In the Nieuwe Waterweg an ongoing pilot takes place in one of the groyne areas. This pilot is a part of the “De Groene Poort” project. The idea for this project is to create intertidal areas by modifying and nourishing groyne areas. These artificially formed intertidal areas will create a new habitat for wildlife and attract different vegetation. For this project, several modifications have been made to the groyne area: a dam has been placed in front of the groyne area, the groynes on either side have been partially heightened and a nourishment has taken place. To better understand the effects of these modifications to the groyne area, research has been done on the effects of the tide and waves caused by shipping on the flow and sediment behaviour inside the groyne area.

Two different measurement campaigns have been carried out for this research. In the first measurement campaign six ADVs were placed in the groyne area between March 24 and April 12 ,2022. These ADVs measured the velocities and pressures with a frequency of 8 Hz. Also, sediment samples were taken during this campaign, which have been analyzed using laser diffraction. In the second campaign, ADCP measurements were carried out with a floating ADCP attached to a jet ski. With this ADCP the vertical velocity profiles have been obtained for several cross-sections at different stages of the tide.

It was found that the flow in the groyne area has changed due to the dam and the nourishment. Typical flow in an emerged groyne field with the eddies is unrecognizable during lower water levels in the modified groyne area. The exchange of water between the main channel and the groyne area is through the gap in the dam, which removes the mixing layer that separates the groyne and the main channel during submerged conditions. The flow in this groyne area is lateral and divided into two main flows along either side of the nourished island. Rocks and a higher entrance in the downstream groyne compared to the entrance in the other groyne, gives the groyne area different flow velocities between ebb and flood. The neap and spring tidal cycle enhances Ebb and flood differences in the groyne area even more. These velocities differences also impact the sediment transport and its absolute direction in the groyne area. The dam also helps reduce the wave influence on the groyne area, although these waves still significantly influence the velocities. Waves also propagate in a lateral motion from groyne to groyne through the groyne area. The water can move material from the nourishment, but the spreading of this material is limited to a number of locations in the groyne area. For the largest part, the nourished material is still at the location where it is deposited.

This study assesses the application of graph theory to examine the connectivity of aquatic habitat in the Sliedrechtse Biesbosch and preserve or improve the area’s ecological value. The study addresses the relation between hydrodynamics and ecology, and evaluates different definitions of connectivity. Graph theory provides a novel and promising approach to assess connectivity in aquatic environments. With increasing availability of data, more accurate and informative analyses can be carried out, resulting in more effective designs of restoration measures. The application of graph theory in such research has, as one of its main strengths, its visual accessibility to laypersons or others without expertise in interpreting numerical model results. Furthermore, graph theory can offer both a holistic system view of a water network by evaluating the system as a whole, as well as a local view which is possible by looking at the single nodes and edges in the graph. This enables investigation of the role of individual channels within the system and the identification of vulnerable spots within the network, limiting the availability of aquatic habitat.

Graph theory is applied in various fields of research. As numerous metrics exist to examine the properties of a graph, an introduction to the most important metrics is given in this study. Adequacy of metrics is dependent on the questions posed and parameters relevant for the specific topic to be investigated. It is shown that in aquatic habitat connectivity, metrics such as betweenness centrality and bridges are indicative to obtain a general view of the network. When temporal variations play a role, as is the case in a tidal area, metrics as the number of components (NOC), the order of the largest component and the length of connected pathways (LOCOP) of the largest component are suitable to determine the connectivity. Whereas these metrics show useful in studying aquatic habitat connectivity, they may be less appropriate in connectivity studies of the same water system aiming at other fields of application, e.g. sediment connectivity.

Results show that graph theory provides a useful instrument in analyzing the aquatic habitat connectivity of the Sliedrechtse Biesbosch, which is investigated in a case study. The ease at which key nodes and edges are identified offer great possibilities for the design of nature restoration measures. In the present layout of the study area, large variation of aquatic habitat connectivity occurs based on a flow velocity fragmentation threshold of 0.3 m/s, corresponding to the maximum tolerable flow velocity for the European flounder (Platichthys flesus). Due to tidal influences in the study area, flow velocities vary continuously and the threshold flow velocity is exceeded during part of the tidal cycle. Considering the available habitat of other species gives different results depending on the tolerable flow velocities of the specific species. As is shown in this research, a combination of graph theory and numerical modelling enables the design and simulation of different nature restoration measures and system layouts to improve the aquatic habitat connectivity of the area.

The method presented in this research can be particularly useful to ecologists investigating suitable habitats for specific fish species. Also for engineers and others involved in the design of nature restoration measures, the method can be helpful since the designs of restoration measures can be evaluated considering the effect on habitat availability. The research provides an informed basis for subsequent applications of graph theory and numerical modelling to aquatic habitat connectivity. By selecting the most suitable design parameters and improvements of the network schematization, a justified decision can be made on the most effective restoration measures concerning the improvement of available habitat. Especially considering a combination of habitat preferences, such as flow velocity, water depth and turbidity, can provide proper insight in the aquatic habitat connectivity of an area for specific species.

Groynes are hydraulic structures commonly applied in the Dutch rivers. Depending on the water depth, groynes can be emerged or submerged. When a groyne is emerged, it has two main functions: maintaining the water depth in the main channel and preventing the river from eroding its bank. When the discharge in the river increases, the groynes become submerged. A submerged groyne acts as an obstacle to the flow, resulting in additional resistance and an increase in the upstream water level.

