The Netherlands faces an urgent need to reinforce its flood defences against rising sea levels. This study investigates the potential of using locally sourced Dutch clays as a sustainable alternative to imported materials for dike reinforcement. A comprehensive experimental campaign was conducted on three types of laboratory-compacted Dutch clays, with clay content varying from 42% to 23% and differing levels of erodibility. Soil characterisation, microstructural analysis (ESEM), and mechanical testing through oedometer and triaxial tests assessed the impact of composition on engineering properties. Results showed that compression behaviour is primarily influenced by the clay content, while shear response, exhibiting both contractive and dilative tendencies, remained consistent across the different compositions. Triaxial tests revealed that samples acted as representative volume elements (RVEs) only up to a certain strain level, beyond which localised deformations occurred due to end-restraint. Additionally, mixing local soils with erosion-resistant materials proved effective in improving the erodibility of unsuitable soils, thereby reducing the quantity of imported material needed. Finally, a new advanced model, JMC-clay bounding surface, was calibrated and validated across the range of soil compositions. The model accurately captured pre-failure and failure behaviour, demonstrating its applicability for predicting geotechnical structure performance and stability.

Over the past decades, the majority of research into coastal development has been carried out with a focus on open-sea beaches. However, sheltered beaches make up a larger part of the coastlines in the world. Recent studies have shown that the system of sheltered beaches cannot be approached as an open-sea beach with a lower wave energy climate. Doing so results in an inaccurate coastline development prediction. Understanding sheltered beaches and their coastline development is vital because the stresses on these beaches worldwide will increase due to climate change.
Due to the lower energetic wave climate, bed ripples are expected more often on sheltered beaches than on open-sea beaches. The possible presence of these is not yet incorporated in current models. Bed ripples can affect the sediment transport along the coast and can therefore have a substantial role in the necessary understanding of the different coastline development of sheltered beaches with respect to other beaches. Fieldwork data from the Prins Hendrikzanddijk was used to research the behavior of ripples on sheltered beaches. The research was divided into three categories: the formation and existence of ripples under varying hydrodynamic conditions, the performance of current ripple prediction formulas, and ripple migration-induced sediment transport.
Ripples were present with varying heights of 0.023 to 0.078 meters and wavelengths of 0.091 to 0.275 meters and the ripple dimensions responded to the changes in forcing on the sheltered beach. The parameter that related the best to the ripple dimensions was a mobility number that used the 98th-percentile wave-orbital velocity and not a current-related velocity part.
Three ripple predictors were used, of which the predictor by O’Donoghue et al. (2006) performed the best. This predictor relates hydrodynamic conditions to a representing ripple height and wavelength, allowing for changing dimensions and varying hydrodynamic forcing. However, this suggests a strong relation between the hydrodynamic conditions and the dimensions of the ripples. Overall, no strong correlation was visible between measured ripple dimensions and the mobility parameter. This supports the usage of the ripple predictor by Van Rijn (2007), which uses a constant ripple height until conditions become too energetic. This approach performs similarly to the best-performing predictor and could be more stable during varying conditions.
Lastly, ripple migration was measured and was shown to be driven by wave skewness and asymmetry. Both on- and offshore migrating ripples were measured. The source of either on- or offshore migration was not identified clearly. However, the offshore migrating ripples were accompanied by lower skewness and smaller asymmetry values than the onshore migrating ripples. The order of magnitude of the induced bedload transport by migrating ripples was of the same order as bedload transport predicted by the model XBeach without the inclusion of the existence of ripples.

In response to the sharp decline of seagrass globally, various restoration techniques have been developed and applied; many at limited scale and with limited success. This research focuses on the fluid mechanics and behaviour of seagrass seeds in a sand mixture through physical laboratory experiments. The objective is to establish a technique that incorporates seagrass seeds with sand-capping to develop seagrass restoration methods suitable for upscaling. Due to the limited amount of available seeds, laboratory experiments were conducted to find a suitable proxy for seeds from both intertidal and subtidal Zostera marina populations by tracking and analysing the particle's terminal settling velocity. The average terminal settling velocity of the seeds was 5.97 cm/s, slightly larger than that of sand particles with a diameter of 0.35 mm with a settling velocity of around 5.2 cm/s. Subsequently, the distribution of proxy seeds in the settled sediment of the "sand-capped layer" was determined after dispersal in five sediment-water mixtures with a volumetric concentration ranging from 5 % to 30 %. Mixtures with three-grain sizes grain sizes were released (d_{50} = 0.175, 0.35, and 0.52 mm) in a column of 1m and subsequently in a column of 1.5 m, where only the top 0.5m had a sediment-water mixture, while the area below consisted of a column of still water. Results show a general trend: seeds segregate to the top of the settled layer, further enhanced by larger grain sizes and higher sediment concentrations. Tests using the lowest concentrations (5-10 %) showed the best result, for which the largest number of proxies were located at an optimal depth (1 cm-5.5 cm) for protection and germination when using medium coarse and fine-sized sand grains. The results provide valuable insights into the dynamics of seed segregation in sediment mixtures and the hindered settling effect of a bimodal mixture, showing that seeds move differently to sand in a mixture, experiencing more rotation and drifting within a mixture not observed when following trajectories in a still water column. The larger seed particles segregated to the top of the settled layer due to the difference in behaviour with the sediment mixture. Even though the terminal velocity of the seeds in a still water column was larger.

