Cross Shore Research Articles

Automated Extraction of Satellite-Derived Shoreline Changes along the Ongole Coast of Andhra Pradesh from 2000 to 2023 Using CoastSat

This paper presents a fully automated methodology for extracting time-series of monthly shoreline changes along the sandy beaches of the Ongole coast in Andhra Pradesh, India, from 2000 to 2023 using publicly available satellite imagery. The methodology involves the identification of sandy coastline sections within the region of interest, creating cross shore transects automatically at each site, and utilizing the open-source global shoreline mapping toolbox called CoastSat. The CoastSat tool is employed to extract time-series of shoreline change at each transect. To account for variations in tide levels among satellite images, the final step includes tidally correcting the shoreline change time-series using predicted tide levels and an image-derived estimation of the average intertidal beach slope. Keywords: - satellite imagery, shoreline change, Ongole coast, Andhra Pradesh, CoastSat, automated methodology, time- series analysis, and tide correction.

MONITORING OF THE COASTAL DYNAMICS ON THE SAND SPIT AT TORTUGUEROS BEACH, MEXICO

Sand spits occur worldwide in different shapes, from a single, relatively simple arc to an irregular, crenulated, and complex barrier. Cross-shore and longshore sediment transport often influence spit dynamics (Nagarajan et al., 2015), strongly linked to wave energy and sediment supply. The present analysis focuses on a dynamic and complex spit at Tortugueros beach, a re-entrant bay, 1 km in length, on the Gulf of Mexico. Tortugueros beach is a wave-dominated beach with very fine to fine sand that forms a fairly gentle sloping beach profile. The sediment sources are longshore sediment transport and onshore sandbar migration, while sediment loss is due to long- and cross shore (during storms) transport. The region is micro-tidal, with mean and maximum high tide levels of 0.18 m and 0.92 m above the mean sea level. Given the high dynamics of the Tortugueros beach spit system and the lack of data measured on the beach, a monitoring system was developed to collect field data regularly to help us improve the understanding of the functioning of the coast on this beach, and the international knowledge related to the formation and morphological evolution of this type of spits in other similar beaches around the world.

SPATIO-TEMPORAL VARIATION OF AEOLIAN SHOREWARD SAND TRANSPORT MEASURED USING NEAR-CONTINUOUS LASER SCANNING

A beach in Mariakerke-Bad (Belgium) was monitored in 2017-2018 for more than a year with a near-continuous laser scan system. From a total of 8500 scans 7700 hourly scan epochs were used to study the spatio-temporal shoreward sand transport at the beach. In order to account for weather influences and other possible disturbances of the scan-system, a time-dependent correction method was applied to reduce rotation errors up to 0.2 degrees in the point cloud orientation (around the zero point of the laser scanner) reducing height errors on the beach to the order of centimeters. Cross shore analysis of the beach profile shows that shoreward transport occurs at most times during the year with an accumulated maximum of 17m3/m throughout the measurement period and maximum transport rates of 0.6 m3/m/day. However most of the shoreward sand transport is redistributed seawards again due to beach shaping leaving a total of about 2 m3/m a year which is below the average values found along the Belgium coast. The spatio-temporal behavior of the shoreward sand transport has been studied with the 4D-OBC analysis technique which identified accumulations of sand in the full 4D point cloud dataset. A total of about 3600 4D-OBC accumulation events were identified and most found accumulations on the beach can be associated with natural (aeolian) processes. Also, accumulations appear to occur during the whole year which is consistent with the previous cross-shore analysis.

