Wim S.J. Uijttewaal
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1
The immersion of the tunnel elements is a critical operation in the construction of an immersed tunnel. During this operation, the tunnel element is lowered to the seabed, guided by vertical cables, whose loads vary continuously as a result of the interaction with environmental and operational inputs, such as water density changes and cable pay out events. Predicting these loads accurately would allow the operation to be optimized, enhancing both the safety and the efficiency of the lowering process.
In current practice, cable loads are estimated using methods of increasing fidelity. Engineering hand calculations (low-fidelity) are quick to compute but rely on simplifying assumptions that neglect hydrodynamic forces, limiting their accuracy. Mid-fidelity models such as OrcaFlex estimate these hydrodynamic forces using potential flow theory and Morison-type force equations, which improves accuracy but introduces calibration coefficients that must be estimated. High-fidelity methods such as Computational Fluid Dynamics (CFD) resolve the Navier--Stokes equations and can capture the fluid structure interaction, but at a high computational cost, which makes them impractical for operational use. Furthermore, none of these methods can adapt to cable loads measured during previous immersion operations. This research investigates to what extent machine learning models, trained on operational monitoring data, can improve the accuracy and generalizability of cable load estimation compared to these traditional engineering methods.
The machine learning models are benchmarked against the engineering estimates: the DEME immersion sheet for the static loads and a two-degree-of-freedom (2DOF) analytical model for the dynamic loads. The monitoring data used in this study comes from the Oosterweel tunnel in Antwerp, from which six immersion sequences were retrieved, each containing operational and environmental variables. Quality control was applied to remove sensor faults, after which a data analysis was performed to characterise the stationarity of the data and the signal was filtered to retain the structural behaviour of the system. The target data were then split into static and dynamic cable loads. For the static loads, a multivariate regression (MVR) and a multilayer perceptron (MLP) were selected: the MVR captures the linear correlation between the input forces, while the MLP additionally captures the non-linear behaviour. For the dynamic loads, a long short-term memory (LSTM) and Fourier neural operator (FNO) were developed because these models both account for sequential inductive bias and the FNO also works with spectral inductive bias. For the MVR, MLP, and LSTM, a weighted mean squared error (MSE) loss function was used, and for the FNO, a Sobolev loss function. The models were evaluated by their coefficient of determination (R2) and root mean squared error (RMSE) against the evaluation set, and for the dynamic models, the period distribution was additionally compared.
The data analysis revealed a two-regime structure in the monitoring data. The boundary between these regimes is the moment the element passes through the waterline. Besides this, the analysis indicated that the oscillation period decreases as the element descends and increases again near the seabed. This contradicts the available literature on immersed tunnels in wave environments. This effect is most likely caused by the depth-dependent added mass.
The machine learning models outperformed the engineering estimates in both regimes. For the static loads, the MLP reached an average of R2 = 0.92 and RMSE = 5.7t, against R2 = 0.33 and RMSE = 16.1t, for the immersion sheet. For the dynamic loads, the FNO and LSTM achieved positive R2 values (0.44 and 0.42 respectively), where the 2DOF estimate scored negative. Both models reproduced the non-constant oscillation period. However, the peak amplitudes remained underestimated. A convergence study showed the number of training sequences required to outperform the engineering estimates (static n = 2, dynamic n = 5).
This study indicates that operational monitoring data can be used to train machine learning models that estimate cable loads more accurately than the engineering methods currently in use. Although the dynamic models still underestimate peak amplitudes, limiting their direct use for optimizing the cable payout rate, the modelling can be transferred to future immersion projects.
...
The immersion of the tunnel elements is a critical operation in the construction of an immersed tunnel. During this operation, the tunnel element is lowered to the seabed, guided by vertical cables, whose loads vary continuously as a result of the interaction with environmental and operational inputs, such as water density changes and cable pay out events. Predicting these loads accurately would allow the operation to be optimized, enhancing both the safety and the efficiency of the lowering process.