The increasing demand for rare minerals, such as lithium, cobalt, and copper, driven by the growth of the world population and the transition towards sustainable energy technologies, has become a pressing concern. These minerals are crucial for electrifying the transportation sector through electric vehicle production and are in high demand for the thriving high technology industry. However, their scarcity and high prices due to supply shortages necessitate alternative sources to meet these demands. In recent years, deep-sea mining has emerged as a promising solution to address the growing need for rare minerals. The vast potential reserves in the ocean floor offer an enticing opportunity for exploration and extraction. However, deep-sea mining comes with its engineering and environmental complexities that require thorough investigation and understanding. This research delves into the experimental study of a Coandă-Effect-Based Collector, aiming to understand its behaviour regarding water entrainment and cohesive sediment erosion. The focus is on understanding the collection mechanism to minimize clay pickup and maintain low clay concentration in the discharged mixture. This is vital in mitigating the impact of deep-sea mining activities on the marine environment. This research provides valuable insights into water entrainment and cohesive sediment erosion in the context of the Coandă-Effect-Based Collector. The findings emphasize the significance of operating parameters and shed light on the complexities of the collection mechanism. Future studies should explore additional data collection to understand the influence of the secondary jet duct better and employ reliable methods for measuring clay concentrations in the discharged water. Overall, these findings have important implications for optimizing collector design and mitigating the environmental impact of nodules mining activities.

Large amounts of oily wastewater which included oil-in-water (O/W) emulsions, also known as produced water (PW), were produced in tandem with the enhanced oil recovery (EOR). Ultrafiltration (UF) was an effective and economic method to separate micron-sized O/W emulsions, while the membrane fouling limited its development. Understanding the fouling phenomena was essential to enhance the efficiency of membrane filtration for oil-water separation, hence this paper investigated the influence of different salinity (1 mM, 20 mM and 100 mM) and types of surfactants on the fouling of the alumina (Al2O3) membrane and the silicon carbide (SiC) deposited membrane filtrating 500 mg/L O/W emulsions with mean droplet sizes of approximately 4 ~ 7 μm, and the UF with the constant flux of 80 LMH and the crossflow velocity of 0.59 m/s was conducted. Sodium dodecyl sulfate (SDS, anionic), alkyl polyglycoside (APG, nonionic), and cetyltrimethylammonium bromide (CTAB, cationic) were chosen in this study due to the frequent use in EOR, and the N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS, zwitterionic) was selected because of its low tendency to foul at high salt concentrations.
Derjaguin-Landau-Verwey-Overbeek (DLVO) and the extended DLVO (XDLVO) models were used to quantify the membrane-oil droplet and deposited oil layer-oil droplet surface interaction. The results showed that the SiC-deposited membrane had less membrane fouling and irreversible fouling resistance compared with the Al2O3 membrane when filtrating O/W emulsions stabilized with SDS, APG or DDAPS. The DLVO model estimated emulsion fouling propensity to rise with increasing salinity when dealing with SDS, APG or DDAPS-stabilized O/W emulsions, while CTAB-stabilized emulsion fouling propensity for the SiC-deposited membrane would decrease with the higher salinity.

Water scarcity and uneven distribution of water resources pose a significant challenge globally. Searching for alternative water resources could alleviate this issue. Municipal sewage reclamation with ceramic NF membrane has gained momentum nowadays. However, the inevitable fouling, especially organic fouling during membrane filtration, is the major limitation of the application. To mitigate the fouling issues and protect the membrane from frequent sodium hypochlorite cleaning, a reaction-based CaCO3 pre-coating method, which could prevent the direct contact of foulant and ceramic NF surface was developed. Acid cleaning was applied to initiate the reaction between CaCO3, which was attached with foulants (sodium alginate) and acid. Lastly, forward flush was implemented to remove the loosened CaCO3 and sodium alginate layers.

The effectiveness of hydrochloric acid cleaning, formic acid cleaning and citric acid cleaning was studied in this paper. Citric acid was found to be the most effective way of cleaning because of the highest permeability recovery rate obtained and the lowest consumption rate of the pre-coating layer. This could be ascribed to the carboxyl groups chelation with calcium ions and the ‘peeled’ chelates adsorbed with more foulants were flushed away. Formic acid was less efficient showing moderate efficiency. Besides, HCl cleaning restored the lowest extent of membrane permeability. Additionally, experiments of increasing the pre-coated CaCO3 amount (7655 mg/m2) to apply for more filtration/acid cleaning cycles were executed. The effectiveness increases in the order of HCl, formic acid and citric acid. The pre-coated membrane cleaned with citric acid could last for the whole six cycles, while the membrane cleaned with HCl only worked in the first three cycles. Lastly, the effect of bubbles generated during the reaction was explored using CaHPO4 as a pre-coating layer. However, the hypothesized positive impact of bubbles was not verified.