To increase the flow capacity of a river during extreme conditions, a couple of measures can be considered: increasing the height of the dikes and embankments, reducing the overall resistance of the river cross-section and increasing the area of a river cross-section.

This thesis focuses on reducing the overall resistance of the river cross-section, and more specifically, on investigating the effect that streamlining the downstream slope of a groyne has on the groyne-induced resistance. Hypothetically, streamlining the groyne by decreasing its downstream slope would decrease the intensity of flow processes like downstream flow separation, which could increase the discharge capacity of the groyne, and thus of the river cross-section, as a result of the decrease in groyne-induced resistance. An increase in discharge capacity would decrease the flood risk during extreme conditions.

To investigate the effect of streamlining a groyne by decreasing its downstream slope, a physical model experiment was set up in the 5 x 40 m^2 flume at the Hydraulic Engineering Laboratory of Delft University of Technology. The physical model represents part of a river cross-section. From the total 5 m width, the main channel and groyne field both took up 2 m and the floodplain took up 1 m. In streamwise direction, the flume contained six groynes and five full groyne fields. The groyne fields had transverse bed slope of 1:25. Electromagnetic flow meters (EMF meters) were used to measure the flow velocity at many points in both streamwise and transverse direction. The water level was measured by laser altimeters.

Decreasing the downstream slope of a groyne to 1:8 compared to a reference situation with a downstream slope of 1:3 resulted in a 4 % increase of the discharge capacity over the crest of the groyne. This increase of discharge capacity was not uniform over the transverse axis. Near the groyne tip, this increase of discharge capacity was more than 6 %, whereas at the end of the groyne, the discharge capacity decreased slightly compared to the reference situation.

A more detailed analysis of the data gave insight in why decreasing the downstream slope of a groyne increases the discharge capacity of a groyne. Streamlining the groynes resulted in a significant decrease of the relative turbulence intensity along the downstream slope of the groyne. This was consistently around 50 % lower for the streamlined groynes compared to the reference situation, indicating less intense turbulent structures. Moreover, auto-correlation functions of the flow velocity signals showed a shorter correlation length in conjunction with lower amplitudes and smaller periods of the fluctuations for the streamlined groynes. This indicates a signal with less correlation and higher frequencies. These results explain why the discharge capacity of a streamlined groyne is larger than of a reference groyne.

The Netherlands, Germany, and Belgium were hit by heavy and prolonged precipitation in July 2021. As time passed, weather warnings escalated, leading to evacuations due to predicted floods, including in the Rur catchment. It was difficult to forecast the flooding of the Rur, raising the question of which elements are crucial in a flood predictionmodel for the Rur river. This question is addressed by addressing both a hindcast of the 2021 flood event and creating forecasts based on the weather forecast of July 13, 2021.

The Rur river basin is characterised by topographic and geological variations, with the steep Eifel responding differently than the flat lowlands, and human intervention in the form of reservoirs and lignite mines. A hydrological Wflow_SBM model has been derived for the Rur river basin, encompassing these characteristics, along with a hydrodynamic ProMaIDes model for the downstream reach of the Rur. These models were compared to investigate various aspects: river routing, floodplain flow, tirbutary interactions, the influence of reservoirs, and the impact of reduced groundwater levels.

The results of the 2021 floods indicate that modelling flows in floodplains is crucial to shaping the flood wave, both in tributaries and the Rur itself. Additionally, the reservoir played a significant role in attenuating the flood wave, with the increase in the outflow of the reservoir primarily affecting the tail of the wave. The reduced groundwater level was simulated by adding a leakage termto the saturated subsurface zone, whose indirect effect is significantly greater than the leakage termitself. Moreover, the tributaries Worm and Inde, particularly, are influential in the Rur’s discharge. These characteristics are also evident in the simulated forecasts, although the spatial and temporal resolution is significantly lower for these meteorological predictions.

Finally, the characteristic response of the Rur demonstrates that not everymodel type is equally practical for flood forecasting. The dominant flow from the reservoirs is highly regulated and is unlikely to induce inundations downstream. Complex flow patterns in floodplains only become relevant in the Dutch Rur, which makes two-dimensional modelling particularly valuable here. Therefore, it is recommended to use a one-dimensional discharge model, incorporating delay effects from winter bed flows. When predicted discharges at the Stah station are exceeded, two-dimensional simulations may provide a solution, the model area reduced to the Dutch Rur, focussing on predictions where a critical value related to floodplain capacity (Qlimit = 300 m^3/s) is exceeded.

The flooding of the River Geul in July 2021 was an eyeopener for the society, the government and many others involved. Besides the major structural damage as a consequence of the flooding, the emotional damage was and still is massive. Therefore, the need for measures to reduce the impact of these extreme events is bigger than ever. Many people had to temporarily leave their house and companies had to shut down. One thing became clear: the impact of comparable or even worse flooding has to be lowered, and one way to achieve that is by implementing measures in the River Geul which reduce the flood risk. The main goal of this research is to find out the impact that certain measures have on the consequences of flooding of the River Geul. Therefore, the main research question is: What is the impact of hydraulic or hydrological measures on the consequences of extreme future flooding of the River Geul? An important aspect is to consider the multidimensional impact of each measure. This can be either social, economic, or ecological impact due to flooding and the implementation of the measure itself.