In current practice, cable loads are estimated using methods of increasing fidelity. Engineering hand calculations (low-fidelity) are quick to compute but rely on simplifying assumptions that neglect hydrodynamic forces, limiting their accuracy. Mid-fidelity models such as OrcaFlex estimate these hydrodynamic forces using potential flow theory and Morison-type force equations, which improves accuracy but introduces calibration coefficients that must be estimated. High-fidelity methods such as Computational Fluid Dynamics (CFD) resolve the Navier--Stokes equations and can capture the fluid structure interaction, but at a high computational cost, which makes them impractical for operational use. Furthermore, none of these methods can adapt to cable loads measured during previous immersion operations. This research investigates to what extent machine learning models, trained on operational monitoring data, can improve the accuracy and generalizability of cable load estimation compared to these traditional engineering methods.
The machine learning models are benchmarked against the engineering estimates: the DEME immersion sheet for the static loads and a two-degree-of-freedom (2DOF) analytical model for the dynamic loads. The monitoring data used in this study comes from the Oosterweel tunnel in Antwerp, from which six immersion sequences were retrieved, each containing operational and environmental variables. Quality control was applied to remove sensor faults, after which a data analysis was performed to characterise the stationarity of the data and the signal was filtered to retain the structural behaviour of the system. The target data were then split into static and dynamic cable loads. For the static loads, a multivariate regression (MVR) and a multilayer perceptron (MLP) were selected: the MVR captures the linear correlation between the input forces, while the MLP additionally captures the non-linear behaviour. For the dynamic loads, a long short-term memory (LSTM) and Fourier neural operator (FNO) were developed because these models both account for sequential inductive bias and the FNO also works with spectral inductive bias. For the MVR, MLP, and LSTM, a weighted mean squared error (MSE) loss function was used, and for the FNO, a Sobolev loss function. The models were evaluated by their coefficient of determination (R2) and root mean squared error (RMSE) against the evaluation set, and for the dynamic models, the period distribution was additionally compared.
The data analysis revealed a two-regime structure in the monitoring data. The boundary between these regimes is the moment the element passes through the waterline. Besides this, the analysis indicated that the oscillation period decreases as the element descends and increases again near the seabed. This contradicts the available literature on immersed tunnels in wave environments. This effect is most likely caused by the depth-dependent added mass.
The machine learning models outperformed the engineering estimates in both regimes. For the static loads, the MLP reached an average of R2 = 0.92 and RMSE = 5.7t, against R2 = 0.33 and RMSE = 16.1t, for the immersion sheet. For the dynamic loads, the FNO and LSTM achieved positive R2 values (0.44 and 0.42 respectively), where the 2DOF estimate scored negative. Both models reproduced the non-constant oscillation period. However, the peak amplitudes remained underestimated. A convergence study showed the number of training sequences required to outperform the engineering estimates (static n = 2, dynamic n = 5).
This study indicates that operational monitoring data can be used to train machine learning models that estimate cable loads more accurately than the engineering methods currently in use. Although the dynamic models still underestimate peak amplitudes, limiting their direct use for optimizing the cable payout rate, the modelling can be transferred to future immersion projects.
The current flood protection strategy in the Netherlands, known as the protect open approach, is increasingly challenged by climate change and sea level rise. Within this approach, river dikes are heightened while maintaining an open connection with the sea. The primary flood defence system along the Waal has been strengthened until 2080 using the current flood protection approach. However, under future extreme climate scenarios, higher river discharges and compound river-coastal flooding are expected to place growing pressure on the primary flood defence system. This research investigates an alternative strategy for the long term: the advance-closed approach, in which the Delta21 concept is implemented. The advance-closed approach combines parts of the advance and protect-closed approaches as defined by the the sea level rise knowledge program. At the Haringvliet outlet there is an advancement towards sea by building Delta21 and the new waterway is closed off by a sluice following the protect-closed approach.
In the Delta21 concept an energy lake in build seaward of the Haringvliet outlet. During extreme river dischargers or sea conditions the Delta21 storm surge barrier can be closed off and water can be pumped out of the river system into the energy lake and subsequently into the sea.
The main objective of this study is to assess to what extent the advance-closed approach can reduce the probability of failure of the primary flood defence system along the Waal River, from Tiel to the Haringvliet outlet, compared to the current protect-open approach. The analysis focuses on extreme conditions under the KNMI’23 high emission, wet climate scenario for the year 2150.
