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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.

Along much of the world's coastline, coastal barriers serve as the first line of defense against oceanic and meteorological forces. Extreme storms cause large morphological changes on coastal barriers through high sediment transport rates, which may degrade their defensive capabilities. The understanding of morphological impacts is therefore important for coastal resiliency, but is often challenged by site-specific characteristics, such as land cover and sediment availability, and their poorly understood impacts on the governing physical processes. The Caminada Headlands, Louisiana, USA presents unique considerations for morphodynamic modeling with regard to its low-lying topography, variable land cover, nearshore muddy substrate and sand deficiency. This study investigates the effects of land cover and limited sediment supply on low-lying barrier island morphology under storm conditions by using physics-based numerical models. A high-resolution, local-scale sediment transport/morphodynamic model (XBeach) of the Caminada Headlands is verified for Hurricane Gustav's (2008) impact using pre- and post-storm LIDAR surveys. When accurate input data are used to create physics-based numerical models these tools are robust in hindcasting storm impacts and provide a wealth of information as to the governing processes, which is otherwise difficult to obtain observationally. The simulation results show that a short-duration overwash regime dominates the morphological change in this low-lying barrier and is influenced by backbarrier wetland deterioration. The morphological response to overwash is modulated by backbarrier land cover and topography, as reduced accommodation space limits landward transport during the subsequent inundation regime. An intact backbarrier marsh reduces landward washover sediment transport distances and promotes deposition at supratidal elevations. In light of these findings, simultaneous restoration/creation of backbarrier wetlands in conjunction with subaerial beach renourishment may be an effective form of increasing the resiliency of low-lying barriers subject to frequent overwashing.

We present a simple one-dimensional process-based morphological model for predicting medium–long term beach profile evolution of a bayside beach with a low tide terrace. Bayside beaches are characterized by low wave energy. In regions with a large tidal range, a beach face is slowly eroded due to erosional waves inside the surf zone which shifts along the beach profile over a wide range during a tidal cycle. The model is developed using an existing model framework proposed by Mariotti and Fagherazzi (2010) , who formulated a model for sediment suspension and transport due to waves and tidal currents in a tidal flat regime. The new developments in this study include an implementation of the bedload sediment transport and modification of the suspended load transport for noncohesive particles. The model parameters were calibrated using beach profile data collected over a one-year span at Xiamen Beach. Numerical experiments indicate that waves suspend sediment in the narrow surf zone, inducing pulse-like high sediment concentration in shallow water. The suspended sediment is advected by the tidal current and wave-induced undertow, causing erosion of the steep beach face at the upper portion and deposition of the flat beach face at the lower portion of a beach profile. The erosion on the upper beach face was not predicted by a bedload-only transport model, suggesting that the sediment suspension associated wave breaking may be the major mechanism for the erosion. Tide-only induced sediment transport is insignificant, but tides play a role in distributing the wave-induced erosion over a wide region on a beach profile.

It is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea. Specifically, a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion, while the reverse is thought to hold for a high beach groundwater table. Here, we use the results of a carefully designed series of tests conducted in the Delta Flume, the Netherlands, as part of the Barrier Dynamics Experiment ( BARDEX ), to unequivocally demonstrate the validity of this assertion. During the experiment, a 4-m high and 50-m long gravel barrier ( D 50 = 11 mm) was constructed within the central region of the 250-m long and 7-m deep wave flume, enabling a back-barrier ‘lagoon’ to be located at its landward side. The groundwater table in the beach was manipulated by lowering and raising the lagoon level, and the gravel beach was subjected to variable wave conditions and sea/lagoon levels. Using as the initial beach profile the morphology resulting from 90 min of wave forcing with the sea and lagoon at the same level, the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion, whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion. The divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the ‘bulk’ swash hydrodynamics (i.e., based on single-point velocity measurements) arising from a difference in the amount of swash infiltration into the unsaturated beach. Instead, application of a sediment transport model that accounts for the effects of in/exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface. Due to the large hydraulic conductivity of gravel ( K = O (0.1 m s − 1 )), the effect of altered shear stresses due to in/exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches.