Swash-by-swash morphology change on a dynamic cobble berm revetment: High-resolution cross-shore measurements

Dynamic cobble berm revetments are a promising soft engineering technique capable of protecting sandy coastlines by armouring the sand and dissipating wave energy to protect the hinterland against wave attack. They also form composite beaches as they are essentially mimicking natural composite beach structure and behaviour. This type of coastal protections and beaches have recently been investigated, and this led to a better understanding of their overall behaviour under varying water levels and wave conditions. However, the short-term dynamics of the wash zone (where all bed changes occur) has never been studied at high-resolution, and this is needed to fully understand the underlying dynamics of such structures and relate it to observed processes at larger scale. To do so, the revetment at North Cove (WA, USA) was monitored for a nine-day period in January 2019 over a spring tidal cycle and with significant wave heights offshore reaching 6 m. A 2-D lidar was used to survey a cross-shore profile of the revetment, and record all surface changes and interaction with swashes at high spatial (0.1 m) and temporal (swash-by-swash) resolution. The revetment was found to rapidly reshape under these energetic conditions, but reached a relatively stable state during the rising tide. The analysis of bed-level changes and net cross-shore mass fluxes over the revetment showed that revetment changes are mainly driven by very small events, with some rare large bed-level changes of a magnitude comparable to the median cobble diameter. The distribution of event mass fluxes nearly balanced out over the duration of a tide, meaning that positive and negative fluxes tended to be symmetrical. Furthermore, measured net fluxes magnitude were 18 times smaller than the absolute fluxes, which demonstrated the dynamic stability of the revetment as substantial movement occur on a wave-by-wave timescale but these balance out over time. The analysis of swash revealed that the revetment section where the swash reaches a maximum depth between 0.15 and 0.45 m undergoes the more extreme fluxes. Swashes deeper than 0.45 m only occurred in zones inundated more than 50% of the time, and smaller extreme fluxes were measured over the revetment section where these deep swashes were recorded. Bed level change oscillations over the revetment were observed, and the cross shore limit of these was correlated with the mean wave period at the toe of the revetment. Overall, the water depth at the toe of the revetment was identified as the key parameter to describe the energy reaching the revetment. This study enables the morphodynamics of dynamic revetment, observed in previous lab and field studies, to be explained at the swash scale, and brought new information on the sediment dynamics of composite beaches and dynamic revetments. These findings allow to suggest some generic guidance for dynamic cobble berm revetment design. Finally, the results are compared to a similar study on sandy beaches.

A new approach to mapping littoral cells within a tide-dominated embayment

Western Port is a large tide-dominated embayment located 75 km east of Melbourne, Victoria that is flanked by a rapidly growing population, significant industrial infrastructure, grazing lands and protected RAMSAR habitats. Remarkably little is known about the sediment dynamics of Western Port despite concerning rates of erosion of the swamp and floodplain deposits including cohesive clay cliffs that fringe the sunkland. As in other tide-dominated systems, sediment dynamics in Western Port are complicated by strong tidal currents, multiple sediment sources and complex circulation. We applied the coastal sediment cell framework to Western Port, in conjunction with high resolution satellite derived rates of coastal change to elucidate sediment sharing among the sub-embayment beaches. Using end member modelling of 20 sediment assemblages based on elemental and mineralogical composition we robustly identified seven end members that correspond to different point and diffuse provenances. Hierarchical clustering of the 20 beaches dispersed across the bay yielded nine coastal cells, delimited by headlands, deep water channels, estuaries or disruptive infrastructure. Analysis of shoreline change within the cells suggests most cells are neutrally or positively balanced but a northward movement of sediments is leading to rotation. The deep channels provide a pathway for Bass Strait sediments to bypass the embayment headlands and tidal currents enable cross shore exchange with the channels beyond wave derived closure depth in some locations. Understanding the sediment cell boundaries and direction of sediment transport can assist with the management of erosion hotspots; the novel approach applied here can resolve complex connected coastal systems such as estuaries and embayments.