The hydraulic response of both approaches is simulated using the one-dimensional hydrodynamic model SOBEK. The results of these simulations are translated into probabilistic water level distributions using a discrete Bayesian Network. Discrete Bayesian networks are probabilistic graphical models representing the joint distribution of a set of variables. The Bayesian Network first calculates the load on the primary flood defence system by calculating the water level statistics using the conditional probabilities to the boundary conditions of the hydrodynamic model. By applying the Markov blanket principle, the Bayesian Network remains transparent and computationally efficient while capturing the dominant dependencies in the system.
This probabilistic framework allows hydraulic loads and dike strength to be combined explicitly. The dike strength is defined by dike failure mechanisms such as backward erosion piping, macro-instability, and overflow which are incorporated through fragility curves derived from OKADER.
The results indicate that the advance-closed approach leads to lower water level exceedance prob- abilities and a significant reduction in the probability of dike failure along the Waal from Tiel to the Haringvliet outlet. Even in the far upstream, discharge dominated region, does the advanced-closed approach reduce the water levels compared tot the protect-open approach. For validated dike rings, the failure probability is reduced by factors ranging between 102 and 104 compared to the protect-open approach. This reduction is primarily attributed to the additional storage and pumping capacity provided by the Delta21 system during extreme river discharges and storm conditions. Although failure of the spillway and pump system of Delta21 results in high water levels, these scenarios have very low probabilities and therefore contribute only marginally to the overall failure probability.
In addition to quantifying failure probabilities, the Bayesian Network enables back-tracing of dike failure to specific hydraulic conditions and failure of individual flood barriers. This makes the approach a valuable tool for identifying vulnerabilities within complex flood-protection systems. At the same time, uncertainties remain, particularly in the representation of dike strength, assumptions of conditional independence, discretisation choices, and the omission of time as an explicit state variable which is especially relevant for pump reliability.
Despite these limitations, the study demonstrates that the advance-closed approach is a promising long-term strategy for reducing flood risk along the Waal under future extreme climate scenarios. Further refinement of hydrodynamic modelling, improved definition of failure mechanism probabilities, and explicit inclusion of time dependent processes are recommended to strengthen the robustness of the conclusions. ...
In the Delta21 concept an energy lake in build seaward of the Haringvliet outlet. During extreme river dischargers or sea conditions the Delta21 storm surge barrier can be closed off and water can be pumped out of the river system into the energy lake and subsequently into the sea.
The main objective of this study is to assess to what extent the advance-closed approach can reduce the probability of failure of the primary flood defence system along the Waal River, from Tiel to the Haringvliet outlet, compared to the current protect-open approach. The analysis focuses on extreme conditions under the KNMI’23 high emission, wet climate scenario for the year 2150.
The hydraulic response of both approaches is simulated using the one-dimensional hydrodynamic model SOBEK. The results of these simulations are translated into probabilistic water level distributions using a discrete Bayesian Network. Discrete Bayesian networks are probabilistic graphical models representing the joint distribution of a set of variables. The Bayesian Network first calculates the load on the primary flood defence system by calculating the water level statistics using the conditional probabilities to the boundary conditions of the hydrodynamic model. By applying the Markov blanket principle, the Bayesian Network remains transparent and computationally efficient while capturing the dominant dependencies in the system.
This probabilistic framework allows hydraulic loads and dike strength to be combined explicitly. The dike strength is defined by dike failure mechanisms such as backward erosion piping, macro-instability, and overflow which are incorporated through fragility curves derived from OKADER.
The results indicate that the advance-closed approach leads to lower water level exceedance prob- abilities and a significant reduction in the probability of dike failure along the Waal from Tiel to the Haringvliet outlet. Even in the far upstream, discharge dominated region, does the advanced-closed approach reduce the water levels compared tot the protect-open approach. For validated dike rings, the failure probability is reduced by factors ranging between 102 and 104 compared to the protect-open approach. This reduction is primarily attributed to the additional storage and pumping capacity provided by the Delta21 system during extreme river discharges and storm conditions. Although failure of the spillway and pump system of Delta21 results in high water levels, these scenarios have very low probabilities and therefore contribute only marginally to the overall failure probability.
