In rapidly growing urban areas, river dynamics have become major hazards, endangering vulnerable populations and their environments. The Msimbazi River Basin in Dar es Salaam, Tanzania, demonstrates these challenges, where unplanned urban expansion, deforestation, and infrastructure development have influenced river morphodynamics. Although prior studies have addressed flood risks, sedimentation, and bank erosion, an understanding of the river’s migration patterns, widening trends, and key drivers at the full catchment scale has been lacking. This research applies a descriptive approach combining manual riverbank tracking from satellite imagery, identification of potential morphological change drivers, and hotspot mapping based on hazard severity and exposure susceptibility. From 2007 to 2024, the Msimbazi River experienced significant lateral migration and localized widening, with notable episodes of instability after 2017. These changes are primarily driven by land cover transformations, such as urbanization and deforestation, which have led to gradual shifts in river morphology, rather than being the result of changing precipitation patterns. In contrast, abrupt and localized changes, particularly after 2017, appear to be associated with infrastructural developments like the Standard Gauge Railway, as well as the coincidence of the El Niño phase with the cyclone season, which contributed to elongating the wet seasons. Findings reveal that river migration rates and widening trends fluctuate considerably, often doubling or tripling during periods of rapid change, with the highest vulnerability observed in the upper catchment. By identifying zones where hazard severity and exposure intersect, this study provides a framework for prioritizing mitigation in the Msimbazi Basin and other urban rivers in rapidly eveloping regions.

The current flood risk assessment framework in the Netherlands aims at ensuring a nation-wide protection level with a long-term vision. It assumes that future river bed level changes will not pose negative effects on flood safety and it adopts a fixed-bed assumption. However, the river bed level shows a strong spatial and temporal variability, where bed aggradation trends could lead to higher water levels in the future. Recent measurements in the Dutch Rhine have shown both bed degradation and aggradation in different river sections along the lower river domain. This raises questions to what implications does future river bed level changes have on flood safety in the Netherlands and whether the current fixed-bed assumption has adverse connotations to it.

The objective of this MSc thesis is to study the impact of river bed level changes on flood safety in the Netherlands. To achieve this, a framework for incorporating large-scale bed level changes into flood risk assessments is developed and applied under the current Dutch context. The implications on the long-term and short-term flood safety are analyzed separately, as fundamentally different approaches and uncertainties relate to the flood safety standards derivation and for the periodic safety assessment in the Netherlands.

In the long-term, I propose to incorporate morphodynamic modelling scenarios into the flood safety standards derivation process to account for future bed level changes and their long-term uncertainties. Modelling scenarios should include future river discharge, sea level rise, river maintenance and the evolution of river bifurcations, as they represent main drivers in the long-term river bed response in the Netherlands. Based on existing long-term morphodynamic modelling studies of the Rhine River, it is estimated that the extreme water levels decrease over the upper Waal, but increase over the lower Waal by 0.15 m and 0.30 m in 2050 and 2100, respectively. These scenarios consider that river dredging is not maintained after 2025.

In the short term, I propose to incorporate the analysis of the recent river bed level behaviour into the safety assessment process to account for its uncertainty in the near future. Based on yearly bed level measurements in the Waal from 2005 to 2020, decreasing and increasing water level trends have been identified in the upper and lower Waal, respectively, with increments in the order of 0.05 m. This is small in absolute terms, but significant compared to the accuracy level of the hydraulic loads used in the safety assessment process. As a consequence, these increments can have important economical implications on dike reinforcement programs.

In summary, this thesis provides a framework incorporating large-scale river bed level changes into the current flood risk assessment framework in the Netherlands. Furthermore, it quantifies the impacts of bed level variability on flood safety in the Waal River. In general, the fixed-bed assumption in the current flood safety framework is a conservative, or safe, assumption for the hydraulic loads’ calculation in the upper Waal. However, it may underestimate the future hydraulic loads in the lower Waal and impose adverse conditions on flood safety.

Predicting and modelling meandering river migration is necessary for river engineering, land development, and risk assessment. One chaotic process that makes predicting the migration more difficult is the cutoff of a river bend, which is the subject of this report. This report describes the research process and results of a study on overbank flood effects on chute and neck cutoffs in single-thread meandering alluvial rivers. The following research question is addressed in this report: “What is the relationship between the duration of overbank flooding and the formation of chute versus neck cutoffs?”. The relationships between the overbank flood shear stress and the frequency of chute versus neck cutoffs, and between the soil type of the floodplain and the frequency of chute versus neck cutoffs are evaluated.

An overbank flood exceeds the bankfull limit of a river, flowing over the floodplain. When a river bend is cut off, two cutoff types are visually distinguished: neck cutoffs and chute cutoffs. Cutoffs of both types were analysed in four rivers in the United States of America: Cheyenne River in North Dakota, Powder River in Wyoming and Montana, Pearl River in Mississippi, and Trinity River in Texas. These rivers have a chute cutoff regime, a mixed cutoff regime, and two neck cutoff regimes, respectively.