Modelling morphodynamic responses of a natural embayed beach to Typhoon Lekima encountering different tide types

Recent developments in process-based coastal area models such as XBeach provide new opportunities to predict coastal responses to primary forcing mechanisms such as storm hydrodynamic by using 2DH grids. However, due to the lack of measured data, there are few application scenarios of the models. Therefore, more measurement and research are needed. In this paper, the Typhoon Lekima that hitting Zhejiang Province during neap tide period was selected to simulate morphodynamic responses of the Huangcheng Beach by assuming encountering with different tide types. Cross shore measurements with eight cross-shore profiles (named S1 ~ S8 from north to south) of the Huangcheng Beach pre- and post- the Typhoon Lekima respectively were presented. Then a 2DH storm surge and wave coupled model was established with Delft3D Flow/Wave. The model was well calibrated with measured water levels and wave data and provided hydrodynamic boundary conditions of different typhoon and tide types coupling situations for a refined model. The refined model was built using XBeach and simulated the morphological responses of the Huangcheng beach with well verifications. On basis of the numerical results, bed level changes at the eight profiles were analyzed, and the character of erosion and deposition under different tide conditions were illustrated. The net sand volume changes were got smaller under the spring tide condition rather than middle tide and neap tide conditions. Further study of the distribution of wave induced current at different stages of collision, inundation and ebb shown that the stronger current under spring tide condition would increase the sediment transport rate and reduce the deposition volume at profiles S3 and S6 ~ S8, and the total amount of sediment involved in transportation had increased for the whole beach, leading to the reduction of net erosion volume at profiles S1, S2, S4 and S5.

A Numerical Model to Simulate Beach and Dune Evolution

Zhang, J. and Larson, M., 2022. A numerical model to simulate beach and dune evolution. Journal of Coastal Research, 38(4), 776–784. Coconut Creek (Florida), ISSN 0749-0208. A numerical model to simulate cross-shore (CS) beach and dune evolution induced by storms was developed in this study. The model development was partly based on previous CS modeling work in which modules describing the response of the beach profile in the offshore, surf, and swash zone were described in detail, but where the dune module is lacking. The dune module, adopting wave impact theory, was integrated into the previous model to complete a new numerical model. To calibrate and validate the new model, high-quality data on hydrodynamics and dune profile response from both laboratory and field data were used. The laboratory data included two experimental cases related to dune erosion from the SUPERTANK data collection project, whereas the field data consisted of two cases from Ocean City, Maryland and one case from Myrtle Beach, South Carolina. Overall, good agreement was obtained between calculations and measurements, illustrating that the model is reliable and robust in simulating beach and dune evolution. However, the poststorm beach recovery in the swash zone could not be well captured by this model. Thus, in subsequent model development, onshore transport and accretion in the nearshore will be emphasized to simulate long-term beach evolution.

Coupled Wave Energy Converter and Nearshore Wave Propagation Models for Coastal Impact Assessments

Future nearshore wave energy converter (WEC) arrays will influence coastal wave and sediment dynamics, yet there are limited numerical methodologies to quantify their possible impacts. A novel coupled WEC-Wave numerical method was developed to quantify these possible influences on the nearshore coastal wave climate. The power performance of an Oscillating Surge Wave Energy Converter (OSWEC) array was simulated to quantify the wave energy dissipation due to the array. The OSWEC’s effect on the local wave climate was quantified by a novel coupling of two numerical models, WEC–Sim and XBeach. WEC–Sim characterizes the power extraction and wave energy transmission across the OSWEC, while XBeach captures the change in wave dynamics due to the WEC and propagates the waves to shore. This novel methodology provides the ability to directly quantify the impact of the effect of a WEC array on the local wave climate. Three case studies were analyzed to quantify the impact of a single WEC on breaking conditions and to quantify the impact of number of WECs and the array spacing on the local nearshore wave climate. Results indicate that when the WEC is placed 1100 m offshore, one WEC will cause a 1% reduction in wave height at the break point (Hsbp). As the WEC is placed further offshore, the change in Hsbp will become even smaller. Although the change in wave height from one WEC is small, WEC arrays magnify the cross–shore extent, area of influence and the magnitude of influence based on the spacing and number of WECs. For arrays with 10 or 15 WECs, the cross–shore extent was on average 200–300 m longer when the WECs were placed one to two WEC widths apart, compared with being spaced three or four widths apart. When the spacing was one WEC width apart (18 m), there was a 30% greater spatial impact on the nearshore region than arrays spaced three or four widths apart. The trend for the average transmission coefficient is within 5% for a 5, 10 or 15 WEC array, with a cumulative average of 78% transmission across all conditions.

