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.

Many sand spits are morphodynamically complex cases that are hard to quantify. Therefore, most case studies on sand spits in a specific type of environment, are descriptive or even non-existent. As is the case for spits in low-energy lake environments, like the two spits at the Marker Wadden islands. Because quantification is necessary for spits in such complex environments, sedimentation was quantified around both spits using polar coordinates and morphologically simplified elevation levels around the spit-platform. It was found that, sediment rich currents that pass over the spit-platform boundary at a certain direction drive spit-platform growth in that direction. The spit-platform growth in turn dictates the growth of the emerged spit. Spit growth quantification enables a detailed understanding of the Marker Wadden spits, which gives insights in spit behaviour in low-energy lake environments. The quantification of spits in other environments could be a powerful tool for the understanding of spit behaviour.

The Noordstrand of the Marker Wadden has been subject to much more erosion than expected. From our current understanding of this low-energy system we cannot explain what has been the cause of this. The goal of this thesis is to create a better understanding of the different processes responsible for the development of this non-equilibrium beach in a low-energy lake environment. A better understanding of the link between hydrodynamic and morphodynamic processes can be used for the maintenance of the existing Marker Wadden beaches and the design of new sandy protections in this kind of systems. By combining the results of a hydrodynamic and morphodynamic data analysis with the results of the Delft3D Marker Wadden model, it is possible to create a conceptual system description. This can be used to improve our understanding of the Noordstrand development and the responsible processes. In this system description the influence of the general Markermeer system cannot be neglected as the different systems (Markermeer, Marker Wadden and Noordstrand) cannot be regarded separately as the different hydrodynamic processes are linked.

Siltation affects navigation in harbors and waterways by reducing the water depth. To regain depth and safeguard navigation, dredging is required. Water Injection Dredging (WID) is one of the available hydrodynamic dredging techniques, in which pumps on a vessel inject water at high flow velocities and low pressure into the bed and fluidize the bed material into a mixture of water and suspended sediment. The fluidized material travels as a turbidity current to deeper areas, driven by natural processes. Sediment transport is then less controlled and the final destination of the dredged material is more difficult to estimate than for other dredging techniques. The passage of a WID-induced turbidity current produces an increase in suspended sediment concentration (SSC) in the water column that increases turbidity. Turbidity increase may have a negative environmental impact. Therefore, to evaluate and mitigate the environmental impact of WID, the increase in SSC should be estimated. Additionally, from an operational perspective, the sedimentation footprint of the turbidity current should be determined. Deltares developed with Boskalis a numerical tool named “Lagrangian 1DV model” (Deltares, 2019). The Lagrangian 1DV model can calculate the thickness and density of the WID-induced turbidity current at a distance from the dredger, as well as the deposition rate. It provides the information to estimate the increase in SSC in the water column and the sedimentation footprint. The tool was defined to be a rapid assessment tool, as it is necessary at the early stages of WID projects when there is usually a limitation of time and available data. Such a tool is useful to analyze different dredging strategies and different solutions to mitigate environmental impact.
As its name indicates, it follows a Lagrangian 1DV (1-Dimensional Vertical) approach. This approach follows the turbidity current in space as it moves away from the dredger. It is an innovative approach that requires less computational effort than a 3D or a 2DV (2-Dimensions in the Vertical plane) approach.
Three main steps were followed by Deltares (2019) for conceptual and mathematical modelling: - Step 1: assume that the turbidity current is a 2DV process, thus neglecting lateral gradients - Step 2: schematize the 2DV process as a Lagrangian 1DV approach. - Step 3: select the 1DV Point Model (Uittenbogaard and Winterwerp, 1997) as the basis to solve velocity and concentration profiles over the vertical. In order to schematize the 2DV process as a Lagrangian 1DV approach (Step 2), two main points were assumed:
- Uniformity of the 1DV Point Model (in the Eulerian frame of reference) was assumed as stationarity in the Lagrangian frame of reference - The Lagrangian velocity was defined as a concentration-weighted velocity over the water column, expressed as the ratio between the mass flux and sediment load.
The validity of these assumptions to estimate sediment transport was analyzed in this report. For that purpose, the Lagrangian 1DV model (Lagrangian 1DV approach) was compared to a 2DV computation in Delft3D-FLOW (called Delft3D model) in four sets of numerical experiments. The validity of the Lagrangian 1DV approach for uniform flow was confirmed with the first set of numerical experiments. Experiment Set 2 showed that the Lagrangian 1DV approach is as valid as the Eulerian 2DV approach to represent sediment transport in non-uniform flow when density differences are negligible. Differences between the Lagrangian 1DV model and the Delft3D model in velocity, concentration and, consequently, in the concentration-weighted velocity (calculated in the Delft3D model as the ratio between mass flux and sediment load), arose in non-uniform flow for the cases in which density differences became significant. The results suggest that the origin of the differences between the Lagrangian 1DV model and the Delft3D model in the concentration-weighted velocity relies on the expression of the advective transport term of the sediment transport equation.
In Experiments Set 3 and Set 4, the numerical models were based on laboratory experiments on turbidity currents by Parker et al. (1987) and van Kessel and Kranenburg (1996), respectively. The baroclinic pressure gradient was higher for these sets experiments. Thus, differences in the baroclinic pressure gradient between the models produced important differences in velocity.
In the case of Experiments Set 3, based on Run 13 of Parker et al. (1987), the concentration-weighted velocity was lower for the Lagrangian 1DV model along the analyzed reach. Experiments Set 4, based on Run 2 of van Kessel and Kranenburg (1996), presented the opposite behavior: a higher value for the concentration-weighted velocity for the Lagrangian 1DV model. A possible explanation for these results was found, based on the variation of the sediment load along the channel in the Delft3D model and the magnitude of the baroclinic pressure gradient. In order to analyze possible implications of the observed differences when the model parameters are in the range of the WID application, the variation of the concentration-weighted velocity was calculated in the Lagrangian 1DV model for a typical case of WID. The trend of the variation along the reach was similar to the case of Experiments Set 3. Then, the results suggest that the estimated concentration-weighted velocity in the Lagrangian 1DV model may be lower than the result for the 2DV approach. As a consequence, the travelling distance of the turbidity current may be shorter. More specific cases can be addressed by comparing the Lagrangian 1DV model and the Delft3D model, following the methodology presented in this report.