For these four rivers satellite imagery on Google Earth Pro was combined with measurements from USGS measurement stations and soil data from SoilWeb. The bankfull river discharge was converted to bankfull river depth to calculate the overbank flood heights and the overbank flood shear stresses acting on the floodplain during floods. Subtraction of the critical shear stresses of the soils resulted in residual shear stresses. These were combined with the corresponding flood durations to calculate the flood impulses of each flood.

The floods associated with chute cutoffs showed larger overbank flood shear stresses than those for neck cutoffs. Rivers with steeper slopes seem to be more prone to a chute cutoff regime than rivers with gentler slopes. The soils in which chute cutoffs were formed contained high sand percentages, while the neck cutoffs occurred in a wider range of soil types. The overbank floods creating chute cutoffs exerted larger residual shear stresses for shorter durations, as opposed to smaller residual shear stresses for longer durations of floods associated with neck cutoffs. The overbank flood impulses associated with chute cutoffs show a larger range and higher values, but are on average not significantly different to those of neck cutoffs.

The processes related to river bend cutoffs are very complex and not entirely understood yet and more research is needed on a local and a greater scale. The formulation of general relationships for chaotic events such as cutoffs will improve the prediction and modelling of meandering rivers. This will be increasingly useful, especially now with more extreme weather events and river floods all over the world.

It is observed that the bed level development of the Pannerden Canal (PC) and the Waal changed since the peak flows of 1993, 1995 and 1998. The erosion rate of the Pannerden Canal decreased greatly just downstream of the bifurcation while the erosion rate of the Waal stayed more or less constant. This leads to an increasing depth of the Waal relative to the Pannerden Canal and therefore the Waal attracts more discharge. The model results from this study confirm that without anthropogenic interventions in the future, the Waal discharge fraction keeps increasing. The shift in discharge partitioning towards the Waal is an undesired development of the system as it causes problems for navigability, ecology, freshwater distribution and flood safety. Currently there is a lack of knowledge on how interventions can be used to mitigate the gradual change in discharge partitioning at the Pannerdense Kop (PK). This study aims at filling the knowledge gap by considering several interventions studying their effect on the discharge partitioning at the PK and on the Rhine branches surrounding the PK.

Firstly, an inventory of interventions which could possibly increase the Waal discharge fraction is made. The resulting selection of interventions is: A) a side channel from the Boven-Rijn towards the PC, B) fully opening the weirs in the NR-Lek, C) widening on the IJssel, D) directly steering the sediment partitioning at the PK and E) dredging in the PC and dumping in the Waal. These interventions are implemented in a 1D-morphological model of the Dutch Rhine branches.

It is found that the side channel from the Boven-Rijn to the PC (A) is not capable of significantly influencing the discharge partitioning at the PK. The backwater effects due to the water addition counteract the added discharge to the PC.

Furthermore, it is found that for the low Lobith discharges opening the weirs in the NR-Lek (B) can reduce the Waal discharge fraction below the initial value from the reference case for the whole simulated period of 60 years. The opening of the weirs does however lead to significant relative decrease in the IJssel discharge fraction which is unwanted regarding the freshwater supply of the IJsselmeer. For low Lobith discharges the widening on the IJssel (C) initially leads to a significant reduction in Waal discharge fraction of 2.4%. The effectivity reduces throughout the simulation because of aggradation along the widened reach. For high flows the opening of the weirs and the IJssel widening are less effective. The final relative Waal discharge fraction decrease is respectively 1.1% and 0.7%.

The results of the directly steering the sediment partitioning (D) are similar for high and low flows. The water level is not changed initially and therefore initially the discharge partitioning is not affected. Throughout the simulation the slope of the Waal adjusts to the increased sediment supply and the slope of the PC adjusts to the decreased sediment supply. For both flows the final relative decrease in Waal discharge fraction is 1.8%.

Dredging and dumping (E) shows similar effects on the bed level and discharge partitioning as steering the sediment partitioning at the PK. Dredging and dumping also does not alter the water level and the discharge partitioning initially. The relative bed level increase of the Waal is somewhat higher for the dredging and dumping simulation than for the simulation in which the sediment partitioning at the PK is steered. Therefore also the relative decrease in Waal discharge fraction is higher with 2.4% for the low Lobith flows and 2.2% for the high Lobith flows.

Currently the IRM program aims at stopping further skewing of the discharge partitioning of the PK. None of the interventions from this study is capable of realising this on its own. Therefore multiple river interventions will have to be combined to be able to reach the ambitions of IRM. The knowledge on the effect of the interventions on the discharge partitioning at the PK and the bed levels of the Dutch Rhine branches can be used as a basis for further study towards to combined effects of river interventions on the bed level development of the Dutch Rhine branches and the discharge partitioning at the PK.

