Sandy beaches can be found all over the world and are on the interface between the sea and the land. Important functions of beaches are the protection of the inland to the forces of the sea and providing local opportunities in recreation. The impact of storm events on the beach is therefore an important topic of research especially with future climate change predicting more extreme events with the influence of Sea Level Rise expected to result in a worldwide decrease in beach area.The famous Copacabana beach, located at the South-Atlantic ocean is one of the most popular tourist attractions in Rio de Janeiro with thousands of visitors per year. The beach is characterized by its parabolic shape with rocky headlands on either sides. In July 2019 a storm event occurred at the beach with a 7-day period of energetic waves. This resulted in significant erosion along the whole beach up to 40 meters leaving not more than 10 meters of beach width in the South part of the beach. The period of erosion was followed up by a period with year-round average wave conditions resulting in rapid natural recovery with the beach returning to its original beach width within a period of 4 weeks. The focus of this research is on the cycle of erosion with subsequent recover which is important in having a long-term sustainable beach cycle.The history of Copacabana beach is marked by one major nourishment in 1970 which resulted in the 55 meter widening of the beach parallel avenue and an average widening of the beach of 35 meters. From 1970 onwards historically available satellite images show a stable beach behavior with the equilibrium profile of the beach showing smaller beach widths in the South compared to the North. A dataset of high resolution Sentinel 2 is analyzed in terms of beach width for a period of 4 years. This clearly shows the short-term variations in beach width of which most are the result of the impact of storm events. This highlights the impact of the July 2019 storm event showing rapid recovery in terms of beach width.Storm events are characterized by a 2 to 7-day period of energetic swell-dominated waves often from in between the South and SSE. The maximum wave height during the July 2019 storm event was of a yearly return period in combination with an erosional impact which was of lower frequency according to locals. What caused the big erosional impact was the long 7-day duration of the storm in combination with an extraordinary wave direction from the SE. Under this wave direction the South part of the beach is most vulnerable due to a convergence of wave energy as a result of bottom refraction. In combination with a lower equilibrium width in this part of the beach due to the lack of sand placement during the 1970 nourishment this part of the beach is most vulnerable to storm impact. The subsequent beach recovery process shows rapid beach width recovery with recovery rates up to 1.4m/day. This is the result of mild wave steepness due to the swell-dominated wave climate in combination with the equilibrium beach state characterized by an attached sandbar. Both these system characteristics are positively related to the recovery rates (Phillips et al., 2017). However, structural erosion is visible in terms of backbeach elevation in the South part of the beach which as of 16 months after the July 2019 erosion event shows no signs of recovery.To further test the beach vulnerability, the July 2019 storm and subsequent recovery period are modelled subsequentially with the XBeach Surfbeat and- stationary mode. With the use of scenario modelling an attempt is made to test the vulnerability related to wave characteristics, erosion/recovery duration and the frequency of storms. Judgement of the model performance resulted in good model applicability and realistic model results for the erosion simulation. The results confirm the highest impact is in the South part of the beach under a SE wave direction. Besides this, the impact of an increased wave height (resulting in a 21% increase in erosional volume with a 10% increase in wave height) is more significant along the whole beach compared to an increased extreme event duration (resulting in a 9% increase in erosional volume with a 20% longer duration). During periods of recovery the swash zone processes become more important. These processes are not well represented in XBeach. To compensate for these effects the Bermslope model can be used forcing the slope in the swash zone to a pre-defined value (Roelvink & Costas, 2017). The model results however still shows a limited interaction between the beachface and the sub-aquatic part of the beach resulting in accretion further offshore than is observed in reality. From this it is concluded that it is not possible to assess the beach vulnerability in relation to recovery rates with XBeach.The third and last part of this research looks into the future changes in beach vulnerability taking into account the effect of climate change. Local long term climate trends are analyzed with the use of multiple data sources. This results in a clear positive trend showing a future increase of mean wave height. For the other climate parameters like the extreme wave height, storm frequency and wave direction a wide range of trends is found. This often shows both a positive and negative trend among the available data. Within the range of future climate trends there is a clear indication of a future increase in beach vulnerability. Both an increase in the mean wave height as a potential increase in extreme wave heights has significant implications on the erosional quantities judging from the model results. Where a 10% increase in extreme event wave heights results in a 22% increase in erosional quantities according to the model results. With a possible eastward change of mean wave direction chances of SE directed storm events increases resulting in increased beach vulnerability in the South under convergence of wave energy. For Sea Level Rise the impact is relatively highest in the South of the beach with beach decay predictions being approximated at a maximum of 8.4 meters as of 2070 with the use of the Bruun rule (Bruun, 1962). From this it is concluded that the vulnerability of the South part of the beach is bound to increase the most in the future with also taking into account the structural backbeach erosion as a consequence of the July 2019 erosion event. Future interventions with the goal decreasing beach vulnerability should focus on either widening or further protecting the South part of the beach.

