In response to the escalating coastal erosion at the Weg naar Zee region in Suriname, this study explores the beneficial reuse of dredged sediment from the Suriname River. The integral question is, ”What is the feasibility of the beneficial reuse of dredged sediment through sediment nourishment to rehabilitate the growth of mangrove forest on the Weg naar Zee, Suriname coast?” To address this, literature research provides a basis for understanding imperative areas related to mud coast dynamics, sediment dynamics, mangroves, and the Suriname coastal system. This culminates in a system analysis and develops into a conceptual model of the Suriname River Estuary’s dynamics. Further development of a hydrodynamic numerical Delft 3D model of the Suriname River Estuary system ensues. This analysis forms the foundation for further assessment of potential sediment input locations throughout the estuary. Simulations are utilized to verify the sediment transport mechanisms, primarily focusing on two transport types: initial transport through the water column as suspended particulate matter (SPM), and migration over the bed influenced by wave forcing. These simulations offer valuable data on the impact of timing and placement of sediment input on the transport and deposition process. Employing recent survey data of the Weg naar Zee shoreline’s foreshore, a schematisation was established to ascertain the total infill volume necessary for a convex-up profile favourable for mangrove rehabilitation conditions. The results demonstrate the feasibility of achieving this profile by strategically inputting sediment, hence, capitalising on both transport types in the estuary. The study concludes by reiterating that the strategic placement of sediment nourishments can be a viable means of restoring the Weg naar Zee coastline. Finally, possible subsequent studies to address the existing uncertainties and streamline the implementation strategy are discussed.

The coastline of Demak, Indonesia has been eroded during the last 15 years. To restore the natural coastal protection which existed out of mangroves forest, permeable dams, consisting of bamboo poles with a brushwood filling, have been built to attenuate the waves and facilitate sedimentation behind the dams and thus creating a habitat for mangroves. However these designs required a lot of maintenance, so a new type of design is proposed without a filling of brushwood, containing only vertical bamboo poles. Next to this the possibility to include aquaculture in the design is proposed. Therefore this study assesses the wave transformation by the new designs in Demak, Indonesia with the numerical wave model SWASH. In order to do that first the hydrodynamic conditions are analyzed to obtain the design conditions for the structures, and then SWASH is validated against laboratory experiments to find the right drag coefficient values. The design wave conditions are based on the local water depth, offshore wave heights and periods and local bathymetry. The offshore waves are based on a dataset from WaveWatch III, which compares well with measurements of a local storm event. The dataset of WaveWatch III is filtered and extrapolated to determine the wave conditions for return periods(R) of 1 and 5 years. This resulted in offshore waves with Hm0 = 2.08 and 2.39m, and Tp = 6.9 and 7.5 s respectively. The water level is mainly influenced by the tidal elevation and the surge levels. The surge levels are obtained from a risk assessment of the coast of North Java (Willemsen et al., 2019), which vary between 0.63 to 0.68mfor R = 1 and 5 years respectively. The tidal levels are determined using the water depth measurements of two transects from Van Domburg et al. (2018) and analysed with Matlab tool Utide by Codiga (2011), resulting in a spring tidal range of 85 cm and a neap tidal range of 50 cm.
Four different configurations from the experiments of Jansen (2019) are used to validate SWASH: single row, longitudinal(the spacing in flow direction is longer than the lateral spacing), open uniform and dense uniform configuration. These configurations are modelled in the numerical wave model SWASH by use of the vegetation module. The most influential factors are: the drag coefficient, the way to describe mass conservation and the number of stems(cylinders) per m2. For the drag coefficient the bulk drag coefficient of Gijon Mancheno et al. (2021) is used, which contains factors for sheltering, blockage and the KC state of the flow. For the densely packed configurations the bulk drag coefficient proved to have a better agreement than the drag coefficient of a single cylinder. The sensitivity to the number of stems per m2 is small when implementing the longitudinal configuration as an average amount of stems perm2 or by specifying the individual rows of the configuration and so locally increasing the number of stems. Three methods of describing the mass conservation in SWASH are evaluated: by means of a cross sectional approach that is expressed by the blockage factor in the bulk drag coefficient Gijon Mancheno et al. (2021), by a volumetric approach due to activating the porosity in SWASH which means that the blockage factor cannot be included in the drag coefficient and by a combination of these two. For the longitudinal configuration the best agreement is found the cross sectional approach and for the single row configuration the best agreement is found by the volumetric approach.
Once SWASH is validated, the designs of several structures are investigated. Firstly, a design consisting out of two rows of bamboo poles is considered where the spacing between the rows is varied to find an optimum distance. The transmission rate Et /Ei decreased from 75% to 55% with a spacing sx = 0.42 m to 5.8 m, larger spacings did not result in less transmission. If one wants to be conservative at least three rows are needed to have a lower transmission rate of 50 %. When mussels are considered, the structures have to be placed in deeper water as mussels can only grow between MLWS and 40 cm above the bed. To provide enough space for mussel growth, the poles have to be placed more sparsely. The effect of a larger water depth in combination with a limited pole length and sparse structures is larger than the extra drag and frontal area provided by mussels, especially since they did not cover the whole pole length, and resulted in high transmission rates. It is thus recommended to, or place a high number of rows of mussel poles or place a few rows without mussels followed by poles for mussels. This decision however also depends on benefits that mussel poles may bring and the cost of the materials, therefore a cost/benefit analysis is required.
This thesis found an efficient design that can be used in reducing wave attenuation along muddy coasts without the need of a brushwood filling. Hereby it provides an economically and user friendly alternative with respect to the current design, as it requires less material and maintenance.