This study is an analysis of sand mining in the Vietnamese Mekong Delta (VMD) with the use of the optical satellite data set PlanetScope. This is done with a detection and classification model of sand mining vessels in the VMD. The classification model is based on machine-learning and it is trained with three classes: sand mining vessels, other vessels, and background. This study shows that it is possible to distinguish vessel types with a 3 metre spatial resolution and it shows great potential for a vessel classification model based on machine learning.

The La Plata Basin is the second largest drainage basin in South America. The Paraná River, the basin’s main river, discharges into the Río de la Plata estuary in Argentina. In the Lower Paraná Delta, near the deltaic front, a complex system of mostly natural and some man-made channels redistribute a part of the river flow. Like the river and the estuary, the channel network has been subject to sediment deposition, limiting the navigability needed for the small-scale transport of goods, leading to hindrance to tourism and other economic activities in the Lower Delta. Compared to the river system on the large scale, not much is known about the characteristics and the morphodynamic behaviour of the channel network. The objective of this research is to set a first step in providing insight on the relevant processes and human activities that influence morphology changes in the Lower Delta channel network.

Making use of existing data, a literature study and data obtained during several field surveys, various hypotheses were formulated. Hypotheses included the potential influence of land use change in the catchment and climate change related trends in precipitation patterns, climatic variability associated with El Niño Southern Oscillation, the effect of artificially deepening one of the two main branches of the Paraná River and the excavation of artificial channels in the Lower Delta in the early twentieth century. The effects of said processes and human activities are tested with a scenario-based hydrodynamic modelling study, making use of Delft3D Flexible Mesh with sediment transport and morphology modules.

Our analysis provided various insights in the behaviour of the Lower Delta channel network, and the influence of human activities and natural processes on this behaviour. A notable finding is that artificial deepening of the Paraná de Las Palmas by dredging its thalweg since 1990 has lead to a significant reduction in river flow entering channels supplied by the river branch and increased sedimentation rates in these channels. In addition, insight was gained on the spatial distribution of depositional and erosive patterns instigated by discharge and sediment input changes.

This research has provided a first, global insight into the relevant processes governing channel morphodynamics. Some of the findings can serve as input for future dredging strategies, as results imply that the current strategy has lead to limitations to the navigability of an intensively navigated part of the channel network. Furthermore, the outcome of this research can serve as a starting point for research on one of the specific topics covered by the hypotheses, including but not limited to the influence of storm surges, the effect of a potential spatial heterogeneity in soil composition and the influence of tidal divides on morphological features in the channel network.

Hydropower plants have proven to generate electricity reliably and predictably, store water to meet water demands during dry periods, improve navigability and reduce flood risk. The reservoirs of these hydropower plants face ongoing sedimentation, negatively effecting the electricity generation, water storage volume, navigability and flood risk. Obtaining an equilibrium of the in- and outgoing sediment flux reduces these negative effects.

The incentive for this report is the planned run-of-river hydropower dam cascade in the main stream Mekong river in Lao PDR. The Mekong river is characterised by the distinct low and high flow seasons and a unique ecosystem. At the location of the planned cascade, the river is located between mountains and the river bed consists of bedrock with alluvial bed forms at the banks and between rock outcrops.

Long, narrow and relatively shallow reservoirs are created due to the construction of the planned dams in the main stream Mekong. Flushing operations have proven to be an effective method to recover reservoir volume from rivers with a high season flow with long, narrow and shallow reservoirs. The Mekong river in Lao PDR has all those properties.

This report attempts to determine operational rules for a run-of-river hydropower dam cascade to increase the sediment flux by flushing operations at the dams, whilst still maximizing the electricity generation.

To do so, two steps are taken. Firstly, a set of experiments on the Mekong river and flushing events at a dam is performed in a Delft3D-FM software with the Real Time Control module. The output of these experiments are used as input for a bucket model with volume conservation to test different operational rules.

Using the Delft3D-FM software with the Real Time Control module, a one-dimensional representation of the Mekong river is made. This model is used for two purposes. First, the reduction of the sediment flux is determined by comparing the sediment flux during a representative year for the situation pre-dam and post-dam construction. Secondly, this model is used to test the influence of the draw down rate, water level set point and duration of flushing operations on the cumulative sediment flux through a dam for four different discharges. The results of the flushing experiments will then be used as input for the second step of the research, the bucket model.

Different simulations are performed using operational rules with different threshold discharges for initiating flushing events, different draw down rates and different frequencies of flushing a reservoir. Using random sampling the influence of these three variables is tested. Additionally, two predetermined strategies are tested and compared to the operational rules tested using random sampling. In the first strategy the dams in the cascade are flushing progressively from the most upstream dam towards the downstream dam. The second operational strategy flushes the reservoirs progressively starting from the downstream dam towards the most upstream dam.


