the concepts of intertidal dispersion and transport concentration has been applied to the case of a schematic lagoon forced by a nodally-modulated tidal range. The effect of such a periodic oscillation has been studied in terms of sediment fluxes, suspended sediment concentration, and morphology. The results of simulations, carried out starting from different equilibrium conditions in which a nodal perturbation was introduced in the tidal signal, were postprocessed via Fourier analysis to detect the characteristics of the nodal perturbation within the domain and to draw some considerations about the spatial differentiation, in terms of both amplitude and phase, of the morphodynamic response throughout the domain. Although taking into account the nodal contribution has little influence in a long-term (several decades to centuries) analysis, as shown in the current study, such a small oscillation in tidal range (approximately 4%) can locally result in bathymetric oscillations of relevant relative amplitude. [ABSTRACT FROM AUTHOR]

A laboratory experiment consisting of five tests was conducted to examine the effects of woody plants on erosion and overwash of high and low dunes. Scarping occurred on the foreslope for three high dune tests and no scarping occurred for two low dune tests. A narrow vegetation zone on a steep backslope of a high dune did not reduce wave overtopping and overwash in comparison with the corresponding bare dune. A wide vegetation covering the high dune reduced foreslope scarping, prevented wave overtopping initially, and reduced sand overwash after the initiation of wave overtopping. A wide vegetation zone covering an entire low dune reduced dune erosion by retarding wave uprush and reducing wave overtopping and overwash. [ABSTRACT FROM AUTHOR]

Laboratory experiments have been carried out to investigate the scour around single piles and twin-pile groups subject to oscillatory flows. The Keulegan-Carpenter number, which is proportional to the ratio between the maximum excursion of water particles and the pile diameter, ranges from 3 to 110 in the experiments. To verify the experimental setup, the scour around a tall monopile was first studied, and the results were found to agree well with the previous research. The effect of the pile height and the influence of the twin-pile layout on the scour have been subsequently investigated. It was found that the scour became independent of the pile height once the pile was four times higher than the diameter. An empirical expression was constructed to describe the exponential variation of the scour depth with the pile height. The individual piles in a twin-pile group were found to behave independently when the separation was three times greater than the pile diameter. The relationships between the scour depths around the twin-pile groups and the group configuration were established graphically. [ABSTRACT FROM AUTHOR]

Long-term changes in the sand balance of a river-estuary system can strongly affect navigation and ecosystems. Here, we examine two sand budget components in the lower Columbia tidal river, fluvial supply and human removal. Rating curves were used to estimate daily sand input between 1900 and 2010. Publications, interviews, and data analyses were used to evaluate sand removal by dredging and mining. Comparison between sand input and removal indicates that a sand deficit has existed for of the last 85 years. Since 1962, the deficit has averaged . Although historic sand transport to the ocean cannot be estimated, it is now small. Several factors contribute to the sand deficit: dredging, sand mining, flow regulation by dams, and climate change. The sand deficit documented here has likely contributed to the lower water levels in the tidal river observed in recent decades, which decreases habitat availability during high flows and channel depths during low-flow periods. [ABSTRACT FROM AUTHOR]

Several empirical formulas have been proposed to predict the near-bed conditions for sediment transport in steady channel flows; however, few are extendable to oscillatory flows. This study presents a method for evaluation of the reference concentration and the entrainment rate near the undisturbed bed under oscillatory sheet-flow conditions. A new expression of the erosion depth in terms of the Shields parameter is adopted in order to describe the conservation of sediment mass more accurately. Both the exponential law and the power law are used to represent the instantaneous sediment concentration profile. The newly obtained formulas explicitly express the reference concentration and the entrainment rate in terms of the near-bed flow conditions and the sediment properties. The maximum value of the reference concentration obtained has a similar trend as given by the classical formulas. However, the variation of the reference concentration within a period of the oscillatory flow shows better agreement with the measured data than the classical formulas. In addition, the newly obtained formulas are found to have an evident advantage over the classical ones because they can reasonably interpret the sediment concentration as the flow reverses. The new formulas on the total vertical flux of sediment are also shown to reasonably agree with the measured data. It is demonstrated that the entrainment functions obtained under steady flow conditions, particularly those over a starved bed, are not directly applicable to oscillatory sheet-flow occasions. [ABSTRACT FROM AUTHOR]

