Worldwide, coastal regions are pressured due to sea-level rise and the increased likelihood of extreme events. Traditionally, hard engineering techniques were used for shoreline protection. However, due to the negative side effects at adjacent beaches, a switch was made to more sustainable soft solutions, such as nearshore berm nourishments. Although several manuals are available describing the preliminary design of nearshore berm nourishments, most of them are based on expert judgment and not on quantitative predictions, which potentially leads to design flaws and, therefore, to unnecessary costs. To overcome this problem, this research aims to increase the understanding of the development of nearshore berm nourishments in relation with the corresponding shoreline evolution by analyzing a shallow concentrated placement at New Smyrna Beach. It is found that the theoretical Feeder and Leeside effects played an important role in shoreline dynamics. The Feeding effect is characterized by shoreward propagating accretionary waves (SPAWs) while the Leeside effect is depicted by shoreline erosion patters downdrift of the nourishment induced shadow zone. Contrary
to most nearshore berm nourishments, the placement at New Smyrna Beach resulted in a significant increase of 45.000 m2 of the sub-aerial beach. Although not validated in this study, it is hypothesized to be a result of
the high cross-shore density of the nourishment, ¼ 875 m3/m, and shallow placement location of 4-5 meters.

Durban is the third largest city of South-Africa, located in the province of KwaZulu-Natal. The city suffers from severe floods from time to time, finding its cause in both the Indian ocean as well as the Umgeni river. The eThekwini municipality wishes a better insight in the occurrence of these floods and searches for a structural solution to protect the coastline. The eThekwini municipality has models in operation to predict the hydraulic characteristics in the ocean and the river. However, the existing models don’t represent the reality sufficiently, since the interaction between the Indian ocean and the Umgeni river is not modelled properly yet. An analysis on the area of interest has been executed. The conclusion was drawn that the Umgeni river delta was (partly) tide-dominant, meaning that the Indian ocean imposes the downstream water level. Furthermore, the wave climate was observed, as well as a look into present coastal protections. The link between the Indian ocean and the Umgeni river has been modelled using Delft3D. Since the Indian ocean imposes a downstream boundary condition (in terms of a water level) for the Umgeni river, a backwater curve might occur. First, the link is made by extending the Delft3D-model which was present for the Indian ocean only. The model has been extended all the way up to the Inanda dam. The part of the river included in the new model is approximately 32 푘푚 long. When comparing the models output at the river mouth, at the same location as a measurement point, similar behaviour can be observed. The same phase (lag) is observed, contrary to the tidal range. The tidal range in the model differs from reality, but this is due to a lack of calibration in the amplitudes of the different tidal constituents taken into account. Hence, the renewed model seems to work, but more validation still has to be done. This was not possible yet, as there is a lack of measurement stations along the river. Next to an extension of the Delft3D model, a script has been written in Python. This script is based on the empirical fit of Bresse and shows an elegant function. The results from the function in Python and the model in Delft3D are similar in a qualitative and a quantitative way. Both the models show an influence of the Indian Ocean, reaching easily to about 12 푘푚 upstream of the river mouth. This can be explained by the mild bed slope in this part. A structural solution for the flooding on the promenade at the height of North Beach was found in the form of a seawall. The most important design demand is to protect against a high water level of a 200 year return period combined with a 50 year return period wave height. These storm conditions are input for the ocean-river model, which delivers wave characteristics at the beach front, linking the structural design to the ocean-river model. After a pre-selection on design options, a Multi Criteria Analysis is carried out for the remaining eight design options. Grading is done based on criteria, representing the viewpoints of the many stakeholders involved and leading to a highest grading of a seawall in combination with an emergency barrier. Following, the water-retaining height for a vertical wall is determined. Given the the ground level height of the promenade to be 푀푆퐿 + 2.2 푚 and a total water-retaining height of 푀푆퐿 + 2.944 푚 this leads a practical construction height of 0.80 푚. Due to the limited height a reinforced concrete seawall is designed with emergency barriers for the beach entrances. The emergency barriers are designed of pinewood. Additionally, in order the fit properly in the surroundings, an integrated design is added with features like benches, thatch umbrellas and plants to disguise the construction and protect the Golden Mile in style.

