Hydropeaking is a widely applied management practice in the generation of hydropower. When the demand in electricity is high, the operator of a hydropower plant rapidly increases released discharges to meet this demand. Vice versa, when the demand is low, no or less water is released. However, while river regulation practices offer valuable resources, they can also inflict adverse environmental consequences on downstream river segments. More specifically, hydropeaking introduces high sub-daily variance in downstream reaches of the hydropower plant. This large sub-daily variance is harmful to the river regime and ecosystems. In Finland, hydropeaking has the highest negative environmental impact of all river regulation practices. The most prominent, known negative impacts due to high flow variations are a direct impact on aquatic biota, such as trout, and a compromised recreational use of the river corridor. The main objective of the thesis research is to investigate the impact of hydropeaking on rapids in a complex riverine system. More precisely, a system that includes multiple subsequent weirs, vegetation, large riverine boulders, a rather flat topography and a small-scale anabranch. Additionally, related to the modelling approach, two state-of-the-art calibration methods and their benefits and limitations are discussed. The formulation of operational and morphological mitigation measures to counter impacts is the secondary objective. A case study for the downstream region of Hamari Hydropower Plant at Ylivieska (Finland), the site Juurikoski, provides insight on the different aspects related to these queries. During a series of simulation runs, including the original situation and three hypothetical mitigation scenarios, the impact of hydropeaking is quantified and studied. Results include post-processed water level, velocity and shear stress data. Furthermore, conclusions and a discussion are given regarding the potential of calibration and validation for a 2D hydrodynamical model by state-of-the-art methods. These methods refer to a hot spot analysis comparison based on LSPIV-data and velocity profile comparisons based on ADCP-data. On a local scale, mitigation recommendations are suggested or excluded from a practical point of view. From a more global perspective, the report provides a modelling approach to tailor mitigation measures according to riverine lay-out, despite limited bathymetry data and increased riverine complexity.

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.

Over the past centuries, the Dutch rivers have been extensively engineered with the construction of hydraulic training works. A changing climate and increasing demands of river functionalities require innovations to the system to ensure its resilience. Exploring potential applications of Xstream elements might contribute to the development of sustainable river management strategies. The 33 cm high concrete three-dimensional cross is the little version of the Xbloc, a widely used breakwater element for coastal protection. Random arrangement of Xstream elements creates 60% porous spaces and the ability to build slopes at a 45∘ angle. Alterations to the riverbed morphology induced in the near-field of homogeneous Xstream hydraulic structures are assessed in the present study. A physical scale model featuring a movable bed of lightweight sediment was employed to simulate a river section. Minimising any compromises on Froude scaling, this material was used to properly scale the Shields parameter, striving dynamic similarity between the model and reality. Bed load transport processes are reasonably well represented by this material, providing well matched equilibrium scour depths and good qualitative comparisons of the influence of structural variations on these processes. Multiple setups differing in material and geometry were tested in a 12 m long and 2.6 m wide sediment recirculating flume. The primary comparisons of this study include:
• the flexible groyne head in the model against field data;
• two abutments with a 1:2.5 slope, varying in material between stone and Xstream elements;
• two abutments made of Xstream elements, differing in slope between 1:1 and 1:2.5.
Water levels were gauged and flow velocities were measured with acoustic Doppler velocimeters during the experiments. High-resolution bed elevation data was collected by means of a laser scanner. Generally, results of the model show an overestimation of bedform dimensions. This is attributed to the concessions necessitated by the limitations of the test facilities due to the low length scale factor. The effect of contraction was exaggerated in the model as the structure width to flow width ratio was 3 times greater and the influence of any upstream river training works was neglected. The flexible groyne head blocked 43% of the cross sectional flow area in the model. Furthermore, due to the laminar flow behaviour, the water encountered increased resistance within the structure. The deepest scour is found along the leading edge of the structures. This can be explained by the intricate flow patterns created by the primary vortex entering the flow acceleration. Inspired by the longitudinal training wall as built in the river Waal, a less porous stone abutment was constructed to compare the effect of porosity and roughness of Xstream elements on local sediment displacement under high water conditions. The increase in water level in front of the Xstream abutment was half that of the stone abutment and streamwise velocities in the main flow were 5% lower. These findings indicate better dissipation of energy by the Xstream abutment. Nevertheless, the relative turbulence level was 17% higher close to the Xstream abutment due to the higher roughness, resulting in equivalent peak velocities in both experiments. Along the Xstream abutment, however, the scour depth was twice as large. Taking into account the live-bed conditions, where sediment is supplied from upstream causing the scour depth to fluctuate around its equilibrium, a significant difference of at least 20% remained. The principle of a falling apron, a mechanism where individual units at the toe of a structure tumble down, covering one slope of the scour hole and thereby increasing the roughness, could be the reason for this. The erratic shaped Xstream elements enhance complex turbulence patterns very locally. Due to the absence of a supporting filter construction or a bed protection layer, the Xstream abutment was undermined, leading to individual elements decaying at the base of the structure. The interlocking ability of Xstream seems to be stronger when the structure is built with a steeper slope. This insight can be taken into account in the design of Xstream hydraulic structures. The substantial discrepancy in density between the Xstream model units and the angular polystyrene particles must be considered as the geotechnical properties may differ from the real world. The present study has shown the kinetic energy absorbing capacity of Xstream. Turbulence levels increase due to higher roughness. Exposing a uniform structure of Xstream elements to high water conditions might lead to instability which alters both positive and negative effects. Future research must give valuable insight into how the design of Xstream structures could look like for a durable implementation in the Dutch river system.