Internal Bore Evolution across the Shelf near Pt. Sal, California, Interpreted as a Gravity Current

AbstractOff the central California coast near Pt. Sal, a large-amplitude internal bore was observed for 20 h over 10 km cross shore, or 100–10-m water depth (D), and 30 km along coast by remote sensing, 39 in situ moorings, ship surveys, and drifters. The bore is associated with steep isotherm displacements representing a significant fraction of D. Observations were used to estimate bore arrival time tB, thickness h, and bore and nonbore (ambient) temperature difference ΔT, leading to reduced gravity g′. Bore speeds c, estimated from mapped tB, varied from 0.25 to 0.1 m s−1 from D = 50 to 10 m. The h varied from 5 to 35 m, generally decreased with D, and varied regionally along isobath. The bore ΔT varied from 0.75° to 2.15°C. Bore evolution was interpreted from the perspective of a two-layer gravity current. Gravity current speeds U, estimated from the local bore h and g′, compared well to observed bore speeds throughout its cross-shore propagation. Linear internal wave speeds based on various stratification estimates result in larger errors. On average bore thickness h = D/2, with regional variation, suggesting energy saturation. From 50- to 10-m depths, observed bore speeds compared well to saturated gravity current speeds and energetics that depend only on water depth and shelf-wide mean g′. This suggests that this internal bore is the internal wave analog to a saturated surfzone surface gravity bore. Along-coast variations in prebore stratification explain variations in bore properties. Near Pt. Sal, bore Doppler shifting by barotropic currents is observed.

Morphodynamic study of sandy beaches in a tropical tidal inlet using RPAS

This study analyzed the seasonal variation of sedimentary reservoirs in sandy beaches located at the insular margin of a tidal inlet (Itamaracá Island, Pernambuco, Brazil). We measured the sedimentary budget and identified the dominant coastal processes (accretion or erosion) from Dec/2017 to Dec/2018. In six field campaigns by a Remotely Piloted Aircraft System, digital terrain models and extracted cross shore profiles were obtained which allowed for the quantification of beach morphology variability by variations in sedimentary volume. The following three sectors were classified and analyzed according to their location and coastal alignment in relation to the tidal inlet: internal (O–L), intermediate (SW–NE), and external (SN) sectors. ERA Interim reanalysis data were used to evaluate the regional standards of ocean surface waves and wind, showing predominance of southeast (109° and 124°, respectively) and wave power with average peaks of 46.5–51.8 kW/m (dry season) and 57–65.3 kW/m (rainy season). Sedimentary gain took place between Apr–Jul/2018, with Sep–Dec/2018 being the period of greatest loss. The internal sector showed positive sedimentary budget (+704.52 m3) with the prevalence of the accretion process, while both intermediate and external sectors lost about 5009 and 14,110 m3, respectively, with the erosive process prevailing at the end of the studied period.

Validation and analysis of a 1-D variational assimilation scheme for bathymetry inversion

Results are presented from a variational data assimilation and nearshore bathymetry inversion scheme based on depth and wave-phase averaged surfzone hydrodynamics for a narrow-banded wave spectrum. 1-D Cross shore bathymetry is inverted based on 17-min-averaged significant wave height and longshore current observations made during the Duck94 field experiment. An inversion scenario is considered in which inversion is carried out separately for each 17-min-averaged set of observations. Results are used to quantify the inversion scheme's accuracy depending on time dependent wave and bathymetry conditions. The model generally produced a root-mean-square error of 0.46 m between modelled and actual bathymetry when both wave height observations and alongshore current observations were assimilated. The RMS error reduced to 0.44 m when only wave height observations were assimilated and increased to 0.69 m when only alongshore current observations were assimilated, suggesting that wave height is a more informative variable for bathymetry inversion. The model performed consistently in inverting bathymetry and thereby tracking morphologic change in varied wave conditions, including during large storm events.

