The Netherlands is a country with a history of human activity along the coast to ensure water safety. In the 1990's a new approach to coastal management was adopted that allowed for more experimentation in the Dutch dunes. Since then a slew of different types of projects have been undertaken, one of which is the construction of foredune blowouts. Foredune blowouts are gaps or indentations in the dunes from which bare sand can erode due to the wind. The motivation for the creation of constructed foredune blowouts can range from wanting to reintroduce gradients back into the landscape to ecological restoration, or water safety.
Over the years different construction methods and designs have been created, however the evaluation of these projects has been difficult in the past due to broadly defined goals and limited monitoring data. The aim of this research is to investigate the potential of constructed foredune blowouts have in achieving water safety and preserving natural values in the Netherlands by modeling constructed foredune blowouts and evaluating the effect of various design aspects.

Insight into the effects of different designs of foredune blowouts is gained through the use of a modeling study that is set up in AeoLiS, a supply-limited aeolian sediment transport model. Different combinations of width, orientation and number of foredune blowouts are simulated in a stretched profile of a section of the Dutch Coast, leading to thirty two simulations. Additionally three alternate methods of implementing foredune blowouts as well as a scenario without a foredune blowout are simulated.

Model results show a pattern of erosion in the intertidal range and deposition along the dunefoot with limited sediment traveling from the beach through the foredune blowout. There is a clear pattern of erosion and deposition along the erosional walls of the foredune blowout and a limited development of a depositional lobe behind the blowout. Simulation of a foredune blowout induced through the removal of top soil and vegetation exhibits similarities with observations in the field.

Constructed foredune blowouts offer a method of creating areas of bare sand which can create space for ecological succession in the vicinity of the blowout. The sand that is removed may also be used to reinforce weaker areas of the dune row. They can offer a diverse looking landscape if that is desirable. However model results do not indicate that constructed foredune blowouts facilitate additional growth of the dunes. The changes in bed level in the model are primarily a redistribution of sediment already situated within the primary dune row.
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The Wadden Sea is a unique and ecologically important coastal region
in the southeastern North Sea, stretching along the coasts of Denmark,
Germany, and the Netherlands. It is known for its vast tidal flats, salt
marshes, and barrier islands, forming a dynamic and constantly changing
landscape, creating rich biodiversity.

The Wadden Sea in the Netherlands is composed of the mainland
coastal areas and the Wadden Islands (such as Texel, Vlieland,
Terschelling, Ameland, and Schiermonnikoog). This area plays a crucial
role in protecting the land and supporting the people who live there. It
serves as a natural defense against storm surges and flooding, supports
local businesses through fishing and tourism, and provides a vital
ecosystem for numerous plant and animal species.

However, infrastructure development in the Wadden Sea area, including
offshore wind farms, shipping routes, and coastal engineering, has
impacted some ecosystems. The development is necessary for economic
growth, such as shipping infrastructure for tourism on the Wadden
Islands and offshore wind energy due to the energy crisis. These
developments will definitely shape the landscape in the coming years.
In the thesis, data on infrastructure and ecology was collected and
analyzed to find conflicts between them and how they affect the
landscape. This research formed the basis for the design phase. Then,
for the territorial scale, three strategies were put forward. Moreover, two
sites are chosen to demonstrate how these strategies can be applied to
site-specific design. Both sites share the idea of preserving and adapting
positive landscape features and restoring the natural process, achieving
minimal intervention. ... Read more

A rise in the global mean temperature induced by climate change is expected to have a large impact on ecosystems in all regions of the world. One of the threats is accelerated sea level rise (SLR). This may induce the loss of intertidal areas in tidal inlet systems. The long-term morphological response of tidal inlet systems can be modelled using reduced complexity model ASMITA (Aggregated Scale Morphological Interaction between Tidal inlets and the Adjacent coast). The ASMITA model simulates morphological development on an aggregated spatial and temporal scale by imposing a morphological equilibrium condition. As such the model is fast, allowing for multiple long-term simulations. The model is physics-based and the parameters can be related to field values.

Currently, salt marshes are not implemented in ASMITA. However, salt marshes could be of importance to the morphological development in tidal inlet systems. Moreover, it is relevant to assess the resilience of the ecologically important salt marshes by themselves. The aim of this research is to implement salt marshes in ASMITA to assess their influence on the rest of the tidal inlet system and to gain insight into the long-term morphological response of salt marshes to accelerated SLR.