The Australian coast contains 10,685 beaches which occupy 49% of the 30,000 km coast and average 1.37 km in length. Their relatively short length is largely due to the presence of bedrock, calcarenite and laterite, which form boundaries to many of the beaches, as well as occurring as rocks, reefs and islands along and off the beaches. This geological inheritance plays a major role in Australian beach systems — determining their length and through wave refraction and attenuation influencing beach location, shape, type, morphodynamics and circulation, which in turn influence sediment transport and the backing dune and barrier systems. This paper uses a database covering every Australian beach to review the role of headlands, rocks and reefs on Australian beaches. Major effects are the short average beach length; reduction in breaker height resulting in lower energy beach types; wave refraction resulting in increased beach curvature; the presence of topographic rips on moderate and higher energy beaches and megarips during high wave conditions; and the interruption of and/or trapping of longshore sand transport leading to beach rotation.

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.

In this study, planform adjustment began during a period of calm weather immediately after nourishment and then the passage of one strong storm caused a substantial portion of the total profile equilibration. Weekly beach profiles, shoreline surveys, and nearshore wave measurements were conducted before, during, and immediately after construction of the 1100-m long Upham Beach nourishment project on the low-energy, west coast of Florida. This project was constructed in three segments: the wide north segment, the central segment, and the narrow south segment. With the exception of the relatively distant passage of Hurricane Charley, calm weather prevailed for 45 days following completion of the south and central segments. Construction of the wide north segment was completed on August 27, 2004. Substantial planform diffusion occurred prior to construction completion via formation of a 300-m long spit extending from the wide north segment. The shoreline orientation was changed abruptly due to this diffusion spit formation, as opposed to the gradual adjustment predicted by most long-term models. Planform adjustment was initiated prior to profile equilibration, and it did not require high-energy conditions. A simple vector sum model for determining the orientation of a potential diffusion spit was developed. This study recommends designing end transitions at the predicted diffusion spit orientation to avoid post-nourishment spit formation during future projects. Profile equilibration occurred rapidly due to the passage of three hurricanes soon after nourishment was complete. Nine days after completion, Hurricane Frances passed by the project area generating high wave conditions ( H sig = 1.7 m) for this region. The steep post-nourishment beach slope of 0.078 was reduced to 0.036, nearly to the equilibrium slope (0.034), due to this storm. Hurricanes Ivan and Jeanne, which were nearly as energetic, passed by the project area within 1 month after Frances and resulted in much less profile slope change. Examination of the ratio of total volume to plan area remaining in the project area also suggested that a substantial portion of the total profile equilibration occurred as a result of Hurricane Frances. This study indicates that profile equilibration can be an event-driven process, which contradicts the concept of longer-term gradual profile equilibration. Both profile and planform adjustment can occur rapidly given the appropriate site conditions and energy levels.

This paper presents the application of a technique that can be easily applied in monitoring programs following beach fills, where sand is dredged from subtidal zones, seabed or bays, usually rich in foraminifera shells. Its utility lies in a simple and rapid estimation of the prevailing longshore transport paths and determination of the main eroding/accreting zones. A beach monitoring program was undertaken in a embayment on the South Atlantic Spanish coast, where several nourishments were carried out in order to recover an eroding beach. Once the nourishment was complete, a temporal analysis of foraminifera shell distribution was made in a nearby beach inside the embayment by monthly sediment sampling. Foraminifera shells were used as natural tracers for estimating sediment pathways. The results showed a complex pattern of sedimentary transport between both beaches, where wind action and reflected/diffracted waves interfered with the dominant longshore current, depending on the prevailing hydrodynamic regime. These results were later confirmed by a 3-year morphodynamic study. Although foraminifera dispersion only accounts for the behaviour of fine fractions, the monitoring of shell dispersion after dumping demonstrated to be a useful tool for studying the stability of nourished beaches. In the case of nourished beaches foraminifera shells could be considered as mixed tracers, with many advantages over both natural and artificial traditional tracers.