The evaluation of the impact of measures is done by using different methods. First of all, an existing SOBEK model is used to simulate two extreme events: July 2021 (recurrence interval ≈ 1/100 - 1/1000 per year) and a stress test (recurrence interval ≈ 1/10.000 per year) which simulates 60% larger discharge and precipitation amounts than July 2021. Based on the bottlenecks in the River Geul, which are either bridges, weirs, culverts or orifices, measures are defined and simulated in SOBEK. A distinction is made between possible measures down- and upstream of Valkenburg and in Valkenburg, dependent on the expected effect of the measure. All the measures are simulated for both July 2021 and the stress test. The measures that significantly reduce the flooding depth and local water level nearby urban areas, which follows from the longitudinal cross-sections of the maximum simulated water level, are rated as effective. The effective measures are also evaluated with a damage victim module (SSM2017) to calculate the reduction of damage and victims, but no cost-benefit analysis is performed. Finally, expert judgement is used to estimate the costs of the effective measures. Social impact and the impact on Natura 2000 area is also examined here.

Eleven measures were considered, and four of them showed effective results and therefore their impact is compared. The effective measures are: widen the river downstream Valkenburg, bypass through Valkenburg performed as a tunnel (in-situ or drilled) or channel, remove obstacles in the River Geul along Valkenburg and enlarge the current basins in the River Geul. For the flooding of July 2021, the optimization of current basins in the River Geul scored by far the worst on damage reduction and costs. River widening and removing obstacles both reduce the amount of damage by 6 percent, while the costs are at least a factor of four lower compared to the bypass (dependent on the type of bypass). However, the bypass reduces the damage by at least 34 percent. The most expensive bypass is the drilled tunnel, but it comes with less social impact, because barely any buildings have to be removed in the city centre of Valkenburg (assuming that the subsoil in Valkenburg is suitable for a drilled tunnel). For the stress test, the damage reduction of the effective measures was not significant compared to July 2021. Thus, for extremer events the measures have no longer a considerable impact. This is not an argument to not implement measures, because the probability that a similar event as the stress test recurs is at least a factor of ten lower compared to July 2021.

Depending on the preferences of decision makers the choice for a measure can be made. Based on this research and looking at the flooding of July 2021, a bypass in Valkenburg reduces the damage along the River Geul the most with approximately one-third. For a bypass performed as a drilled tunnel the social impact is limited as maximum five buildings have to be removed but a cost estimate of 112 - 207 million euros is associated with this choice. River widening downstream Valkenburg or removing obstacles in Valkenburg comes with lower costs of 4 - 23 million euros in combination with no social impact but this results in a damage reduction of only 6 percent.

The Rhine-Meuse estuary is part of the Southwestern Delta area in the Netherlands. The nature present in the estuary suffered a great impact due to urbanization, as a natural delta transformed into an industrialized river, mainly due to port activities. Various parties decided to collaborate in order to return the tidal nature in the Rhine Meuse estuary through constructing tidal parks. Although the idea of reintroducing tidal nature into an industrialized estuary seems promising, problems arise when the projects are being executed. Human interventions necessary to complete the design of the tidal parks often lead to undesired morphological changes. These either consisted of an excessive amount of cohesive sediment import, or hardly any import. Consequently, maintenance in form of dredging or nourishing activities is required. When introducing tidal nature, little maintenance is desired, both from a financial perspective and from an ecological perspective. The undesired morphological changes result from limited knowledge on the impact of human interventions on the hydro and morphodynamics in tidal parks. This research therefore primarily focuses on gaining new knowledge on the hydrodynamics and morphodynamics inside tidal parks and assessing the effect of different elements such as groynes and longitudinal walls on the latter. This is done through a case study, the Groene Poort, a collective name for the tidal parks located in the Nieuwe Waterweg.

A depth-averaged (2DH) Delft3D model is used to research the hydro and morphodynamics of the tidal park. A constant tidal forcing and a constant fresh water discharge are used as boundary conditions. The effects of wind, waves and density driven currents are neglected. The effects of changes in hydrodynamic forcing, including a morphological tide, a spring tide and a spring tide in combination with a surge on the morphodynamics are determined. This research showed that the tidal flow results in relatively small velocities inside the studied tidal park with mean velocities around 5 cm/s. The critical velocities for transport of noncohesive sediment transport are only reached at the west entrance of the studied tidal park. At this location the sediment deposits, further transport towards the river bank is not possible resulting from the magnitude of velocities. A spring tide is responsible for an increased import of noncohesive sediment at the river bank area.

This research provides a guide on the effect of relatively small adaptations in geometry which will enhance or decrease the natural processes of sedimentation and erosion in the tidal parks. Tables are included providing the important parameters both with respect to the hydro and morphodynamics of various adaptations in geometry. These tables can be used in future design and adaptations of already constructed tidal parks. However, the effect of the surrounding area including the location in the river greatly impact the hydrodynamics and morphological development of the tidal parks.