Salt marsh development is governed by horizontal and vertical processes. The marsh height increases by capturing mineral sediment and by the accumulation of plant biomass. Autocompaction and deep subsidence lead to a decrease in marsh height. The implementation of salt marshes in ASMITA relies solely on the input of mineral sediment. At the marsh edge, generally, a cyclic behaviour of sedimentation and cliff erosion occurs. Due to the high degree of spatial aggregation, cliff erosion is excluded from the model extension. The governing processes for salt marsh development in the ASMITA model extension are mineral sedimentation, sediment availability and relative SLR.

The spatial and temporal aggregation of governing processes for salt marsh development are included in the aggregated advection-diffusion equation and model parameters for the horizontal & vertical exchange of sediment, and sediment availability. Data analysis on hydrodynamic conditions and salt marsh development was conducted for the derivation and calibration of these model parameters. To verify the salt marsh implementation, three ASMITA models were created. A one-element salt marsh model consisting of only a salt marsh element, and two different multiple elements models, which contain the ebb-tidal delta, channels, tidal flats and salt marshes.

It can be concluded that ASMITA can model the mineral sedimentation on a salt marsh but depicts a large sensitivity to the parameter setting, particularly for the sediment concentration. Based on the chosen parameter configuration, the Oosterkwelder salt marsh is preserved when subjected to SLR rates below 16 mm/year.

The ASMITA salt marsh extension can be employed to obtain an expeditious first impression of long-term morphological salt marsh development. However, due to the lack of incorporation of detailed processes, the model should not be employed for in-depth analyses of salt marsh development. The interaction between the salt marsh element and the remaining tidal inlet system components requires further model improvements.
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For the past 2000 years river training works have been performed on the Dutch rivers. These training works have shaped the river system of today. Another result of the river training works, especially over the last two centuries, is a decrease in biodiversity. To protect the biodiversity some floodplains in the Netherlands have been classified as Natura2000 areas. Construction works on these floodplains are not allowed, unless these measures are a last resort. Also, if this is the case, compensating measures have to be taken elsewhere.

Before 2050 about 1500 kilometres of dikes and 500 sluices and pumping stations need reinforcements. Dike reinforcements could be executed by only adding soil to the dike. Another option is to add structural elements to the dike. A soil-based approach is preferred because there is more experience and a higher level of security of the reliability for a soil-based structure.

One such soil-based approach is a longitudinal mound. A longitudinal mound is a body of soil which is parallel with the dike, with the goal to reduce the wave height at the dike itself. As a result of the wave height reduction the necessary dike crest level will be reduced as well. Therefore, a reinforcement of the dike itself is not needed. The crest of this longitudinal mound is lower than the crest height of the dike. The longitudinal mound will be submerged during design conditions and will act like a submerged wave breaker.

Costs, emissions and construction time could potentially be reduced by using local soil. This local soil can be obtained in two different ways. Firstly, it is possible to use the surplus of soil of another local project for the longitudinal mound. Secondly, the soil for the longitudinal mound could be taken from the floodplain itself.

However, only little is known about the hydrodynamic effects of a longitudinal mound on the floodplain. This thesis research is done to find possible locations for a longitudinal mound, the hydrodynamic effects and the differences between a simple and more complex model of the longitudinal mound. This is done with a multicriteria analysis for the location study and with a conceptual model and a 2D D-Flow FM model for the hydrodynamic effects.

In the multicriteria analysis the studied criteria are the size of the floodplain, structures on the floodplain and inside the dike, the availability of clay on the floodplain, the habitats on the floodplain and the wave height at the dike.

The multicriteria analysis has been performed from the point of view from multiple stakeholders. For all locations a compromise is necessary. Different locations for a longitudinal mound are preferred depending of the point of view of the stakeholders.

In the conceptual model three design parameters for the longitudinal mound are taken into account, the crest height, the crest width and the slope. For each combination of these three parameters the conceptual model calculates the new equilibrium water level and the transmitted wave height from the longitudinal mound towards the dike. The transmitted wave height is calculated with the best empirical fit on multiple datasets by Friebel and Harris in 2003.

With the Van der Meer overtopping formula the freeboard of the dike above the water level can be determined. This is done for the original situation without longitudinal mound and subsequently for the situation with all combinations of the longitudinal mound. From these calculations it can be concluded that the necessary dike crest height decreases when a longitudinal mound is present. However, more soil is needed than for a traditional dike reinforcement.