About 80-90% of U.S. East Coast barrier beaches have experienced erosion in the last 100 years. South Carolina’s coastline forms no exception, a third of its developed shoreline experiences erosion. Among these eroding shorelines is Hilton Head Island, the second largest barrier island on the U.S. East Coast. Until now, erosion here has been addressed through traditional local beach nourishments. An alternative approach to the traditional nourishment method, are so-called feeder nourishments or feeder beaches. The potential advantages of the feeder nourishment concept over the traditional method are reduction of the nourishment frequency, containment of the ecological stress in a relatively small area, and a short to medium term increase of local available space for recreation and the environment. Given the potential advantages above, the residents of Hilton Head Island asked TU Delft to investigate the possibility of applying a feeder nourishment at their shoreline. Currently, a pilot project known as “The Sand Engine” is examined along the Dutch coast. Several studies into its morphological behaviour show that this feeder nourishment can be beneficial to the sediment budget of a larger coastal cell. Because of the promising results at the Sand Engine pilot project, it is tempting to state that a feeder-nourishment could also be applied at Hilton Head Island. The problem, however, is that the conditions at Hilton Head Island and the Sand Engine are different. There are two main differences between Hilton Head Island and the Sand Engine. First, Hilton Head is subjected to a relative calm wave climate in comparison to the Sand Engine. Second, the presence of two tidal inlets at Hilton Head, compared to a relative straight and uninterrupted coastline at the Sand Engine. As a result, the conclusions drawn from the Sand Engine pilot project do not necessarily hold for Hilton Head Island as well. The main objective of this thesis is to analyse the morphological behaviour of a feeder nourishment located at Hilton Head Island. First, to study its potential as a measure against erosion at Hilton Head. Second, to compare its morphological behaviour to that of the Sand Engine. And third, to be able to examine the potential of the concept for the Atlantic southeast coast of the U.S. in general. The morphological development of a feeder nourishment at Hilton Head Island was simulated with Delft3D over the course of 1 year for different model scenarios, with varying forcing conditions and varying bathymetric features. The effect of the relative calm wave climate at Hilton Head Island in comparison to the Sand Engine is twofold. First, the contribution of wave forcing to the total erosional volume of the feeder nourishment after 1 year is smaller as compared to the Sand Engine. Eliminating all driving forces besides wave forcing reduces the total erosional volume to 58% at Hilton Head, in comparison to 75% at the Sand Engine. Second, the contribution of storm events to the total erosional volume after 1 year from the feeder nourishment is smaller at Hilton Head compared to the Sand Engine. It measures 23% at Hilton Head, in comparison to 60% at the Sand Engine. To assess the impact of the two tidal inlets on the feeder nourishment, they were closed off. Closing of the tidal inlets eliminates any (potential) residual currents. This reduces the total amount of sediment that is eroded from the feeder nourishment by 7% compared to a reference scenario with open tidal inlets. Before construction of the feeder nourishment the coastline south of the nourishment experienced a net sediment outflux of approximately 4000 m3/year. After construction of the feeder nourishment, the southern section experiences a net import of sediment of approximately 100.000 m3/year. Meaning that the southern section, on average, has transitioned from being erosive to accreting. Up to 500 meter away from the nourishment the cross-shore profile shows a seaward movement of the shoreline position of approximately 25 m compared to the original situation without nourishment. Before construction of the feeder nourishment the coastline north of the nourishment experienced a net sediment outflux of