Mangroves trap sediment and are the first coastal defence line for many coastal areas. Unfortunately, mangrove coasts worldwide are eroding due to deforestation, exposing local communities to flood hazards. In Demak, Indonesia, a Building with Nature approach was chosen to counteract erosion. Permeable dams were built on the foreshore to attenuate waves and restore the sediment balance. The dams have increased the bed level locally and mangroves expand after construction. A new project called MuMaCo (Mussels as Mangrove facilitators for Coastal defence) is launched to integrate mussel aquaculture into the mangrove rehabilitation project in Demak. Mussels increase the roughness and diameter of the bamboo poles, which could increase their wave attenuation capacity. Moreover, mussel culture gives the local communities an economic incentive to sustain the structures. This thesis describes and quantifies how mussels' growth influences the forces acting on bamboo poles. Small-scale experiments are performed in the wave flume of the Delft University of Technology on a scale of 1:3 and 1:6. Physical models were used for experiments with steady flow and waves. The steady flow experiments cover a range of Reynolds (Re) numbers between 10^3 and 10^4 to seek the drag crisis. Single mussel covered cylinders for both scales are compared to smooth cylinders and cylinders with an equivalent diameter. For the wave experiments, cnoidal waves with Keulegan-Carpenter ($KC$) numbers ranging from 3 to 113 that correspond with measured waves in Demak are chosen. Moreover, only mussel covered cylinders are compared to a smooth cylinder for a scale of 1:6. During the experiments, the flow velocity, force, and surface elevation are measured, and the drag and inertia coefficients are obtained with the help of the Morison equation. The drag coefficient shows a clear relationship with the Reynolds numbers for steady flow. Although the drag coefficients display the same qualitative behavior as in other studies in the literature, the drag coefficients of the smooth cylinder are more than 40 % larger than in the literature. This is probably due to large variations in the offset of the velocity meters (EMS) during the experiments. The large mussels show higher drag coefficients than the smooth cylinder. For the wave experiments, the drag coefficients show good correspondence to other studies in the literature, but the inertia coefficients are a factor two larger than expected for smooth cylinders. Treating the peak and trough of the cnoidal wave as individual sinusoidal waves shows similar results and suggest that cnoidal waves can be represented by KC numbers, as it is done for linear waves. The best fit to the literature values was found by solving the Morison equation with the measured force with the depth-integrated velocity squared and acceleration from the Fenton theory. This suggests that the results of the wave experiments have been uncertain due to inaccuracies in the EMS recordings. This thesis presents a method to schematize mussels for laboratory experiments and provides a qualitative comparison of the forces acting on poles with and without mussels

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.