Also the conceptual model does not include a backwater effect. The water level does not immediately jump to the new equilibrium water level, so the water level increase should be smaller than calculated in the conceptual model. On the other hand, in the conceptual model all waves are assumed to be perpendicular to the dike. If waves are not perpendicular the necessary freeboard is smaller. The absolute dike crest height reduction with a longitudinal mound is therefore smaller for non-perpendicular waves than for perpendicular waves.

The 2D D-Flow FM model has been supplied by Deltares. The grid consists of cells of 20 by 10 square metres on the main river channel and 20 by 20 square metres on the floodplain. To model the longitudinal mound with a higher accuracy the grid on the floodplain has been refined to 5 by 5 square metres. On this refined grid three different variants have been modelled. All variants have a crest height of about half a metre below design water level and their alignment is identical. For Variant 2 a connection of half the longitudinal mound height has been made with the dike. For Variant 3 the same volume of soil needed for the longitudinal mound has been removed from the floodplain by lowering it by 0.3 metres.

There are only small differences between the three variants. Compared to the original situation there was only a difference in the order of millimetres of water level at the main river channel. The main differences are found between the dike and the longitudinal mound. In this area the Bernoulli effect is found, at locations of increased flow velocity lower water levels are found and vice versa. The subsequent difference in water level is about 5 to 10 centimetres.

The flow velocity depends on the difference of flow area in longitudinal direction between the longitudinal mound and the dike, following the Bernoulli principle. So, the main contributor to the water level change on the floodplain is the alignment of the longitudinal mound. Therefore, the alignment of the longitudinal mound is an important design parameter and can be used to find a trade-off between increased water levels and increased flow velocity.

As this process is not incorporated in the current version of the conceptual model the results between the conceptual model and the 2D D-Flow FM model are different. Therefore, it is recommended that the water levels between the longitudinal mound and dike are calculated separately in the conceptual model. To do this the area between the dike and longitudinal mound can be split into multiple segments. With energy and momentum balances the water levels in these segments can be calculated.

It is also recommended that the 2D D-Flow FM model is used at a smaller floodplain as well to see if the effect on the main river channel is similarly small. Next, it could be helpful to try different alignments for the longitudinal mound to see how these influence the water levels and flow velocities.

Finally, in this research only the flow has been modelled in 2D. However, the wave reduction is also of importance. The next step is to add a wave model to the 2D model to as well. With this addition it would be possible to make the comparison between the wave height reduction in the conceptual model relative to a 2D model as well as for the water level.
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Nature-based Solutions (NbS) have recently gained more interest in hydraulic engineering. It is based on the concept of using forces of nature rather than working against them. In addition, it focuses on using natural processes to fulfil co-benefits for the parties involved.
One of the parties involved is nature. However, a quantitative analysis of ecological development is necessary to determine possible co-benefits for nature. This is still found challenging due to the dependency on many variables, the difference in spatial and temporal scales, the limitations in available information, and the non-linearity.

Ecological development can be expressed with ecotopes, linking geomorphological and hydrological characteristics to abiotic characteristics. A Dutch Ecotope System for Coastal Waters (ZES.1) is a classification system of Rijkswaterstaat. It is a hierarchical system based on abiotic characteristics that classify ecotopes based on thresholds that are determined by ecological differences.

In this thesis, the Ecotope Map Maker based on Abiotic characteristics (EMMA), is developed. It uses data from a validated hydrodynamic model as input and subsequently maps ecotopes based on the ZES.1. Ecotope labels are composed by combining labels that are given to values of salinity, inundation, flow velocity and substrate composition.

The thresholds are calibrated using an ecotope-map of the Western Scheldt of RWS. This map is based on aerial photographs, laser altimetry, soundings, field measurements, and several models. The performance increased from 63 % to 84.6 % after the calibration. This increase is mainly due to (1) differences in the underlying data and (2) the application of deviating thresholds in the ecotope-map of RWS compared to the ZES.1.

EMMA is developed for the preliminary design stage. How EMMA can be implemented is demonstrated by applying EMMA on an idealised estuary. Different ecotopes and varying acreages of ecotopes are found when the depth of the estuary is modified.