approximately 40.000 m3/year. After construction of the feeder nourishment, this net outflux of sediment has decreased to approximately 25.000 m3/year. This shows that the feeder nourishment is feeding sediment to the northern section, but at a rate that is not sufficient to keep up with the underlying erosion rate. The northern domain, on average, still experiences a sediment outflux and stays erosive. Roughly 50 m of coastline directly north of the feeder nourishment experiences a seaward movement of the shoreline position. However, moving further away from the nourishment, the shoreline remains erosive. The Atlantic southeast coast of the United States is made up of North Carolina, South Carolina, Georgia and Florida’s east coast. The South Carolina and Georgia coastline are comparable in both hydrodynamic conditions and geomorphological setting. They are mixed-energy coasts, broken up by numerous tidal inlets, and home to short barrier islands with complex sediment transport patterns. North Carolina’s and Florida’s east coast are wave-dominated, with relative straight shorelines. Which is distinctly differences from the conditions found at Hilton Head Island. Therefore, the potential of the feeder nourishment concept is only analysed for South Carolina’s and Georgia’s coastline. The presence of numerous tidal inlets leads to strongly varying conditions along the coastlines of both states. The developed locations along South Carolina’s coastline that require erosion mitigating measures are south Debidue beach, North Island, Hunting Island and Daufuskie Island. Along Georgia’s coastline there are only some erosion hotspots along Sea Island’s coastline that require erosion mitigation measures. The wave climate at all the above mentioned location is similar to Hilton Head. A southeast swell, with a narrow range of directions and an annual wave height of roughly 1,0 m. The same goes for the tidal range. The results at Hilton Head show that erosion on adjacent coastal sections can be lessened and/or prevented by constructing a feeder nourishment. Given that these locations are subjected to similar conditions, the construction of a feeder nourishment could potentially be an effective measure to prevent or lessen the occurring erosion.

All over the world coastal communities are at risk due to sea-level rise and intensifying weather conditions. Many sandy beaches are eroding as a result of human-induced factors. Currently, the preferred coastal protection measure in the United States are beach nourishments. In Europe, there also is a general shift from hard to soft coastal protection measures. However, beach nourishments are not a long-term solution. Recently, in the Netherlands, a new concept called a large-scale (mega-feeder) nourishment has been introduced (the Sand Engine). Numerous studies on this new concept have been conducted. However, not for a mega-feeder nourishment nearby a tidal inlet system. About 10\% of the world's beaches consist of barrier islands. Emphasizing the importance of investigating the development of a mega-feeder nourishment nearby a tidal inlet system, under various hydrodynamic conditions. Therefore the research question is as follows: “How does a nearby tidal inlet system influence the development of a mega-feeder nourishment?” The research question is answered by investigating the effects various hydrodynamic conditions have on the development of a mega-feeder nourishment nearby a tidal inlet system. This is done for fixed morphodynamic features, such as the dimensions of the tidal basin and the dimensions and orientation of the tidal inlet. The only variable morphodynamic feature is the alongshore position of the mega-feeder nourishment. Four distinct hydrodynamic scenarios are modelled to investigate their effects on a mega-feeder nourishment. The tidal range (η), significant wave height (Hs), peak wave period(Tp) and peak wave direction (Dp) are varied. This resulted in the following hydrodynamic scenarios: 
•Mild wave conditions: (η = 1.5m; Hs=1.0m and Dp=0°);
•Oblique wave conditions: (η = 1.5m; Hs=1.0m and Dp=-45°);
•Storm wave conditions: (η = 1.5m; Hs=variable and Dp=0°);
•High tidal range: (η = 3.0m; Hs=1.0m and Dp=0°).
