This study is the first to experimentally show two wave mechanisms regarding density wave amplification with long horizontal slurry transport. There is bed-driven and suspended-driven density wave amplification, in which the grain size determines which mechanism is dominant.

Density wave amplification in hydraulic pipeline transport causes significant risk during operation with the consequences of blockage. Current design methodology for pipeline transport considers mixture velocity and density constant over space and time. However, these conditions are only possible in laboratory circuits where conditions can be controlled carefully. In real-world conditions, concentration varies significantly over time due to the natural dredging process in which a dredging vessel takes slurry from the seabed. Density wave amplification can be differentiated into two different flow categories. Both long horizontal transport and a combination of vertical and horizontal transport. With the first category, there are two main theories that explain the amplification of density waves: 'erosion and sedimentation imbalance' and 'the unstable slip point of the bed'. Here, density wave amplification only occurs in the presence of a bed. 
In the second category, there is one theory called the: 'transient accumulation theory' which is applicable to a combination of horizontal and vertical transport. With this density wave, amplification can occur far above the deposit limit velocity. Mixture velocities change when density waves travel from horizontal to vertical orientation and vice versa. When mixture velocity changes density will change. The influence of grain size, concentration and the centrifugal pump on density wave amplification has not been researched yet.

A test loop has been built with an inner diameter of 46mm and a length of 46 meters. The goal of this laboratory circuit is to investigate the mechanisms that result in the amplification of density waves. Two types of density waves were measured: bed-driven density waves occurring with coarse sediments (Dorsilit 7: d₅₀=1040 μm and Dorsilit 8: d₅₀=619 μm) and suspended-driven density waves occurring with fine sediments (Dorsilit 9: d50=316 μm and Zilverzand: d₅₀=240 μm). With bed-driven density waves, there is fast amplification and multiple sharp waves which can result in areas where no concentration is left. With suspended-driven density waves, there is one smooth wave, and amplification takes multiple loop lengths.

The Port of Rotterdam experiences large amounts of siltation from the upstream rivers in its basins and canals every year. Furthermore, container vessels increase in size every decade and therefore require a larger navigational depth. These two factors cause the yearly amount of dredged material to increase. Currently, mainly trailing suction hopper dredgers are used to remove the large amounts of sediment, but these vessels come with high costs and operational time. A more time and cost-efficient dredging method is therefore desired.

A potential solution to the increasing problems of costs and operational time by dredgers is the technique of water injection dredging. To make this technique as efficient and effective as possible, this thesis has the objective to measure and analyze flow and sediment properties for different parameter settings of water injection dredging and find the optimal parameter settings of this dredging technique on mud from the Port of Rotterdam. Large-scale experiments have been conducted in the water-soil flume of Deltares, where a jetbar was trailed (or run) over a bed 27 meters long and 0.5 meters deep of port mud while injecting it multiple times with water.
A positive correlation is observed between the production rate and jet momentum. The production is related linearly with the jet momentum using the Vlasblom equation combined with a non-dimensionless empirical fitting parameter per run per traverse velocity.
What is remarkable is that the intrusion depth by the jets increases with ascending runs while the jet parameter settings stay the same. The data shows that the difference between the mass flux by the density current and the mass flux stirred up by the jets when the sediment concentration of an undisturbed bed is assumed, increases between runs when an increased intrusion depth between those runs is observed as well. This indicates that the volume penetrated by the jets contains a smaller amount of sediment than was initially assumed, thus is disturbed by the previous run and is therefore decreased in strength. This decrease in strength results in a larger intrusion depth during the run itself in comparison to the previous run.

The influence of the SOD of the jets is analysed by comparing runs with a SOD to runs without a SOD but with similar remaining jetting parameter settings. When a SOD is applied, the jet pressure applied to the bed is outside the flow development region and therefore the jet pressure decreases with distance from the jet nozzle. The mass of sediment stirred up by the jets, for a SOD of 300 mm, is lower in comparison to a SOD of 0 mm. The density current transports relatively more sediment, however, when a SOD of 300 mm is applied. So, if a large amount of sediment needs to be stirred up, and therefore a large intrusion depth is required, no SOD should be applied and when large horizontal transport by the density current is desired, a SOD outside the flow development region of the jets should be used.