The Gulf of Mottama, located in the southwest of Myanmar, is home to morphologically interesting processes. An entrance of around 100 km wide narrows into a funnel­shaped bay towards the Sittaung River in the north. The entire estuary region is subject to strong dynamic morphological activity which is alleged to be driven by the large tidal energy and sediment inputs. The dynamics of the tidal channels in the Sittaung estuary have resulted in rapid bank erosion of up to 3 km/y. The Sittaung estuary harbours a unique set of characteristics. This has made the question of which processes and mechanisms cause the bank erosion a complex one for which no clear cut answer is currently available. The knowledge of the main processes and mechanisms is valuable to improve the understanding of morphological functioning in dynamic estuaries. The main research question has thus been formulated as: • What is the effect of the large incoming tide and storm events on the bank erosion of the Sittaung estuary and to what extent can this erosion be simulated with a numerical model? The research objectives have been achieved through a literature analysis, system analysis, satellite analysis and modelling simulations. Main conclusions of the research have been as follows: The satellite analysis has shown little to no correlation between the wet season discharge increase and the bank erosion rates. It also showed large differences between erosion rates at different heights of the estuary. Modelling results indicate a prominent role but cannot substantiate a quantitative impact of the tidal forcing and associated tidal bore. River discharge fluctuations were shown to have little effect on the bank erosion. • The results of both the satellite and numerical modelling analysis have shown no additional implications on the dynamic morphology caused by large incidental storm events. Long­term simulations with respect to the bank erosion resulted in several hindrances. Heightened levels of channel incision occurred through a fault in the numerical schematization. The representation of bank erosion in the model has also been subject to stalling.

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.

Ships in rivers create waves and these can have a negative impact on fish habitats along the river banks. A modelling study is carried out to investigate how these ship-induced waves can be damped in groyne fields by making structural modifications to the groynes. For this purpose, different types of openings (notches) are applied to the groynes. Next, hydro-ecologic indicators are used to assess the impact of notching of groynes on fish habitat suitability. The results suggest that relatively simple modifications can significantly improve the ecological value of the groyne fields.

Rivers provide many of our day-to-day needs. They allow, for instance, the production of drinking water and the movement of goods via inland waterways. However, river systems experience disturbances, such as droughts and pollution plumes. These disturbances can impair the functioning of river systems and their ability to provide the desired functions and services. Since some of these disturbances have very little impact while other cause many problems, it is important to determine how a river system handles different disturbances. Resilience is often used to indicate and assess the behaviour of systems with regard to disturbances. Using the concept of resilience with regard to river systems can help determine how well river systems handle disturbances. In order to determine how resilient a river system is, a method to assess the resilience of river systems is needed. Research into the resilience of river systems has only been done with regard to flood resilience. This resilience does not consider other disturbances, such as droughts, and therefore does not represent the full resilience of the system. Furthermore, this research often resulted in suggestions and pointers to create and improve resilience, but not in a clear method to help assess it. Hence, the objective of this study was to develop a method to assess the resilience of river systems. In order to create this method several questions need to answered. First, a clear definition of resilience of river systems is needed. For this it should first be determined what resilience is. This is done using a literature study. The first part of this literature study focussed on general and field-specific definitions of resilience. This resulted in the definition of resilience of river systems as used in this study: the resilience of a river system is the ability of the system to continue functioning during a disturbance. Where continuation of functioning is defined as the continued achievement of the goal of a certain function, such as the continued production of crops for the function of agriculture, even if this only occurs to a smaller extent, and the continued shipping of goods for the function of shipping. The disturbances considered are short-term disturbances, such as droughts and pollution plumes. After the determination of the definition of resilience of river systems several remaining questions need to be answered. The impact of disturbances on the different river system functions has to be determined and visualised. Next, the impact of these disturbances has to be classified. Finally, the resilience of river systems should be assessed using the classification for the impact of these disturbances. The second part of the literature study, focussing on the assessment of resilience, is used to help determine, visualise and classify the impact of disturbances. The development of the final method is an iterative process between application to a case study and the amendment of the method based on this application. Using the results of the literature study, a first design of the resilience assessment approach, the method for the assessment of resilience of river systems, was made. This approach consists of four steps with several sub steps. In the first step a system overview is created. This step is based on the ideas of flood resilience theory. It states how a system overview should be created, what external factors, characteristics and functions should be included and how to categorise them. The second step consists of the creation of disturbance-impact graphs for the different functions and disturbances. These graphs, based on the idea of stressor-response graphs of system robustness analyses, are used to visualise the impact of the disturbances. The third step gives an assessment of the resilience of a function based on the disturbance-impact graphs and a resilience classification with associated scoring system, which is based on the ideas of a current impact classification used for droughts. The fourth and final step consists of the assessment of the resilience of the entire river system based on the assessment of the individual functions. The approach was applied to a case study, the Meuse river system, to test it. This case study focussed on low discharges caused by droughts. The approach was applied to the whole system, thus to all its characteristics (water quality, water quantity, vegetation and fauna and sediment) and all its functions (shipping, electricity, industry, drinking water production, agriculture, flood protection and recreation), to create a system overview (the first step of the approach). The application focussed specifically on the functions shipping and drinking water production. This application was used to check the content and applicability of the sub steps of the first step of the approach, using the system overview, and to check the content, applicability and order of the sub steps of the second step of the approach, using the functions shipping and drinking water production. The application of the system overview led to a clear distinction between external factors, characteristics and functions, which has been adopted in step 1. Furthermore, the application to the specific functions resulted in a clearer definition of system boundaries and a clearer link between the external factors and the disturbance. Finally, the application led to an additional sub step. This sub step consists of a check to determine whether the chosen disturbance is actually relevant for that specific function. The application of the approach showed that both shipping and drinking water production of the Meuse river system appear to be very resilient with regard to low discharges due to droughts. This is likely due to fact that both functions have already been adapted to this disturbance. For shipping this is likely largely due to the fact that the water level in the Julianakanaal is managed to ensure continued shipping possibilities during discharge fluctuations. Pumping facilities have been constructed in order to maintain water levels even when very small discharges occur. The large resilience of the drinking water production by Waterleiding Maatschappij Limburg is likely largely due to the fact that the intake point is located in the Lateraalkanaal. The water level of this canal is managed using weir and sluices for shipping and drinking water production. Only the first two steps of the approach have been tested using the case study. The final version of these steps, as found in this report, can be used in practice. The tested steps have shown to be applicable to the tested functions and it assumed that these steps are also applicable to the other functions. The third and fourth step should be tested before they are used in practice. Especially step 3a (the assignment of the different levels of the resilience classification to the disturbance-impact graphs) might require additional adaptation.