Mangrove forests, which serve as a natural sea defence, have been degraded by human action during the last decades. To protect and recover these areas, different types of permeable structures consisting of bamboo have been proposed and applied. However, these structures are currently based on engineering judgement, as design rules are not available. The goal of this research is to make a step forward in the design optimization of permeable structures and gain a better understanding of the processes causing the wave dissipation inside the structure. In this study, scale experiments are conducted in the wave flume at Delft University of Technology. An array of aluminum cylinders is used as a schematization of the structure, with an element diameter of 4 cm and a minimum spacing of 2 cm. The tested wave height is 0.13 m,with a water depth of 0.6 m for the first set of experiments. These experiments evaluated wave transformation through a selected number of configurations. The water depth was 0.55 m for the second set, where the velocities and forces were also measured inside the structure. As the applied wave periods are short (T = 1 − 2 s), the tested wave conditions are in the range of small KC-numbers (4 < KC < 13). The first part of this research focuses on effect of different configurations and arrangements on the amount of energy dissipation, by measuring the incoming and reflected wave heights in front of and behind the structure. For the short waves, the horizontal arrangements dissipate more energy, as energy is dissipated by both the vertical and horizontal drag forces. However, the effect diminishes with increasing wave period. Considering the total dissipation and the amount of dissipation per element, the placement of the elements in rows perpendicular to the direction of wave propagation is found to be the most effective. To study the effect of the element diameter on the dissipation, the results are compared with previous research by Haage (2018) on a model with a diameter and spacing of 2 cm. As with the change in diameter also the structure porosity changed, a direct comparison was not possible and a comparison based on a simplified drag coefficient is done. No direct effect of the diameter is observed, as the obtained drag coefficients show the same trend and magnitude when plotted against an adapted Keulegan-Carpenter number (KC∗), which is based on the element spacing instead of diameter. Small KC∗-numbers result in large drag coefficients,which decrease when KC∗ increases. The second part of this research focuses on the processes inside the structure that cause the energy dissipation. A force and velocity sensor are applied at three locations inside the structure in separate experiments, to determine the relation of the force and velocity inside the structure with the undisturbed values. Two methods are applied for the analysis, based on two different principles. Method 1 is based on the assumption of a constant pair of force coefficients and an increase in velocity inside the structure, method 2 is based on the assumption of a constant velocity and an increase in force coefficients inside the structure.By comparing both methods, it is found that an increase in velocity is the most important factor for the increase in drag force, which is the driving factor for the energy dissipation. It is also found that the amplification factor for the velocity is dependent on both the structure porosity and frontal porosity.

Demak is a regency within the province of Central Java, Indonesia, with a mud-mangrove coast bordering the Java Sea. The region is facing a rapid retreat of the coastline, threatening the livelihood of a large part of the population. The main cause of the erosion is the deforestation of the green belt of mangroves. This has disturbed the delicate sediment balance in the area drastically. This MSc thesis was carried out within BioManCO. This is a project of Delft University of Technology and Universitas Diponegoro and aims to develop a bio-morphodynamic model for mangrove-mud coasts. This will eventually be used to identify the conditions under which autonomous reforestation of a sustainable mangrove green belt will take place, restoring the natural coastal protection. Semi-permeable dams are already being implemented to restore the sediment balance in the area. In this approach, however, the existence of a fluid mud layer is neglected. The observation of relatively steep slopes of the interface between mud and water indicates potential mud transport within the mud layer. Such a transport would contribute to the shoreward flux of sediment and thus to the restoration of the coastal profile. If a hybrid dam is implemented, it will block the flow of sediment and might therefore defy its own purpose; attenuating flow and waves in order to capture sediment and restore the eroded coastal profile. The objective of this thesis is to assess wave damping as a driving mechanism for set-up of the fluid mud layer at the coast of Demak and to identify under what conditions such a set-up can exist. Significant attenuation of waves can be achieved by viscous dissipation of wave energy in the mud layer. The set-up of the fluid mud interface is hypothesised to be balancing the wave force resulting from the reduction of wave energy in shoreward direction. To gain insight in the damping of waves and, more generally, in the dynamics of the coastal system of Demak, a field campaign has been carried out. Based on these measurements a SWAN-Mud model has been set up and has been coupled to an idealised model that calculates the equilibrium slope based on modelled wave-damping. The field observations show that the interface level is indeed sloping upwards towards the coast. This slope, however, does not seem to change significantly during the field campaign, indicating that the occurring waves are not able to move the layer. A strong daily variation in wave height and period, dependent on the prevailing wind system, is observed. SWAN-Mud is able to reproduce these measurements convincingly, even with the simple schematisation used in this thesis. The damping of the waves is influenced by the water depth and the wave period, and to a lesser extent by the wave height. It is also strongly dependent on the thickness and viscosity of the mud layer. The use of a fluid mud module to model the dissipation of waves at the coast of Demak is proven to be necessary. The developed conceptual model assumes a balance between the wave force in the mud layer and a pressure gradient due to a set-up of the fluid mud interface. This model shows that waves are able to force positive slopes in shoreward direction. However, for the range of mud parameters, water depths and wave characteristics as measured in Demak, these calculated slopes are too mild in comparison with the observed slopes. The adopted approach neglects the yield stress in the fluid mud layer. This internal strength might be able to balance and thus maintain the observed slopes after first being forced by the waves. Over time, this could lead to a build-up of sediment against the coast which could potentially be colonised and fixated by mangrove species. This build-up has a possible implication for the management of the coastal area of Demak. The hybrid dams might indeed be blocking a restoration mechanism of the mud coast which defies the original purpose of building these dams.