In addition to quantifying failure probabilities, the Bayesian Network enables back-tracing of dike failure to specific hydraulic conditions and failure of individual flood barriers. This makes the approach a valuable tool for identifying vulnerabilities within complex flood-protection systems. At the same time, uncertainties remain, particularly in the representation of dike strength, assumptions of conditional independence, discretisation choices, and the omission of time as an explicit state variable which is especially relevant for pump reliability.
Despite these limitations, the study demonstrates that the advance-closed approach is a promising long-term strategy for reducing flood risk along the Waal under future extreme climate scenarios. Further refinement of hydrodynamic modelling, improved definition of failure mechanism probabilities, and explicit inclusion of time dependent processes are recommended to strengthen the robustness of the conclusions. ...
The current flood protection strategy in the Netherlands, known as the protect open approach, is increasingly challenged by climate change and sea level rise. Within this approach, river dikes are heightened while maintaining an open connection with the sea. The primary flood defence system along the Waal has been strengthened until 2080 using the current flood protection approach. However, under future extreme climate scenarios, higher river discharges and compound river-coastal flooding are expected to place growing pressure on the primary flood defence system. This research investigates an alternative strategy for the long term: the advance-closed approach, in which the Delta21 concept is implemented. The advance-closed approach combines parts of the advance and protect-closed approaches as defined by the the sea level rise knowledge program. At the Haringvliet outlet there is an advancement towards sea by building Delta21 and the new waterway is closed off by a sluice following the protect-closed approach.
In the Delta21 concept an energy lake in build seaward of the Haringvliet outlet. During extreme river dischargers or sea conditions the Delta21 storm surge barrier can be closed off and water can be pumped out of the river system into the energy lake and subsequently into the sea.
The main objective of this study is to assess to what extent the advance-closed approach can reduce the probability of failure of the primary flood defence system along the Waal River, from Tiel to the Haringvliet outlet, compared to the current protect-open approach. The analysis focuses on extreme conditions under the KNMI’23 high emission, wet climate scenario for the year 2150.
The hydraulic response of both approaches is simulated using the one-dimensional hydrodynamic model SOBEK. The results of these simulations are translated into probabilistic water level distributions using a discrete Bayesian Network. Discrete Bayesian networks are probabilistic graphical models representing the joint distribution of a set of variables. The Bayesian Network first calculates the load on the primary flood defence system by calculating the water level statistics using the conditional probabilities to the boundary conditions of the hydrodynamic model. By applying the Markov blanket principle, the Bayesian Network remains transparent and computationally efficient while capturing the dominant dependencies in the system.
This probabilistic framework allows hydraulic loads and dike strength to be combined explicitly. The dike strength is defined by dike failure mechanisms such as backward erosion piping, macro-instability, and overflow which are incorporated through fragility curves derived from OKADER.
The results indicate that the advance-closed approach leads to lower water level exceedance prob- abilities and a significant reduction in the probability of dike failure along the Waal from Tiel to the Haringvliet outlet. Even in the far upstream, discharge dominated region, does the advanced-closed approach reduce the water levels compared tot the protect-open approach. For validated dike rings, the failure probability is reduced by factors ranging between 102 and 104 compared to the protect-open approach. This reduction is primarily attributed to the additional storage and pumping capacity provided by the Delta21 system during extreme river discharges and storm conditions. Although failure of the spillway and pump system of Delta21 results in high water levels, these scenarios have very low probabilities and therefore contribute only marginally to the overall failure probability.
In addition to quantifying failure probabilities, the Bayesian Network enables back-tracing of dike failure to specific hydraulic conditions and failure of individual flood barriers. This makes the approach a valuable tool for identifying vulnerabilities within complex flood-protection systems. At the same time, uncertainties remain, particularly in the representation of dike strength, assumptions of conditional independence, discretisation choices, and the omission of time as an explicit state variable which is especially relevant for pump reliability.
Despite these limitations, the study demonstrates that the advance-closed approach is a promising long-term strategy for reducing flood risk along the Waal under future extreme climate scenarios. Further refinement of hydrodynamic modelling, improved definition of failure mechanism probabilities, and explicit inclusion of time dependent processes are recommended to strengthen the robustness of the conclusions.
