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Beaches are important coastal features that provide vital ecosystem services; however, these systems are threatened by coastal erosion, sea-level rise, and coastal squeeze. Beach nourishments are a commonly applied coastal protection measure to mitigate erosion and flood risks while maintaining or enhancing recreational values. Nourishments vary in scale from mega-nourishments to small-scale nourishments, where the latter has typically been less studied due to the limited resources for monitoring. Meanwhile, with rising sea levels, the implementation of small-scale nourishments is expected to increase, and there is a need for more knowledge about the morphological evolution and technical lifetime of these interventions. In this study, the morphological responses of small-scale beach nourishment (total volume 20,000 m3 which amounts to 30 m3 added per m alongshore) are observed and quantified over various timescales, considering the initial adjustment, long-term development, and event-driven response. The investigated nourishment is implemented in a partly sheltered coastal embayment in the semi-enclosed Baltic Sea, which has a complex interaction between waves and water levels. Furthermore, the beach is surrounded by hard structures, a rock revetment at the back, and a harbor mole and a groin, influencing the longshore and cross-shore sediment transport. The results show that substantial reduction in subaerial volume can be attributed to specific events. In addition, we observed considerable spatial variation in the sediment re-distribution induced by hard structures and variability in the nearshore bathymetry. The lifetime of the beach nourishment is just over two years. The nourished material remains in the system at the end of the lifetime but is not available for beach recovery. Still, the added subaerial volume has eroded at the midsection, and the protective beach width has been reduced, leaving the rock revetment exposed with reduced protection for the hinterland. The energy conditions at the site are highly episodic, which impacts morphological evolution, and observations indicate that the development is event-driven. • Beach morphodynamics in a low-energy coastal embayment • Episodic wave activity and water level variations are influenced by basin effects. • Morphological response of a small-scale beach nourishment at different timescales • Beach nourishment performance during an extreme storm surge [ABSTRACT FROM AUTHOR]

An approach involving data on wave-induced sediment transport estimates is essential for managing coastal environments. Numerical models are powerful tools to understand and investigate many processes responsible for longshore sediment transport (LST) in a systematic way, since direct measurement of LST is a difficult task. This paper presents estimates of longshore sediment transport through numerical modeling of wave-induced sediment dispersion patterns in the Formosa Bay, State of Rio de Janeiro - Southeast Brazil. The analysis was conducted using the computational package Coastal Modeling System/SMC-Brazil and mathematical formulations proposed by Cerc (1984). The results suggest average residual solid discharge (Qsr avg) in the order of 131,442.745 m3/yr in northern sector, −151,908.32 m3/yr in central sector, and 71,987.69 m3/yr in southern sector of investigated area. In addition, it is important to highlight that minor variations in the wave incidence angle may cause changes in the longshore sediment drift, promoting the convergence and divergence zones throughout the investigated area. The results presented contribute to the advancement of knowledge on the topic addressed here and will be useful in future engineering projects related to beach nourishment and the management of coastal areas subject to erosion processes. • Data are presented on simulations of wave-induced longshore sediment transport rates in Baia Formosa Bay, southeastern Brazil. • The Coastal Modeling System SMC/Brazil were used. • Results suggest different solid outflow rates for each sector of investigated area. • The model may provide a basis for planning actions and environmental management in coastal zones. [ABSTRACT FROM AUTHOR]

During August 2018 – November 2019, the transport pathways of dredge material from a specially constructed nearshore feeder berm were investigated as part of a collaborative study by the City of South Padre Island, U.S. Army Corps of Engineers–Galveston District, U.S. Geological Survey, Partrac GeoMarine Inc., and Texas A&M University, into the efficacy of beneficial use dredge material (BUDM) as a method of replenishing the beach profile and shoreface at South Padre Island, Texas with sediment. Dual-signature (fluorescent and ferrimagnetic) tracer particles, designed to be hydraulically equivalent to the dredge material, were placed on the berm, and a sampling program was initiated to monitor the spatiotemporal movement of tracer particles under the influence of the prevailing hydrodynamic regime. Wave and current data were collected and were used together with available metocean data to identify the forcing mechanisms of sediment transport; improved understanding garnered from the consideration of multiple datasets can be used to inform future coastal management decisions. Tracer analysis results indicated low magnitude, shoreward transport of dredge material from the berm and along shore transport in both northerly and southerly directions. Small amounts of tracer detected in beach face samples demonstrated connectivity between the constructed feeder berm and the shoreface. However, the generally low tracer concentration within beach face samples indicated low rates of sediment transport for berm sediments, and a low magnitude sediment transport pathway from the berm directly to the beach face, with possible storage of sediment in the nearshore bar system. Given that the berm was at or beyond the closure depth and considering the relatively weak prevailing near bottom hydrodynamic conditions, the potential for sediment to be mobilized and transported during the study period was generally low. Periods of higher energy waves, driven by north-northwest winds, were identified as a key driver of sediment transport but due to the infrequent nature of these events the sediment transport regime across the area of interest was temporally limited. Longshore movement of sediment was both north and south, mainly dependent on prevailing wind directions and resulting longshore currents. We discuss implications for coastal zone management and the use of feeder berms as an artificial beach nourishment mechanism to replenish sediments lost by coastal erosional processes. The insight into nearshore emplacement of material can be used by local governments and coastal managers to optimize the efficacy of berm emplacement and implement such schemes as a cost-effective nourishment option, or when onshore placement of material is not feasible. • Hydrodynamic and tracer measurements were effective monitors of sediment transport. • Hydrodynamic monitoring indicated relatively weak sediment transport conditions. • Tracer sampling confirmed that transport to replenish the beach was low magnitude. • Consider sediment transport regime before selection of BUDM placement area. • Licensed BUDM placement areas may not be optimal for beach nourishment. [ABSTRACT FROM AUTHOR]

Depth of Closure (DoC) calculation has been analysed for engineers and researchers during decades due to its relevant importance on marine works, such as beach nourishments or littoral defense projects. Several methods can be found in the literature related to the evaluation of DoC. However, they just focus on the bottom elevation change, leaving aside the cross-shore sediment transport issue. This work deals with all requests of the DoC definition and presents a new method based on the comparison of repetitive beach profiles. The main contribution of this research is the methodology presented to quantify the cross-shore sediment transport by the calculation of the Net Cross-shore Sediment Transport Parameter (NCSTP C). Its application to a complex area of the East Spanish coast concludes that NCSTP C values less than or equal to 10% can be considered as no significant. The differences between several criteria based on the change of the bottom elevation are also studied in order to evaluate if they are relevant for engineering works. The new methodology developed is a great advance in the knowledge of this imaginary boundary (DoC), since it allows to discriminate between different possible DoC values when applying any method based on profile surveys comparison. • New method to obtain the Depth of closure from profile surveys. • Quantification of the net cross-shore sediment transport. • 762 periods of time analysed over 22 years (1992–2014). • Five profile survey criteria have been compared. • The new method permits the selection of the DoC among several possible values. [ABSTRACT FROM AUTHOR]

