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Storms and extremely energetic events may significantly impact the form and structure of beaches, and so cause erosive processes and coastal damages. Efficient management actions require an up-to-date and accurate knowledge of beach morphological changes, with the shoreline position being a good indicator of such changes. This work proposes the use of the open-source Shoreline Analysis and Extraction Tool (SAET) software for the definition of satellite-derived shorelines (SDSs) from L8 and Sentinel-2 imagery to reveal the shoreline position changes at the beaches of the Ebro Delta, NE Spain. Spatial-temporal models (STMs) of shoreline changes enable a characterisation of how the beaches responded to the storms of 2020. In conjunction with wave data, STMs enable an analysis of the erosive response to storm events, as well as a monitoring of subsequent beach recovery in the short and medium term (<1 year). Results show how Storm Gloria (January 2020, Hs max = 7.62 m) acted as a disruptive event and shifting point in the shoreline trend. As a response to that storm, major erosive processes occurred along the delta that caused an average shoreline retreat of 47 m. A progressive recovery during the spring and summer was mainly associated with periods of low wave energy. Nevertheless, by the end of the year a complete recovery had been achieved for about half of the coast, while the other half showed an average erosion of more than 10 m when compared to the pre-storm situation. Both the erosive and the recovery processes took place unevenly on different sections of the coast, probably dependent on factors such as the orientation of the beach and the pattern of longitudinal sediment transport along the coast. • Automatic shoreline extraction from Sentinel 2 and Landsat 8 imagery using SAET. • Pre and post-storm characterisation of SDS position in time and space using STMs. • Storm Gloria (January 2020) caused an unprecedented and heterogeneous impact on the Ebro Delta. • Slow recovery occurred in the months following the event conditioned by orientation and wave patterns. • About half of the delta showed a significant shoreline retreat by the end of 2020. [ABSTRACT FROM AUTHOR]

Training walls to improve navigability at river mouths alter natural sediment transport regimes, occasioning morphological changes in the nearby littoral zone. In addition, harbor channels and shorelines are susceptible to on-going changes in global circulation conditions and large-scale engineering interventions. Here we present a process-based modeling approach to determine the relationship between spatial patterns of erosion and deposition, seasonal river discharge, and the geometry of coastal defenses. The study uses the Magdalena River delta as an example, where the redistribution of freshwater and sediments after the construction of the "Tajamar" training wall heralded significant morphological changes in the area. The numerical experiments are used to describe how the erosion and deposition patterns within the estuary and delta of the Magdalena River are linked to the seasonal cycle of the Magdalena River and to the geometry of the hard structures. We demonstrate that the construction of the Tajamar and complementary hard structures would have decreased depositional fluxes in the littoral zone, leading to the observed shoreline retreat and disappearance of an extensive coastal lagoon system. It is shown that an aperture in the training walls may help restore the wetlands without compromising navigability. In addition, projected increases in mean sea level are shown to decrease velocities within the lower estuary, potentially causing increased sedimentation within the channel and more complex conditions for the management of safe navigation over the Magdalena River estuary. • Seawall construction on the Magdalena River, Colombia, resulted in the redistribution of freshwater and sediments. • Numerical experiments provide evidence that shoreline retreat was caused by the altered sedimentation regime. • A diversion system in the training walls may help restore sediment supply to the shorelines without risking navigability. • Sea level rise may increase rates of sedimentation within the estuary. [ABSTRACT FROM AUTHOR]

In this study the numerical model Delft3D is implemented on high-resolution grids to evaluate beach morphological response to groins and submerged breakwaters under sea-breeze conditions. The numerical model is compared with field measurements from three sites on the northern Yucatan coast of Mexico. At these sites, relatively low energy waves with significant wave heights arrive at a steep oblique angle to the coast that drives high sediment transport rates. After calibration of the model, by adjustment of model free parameters, the model results show accurate representations of the diurnal variation of hydrodynamic conditions (wave height and current velocity) driven by the daily sea-breezes. Moreover, the morphodynamic model shows a good representation of the rapid morphological changes, particularly of the accretion pattern caused by a temporary groin and the subsequent recovery following the structure removal. However, erosion patterns at the downdrift areas of structures were not reproduced, owing to the numerical model limitations of simulating swash morphodynamics. Model validation with field observations of the beach response behind submerged breakwaters enabled the model to be used for a parametric study. Following previous work, new equations are developed in the present study that show an improvement for predicting shoreline changes near submerged breakwaters under sea-breeze conditions. Despite the limitations in reproducing downdrift erosion, overall the high-resolution modelling approach satisfactorily simulates the hydrodynamic and the updrift accretion responses to coastal structures on sandy beaches with oblique waves. • Simulations of beach change near groins and submerged breakwaters are performed. • Results are compared to measurements at three sites with high sediment transport rates. • New equations show improved prediction of shoreline change near submerged structures. [ABSTRACT FROM AUTHOR]