Dense suspensions can be found in various industrial and natural processes. A relatively new technique uses the principle of additive manufacturing to produce products from a wide variety of materials by printing with dense suspensions. To reach a high print quality the suspension rheology must be understood very well. Current knowledge about suspension rheology however lacks the capability of predicting the exact behaviour of a predefined suspension, especially for dense suspensions. Direct numerical simulation (DNS) in combination with a second order accurate immersed boundary method (IBM) (Breugem, 2012) can be a useful tool to research suspension rheology. However, currently no numerical results are known for suspensions close to the jamming limit produced with this method.
The current work validates the capability of the IBM to simulate dense suspensions by comparing produced results with existing numerical and experimental data. This is done by simulating a plane Couette flow for a range of particle volume fractions 𝜙=0.2−0.6, all of which are simulated with two friction coefficients (𝜇𝑐=0 and 0.39). Furthermore, the focus is on Stokes flow of neutrally buoyant non-colloidal suspensions with monodisperse spherical particles and the channel height was chosen equal to 13.5 particle diameters. DNS has been used to analyse the suspension rheology in terms of mean concentration profiles, velocity profiles, interactions in the microstructure and particle stress profiles. Steady-state concentration profiles of the simulated cases show a particle layering effect close to the confining walls. This layering effect alters the suspension rheology significantly and for that reason the wall regions are analysed separately from the core region. For both regions the microstructure, the relative viscosity and the normal particle stresses are analysed. The results agree well with existing numerical results (Gallier et al., 2016) (Yeo & Maxey, 2010a). Comparison with experimental work (Dbouk et al., 2013) (Zarraga et al., 2000) shows that results for the relative viscosities of the unlayered core regions are lower in general, reasons for this difference can be higher friction factors or the use of non-spherical particles in experiments. However, the same asymptotic trend is observed for increasing 𝜙. The maximum packing fraction 𝜙𝑚 was found by fitting the relative viscosities to the Marron & Pierce equation (Maron & Pierce, 1956), which gave 𝜙𝑚=0.69 for 𝜇𝑐=0 and 𝜙𝑚=0.635 for 𝜇𝑐=0.39. These results for 𝜙𝑚 are in good agreement with results from (Gallier et al., 2014).
In general the IBM turns out to be capable of reproducing existing numerical data. Furthermore, results have been obtained for suspensions closer to the jamming limit than known so far in numerical work on this particular flow regime. Besides that, the present results are obtained with an advanced soft-sphere collision model, including lubrication corrections for close approach of particles, which has been extensively validated with collision experiments in a previous study. Comparison of the results from this work with experimental data shows larger differences. The reason for this can be that the suspensions in experimental set-ups deviate from the idealized suspension in the simulations. Besides that experimental results differ significantly from each other, indicating that differences also exist between the experimental suspensions. These differences have to be clearly defined in order to make a valuable comparison. Therefore it is currently difficult to determine how accurately the IBM simulates suspension rheology.

Due to the increased demand for materials like cobalt and nickel, there is an interest to mine polymetallic nodules from the deep-sea. These nodules are abundantly distributed along the abyssal plains, e.g., the Clarion Clipperton Zone (CCZ) in the North East Pacific. These nodules lay spread on top of a seabed consisting of very fine clayey sediment and will be collected by a seafloor mining tool (SMT). During the operation, the seabed will be disturbed, resulting in a suspended sediment plume discharged by the SMT. This plume can have a significant environmental impact through a blanketing effect on the abyssal fauna and create a disturbance in the water column affecting the entire food web structure. Hence, identifying the critical processes and quantification of sediment plume dispersion is essential to predict the potential environmental impact better and determine what technologies would enable a lower ecological impact. Spearman et al. (2020) investigated turbidity plumes generated by deep-sea mining experiments and discovered faster settling velocity than the theory described. They hypothesize that this is due to flocculation. The settling speed depends on the density, concentration, shape, and cohesive properties of the sediment. Flocculation in the deep-sea can occur in two ways, by salinity or by organic matter. Gillard et al. (2019) showed that the flocculation response of CCZ sediment strongly depends on the concentration and applied shear rate. To analyze to what extent aggregation could influence the plume dispersion, experiments are conducted in which the effect of aggregation can be adjusted selectively. Lock exchange experiments are used to analyze the impact of aggregation by comparing results with illite based on freshwater, saltwater, pre-existing bed, and added flocculant. Additional experiments with artificial CCZ sediment are done to ensure that the illite experiments are not too idealized. To prove that the settling velocity is increasing in saltwater, settling velocity tests have been performed. I performed experiments with illite suspensions in a settling column. An increase in settling velocity is observed due to the rise in salinity up to 75 g/L of illite. Lock exchange experiments are performed to mimic the particle-driven currents. The lock experiments involve a lock release of a fixed volume suspension of sediment from the mixing section into the outflow section. Similar observations were made by doing lock exchange experiments. A decrease in average head velocity is shown for all experiments up to 75 g/L of illite in saltwater. To further induce flocculation and mimic organic matter in the water column, experiments with flocculant were done. Mixing the flocculant, Zetag 4120 or Zetag 8125, in the mixing section will further decrease average head velocity compared to saltwater. Zetag 4120 even ensures very fast settling as the end of the tank will not be reached For low concentrations in saltwater, flocculation is shown as the tail decreases more rapidly than freshwater. Flocculation with higher mass concentrations of illite is shown when flocculant is added to the mixing section. Adding Zetag 4120 to saltwater makes the current even settle quicker. As the SMT will move over a pre-existing bed, experiments were done to see if a pre-existing clay bed has consequences for the behavior of the flow. A clay bed has been made by running a lock exchange experiment with a concentration of 100g/L. This test then had, depending on the next experiment, one day or two days settling time before it was used for the new experiment. One-day bed experiments overall encountered a decrease in average head velocity. Two-day bed experiments overall experienced an increase in average head velocity. To mimic the existing sediment in the CCZ and determine if illite experiments are not too idealized, experiments were done with artificial CCZ sediment. The currents behaved differently compared to illite, as they produced more coherent flows for low concentration. Also, it showed better effects on lowering the ecological impact when looked at mass concentrations of 100g/L of artificial CCZ sediment as gelling occurred. To minimize the environmental impact created by deep-sea mining, the SMT should produce a discharge between 50 and 100 g/L of artificial CCZ sediment. Gelling will occur, which has a positive effect on minimizing the plume dispersion.