Digital Soil Mapping (DSM) of soil types in geotechnical project areas is a top priority. These maps are often used in decision making and can have significant consequences related to costs and risks. Usually, these maps are generated by digital soil models that interpolate soil types at known locations. In practice, conventional spatial interpolation techniques are still often used for DSM of soil types, such as inverse distance weighting and kriging. However, conventional models are not well suited for predicting or interpolating soil types because of their inability to deal with categorical data properly. Besides, the design of the conventional models does not allow for incorporating the abundance of meaningful covariate information that is available nowadays. The flexibility of machine learning algorithms vanquish both problems and has become increasingly popular for DSM of soil properties in recent years. The results of machine learning techniques for DSM of soil properties are promising and generally outperform conventional models. However, few studies have used machine learning for DSM of soil types and is therefore still a relatively unknown field. Moreover, at the time of writing, there are no studies that use sequence models for DSM of soil properties or types. Hence, the author proposes to introduce a new method for DSM of soil types, namely a Long Short-Term Memory (LSTM) network. The intuition behind this introduction is that the spatial correlation can be captured in sequences and can improve soil type prediction.

Real project data from a cable burial project is used to evaluate and compare the performance of the conventional interpolation methods triangulation and kriging, the machine learning models random forest and XGBoost, and the newly proposed deep learning model LSTM. The project data consist of 757 vibro cores (VC), 718 cone penetration test (CPT), bathymetry data and sub-bottom profilers. The geotechnical data, i.e. VCs and CPTs, is received on separate PDF pages that require to be digitized first. This thesis describes a simple yet precise manner to extract this data from the PDFs. The VCs and CPTs are provided with a soil type interpretation and can be used directly for developing the models. The data is split into a training set to develop/train the models and a test set for evaluation. Ultimately, the best performing model is used to build a 3D stratigraphic soil model for the project area with associated prediction accuracies.

All state-of-the-art techniques outperform the conventional models and especially in predicting minority classes. The best performing model is random forest with an overall accuracy of 85.44\% and is comparable to the performance of XGBoost of 85.11\%. LSTM network achieved a slightly lower accuracy of 84.27\%. The results show that LSTM is suitable for DSM of soil types and has considerable potential for improvement as only a few possibilities of the model have been examined.

Subsea rock installation is a process in offshore engineering where rocks are placed on the seabed or subsea structures using a fallpipe. An example of a subsea structure could be a cable or pipeline that must be protected. In this research, the main scope is rock installation for scour protection of the foundation of offshore wind turbines. As the US government is planning to build 30 gigawatts of offshore wind capacity by 2030, many rock installation projects are planned. This is where GLDD wants to contribute by being part of a more sustainable future by building a subsea rock installation vessel. This vessel with a 20.000 ton rock capacity is placing rocks using a solid fallpipe. Accurate knowledge of how rocks are placed using a fallpipe is necessary to plan, manage and estimate the costs of a project. The main focus of this thesis project is to establish an optimal computer model for an inclined fallpipe for subsea rock installation. This model can be used to calculate rock velocity during operating the inclined fall pipe (IFP). Additionally, the particle concentration and the distribution of particles over the pipe’s cross-sectional area can be determined. The velocity of particles is essential for future models calculating where the rocks settle down after leaving the fallpipe. Based on the literature two models were made: Vertical fallpipe model 1 (VFM1) and Sliding bed model 1 (SBM1), these models are improved based on data and observations from lab research. These improvements lead to Vertical fallpipe model 2 (VFM2) and Sliding bed model 2 (SBM2). In the lab research, a scale model of a fallpipe is made. This is done by placing a transparent fallpipe in a 5x2.5x2 meter tank of water. This fallpipe is attached to a conveyor belt, making it possible to precisely control the amount of rocks per second placed in the fallpipe

When a ship reaches the shore, the water depth reduces and thus the under-keel clearance also reduces. The ship keel clearance influences the maneuverability of the sailing ship.

In this thesis project, the link between the fluid mud rheology and its density is first investigated. The exponential relation reformulated between the density and yield stress necessitates the direct measurement of rheology for navigability. It was confirmed true that the yield strength grows exponentially with the density of the fluid mud. However, at higher densities of mud, more thixotropy is observed in the flow curves. Besides, the Power-law relations were found for the relation with volumetric concentration, for yield stress in agreement with fractal dimension theory.