CROSS-SHORE MODEL APPLICATION TO HASAKI BEACH, JAPAN: EVALUATION OF PARAMETER SETTING

Japan's coasts is being suffered by significant erosion. There is already a high demand to protect coasts from the erosion but climate change threatens further erosion. Udo and Takeda (2017) projected future beach loss in Japan due to sea-level rise using Bruun rule. However, its restrictive assumption that they probably do not exist in nature makes difficult to assess uncertainties of the projection results. In this paper, Cross-shore (CS) model developed by Larson et al. (2016), which is more realistic model considering the cross-shore sediment exchange, is applied to calibrate the parameter settings at Hasaki beach in Japan, and model applicability was evaluated.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/sOFr9Jb5a_s

Bore collapse and wave run-up on a sandy beach

Wave run-up on beaches and coastal structures is initiated and driven by collapsing incident bores, this process is often considered to define the seaward limit of the swash zone. It is hence a key feature in nearshore wave processes as extreme run-up can lead to structure overtopping and coastal inundation during storm conditions. In addition, the turbulent nature of incident bores and their collapse suspends and advects sediment, resulting in a highly morphologically dynamic swash zone. The cross shore bore collapse location varies from wave to wave and the process is very limited in both spatial and temporal extent, making direct measurement problematic. This paper presents high spatial-temporal resolution LiDAR field measurements of the evolving free-surface in the surf and swash zone which enable the bore collapse detection for 166 waves. These measurements are used to investigate the link between broken wave properties at bore collapse and wave run-up. Incident bores are identified at the seaward boundary of the LiDAR profiles and tracked through the inner surf and swash zones to the run-up limit. It is found that the vertical run-up height exceeds that which would be expected for a perfect conversion of potential to kinetic energy during bore collapse for 24 % of the bores measured. By returning to an existing ballistic-type model to describe the run-up of individual waves, we show that wave run-up can be divided into three components: the bore collapse, terminal bore celerity and their non-linear interaction. For the present dataset, the contribution of the bore collapse and terminal bore celerity is 26 % and 27 % respectively, while non-linear interactions between the two dominates and account for 47% of the measured run-up. By including the terminal bore celerity, the ability to predict run-up is increased by 30 % with the determination coefficient r increasing from 0.573 to 0.785. Likewise, the RMS-error for the wave run-up shows an approximately 10 % reduction from 0.325 to 0.295 m.

LONG-TERM COASTAL EVOLUTION MODELLING OF LONGSHORE BARS

An extended version of a numerical model introduced by Larson et al. (2013) to simulate long-term cross shore material exchange for the subaqueous portion of the profile has been developed. Efforts have focused on improving the model to better account for beach systems consisting of two bars (inner and outer bar), as well as simulating the feeder response over time of nearshore dredged material bars, intended to function as beach nourishment. The theory for the evolution of a single-bar to a two-bar system was modeled, considering an inner and an outer bar, where the outer bar is of primary interest with the purpose of predicting the behavior of placed dredged material. The cross-shore sediment transport rate is based on the evolution equation for the bar system response to the hydrodynamic forcing by reference to its equilibrium condition, where the change in the bar volume is based on a set of wave criteria, describing the onset of a new breaking zone when the outer bar forms. Empirical formulas are employed for the bar equilibrium volume and for coefficients determining the bar response rate. In this study, a description of the extended model and the results from the model component validation at two different sites in USA (Duck, North Carolina, and Cocoa Beach, Florida) are presented. Duck measurements have detected that some bars form in the nearshore and move all the way offshore (eventually deflating by non-breaking waves). At the same time, it was equally observed that a lot of inner bars formed in shallow water do not move offshore but remain as inner bars all the time. According to this, the developed model considers that the inner bar will not become the outer bar, but material previously dedicated to the inner bar will be available for the outer bar. Overall, the present study demonstrates the potential for using rather simple models, based on the definition of an equilibrium state that is compared to the current state and the magnitude of offshore wave forcing to drive the changes in the profile. The methodology employed here allowed to quantitatively reproduce the main trends in the subaqueous beach profile response in a long-term perspective as a function of the bar volumes disequilibrium, the magnitude of the incident wave height and the dimensionless fall velocity to move the sand with a time varying forcing.