Colloidal particle swarms can show settling velocities over a thousand times as fast as that of a single particle. The transport of colloidal particles is thus strongly affected by the formation and behaviour of these particle swarms, which could have important implications for the widespread use and prevalence of colloidal particles. Swarming effects may for example pose possibilities and limitations to the use of (colloidal) DNA tracers in various systems. Furthermore, contaminant transport in blue-green porous infrastructure may be greatly enhanced due to the rapid settling of swarms of colloidal contaminants, resulting in rapid spreading of contaminants into the environment. To better understand colloidal particle swarms in these systems, this thesis studied the effect of particle concentration on the behaviour of colloidal swarms in varying confining geometries. To this extent, colloidal particles were injected at various concentrations in a macro-model that was suspended in a stagnant water column. The macro-model consisted of three different artificial confining geometries: a smooth fracture, a rough fracture and a pore network. Released swarms were imaged to determine their velocity, width, travelled distance to bifurcation and particle leakage rates from the swarm. In the smooth and rough fracture, the settling velocity of colloidal particle swarms was modelled with the Hadamard & Rybczynski (HR) equation, using the particle leakage rate of the swarm. The average swarm velocity in the pore network was modelled with equations that described the Boycott effect. In both the smooth and rough fracture, the average velocity of the swarm showed a slight decreasing trend with increasing particle concentration. Presumably, this was caused by the linear relationship between particle concentration and width of the swarm. Consequently, wider swarms experienced lower velocities due to increased hydrodynamic drag forces imposed on the swarm. In the pore network, a strong linear relation was found between the average swarm velocity and the particle concentration. A larger mass of the swarm may have been the cause for this. The travelled distance before bifurcation took place did not show a clear relationship with particle concentration. However, in the performed experiments, swarms did bifurcate at a threshold width in both the smooth and rough fracture. This threshold width increased with concentration. The HR model did not fit the swarm velocity in the smooth fracture well, because confining forces of the fracture walls enhanced swarm velocity, which was not accounted for by the HR model. Yet, in the rough fracture the HR model did fit well to the observed swarm velocity since the increased drag forces of wall on the swarm counteracted the confining forces. The effect of particle concentration on the average swarm velocity in the pore network was sufficiently well modelled in terms of the Boycott effect. It was recommended that in future studies laminar flow is introduced to enable better interpretation of results for natural systems. In addition, a more simple pore network geometry provides a more gradual transition to the used complex pore network geometry. This would allow for clearer investigation of swarm behaviour in porous media. Also, more research on swarm behaviour after bifurcation may provide more insight in the longevity of swarm effects. To determine if colloidal particle swarms may occur in natural fractured media, results of this study should be compared to a field study. Both physical and chemical disturbances may severely hinder colloidal swarms. For both fractured and porous media, injection into a natural sample may provide more insight in behaviour in natural systems. It is however unlikely that swarming effects play a big role in urban colloidal contaminant transport in porous media.

To meet energy demand towards a low-carbon future, the global market demand is growing for metals such as cobalt and nickel which are major elements in batteries. Polymetallic nodules, which are formed on abyssal plains at depths ranging from 4 to 6 kilometres and are distributed in high abundance on the top of the seabed, contains several times more cobalt and nickel than the entire global terrestrial reserves. This has raised the interest to exploit these resources from the deep ocean. The seafloor mining tool (SMT) can move along the soft sea bottom and can collect polymetallic nodules. While doing so, it will also entrain sediments and water. The excess of water and sediment entrained is discharged at the back of the SMT, forming a sediment plume. The sediment plume dispersion has strong adverse impacts on deep-sea environment.Thus, it is essential to study the sediment plume behavior in order to limit plume dispersion and thus to reduce its environmental impact.
Experimental research is a powerful technique to study the plume behaviour. However, experiments sometimes take a long time due to complex set-up. In comparision, numerical analysis can save time and costs when solving complex problems. Furthermore, numerical modelling can provide deeper understanding and flexibility for boundary conditions and sediment types, which is applicable on both model and prototype scale. Previous numerical studies have noted the significant role of flocculation in limiting plume dispersion, but flocculation process has not been modelled explicitly. This study aims to establish a numerical model to study flocculation process and its effect on sediment transport.
Previous flocculation-fluid dynamics modelling has applied a Euler-Euler method with additional population balance equations. The disadvantage is that many equations need to be solved. To avoid excessive computational costs, the sediment transport is described by a multiphase drift-flux model in this study. The flocculation process is modelled by a discretized form of population balance equations. The author has found that, by multiplying the particle volume, the population balance can be efficiently incorporated in the phase continuity equations in the drift-flux model. The population dynamics of particle aggregation and breakup can thus be characterized by the phase transition terms in the phase continuity equations. Hence, no additional equation needs to be introduced and solved.
Verification is carried out to check conservation relationships and iterative convergence of numerical results. Then, an initial numerical investigation has shown the results can qualitatively show the three settling stages (i.e., flocculent settling, hindered settling and compression settling) found in the experimental studies. Afterwards, the collision efficiency is calibrated using the settling column tests conducted by Enthoven (2021). The results of calibration show a good fit to the experimental data. Another advantage is that numerical simulations can provide the particle size distribution over time, which is not measured in the experiments.
The major novelty of this study is the coupling of the drift-flux model and the population balance equations, which inherits both the characteristics of population balance and the merits of drift-flux model in reducing computational costs. The flocculation modeling technique as proposed in this study can be incorporated as a module into an extended drift-flux model to predict the dispersion of deep-sea mining plumes.