In the Delta21 concept an energy lake in build seaward of the Haringvliet outlet. During extreme river dischargers or sea conditions the Delta21 storm surge barrier can be closed off and water can be pumped out of the river system into the energy lake and subsequently into the sea.
The main objective of this study is to assess to what extent the advance-closed approach can reduce the probability of failure of the primary flood defence system along the Waal River, from Tiel to the Haringvliet outlet, compared to the current protect-open approach. The analysis focuses on extreme conditions under the KNMI’23 high emission, wet climate scenario for the year 2150.
The hydraulic response of both approaches is simulated using the one-dimensional hydrodynamic model SOBEK. The results of these simulations are translated into probabilistic water level distributions using a discrete Bayesian Network. Discrete Bayesian networks are probabilistic graphical models representing the joint distribution of a set of variables. The Bayesian Network first calculates the load on the primary flood defence system by calculating the water level statistics using the conditional probabilities to the boundary conditions of the hydrodynamic model. By applying the Markov blanket principle, the Bayesian Network remains transparent and computationally efficient while capturing the dominant dependencies in the system.
This probabilistic framework allows hydraulic loads and dike strength to be combined explicitly. The dike strength is defined by dike failure mechanisms such as backward erosion piping, macro-instability, and overflow which are incorporated through fragility curves derived from OKADER.
The results indicate that the advance-closed approach leads to lower water level exceedance prob- abilities and a significant reduction in the probability of dike failure along the Waal from Tiel to the Haringvliet outlet. Even in the far upstream, discharge dominated region, does the advanced-closed approach reduce the water levels compared tot the protect-open approach. For validated dike rings, the failure probability is reduced by factors ranging between 102 and 104 compared to the protect-open approach. This reduction is primarily attributed to the additional storage and pumping capacity provided by the Delta21 system during extreme river discharges and storm conditions. Although failure of the spillway and pump system of Delta21 results in high water levels, these scenarios have very low probabilities and therefore contribute only marginally to the overall failure probability.
In addition to quantifying failure probabilities, the Bayesian Network enables back-tracing of dike failure to specific hydraulic conditions and failure of individual flood barriers. This makes the approach a valuable tool for identifying vulnerabilities within complex flood-protection systems. At the same time, uncertainties remain, particularly in the representation of dike strength, assumptions of conditional independence, discretisation choices, and the omission of time as an explicit state variable which is especially relevant for pump reliability.
Despite these limitations, the study demonstrates that the advance-closed approach is a promising long-term strategy for reducing flood risk along the Waal under future extreme climate scenarios. Further refinement of hydrodynamic modelling, improved definition of failure mechanism probabilities, and explicit inclusion of time dependent processes are recommended to strengthen the robustness of the conclusions.
Master thesis
(2025)
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T.P. van Oudenallen, T.S. van den Bremer, M. Zijlema, Wim S.J. Uijttewaal, P.B. Bayle, J. Mol
Surface gravity waves are one of the hydrodynamic processes in the nearshore area that play a key role in the transport of plastic, plankton, sediment and other particles. Previous research has studied the combined effect of the Earth's rotation and turbulent mixing on the wave-driven cross-shore velocity profile in both the surf zone and on the inner continental shelf. However, these studies either used eddy viscosity profiles typical for wind-driven currents or determined the turbulence characteristics based on the amount of energy dissipated by wave breaking. This research aims to unravel the connection between the Coriolis force and momentum diffusion in the absence of wave breaking by using a turbulence model that is based exclusively on wave-driven flow dynamics. To this end, the existing one-dimensional wave-averaged model of Lentz et al. (2008) was improved by incorporating a low-Re one-equation turbulence model to determine the eddy viscosity generated by the Eulerian-mean flow. Furthermore, a complementary three-dimensional RANS model was constructed in SWASH.