Obtaining free flowing conditions during a flushing event increases the sediment flux significantly compared to flushing events that do not reach free flowing conditions, especially for lower discharges. Increasing the draw down rate proves to have limited influence on the sediment flux further upstream in the reservoir, while the flood wave released at the dam increases. Extending the duration of free flowing conditions after draw down proves to be an effective method to increase the sediment flux at the lowest reducing in electricity generation.

Performing a flushing event with 48 hours at free flowing conditions during the flood season increases the yearly cumulative sediment flux on average by a factor three. The cumulative electricity generation is reduced by just 2.5 %. Extending the duration of the free flowing conditions in a flushing event increases the sediment flux per lost GWh electricity generation.

Current operational rules at the planned cascade in the main stream Mekong do not consider flushing at all. It is recommended to include flushing events in the operational rules which are initiated if the discharge is above the design discharge of the turbines and below extreme discharges to increase the sediment flux and minimize electricity generation loss.

The Rhine-Meuse delta is characterized by the presence of many scour holes. Koopmans (2017) showed that these scour holes have very different growth rates, even if they are located within the same river branch. Most likely this is caused by either the heterogeneous subsoil, the presence of hydraulic structures, the geometry of the river or anthropogenic influences. Therefore, Koopmans (2017) advises to individually study scour holes in the delta since the local variations in conditions cause different shapes, sizes and growth rates, making every scour hole unique. One of these is the scour hole Beerenplaat, which is located at the confluence/bifurcation of the Oude Maas and the Spui. It is a large scour hole which recently gained much more attention due to the construction of a pilot nourishment by Rijkswaterstaat.

This thesis investigates the morphological development of the river bottom at the scour hole Beerenplaat and the location of the pilot nourishment, by analyzing measurements taken with Multibeam Echosounder. Due to the lack of knowledge on the composition of the heterogenous subsoil, it is tried to understand the observed morphological development based on the hydraulic conditions. At the scour hole Beerenplaat, the hydraulic conditions are characterized by two types of flow processes. The first type of flow process is caused by the confluence/bifurcation Oude Maas and Spui. With the help of Acoustic Doppler Current Profiler (ADCP) measurements and the output of a Delft3D model, the flow field at the confluence/bifurcation was investigated for four scenarios: peak ebb flow, flow changing from ebb to flood, peak flood flow and flow changing from flood to ebb. These scenarios are each paired with different flow features such as flow accelerations, flow stagnation and additional turbulence. It is expected that the second type of flow processes at the scour hole Beerenplaat are the 3D flow processes, which are flow contraction, a (curved) recirculation zone and the horseshoe vortex. Again, the output of the Delft3D model and the ADCP measurements are used to investigate them. Unfortunately, the limitations of both the measurement and the model and the use of an incorrect geometry of the scour hole Beerenplaat, made it not possible to succeed in this. Based on the actual profile of the scour hole, it is expected that the (curved) recirculation zone develops at the steep slope of the scour hole Beerenplaat during ebb flow.

By computing bed shear stresses and using literature, it was investigated how these flow processes attack the river bed during ebb flow, indicating areas vulnerable to scour. It was found that these areas were no match with the observed morphological development. Due to the incorrect geometry of the scour hole in the model, it was not possible to include the hydraulic forcing during flood flow. Most probably, it should be included to describe the expansion of the scour hole and growth towards the Spui. Despite, this research has given better understanding of the flow processes occurring at the scour hole Beerenplaat are shaped and affected by the tide.

The river Waal is part of an economic important transport-corridor that connects the ports of Antwerp, Rotterdam and Amsterdam to Germany. Ongoing processes such as (1) climate change, (2) large scale river bed erosion and (3) up-scaling of vessels threaten the future navigability of the river. This will lead to massive economic damages as taken in 2018 (Strengs et al., 2020). Canalisation of the river by means of weir-lock complexes is a considered by Rijkswaterstaat to improve inland navigation during periods of low discharge and prevent economic damages. This leads to the primary goal of this study; investigate the required lock capacity to provide smooth and reliable passage of the river Waal now and in the future.

A literature review was conducted to assess the future development of the drivers of the worsening navigation conditions and to gain insight in market- and fleet developments. The developments in the drivers underline the urgency for measures. The development of the fleet navigating on the river Waal is characterised by up-scaling for the past 20 year. This trend is expected to continue the coming years. Future market developments are very uncertain due to the energy transition and the nitrogen crisis, making it very difficult to make accurate projections on future fleet intensities and compositions. Therefore a range of traffic intensities is used to characterise future fleets that encounter the lock complexes.