This experimental study is about the bed-load transport over inlet sills of longitudinal training walls. The focus is on the flow structures around the inlet: the shape, the processes and the effect on sediment transport. Groynes have been replaced by longitudinal training walls in an 11-km long pilot project to optimize training of the river Waal in the Netherlands. These training walls have many advantages, making it worth exploring the performance of these new river training structures further. The inlet sill affects the discharge and sediment transport distribution and hence the morphological stability of the system. However, currently operational morphodynamic models cannot reliably compute the sediment flux from the main channel towards the sheltered side channel behind the longitudinal training wall. Therefore, the research aim was to develop a description of the sediment transport over the inlet sill of these longitudinal walls for implementation in two-dimensional depth-averaged river models. Since knowledge on the flow structures and validation data lacked, a series of flume experiments with the inlet area has been performed. This study shows that the blocking effect due to the sill that functions as obstacle is dominant at the upstream side of the inlet and helical flow due to curvature at the downstream side of the inlet are the dominant three-dimensional flow structures at the upstream side of the sill. Further research is needed for the identification of the shape of the flow structure due to blocking.

In submerged conditions groynes add resistance to a river, thereby increasing the water levels for a particular discharge. Groynes are modelled in two ways, either they are included in the bed topography when the grid resolution is sufficiently high or with a sub-grid parametrisation when the grid cell-size is larger than the geometry of the groyne. To investigate the flow patterns over and around groynes, data from a groyne flume experiment, as carried out by the BAW, is analysed. This to investigate to what extent a groyne behaves as a weir. The experiment is modelled in 2DH and in 3D to compare the performance of the sub-grid parametrisation with full 3D non-hydrostatic simulations.

Along river banks, on the transition zone between the river and see, tidal marshes can develop. The tidal marshes accommodate multiple plant and fish species. As a result of the stressful conditions in tidal marshes, unique intertidal ecology develops. However, due to the densifying of the river banks, tidal marshes are disappearing.
Restoration of tidal marshes can reintroduce the unique intertidal ecology on several locations in the estuary. To obtain restoration of tidal marshes, constructed tidal marshes come into play, which can be built at designated places along the river.
However, constructed tidal marshes are not necessarily built to restore the unique tidal nature, but can also have other functions as recreation and contribution in green city area.

Nevertheless, is it still unknown how constructed tidal marshes behave and what the optimal design is. Namely, a mismatch exists between the policymakers and designers on the one side and academic knowledge on the other side. To fill up this gap, accessible knowledge from the experts should be available for designers.
Therefore, this research provides guidelines for designers and gains more insight into the behaviour of constructed tidal marshes. This thesis focusses on extracting general knowledge from the results of a numerical model, applied on a case study.

Simulations of a numerical 1D Sobek model applied on the case study achieves the influence of model configurations on accretion. Therefore, tidal forcing, marsh design and system adjustments are divided into multiple components. The model simulations of the separate components give the influence on bed shear stress and potential sedimentation.
Furthermore, executed fieldwork calibrates the model on measured flow velocities. Besides, the Manning coefficient is estimated, and cross-sections are obtained by gps measurements. The parameters are subsequently used as model input.

From the simulations, it can be concluded that tidal asymmetry determines the duration of stagnant water and thus the settling of fine particles. A considerable increase in sedimentation is reached when flats are participating. However, an increasing flat area encourages ebb-dominance and can even lead to erosion.
Next, when the width of the cross-section is large compared to the depth, more sedimentation is predicted. With flood-dominant bed shear stresses, a broad cross-section leads to accretion.
In the case study, the presence of sand particles is not expected, as sand is deposited close to the inlet, where the bed shear stress is ebb-dominant. In contrast, silt settles throughout the system. Especially at low energetic conditions, such as bends, silt settles. As the occurring bed shear stress is mostly flood-directed, it is likely that sediment entering the system, does not leave the system anymore, and accretion of the bends is presumed.
The placement of gate culverts in flood direction leads to higher accretion rates due to the longer slack duration. However, at the exact locations of structures, higher bed shear stresses can develop, and erosion is expected.