All over the world, coastal protection measures are taken, which can be soft (e.g. sand nourishments on sandy beaches) or hard (e.g. seadikes or seawalls). Special care has to be taken to design the transition between these hard and soft flood defences, as they are often vulnerable components of a coastal defence system. This study therefore aims to give more insight into the morphological processes around hard-soft transitions, in order to make recommendations on design and nourishment plans for hard-soft transitions in the future. To this end, the hard-soft transition of Maasvlakte 2 (MV2) was studied. For the case of MV2 the limited knowledge of hard-soft transitions resulted in a conflict of the assessment method of the flood defence and the nourishment strategy according to the client requirements. The most important factors governing the morphological behaviour were studied using different numerical models (UNIBEST-LT/CL , SWAN and XBeach. From the results of the case study of Maasvlakte 2, it was found that the most severe erosion at the hard-soft transition is found during periods with strong southward longshore transports, which causes positive longshore transport gradients at the transition. Cross-shore processes such as storm erosion also indirectly contribute to this by transporting sediment from higher in the profile to lower in the profile. Regarding the influence of wave reflection, preliminary results were found. Using SWAN and UNIBEST, the effect of short waves was investigated, which showed that reflection of short waves is larger at the deeper located part of the hard flood defence. The preliminary results from XBeach showed that bound long wave reflection is larger closer to the hard soft-transition, and that these reflected waves also reach quite far offshore. As regards to the role of the tide, it was found that the dominant northward directed flood tidal current along the soft flood defence strengthens the supply of sediment from south during northward transport. On the other hand, the dominant southward directed ebb current along the hard flood defence hardly picks up any sediment and therefore it does not contribute to the morphological changes at the hard-soft transition.
Some generic observations in the morphological behaviour of MV2 are likely to be found at other hard-soft transitions: - A strong dynamic variability is usually present at the hard-soft transition, in the form of coastline retreat which gives a rotated coastline shape. - The reflection of short waves will likely be larger at the deeper part of the hard flood defence. Closer to the transition zone, where sediment from the soft flood defence is deposited, short wave reflection will be smaller, but long wave reflection will be larger. - In general the highest erosion will be observed in periods with oblique wave incidence where sediment is lost due to longshore sediment transport gradients. Based on these findings, several recommendations are proposed to design a hard-soft transition. Moreover this study presents some other design examples to minimise the nourishment frequency. Finally, recommendations are presented for further research.

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.