Second, quantification of the thixotropy effect of fluid mud is conducted to justify the importance of the time-dependency effect in the rheological modeling. We found that an unremolded fluid mud has high thixotropy even at high shear rates. However, diluted and remolded fluid mud at high shear rates found a negligible thixotropy effect. We also observed that Houska's modeling curve coincides perfectly with the flow curve of fluid mud at high shear rates, and also it integrates the thixotropy into the modeling.

Third, the total resistance of a plate moving through fluid mud is measured and compared to the frictional forces calculated using the available analytical formulas of a plate moving in Bingham fluids and Power-law fluids. The moving plate is an abstraction of a vessel's keel sailing through the fluid mud. We found that the total resistance of the plate moved in fluid mud at low velocity agrees with the frictional force of a plate moved in Bingham fluids. As the velocity increases, the stagnation pressure becomes significant, and the deviation of the total resistance of plate and frictional force of a plate increases. Thus, to estimate the total resistance of a plate moved in mud, normal forces (stagnation pressure) and vortices at edges should be investigated because these need to be subtracted.

The experimental data in this thesis are made resourceful to help researchers validate their Computational fluid dynamics(CFD) models in the application of sailing through the mud.

One classic challenge in pump operation is the occurrence of cavitation. Cavitation is the forming of vapour bubbles in a fluid due to a local drop in pressure, followed by a subsequent implosion of those bubbles due to an increase in pressure. The vapour formed can significantly decrease pump efficiency and the implosion can be detrimental to the pump and damage components. Centrifugal pumps play an essential role in dredging, here cavitation can be problematic, both due to loss of efficiency and because of damage to the pump. The condition related to the onset of cavitation is called the Net Positive Suction Head (NPSHr). Knowing the NPSHr conditions of a pump is important for its design and to define the conditions for operating a pump. Unfortunately it is difficult to predict NPSHr properties of a newly designed pump and it is expensive to test a full scale dredging pump. Therefore it is relevant to be able to predict NPSHr conditions of a full scale pump by performing small scale experiments in a lab environment. In order to do this a lab setup was designed for centrifugal pumps with an inlet diameter of 100 [mm]. In this setup the inlet conditions (flow rate, inlet pressure, water temperature) of a centrifugal pump were controlled to determine the NPSHr properties of the small scale pump for a range of shaft speeds and flow rates. The relation between the flow, shaft speed and inlet pressure were investigated for the lab scale experiment. Also the data was compared with available full scale data and analysed to find an expression for NPSHr conditions as a function of flow, shaft speed, inlet pressure and pump diameter for geometrical identical centrifugal pumps. The relation of the NPSHr with shaft speed and diameter appears to be quadratic, provide the flow profile is comparable (i.e. the specific capacity is constant). This relation is optimal at the Best Efficiency Point .

The rising demand for minerals and metals and the depletion of land-based resources has created a renewed interest in the extraction of resources from the deep ocean, i.g., deep sea mining. This research focuses on the mining of manganese nodules, these are potato-shaped objects, 5-10cm in size, composed of metals half buried in the seafloor. A Seafloor Mining Tool (SMT) is used to mine the nodules, however, during mining besides the nodules, also the sediment around the nodules is collected. This sediment is separated in the SMT and discharged through a horizontal diffuser located at the rear of the SMT, thereby creating a sediment plume. The sediment plume needs to be reduced for environmental, economic and legal reasons. The sediment plume causes changes in the sediment characteristics, clogging of pores of suspension feeding organisms and burying of the benthic fauna. The plume will spread in all directions, thereby burying still to be collected nodules and reducing the pick-up efficiency, making the process inefficient from an economical perspective. Legal issues will arise when the discharged sediment plume spreads to other exploration areas owned by other parties or to environmentally protected areas. The aim of this research is to investigate the influence of the choice of diffuser height on the reduction of the sediment plume. To achieve this goal a Matlab model was made and small-scale experiments in the laboratory of Dredging Engineering were done. The Matlab model is based on the JETLAG model, described in 'Jets and Plumes' by Lee and Chu (2003), and is a Lagrangian model predicting the centerline trajectory of the plume. The small-scale experiments provide insight in the behaviour of the horizontal discharge plume at different diffuser heights and generate measurements to validate the model. A diffuser designed specifically for these experiments is produced and the height and flow velocity are differed. The experiments consist of visualization experiments, capturing top view and side view images of the buoyant jet, and experiments measuring the velocity and bottom concentration at different locations. The velocity profiles, sediment concentration, deposition pattern and impingement range are compared and analysed. The combined results from the model and the experiments show that the start of the impingement range increases with increasing diffuser height. Furthermore, a lower diffuser height increases the amount of bottom deposition near the diffuser outlet. The measured velocity profiles, near bottom concentration and impingement range are in agreement with this observation. The measured near bottom velocities at 15D from the diffuser outlet are approximately 0.1 and 0.2m/s, depending on the discharge velocity, both have the potential of resuspending settled sediment. This research suggests that the spreading of the plume can be reduced by the choice of diffuser height above the seafloor. Based on the diffuser heights tested in this research a diffuser height of 100mm is recommended. Since a higher diffuser decreases the amount of particles settling close to the source and a lower diffuser increases the potential for erosion. This research has shown that up to a distance of 15D from the diffuser, the near bottom velocities are large enough to cause erosion. Research into the near bottom velocity decay and magnitude further away from the source, inside the turbidity current, is necessary as well to understand the full spreading behaviour and the potential for erosion. Furthermore it is recommended to do research into spreading behaviour of finer particles, especially the behaviour of the actual deep sea sediment in combination with salt water causing flocculation. Moreover, research into the influence of the forward motion of the SMT is recommended since the SMT will create a wake that will influence the spreading behaviour of the plume. Research into the potential creation of a recirculation region caused by the limited entrainment at the rear of the SMT is recommended as well, this can be done by aligning the diffuser outlet with a screen.