In coastal engineering studies, coastal protection procedures can be provided by hard and soft methods. Soft methods applied using the right techniques and methods are not only long-lasting but also adapt to the natural structure of the coast. This study aims to present monitoring the development of a small-scale artificial nourished beach between the groins for 15 months and analyze its performance. For this purpose, field studies were carried out with land and sea observations taken once before nourishment and at 8 different times after nourishment. The seabed and profile variations observed at different sections were analyzed after processing field data. For determining the characteristics of the natural beach and borrow area before nourishment a sieve analysis was done for sediment samples taken from the shoreline, beach face, and 1-m depth on the nourished area. Sediment transportation of nourished material was observed by monitoring the amount of material remaining in 3 sub-regions (a nearshore region between the groins - A, a region representing the seaward end of the groins - B, and a region offshore of the groins - C) in the nourished region over time. The relationship between this behavior and waves was examined by considering the wave roses and time series of wave parameters produced as a result of wave simulations performed with the third-generation wave hindcast model SWAN. Lastly, as well as the variation of the mean layer thickness, the retreat of coastline, and mean beach width on the nourished area by the time were extracted for 8 different surveys. The results show that artificial beach nourishment materials were eroded in less than five months and the beach width returned to its initial position. The nourished material transported out groin-protected area moved eastward due to north-west dominated waves and the eastward longshore transport. [Display omitted] • Field studies on project area are carried out before and after the nourishment. • Nourished area is monitored by producing bathymetric maps periodically, analyzing wave data and taking sediment samples. • The path of sediment transport on nourished area are monitored and analyzed with wind data. • Retreat of coastline, loses of nourished volume and mean layer thickness of project area are determined and visualized. [ABSTRACT FROM AUTHOR]

Beaches provide natural protection for coast and ecosystems. Storm surges and waves make significant impacts on the topographic changes of beaches, subsequently causing crises of coastal erosion and management. Beach protection and nourishment projects is growing considerably along the world. Five profiles of Dongsha Beach located in the southeast of Zhujiajian Island, eastern China, were measured and used to analyze the cross-shore profile changes, longshore sediment transport, beach rotation and equilibrium shoreline and profile. Delft3D Flow/Wave and XBeach models were established and calibrated to investigate the morphological responses of Dongsha Beach. It was found that: (1) the longshore sediment transport dominated the changes of erosion and accretion sediment volume compared to the cross-shore sediment transport; (2) the shoreline of Dongsha Beach was not in equilibrium condition compared to the profile equilibrium conditions; (3) the longshore sediment transportation was the main reason of the erosion because the shoreline changes caused by longshore sediment transport during the storm condition could not be restored during calm sea periods; (4) the correlation between wave induced currents and Hs2·T was good and the dominating wave direction was 90°. Finally, sediment nourishment projects named N1∼N3 were assumed and simulated to identify the optimum for the dynamic balance of Dongsha beach. Sediment sources with D 50 of 0.5 mm should be chosen in sediment nourishment projects, and the nourished area should be selected in N1 or N3 of the beach. The numerical model established in this study could be a useful tool to predict the future erosion and accretion of beaches. This study can provide a useful understanding and reference especially for the embayed beach nourishment, making the beach management decisions more scientific and reasonable. [ABSTRACT FROM AUTHOR]

Four southern California beaches were nourished with offshore sand placed as subaerial pads several meters thick, ∼ 50 m wide, and spanning between 500 and 1500 m alongshore. Three nourishments constructed with coarser than native sand, placed in 2012 at Imperial, Cardiff and Solana Beaches, elevated subaerial sand volumes for several years even when exposed to the energetic winter waves of the 2015-16 El Niño, followed by a stormy 2016-17 winter. As these relatively resilient pads were overwashed, landward tilted subaerial profiles (accretionary crowns) formed at the eroding front face of the originally flat-topped pads and pooling occurred in the backbeach. At Imperial Beach, nourishment sand helped prevent waves from directly impacting riprap fronting houses, while groundwater flooding behind the pad was observed at a location where the pad was elevated ∼ 1.6 m above the street. As the nourishments retreated, alongshore oriented spits grew downdrift from the eroding face. The alongshore displacement of the subaerial center of mass of the 2012 nourishments is positively correlated with the seasonally varying S x y (the alongshore radiation stress component). After four years, the net southward drift of the Imperial Beach nourishment contributed to the winter 2016 closure of the Tijuana River mouth and the associated hyper-polluted and anoxic estuary conditions. Nourishment impacts on sand levels on rocky reefs were not unambiguously detectable in the background of natural variability. Over several years, gains or losses in the total sand volume (integrated from the back beach to 8 m depth, over the few km alongshore survey spans) are sometimes comparable to nourishment volumes, suggesting relatively large interannual sediment fluxes across the control volume boundaries. The clearest trend in total volume is at Torrey Pines; during 16 years since the 2001 nourishment, about 300,000 m 3 of sand has been lost. If the trend continues, the thinning veneer of sand will be removed more often from the subaerial winter beach, exposing rocks and cobbles. [ABSTRACT FROM AUTHOR]