The number and locations of the lock complexes is investigated by analysing available nautical depths and water levels along the river Waal for several stationary discharges at Lobith. Water levels are set up to a level such that navigation for all vessels (fully loaded) is possible. From a financial perspective it is most attractive to minimise the number of weir-lock complexes, however this is contrary to flood safety aspects on the river Waal. Installation of two weir lock complexes is considered plausible taking into account minimising the number of weir-lock complexes and flood safety.

Vessel traffic simulations are conducted in SIVAK III to investigate the performance of multiple lock configurations in terms of average waiting time and service level. SIVAK III is able to simulate the passage of vessels at an individual level in a network of waterways and locks. A fleet analysis on a representative IVS data set is conducted to provide SIVAK III with fleet intensities, fleet mixes and arrival patterns.

For the upstream (rkm 905) lock complex is recommended to use a lock complex with 4 chambers with dimensions 28.4x305m, but with in mind the option for a 5th chamber in the future. This lock complex is able to handle the current fleet +10% intensity within the considered requirements. A 5th lock chamber of the same size can handle an increased intensity of +30% including strong up-scaling effects. For the downstream lock complex (rkm 941) it is recommended to use a lock complex with 4 chambers and dimensions 25x330m. The lock complex is able to handle the current intensity +30%.

Implemented in river landscapes, Nature-based Solutions (NbS) have the potential to reduce flood risk, while also playing an important role in restoring many of the ecosystem services that are lost as result of human interventions and global warming. A barrier to succesfull implementation of NbS is the lack of a global and common framework with guidelines for its implementation and evaluation. In response, the IUCN Global Standard for NbS was published. Even though the IUCN Standard has been designed to be applicable to NbS in all sectors and over the entire globe, knowledge on its applicability and usefulness for specific sectors remains limited at present. Therefore, this study aims to identify the challenges that occur in ex-post application of the IUCN Standard to river restoration projects with a focus on flood risk mitigation, and the added value that this application may provide.

At first, a literature study is conducted in which the content of the IUCN Standard is related to twenty-two other assessment frameworks for NbS and compared in-depth to the three most relevant frameworks. These comparisons indicate that that the IUCN Standard has a broad scope of application, provides limited flexibility in assessment to its users and is descriptive. Furthermore, the comparisons reveal that the IUCN Standard can be used as a tool to evaluate the extent to which the essential processes of a NbS, established by the IUCN, have been incorporated in the project (i.e., process-oriented framework). The standard can, however, not be used to evaluate project results, including biophysical and social results.

In the next part of the research, the IUCN Standard is applied to three case studies of river restoration projects with a focus on flood risk mitigation, of which at least two differ significantly in the surface area, position in the catchment, kinetic energy of the river, data accessibility, resources and the type of riverine NbS measures that were implemented. The selected case studies are the Eddleston Water Project, the “Room for the River” Deventer Project and the Missouri River Levee Setback Project. Despite facing challenges in the interpretation of indicators, data accessibility, a relatively coarse scale for evaluation, and tensions between the project objectives and the use of the IUCN Standard, the standard is successfully applied to all case studies. The case study results consist of (1) a total percentage match to the IUCN Standard and a statement on being in adherence to the standard, which may provide credibility to the project processes, (2) the strenghts and weaknesses of a project, which may be used to guide projects and strengthen (future) projects, and (3) a radar chart, which may provide possibilities to compare to and learn from other projects. Based on these results, it can be concluded that, despite of a few challenges, the IUCN Standard is applicable to river restoration projects with a focus on flood risk mitigation, and that application of the standard may provide added value in various ways, although restricted by the limited evaluation of flood risk mitigation.