Observations of Time‐Dependent Bedform Transformation in Combined Wave‐Current Flows

AbstractAlthough combined wave‐current flows in the nearshore coastal zone are common, there are few observations of bedform response and inherent geometric scaling in combined flows. Our effort presents observations of bedform dynamics that were strongly influenced by waves, currents, and combined wave‐current flow at two sampling locations separated by 60 m in the cross shore. Observations were collected in 2014 at the Sand Engine mega‐nourishment on the Delfland coast of the Netherlands. The bedforms had wavelengths ranging from 14 cm to over 2 m and transformed shape and orientation within, at times, as little as 20 min and up to 6 hr. The dynamic set of observations was used to evaluate a fully unsteady description of changes in the bedform growth with the sediment transport continuity equation (Exner equation), relating changes in bedform volume to bedload sediment transport. Analysis shows that bedform volume was a function of the integrated transport rate over the bedform development time period. The bedform development time period (time lag of bedform growth/adjustment) is important for estimating changes in bedform volume. Results show that this continuity principle held for wave, current, and combined wave‐current generated bedforms.

The influence of wave groups and wave-swash interactions on sediment transport and bed evolution in the swash zone

Large scale laboratory measurements of sediment dynamics in the swash zone are presented. Two bichromatic wave group conditions were generated, having the same energy content but different wave group period (Tg=15.0 s and 27.7 s). For the shortest wave group, due to bore focusing, the shoreline fluctuates predominantly at the Tg time scale, showing a large runup and the presence of wave–swash interactions with strong momentum exchange. In contrast, for the longer wave groups, the swash excursion is dominated by the individual waves. The uprush generally promotes onshore sediment advection with consequent erosion at the rundown location but accretion close to the runup. On the contrary, the backwash promotes seaward sediment advection and accretion at the rundown location. The presence of repeated wave–swash interactions modifies these patterns slightly. A wave overrunning a previous uprush promotes a reduction in onshore sediment advection while weak wave–backwash interactions reduce seaward advection. Consequently, the measured sediment dynamics shows stronger intra–swash cross–shore sediment advection for the swash events produced by the short wave groups. Measurements of the sheet flow layer near the shoreline show that for the shortest wave groups the vertical structure of the concentration is influenced by horizontal advection, leading to large sheet-flow layer thickness. However, for the longer wave groups, the local vertical exchange of sediment in the sheet–flow layer is dominant, with the presence of a pick–up and mirroring upper layer similar to oscillatory sheet–flow measurements. These results reaffirm the important effects of the wave group structure and the wave–swash interactions on the swash zone sediment dynamics and beach face evolution.

Laboratory Study on Cross Shore Sediment Budget over Submerged Breakwaters

The objective of this study is to understand the characteristics of the cross-shore sediment transport over the submerged breakwater through quantitative observations of wave breaking, undertow, and the characteristics of near bottom velocity profiles such as skewness, asymmetry around the permeable or impermeable submerged breakwaters. A series of laboratory experiments were conducted in a 2D wave flume with uniformly sloping 1/20 movable bed of uniform sand grains (D50 =0.15 mm). Either permeable or impermeable breakwaters was installed and four regular incident wave conditions were selected so that generated waves cover both daily or stormy wave conditions. Boundary detection technique was used to obtain the temporal and spatial variation of bed profile and then to calculate cross shore sediment transport rate, CTR, from the images captured by multiple high speed and normal video cameras. Tracer particles were used in the experiment and PIV was applied to capture the velocity field around the submerged breakwater. The experimental results indicate that the impermeable breakwater is generally more effective than the permeable breakwater in terms of the reduction of the seaward CTR over the submerged breakwater but the amount of CTR was very sensitive to the breaking point especially in the case of impermeable breakwater. Increase in acceleration skewness caused low CTR in impermeable breakwater case even with a relatively high wave action on the lee of the breakwater.