In conclusion, EMMA creates many possibilities for ecotope-maps since it no longer depends on aerial photographs and other real-time data. A translation can be conducted between ecotopes and ecosystem services when a monetary value is preferred, or ecotopes can be broken down into eco-elements, which can subsequently be linked to biodiversity. With EMMA it is possible to predict ecological development, which contributes to the design of NbS. ... Read more

KEY POINTS (I) A biophysical model framework (BMF) for corals is developed in which four environmental factors are included: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. (II) The full feedback loop between corals and their environment forms the core of this model framework, where the morphological development is new and closes the feedback loop. (III) The developed BMF predicts the coral response to environmental input via (mainly) process-based relations within the accuracy of climate projections. (IV)- The BMF supports both the deep reef refugia hypothesis and the turbid reef refugia hypothesis. (V) The BMF contributes to the development of protection and recovery programs and is not site-specific. (VI) The BMF is developed for long-term predictions - in the order of decades to centuries - but runs on daily averages and is therefore applicable for assessing the response of corals on shorter time-scales; such as months to years. SUMMARY The increasing pressure on Earth’s ecosystems due to climate change becomes more and more evident. These pressures are especially visible at coral reefs. Therefore, a good understanding of the biophysical mechanisms controlling these ecosystems is needed, so that accurate predictions of their survival can be made. Such an understanding is also needed to develop efficient recovery and protection programs vital to the maintenance of these ecosystems. Because the research on marine ecosystems is relatively young and the phenomenon of coral bleaching is yet to be fully understood, there is no comprehensive framework in which the complex interactions between corals and their environment are combined. In this study, a biophysical model is developed in which four environmental factors are included in a feedback loop with the coral’s biology: (1) light; (2) hydrodynamics; (3) temperature; and (4) acidity. Literature from multiple disciplines is combined to find the interdependencies between the corals and their environment. These relations include coral growth, coral bleaching, storm damage, and recruitment/recolonization of corals. For the connection with the hydrodynamics, a coupling is made between the biological model developed here and Delft3D-FM. The composed biophysical model is a big leap forward in understanding the world of coral reefs, as it is the first construction of a model framework including four environmental factors in which the hydrodynamics are included in the feedback loop. Furthermore, it creates the ability to assess recovery and protection programs based on the four aforementioned environmental factors; e.g. the susceptibility of coral bleaching can be reduced by increasing the attenuation of light through the water column. Because more environmental factors have a role to play in the coral dynamics, the framework is constructed such that these can be added relatively easily. ... Read more

Bardawil Lagoon is a tidal lagoon situated at the northern coast of the Sinai Peninsula in Egypt. It’s two artificial inlets, Boughaz 1 in the West and Boughaz 2 in the East, provide a connection to the Mediterranean Sea. They enable the water bodies to interact and support fish migration. Currently, regular maintenance dredging works are necessary to keep the two inlets open.
The objective of this thesis is to analyse the effect of interventions applied to the two inlets on the lagoon-sea interaction, with the goal of transforming the present, unstable inlet system towards a stable tidal inlet lagoon by adapting one or both of the present inlets. This study is conducted on three system phases, being Phase 0, Phase 1 and Phase 2. Phase 0 consists of the initial situation without any interventions; Phase 1 contains the effect of adaptations to the Boughaz 1 inlet, and Phase 2 includes adaptations to Boughaz 2 in addition to the changes made in Phase 1. The new design in Phase 1 and Phase 2 consists of a deeper inlet cross-sectional area, the dredging of an approach channel, the addition of a nourishment, and the removal of the present breakwaters. Design elements are processed using a 2D-H Delft3D Flexible Mesh model and analysed under tide-only conditions with and without a prevailing wind climate added. Evaporation effects are included after the model calculations are made. The results are mainly assessed are the interaction with the Mediterranean Sea, the sediment transport character, and the inlet stability according to the Escoffier curve. Moreover, an analysis is made on the flushing of the lagoon and the effect of a prevailing wind pattern on the system. It is clear from both literature and the initial model results of Phase 0 that Bardawil Lagoon currently does not function as a morphologically stable tidal inlet system, as sedimentation occurs in both inlets. The water exchange between the Mediterranean Sea and Bardawil Lagoon is restricted by the inlets, which is indicated by the difference in tidal elevation on both sides of the inlet. Both inlets are positioned near the unstable equilibrium point on the Escoffier curve, indicating possible closure of the inlets in the future. Hence, interventions are required to establish a morphologically stable lagoon inlet system. By applying the proposed designs in Phase 1 and Phase 2, the limitations on the incoming tide shift from the inlets to the inner basin induces friction, thus removing the inlets as limiting factor. Moreover, taking into account both the prevailing winds and high evaporation effects, the total system is classified as having a sediment exporting character after Phase 2. High evaporation rates have a significant importing effect on the sediment transport character of the inlets. However, after Phase 2, these effects are reduced by a factor 3-5 compared to Phase 0, depending on the wind. The new cross-sectional area design also results in both inlets being positioned near the stable equilibrium point on the Escoffier curve after Phase 2, which is supported by the sensitivity analysis. Hence, it is concluded that the proposed adaptations achieve the goal of developing Bardawil Lagoon into a morphologically stable inlet system. The study provides good insight into the effect of system interventions on the morphodynamic stability of the inlets as well as the flow dominance regarding those inlets. It is recommended to construct a validated morphological 3D model which can provide insight in the long term response of the system to those adaptations. ... Read more

