Intertidal flats and salt marshes are critical ecosystems offering significant services but face degradation due to anthropogenic pressures. To mitigate this, restoration efforts like the "Mud Motor" have been introduced, where fine sediments dredged from ports are strategically relocated to nourish intertidal areas and salt marshes. This approach enhances ecological development while reducing maintenance dredging. This dissertation, conducted within the Mud Motor Pilot Project (2016–2017) in the Dutch Western Wadden Sea, investigates the role of wind in the hydro-morphodynamics of intertidal flats, focusing on sediment dynamics and morphological evolution.

Field campaigns across three years (2016–2018) in the Dutch Wadden Sea provided comprehensive datasets on water levels, sediment concentrations, currents, waves, and bed-level changes. Analysis revealed wind's significant influence on hydrodynamics. Opposing winds to tidal currents could reverse tidal flows, especially in higher intertidal zones. A newly developed analytical model validated with field data quantified the nonlinear interactions between wind- and tide-driven flows.

The findings emphasize the pivotal role of wind direction in sediment transport. Low to moderate winds in alignment with tidal residual transport facilitate sediment accumulation in low-energy zones, while short periods of opposing winds resuspend and redistribute this sediment. These wind-driven sediment fluxes critically shape short- and long-term sediment dynamics in systems like the Wadden Sea.

Moreover, the research identifies a "window of opportunity" for tidal flat accretion, driven by temporal sequences of sediment deposition and over-consolidation under favorable wind conditions. Sediment gains sufficient strength to resist erosion only through prolonged drying processes influenced by wind-driven water level set-down.

This study underscores the complexity of wind's impact on intertidal ecosystems, offering insights for restoration projects to better integrate natural processes. By accounting for wind effects, these projects can improve predictions and identify new restoration opportunities.@en

The Sandwindmill system could decarbonize the Dutch coastal protection whilst harmonizing with the building with nature approach. The system consists of a pipeline connecting an offshore borrow location to a nearshore area, where the mined sediment is discharged. The equipment is powered by wind turbines. As long as the wind blows sufficiently, sediment is pumped through the system, leading to a near-continuous nourishment. After the sediment has left the pipes, natural forces should distribute the material. Despite the considerable environmental benefit, one substantial challenge is the financial competitiveness with the traditional hoppers. This research aims to provide insights that can enable the system to be also financially competitive to the hoppers. In the first part, an integral analysis of the Sandwindmill is carried out. The second part of this thesis focuses on the optimization of the dispersion of the nourished sediment.

In the first part, all sub-systems of the Sandwindmill concept are treated separately. Wind data, theoretical formulations, and an exploration of the mining options are used to identify optimization opportunities. From the assessment, it becomes apparent that the interdependency of these sub-systems complicates the cost-optimization. Hence, a competitive system design requires an accurate harmonization of these sub-systems. Three main conclusions are drawn. First of all, the costs per cubic meter decrease with an increasing nourishment volume. Finding the marginal costs is essential in determining the feasibility of the system for certain volumes. Secondly, it is concluded that - given an annual nourishment volume - the pump capacity and windmill size should be attuned. Their cost-optimum is found at a set-up that leads to a yearly operational time of approximately 70%. Lastly, the analysis shows that the application of batteries to support the system in case of lower wind velocities can contribute to a more economical system. This is mainly the case if the system has wave-induced limited operational times.

Due to the costs of the displacement of the pipe outlet and the financial benefits of nourishing large volumes, the second part of the research aims at generating guidelines to designing a dispersive nourishment. Both wave- and tide-dominated systems are a potential field of application for the Sandwindmill. North-Holland is selected as an appropriate case study, containing the Marsdiep tidal inlet and a wave-dominated closed coastal section. A process-based coastal area model is set up to determine the sensitivity of different nourishment strategies on the dispersion at a one-year timescale. A tidal channel wall nourishment at the Marsdiep and a shoreface nourishment at Callantsoog are assessed.

One of the key findings of the second part is that the strong tidal velocities at the Marsdiep inlet are more capable of transporting the nourishment than the conditions at the wave-dominated coast. After one year, the distance travelled by a significant part of the nourished sediment is a factor four higher for the Marsdiep nourishment. Secondly, the research shows that the grain size plays a vital role in the local and regional dispersion. Therefore, the borrowed grain size should be part of the system design. Under the evaluated scenarios, the nourishment application under forcing conditions with a higher transporting potential has a smaller effect in the longer term. This implies that the optimal operational time could be determined solely based on the cost-optimization and should hence be around 70%.

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.

The Port of Rotterdam (PoR), located in the Rhine-Meuse estuary, is subject to sedimentation. In order to keep the port accessible for vessels with high drafts, maintenance dredging works are done. The maintenance dredging over the port area is executed by two parties, PoR itself regarding the harbour basins and Rijkswaterstaat (RWS) regarding the river and waterways.

Since 2013 a substantial increase of the yearly total maintenance dredging volume of the area under control of PoR is observed. The problem of this research is the increase in maintenance dredging volume, from an average of 5.2 mln cubic meters a year (over 2005-2012) to an average of 8.9 mln cubic meters a year (over 2013-2016). By analysis of the administrated maintenance dredging volumes database of PoR it is concluded that the problem is concentrated at Maasvlakte I. Including the maintenance dredging volumes data of RWS results in the conclusion that over the entire port area no occurrence of an increase in maintenance dredging volume is observed. A decrease administrated by RWS at the same period of time is concentrated at the area in front of Maasvlakte I, the harbour basin responsible for the increase in maintenance dredging volume of PoR. These findings lead to the conclusion that not an increase of sedimentation over the port area is responsible for the research problem, but a redistribution of the sedimentation rates from the area in front of Maasvlakte I to Maasvlakte I is.

