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. ... Read more

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. ... Read more

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. ... Read more

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. ... Read more