Many deltas across the globe are retreating, and nearby beaches are undergoing strong erosion as a result. Among soft and prompt solutions, nourishments are the most heavily used. This paper presents an integrated methodology to forecast the efficiency of nourishment strategies by means of wave climate simulations, wave propagations with downscaling techniques, computation of longshore sediment transport rates and application of the one-line model. It was applied to an eroding deltaic beach (Guadalfeo, southern Spain), where different scenarios as a function of the nourished coastline morphology, input volume and grain size were tested. For that, the evolution of six scenarios of coastline geometry over a two-year period (lifetime of nourishment projects at the study site) was modelled and the uncertainty of the predictions was also quantified through Monte Carlo techniques. For the most efficient coastline shape in terms of gained dry beach area, eight sub-scenarios with different nourished volumes were defined and modelled. The results indicate that an input volume around 460,000 m 3 is the best strategy since nourished morphologies with higher volumes are more exposed to the prevailing storm directions, inducing less efficient responses. After setting the optimum coastline morphology and input sediment volume, eleven different nourished grain sizes were modelled; the most efficient coastline responses were obtained for sediment sizes greater than 0.01 m. The availability of these sizes in the sediment accumulated upstream of a dam in the Guadalfeo River basin allows for the conclusion that this alternative would not only mitigate coastal erosion problems but also sedimentation issues in the reservoir. The methodology proposed in this work is extensible to other coastal areas across the world and can be helpful to support the decision-making process of artificial nourishment projects and other environmental management strategies. [ABSTRACT FROM AUTHOR]

Decision-making in a coastal socio-ecological system involves managing a site-specific complexity arising not only from the interaction between hydrodynamic and morphological conditions, but also from the interactions between human structures and ecological systems, as well as the conflicting needs and interests of local actors. In addition, the projections of climate change impacts on coastal systems have a degree of uncertainty, which increases the general unpredictability of coastal dynamic behaviour, and adds a layer of complexity to the decision-making process. Scientific knowledge can help reduce some of the inherent uncertainties, and is essential when it comes to making sound decisions on the choice of appropriate coastal defence measures (CDMs) that are adapted to specific coastal environments and improve the resilience of coastal communities. This paper is based on a meta-analysis of 355 CDMs case studies drawn from 301 publications. From these published case studies, the objectives were to analyze the geographical and physical contexts in which CDMs monitoring was carried out and, based on the findings, to recommend areas of improvement necessary to help make sound decisions in any type of coastal environment. The meta-analysis showed that study sites are not evenly distributed around the world. Most originate from Europe (n = 106), the USA (n = 151) and Australia (n = 30), while few studies have been carried out in Africa and Asia where dense population resides in high-risk zones. Also noticeable is the absence of sites in high latitude climates where ice plays a major role in the erosion process. Five basic variables (coastal type, sediment type, wave characteristics, tidal range, and currents or sediment transport characteristics) are used in publications to characterize study sites according to their physical components. However, only 13 of the 355 sites included a complete characterization using the 5 variables, of which coastal and sediment types are the most frequently identified (77.2% and 72.7% respectively). In general, CDMs are studied in the context of unconsolidated low shore (59.4%) and in sandy environments (74.6%). Information on tidal range, wave climate, and currents, or sediment transport characteristics, is much scarcer. Since 1990, 3 of the 10 CDMs identified in the studies have received more attention than the others; these are beach nourishments, seawalls and breakwaters, with respective cumulative study sites of 164, 67 and 50. The geomorphological effects of CDMs are the most studied (55.1%), followed by ecological (31.2%), hydrodynamic (9.1%), and social (4.6%). Overall, this meta-analysis helped identify knowledge gaps regarding geographical and physical contexts in which CDMs monitoring was held. It also gave an indication of the kind of improvement necessary for global-scale adaptation planning, and for a better decision-making process to reduce coastal risks in the most vulnerable coastal communities. Finally, the analysis shows that 4.4% of the studies on defence measures include monitoring of their effects on the coastal zone. A conceptual scheme is proposed for the evaluation of adaptation solutions based on the global monitoring of coastal zones to measure coastal change trajectories in the context of climate change. [ABSTRACT FROM AUTHOR]

Beach accretion is the natural mechanism that allows dry beaches to recover. Human response to climate change produces hardening of the coasts and the incident marine climate, which increases beach erosion produced during winter and prevents a full recovery during summer. Beach nourishments are performed all around the world to fight coastal erosion with a nature-friendly philosophy. Softer techniques as beach scraping are also widely applied. A kind of beach scraping is proposed here as an innovative nature-assisted beach enhancement technique, that aims to accelerate naturally produced sand accretion on the beach profile. It consists of mechanically ploughing the intertidal area of a beach to create ridges and furrows. Prototype-scale laboratory experiments were performed to analyse its effectiveness under controlled conditions. Seven 1 h tests having different water levels and the same initial bottom geometry and sea state conditions (H s = 0.3 m, T p = 7 s) were performed. Sea state, sand, and initial slope characteristics assured accretive conditions. Ploughed and flatbed initial slope geometries were simultaneously tested into two sub-channels of the wave flume. The results indicate that the bottom roughness is 3.57 times larger for the ploughed geometry. Consequently, wave energy dissipation is larger for the ploughed geometry, and therefore, the significant wave height at the shoreward end of the study area is 11% smaller for the ploughed geometry. This smaller wave height under the ploughed morphology leads to more accretive conditions, as observed from the measured onshore sediment transport, which is 2.9 times larger than the natural transport, and the larger accreted sediment volume in all seven test cases. These results demonstrate the effectiveness of ploughing to enhance natural beach accretion under highly probable accretion conditions. Further research is required to define the thresholds of marine conditions in which the potential of beach ploughing can be exploded. • Working with nature. • Ploughing the intertidal area of a beach enhances natural accretion. • Real scale laboratory experiments measuring sediment transport. • Mechanically ploughing increases bed roughness. • Extra wave energy dissipation is produced by ploughing. [ABSTRACT FROM AUTHOR]

A moderate-size (344,000 m3) subaerial beach nourishment was placed in 2012 in front of flood-prone homes at Imperial Beach, California. The subaerially persistent coarser-than-native nourishment sand spread alongshore over a ∼ 4 km span. By winter 2018/19 subaerial sand volumes in front of the flood-prone homes were eroded to near pre-nourishment levels, while sand accumulated near a river mouth ∼ 1.5 km to the south. The observed alongshore patterns of post-nourishment erosion/accretion are consistent with the modeled convergence/divergence of alongshore currents driven by wave radiation stress S x y gradients associated with refraction over a relic cobble ebb shoal. The same alongshore patterns of subaerial erosion/accretion were observed in the 6 years preceding the nourishment, indicating a wave-driven erosion hotspot in front of the flood-prone homes, and an accretion hotspot near the region of river mouth migration. Over the 13-yr observation period, the river mouth migrated 600 m southward and closed in 2016, possibly owing to nourishment sand and El Niño intensified local drift convergence. The computationally efficient drift (radiation stress) gradient model uses simplified wave and surfzone dynamics, assumes proportionality between alongshore sediment transport and the radiation stress component S x y , but nevertheless captures the overall patterns of alongshore nourishment evolution and provides a framework to inform sand management. • The subaerial influence of relatively coarse beach nourishment sand spans 4 km of coast 6 years after placement. • Accretion and erosion hotspots are persistent, 6 years before and after nourishment. • A simple drift divergence model that captures refraction over an ebb shoal describes the alongshore variable sand volume trends. [ABSTRACT FROM AUTHOR]