Experimental results involving shoreface nourishment scenarios are presented. The experiments are performed at small scale and the effects of nourishment placement and timing in relation to long-term cross-shore profile development are investigated. Four different nourishment scenarios are tested experimentally, with nourishment positioned both in the trough of a pre-developed profile as well as along the bar of the profile. The results demonstrate that under all scenarios the erosion of the shoreline slows relative to the case without nourishment. The two cases where the nourishment was placed along the bar reduced erosion of the shoreline more compared to the two cases with nourishment in the trough onshore of the bar. Compared to past experiments on nourishment presented in the literature, the present experiments were run for a longer duration, and the concepts of equilibrium profile and the development towards such an equilibrium were investigated. Curiously, the experiments showed a reversal of the sediment transport rate from being primarily offshore directed across the entire profile to onshore directed in the inner surf zone region closest to the shoreline. This reversal of transport rate occurred without changing the incoming wave conditions and resulted in deposition at the shoreline. This either questions the existence of equilibrium beach profiles or at the very least shows that the development towards such an equilibrium will not always be monotonic in time. • Shoreface nourishments are performed at model scale investigating the influence of timing and placement on long term profile development. • Placement of nourishment can disturb the cross-shore profile shape over long time. • After long time running with the same wave climate the transport rate changed from offshore directed to onshore directed in the inner surf zone. • The change in sign was related to cessation of wave-breaking and resulted in sand returning to an otherwise eroding beach. [ABSTRACT FROM AUTHOR]

This paper concerns numerical modelling of the impact on the littoral drift and the shoreline from groynes forming a field of equidistant and identical groynes. The most important effect of a groyne on the shoreline morphology is that the littoral drift is blocked completely or partially. A local reduction in the littoral drift around the groyne introduces alongshore gradients in the alongshore sediment transport and sedimentation and erosion around the groyne which will cause re-orientation of the bed contours towards the prevailing wave direction until an equilibrium is reached. A discussion of this mechanism is presented including effects of scales, e.g. the effect of the relative length of the groynes (compared to the width of the surf zone). The model results indicate a strong dependency of the reduction in littoral drift on the initial geometric bypass ratio (Q geo *), which is defined from the groyne length and the littoral transport on the undisturbed coastline; Q geo * is the transport occurring outside the tip of the groynes divided by the total transport. It is found that the sensitivity of the littoral drift to variations in groyne spacing and the angle, of the approaching waves, is inversely proportional to Q geo *. [ABSTRACT FROM AUTHOR]

Nowadays there are numerous computational tools to forecast the evolution of the shoreline position in sandy coast environments. However, few studies have waited for the time horizon of the predictions to actually check the accuracy of the forecasted scenarios. Thus, this work proposed to assess the accuracy of medium-term predictions made with Long-Term Configuration (LTC) and GENEralised model for SImulating Shoreline change (GENESIS) numerical models for the time horizon of 15-year and evaluate the models' performance in forecasting the actual status of a complex sandy coastal stretch in 2018, the targeting year. The projection premises were already presented in Baptista et al. (2014) on which observational data used to calibrate and blind hindcast future scenarios of shoreline development was discussed. The case study focused on an area located downdrift of Poço da Cruz groin, on the northwest Portuguese coast, and considered two beach sectors in accordance with Baptista et al. (2014): sector AC, about 3.5 km long, and sector AB, about 2.4 km long and included in the first one. The whole coastal stretch is composed of sandy beaches, and past trends highlight erosion downdrift of Poço da Cruz groin due to the interruption of sediment transport. A monitoring program performed by the University of Aveiro between 2003 and 2018 (corresponding to the period of simulation presented in Baptista et al., 2014), including six topographic surveys, was considered for comparison with the projections previously made. An additional topographic survey performed in 2018, within COSMO programme, was also considered. Simulations results have proved divergent performances of LTC and GENESIS models, despite the equity of inputs parameters and modelling processes. It is concluded that GENESIS and LTC, considering the typical (TYP) wave climate (randomly generated to represent the typical frequencies of wave height and direction during five years), create an envelope (GENESIS below and LTC above) to the real average results. For TYP, GENESIS underestimates the mean retreat rates up to 23 m in sector AB and up to 23 m in AC; LTC overestimates the retreat up to 33 m in sector AB and up to 13 m in AC. Conversely, observed (OBS) wave climate (shorter characterisation period but maintaining the registered data sequence) projections overestimate the shoreline retreat in both coastal stretches, suggesting that a larger characterisation period should be more important than maintaining the sequence of recorded waves. For OBS, the models overestimate the mean retreat rates in both sectors: GENESIS overestimates up to 90 m in sector AB and up to 51 m in AC; LTC overestimates up to 60 m in AB and up to 60 m in AC. Also, the consideration of the artificial nourishment operations executed during the simulation period leads to better results in the LTC, which was overestimating the erosion rate. This showed that if all man-made interventions could be anticipated, the average retreat in the main sector, AC, would only be up to 5 % different from the projections made by Baptista et al. (2014) with LTC model and TYP wave climate. • Checked accuracy of 15-year forecasts. • Checked performance of LTC and GENESIS shoreline evolution models. • The wave sampling period used in calibration has relevant impact on forecasts made. • LTC and GENESIS create an envelope to the real average retreat surveyed. • Better projections would be achieved if planed interventions were known in advance. [ABSTRACT FROM AUTHOR]