Phenomena like sea level rise, global warming and erosion together contribute to increasing flood risk in vulnerable coastal areas. As this flood risk increases, initiatives to mitigate the effects of climate change in the coastal zone are also increasingly sought. During recent years, the view that these measures should be circular has gained significant momentum. In line with this, the idea that sediment should not be treated as waste, but as a valuable product in a circular economy has been widely accepted. Within this theme, the sediment uses as resources in circular and in territorial economies (SURICATES) was created to develop and execute eco-innovative solutions for the reuse of sediments in Western Europe. As a part of SURICATES, over the course of a nine week pilot, a total of 500 tonnes of sediment was reallocated in a designated area in the Rotterdam Waterway, with the expectation that this sediment would be transported out of the Rhine-Meuse estuary into the North Sea. The SURICATES project is one of the first real large-scale efforts to reuse sediment for economic as well as ecosystem services. Effective implementation of the SURICATES project, however, requires a thorough understanding of the governing physical processes impacting the distribution of the deposited sediment locally. Furthermore, to assess the feasibility of similar future applications, efficient modelling of the pilot project is necessary. The work presented here aims to elucidate the hydrodynamic processes that are governing in the Rotterdam Waterway, within the framework of the SURICATES pilot project, and assess the reproducibility of these processes by (two) predictive models that are currently operational at the Port of Rotterdam. A special 6-hour monitoring survey was set up to measure salinities, velocities, temperature, and suspended particulate matter (SPM) along a transect crossing the reallocation location. In combination with a literature review, this dataset provides the basis for research into the predictive capabilities of two currently operational hydrodynamic models. Analysis of this dataset reveals the dominant terms in the momentum balance, the influence of Coriolis, the occurrence of internal waves, and the effect that all these mechanisms may have on the SPM distribution around the reallocation location. When the system dynamics are elucidated, the model performance of the two hydrodynamic models is assessed—both quantitatively and qualitatively. It is also investigated whether phase shifts are introduced in the models. It is found that the primary hydrodynamic processes in the Rotterdam Waterway are related to the barotropic tidal asymmetry imposed at the river mouth, the tidal excursion of the salt wedge, baroclinic exchange flow processes, and turbulence damping at the pycnocline. Turbulence damping at the pycnocline generally poses an upper limit to the (re)distribution of SPM over the water column, although field data suggests that this damping may not be sufficient to counteract diffusion processes locally. This effect occurs under certain forcing conditions and during low water slack. Furthermore, an internal Froude number analysis provides evidence for the possible generation of internal waves in one of the river’s bends. The evaluated models, however, are not capable of reproducing all of these hydrodynamic processes adequately. Although both models adequately reproduce water levels and the vertical velocity structure, they have difficulties predicting the pycnocline height. Additionally, it is found that both models introduce a small phase shift in the velocity and salinity prediction. The research presented here is a contribution to the understanding of the governing hydrodynamic processes in the Rotterdam Waterway, and the effect that (in)accurate modelling of these processes may have on future studies. Recommendations following from this research could improve future modelling practices.