A combined field and laboratory investigation was conducted to assess five options for creation of a recreational beach on a steep, armored shoreline on the eastern Black Sea coast. All designs incorporated a beach nourishment project placed between two existing, shore-normal, rubble-mound groins. Alternatives included the placement of a nearshore berm, longshore extensions added to the existing groins, and shore-parallel breakwaters. Several alternatives are reviewed for quantifying the performance of each design, including assessment of the change in shoreline position and project volume retained between the groins. Dimensionless benefits and benefit-cost ratios are quantified, and recommendations made on how to select the best outcome from a benefit-to-cost standpoint when options including hard structures are incorporated into a beach nourishment project design. [ABSTRACT FROM AUTHOR]

Shoreline erosion is often exacerbated by reduction of sediment inputs because of interference with sediment transport by human structures. We evaluate use of sediment dredged from a navigation channel to establish a feeder beach adjacent to a bulkhead as a solution for addressing erosion of landforms and habitats on sandy estuarine shores. The objectives are to determine how beach volume, position and shape within and downdrift of the fill area change and whether the volumes supplied by dredging match sediment losses caused by human actions. The fill was placed along a 75 m length of shoreline adjacent to a marina in Great South Bay at Fire Island, New York, USA. Changes in beach shape and volume were determined from topographic surveys conducted before and after fill and at half year intervals for 18 months. The quantity of fill was 1747 m 3 . Maximum shoreline advance due to fill emplacement was 20.7 m. The maximum volume placed at any transect was 28.6 m 3 m − 1 of shoreline length. Erosion of the fill occurred rapidly, with landward migration of a conspicuous scarp. The edge of the upland 18 months after the fill was placed was up to 4.6 m farther landward than prior to the fill. Movement of sediment alongshore downdrift of the fill occurred as wave-like pulses, extending the active foreshore bayward, causing accretion of the inner low tide terrace, burying saltmarsh peat outcrops on the foreshore and creating a higher and wider overwash platform over portions of the saltmarshes. Landforms downdrift of the fill area underwent successive stages including erosion (pre-nourishment), accretion, stability (with throughput of sediment) and then erosion. Beach nourishment compensates for human-induced sediment losses. The volume of sediment added from maintenance dredging can slow the rate of erosion but may not prevent long-term shoreline retreat. Restoration and maintenance of coastal landforms and habitats to specific target states at a given location is difficult, but augmenting longshore sediment inputs can allow those locations to undergo cycles of erosion and accretion, creating a variety of landforms and habitats where only erosional forms existed previously. Alternatively, nourishment could occur more frequently and in smaller volumes to reduce fluctuations in accretion-erosion cycles. [ABSTRACT FROM AUTHOR]

Wave nonlinearity is a main driving force for near-bed sediment transport, and thus affects the beach evolution. Accurate prediction of wave nonlinearity is an essential need for the design of beach nourishment and restoration projects. So far, wave nonlinearity evolution patterns on the nourished beaches with abrupt changes of bottom slopes and water depth are not fully understood. This paper presents experimental results of nonlinear wave transformation across the submerged artificial sandbar. It can be found that the artificial sandbar intensifies wave shoaling processes and increases the magnitudes of the wave nonlinearity. Wave skewness and asymmetry are parameterized and both dependent on Ursell number and bottom slopes. By taking bottom slopes into consideration, the prediction accuracy for wave skewness is improved 17% with dataset measured in this study and 21%–65% with an independent dataset, compared with a common-used formula also calibrated on a steep low-crest breakwater without considering the bottom slope. Wave skewness decreases with increasing Ursell number in the inner surf zone, indicating the artificial sandbar influences its shoreward wave nonlinearities through the wave history. Finally, it is found that wave triads interactions can be enhanced by the steep seaward slope and small water depth of the artificial sandbar. • The composite dependence of wave skewness on both Ursell number and local bottom slope. • Parameterizations of wave skewness and asymmetry leading to improve prediction accuracy. • Artificial sandbar affects wave nonlinearities in the inner surf zone through wave history effect. [ABSTRACT FROM AUTHOR]

Hydrodynamic forces from ships operating in sheltered, confined fairways can result in increased wave impact and sediment transport leading to loss of land and habitats. Nature-based solutions (NBS) offer the potential to mitigate ship-induced erosion and increase biodiversity and ecosystem services. The aim of this study is to evaluate the performance of NBS in a sheltered, confined fairway located in a cold, temperate region. The case study presents the results of a 2.5-year study of the morphologic response at two sites where NBS was implemented to mitigate bluff erosion and at one site where NBS was implemented to mitigate the retreat of a reed belt. Moreover, a qualitative assessment was made of the vegetation development at the sites. The results showed that fine sediments with planted vegetation could not withstand the hydrodynamic forces induced by the ships. However, by adding sills as stabilizing structures, the forces were sufficiently attenuated for the vegetation to establish. The vegetation, which reduced the ship-generated waves and currents, was especially important during high water-level events when the energy dissipation by the sill decreased. Moreover, a small-scale nourishment was successfully applied to mitigate bluff erosion without negatively affecting sediment supply to an adjacent sandy beach. This study demonstrates that NBS can be implemented to retain erodible sediment and favour vegetation growth in fairways experiencing primary and secondary waves produced by large, ocean-going ships. • Five prototypes of NBS at three sites were tested in full scale in a sheltered, confined coastal fairway. • The study aimed at evaluating the effectiveness of NBS against ship-induced erosion at bluff escarpments and reed-belts. • The morphologic response, vegetation development, and durability of the implemented NBS were studied for 2.5 years. • A stone-based sill combined with vegetation was most effective in reducing bluff erosion and promoting reed growth. [ABSTRACT FROM AUTHOR]