Due to river training in the past centuries, the bed level of the Waal started and is still decreasing by several centimetres a year. Erosion of the riverbed causes problems for objects underneath the riverbed like cables, pipelines and foundations of structures. Furthermore, some parts of the river are eroding at a higher velocity compared to other parts due to a difference in the composition of the bed material. This can result in a jump in the bed level while the water level cannot follow this jump. This results in less available draught for inland vessels. If no mitigation measures are applied and the bed level keeps decreasing, more problems are likely to occur resulting in less transport over the Waal. A possible solution to reduce bed erosion inside the Waal locally is the use of groyne field nourishments.
The objective of this research is to obtain more knowledge about the flow in a real-life groyne field and the effect of vessels on this flow. The research question formulated for this research is, therefore: \textit{what is the influence of vessels on the flow properties inside a groyne field and in what way do the characteristics of the vessels influence this?} To answer this research question a literature study is done first. Secondly, a measurement campaign is performed and finally, the results are analysed to investigate the effect of the characteristics of the vessels.
The literature study is done to obtain more knowledge about the flow properties inside a groyne field. The distinction is made between emerged and submerged groynes and the scenario with and without vessels. The situation where the groynes are emerged is dominant for the erosion inside the groyne field. In this scenario, the flow inside the groyne field consists out of one or two circulation patterns. The first circulation pattern is a large eddy in the downstream part of the groyne field, referred to as the primary eddy. When the groyne field is long enough, a second eddy is present in the upstream part of the groyne field, the secondary eddy. This eddy has a flow direction opposite to the primary eddy and a smaller flow velocity. When a vessel passes a groyne field, the flow pattern inside the groyne field changes due to the primary waves created by the vessel. Firstly, the water level inside the groyne field is raised due to the bow wave. Secondly, due to depression in the water level caused by the primary wave the water level inside the groyne field is lowered. Finally, the water level inside the groyne field is increased again due to the stern wave.
To investigate the effect of vessels on a groyne field, a measurement campaign is performed. The flow direction, flow velocity and water level inside the groyne field are measured with the use of several measurement instruments for two weeks. The obtained data by the measurements is analysed and visualised. The results show that the primary eddy remains partly intact when a vessel sails past the groyne field. Since the primary eddy remains partly intact, the water is guided towards the upstream part of the groyne field. In the upstream part of the groyne field, the secondary eddy does disappear and the flow is directed out of the groyne field. This results in the water, and sediment, flowing out of the groyne field mainly in the upstream part of the groyne field. This has resulted in a scour hole present in the upstream part of the groyne field.
In this research the effect of multiple vessel characteristics on the water level and flow velocity inside the groyne field is investigated. The vessel characteristics investigated are the draught, the sailing speed, the vessel length, the vessel width and the distance of the vessel towards the measurement instrument. The effect of vessels on the water level and flow velocity inside the groyne field differs for each vessel. Information about the vessels has been obtained by using AIS (Automatic Identification System) data. During the processing of the AIS-data, irregularities and errors were found and mostly removed from the AIS-data. According to the final results, the draught of a vessel does not influence the water level and flow velocity inside the groyne field. An increase in the sailing speed of a vessel and a decrease in the distance of a vessel towards the groyne field does have an enlarging effect on the water level difference and the flow velocity inside a groyne field. The combined effect of increasing the length and the width of a vessel also has an enlarging effect on the water level difference and the flow velocity inside the groyne field. It should be noted that the results show a large variance and it is impossible to predict the effect of a single vessel based on the vessel characteristics.
The measurement campaign showed that a constant water level fluctuation is present inside the groyne field even when no vessel is affecting the flow inside the groyne field. Multiple explanations for this fluctuation are given with transverse oscillations between both riverbanks being the most likely.
The measured flow pattern inside the groyne field without vessel is according to the literature. When the flow is affected by a vessel, the flow pattern differs from the flow pattern described in the literature. Furthermore, the effect of a vessel is likely not only depending on the characteristics of a vessel but also on the flow mechanism inside the river system such as the helical flow, the angle of the groyne field with respect to the main channel and the constant water level fluctuation inside the groyne field.
This research adds to the already existing knowledge about the flow in groyne fields. To investigate the effectiveness of groyne field nourishments, a pilot is planned where the actual nourishment will take place at the same location as the measurement campaign. Therefore, this research can be used to better prepare the planned nourishment pilot to investigate the effectiveness of groyne field nourishments. Furthermore, this research contains data about the flow pattern inside the groyne field without nourishment which can be compared to the situation during and after the nourishment pilot. In the end, this research can be a part of the answer to whether groyne field nourishments can reduce or stop the erosion inside the Waal river. 

This master thesis is about the positive effects of river system behaviour along the river IJssel. Due to failure of the flood defences along the IJssel, the protected areas will flood and water will flow out of the river. The discharge in the river will decrease and thus the water level at the downstream ends of the river will also decrease. This will have an impact on the required dimensions of the flood defences downstream as the loads will be lowered due to the decrease in water level. The design of the dimensions will change and the costs of the flood defences downstream are lower. In this research, flood simulations are done in the dike-rings along the river IJssel due to overtopping with and without breach formation. The simulations are done in a developed HEC-RAS model and eventually the decrease in water level is generated within the model computations. The tool OKADER is used for the calculations of the required dimensions of the flood defences in 2050 and the associated costs when changes in water level is incorporated. At the end the interest is to quantify the positive effects of system behaviour in terms of differences in required dimensions of the flood defences along the river IJssel and the amount of saved costs.