An analysis of the events that are potentially of influence on the research problem is performed. Based on the correlation of time and potential impact on the hydrodynamics of the water system, the event 'Construction of Maasvlakte II' is selected for an assessment. Two simulations with an extensive hydrodynamic flow model managed by PoR are run. One simulation includes the layout of the Maasvlakte before the construction of Maasvlakte II, the other includes the layout of the Maasvlakte as it is today. Both simulation use exactly the same initial and boundary conditions. With use of the simulations, the impact on the hydrodynamic conditions within the area of interest is assessed. The results show a significant increase of the tidal filling volume of the Maasvlakte harbour basins with a factor of 1.4. This increase is associated with in particular a significant increase of the horizontal flow velocities, and strengthened by a higher horizontal density gradient as a result of higher mixing rates of fresh and saline water at the Maasvlakte. The increase of the horizontal flow velocity is in particular measured in front of Maasvlakte I and in the connection to Maasvlakte I itself. Within the Maasvlakte harbour basin, the velocities are quickly dampened by the large width of the basin.

The results of the assessment correspond accurately with the results of the data analysis. At the area subject to an increase of the horizontal flow velocity, a decrease of the maintenance dredging volume is observed. At the area where an increase in maintenance dredging volume is observed, no to slight changes of the flow velocity are measured. This is explained as follows. The increase of the tidal filling volume by the construction of Maasvlakte II, results in an increase of the horizontal velocities over the entire area connecting the North Sea to the Maasvlakte. Sediments that were able to settle within that connection before are now kept in suspension and transport to the Maasvlakte. The sediments kept in suspension reach the harbour basins where the horizontal flow velocities are quickly dampened by the large width of the basin, enabling the sediments to settle.

It is concluded that the dominant mechanism leading to the increase in maintenance dredging volumes at the Port of Rotterdam is a change in local hydrodynamics by the construction of Maasvlakte II, resulting in a redistribution of the sedimentation rates within CaBe-system. A potential reduction measure in the form of a sediment trap is recommended to improve the current situation, but is unable to bring the hydrodynamics within system back to the situation as before the construction. The research problem is one of the consequences of the construction of Maasvlakte II, and hence partly have to accepted as well. A detailed study to the design of the problem specific sediment trap is required. Other studies that are recommended to improve the understanding of the actual problem regard the used dredging strategy, the exact pattern of sedimentation and the development of the composition of the bed material in the area the problem is concentrated.

This study aims for a better understanding of the sediment pathways in San Francisco South Bay (South Bay). Many issues relevant to the Bay Area community such as shipping, recreational and commercial fishing, habitat restoration, human health, and environmental water quality are reliant on understanding sediment pathways (McKee et al. [2006]). Existing theories suggest that the Sacramento-San Joaquin Delta deliver sediment to South Bay during periods of high river flows. Different hydrodynamic forces, such as the tide, wind and baroclinic flows, redistribute these sediments around South Bay. In this research, trends are analysed using a new set of data (WY2015-WY2017) and sediment pathways in time and space are investigated using a 3D numerical model. In this model, the pathways of three sediment classes with different settling velocities are traced from their source throughout the Bay Area. No such study has yet been undertaken in the South Bay Area. There is a high Delta sediment input to South Bay during periods of high river flow. The local tributaries contribute only marginally to the suspended sediment concentration of South Bay. With a decreasing sediment load from the Delta, the importance of the local tributaries as a sediment source for South Bay could increase. In this research, three different types of sediment exchange between Central Bay and South Bay are observed. The first type is observed during periods of low river flows (Q < 800m3/s). A seaward directed residual flow is found in the channel at Bay Bridge. Sediments are slowly transported out of South Bay. The second type is observed after a period of moderate river flow (Q > 800m3/s). A pulsed sediment flux from the Delta increases the turbidity of Central Bay, resulting in a horizontal spatial variation in SSC from Central Bay to South Bay. The diffusive character of the tide transports the sediments slowly from the turbid Central Bay to the relatively clearer South Bay. The third sediment exchange type is observed after an extreme Delta river flow (QDel ta È 5000m3/s)). The extreme Delta flow refreshes a large part of Central Bay and South Bay. The salinity of Central Bay increases slowly, resulting in a substantially more saline Central Bay than South Bay for a couple of months. The resulting baroclinic flow transports the sediments from Central Bay into South Bay through the landward directed bottom current. Two dominant pathways with opposite transport direction characterise the sediment transport in South Bay. One pathway is located in the channel and is directed southward during periods of high river runoff. The second pathway is located on the extensive east flat and is directed northward during periods of high river runoff. The transport in the channel is dominant during the wet period, resulting in a net transport landward. Besides these two dominant pathways, four re-circulations cells are found, facilitating the exchange between the channel and the shoals. The next step in gaining more insight into the sediment physics is a model studywhich includes bed-interaction with the suspended sediments. A study like this could confirmthe hypotheses opted in this research.