We used modelling and field approaches to assess the influence of beach nourishment on a relatively distant Posidonia oceanica seagrass meadow in the NW Mediterranean. Both sediment transport models and in situ observations showed that, two years after the nourishment and under wave climates prevalent during the study period, sediment movement was restricted to shallow waters (<7 m), above meadow shallow limit. The only significant impact on seagrass meadows during this period was an increase in fine sediments, associated with vertical rhizome growth rates 1.5–1.7 times higher than normal. However, running the model with data of wave climate over several decades indicates that strong storms able to transfer these sediments much deeper, potentially burying meadows, occur with a return period of about 25 years. Taken together, our results suggest that beach nourishment could result in significant sub-lethal and lethal consequences for seagrasses that may go unnoticed with short-term evaluations. [ABSTRACT FROM AUTHOR]

The S ubmerged A rtificial sand B ar (SAB), recognized as one of the nature-based solutions for beach protection and restoration, has become increasingly popular in coastal engineering applications. However, its morphological response to waves and the resulting impacts on beach evolution are yet not well understood. Here, laboratory experiments are conducted considering different background profiles and various SAB designs. Morphological evolution of the SAB and berm are inspected from the measured beach profile data in the wave flume. Results show that the SAB migrates onshore with its bar shape decaying, providing a paradigm shift away from the traditional understanding that the net subaqueous sediment transport is always offshore directed under storm wave conditions. SAB can alter the beach state and berm behavior by triggering onshore sediment transport locally and temporarily. The stability of the SAB is controlled by its seaward slope and the ratio of crest water depth to the bar height. A morphological coupling is found between the SAB and berm, and an empirical relationship is proposed to quantitatively capture it. Finally, the experiment results are used to validate a process-based beach profile evolution numerical model, and an explanation for the morphological coupling is provided from the perspective of wave energy dissipation. • The responses of artificial sandbar to storm waves are modelled in the wave flume. • Artificial Sandbar can temporarily alter the beach state and berm behavior. • Artificial Sandbar migrates onshore and its bar morphology gradually dissipates. • A relationship is proposed for morphological coupling of artificial bar and berm. • Experimental results are validated using a process-based numerical model. [ABSTRACT FROM AUTHOR]

Beaches are dynamic systems characterized by frequent morphological changes due to storm events, gradients in longshore sediment transport, seasonal variations in wave climate and more. The complexity of variations in beach morphology can increase significantly after a beach nourishment, particularly when coastal structures are involved. This study investigates the impacts of a groin field, consisting of both notched and traditional groins, on the morphological evolution of a beach in Deal, New Jersey, USA. More specifically, an evaluation of the performance and specifications of the notched groins is undertaken. In 2016, the beach in Deal was nourished and three of the eight groins comprising the groin field were concurrently notched in order to promote increased movement of longshore sediment transport while maintaining a stable shoreline. The study site was monitored nine times over a period of two years (2018–2019) using Unmanned Aerial Systems Structure from Motion (UAS-SfM) photogrammetry. The near-term morphological response of the study site was evaluated by analyzing high-resolution digital elevation models (DEMs) and longshore sediment transport estimates based on measured wave data. The elevation change maps established that in general, the groin notching was partially successful in reducing shoreline asymmetry in consequence of sediment transport bypassing through the notches. Differences in behavior and patterns of elevation change adjacent to each individual notched groin was observed even though they were all notched according to the same specifications. While all three notched groins were effective in stabilizing the adjacent shoreline, they varied in their effectiveness at promoting longshore sediment transport through the notch. This is likely attributable to the relative location of the notched groins within the groin field and the characteristics of the post-nourishment morphological evolution; the direction of net annual longshore sediment transport at Deal beach is northward, which caused the southern areas of the study site to narrow and the northern areas of the study site to widen. Consequently, the notched groins in the wider sections of beach did not function as intended, as the notches filled in with sediment causing them to mimic the behavior of a traditional groin, including restricted longshore sediment transport and significant erosion/accretion offsets. In the narrower section of beach, the notched groin functioned as designed, such that the notch was located in the swash zone and therefore allowed bi-directional sediment transport and maintained a stable and relatively symmetrical shoreline. Thus, the notched groins performed most effectively when the notch was consistently located toward the seaward end of the swash zone. • Groin notches function optimally when the notch is located in the swash zone. • Improperly constructed notches can fill-in with sediment and behave like traditional groins. • Notch specifications can vary to account for position and uncertainty in the equilibrated beach. • Notch designs should reflect the direction and magnitude of net longshore sediment transport. [ABSTRACT FROM AUTHOR]

Abstract: Humans are increasingly altering the Earth''s surface, and affecting processes that shape and reshape landscapes. In many cases, humans are reacting to landscape-change processes that represent natural hazards. Thus, the landscape is reacting to humans who are reacting to the landscape. When the timescales for landscape change are comparable to those of human dynamics, human and ‘natural’ components of developed environments are dynamically coupled—necessitating coupling models of human and physical/biological processes to study either environmental change or human responses. Here we focus on a case study coupling models of coastal economics and physical coastline change. In this modeling, coastline change results from patterns of wave-driven sediment transport and sea-level rise, and shoreline stabilization decisions are based on the benefits of wide beaches (capitalized into property values) balanced against the costs of stabilization. This interdisciplinary modeling highlights points that may apply to other coupled human/natural systems. First, climate change, by accelerating the rates of landscape change, tends to strengthen the coupling with human dynamics. In our case study, both increasing sea-level-rise rates and changing storm patterns tend to increase shoreline change rates, which can induce more vigorous shoreline stabilization efforts. However, property values can fall dramatically as erosion rates and stabilization costs rise, which can also lead to the abandonment of expensive stabilization methods as shoreline change rates increase. Second, socio-economic change can also strengthen the human/landscape coupling. Changing costs of shoreline stabilization can alter stabilization decisions, which in turn alters patterns of coastline change. The coupled modeling illuminates the long-range effects of localized shoreline stabilization efforts; communities arrayed along a coastline are unwittingly affecting each other''s erosion rates, and therefore each other''s economies. Our coupled modeling experiments show that spatial distributions of property values and erosion rates can jointly affect economic outcomes, resource allocation between communities, and patterns of shoreline change. These findings raise questions about coastal management strategies, and efficient and equitable allocation of scarce resources among coastal communities. [Copyright &y& Elsevier]