Large-scale measures within the river programmes such as Room for the River, Natura2000 and Water Framework Directive have increased the biodiversity in Dutch rivers and have achieved a more natural landscape. However, recent river programmes have shown conflicts between safety against flooding and riverine nature rehabilitation with maintaining navigational water depths. Therefore, an integrated approach is called out upon to improve the river management within these programmes. Conventional groynes are typically used to improve functions within the river programmes, whose primary function is to maintain navigational water depth. Groynes are transverse structures in which large turbulent structures are observed around the groynes. Consequently, significant bed shear stresses are developed, leading to significant local scour. Investigations for improving alternative groyne configurations are often studied for optimizing the groyne structure. The flexible groyne is considered an optimization of the conventional groyne structure. The flexible groyne consists of steep slopes and has a permeable characteristic. Although a fair amount of research has already been carried out on various groyne configurations, detailed flow characteristics around and through permeable, sloped groynes are limited. Hence, this research aims to numerically quantify the effects of permeability and head steepness of groynes. A literature study is executed to investigate the critical processes required for capturing within the numerical model to answer the research question. From the literature study, it appears that the most important processes are the non-hydrostatic effects, adapting large turbulent structures and implementing the porous zone using a non-linear function. Multiple software packages have been analyzed. Fluent is chosen, which is analyzed to capture the required processes adequately.
A new numerical model has been set up for investigating the research question by simulating flow around groynes. The model is validated against three experimental studies for various characteristics. The important mean flow characteristics have been validated within an acceptable range. Still, it appears that the numerical model tends to underestimate the mean streamwise flow velocities, overestimate the Reynolds shear stresses and shift the peak values of the Reynolds shear stresses downstream. Four configurations are identified for the simulations of varying head steepness and porosity. It appears that the increase of the porosity reduces the large turbulent structures and bed shear stresses close to the groyne and shifts the peak values of the Reynolds shear stresses, and bed shear stresses further downstream. The porosity reduces the maximum Reynolds shear stresses and bed shear stresses compared with the Reynolds shear stresses, and bed shear stresses for an impermeable groyne. These reductions are because of the momentum exchange between the free flow region and the flow through the porous structure, which reduces the mean flow velocity in the free flow region. For decreasing steepness, the large turbulent structures and bed shear stresses are observed close to the groyne due to increasing deflection. The flow appears to follow the geometry of the sloped groyne more smoothly. This research is seen as a first approach for modelling a porous, sloped groyne. Further improving and analyzing numerical modelling for porous, head sloped groynes are advised to increase the model's accuracy. Furthermore, more simulations for varying the head steepness and porosity is suggested to improve the relations between the increase of porosity and head steepness for the flow characteristics. In addition, including sediment transport models within the model is expected to increase the understanding of the hydrodynamics and morphology around these specific groynes.

In the Waal bed degradation occurs, which is mainly induced by a large number of river regulations measures done in the past. Rijkswaterstaat develops possible measures and new techniques to stop riverbed erosion and/or mitigate the negative effects. One of the possible new techniques to reduce riverbed erosion locally is groyne field nourishments. The objective for this research is to deepen insights how groyne field nourishments provide enough sediment to the river such that bed degradation locally does not develop further. The following research question is formulated for this: How can groyne field nourishments act as small feeder nourishment that release sediment slowly to the main channel? To answer the research question a literature study is done and a XBeach model is set-up. The literature study is done to obtain knowledge about the hydrodynamic and morphodynamic processes in a groyne field in case of emerged and submerged groynes. From this literature study it appears that the effect of navigation on the morphology in a groyne field is dominant over the effect of the river discharge when the groynes are emerged: net sediment is transported from the groyne field to the main channel mainly by suction. When the flow conditions increase and the groyne get submerged, the effect of navigation on the morphology in the groyne field decreases rapidly and the net sediment transport is from the main channel to the groyne field induced by the river discharge, mainly the large-scale eddies. Extra literature study is done to possible relevant coastal and river processes to get knowledge of the effects of waves and currents on the behaviour of nourishments in a groyne field since very limited research has been done before on groyne field nourishments. It appears that especially dune erosion and river bank erosion by waves and currents can be used to explain how nourishments erode by the primary and secondary ship wave system. After the literature study a XBeach model is set-up of for a series of emerged groynes on a straight section in the Waal. The model is calibrated and validated with data from Rijkswaterstaat and literature. In this model three possible nourishments with the same volume are applied at different locations in the groyne field: 1) one upstream in the groyne field; 2) One downstream in the groyne field; 3) And one in the middle of the groyne field. From this research it can be concluded that groyne field nourishment at all three locations can work as small feeder nourishment that release sediment slowly to the main channel in the case of emerged groynes for about 200 days per year. The nourishment placed in the centre of the groyne field appears to be the most effective nourishment, since 1) the waves and currents induced by navigation attack the nourishment along all its edges, 2) the centre nourishment causes in almost the whole groyne field an increase of sediment transport to the main channel and 3) the flow pattern in the groyne field is changed favourably for the sediment transport of already suspended sediment to the main channel. This research should be seen as first indication if nourishment could work at all. It is advised to research the material of the nourishment and to simulate the groyne field nourishments for a longer period, such that more flow conditions and more ship passage are included, to get a more complete picture of how groyne field nourishments act as small feeder nourishments. Furthermore a practical test with a centre nourishment is recommended to collected data of the hydro- and morphodynamics in a groyne field with nourishment.