This paper provides a review of available studies on wave transformation by bathymetric changes and the resulting shoreline impacts. Three case studies of beach nourishment projects with significant nearshore borrow areas are examined: Grand Isle, Louisiana constructed in 1984, Anna Maria Key, Florida in 1993, and Martin County, Florida in 1996. A review is presented of field and laboratory scale studies that have examined the impact of offshore pits on the local wave field and sediment dynamics. Solutions for wave transformation by changes in bathymetry are outlined primarily in chronological order following the development from analytical solutions for long waves in one horizontal dimension (1-D) through numerical models for arbitrary bathymetry that include many wave-related nearshore processes. Modeling of shoreline responses due to wave field modification owing to changes in offshore bathymetry is examined with models that include both wave field and shoreline changes and by coupling models that evaluate these processes independently. The wave transformation processes included in nearshore models are important factors in the capability to predict a salient leeward of a pit; the shoreline responses observed in the limited laboratory experiments and at Grand Isle, LA.

Based on the available short-term morphological data (1964–1992), the net yearly-averaged sand volume change in the surfzone ( 3 −8 m NAP; to local datum approximately mean sea level) along the coast of Holland was found to be 125,000 m 3 year (sedimentation), including beach nourishments. A sand budget model has been developed, which describes the sand volume change (in m 3 year ) in each compartment of the coastal area given known gradients of the computed longshore and cross-shore transport rates and known source/sink terms (nourishment, dumping and dredging). The model area extends in cross-shore direction from the +3 m NAP contour to the −20 m NAP contour. The sand budget model has been calibrated (hindcast study) using the yearly-averaged sand volume changes derived from bathymetry data (Jarkus-data base) collected during the period 1964–1992. Input data are the gradients of the yearly-averaged longshore and cross-shore transport rates at the boundaries of the compartments and the available data of beach nourishment, dumping and dredging in the same period. A 2DV-mathematical model representing the hydrodynamic (waves and currents) and sand transport processes in a cross-shore profile was applied to compute the yearly-averaged transport rates in various profiles along the coast at depths of 20 and 8 m and in the surf zone. A detailed sensitivity study was performed to determine the variation ranges of the transport rates.

Descriptions of refraction and shoaling for input to one-line planform models of beach nourishment response are discussed. Three equations for bulk longshore sediment transport rate are compared to a small-scale laboratory data set, using up to three different descriptions of wave transformation. A simple, analytical description of wave transformation is presented that is consistent with the accuracy of the available equations describing longshore sediment transport rate. The simple approach appears favorable when compared to more rigorous descriptions of wave transformation for a gross estimate of beach nourishment evolution on a shoreline that is initially relatively straight. A new governing equation and analytical solution for beachfill evolution, including the effects of project-induced wave transformation, are presented. The analytical solution may be used as a design aid to indicate the influence of beachfill parameters (depth to toe, taper length) on beachfill lifetime.

The possibility of using offshore sand deposits as a source of material was recently studied as part of a beach nourishment project at Waikiki Beach, Hawaii. The borrow site is located approximately 1100 meters off the beach. A finite difference model of water circulation and fine particle transport is used to study dredge-induced far field turbidity concentrations. The influence of the dredging pit at the borrow site on the stability of the nearshore ocean bottom and on the beach is analyzed using the Bailard sediment transport model in the onshore-offshore direction. Model results show that effects of the dredging operation on the beach would be negligible. A maximum sediment accumulation on the ocean bottom of 0.3 kg/m 2 (or equivalently, a 0.2 mm thick layer) is predicted for one day of operation, which is considered acceptable.