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.

The coastal area of the Murcia region in Spain experiences more frequent and more intense flash floods caused by inland heavy rainfall due to climate change. This results in high water levels in towns and cities, leading to risk of loss of life and many financial damages. Currently the region is vulnerable, because there are no hydraulic structures that regulate the flow safely downstream towards the coastline. Instead, at this moment the current channels are inadequate dry rivers. To reduce the risk of flooding, the objective of this design was to design a flood abatement control zone (ZAC). This design followed the design approach for Hydraulic Engineering.

A ZAC consists of a series of dikes that enclose separate reservoirs that are able to temporarily store water. This dampens the peak discharge of the flash flood, which reduces the flood risk of the downstream area. The peak reduction is the main function. The water that is stored is being discharged with a delay, spreading an acceptable discharge over a longer time to discharge the same rainfall event volume.

The first step of the design was to define the system of the ZAC. The ZAC was combined with the creation of an up- and downstream channel with short lengths to fit the structure into the environment. Its design life was set at 50 years, corresponding to a design rainfall event of once per 474 years. To design this structure, it was important to determine the maximum rainfall event discharge and the existing maximum discharge capacity without floods occurring downstream. These 2 factors, together with soil properties and land boundaries, acted as boundary conditions to the system.


In step 2, two locations were considered as potential construction location, both indicated by the client Universidad Polytechnica de Cartagena (UPCT). By applying a multi-criteria analysis (MCA) based on predominantly the water inflow, potential storage area, close company buildings and houses, the more upstream location was chosen.

Step 3: in order to design an adequate ZAC, a model was required to create the before-and-after-construction situation. A hydrological 2D-flow model was created in HEC-RAS. This was closely tied to functional design and design steps were taken iteratively. The 2D-model was able to compute flow in longitudinal and lateral direction, which is strongly needed in a flooded terrain. The most important design parameters to test in the model were the culvert-spillway-structure and the number of reservoirs. The model was validated qualitatively by flood maps from Centro de Descargas del CNIG.

Then, the functional design of the ZAC was done in step 4. The ZAC was placed partially dug into the soil upstream, and partly sticking out of the soil downstream. Upon iteration, it was decided to create 5 reservoirs, because of costs and a smaller marginal peak reduction effect of extra reservoirs. The ZAC is created in combination with a downstream funnel, downstream outflow channel and upstream channel. This means that the reservoirs are enclosed by 2 side dikes and 6 lateral dikes.