Concerns regarding plastic pollution arise as large quantities of plastic enter the ocean and affect wildlife and possibly human health. Rivers form a dominant pathway for macro plastic particles into the ocean. Plastic pollution in rivers can result in blockage, where it affects water quality and ecology. This increases risks of flooding and provides health concerns. To prevent further dispersion of plastics into the ocean and reduce health and flood risks, reduction of plastic concentrations in rivers is desired. Buoyant macro plastics are a dominant polluter and understanding their cross-sectional distribution in rivers could promote areas for efficient extraction or monitoring. As field measurements are expensive and time consuming it is desired to accelerate research with modelling techniques. To improve modelling of buoyant macro plastics and translate cross-sectional distributions it is necessary to model relative motion of buoyant macro plastic particles to the flow and one another. Previous research has shown that the understanding of macro plastic forces and transport is limited. The range of macro plastic properties complicates modelling approaches to macro plastic transport. To simplify, a classification of macro plastics is introduced according to cornerstones in behaviour. A basic force model is constructed (derived from riverine wood transport studies) to provide an understanding of the effect of size, density, wind and discharge on transport of different macro plastic types. This new understanding is applied to a variety of flow features induced by a range of river elements (river bend, channel widening, river confluence and groyne) to develop a hypotheses on the cross-sectional distribution of the different macro plastic objects in these environments. These hypotheses are tested in a numerical transport model. A theoretical background study on particle response times and Stokes numbers is performed to identify a relation between the particle response time and relative particle dispersion (compared to the flow). This provides a possibility for translating the transport of the different macro plastic objects into the numerical model. To define numerical modelling input of different buoyant macro plastic objects, particle response times are calculated and translated to horizontal particle dispersion coefficients in D-WAQ PART (software package of choice). Each of the previously formulated river elements is modelled as well in the numerical model. The modelling results show that river bends cause an increase in particle concentrations along the river bend. Channel widening increases the concentration along the boundaries. A river confluence increases the concentration along the tributary side of the channel. A groyne increases the macro plastic concentration along the groyne-free side of the channel. These results show that particle response times and their relation to Stokes number and particle dispersion propose an interesting tool for the modelling of relative particle motion towards the flow and the different macro plastic objects. This study identifies the significance, diversity and complexity of macro plastic particles in riverine environments. It highlights the need for classification and simplification to facilitate modelling and still be able to obtain relevant results. Describing macro plastics according to cornerstones in behaviour provides an efficient tool to simplify modelling. Coupling of different macro plastic classes to a range of riverine environments and understanding the differences in their cross-sectional distribution provides practical use.

Like many rivers around the world, the Loire river in France has a history of human interventions in order to facilitate navigation and port development. Next to affecting bed levels directly, the heavy modification of the river-estuary has induced significant changes in the hydrodynamic and morphodynamic behaviour of the Loire. As a result, the Loire river is experiencing an ongoing bed degradation. In the estuary, the interventions have led to an amplification of the tidal amplitude, a shift of the tidal and salt intrusion limit in upstream direction and a larger tidal asymmetry. According to Winterwerp and Wang (2013), this tidal deformation leads to an increased import of fine sediment in the estuary and a reduced hydraulic drag. This in turn enhances tidal deformation further. Due to this positive feedback mechanism the Loire estuary has evolved into a hyper-turbid state, associated with large suspended sediment concentrations and the formation of fluid mud.

The behaviour of the river-estuary on large temporal and spatial scales and its response to historical and possible future interventions is not yet sufficiently understood. Therefore, an idealized, computationally efficient, three-dimensional morphodynamic model of the river-estuary is developed with the FLOW module of the Delft3D software suite, in which the main processes influencing the morphology of the Loire river-estuary are included.

The current estuarine geometry, lacking the presence of large intertidal areas, induces a flood-dominant tidal signal. In the mouth of the estuary, the baroclinic pressure gradient introduces a mean landward-directed velocity near the bed and amplifies the mean seaward-directed velocity near the surface. This gravitational circulation causes the formation of an Estuarine Turbidity Maximum at the tip of the salt wedge, which is strengthened further by the flood-dominance of the tide. Model results confirm the feedback mechanism between tidal deformation, the import of fine sediment and the effective hydraulic drag as described above. However, next to tidal deformation, strengthening of the gravitational circulation also plays a large role in this mechanism for the Loire.

To mitigate bed degradation, several measures are simulated that decrease the transport capacity of the flow, increase the sediment supply or do both. Over the first 10 years, sediment nourishments are the most effective according to the model. However, after 100 years of simulation the removal of all groynes present within the domain leads to the most sedimentation relative to the reference scenario. To decrease the import of mud into the estuary, two measures have been investigated. Increasing bed levels in the main channel of the estuary mainly leads to a decrease of the tidal range, whereas restoring tidal flats turns the tide from flood- into ebb-dominant. In both cases, a decrease of the salt intrusion length and a significant weakening of the gravitational circulation occurs, leading to a tidally averaged export of fine sediment and very low mud concentrations.

Braiding rivers are characterised as highly dynamic, and experience annual morphological changes in plan- form. This dynamic nature of the river leads to navigational hindrance and risk of unstable bifurcation points where discharge distributions might switch. In pilot studies, porcupines have shown promising results in re- tarding the flow and cause sediment deposition near river banks to prevent bank erosion. However the aim now becomes to apply the porcupines on a much larger scale to increase the channel roughness and influ- ence discharge distributions of bifurcation points such that the flow is mainly diverted to the channel where the highest discharge is required. This way the main channel receives the largest discharge and therefore sedimentation in these channels is prevented. Currently it is not known how porcupines should be modelled in a numerical model. It is simply assumed that porcupines can be modelled similar to vegetation which is schematised as rigid cylinders with a certain density, drag coefficient and resulting representative roughness. No measurements are available to validate the assumed roughness of porcupines and if the hydro- and mor- phodynamic behaviour, represented by the model, is true.