Over recent years, there has been an increase in demands for rare and precious minerals worldwide. Mostly this is due to the rise of the world’s population and the drive towards a green energy transition and low carbon economy. Prices are rapidly increasing, and there is an identifiable risk of an increasing supply shortage of raw materials, including those identified as critical to Europe’s high technology sector. The development of surveying techniques and advances in new technologies in remotely operated vehicles (ROV) has allowed detecting that the most valuable and rare mineral resources are spread out in the sea-floor and international waters. Currently, the most significant setback towards exploitation licenses is not because of lack of technology but because of a lack of knowledge on deep-sea biodiversity and the impacts of mining on ecosystems. The ISA (International Seabed Authority) is responsible for the regulation, and the control of mineral-related activities in the international waters is currently working on drafting environmental regulations. This presents significant opportunities for research on the development of technologies that incurs in the least environmental impact possible. Currently, the main concerns are regarding the horizontal sediment-laden plume that is generated as a result of the mining process. Therefore, the industry is working towards the development of equipment that lessens the plumes spread. Work done in this research focuses on small scale sized laboratory experiments in which the sea-floor crawler’s outlet shape is varied, and its plume’s effects of the sediment waste and other effluents (SWOE) are measured. Besides gaining insight in the horizontal plume spreading under different conditions and geometries, the outcome of the research is to provide a set of measurement data that can be used for future numerical model validation towards determining an optimal outlet shape for the seabed crawler. For this purpose, a total of three diffusers were designed and tested based on a specific scaling factor and input parameters defined by IHC Mining. Experiments consisted of capturing visual imagery of the generated plume on both top and side views for further analysis and performing velocity and concentration profile measurements in different locations. The offset jet transition from jet to plume and the respective impingement point for all diffusers was compared. Velocity and concentration measurements were analyzed and compared to determine an ideal diffuser. Using diffusers reduces the plume’s initial momentum while maintaining the density differences and therefore reduces the transition from jet to plume, allowing for gentler deposition over the surface and resuspending less material. All experiments show similar behavior in which a free jet can be observed initially. Then, after substantial entrainment takes place, the jet impacts the bed due to the negative buoyancy. Once the discharge impinges the lower boundary, it forms a radially spreading layer along the boundary which transitions into a wall jet. Lowering the momentum of the jet by diffusing the outlet gave better results in terms of drawing the impingement point, and the deposition profiles nearer to the diffuser. Also, the measured velocity and concentration profiles considerably decreased, reducing the plumes spread.