Then, detailed design in step 5 followed. The culvert-spillway structure was designed. The aim of this structure is to let water through the reservoirs without overflowing and therefore damaging the dikes. The structure consists of a culvert, spillway and retaining walls. For each element an MCA was set-up to determine the optimal shape, followed by choosing the design alternative. The design is a trapezoidal spillway, an arched culvert and a retaining wall.

With the optimal design, a conceptual design is constructed. In this conceptual design, the reinforced concrete dimensions and governing load combinations are determined. From this, the strength of the ZAC structure is evaluated in the finite element method program DIANA.

Finally, the final design was created. The conclusion is that the combination of structural elements that have been modelled in the system satisfies the aim to reduce the design rainfall event flood wave enough to avoid flood risk to the downstream areas of Murcia. The main uncertainties are the scaling of the data of the design rainfall event and the used soil characteristics. Further research could look into quantitative validation of the 2D-flow model, the implementation of sediment transport in the model and into optimizing bed protection downstream of the ZAC.

Myanmar lacks a water quality monitoring system to monitor changes in water quality in the Ayeyarwady Basin. This study aims to find to what extent changes in water quality can be measured in the Ayeyarwady basin and to identify requirements for a water quality monitoring system. In this study, the current water quality monitoring systems of the Ayeyarwady, Mekong, Chao Phraya and Hong (Red) River Basins were compared. Several contamination sources were used to identify contamination scenarios. A river model of the Ayeyarwady and its main tributary, the Chindwin, was made to understand the workings of the river system and the distribution of contaminants throughout the Basin after contamination events. This study found that contamination is diluted to a high degree over long distances in the Ayeyarwady Basin. At low river discharge, the remaining contamination peak downstream of large contamination events like waste water treatment plant failure or tailings dam failures occurring upstream in the river near the limits of detection. During high river discharge these concentrations can be over 17 times smaller. The study showed that in case of pulse water quality incidents for most common water quality parameters, the monitoring system should have a temporal frequency of once per week with an analytical accuracy of around 0.1 microgram/l. A high-quality monitoring station is required in both river branches just upstream of the confluence of the Ayeyarwady and Chindwin rivers as significant dilution occurs here. Finally, it is crucial to clearly define and distribute measurement responsibility.

The seasonal Chindwin river (Myanmar) forms the central artery for transportation in the region. However, the dynamic river behaviour, archaic boat equipment and limited monitoring, yearly results in large numbers of grounding ships, causing injuries and economic losses. A pilot project involving CoVadem technology was initiated in the beginning of 2019 to benefit safer navigation on the Chindwin. CoVadem technology can chart the most up to date water depths by collecting under keel clearance measurements from the commercial fleet. The pilot project aims to increase safety on the Chindwin through sharing information about safe routes and forecasted water depths with captains sailing the river.

The added value of using CoVadem technology, however, is vulnerable to the number of participating vessels. A combination of morphological changes and the typical spatial spread of CoVadem data limits the extent of the navigation channel that can be derived from the data. With only a small part of the navigation channel known it is unclear where passing of other vessels is possible, where speeds should be adjusted due to e.g., bottlenecks and where shorter routes are present.

The objective of this research is to provide more information about the navigable area around CoVadem data in order to assist captains with navigation. During this research, two physics-based models have been developed, able to carry out this task. The ‘soil-model’ combines CoVadem data with assumptions about the maximum slope in the bed.
The ‘axi-symmetric model’ utilises CoVadem data, the axi-symmetric solution and assumptions about sand dunes and river banks in a model to estimate a navigable area.

Two ‘reliability indicators’ have been developed that can indicate areas of the river where the output of the axi-symmetric model is reliable in its estimate. One indicator is related to the channel stability, it is calculated from many years of satellite imagery. The other indicator is related to channel curvature.