In riverine environments under anaerobic conditions, methane and carbon dioxide are produced as a result of biological activity, causing degradation of organic matter. Under aerobic conditions, the bacteria present degrade the organic matter, whereby the concentration of dissolved oxygen may be lowered. Thus, issues experienced in the investigation area (the Port of Hamburg) are hindered construction operations, increased greenhouse gas emissions and the echo-sounding equipment used for sonic-depth finding for ships possibly showing an erroneous depth. The purpose of this investigation was to find out how gas generation and respiration relate to the basic sediment properties and what mathematical model with the highest accuracy can predict gas generation and respiration (separately), while maintaining within a given (precision) error (1%). Gas pressure was measured at the TU Delft for an incubation period of 100 days, which was later used to calculate the gas generation (mg C/g DW) with the use of the ideal gas law. Statistical methods used to analyze the data were: Pearson’s correlation coefficient, multiple regression analysis, adjusted coefficient of determination and error analysis. The results show that both gas generation and respiration have the highest Pearson’s correlation coefficient with TOC. Furthermore, in the multiple linear regression, gas generation had the highest coefficient of determination in a regression between TOC as the primary parameter and iron content (in solids) as the secondary parameter (푅2=0.91495). For respiration, it was displayed in a regression between TOC (as the primary parameter) and copper content in the solids (as the secondary parameter) (푅2=0.881). This concludes that organic matter degradation is driven by the quantity of organic matter. The residual sum of squares showed a decrease from the linear (and non-linear) model to the multiple linear regression model. The prob>|t| value (which determines the probability of error for the multiple linear regression) was much lower than 1% for all parameters in both the gas generation and respiration model, so it can be deduced that the variables are contributing to the model in a statistically significant way. Together with the previously mentioned highest coefficient of determination, the most accurate model for both gas generation and respiration found in this investigation was the multiple linear regression model, although the model for gas generation presented little difference to that of the simpler non-linear model. The exponential nature of the optimal fit for the data suggests that there is a threshold. In areas with low organic matter content, the organic matter present is much less degradable, falling into the “slow” pool category. It is recommended to investigate other mathematical models further. There is a possibility of a more accurate model (possibly a combination of a linear and non-linear model) for both gas generation and respiration which can model the parameters even better (higher coefficient of determination while still remaining within the permitted range of error). Furthermore, it is recommended to find out why the samples listed in tables 6 and 10 deviate more than accepted from the calculated value.

Regular maintainance dredging is a large expense to the Port of Rotterdam, therefore the installation of sediment traps is considered. By increasing the bathymetry locally, an increase of local accumulation is expected and a decrease deeper in the harbour basin. This thesis describes the functioning of sediment traps in a stratified tidally energetic estuary, where sediment is supplied by the river and sea. A numerical 2DV representation is set up for the Botlek Harbour with the hydrostatic Delft3D software. A calculated salinity time-series by Operationeel Stromingsmodel Rotterdam (OSR) is combined with a measured water level time series for the same time period to describe the hydrodynamic boundary conditions. Simulations are done with a variable and constant Suspended Particulate Matter (SPM) time series boundary conditions, that were generated based on the measurements of De Nijs (2012). Flow expansion caused by the sediment trap reduces the flow velocity, but increases the turbulent kinetic energy locally. A reduction of bed shear stress is observed in the trap, except near the edges where an increase is observed. Density currents caused by salinity differences govern the vertical flow velocity distributions, while tidal filling causes the net exchange. The depth of the trap plays a significant role in the internal flow characteristics. The sediment trap changes the properties of the internal flow, which may change the hydraulic state of the flow, i.e. from supercritical to subcritical, resulting in large instabilities and even an internal hydraulic jump. Shallow sediment traps result in less frequent internal hydraulic jump and weaker jumps compared to deeper sediment traps. To investigate the dominant mechanism for the trapping of sediment in the sediment trap, a distinction is made between an erosion and a fluid mud scenario. The erosion scenario shows the largest agreement with the survey data, i.e. maintenance dredging data and Echosounder multibeam surveys, but contribute only marginally to the trapping of sediment. The fluid mud scenario yields the largest contribution to the trapping of sediment. The decreased amounts of accumulated sediment in the basin for substantial to lots of fluid mud behaviour may vary between 10% and 14%, depending on how this fluid mud behaviour is modelled. Various shapes have been tested on erosion and fluid mud scenarios. Both for erosion and fluid mud a more extreme choice of parameters might yield also more extreme results, this is however not considered realistic. The creation of an overdepth has shown to result in a marginal improvement in the capturing of sediment in an environment where erosion is important. A regular sediment trap decreases accumulation in the harbour basins by 2%. A trap twice as shallow increases this amount to 4%, but deepening the trap further may even enhance accumulation in the basins. A shorter or longer trap did not improve the situation. Installation of a sill did however result in a decrease of 6% compared to the situation without trap. It is concluded that this effect can be largely contributed to the internal flow properties and the presence of internal hydraulic jumps. The presence of an overdepth results in a significant improvement in the capturing of fluid mud flow. For the trapping of fluid mud flow, an overdepth results in 6% less sediment in the harbour basins no matter the depth or shape of the trap. The length of the trap did influence the accumulation in the basins. A trap twice as short shows an increase of 4 % of accumulation in the basins compared to a regular trap. A trap twice as long or installation of a sill results in similar accumulation in the harbour basins as a regular trap. For fluid mud flows, any type of overdepth decreases accumulation of sediment considerably. The amount of overdepth or the shape does not influence this. The length of the trap should be sufficient. A trap that is too short results in an increase of accumulation in the basins. For environments where erosion is important, only shallow sediment traps have proven to reduce accumulation in the basins. Traps that are too deep actually increase accumulation in the basins. A sill has proven to be the best measure for both mechanisms. If overdepth is desirable for navigation a shallow sediment trap is advised. This leads to a reduction of accumulation in the harbour basins for both erosion and fluid mud scenarios.

Due to microbial activities, the anaerobic degradation of organic matter happens in the sediments and leads to considerable gas production. Especially for low flow areas gas production is more easily fostered. To prevent the potential problems caused by gas production from the riverine sediments, this study focuses on magnitude of gas formation and its relation with soil properties. Nine locations of known at Port of Hamburg were sampled; for each location the fresh sediment samples were collected at different depths and on different seasons. Samples were stored and transported to several institutes for various analyses, including analysis on sediment standard properties, and on gas production by incubation.