In this thesis laboratory experiments are conducted to assess the near-field hydro- and morphodynamic ef- fect of porcupines and generate more knowledge about their behaviour. Experiments with a concrete bottom give a detailed insight in the hydrodynamic behaviour of porcupines without the interference of bedforms and morphological developments. Experiments with a sediment bottom give more insight in the morpho- logical development and flow patterns over time which clearly influenced the initial hydraulic behaviour. Experiments are conducted in a 12 metre long and 0.8 metre wide flume with a recirculating pump. The wa- ter level, discharge, density of the porcupine field and configuration of the field are systematically varied to identify the dependences on the drag and sedimentation/erosion volumes in the near-field domain of the porcupines. Additionally, general observations are performed, describing the flow structures and sedimenta- tion patterns in and around the porcupine field.

From fixed-bed experiments it is observed how the flow is retarded by the presence of porcupines. Flow is pushed around the field in both transverse and vertical direction. Behind the porcupines, longitudinal flow vectors are downward directed and the flow velocity near the bed is significantly reduced. It is observed that staggered porcupine grids help to retard the flow stronger and captures sediment behind the field in wider strokes. Non-staggered grids only work effectively in the line of porcupines. Between those lines barely any retardation is observed and therefore only narrow strokes of sedimentation are observed behind the lines of porcupines. The reduction in flow velocity behind the porcupines is similar to the velocity reductions ob- served in experiments with vegetation. The velocity retardation is gradually restored in longitudinal direction where the effect of porcupines gradually diminishes. For different experiments this deceleration of the flow has been observed and it follows a linear trend line, that by means of extrapolation can be used to quantify the effective retardation length in longitudinal direction. Water level differences over the porcupine field are observed indicating loss of energy, and pushing up the water level upstream. Porcupines can effectively in- fluence bifurcation points in braiding rivers this way. The local water level gradient over the porcupine field, combined with the velocity measurements, is used to determine the drag and representative roughness of the porcupines by using the equations of Baptist. The obtained values for the roughness are validated by sim- ulating the flume in SOBEK with the corresponding roughness coefficients. Comparing the measured water levels with the computed water levels by the model gave a relatively good fit indicating that porcupines can be schematised by the equations of Baptist with a few adjustments. The Reynolds stresses give an indication of the height of the bed shear stresses. Measurements show that the shear stress in the near-bed region behind the porcupines is lower or the same compared to the undisturbed velocity profile. Lower bed shear stresses indicate a reduction in sediment transport and is therefore an important mechanism to reduce the bedload sediment transport.

Mobile-bed experiments show clear erosion patterns inside the porcupine field due to the increased turbu- lence intensity generated by the porcupines themselves. For the experiment with low water levels and high flow velocities erosion is observed to be most severe, whereas in experiments with lower field density an

overall sedimentation is observed inside the porcupine field. Due to the erosion porcupines sink into the bed significantly reducing their effectiveness on retarding the flow. To prevent scour larger spacing between the porcupines seems beneficial. A growing sedimentation ridge behind the porcupines is observed that influ- ences the flow retardation even stronger, enhancing further sedimentation. Once maximum sedimentation height is reached, the ridge will migrate downstream as a growing sedimentation bar gradually sloping down towards its initial bed level. This length scale of the sedimentation bar is comparable with the retardation length scale. Combined with the migration rate of the sedimentation bar an estimation of the time scales can be obtained. Based on the mobile-bed experiments it is concluded that least erosion within the field is beneficial and therefore low water levels and high flow velocities should be avoided.

Although initial results show that porcupines show similar behaviour compared to vegetation and that the roughness can be estimated by using the equations of Baptist it has become clear that there are still major differences between the behaviour of vegetation and porcupines. Therefore further research is required to improve schematisations of porcupine behaviour, especially to improve the schematisation of the sediment transport around porcupines since no descriptions are yet available.

The reach of the Magdalena River around the city of Barrancabermeja experiences large issues concerning its navigability since the construction of the Yondó Bridge. The purpose of this study is to investigate possible causes of this poor navigability and to come up with an improvement to the current situation. The influence of bars and scour holes around bridge piles are seen as hypothetical problem causes. A bar mode analysis shows that, for the examined river section, the river contains one alternate bar over the years. It is plausible that the construction of the bridge has induced changes in flow conditions in such way that the original alternate bar started to erode and eventually totally disappeared. Therefore, it is highly possible that the construction of the bridge forms the main reason for the shift of the thalweg. The scour holes around the piers of the Yondó Bridge that were approximated by the empirical method of Melville and Coleman. These scour holes are incorporated in the Delft3D-model to assess their influence by adapting the initial bed elevation profile. From the model simulation it turns out that the presence of the holes does result in more erosion in the vicinity of the bridge.

Three possible solutions (null-solution, groynes and guide bunds) have been weighed using Multi-Criteria Analysis. Based on this analysis the guide bunds appeared to be the most suitable solution. The structure was implemented in the Delft3D-model and some additional simulations proved that the effect of this structure on the hydro and morphodynamic conditions in the river is twofold. First, the guide bunds improve the distribution of the flow over the cross section of the river. More flow is forced through the right side and indeed the flow velocities turn out to be higher at that location. Moreover, the flow velocities on the left side decrease, as expected. However, the structure has an opposing effect on the cumulative erosion and sedimentation. More sedimentation takes place at the right side of the channel, whereas the left side of the channel gets deeper. It can be concluded that the best way to improve the situation in Barrancabermeja, is the construction of a guide bund structure in the vicinity of the Yondó Bridge. However, more detailed (physical) model tests should be performed to gain better insight in the effect of the guide bunds.