To measure the performance of the models and the reliability indicators, two dimensionless performance indicators have been developed: the safety score and the channel coverage score. The models and the reliability indicators were consecutively tested and evaluated for four study cases located along the Chindwin river.

The results are promising. It follows from this research that navigation channel estimates around scarce CoVadem ship track data can substantially benefit from application of a physics-based model. The soil-model is very robust, but has limited added value for navigation. The axi-symmetric model increases the navigable width estimate around a single CoVadem trackline significantly O(100 m). The performance indicators can improve the reliability of the axi-symmetric model significantly.

This research combines Big Data, physics-based models and remote sensing in a not early demonstrated way: with models tailored for navigable area estimates and with measured data as the starting point. The correlation between axi-symmetric model reliability and remote sensing/curvature is, moreover, something that has not been demonstrated before. Finally, the two developed performance indicators show great promise for the evaluation of navigable area estimates. As such, this research adds to current advancements in (open-access) cross-platform data accumulation and utilisation.

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.

In this study, the effects of extreme flood events on vegetation and morphological patterns in a natural river were investigated. For this purpose a new vegetation-development model was introduced and linked to a hydro-morphodynamic Delft3D Flexible Mesh model. Based on the results in this study it can be concluded that the direct effects of an extreme flood are relatively low, with almost no vegetation removed during a flood event. However, the extreme floods lead to an increased area suitable for seedling colonization within the river floodplain, which is partly caused by the formation of a secondary channel in the extreme flood scenarios. This causes an increase in the seedling recruitment rate in the years directly after an extreme flood and in a higher vegetation coverage.

This research focuses on the impact of extreme low river discharges, meaning discharges below 1200 m2/s at Lobith. In 2018 extreme low river discharges in the river Rhine led to congestions in the main Dutch part, called the river Waal. The river Waal is an important river for inland navigation, but during low discharges the vessel draught reduces and consequently the transported cargo volume per shipment reduces. To compensate the loss of transport volume, the total number of shipments increases, leading to an increased traffic intensity on the river Waal.  The purpose of this study was to investigate the effects of extreme low discharges on the traffic flow and traffic capacity in the river Waal. The study consisted of two elements: a study combining fleet data and hydraulic information and a traffic simulation study. During this research IVS90 data was used as the source for inland waterway transport data. Based on literature and previous river Waal studies the river section between the Pannerdensche Kop and the Maas-Waal canal was selected as the river section to investigate in more detail. Multi-beam measurements in combination with water level data were used to generate cross-sectional profiles in order to carry out the simulations. The cross-sectional profiles were highly variable. From these cross-sectional profiles the navigable river width was determined. It was found that a river depth of 2.80 m was no longer available at all cross-sections from a discharge of 900 m2/s and lower. Therefore, the navigable width was determined at a river depth of 2.0 m for the discharges 1020, 900, 800, 700 and 600 m2/s. Also, it was found that with reducing discharge the navigable width of the cross-sections reduced.   The fleet composition was determined in detail for four weeks representing the drought of 2018. These four weeks in 2018 represented weeks with average discharges around 1020(2x), 800 and 700 m2/s. The river Waal fleet composition was determined based on the Rijkswaterstaat vessel classification system (RWS-class) and categorised in three groups: coupled units (all RWS-classes with index C), push-tow units (all RWS-classes with index B) and motorised vessels (all RWS-classes with index M). It was found that the number of passages by coupled units and push-tow units was effected largely during the drought of 2018. The number of passages by push-tow units reduced significantly from October 2018 as the discharge dropped below 1500 m2/s and the number of passages remained low until the discharge raise above the 1020 m2/s at the end of 2018. The number of passages by coupled units increased already before the discharge reached the 1020 m2/s limit and continued to increase throughout the period of drought. The number of passages by coupled units started to decline only after the discharge rose above the 1020 m2/s again. Even though the daily average number of passages increased during the drought of 2018, the total transported cargo volume per day decreased. There was a strong relationship between discharges below 1200 m2/s and the transported cargo volume per day.  Within this study special attention was given to the occurrence of congestion in the river Waal. The occurrence of congestion was investigated using the traffic simulation model SIMDAS. As indicators for congestion a fluency and safety limit of 8% was used to evaluate the simulated traffic, as well as simulations of the traffic flow. As safety parameter the penetration of the safety margin of a vessel in percentage of the total number of vessel interactions was used. While the percentage of the number of vessels that need to reduce their speed fully during their passages was used as the fluency parameter. With SIMDAS also the impact of increased traffic intensity and reduced navigable width were analyzed. The simulation results showed that the reduced navigable width had more impact on the delay time, the fluency parameter and the safety parameter than the increase of the daily intensity. During the simulations large congestions occurred for discharges of 800 m2/s and lower, but small harmonically moving congestions already occurred for a discharge of 1020 m2/s. Harmonically moving congestions, meaning seven or more vessels traveling behind one larger or slower vessel while awaiting room to overtake, were observed in the traffic simulations. Permanent congestions with ten or more vessels were observed in the simulation of the river width with a 800 m2/s discharge. The data analysis and the traffic simulations clearly showed the effects of the extreme low discharges on the traffic flow and traffic capacity. The conclusion of this study is that the traffic capacity of the river Waal is at its limit at discharges of 800 m2/s and lower.  This study made also clear the need for correct fleet data and river bed levels. The limited available fleet data reduced the accuracy of the results. The river bed should be monitored regularly in order to know the actual water depth particularly during low discharges. Furthermore, it is recommended that highly variable river profiles are implemented in the traffic simulation model SIMDAS to improve the simulation of the vessel's sailing trajectories. Also, the validation of the vessel trajectories in SIMDAS with AIS data is recommended in order to evaluate the traffic intensity on the traffic lanes in the river.  