Seagrass meadows are essential and valuable to many shallow coastal ecosystems, due to the many important ecosystem services they provide. The interaction of feedbacks between hydrodynamics, sediment dynamics, and eelgrass can be described with a feedback loop. At locations where eelgrass is present, it favours its growth by modifying the local hydrodynamics (both waves and currents) and the sediment transport. Sediment resuspension is reduced by eelgrass presence, the light availability is subsequently increased, and growth is stimulated, i.e. further reducing the sediment resuspension. However, when eelgrass is absent, its growth is adversely affected. Sediment resuspension and, therefore, turbidity is enhanced, the available light is reduced, and eelgrass growth (or invasion) is hindered. Therefore, these systems are vulnerable and prone to external factors that influence the environmental conditions to become adverse. Especially hindered light penetration or changes in water temperature can push the system to an alternative ecological state, i.e. from dense eelgrass cover to a bare sediment state, with a little chance of return. Climate change effects, such as sea level rise, water temperature increase, and increased storminess, can increase these threats to the seagrass ecosystem and are, according to the literature, able to push the ecosystem into the bare seabed state. Because of its vulnerability and valuable benefits, conservation of and prevention of damage to the ecosystem are strongly demanded. To this end, the shallow coastal (eco)system response to possible adverse conditions of a changing environment due to the mentioned climate change effects is assessed in this research. The Rødsand lagoon in Denmark was found to be an ideal study site, as it is characterised as a sheltered, shallow microtidal coastal system that accommodates eelgrass and that has been intact for many years. It is a good example of a thriving eelgrass ecosystem in a temperate climate, and a low-nutrient environment, where anthropogenic influences are limited. The environmental conditions of the study site could be assessed by means of the available literature and the data that was provided. In general, the hydrodynamic conditions are primarily dependent on wind, as this is the main forcing of both flow and waves. The flow- and wave conditions are, in general, relatively calm, which means that only for dynamic (storm) events sediment resuspension is induced. In order to assess the interaction of feedbacks between hydrodynamics, sediment dynamics, and eelgrass, and the impact of climate change effects on the coastal system, a predictive tool in terms of a numerical model that includes these feedbacks was developed. This resulted in the coupled model: an interactive coupling between a physical model and a growth model was established. The physical model, developed as an online coupling of Delft3D-FLOW with Delft3D-WAVE, includes the effects of flow and waves on the sediment entrainment and therefore on the vegetation. The growth model simulates the eelgrass development over time based on the environmental conditions computed by the physical model and the subsequently calculated light climate. The simulated eelgrass development by the growth model was subsequently used as an input for the physical model for the next simulation period. The developed coupled model was used as a predictive and pragmatic tool: simulations comprising idealised singular climate change effects of relative sea level rise, water temperature increase, and increased storminess were performed. The results of the coupled model and the provided data of DHI showed the same behaviour in terms of eelgrass development, hydrodynamic conditions, and sediment transport at most locations, except in the deepest depth zone (4-6 m). This indicates that the general performance of the coupled model is adequate. The environmental conditions in the coupled model are apparently more benign than in the model of DHI, i.e. more beneficial for the eelgrass growth, as the eelgrass biomass was far higher at the shallow depths than that the data of DHI showed. Two reasons can be given for these more beneficial conditions: 1) the sediment import from the offshore boundary and spreading into the domain is underestimated, resulting in more beneficial light conditions at the bottom and 2) the model only takes into account the forcings and, therefore, the hydrodynamic processes in the direction of the transect, whereas processes (related to hydrodynamics and sediment transport) acting perpendicular to the transect are omitted. The results showed the impact of these climate change effects on the coastal system, especially on the eelgrass development. Decreased growth could be observed for all simulated climate change effects compared to the results of the baseline case with dense eelgrass cover. As the eelgrass at the deepest locations is the closest to its light-/depth-limit, it was found to be more susceptible to changes in the environment than eelgrass at shallower locations, leading to increased decay at larger depths. However, no indication or no clearly defined threshold of the system shifting to the alternate and undesired bare state due to the studied climate change forcings, i.e. relative sea level rise, water temperature increase, and increased storminess, could be derived for this specific study site. This means that a large-scale die-off of eelgrass in a shallow microtidal coastal system such as the Rødsand lagoon is unlikely to happen due to the studied forcings. ... Read more