Abstract: Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify that sediment mobility is caused by waves and wind driven currents from three predominant types of storm patterns that pass through this region: (1) cold fronts, (2) warm fronts and (3) low-pressure storms. The passage of a cold front is accompanied by a rapid change in wind direction from primarily northeastward to southwestward. The passage of a warm front is accompanied by an opposite change in wind direction from mainly southwestward to northeastward. Low-pressure systems passing offshore are accompanied by a change in wind direction from southwestward to southeastward as the offshore storm moves from south to north. During the passage of cold fronts more sediment is transported when winds are northeastward and directed onshore than when the winds are directed offshore, creating a net sediment flux to the north–east. Likewise, even though the warm front has an opposite wind pattern, net sediment flux is typically to the north–east due to the larger fetch when the winds are northeastward and directed onshore. During the passage of low-pressure systems strong winds, waves, and currents to the south are sustained creating a net sediment flux southwestward. During the 3-month deployment a total of 8 cold fronts, 10 warm fronts, and 10 low-pressure systems drove a net sediment flux southwestward. Analysis of a 12-year data record from a local buoy shows an average of 41 cold fronts, 32 warm fronts, and 26 low-pressure systems per year. The culmination of these events would yield a cumulative net inner-continental shelf transport to the south–west, a trend that is further verified by sediment textural analysis and bedform morphology on the inner-continental shelf. [Copyright &y& Elsevier]

Abstract: This paper illustrates the results of an experimental investigation (model-to-prototype length ratio equal to 12) carried out to reproduce the cross-shore evolution of nourished sandy beaches. New two-dimensional experiments were performed to study the short-term response of the cross-shore profile for both “soft” (unprotected) and “mixed” (protected by submerged breakwaters) beach fill projects. Due to the simplified reproduction of prototype conditions in a two-dimensional geometry, only cross-shore sediment transport is considered. The results are related to the immediate post-nourishment evolution and far from beach fill boundaries where long-shore gradients of long-shore sediment transport are likely to be negligible. Three different pseudo-random wave trains were generated in order to simulate both accretive and erosive conditions. A fourth wave train, characterised by time-varying incident wave spectrum was generated for the investigation of the beach response to simplified storm time evolution. Dimensionless experimental results are given in terms of wave parameters, key features of cross-shore profile evolution and sediment transport rates. Furthermore, being highly resolved in both time and space, experimental data are suitable for mathematical model validation. It was observed that submerged breakwater switches erosive conditions to slightly accretive, at least within the tested experimental range. [Copyright &y& Elsevier]

Abstract: Beach profile equilibrium is the principal concept assumed by most numerical modelling. The response of beach profile configuration to natural and anthropogenic changes could be predicted to help in selecting the most appropriate engineering design required to mitigate coastal erosion and accretion alongshore. Thus, in order to apply coastal engineering projects, the predicted profile of equilibrium should be close enough to the measured profile. Therefore, before application of numerical modelling techniques, equilibrium expressions have to be validated at the study site. This research aims to assess the validity of the equilibrium profile concept on the Nile Delta coast based on beach profiles surveyed in 1990 from the main promontories; Abu-Quir Bay, the Rosetta promontory and the El-Burullus promontory. The results indicate that the equilibrium beach profile is consistent with the measured profiles at the study sites beyond 200 m distance offshore at −4 m depth. In contrast, the equilibrium status is not valid along the beach face at −1 m depth. Accreted beaches at Abu-Quir bay and Burullus promontory are characterized by wide berms and gentle beach face whereas eroded stretches at Rosetta promontory have a narrow berm and steep beach faces. The measured profiles are also compared with the exponential beach profile concept. An exponential hypothesis is not valid along the Nile Delta coast. Profiles measured at Abu-Quir, Rosetta and El-Burullus depart significantly from the exponential equation. Despite the fact that equilibrium expression can describe beach profiles along the Nile Delta, one equilibrium profile equation is not sufficient to assess all beach profiles. This can be explained as the morphology of beach profiles is subjected to some factors including; sediment characteristics, wave parameters and closure depth, which vary alongshore. Analysis of the validity of the equilibrium beach profile is recommended to get accurate results in modelling simulations and design the most appropriate engineering projects required for shore protection. [Copyright &y& Elsevier]

Abstract: Numerical modeling of a beach nourishment project is conducted to enable a detailed evaluation of the processes associated with the effects of nearshore dredge pits on nourishment evolution and formation of erosion hot spots. A process-based numerical model, Delft3D, is used for this purpose. The analysis is based on the modification of existing bathymetry to simulate “what if” scenarios with/without the bathymetric features of interest. Borrow pits dredged about 30 years ago to provide sand for the nourishment project have a significant influence on project performance and formation of erosional hot spots. It was found that the main processes controlling beach response to these offshore bathymetric features were feedbacks between wave forces (roller force or alongshore component of the radiation stress), pressure gradients due to differentials in wave set-up/set-down and bed shear stress. Modeling results also indicated that backfilling of selected borrow sites showed a net positive effect within the beach fill limits and caused a reduction in the magnitude of hot spot erosion. [Copyright &y& Elsevier]

Land uses have long modified aeolian sedimentary dynamics as has occurred in the Jandía isthmus (Fuerteventura, Canary Islands, Spain), where changes in vegetation cover, the reduction of sediment available for transport and the building of barriers to sediment transport have induced beach erosion. In the last 62 years the beach area has experienced a reduction of 800,000 m2. The aim of this paper is to analyse the current situation (in terms of sediment availability, longshore drift and the distribution of protected plant species) in order to make soft management proposals to respond to the current erosive situation. Based on a methodology that combines field work, coastline digitalization and longshore drift calculations, it is found that each year the system loses about 96,000 m3 of sediment which needs to be replaced in order to stop erosion. Four possible ways to manage the system are discussed: passive non-intervention management to allow the ecosystem to evolve and adapt to the new conditions; remobilization of the sedimentary deposits of the isthmus that feed the beaches; beach nourishment from other areas of the system or from outside the system, and; mechanical recirculation of the sands. The viability of each management system is analyzed, particularly with regard to long-term sustainability, as well as its compliance or otherwise with the protection measures that are in place. Paradoxically, the only measures that can alleviate the problem in the long term are incompatible with the current protective measures. In other words, the isthmus and the Sotavento beaches in Jandía are an example of an ecosystem in which the restrictions imposed as a result of its protected status, that do not take into account the tendences of the ecosystem, in fact constitute an obstacle to its conservation and do not allow the adoption of measures that could slow down the degradation process and, ultimately, impede its disappearance. [Display omitted] • Beach evolution is analyzed for a period of 62 years. • Protected species, marine dynamic, sediment availability and land uses are analyzed. • Four management ways are proposed from the current status of the ecosystem. • Erosion problems cannot be solved with the current legislation. [ABSTRACT FROM AUTHOR]