Dam reservoirs form a crucial part for human society storing water, controlling floods, providing hydropower, water for irrigation and drinking. Annually 1% of the worldwide dam reservoirs storage capacity is lost, caused by sedimentation. The inflow of sediment and reduction of flow velocity and turbulence in the reservoir pro- vides favourable conditions for settling. Several sediment transport mechanisms are responsible for this, one of these is the turbid density current. The turbid density currents settle as the reservoir becomes wider, and it is affected by forces along the top and the bottom of the current. Recently, focus on reservoir engineering has shifted from primarily structural dam design towards complete sediment management strategies. In order to improve the sustainability of dam reservoirs, many management techniques are developed that inhibit or mitigate sedimentation. However, the effectiveness of these techniques is not yet known. This thesis provides an additional concept for sediment management in dam reservoirs consisting of channelling of turbid den- sity currents in dam reservoirs. The channel provides controllable parameters. The aim is to study the effects of channelling turbid density currents.
The study starts with a literature review, to describe sedimentation, sediment transport, and turbid den- sity currents in dam reservoirs, including their analytical and numerical descriptions.
Two computational models study the concept: a steady-state model and a numerical model. The steady- state solution and is based upon an equation for open channel flows modified for turbid density currents. This model is used to investigate the effects of hydraulic radii and slope of the channel on the turbid density current — secondly, the dynamic numerical solution. An analytical description is provided using the one- dimensional shallow water equations, consisting of the continuity, momentum and particle conservation equations. The solution includes four sources: deposition, erosion, gravity and friction. It omits water en- trainment and bed deformation. The model is discretised using the Generalised Lax Friedrichs method. First validation and investigation of the quality of the source terms are done. Subsequently, the model, including the four source terms, is used to study the effect of slope, hydraulic radii, concentration and sediment size in the channel. Expanding the numerical study by a Water Injection Dredging case in which local velocity, concentration and height are increased along a certain length to study possible effects.
To conclude, channelling turbid density currents is a viable solution to improve sediment transport. The slope and depth of the channel have the most significant effects. The generalised Lax Friedrichs method provides a valid and straightforward discretisation method for the numerical model. Furthermore, the model provides an easy, quick and simple to use tool to make first estimations of the effects of channel dimensions.