To protect the coastal system, nourishment of the coast is nowadays being applied more frequently. Within these coastal systems new elements are often implemented to add value to the design without compromising on the function of the design of the nourishment. One of these possible purposes is the creation of an artificial lagoon. However, to be effectively applied a deeper understanding of the behaviour of these lagoons is required. In 2015 the Hondsbosse Dunes (HD) were realized at the Dutch coast at the former “Hondsbosse en Pettermer Zeewering” near Camperduin, and an artificial lagoon was created for nature and recreation purposes within this design. The lagoon provides a boost for both the beach itself as well as the surrounding region. However, the lagoon’s inlet is not stable and continuous maintenance is needed. The objective of this study is to explore the behaviour and longevity of this artificial lagoon, considering the frequency and moments of closure of the lagoon’s inlet. This is achieved by assessing and studying offshore hydrodynamic conditions, satellite imagery, geographical measurements, dredging activity, and water level measurements inside the lagoon. Whether the lagoon is stable or not depends on the inlet stability. Key factors that affect the inlet stability are the tidal prism and the annual littoral drift. The lagoon at the HD can be characterized as an intermittently closed estuary, which is a water body that become isolated from the open coast for a period of time. This system can be divided in a perched or a non-perched system. A perched system has a high berm that closes of the system, where a non-perched system does not necessarily have a berm but has a lack of channel surface area. To get a better understanding on how local hydrodynamic conditions can cause the lagoon’s closure, the hydrodynamic conditions and available data were analysed. The significant wave height for storm events and the total water level at the shore, which includes the tide, the surge and the runup, are considered for the hydrodynamic conditions. Geographical measurements, satellite imagery and dredging moments are used to achieve a better insight of the system. The lagoon surface area is examined above 2.03 m NAP, to establish the behaviour of the lagoon basin and its inlet in time. The result of the data analysis performed in this thesis suggest that the lagoon surface area does not move spatially in time. However, due to the lack of bathymetric measurements the lagoon could not be studied in further detail. Closure of the system occurs due to its highly dynamic channel, which is supported by an analysis of the cross-sections of the channel area in combinations with satellite imagery. A detailed view on the water level inside the lagoon and the exchange between the open coast resulted in four stages that were indicated visually: 1.Closed stage, resulting in a closed channel. The water level can only increase when the water level at the open coast overflows the berm. It leads to a stepwise increasement of the water level, referred to as a perched system. .Open stage. The channel is open and water exchange is possible with the open coast. The effect of the tide can be observed clearly in the water level of the lagoon. 3.Dredging stage. The water level decreases rapidly from a level above high tide at the open coast, to a value near or below high tide level. Afterwards water exchange with the open coast may occur, but this is not always the case. 4.Episodic event. The water level fluctuates, for which the cause cannot be stated beforehand. It depends among others on the type of system, hydrodynamic conditions and on the shape of the channel. The system is called non-perched when a high-water level overwashes the berm in the channel. It seems that the system is open, but water exchange does not occur and the water level in the lagoon increases Analysis of these stages indicates that the system is closed almost 70% of the time. The system is most often closed between October and April, when the channel is dredged again leading to an open system. An open system occurs after dredging in spring, where the results shows that the water level inside the lagoon follows the tide. The data indicate that the system is open for 10-17% of the time. Storm events highly influence closure of the channel. Although storm events on the North Sea are indicated by a significant wave height larger than 400 cm, the results demonstrate that storm events with a significant wave height of 300 cm provoke closure of the channel. This is the result of the small catchment of the lagoon. These storm events increase in winter periods, whereas summer storms appear two to three times a year. The impression that storm events lead to closure of the channel is therefore confirmed. The results show that the lagoon remains the same over a timespan of three years, which suggests that the frequency of closure and opening is not time dependent. This leads to different dredging strategies that are possible for the near future. To create an open lagoon all year round, dredging frequency needs to increase, as it is implied that storm events lead to closure. This increases the dredging costs. If the preference lies in low dredging costs, the system will be closed during certain periods of the year. Since the lagoon is created for recreation purposes closure during the winter season and dredging during the recreation season is proposed as a strategy. These findings correspond to the currently considered strategy for the HD. The data suggest that artificial lagoons, like the investigated case at the Hondsbosse Dunes, never stay open or open without human intervention. This indicates that active management is needed to keep these lagoons open.

Sandy barriers comprise 12% of coastlines around the world, and most of these barriers enclose tidal bays and lagoons. These systems accommodate human settlements vulnerable to climate change, which offer enough economic, social, and environmental utility to require further research on the impact of climate change and subsequent best management practices.

The present work aims to analyze how climate change impacts the hydrodynamics and morphodynamics of two barrier inlet systems: Katama Bay (United States of America), and the Santa Lucia Estuary (South Africa). The goal is to estimate future changes in forcing variables (e.g., sea level rise, wave climate, river discharge, tides), implement them in process-based models (coupled SWAN and Delft3D), and identify changes in the dynamics of both systems by comparing present and future state simulations.

This thesis develops a replicable and flexible methodology that can be used as a systematic tool to assess the impacts of climate change on the overall dynamics of tidal inlet systems. A novel approach (copula analysis) was used to derive the wave climate implemented in Delft3D, which was then qualitatively validated for both sites. Model results were used to compare changes to inlet stability, inlet geometry, and sediment pathways for present and future hydrodynamic conditions.

Results show that sea level rise is the primary contributor to the overall morphodynamics at both sites, whereas changes in wave direction strongly impact the rate of inlet migration. Other changes (e.g., significant wave height, wave period, and river discharge) play a secondary role in the dynamics of both systems. Comparisons with previous studies suggest that wave direction impacts each system differently. These impacts must be specifically addressed for each tidal inlet, as the results from one site should not be used to determine a general behavior for the assessment of CC impacts in tidal inlet systems.