Being part of the BIOMUD project, this study analyzed data from several research institutes. A strong correlation was found between magnitude of gas production and some of the soil properties including content of TOC, TN, ratio of TOC/P, TOC/S, density fractionation, and content of various types of metal elements. A clear relationship was found between magnitude of short-term and long-term gas production, providing possibilities for estimation work on gas formation in the future. The modified Afvalzorg multi-phase model was applied in analyzing gas production on the timeline, which played a key role in describing and predicting gas production in the long-term. The total gas potential of the river sediments at the Port of Hamburg was then predicted as 105.3 mg C/g TOC on average, relating to 10.5% of the organic matter being degraded. By temperature experiment a Q10 value of 2.06 was determined for assessing the sensitivity of gas production to temperature. Gas composition inside the bottles was also measured after four months’ incubation in the temperature experiment, with the results of CH4/CO2 ratio ranged from 0.92 to 1.86 for different temperature conditions. Parts of the results acquired from the experiments mentioned above were also compared with the results from previous studies made by other researches.

A lot of uncertainties exist about the impact of deep-sea mining on the Benthic environment. One of these uncertainties concerns the sediment plumes created by the mining operation. The return slurry released above the sea floor creates a large plume of sediments. With numerical models the behavior of such plumes is modelled in order to minimize these uncertainties. Particle size distributions in these plume models are currently based on individual particle sizes. In situ, at the bottom of the ocean in an salt water environment, flocculation can occur. Flocculation can have effects on the particle size distribution, settling rates and floc structure. The objective of this research is to investigate the significance of flocculation on the settling behavior and if it should be taken into account in these plume models. Shear rate and particle concentration, as function of time, are the most governing processes that have effect on the flocculation behavior. The influence of these parameters on the flocculation process are investigated. Different methods are used in the search for a suitable technique to measure the in situ particle size distribution. Next to the particle size distribution the floc shapes, structure and settling rates are measured under the influence of the factors mentioned above. In the shear range of 6 s-1 and particle concentration of 0.7 to 40 g/l flocculation does occur and has a large impact on the settling behavior of the sediment. Flocculation at other shear rates and particle concentrations remain unknown. Figure \ref{fig:vol_dem_salt_floccu1} shows the time until 100 $\%$ of the mass is settled when the suspension is released at a height of 10 m. This graph shows the difference in settling time between a suspension in demi and salt water. A settling time difference of 85 days (25 days for salt water and 110 days for demi water) shows the importance of including flocculation behavior in plume models.

The new concept of sewer mining which utilizes the ceramic nanofiltration (C-NF) membranes offers a compact solution for water and other resources recovery. However, since it has very limited pre-treatment process, membrane fouling is a common problem due to the direct contact between the membrane and sewage water. Sewage water contains a lot of extracellular polymeric substances (EPS) that can block the membrane pores. One of the most persistent EPS is sodium alginate which responsible for the gel layer formation on the membrane surface.

Removal of the alginate gel layer can be done by implementing chemical cleaning. However, too frequent chemical cleaning can damage the membrane and environmentally dangerous. Therefore, to make this new concept of sewer mining more feasible, the correct cleaning method to remove the fouling layer need to be found. From this point, the research objective for this research is formulated as “Investigation of fouling control methods that can prolong the time before chemical cleaning needs to be performed to achieve higher water production.”

Several methods such as forward flush, iron coating and calcium carbonate coating were investigated. Alginate filtration was done under constant pressure experiment and the effectivity of each cleaning method was calculated by measuring the change in water permeability after the cleaning. The results show that the iron and calcium carbonate coating followed by 5 min forward flush are able to achieve a permeability recovery of 40 to 90 %. Iron coating required 400 mg/l of iron hydroxide to be dossed and a minimum of 5 min reaction times with hydrogen peroxide to have a high permeability recovery. On the other hand, only 1 minute is required by 200 mg/l calcium carbonate dosing concentration with citric acid as a cleaning solution to achieve a similar improvement as the iron hydroxide coating. Both of the processes produce higher water productivity in 2 h of experiment than the chemical cleaning with 0.1 % sodium hypochlorite.

In the end, a theoretical projection on the real sewage water filtration was made to study the economic and environmental impact of the coating process. The results show the cost of production per m3 of clean water is 0.22 euro for iron hydroxide and only 0.12 euro for calcium carbonate. Furthermore, environmental impact assessment using Chain Management by Life Cycle Analysis (CMLCA) software which produced by Leiden University with Eco-indicator 99 (EI-99) categorization shows that calcium carbonate has less environmental burden than iron hydroxide coating.

Controlling subsurface flow is crucial to prevent: the spreading of contaminants, the failure of dikes or any undesirable water flow. Subsurface flow can be controlled by changing the soil permeability. In order to change soil permeability rigid structures are often installed (for example the installation of sheet pile walls into dike bodies), however, these solutions are costly and disrupt the environment. Alternatively, the SoSEAL project aims to provide an in-situ solution to reduce the permeability of highly permeable soil layers in an ecological friendly and cost-effective way. The SoSEAL project is inspired by podzolization, which is a soil formation process. It reduces soil permeability via the precipitation of metal-organic matter complexes in the pore space. During earlier practices a need has arisen for a cheap, environmentally friendly and naturally available aluminum source. Accordingly, the goal of this research is to investigate if gibbsite can be used as the aluminum source to form metal-organic matter precipitates.