Hydrodynamic modeling along the southern tip of India: A special emphasis on Kanyakumari coast

Hydrodynamic models are important to many coastal engineering designs and application, especially addressing sediment and water quality. In this study, MIKE 21 two-dimensional (2D) hydrodynamic model based on the flexible mesh (FM) technique was used to simulate the surface currents forced by tides and winds in Kanyakumari coast. The model results of the tidal level along shore and cross shore currents are agreed well with measured data in Kanyakumari coast. The major components of tides and currents are analyzed by harmonic analysis methods. Root mean square error (RMSE) values for the measured and model tides (0.017 m and 0.079 m) and currents (0.025 m/s and 0.009 m/s) during the northeast (NE) and southwest (SW) monsoon period are calculated. A series of scenario runs for NE and SW monsoon season are used to understand the regional circulation. The model result shows that the Kanyakumari coast is dominated by tides and surface currents flow, which are influenced by the seasonal reversal wind pattern. Flows around this coastal water have been evidenced small scale cyclonic and anti-cyclonic eddies ranged from ∼55 to 120 km in diameter. The cyclonic and anti-cyclonic eddies are mostly appeared in near Kanyakumari and SE coast of Kerala due to local/ remotely generated forces.

Linkages between sediment composition, wave climate and beach profile variability at multiple timescales

The paper analyses, compares and contrasts cross-shore morphodynamic behaviour of four diverse beaches that have very different regional settings, wave climates and sediment characteristics, with the aid of rarely available long term measurements of beach profiles and incident waves. The beaches investigated are Narrabeen Beach, New South Wales, Australia; Milford-on-Sea Beach, Christchurch Bay, UK; Hasaki Coast, Ibaraki Prefecture, Japan; and Joetsu-Ogata Coast, Niigata Prefecture, Japan. A statistical analysis, equilibrium beach profile analysis and Empirical Orthogonal Function analysis are used to investigate, compare and contrast spatial and temporal variability of cross shore beach profiles of the selected beaches at short-, medium- and long-term timescales. All beaches show evidence of multi-timescale morphodynamic change. Narrabeen Beach profile has the highest sensitivity to local weather patterns. Milford-on-Sea, Joetsu-Ogata and Hasaki profiles are sensitive to seasonal variation of the wave climate however, they also show some correlations with regional climate variabilities. The nature of sediment exchange across the profile, which contributes to profile shape change with time, is found to be related to sediment characteristics across the profile. At Milford-on-Sea and Joetsu-Ogata, both of which have composite profiles, sediment exchange between the upper beach and the inter-tidal zone dominates profile change, irrespective of the distinct differences in sediment composition found in the two beaches. On the other hand in Narrabeen and Hasaki where beach sediment comprises medium to find sand, sediment exchange and hence profile change occur mainly in intertidal and subtidal zones.

Simulating cross-shore material exchange at decadal scale. Model application

A model developed to describe long-term cross-shore (CS) exchange of sand and resulting profile evolution at regional scale was employed to simulate the evolution at three different sites. The model consists of modules for calculating dune erosion and overwash, bar-berm material exchange, and dune build-up by wind-blown sand transport, as described in detail in a companion paper (Larson et al., 2016). Selected study sites represent coastal stretches influenced by beach nourishment (Barra in Portugal), overwash and breaching (Macaneta spit in Mozambique), and dune development (Ängelholm in Sweden). The model applications showed overall good performance and the results of the simulations are promising. Due to limitations in data availability in Ängelholm and Macaneta, values on calibration parameters were mainly determined based on previous studies. For Barra, where more field measurements were available, the application showed good agreement between the simulated results and observations. The CS-model proved to be a useful tool to predict long-term evolution of beach-dune systems in a time perspective from years to decades. However, additional efforts should be directed towards improving the schematized model profile so that it can better represent other beach shapes such as a sloping berm or a barrier shape.