Sediment tracer studies use uniquely identifiable particles to track the pathways and fate of individual sand or silt grains in marine environments. These techniques are best applied to assess connectivity between potential sediment sources and sinks, such as between a sand nourishment and an ecologically sensitive area. Significant challenges exist when applying sediment tracing techniques to further understanding of systems with complicated hydrodynamic, sediment, and morphological regimes. Ebb-tidal deltas are highly dynamic coastal environments shaped by the complex interplay of waves and tides, but have been under-explored. In this study, we use dual signature (fluorescent and ferrimagnetic) sediment tracers to simulate the dispersal of dredged sediment placed as a sand nourishment on an energetic ebb-tidal delta (at Ameland Inlet, the Netherlands). After deployment, sediment dispersal and grain size sorting behaviour were monitored via the collection of seabed grab samples and magnetic sampling of sediment transported in suspension. The tracer content within collected samples were put in context with hydrodynamic conditions observed during the study period. Here we show that the use of such dual signature tracers, in addition to novel tracer recovery and analysis techniques, enables the dispersal of sediment to be monitored even in such complex settings and energetic conditions as an ebb-tidal delta. Our observations show that tracers transported in suspension are significantly finer than tracers that accumulated in the seabed. These suggest that preferential transport as a function of grain size is a key process in shaping the morphology of ebb-tidal deltas and thus governing the dispersal of sand nourishments there. The findings of this study and the approach used here provide valuable tools for assessing the baseline conditions of complex coastal environments today, and for planning the interventions which may be necessary in future responses to climate change. Lessons learned from the application of sediment tracers in this study are provided to assist future researchers and practitioners in applying this technique in dynamic coastal environments. • Large-scale sediment tracer study conducted on a highly dynamic ebb-tidal delta. • Despite the challenges presented by such an energetic setting, tracer was recovered. • Tracer recovery and processing were enhanced by its fluorescence and ferrimagnetism. • Tracking grain size of recovered tracers is essential for interpretation. • Tracers prove to be useful tool for sand nourishments planning and monitoring. [ABSTRACT FROM AUTHOR]

Rising sea level and increasing tropical storm frequency caused by the changing climate are threatening small Island economies which depend on their coastal environments and resources. Owing to the high socio-economic and environmental values of tropical sandy beaches, monitoring the evolution trends of shorelines are regarded as an essential strategy to improve the resilience of Island states. The present study conducted in Mauritius, indicates a net erosional effect at Le Morne amounting to 8049.7 ± 5% m2 which is attributed to the hydrodynamics of the lagoon, whilst a net accretional effect has been observed at Flic-en-Flac, equivalent to 6571.3 ± 5% m2 and attributed to periodic beach nourishments. The shoreline evolution at Le Morne is predominantly influenced by Passe de la Prairie where an average energy of 0.162 m2/Hz, corresponding to an average wave height of 1.16 m, carries enough energy and momentum to influence the sediment transport near the peninsula. At Flic-en-Flac, longshore currents propagating on either sides of the central region and directed northwards and southwards influence the shoreline, resulting in an accretion zone extending 62.5 ± 15 m near Villa Caroline over the 2009–2018 period. To dampen this problem, a beach management strategy is proposed which revolves around the restoration of corals in front of eroded shores, replacement of casuarina trees, and enforcement of regulatory laws. [Display omitted] • The evolution of shoreline is detected using satellite imagery and GIS. • In-situ measurements are used to comprehend sediment transport. • Hydrodynamic modelling is performed to support the analysis. • The link between shoreline changes and coastal current propagation is presented. • Management measures to dampen the impacts of erosion are proposed. [ABSTRACT FROM AUTHOR]

A modified 2DH morphodynamical model was employed to simulate the evolution of large-scale features with major implications for beach nourishment. The study was focused on modelling the evolution of material artificially placed in different parts of the profile, extracting or adding material to the natural bars, and quantifying how the profile responds to different wave climates and nourishment placements. The simulated results were compared with field data from a Mediterranean beach. [Copyright &y& Elsevier]

Abstract: Although beach nourishment policy in the Netherlands is generally successful in maintaining the 1990 shoreline, the efficiency of nourishments at several locations along the North Sea coast is unacceptably low. These locations are identified as “erosion hotspots”. Egmond aan Zee is such a hotspot. The bathymetric longshore irregularities make this coastal stretch highly susceptible to rip currents and horizontal circulations, which transport large volumes of (nourished) sand to the sea. In 1999, an alternative nourishment design was implemented. This consisted of a shoreface nourishment at the outer bar (at 7.5-m depth) combined with a nourishment of the beach behind it. High-resolution bathymetric surveys, carried out with the WESP, revealed that the shoreface nourishment resulted in a significant shoreward migration of the outer bar during 1999–2001. After 2 years, the system started to return to its natural dynamic equilibrium and lost the positive influence of the shoreface nourishment area: shoreward movement of bars and increase of bar height, which forms the first defense line of the mainland against the sea, and positive contribution to the sand budget, which increased as a result of the nourishment. After 3 years (May 1999 to April 2002), the sediment volume still had an increase of 477,500 m3 (45% of the applied sand) relative to May 1999. The shoreface nourishment area did not have a direct effect on the beach. The shoreface nourishment area probably will have to be maintained to retain the sediment on the beach in the long run. In Egmond, the shoreface nourishment started to disappear before the sediment could reach the beach. The time scale of sediment feed to the beach zone probably is of the order of 5–10 years. The shoreface nourishment seems to function as a reef, creating a lee-side effect that influences both cross-shore and longshore sediment transport, resulting in two main hypotheses. Firstly, the longshore effect, in which large waves break at the shoreface nourishment, cause a calmer wave climate shoreward of the shoreface nourishment area and a reduction of the longshore current. The shoreface nourishment partially blocks the wave-driven longshore current. Secondly, the cross-shore effect, in which shoaling waves generate onshore transport. These hypotheses are supported by generated model results with both a process-based profile model, UNIBEST-TC, and a process-based coastal area model, DELFT3D-MOR. The UNIBEST-TC model was able to predict the detachment of the outer bar from the shoreface nourishment and, to some extent, the shoreward bar movements. In the lee of the shoreface nourishment area, the model found an increase in sediment, confirming the shielding effect of the shoreface nourishment area. The DELFT3D model found, as a result of the shoreface nourishment area, a decrease of the flow velocity and the wave height just shoreward of the shoreface nourishment area. The model was able to predict the similar trend in sedimentation/erosion pattern, although the intensities were smaller. In the lee of the shoreface nourishment area, a clear sedimentation was found. Erosion was found south and seaward of the shoreface nourishment area. The modeled profiles did not follow the measured profile changes. The separation of the shoreface nourishment from the outer bar and the shoreward migration of the bars could not be accurately modeled. Because the cross-shore transport caused by wave asymmetry is not taken into account in the standard version of DELFT3D, these results were in line with the expectations. [Copyright &y& Elsevier]