Bed roughness is an important parameter for the prediction of sediment transport as well as calculating flow conditions near the bed. Numerical models are extensively used to make these predictions. In these models it is fundamental to have proper values for bed roughness. The bed roughness is being estimated using a dataset from an ongoing pilot project in the Dutch western Wadden Sea. This dataset consists of 40 days of velocity measurements using ADV (8 Hz) and ADCP (1 Hz) instruments and concentration of SPM measurements using OBS instruments.
To estimate the bed roughness, the dataset is analyzed using four methods for calculating the bed shear stress. The logarithmic profile, turbulent kinetic energy, vertical turbulent kinetic energy and the Reynolds stress method.

The data has been processed and averaged per tidal phase, so statistical analysis can be applied to it. From this analysis, it is found that the concentration of SPM increases at 6 cm with increasing wind speed. As a result of this increasing of SPM the bed roughness also increases. This leads to the hypothesis that suspended sediment makes the bed rougher, and is not primarily governed by horizontal advection but also local resuspension.
A 1DV numerical model is used in which horizontal advection is excluded to test this hypothesis.

Simulations are performed with stationary boundary conditions, using combinations of water depth (0.2 to 2.8 m) and velocities (5 cm/s to 70 cm/s). These simulations are imposed with an initial homogeneous concentration. For every combination, the concentration is increased gradually until the concentration profile becomes L-shaped.

Besides simulations with stationary conditions, timeseries of water depth and velocity are used to simulate one tidal cycle.
All simulations performed with this numerical model do not take wind and waves into account and water-bed exchange is excluded.
From the simulations with stationary boundary conditions the roughness is calculated using the LP method. It is found that bed roughness increases with increasing initial homogeneous concentration.

From the simulation of one tidal cycle, it is found that the roughness increases towards the turn of the tide. After the turning of the tide, the concentration profile becomes L-shaped, and the roughness is decreased. The concentration profile becomes homegeneous again after a certain threshold of velocity and waterdepth and at the same time the roughness increases again. During a tidal cycle, it is possible to have a collapsed concentration profile, which indicates a lower bed roughness and thus a smoother bed. ... Read more

Shallow bays in the Caribbean, like Baie Orientale and Baie de L'Embouchure in Saint Martin, are often sheltered by coral reefs and covered by seagrass meadows. They provide valuable services as tourism and coastal protection. The ecosystems are linked through biological, chemical and physical processes. But they are under pressure due to sea-level rise. The response of one of the ecosystems to climate change could impact the other ecosystem.

In order to predict the impact of sea-level rise on the biogeomorphology in Baie Orientale and Baie de L'Embouchure, the hydrodynamic model Delft3D Flexible Mesh is applied. The effect of seagrass meadows and coral reefs on both flow and waves are captured with this model. In this way, the long term change in average hydrodynamic conditions due to sea-level rise is determined depending on the response of the ecosystems.

A wave-driven circulation is found in both bays with flows of 0.5 m/s over the reefs and currents of 0.2 m/s inside the bays. The hydrodynamic conditions are mainly determined by the reef height. Depending on the response of coral reefs to climate change and the amount of sea-level rise, the wave height inside the bays and the wave-induced currents increase. Under the worst-case scenario, where coral reefs degrade and seagrass meadows die, flow velocities increase by more than 100% in Baie de L'Embouchure and by 200% in Baie Orientale under a sea-level rise of 0.87 m. The significant wave height rises to 300% in Baie Orientale and doubles in Baie de L'Embouchure. But this increase of hydrodynamic stresses is not expected to lead to devastating damage to coral reefs and seagrass meadows. Instead, the response of coral reefs will be determined by changing water temperatures and ocean acidification. A shift in seagrass occurrence due to the changed hydrodynamics is expected.

The long term impact of sea-level rise on the biogeomorphology of Baie de L'Embouchure and Baie Orientale seems to be limited. The ability to mitigate the impact of sea-level rise is shown and the resilience of the ecosystems proved, which is very promising for other shallow Caribbean bays that are threatened by sea-level rise.
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