The first head loss prediction methods for hydraulic transport of solids in pipes, date back to the years '50 of last century. The principles are still applied today. Although it is observed that obtained results may differ from reality, when the circumstances do not represent the situation of the original experiment. To investigate this, the performance of various prediction models is analysed on a large scale laboratory test set-up. In recent publications, several researchers observed disturbances in their expected flow patterns. Described as either 'unsteady flow’, ‘instability’ or 'unexpected mechanism'. Talmon developed the theory that the occurrence of these events could be explained by transient processes in the pipe flow. It is recommended to use a test pipe with great length. To verify, by longitudinal pressure profile measurement, that equilibrium is measured, and that indicated transients are captured by the measuring system. A laboratory test set-up is provided by the CCCC National Engineering Research Center of Dredging Technology and Equipment Co., Ltd. In a joint research program with Delft University of Technology: the pressure drops for water and mixture flow over the pipeline length are analysed. This is done for horizontal hydraulic transport. The focus is on comparing test results with existing theories and find explanations to deviating results. If instabilities are observed, the gathered data can be used for further research on density waves in pipelines. In the liquid flow experiment, three prediction methods derived from the Colebrook-White equation are analysed: Darcy-Weisbach, Swamee & Jain and RangaRadju & Garde. Considering the pipeline to be smooth, the predicted values are similar. The difference between them is almost nil. Furthermore, the result shows good correspondence with the data acquired on the test set-up. In the mixture experiment, four prediction methods are analysed: Durand, Führböter, Jufin & Lopatin and Wilson. They are compared with laboratory data of test conducted in a heterogeneous flow regime. With a velocity ranging from three to six meter per second and concentrations of: 4.4, 8.1, 12.3 and 14.6 percent. In a general approach, considering all transport velocities and concentrations. It is observed that the theoretical principle described by Durand shows the closest resemblance with the experimental data. When only the concentrations are considered, a distinction has to be made. For the two lowest mixture densities, the Führboter method gives the best fit. For the highest two, the best correlation is according to the Durand theory. The principles of Jufin & Lopatin and Wilson underestimate the pressure loss. Where the difference of the former is significantly larger in comparison to the latter. For the lowest velocities of the twelve and fifteen percent slurry experiments, stationary waves over the pipeline length are observed. Due to the length of the test set-up, the transition to equilibrium flow is clearly visible. It demonstrates that longer flow loops give opportunity to conduct further research into the extent of waves.

Little is documented in literature regarding hydraulic processes in inclined and large diameter pipelines. The bulk of the previous research dates back 20 to 50 years and was done for small diameter pipelines of up to 150 mm.

This research focuses on gathering data and testing the existing models and ideas with regard to large diameter inclined pipelines and the hydraulic transport within them. The overall goals of the project are to gather knowledge on the less documented and studied principles of pipeline flows and validate ideas and
semi-empirical models from previous researches.

Extensive laboratory experiments were conducted as part of a joint research programme between Delft University of Technology and the National Engineering Research Center for dredging equipment and technology in Shanghai. The experiments were executed with a flow loop with a pipe diameter of 300 mm. It contains a measurement section of over 110 meters, part of which is inclinable. Pipe inclination angles of 17.9, 28.9 and 44 degrees were tested with slurry concentrations up to 15 % at flow velocities between 2 and 7 m/s. The flow velocities, delivered concentrations, total pressures, differential pressures and pump data were recorded. Conducting these experiments on this scale under controlled laboratory conditions is a unique research.

Three semi-empirical models by Worster and Denny, Gibert and Wilson for inclined slurry transport are validated. A comparison is made between ideas from literature regarding deposition limit velocities, delivered concentrations, pipe inclination angles, stratified flow regimes, particle suspension and different flow directions. The observations from previous researches with small pipe diameters are generally in line with the results of the experiments conducted for this thesis. The semi-empirical models prove to deliver accurate predictions of the total pressure gradients in heterogeneous flow regimes. With regard to stratified flows, it is proposed to modify the semi-empirical models by adding a factor to the suspension and solids effect terms. The factor is a function of deposition limit velocity, flow velocity, inclination angle and flow direction.