These hydrodynamic conditions and their effect on a mega-feeder nourishment are modelled by utilizing a process-based numerical model called Delft3D. In Delft3D, two locations of the mega-feeder nourishment per hydrodynamic scenario are evaluated. A mega-feeder nourishment is placed at an alongshore distance of 2 kilometers and 5 kilometers from the tidal inlet. This to get insight in the tidal flow nearby a tidal inlet and up to what alongshore distance this tidal flow affects the development of a mega-feeder nourishment. The hydrodynamic conditions were simplified, meaning steady wave characteristics and a single M2 tidal constituent. Using real time-varying hydrodynamic conditions yields similar results compared to the simplified hydrodynamic conditions. Therefore, simplifying the hydrodynamic conditions is justified. The results show that there will be additional erosion near a tidal inlet if the mega-feeder nourishment is located inside the influence of the tidal inlet. The influence is the alongshore distance where the currents owing to the tidal inlet (residual currents) still affects the total alongshore sediment transport (larger than 50 m³/6y/m). The alongshore distance of the influence increases with an increasing tidal range (tidal prism). However, there is no shoreline retreat owing to the tidal inlet at the location (2km from the tidal inlet) of the mega-feeder nourishment over a time period of 6 years. Only the adjacent coast on the inlet-side of the mega-feeder nourishment erodes significantly more than without a tidal inlet, with an increasing magnitude in the shoreline retreat towards the tidal inlet. Hence, it is expected that if the mega-feeder nourishment is placed close to the tidal inlet (i.e. several hundreds of meters), then the influence of the currents owing to the tidal inlet will enhance the shoreline retreat at the location of a mega-feeder nourishment. To conclude, the tidal inlet does influence the development of a mega-feeder nourishment nearby a tidal inlet (order several hundreds of meters). However, this is not necessarily seen in the retreat of the shoreline but instead in deeper depth contours. The governing process in the sediment transport at a mega-feeder nourishment is the incident wave angle for small tidal ranges (η < 1.5m) and mild wave conditions (Hs > 1m). However, for a large tidal range (η > 3.0m) the residual currents owing to the tidal inlet will become the governing process.

Sand ripples are small (10 cm height) bed forms which occur in the nearshore and surf zone under the impact of both waves and currents. They impact the roughness of the bed used in models of this zone, and contribute to sediment transport. Predictions of their geometry are important to properly model roughness, so correlations between the waves and ripples need to be established. In this project, data about the instantaneous bed level and wave conditions at two point locations in the surf zone was used to analyze the relationship between wave conditions and ripples on the bed. Values for significant wave height, peak period, skewness, ripple height and ripple period were found over bins of 15 minutes in length. It was found that there are relationships between ripple height and wave height, wave skewness and ripple height. These correlations are strongest for a zero shift in the signals, meaning the ripple height can adjust to the wave height and/or skewness within 15 minutes. These results can be used with further research, which includes local current measurements, to make more accurate estimates of the ripple height.

Coastal regions are more and more affected by changes in water levels, storm patterns etc. owing to climate change. Nourishments and other human interventions constitute common practice in order to maintain and secure these areas. However, many aspects, especially the hydrodynamics, are not yet fully understood due to the complexity of the acting processes. This study investigates the evolution of submerged sandmounds under wave, current, and combined flow conditions, and examines the relation between the observed morphodynamic response, and the imposed hydrodynamic forcing. It aims to provide insight towards a better understanding of the hydrodynamics and morphodynamics that will lead to more efficient design, and accurate behaviour prediction of the nourishments. A physical experiment (MODEX) provided a reference dataset of hydrodynamic and morphodynamic measurements (wave height, flow velocity, bathymetry). The extent to which the dataset covers the full spectrumof acting processes was examined via a literature study of the documented mechanisms under wave, current, and combined flow conditions. It was found that the data do not capture slope effects, flow separation, and ripple influence on flow velocity. The analysis of the data resulted in the quantification of the flow types effect on several geometrical aspects (mound height, footprint area and shape, ripple pattern), and the position of the mound. In order to examine the extent to which the measured velocities are responsible for the observed response, sediment transport rates were estimated using an energetics model that depends on total, and orbital velocity. The results provided evidence that the observed response can not be fully explained using mean and orbital velocities. For this reason the study suggests an interpretation of the sediment pathways under the various flow types. Nevertheless these are on based on reasoning, and thus are not considered to be proven. Moreover, the results revealed a relation between aspects of the morphological response and Umax2 (which relates to the instantaneous maximum flow energy). The mound height reduction rate (dHm/dt), and migration rate (dx/dt) scale linearly with Umax2 , while the mound footprint length/width ratio displays an inverse linear relation. Lastly, the relation betweenmound area change rate (dA/dt), and flow energy is linear for non-oscillatory, and combined flow, and a parabolic for oscillatory flow. Finally, despite the limitations and omissions, this study provides significant insight on the evolution of submerged mounds. It is first step in the direction of more accurate prediction of morphological change, and more efficient design of nourishments.