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.

River discharge is an essential parameter in morphodynamic modelling. It proves to be highly variable in both time and space. In this thesis the impact of the schematisation of time-dependent discharge series on morphodynamic change is studied. The impact is governed by several factors such as the long-term discharge statistics, and both short- and long-term sequences of discharge stages. A variable river discharge itself does not necessarily result in morphodynamic change. Changes in conveyance area and roughness are dominant sources of bed fluctuations and bed waves. Moreover, backwater dominated segments are subject to mild fluctuations in the river bed. The combination of natural variation of hydrological processes in the upstream river catchment and the absence of a significant correlation among statistical characteristics of subsequent years makes it hard for river engineers to construct discharge time series for river models that simulate morphodynamic development. The limited predictability of future discharge time series is an important source of uncertainty in model predictions. A way to estimate this uncertainty is by means of a time-consuming Monte Carlo approach, resulting in a mean long-term morphodynamic trend and the associated uncertainty. An alternative method is the application of a deterministic series for which the long-term discharge statistics are translated into a cycled annual hydrograph (CAH). It is expected to yield similar morphodynamic changes with respect to the mean trend from the Monte Carlo approach without the need for a large number of computations. However, as is demonstrated in this study, the CAH-method lacks in performance in simulating average long-term development and the amplitude of fluctuations in the river bed, especially at locations where strong sediment transport gradients are experienced. Using a simplified two-dimensional model that represents a locally widened floodplain, the impact of the included bandwidth, short-term and long-term sequences on morphodynamic change is investigated. The aim is to improve the deterministic hydrograph schematisation and to find a more convenient way to get insight into uncertainty in simulated morphodynamics. These findings result in a set of recommendations for future schematisations of discharge time series in morphodynamic river models. An improved deterministic approach is proposed. Using historical measurements of daily discharge data, years with a similar statistical maximum, mean and standard deviation can be classified. The classified years are translated into multiple cycled annual hydrographs (MCAH). By using these hydrographs, synthetic time series are constructed. Compared to the CAH-approach, the proposed MCAH-method yields a significant reduction of the root mean square error with respect to the long-term average morphodynamic trend from the Monte Carlo simulations. Moreover, the MCAH-series result in amplitudes of bed fluctuations that are closer to the response to natural discharge time series. Finally, the MCAH-series can be used to give a rough indication of the uncertainty in future morphodynamics.

Hydrological modifications to the natural flow regime through the regulation of a river threaten the integrity of river ecosystems. In Myanmar, the exponentially growing hydropower sector poses a threat to the ecohydrology of some of the last large free-flowing rivers in the world. This study investigates to what extent the natural flow regime of the Myitnge in Myanmar has been hydrologically altered by the Yeywa dam, which is currently the largest hydropower dam in Myanmar. The study furthermore examines which ecological processes have been or could potentially be most affected by these hydrological modifications. This is done by modelling the natural flow regime of the dammed Myitnge river in Myanmar using the distributed hydrological rainfall-runoff Wflow\_sbm model, which consists of a set of python programs to perform hydrological simulations. The suitability of this model as a tool for environmental flow management in Myanmar is simultaneously investigated. The model uses PCRaster, which in turn makes use of a dynamic modelling language within a GIS framework. It was forced using static and dynamic data which is mostly globally available from different satellites, and derivatives of this, and calibrated and validated on data collected during field visits in 2018 as well as some secondary data sources. The field data collection focused on river bathymetry and soil properties such as infiltration capacity. Furthermore, scenarios were developed and simulated that varied in dam operational capacity (29\% and 80\%), reservoir management (for flood mitigation), and irrigation demand. Using modelled discharge results, multiple environmental flow assessments were carried out, comparing pre- and post-dam scenarios. The results demonstrated that different elements of the flow regime can be altered slightly depending on the Yeywa operational scenario. For the irrigation scenario, the high water uptake to meet the crop demand alters the magnitudes and duration to the largest extent of all the scenarios. According to the results, the dam alone does not alter most of the components of the natural flow regime (and hence presumably the associated ecological factors) to a very large extent, regardless of the capacity it is operated at. This is because the attainable operational capacity is limited by inflow: raising the capacity at which the dam is operated can only be done for a limited amount of time due to the extreme seasonality. For the current operation and in the simulated scenarios, habitat availability for different species of plants and animals, as well as the river's ability to structure the channel morphology are the elements most at risk due to the Yeywa dam. This is mostly because the occurrence of large floods has significantly reduced or completely disappeared from the flow regime, as also demonstrated by a habitat inundation analysis for the Myitnge. There is potential for the optimisation of the operation of the Yeywa reservoir, but it remains limited to the availability of inflows, which in turn is dependent on the natural seasonality and the size of the reservoir. Therefore, one of the main recommendations is to avoid keeping the outflow below the natural inflow in the dry season, and to run the turbines at maximum capacity during the monsoon period. This is advised in order to protect the downstream channel area from dewatering in the dry season, and to maximize the electricity generation during the wet season, while simultaneously keeping the released discharge very close to the natural flow regime.