Due to the removal of mangrove forests, coastal zones can suffer from severe erosion. One of the proposed solutions is the construction of permeable structures. This study aims to optimise the design of permeable (brushwood) structures in order to restore the sediment balance and encourage mangrove re-establishment on tropical mud coasts. Preferably wave transmission should be low in order to create a calmer climate behind the structure. In that way sediment is able to settle down, which could lead to a recovery of the mud profile. It is also preferred that reflection by the structure is low. High reflection rates cause scour holes that lead to instability of the structure. Furthermore, scour holes could hinder future mangrove re-establishment. Aiming to achieve low reflection and transmission rates, the dissipation inside the structure has to be as high as possible. Experiments were conducted in the 40 meter wave flume at the Environmental Fluid Mechanics Laboratory at TU Delft. The permeable structure was schematized as an array of cylinders. With the physical scale model various effects could be tested, including the porosity, structure width, arrangement, orientation, etc. The tests were done for 5 different wave cases, from which the wave energy distribution over reflection, dissipation and transmission was determined. The existing brushwood structures require intensive maintenance. This is partly due to the sinking of the material into the soft mud. Also, the brushwood material washes away often as it is lighter than water and difficult to constrain in vertical direction. An alternative design that requires less maintenance would be preferred. Therefore, it was interesting to see whether a comparable amount of wave dissipation could be achieved by using vertical elements only. One important finding is that in more shallow water regions, vertical and horizontal orientations have similar dissipation rates. In water regions that go more towards deep water, the horizontal structures have higher dissipation rates. This can be explained by the relative importance of the horizontal and vertical velocities due to the wave motion. In deep water vertical velocities are relatively high. As the horizontal elements have more exposure to this component in comparison to the vertical elements, they provide more dissipation. In shallow water the relative importance of the vertical velocities is lower, which explains the similar dissipation rates of the two orientations. The analytical model of Dalrymple (1984) was used to describe the energy dissipation through the structures. Drag coefficients were derived by using the calibration method. For KC<15 the drag coefficients start increasing. This is possibly due to the relative importance of the inertia force. Comparing the drag coefficients to the ones derived from direct force and velocity measurements in previous studies showed relative high values. This could be due to an underestimation of the horizontal velocity due to the wave motion. The velocity that is used is the undisturbed velocity in front of the structure. However, the velocity inside the structure might be higher as the flow accelerates in between the gaps of the elements. Furthermore, the wave cases in this research are in the Stokes 2nd and 3rd order region, indicating that the waves cannot be fully described by linear wave theory. The inertia, permeability and non-linear effects among other possible effects are not included in the analytical model of Dalrymple. Therefore, the drag coefficients do not only represent drag forces, but also other processes. To gain more insight on the physical mechanisms that affect the wave energy dissipation, it is recommended to test the same scale model with direct force and velocity measurements.