In many places, sandy coastlines and their associated assets are at high risk of erosion and flooding, with this risk increasing under climate change and sea level rise. In this context, dynamic cobble berm revetments represent a potentially sustainable protection technique to armour sandy beaches, reduce wave runup and protect the hinterland against wave attack. However, the behaviour and performance of such structures is not well understood. The dynamic cobble berm revetment located in North Cove, WA, USA, was monitored over a spring tidal cycle in January 2019. A representative 60 m alongshore section was monitored over 10 days using 2D laser scanner (lidar) measurements, GPS ground elevation surveys, Radio Frequency Identification of individual cobbles and revetment thickness measurements. These data were used together to assess the dynamic behaviour and functionality of the revetment throughout the experiment. Over the course of the experiment, the surface elevation changed by up to ±0.5 m, and the revetment volume reduced by an average 0.67 m3/m. These changes were found to be caused by relatively large significant wave height and high water levels. The revetment demonstrated a dynamic stability and the capacity to quickly reshape under changing hydrodynamic conditions. The instrumented cobbles were transported along and cross-shore and accumulated at the toe of the revetment, but were never transported seaward of the toe. The revetment also managed to recover some of the lost volume under moderate wave conditions. The revetment behaviour was found to be influenced by variation in the cobble-sand matrix. The underlying sand dynamics – i.e. , accumulation or removal of sand within the cobbles – were found to govern the overall volume changes and were important to the overall stability of the revetment. Seven possible transport regimes were identified, and a model of the internal sand dynamics was developed. During the spring tidal cycle measured here, the revetment protected the sand scarp immediately landward and prevented flooding of the hinterland, while armouring the underlying sand. Over time, renourishment will likely be required due to longshore sediment transport, and preliminary guidelines for this and other aspects of design are suggested. • A field experiment was undertaken on a dynamic cobble berm revetment in North Cove, US. • The revetment showed a dynamic stability and a rapid adaptability to external forcing. • The water level at the toe of the structure appeared to be the primary driver of change. • A novel model highlighting the importance of internal sand dynamic was created. • Guidelines are proposed for design and nourishment of the structure. [ABSTRACT FROM AUTHOR]

Geomorphological and sedimentological surveys of the emerged and submerged beach-dune system are fundamental for a successful management and protection strategies for coastal planning and development. In particular, these surveys can reveal if coastal areas are affected by erosion, pollution and loss of habitats under the seasonal anthropic pressure related to tourism, leisure and professional fishing, urbanisation and/or other activities impacting the coastal marine resources. In the present study we discuss the results of the multidisciplinary monitoring activities carried out within the Sentina Natural Reserve (Municipality of San Benedetto del Tronto, Adriatic side of Central Italy, at the south-eastern end of the Marche Region) proposing an exportable methodological approach. Due to the absence of buildings, the study area has not been considered in the coastal protection plan by regional and local authorities and, as a consequence, it is currently exposed to severe coastal erosion, the rate of which has been more precisely determined during the present study. This monitoring testifies that most of the seaward surface of the beach disappeared resulting in a general set back of the whole beach environment. In the last decades, several restoration strategies have been adopted to protect and restore the dunes and the back dunes habitats and the municipality also carried out an emergency action to nourish the beach, including the use of sand dredged from the nearby city harbor. With this sediment management approach, a tradeoff between safety of navigation of harbor inlet and habitat conservation of Natural Reserve have been reached, since beach nourishment can reduce coastal vulnerability and risk, even though its sustainability in the long term is still debated. Image 1 • Beach-dune system are complex and dynamic environment. Ephemeral from the geological point of view but important from ecological and economical perspective. • Coastal system characterisation and monitoring. • Beach-dune dynamic and resilience. • Sediment management for conservation of coastal habitat (dune) and adaptation strategies. [ABSTRACT FROM AUTHOR]

Artificial submerged sandbar is regarded as an assistant structure for beach nourishment with two beneficial functions of protecting beach and supplying sand source. Due to local representative physiognomy of subaqueous sandbars and the aim of longer resident time of beach nourishment, two artificial submerged sandbars parallel to the shore, are implemented at Tiger-Rock Beach, Qinhuangdao, China. It is essential to investigate and identify the systematic morphological implications of artificial submerged shore-parallel sandbars to beach nourishment practice. In this study, a three-level nested flexible triangular unstructured mesh system is set up for a three-dimensional sediment transport and morphological model. The sediment transport and morphological model, driven by coupled tidal currents and waves, is well validated by field measurements. The validated model is used to evaluate the responses of sediment transport and morphological evolution to beach nourishment with two submerged shore-parallel sandbars. The most significant effect of the artificial submerged sandbars is inducing wave breaking (even secondary wave breaking) and forming shadow zones. The artificial submerged sandbars increase westward sediment transport at Public Bathing Place and Specialist Bathing Place, and eastward sediment transport at Langtaoyu Bathing Place. Sediment from sandbars can be transported in three pathways: i) onshore by a wave-induced current due to breaking wave at the crest; ii) longshore due to a longshore current; and iii) seaward by a reversed asymmetrical current. Overall, the sandbars protect beach through forming wave shadow area in their rears with lower wave height and the sediment transport capacity, and supply sediment toward the shore by sacrificing themselves, i.e., sandbars are eroded and have a low-crest asymmetrical shape. The findings in this study contribute to the understanding of morphodynamics of artificial submerged sandbars and can provide a reference for beach nourishment to preserve their eco-friendly nature. • A 3D sediment transport and morphological model coupled with real tidal currents and waves. • A nested flexible triangular unstructured mesh system in three levels. • Performances of morphological process of two artificial submerged shore-parallel sandbars. • Sandbars have stronger response to wave than to current, and reduce longshore sediment transport rate. • Sandbars have a significant effect on mitigating erosion in wave shadow zones. [ABSTRACT FROM AUTHOR]