A literature study was conducted to investigate the interplay between gibbsite and dissolved organic matter (DOM). Four processes are primarily studied in this research, they are: the release of free Al via dissolution of gibbsite; the complexation between free Al and DOM; the protonation and subsequently precipitation of DOM and the adsorption of H⁺/DOM onto the gibbsite surface. Thereafter the following hypotheses were formulated:

•The extent of gibbsite dissolution is larger at low pH. However, due to its low solubility and slow dissolution kinetics, a low concentration of free Al is expected.
•The organic matter (OM) source used in this study is a humic acid, therefore it is expected to become completely insoluble when the pH is below two.
•The contradicting pH dependency of gibbsite dissolution and OM solubility leads a narrow transitional pH range, that is favourable for the occurrence of complexation between free Al and DOM.

These hypotheses are tested by performing experiments in the laboratory, where the pH varies from 2 to 8 and the aluminum/carbon (mol/mol) ratio is 0; 0.05; 0.1; 0.3 and 1. A synthesized crystalline gibbsite powder and a potassium humate are used.
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The results are subdivided into three pH ranges in which similar behaviour was found. In the low pH range (pH = 2 - 2.5), the protonation and subsequently precipitation of DOM is the dominant process in short term. However, when considering the long term behaviour, gibbsite dissolution is the dominant process as the DOM has precipitated. Due to the difference in time scale, there is very little complexation between free Al and DOM. In the transitional pH range (pH = 3 - 3.5), the competition for H⁺ between DOM and gibbsite is profound. This increases the solubility of DOM and slows the dissolution of gibbsite down. As a consequence, this favours the gradual complexation between free Al and DOM. Nevertheless, due to the ambiguity of free Al measurement method used in this research, it is difficult to quantify the complexation. In neutral to high pH range (pH = 4 - 8) DOM undergoes protonation over time but stays soluble. The release of free Al via the dissolution of gibbsite is negligible in this pH range. Therefore complexation between free Al and DOM should not be expected.

The results presented in this research indicate that gibbsite may not be suitable as the aluminum source to form precipitates with organic matter in engineering solutions that require fast soil permeability reduction. However, the slow release of free Al from gibbsite in combination with the gradual formation of precipitates with organic matter might be interesting for robust problems that require a self-healing ability. For efficiency concern, another OM source that is rich in fulvic acids (higher solubility at low pH than humic acid) and a natural gibbsite source (higher solubility than synthesized gibbsite) should be investigated.

Four kilometers west of the Norwegian island Fedje, mercury, leaking from the U-864 wreck, has highly polluted a seabed area of approximately 40 000 m2. The bow section of the wreck is located on a stability critical slope of 15 degrees. In 2016, Van Oord used a flexible fall pipe system to install a counter fill to stabilize the wreck and simultaneously cap a portion of the contaminated area. In the future, the Norwegian government plans to cap the complete area to prevent further dispersion of mercury. This research aims to gain more knowledge about the spreading of sediments during such an operation occurring under realistic hydrodynamic conditions. A more complete understanding of the process will allow for better risk assessment of future capping operations. To this end, the unique data set gathered during the counter fill project has been analyzed.

In order to predict extreme flow events, the bottom currents are decomposed. By decomposing the erratic velocity signal, tidal (25 %) and inter-tidal residual current (38 %) components are identified and understood. However, the driving force for the remaining intra-tidal part, which contains the highest current anomaly events, cannot be identified. Evidence is found for the occurrence of internal waves providing a possible explanation. Due to a lack of data, a quantitative prediction cannot be made. Consequently, the exact maximum currents at the site are unpredictable, but stayed below 0.4 m/s during the project.

During the installation work, high turbidity clouds have been measured. The origin is investigated by analyzing the particle size distribution and the mercury concentration of sediment samples; said samples are drawn from the capping material, the installed capping layer and sediment traps placed around the wreck. The findings indicate that the clouds are caused by a loss of clean material and are not from the contaminated seabed. This is supported by modeling the dispersal of clean particles from the flexible fall pipe. The promising results regarding the use of a flexible fall pipe for capping layer installation are not only applicable for the U-864 area but also for other polluted offshore areas.

This thesis describes the research about the effect of movement on fluid mud. This was done by exposing several samples of fluid mud from the port of Hamburg to different types of movement for an extended amount of time. It was found that when fluid mud is exposed to kinetic energy of the type used in this experiment, particles will arrange themselves. Dense material and larger particles can be found lower than less dense material and smaller particles. The amount of kinetic energy has no effect on the settling velocity once fluid mud settles. In this research energy level 6 created waves with a frequency of about 3 to 4 waves per second with an amplitude of 1.5 cm. This is the least amount of kinetic energy needed to keep the fluid mud homogenised. A lower density fluid mud will settle faster than a higher density fluid mud. It is not yet clear if this is caused by the density, or that the relation of the difference in density and settling velocity is coincidental.