Deterioration of the ecological quality within the Markermeer, due to the elimination of natural flushing and a resulting increase in turbidity, has created a need to revitalize the region for the benefit of the local wildlife. One major way in which this is being achieved is through the Marker Wadden, designed as a wetland area featuring a combination of islands, marsh-pond areas, mud flats, and sheltered shores which will serve as bird and wildlife spawning area. One of the primary innovations within the Marker Wadden project is the utilization of locally dredged material to form many of the wetland areas. This dredged material −often referred to as mud− is characterized as a soft, cohesive, fine-grained soil material with a mixed sediment composition of clay, silt, fine sand, organic material, water, and often gas (Winterwerp and van Kesteren, 2004). This material has a lot of inherent uncertainties in regards to its behavior and use in construction, stemming from its general non-homogeneity and less predictable/studied behavior. When considering the use of this material to construct areas with specifically designated elevation and strength ranges, the additional strength and settlement effects due to desiccation and crust formation once the material surface has been exposed to atmospheric conditions must be carefully considered. The assessment of this process includes the outlining of a conceptual model emphasizing two distinct stages of desiccation, lab testing to define material behavior during this phase, large-scale testing, and finally an evaluation of an existing numerical model for this process. The conceptual model was then compared and validated in part through both physical, in-situ measurements from a large-scale test setup, as well as to a numerical model developed at Delft University of Technology and further adapted for this process. In addition, the numerical model was utilized as a prediction tool for the Marker Wadden, under various atmospheric conditions and surface water conditions. These effects were evaluated in terms of water content, void ratio, settlement, and strength.

The large-scale test setups −representing three varying degrees of atmospheric conditions and surface water conditions− exhibited similar trends in both the in-situ measurements and modelled results, with increasing levels of active surface water removal and precipitation minimization correlating to increased void ratio profile reduction −and therefore increased desiccation and drying− especially at the surface. However, due to the short-term nature of the large-scale testing, none of the large-scale tests ever reached the second stage of desiccation, and it can be concluded that in the initial stage of desiccation, minimal shear strength development will occur in the surface material. Modelling of variations in surface water conditions show that active removal of surface water promotes faster progression into the second stage of drying, and therefore faster initial development of shear strength. Other significant findings include the long-term stabilization in terms of total additional settlement, and that neither short-term re-submergence of the material surface nor initial seasonal start date will hinder this long-term settlement stabilization. Furthermore, the reality of the large-scale test material, including the presence of increased sand content layers, also highlights the importance of assessing the profile material variation, as deviation between the various in-situ measurement profiles and modelled “uniform” profile results show a high deviation. Modelling of this process is limited to the selection of the proper material input values utilized for the complete profile. During this modelling process, it was determined that the special consideration should be given to how the soil water retention properties are obtained, as well as the hydraulic conductivity relation and values utilized, as small deviations in these inputs impact the model significantly in comparison to other inputs.

Flushing basins have been used at several locations in Germany, Belgium, and the Netherlands in the past centuries to maintain the navigational depths of harbour channels. These locations are not in use anymore or are only partly responsible for channel maintenance. This thesis encompasses a study to optimize the geometric parameters of a flushing basin system in a tidal back barrier basin. The addition of a flushing basin behind a tidal harbour channel is meant to affect the sediment regime in the channel from a flood-dominant towards an ebb-dominant regime. With a one-dimensional model of a schematized reference situation, the role of three parameters: the sluice width, the horizontal area of the flushing basin and the ratio between the tidal amplitude and the channel depth, in the tide-residual sediment transport is investigated for the flushing basin system. Three conditions need to be met simultaneously to create ebb dominance along the total length of the channel: a sufficiently large flushing basin area, a small sluice width, compared to the channel width and a relatively deep channel compared to the tidal amplitude.