Flexible river training structures such as tetrahedron frames (`porcupines') can be attractive for control of braided river channel networks in regions where permanent control structures (e.g. groynes or dams) are too expensive or potentially inefficient, such as systems with highly dynamic flow regimes and morphology. Porcupines provide hydraulic resistance, generating energy loss and reducing velocities that may further encourage sediment deposition. Porcupine systems have seen increasing implementation, especially for bed or bank protection, but were also recently implemented in a channel-control pilot project on the Ayeyarwady River in Myanmar. Many porcupine systems to date are designed by trial and error due to lack of quantitative design criteria. The 2019 pilot project used large-scale numerical modelling of resistance areas to evaluate the potential impacts of porcupine structures; however, how to best incorporate the impacts of porcupine structures on flow and sediment transport in numerical models has not been systematically evaluated. Improved models or better estimates of uncertainties could facilitate future porcupine system design. Therefore, this study examines methods for incorporating porcupine fields into numerical models and interpreting those models to make informed design choices. Data and observations from the 2019 pilot project implementation, a 2018 porcupine flume experiment, and extensive literature review have been used to examine the expected hydrodynamic and morphodynamic impacts of porcupine systems that need to be accurately captured in large-scale numerical models. A 2DV model using two resistance formulations representing porcupines was elaborated and tested against experimental porcupine performance. The Uittenbogaard (2003) rigid cylinder model was found to replicate well porcupine behavior for less dense systems under limited flow conditions; however further verification is needed for more dense systems, variable flow regimes, wider boundary conditions and mobile beds. The 2DV model was collapsed to 1DH, using two different resistance formulations, to examine the strengths and weaknesses of large-scale models in predicting porcupine performance. The Baptist (2005) resistance model was found to best represent porcupines; however, parameterization was not straightforward from porcupine geometry, indicating that further studies will be needed to confidently translate porcupines into `rigid cylinders' for input into the model. In addition, neither the 2DV nor 1DH models were able to capture the hydrodynamics at the leading and trailing edges of porcupine fields, which were found to be critical for design considerations from the pilot study data. Therefore, these important limitations need to be taken into account when interpreting model results and examining how to improve them in the future.

This thesis research has been conducted to analyse the sediment dynamics in the Yangon Estuary, in order to define the cause for the sedimentation in Monkey Point Channel. For years, Yangon Port has been suffering from limited accessibility due to the sedimentation in the channel and currently daily dredging is required in order to let ships enter the port.
The main characteristics of Yangon Estuary are; tidal range of 6 m, high suspended sediment concentrations (up to 6 g/l), a monsoon climate and the presence of a confluence within the tidal range. Research to the cause of sedimentation is done by making a conceptual model of the estuary based on a study area analysis and a literature study to estuarine, riverine and sediment processes. In addition, numerical models are used to improve the conceptual model in a quantitative manner. The conceptual model resulted in the following findings.
The fluctuations in SSC are dominantly determined by the tide. During the monsoon season suspended sediment is brought in the system mainly by the Yangon River discharge, causing for averaged SSC values of 1 g/l during the season. In dry season, the SSC shows a fortnightly rhythm caused by the spring/neap cycle. Strong spring tidal currents cause for high bed shear stresses on the shoals, exceeding 1 N/m2, which erodes the stationary fluid mud layers. Due to the dispersion of the mud, the SSC rises rapidly up to 5 g/l. During neap tides the bed shear stress is much less, enabling the fine sediments to settle on the shoals and restore the fluid mud layers. Hence, the SSC values reduce to less than 0.5 g/l. During the monsoon, the spring flood current is reduced due to the seaward directed river discharge. Therefore, the spring flood currents are insufficient to erode the stationary fluid mud layers, hence the SSC are less than during spring tide in the dry season.
In contrast to the fluctuations in erosion and deposition of mud on the shoals, almost continuously deposition and consolidation of mud is possible in Monkey Point Channel. This is possible because the channel is located in the stagnation-zone where both during flood (bifurcation) and ebb (confluence) the flow velocities and bed shear stresses sufficiently low to let mud settle. After deposition the mud is not resuspended, and consolidation causes the mud layer to become thicker and become problematic for the ship traffic.
To conclude; the combination of high SSC with the possibility of consolidation of deposited mud in the stagnation-zone results in too hard layers to sail through. This potential cause corresponds with the dredged material from the channel bed and the sedimentation rate in the channel.
It is recommended to relocate the navigation channel outside the stagnation-zone. The combination of land reclamation at the western estuary bank downstream of the confluence and a dredged channel shows the most promising results. However, more research is required to determine the long-term sedimentation rates in the new channel.