Manganese nodules have been lying on the deep sea soil for centuries before they became known. The first ones to discover the nodules were Murray and Renard, during their scientific cruise between 1872 and 1876 (Murray and Renard, 1876). The Clarion-Clipperton Zone, located between Mexico and Hawaii, appears to have a virtually inexhaustible amount of mineral resources. The manganese nodules consist mainly of man- ganese, but because they also contain metals such as copper and cobalt, the nodules become more and more interesting for our modern society. Another name for the manganese nodules is polymetallic nodules, be- cause of the content of many other metals.
By means of a vertical hydraulic transport system the manganese nodules will be transported upwards from the seabed. Given that the nodules are located at a depth of about 5000 meter, it is plausible that they come into contact with the pipe wall during transport. When a nodule interacts with the wall, abrasive wear can occur. Abrasive wear, or sliding wear, causes the nodule to degrade, or decrease in mass, through the sliding contact with the pipe wall.
The main research question of this Master Thesis is formed as follows:
What is the contribution of abrasive wear to the degradation of polymetallic nodules, in a vertical transport system?
The contribution of abrasive wear is tested on the basis of the equation of Archard (1953). In the MTI laboratory in Kinderdijk various manganese nodules are tested in a specially designed experimental setup. The polymetallic nodules available for this Master Thesis originate from the Clarion-Clipperton Zone (CCZ). The first set of experiments is focused on single nodule degradation. The nodules are weighted before and after a test run, hereafter the nodule mass after a test run is divided by the initial nodule mass, resulting in the normalized remaining mass. Each test run consists of a specific sliding length. With the sliding length and normalized remains mass, a prediction can be made of the material specific wear rate factor, noted as k [m2/N]. The experiments resulted into a value of k = 4.16·10−9 [m2/N]. With this k-factor, in the worst case, 97% of the original nodule mass is remaining after 1000 meters of sliding contact.
Subsequently, a batch of nodules is tested in the experimental setup, with the expectation that the con- tribution of abrasive wear increases to the total nodule degradation, due to the presence of particle-particle interaction. Recently, Blue Mining has conducted trials in Freiberg, Germany, in an abandoned mine shaft. A vertical pipe of almost 130 meters has been placed inside, and the effect of abrasion on a batch of nodules has been observed. During the batch experiments in Kinderdijk, where the batch of nodules was in a horizontal position, it is seen that the contribution of abrasion is greater, compared to the tests in Freiberg.
Using the open-source program OpenFOAM, a vertical turbulent pipe flow is modeled. The pipe has simi- lar dimensions to the pipe of the experimental setup. The simulation was done using a Large Eddy Simulation (LES). By means of a one-way coupling, the data of the flow field is linked to the movement of the simulated particle. Subsequently, point particles were released at various points at the entrance of the pipe. The first series of point particles consists of a diameter of one-third of the pipe diameter, corresponding to the com- mon size of a manganese nodule. The collisions between the point particle and the pipe wall are solved with a Discrete Element Method (DEM), which makes use of a (non-linear) spring-damper system.
To test the sensitivity of the model, point particles of one-sixth and one-tenth of the pipe diameter are also released. The number of collisions per total number of simulations are compared with each other. After the sensitivity analysis it turned out that in 15% of the simulations there was contact with the pipe wall, regardless of the diameter of the particle. When this 15% is compared to the experimental results using single nodules, there is a weight loss of around 0.5%. This holds a weight loss of only a single - to a few - gram(s) for the average polymetallic nodule.
It can be concluded, according to the experimental trials with polymetallic nodules from the Clarion- Clipperton Zone and by means of a one-way coupled CFD-DEM model, that the contribution of abrasive wear results into a (maximum) remaining mass of 97%. However, it is advised to extend the computer model with a two-way (or multi-way) coupling between the liquid and the solids. It is also recommended to conduct vertical abrasive wear tests with nodules, in order to validate the model and gain more insight in degradation behaviour.

The Trailing Suction Hopper Dredgers (TSHD) are typically used for the transportation of soil. The soil in the hopper can be removed by hydraulic transport using water jets and the discharge at the bottom level of the hopper. The soil fluidization and transportation is jet assisted. The unloading process can take quite some time; the unloading process can be limited by the soil transportation instead of the pumping system. The scope of this research is the optimization of the jetting system in order to deliver high mixture densities, to increase the unloading production and therefore decrease the unloading time.