Nearshore submerged structures made of sand-filled geosystems are an interesting use for this type of coastal protection technology. These systems have an advantage over more traditional materials such as concrete units or rock, which is the limited and non-permanent impact on natural coastal processes. On top of that are also some important research achievements and improvements at the level of the materials. However, at more exposed hydraulic conditions under high wave energy its application is still hampered by the lack of knowledge about their performance. This paper describes research results based on a series of laboratory measurements of the hydrodynamic and morphodynamic change produced in the vicinity of submerged nearshore structures. An analysis of the different model outputs produced, with respect to sediment transport, wave reflection and wave-induced pressures, has been made and is discussed throughout the paper. Such a comparative analysis provides insights into the efficiency of each defence scheme in maintaining a beach and in protecting the shoreline. The sand-filled geosystems as nearshore submerged structures proved to be efficient in retarding the offshore movement of sediments and in maintaining the shoreline, even if instabilities due to elements' displacement and local scour have been observed. [ABSTRACT FROM AUTHOR]

Abstract: Indian River Inlet is located at roughly the mid-point of the Atlantic coast of Delaware and connects the ocean to two Delaware inland bays. Jetties constructed in 1940 have maintained the inlet for navigation purposes but have also acted as a barrier to net northerly alongshore sediment transport causing downdrift erosion. A mobile, land-based bypassing system was initiated in 1990 in an effort to counteract this erosion. Beach profile data from 1985 (pre-bypassing) until 2008 are used to investigate the effect of the sand bypassing system on beaches adjacent to the inlet. The downdrift beach experienced horizontal shoreline erosion between 10 and 60m during the pre-bypassing period but accreted 10–20m during the bypassing period. The mean shoreline location on the updrift beach during bypassing is 10–20m landward (erosion) of its position during the pre-bypassing period. Empirical orthogonal function (EOF) amplitudes from analyses performed on mean-removed elevation surfaces during the periods of highest bypassed volume (average of 83% of design rate) showed that the influence of the bypassing system on the downdrift beach extends to about 1500m of the inlet. An EOF analysis showed that different morphologic responses were evident following the initiation of bypass operations. Temporal variations of shoreline and beach morphology were correlated to the temporal variations in bypassing rates on the downdrift beach only. The downdrift beach response was greatest near the inlet for larger bypassing volumes. Correlation in these instances occurred with a roughly 1-year time lag suggesting that the beach quickly redistributes the bypassed sand. EOF amplitude and shoreline response are weakly correlated to bypassed volumes when the system bypassed smaller volumes (average of 56% of design rate) of sand suggesting that there is a minimum bypassing rate, regardless of yearly variability, below which the effect on the downdrift beach is obscured. [Copyright &y& Elsevier]

The response of nourished beaches to sea level rise is investigated experimentally with random waves in a laboratory wave flume (20 m × 1 m × 1 m), following on from a previous investigation of the response of non-nourished beaches (Atkinson et al., 2018). The nourishments are placed on beach profiles previously exposed to sufficient durations of waves to have approached a near-equilibrium state, i.e., with stable shoreline, bars and berms. Nourishment was placed in three different locations: on the berm, within the bar trough, and as a shoreline placement. In the latter case, and following Bruun rule concepts (Bruun, 1962), the volume of sediment placed was estimated a priori to lead to zero recession under the chosen water level rise. The nourished beaches were then exposed again to sufficient durations of waves to reach a near-equilibrium state at the raised water level. The shoreline recession and the mean recession of the profile following a rise in water level are compared for both the nourished and non-nourished beaches, and to theoretical estimates based on Bruun rule concepts and a previously developed Profile Translation Model (PTM). Quantitative agreement is found with the variants of the Bruun Rule that account for nourishment and with the PTM, and the predicted recession is within an order of ±30% of the observed recession. Overall, the PTM provides the best estimate of the recession. The mean recession of the profile is found to be in better agreement with the model predictions than the recession measured at the shoreline, because the latter is affected by changes in profile shape around the still water line. The efficacy of the nourishment was investigated from the reduction in the observed recession. The efficacy depends on how the recession is measured. For the mean recession, highest efficacy was observed when all the nourishment is added into the active profile. Conversely, for the shoreline recession, highest efficacy was observed with the nourishment placed on the upper beach because it prevents additional recession through wave overtopping. • Direct comparison of nourishment and non-nourishment experiments. • Nourishment reduces recession associated with sea level rise. • Nourishment placed further landward reduces chance of loss of sediment offshore. • The effective nourishment volume is important to consider when predicting recession. [ABSTRACT FROM AUTHOR]