Our capability for predicting beach and dune erosion has improved in the last three decades, but the recovery of an eroded beach above the mean sea level (MSL) cannot be predicted at present. The cycle of beach erosion and recovery will need to be predicted for the long-term maintenance of a sand beach with a dune for coastal flooding reduction. The cross-shore numerical model (CSHORE) is extended and evaluated using natural beach erosion and recovery data along 16 cross-shore lines spanning 5 km alongshore for the duration of 272 days. The CSHORE predicts beach and dune erosion fairly well, as has been shown in previous comparisons. The bed-load formula used in the CSHORE is adjusted to predict the accreted beach profile with a berm. The computed beach profile evolutions are shown to be affected little by the alongshore gradient of the longshore sediment transport rate along the straight beach. The extended CSHORE predicts both erosion and accretion above MSL within a factor of about 2. [ABSTRACT FROM AUTHOR]

Longshore sediment transport (LST) is a major driver of coastal evolution. However, despite the recognition that it presents an unsteady behavior at the seasonal scale, the variability at longer term scales (interannual and decadal) is still far from being properly acknowledged. The present work contributes to the understanding of the seasonal to decadal variability of the LST, benefiting from recent developments in wave hindcast modeling. This work was developed for the northwest coast of Portugal, which is fully exposed to the highly energetic wave regime generated in the Northeast Atlantic Ocean that induces unusually large LST rates. Hindcast offshore waves, between 1953 and 2010, were used as offshore forcing to deduce LST estimates. The mean annual LST, between 1953 and 2010, shows an irregular and noncyclic pattern. Computed mean annual LST, for this coastal stretch, is around 1 million cubic meters directed to the south, with yearly averages ranging from 108,000 to 2.24 million m3 year−1 always directed to the south. The maximum observed annual LST magnitude exceeds the mean magnitude by more than 100%. The variability in LST magnitude was found to be mainly related to the LST magnitudes of autumn/winter months in response to the wave regime seasonality. Results show that to estimate the long-term LST within an error of about 20%, a period of about 10 years of data/observations is required. Interannual variability in the magnitude of the LST was found to be correlated () with the annual North Atlantic Oscillation (NAO) index. In the years where the NAO index was higher, the mean annual LST was generally greater than the long-term average, while negative NAO index corresponds to lower than average LST estimates. [ABSTRACT FROM AUTHOR]

Ridge-runnel features can comprise large volumes of sand, and their migration can have a significant influence on the coastal sediment budget and beach recovery after a storm. Numerical modeling of ridge-runnel migration is challenging partly because of the strong interactions between the hydrodynamics and morphology and partly because of limited available field and laboratory measurements. This study investigated the effect of water ponding and runnel drainage on onshore ridge migration in an experiment in a sand flume where detailed free-surface and velocity measurements were taken in the ponded water zone of the runnel and in the intermittently wet and dry zone on the ridge crest. The test scenario with a drained runnel showed a ridge migration speed five times larger than the scenario in which water and sediment could only exit the runnel as offshore return flow over the ridge. The time-averaged numerical model CSHORE was modified to include the ponded water effect in the sediment transport formulations. Results show the capabilities and shortcomings of CSHORE in reproducing the hydrodynamics, morphological evolution, and sediment transport rates measured during the experiment. [ABSTRACT FROM AUTHOR]

Water oscillations observed in a 10-m-diameter, 2-m-deep hole excavated on the foreshore just above the low-tide line on an ocean beach were consistent with theory. When swashes first filled the initially circular hole on the rising tide, the dominant mode observed in the cross-shore velocity was consistent with a zero-order Bessel function solution (sloshing back and forth). As the tide rose and swash transported sediment, the hole's diameter decreased, the water depth inside the hole remained approximately constant, and the frequency of the sloshing mode increased according to theory. About 1 h after the swashes first reached the hole it had evolved from a closed circle to a semicircle, open to the ocean. When the hole was nearly semicircular, the observed cross-shore velocity had two spectral peaks, one associated with the sloshing of a closed circle, the other associated with a quarter-wavelength mode in an open semicircle, both consistent with theory. As the hole evolved further toward a fully semicircular shape, the circular sloshing mode decreased, while the quarter-wavelength mode became dominant. [ABSTRACT FROM AUTHOR]

Results from a numerical modeling study are presented to investigate the tidal elevations, tidal current velocity, bed deformation, and suspended sediment concentration in the Qiantang Estuary, China. The Qiantang Estuary is well-known for its macrotide, which generates a hydrodynamically complex environment. This presents challenges for numerical modelers to accurately simulate the flow field and sediment transport in the region. This paper presents a mathematical model using finite volume method with unstructured mesh to simulate the tide-induced water elevation, current velocity, bed deformation, and suspended sediment transport in the Qiantang Estuary. The parameters in the model were determined using the long-term observed field data of the Qiantang Estuary. The simulated tidal elevations and current velocities agree well with the field observations. The numerical prediction of the bed deformation in 5 months is reasonably compared with the field measurements carried out in the same period. However, relatively large deviations exist between the simulated and observed suspended sediment concentrations, which are discussed in this paper. [ABSTRACT FROM AUTHOR]