Canal Emilio Mitre is a navigation channel that runs through the Rio de la Plata estuary in South America. It grants access to the second largest inland waterway system in South America, covering (parts of) Argentina, Uruguay, Brazil, Paraguay and Bolivia. The channel is a main bottleneck for navigation for two reasons; the channel has a continuous need for maintenance dredging and it is only navigable during a tidal window. Furthermore, the dredging effort shows high interannual variability, resulting in risks for the contractor and users. The current study identifies the dredging effort and strategy, and a conceptual model is made of what physical processes force the sedimentation. The IPCC reports are used to identify the effect of climate change and variability on the drivers of the sedimentation. The interannual variability is shown to be linked to climate variability, due to the ENSO phenomena. The drainage basin of the Rio Parana is affected by an increase in precipitation and sediment input during El Nino events as a result of the teleconnections of ENSO. A depth-averaged numerical model (Delft3D) is set-up to address the effect of climate, deepening and wind scenarios on the dredging effort and its variability. The numerical model was validated by comparing the reported dredged volumes in the system to the simulated sedimentation. Overall, the sedimentation in the system is found to be sensitive to highly energetic events due to a redistribution of the fine sediments over the estuary. The acquired knowledge on the physical processes of the system in combination with the outcomes of the scenarios are used to make recommendations on the future dredging strategy to reduce the risk due to variability. This study highlights the importance of taking into account the risks and chances due to climate variability in dredging projects in regions affected by teleconnections with a duration of around 10 years.

Understanding the river dynamics is very important to be able to make use of all river functions and to protect ourselves against floods. Hydrodynamic models are used to predict river behaviour and one of the input parameters is the river geometry. In-situ measuring of river geometry can be very expensive and time consuming. Remote sensing offers a more efficient method to monitor rivers, because it has the ability to continuously monitor the Earth surface at multiple scales. Rivers in monsoon dominated regions show a strong seasonal variation in discharge and have a high variability in morphodynamics. Therefore it is very important to have a high spatial-temporal resolution of river geometry data as input for hydrodynamic models to keep up with the changes in the river. Both optical and microwave images can be used in providing information about the river geometry. The microwave images need a lot of processing to deal with noise, but they are not limited by clouds, whereas optical sensors are troubled by clouds but produce less noise. The benefit of combining these methods is because the microwave images could fill the gap of cloud covered optical images during the monsoon. The main result from this thesis is that more investigation is needed on how to deal with the noise produced by the microwave images before the methods can be combined. Nevertheless it is shown that using the Canny Edge detector and Otsu thresholding improves the results. With this research we are a small step further in global river monitoring. This is important in particular for parts of the world where rivers are not continuously monitored because they are situated in hard to reach terrain and because the country will not invest in local gauge stations. Having more knowledge about river behaviour will help to get a better understanding of water losses along the river course, habitat change and flood risks.