The Demak coastal area faces severe erosion problems. The main cause of the erosion of the coastline, which is at some places as high as 1.5 km of land, is the deforestation of the green belt of mangroves for the purpose of building fishponds. This has disturbed the delicate sediment balance in the area drastically. The BioManCO project aims to develop a bio-morphodynamic model for mangrove mudcoasts like the coast of Demak, which will eventually be used to identify the conditions under which restoration of the sediment balance may lead to autonomous reforestation of a sustainable mangrove green belt and thus the natural coastal protection. A measure to restore this sediment balance that is already being implemented in the area is the construction of semi-permeable dams. It is not clear yet however, why some of these dams work as intended and why some do not. In an earlier study a 2DH model has been set up to better understand and optimise the design of these structures using the large-scale morphodynamics of the area. A large obstacle that the development of this model and the BioManCO model faces however, is the scarcity of data in these areas. The flow patterns around these semi-permeable dams have been identified in the model, but cannot yet be verified.
The aim of this thesis is to visualise flow patterns around and the permeability of a selected dam in the field to be able to get a better understanding of the hydrodynamics of the area. As the coastal area of Demak is quite remote, low-tech drifters will be used for this purpose, made only of locally available, inexpensive materials. They will be released at different locations at different moments in the tidal cycle. Data acquisition will take place by visual observation and by a camera attached to a drone. An algorithm will be developed to process the data digitally. It will automatically detect the drifters in the images taken by the drone. Using several Ground Control Points, of which the GPS-coordinates are known, the images can be rectified, so that the relation between the pixels in every image and their location in the real world is known. Using this information and the pixel-coordinates of the detected drifters, the paths of the drifters can be extracted from the images in real-world coordinates. From these paths, flow velocites can be deduced. The permeability of the dam will be assessed by releasing milk into the flow in several configurations during which data will be acquired by means of a GoPro camera mounted above the semi-permeable dam.
The results show, that tide is the main driving force behind the flow patterns around the dam focused
on in this research. During falling tide, a circulation pattern can be seen, which is caused by a combination of the local bathymetry and a wind driven mass transport over the plot. The flow patterns however do not resemble the patterns found in earlier model runs of the area. The cause of this is
thought to be the combination of simplifications in the model and the permeability of the dams, which is not taken into account by the model, but is shown to be influential by the permeability tests. These
tests show that there is definitely mass transport through the dam considered, but also that this may not be universally applicable to all semi-permeable dams in the area, depended on their location. The drifter paths found by the developed algorithm resemble the visual observations convincingly. The found velocities are difficult to interpret, because of the large scatter on the found drifter paths. The scatter is believed to be a result of errors in the rectification process, which should be improved in the future if this technique is to be used more frequently. Also the design of the drifters and the flight plan of the drone should be revisited to increase the detected amount of drifters in the images. All in all, the technique does show great promise to acquire more data in this remote area, but needs further refinement before it can be used for scientific purposes.

This thesis investigates the origins of large sedimentation volumes in the Port of Santos, São Paulo - Brazil. The port is located in the Santos - São Vicente estuarine system, delimited by scarps and subject to intense rainfall. The terminals are placed inside the estuary and their access is provided by a 24 km long channel with mean depths of 15 m DHN, subject to annual maintenance dredging with volumes in the order of 4 Mm³ [CODESP, 2016a].
A literature-based sediment mass balance is formulated for the system. Sediment sources and sinks are assessed based on data of the period 2005 to 2012 and expert judgment. The largest sediment input is given by winter storms (65%) followed by river sediment loads (25%). Up-estuary import of fine sediment is found as a third source, computed from the deficit between sources and sinks (trapping in the mudflats and maintenance dredging).
An explorative process based model is set to evaluate the hypothetical sediment balance and expand the understanding of the system behavior. A period of six months is simulated to capture the expected seasonal variability in salinity gradients. Conditions for fluid mud formation are found in the entire channel. A rerun with salinity switched off promotes an expressive reduction (70%) in the cumulative fine sediment import. Up-estuary sediment transport is found as a result of salinity-induced residual currents, which increase in strength with deeper channels [van Maren et al., 2015].
Fine sediment deposits in the final stretches of the channel that probably have been accounted in previous studies as from river discharges, according to this study are provided from marine sources. Model results suggest an annual import of 1.1 Mton of sediment, six times larger than the literature-based estimate. Additionally, results indicate that little quantity of riverine sediment reaches the channel. The literature mass-balance is therefore modified to incorporate these findings: river contribution is set to 15%, up-estuary transport to 30%, and winter storms to 55%.