Vegetation on river banks and bars contribute to the stability of these morphological features; however, the exact processes that contribute to this stabilization are still subject to research. This study has looked into the flow phenomena at the streamwise interface between a vegetated and non-vegetated river bed. Flow velocities in vegetated flows are lower than in non-vegetated flows under otherwise similar conditions due to the increased drag by the plants. Therefore, a shear layer develops across the interface. Within this shear layer, Kelvin-Helmholz like vortices develop, inducing exchange of mass and momentum through the interface. These vortices are present in the water column, but their strength near the bed governs sediment transport mechanisms, which are the basis of morphological activity. The objective of this study was therefore: to obtain a better understanding of the coherent flow structures in the interface between vegetated and non-vegetated river beds and the effect of these structures on sediment transport mechanisms. This has been done in a series of flume experiments with a compound channel.

Shock Safe Nepal was founded as a response to the 2015 Nepal earthquakes to function as a platform to contribute to the development of knowledge on earthquake safe housing. The goal of the report of team 5 is to validate and optimise the design of the pilot house that was created based on the work of previous teams, and the development on implementation plans for a validated and optimised house. Literature study, field work and interviews have been performed resulting in main findings of this report.
Primarily, the used materials were analysed in the report, including bamboo, CSEB bricks and concrete. They were analysed consulting literature, conducting laboratory tests in cooperation with the University of Tribhuvan. Bamboo was mainly analysed consulting literature sources, since laboratory tests were not feasible. It was found that its material properties are immensely difficult to determine and can vary from one column to another. However, it remains a strong and cheap building material. CSEB bricks were used due to its availability, strength and price. The material properties were derived from tests done by Build Up Nepal and from literature sources. Its mechanical performance is like that of concrete. It’s an easy material to build with and incorporate steel rebar’s. However, its durability and consistency is something which was not thoroughly investigated and remains debatable. The concrete used, was thoroughly tested, conducting slump cone, compression and Schmidt Hammer tests. It was found that the concrete used in the pilot house is of acceptable quality, but there is room for improvement by following clear guidelines and technical assistance. Subsequently, static calculations were executed, regarding the roof, the load bearing structure and the foundation. It was found that these different components, perform safely under static conditions, with the applied loads, separately and combined. The load bearing structure has turned out to be a wall-bearing structure. This was not assumed at first. Furthermore, after calculations, it was found that the roof and foundation were largely over dimensioned. This is, however, determined considering many assumptions, such as the soil properties.
Regarding an earthquake situation, the walls and bearing capacity were researched and calculated following quasi-static conditions. The earthquake conditions were derived from the Peak Ground Acceleration. Primarily the walls were researched. Two scenarios were considered, a 3-point collapse failure mechanism and punctual overturning collapse failure mechanism. Both mechanisms were tested for different wall compartments. These calculations give a small insight in the actual situation, because dynamic loads are applied statically, non-linear or dynamic calculations should be conducted as well as FEM modelling, for more thorough understanding. It must be said that the rebar and resonance effects were not considered. Regarding the bearing capacity, a PGA of 0.6 was used and from calculations, partly considering the soil and superstructure inertial effects, the bearing capacity would not fail. However, superstructure resonance was not considered. Larger PGA’s were not investigated, which means that it is not determined under which conditions failure would occur. From these analyses the Structural optimisations are made to the design. This includes improving the joints between different elements of the house. Regarding the materials used the optimisations include 5 protecting the CSEB bricks from weather as they are load-bearing. Guidelines are given on the placement of the house regarding the foundation and the slope. According to the calculations the foundation is over- dimensioned.
For the stakeholder analysis, extensive research was done through interviews which was combined with literary information available. This was then used to create a power interest grid and a network analysis, which shows the links between different categories of stakeholders and different specific stakeholders. This analysis also gave insight in the sheer number of stakeholders involved in rebuilding Nepal and the importance of defining the role of SSN further. The external factors that are important in working in Nepal were analysed, this was done regarding social, technical, economic, environmental, political, legal and ethical aspects and based on literature research, field research and interviews. Implementation methods of different types of organisations in Nepal were analysed. These findings were concluded in a SWOT analysis of the organisations. Defining the strengths, weaknesses, Opportunities and threats of other organisation help to define the direction that SSN should move in and those aspects of building in Nepal that can also be defined as strengths, weaknesses, opportunities and threats to SSN or make SSN different to other organisations. The risks of building in Nepal must be considered to create a realistic and feasible long-term plan and need to be mitigated a risk analysis is done. The findings in the risk assessment are found in external risks, design risks and construction risks. A plan is then set up to mitigate external risks and construction risks are the. The findings of the long-term plan are organised into a strategy for SSN, an engagement plan and an implementation pathway. The strategy is concluded in a SWOT analysis which is then used to create a TOWS analysis. This TOWS analysis combined the internal and external strengths and weaknesses to bring new creative ways of maximising strengths and opportunities and minimising the weaknesses and threats. The Implementation pathway contains long- term goals for SSN, that are structured into regulatory, implementation, technical and organisational goals and that can be added onto by future teams.
This research is to be a logical step in a series of research projects which will contribute to the reconstruction of an earthquake safe environment in Nepal. It can be used as consultation advice, guideline or as a base for in-depth follow up research on one of the included topics.