Dams are an essential part of the Dutch flood defence works to protect the hinterland from flooding by the sea. Sand closures are the construction of closure dams with sand as the main building material. The rising and falling tide generates a current through the closure gap, which increases in strength as the gap becomes smaller. This current is quite strong and transports a significant amount of sand from the gap to areas where the current is weaker. The sand that is transported away from the closure gap is called the sand loss. The changing tide and constantly moving sand grains result in a dynamic environment. This makes it difficult to estimate the total amount of sand that is necessary to close the dam. It is important to be able to assess the amount of sand loss accurately, because it could make the difference between needing an extra dredging vessel or not. The costs of these dredging vessels are about 1 million euro's a week; therefore, having an unnecessary vessel present due to very conservative sand loss predictions is costly. Laboratory experiments and a numerical model were used to investigate the morphology during bedload transport under a lateral expansion. A streamwise bar formed behind the tip of the lateral expansion for both the laboratory experiments and the numerical simulations. However, it was not possible to replicate the bedforms that occurred during the laboratory experiments with the numerical model. These bedforms are deemed to be important for the morphology during bedload transport. The numerical model was used to expand the research to suspended sediment transport by decreasing the grain size of the sediment. In the obtained morphological patterns, four areas are distinguished where the morphology was found to depend on the flow velocity and the degree of turbulence in the flow. It is expected that a variation of these patterns can be found during a sand closure, although these findings should be validated with a laboratory experiment or in situ measurements. Therefore, it is recommended to set up a laboratory experiment to investigate the morphology under a mixing layer for suspended sediment transport. Based on the results of the laboratory experiments and the numerical model, it is advised to look into the possibility to use the sand deposited as a streamwise bar during a sand closure as an additional borrow pit to aid the closure process, since it would lead to less sailing time for the dredging vessels. For the first stage of a sand closure, it is advised to use a two-dimensional model that incorporates a bedload transport formula to model the sediment transport. It is important to use a parametrization of the bedforms that occur during bedload transport. For the final stage of a sand closure, which is the most critical phase due to high flow velocities, high degree of turbulence and time restriction, it is advised to use a three-dimensional model with a pick-up equation that takes the influence of turbulence on the grains into account, such as the pick-up formula of Okayasu et al.

In the dredging industry, centrifugal pumps are most commonly used and selected based on their operational capacities and expected slurry characteristics. The handling capacity of a centrifugal pump is however supplied for handling water and cannot be applied to other slurry conditions without an applicable correction. For handling Newtonian fluids there exist a well established de-rating method by {HI1983} and further improved until most recently {ANSI2015} was obtained. For non-Newtonian fluids however, no such generally accepted method exist, especially not for large centrifugal pumps as encountered in the dredging industry. In order to obtain a de-rating prediction for non-Newtonian fluids, researchers have tried to predict pump de-rating by applying the {HI1983} method. This is only possible if all fluid characteristics of a non-Newtonian fluid are summarized into a single value as used to characterise a Newtonian fluid. Several approaches are suggested by \cite{Walker1984}, \cite{Graham2009} and others. Dependant on which non-Newtonian parameter was found to be governing, apparent viscosities, Bingham plastic viscosity, and limiting viscosity were used in time.

Because all methods developed until today are based on small centrifugal pumps handling a mixture with a constant rheological behaviour, validity on centrifugal pumps with larger impellers and additional features as cover flushing cannot be guaranteed. Therefore the aim of this thesis research is to obtain a valid input parameter for a Newtonian de-rating method to predict the pump performance when handling a non-Newtonian fluid and determine the validity for large centrifugal pumps. To achieve this research goal, a measurement campaign on board the Trailing Suction Hopper Dredger `Pallieter' of DEME - Dredging International NV, working in a viscous environment was carried out. Measurement data for pump head, power and efficiency were obtained by installing a torque measurement device. Additional a device was installed to measure the dissolved gas volume fraction in order to separate effects caused by increased viscosity from multi-phase flow problems. After measurement data is obtained, available de-rating methods are compared and conclusions are drawn with respect to applicability.

Dissolved air in the mixture is of significant influence on the complete pumping process. After filtering the data to remain with performance data only influenced by the higher viscosity, de-rating models are analysed. Head showed very little to none de-rating when a viscous mixture was handled. At lower viscosities the de-rating method showed little deviation from the theoretical pump head, only at higher viscosities a significant de-rating was predicted but measurements didn't confirmed this. The same effects as for head yields for power. Significant de-rating was expected at high viscosities but measurements contradict this phenomenon. Although the Bingham plastic viscosity is the most conservative characterisation of a non-Newtonian viscosity, over-prediction still exist at high viscosities. This is most probable caused by the absence of viscous material in the axial gap between impeller and casing which in turn result in much less disk friction losses as would be expected.

The cable between Vlieland and Terschelling needs to be replaced. The thesis focusses on the replacement of this cable. Because of the sensitive environmental situation some additional hurdles will need to be taken in order to come up with a decent placement plan.