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.

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.