In an inertial frame of reference, the models predict velocity profiles that are similar to the theoretical inviscid depth-uniform return flow in the inner part of the water column, while in a rotating frame of reference, the results approach the anti-Stokes drift profile based on the theory of Hasselmann (1970). Deviations are observed near the bed, caused by vertical radiation shear stresses, especially in relatively shallow water. The inverse wave Ekman number is shown to be a key indicator of the relative importance of the Coriolis force with respect to turbulent mixing. The results emphasize the importance of including the Coriolis force in nearshore wave-driven flow models. Compared with laboratory measurements, the theoretical model accurately predicts the near-bed velocity profile, indicating that a turbulence model that is based on wave-driven flow dynamics is essential to properly model wave-induced currents. ...
In an inertial frame of reference, the models predict velocity profiles that are similar to the theoretical inviscid depth-uniform return flow in the inner part of the water column, while in a rotating frame of reference, the results approach the anti-Stokes drift profile based on the theory of Hasselmann (1970). Deviations are observed near the bed, caused by vertical radiation shear stresses, especially in relatively shallow water. The inverse wave Ekman number is shown to be a key indicator of the relative importance of the Coriolis force with respect to turbulent mixing. The results emphasize the importance of including the Coriolis force in nearshore wave-driven flow models. Compared with laboratory measurements, the theoretical model accurately predicts the near-bed velocity profile, indicating that a turbulence model that is based on wave-driven flow dynamics is essential to properly model wave-induced currents. ...
Surface gravity waves are one of the hydrodynamic processes in the nearshore area that play a key role in the transport of plastic, plankton, sediment and other particles. Previous research has studied the combined effect of the Earth's rotation and turbulent mixing on the wave-driven cross-shore velocity profile in both the surf zone and on the inner continental shelf. However, these studies either used eddy viscosity profiles typical for wind-driven currents or determined the turbulence characteristics based on the amount of energy dissipated by wave breaking. This research aims to unravel the connection between the Coriolis force and momentum diffusion in the absence of wave breaking by using a turbulence model that is based exclusively on wave-driven flow dynamics. To this end, the existing one-dimensional wave-averaged model of Lentz et al. (2008) was improved by incorporating a low-Re one-equation turbulence model to determine the eddy viscosity generated by the Eulerian-mean flow. Furthermore, a complementary three-dimensional RANS model was constructed in SWASH.
In an inertial frame of reference, the models predict velocity profiles that are similar to the theoretical inviscid depth-uniform return flow in the inner part of the water column, while in a rotating frame of reference, the results approach the anti-Stokes drift profile based on the theory of Hasselmann (1970). Deviations are observed near the bed, caused by vertical radiation shear stresses, especially in relatively shallow water. The inverse wave Ekman number is shown to be a key indicator of the relative importance of the Coriolis force with respect to turbulent mixing. The results emphasize the importance of including the Coriolis force in nearshore wave-driven flow models. Compared with laboratory measurements, the theoretical model accurately predicts the near-bed velocity profile, indicating that a turbulence model that is based on wave-driven flow dynamics is essential to properly model wave-induced currents.
In an inertial frame of reference, the models predict velocity profiles that are similar to the theoretical inviscid depth-uniform return flow in the inner part of the water column, while in a rotating frame of reference, the results approach the anti-Stokes drift profile based on the theory of Hasselmann (1970). Deviations are observed near the bed, caused by vertical radiation shear stresses, especially in relatively shallow water. The inverse wave Ekman number is shown to be a key indicator of the relative importance of the Coriolis force with respect to turbulent mixing. The results emphasize the importance of including the Coriolis force in nearshore wave-driven flow models. Compared with laboratory measurements, the theoretical model accurately predicts the near-bed velocity profile, indicating that a turbulence model that is based on wave-driven flow dynamics is essential to properly model wave-induced currents.
Investigating Mass Transport of Ocean Wave in Nearshore Area
A Study of Wave-Current Interactions
This thesis presents a comprehensive study of Lagrangian and Eulerian mass transport in a wave flume experiment, aiming to improve understanding of mass transport mechanisms and their role in wave-current interactions. This has important implications for nearshore particle transport and pollutant dispersion. The research utilizes state-of-the-art Particle Tracking Velocimetry (PTV) to directly measure the Lagrangian velocity of individual particles, providing higher temporal resolution and precision in capturing unsteady flow phenomena compared to traditional methods. The study compares experimental mass transport data with existing mathematical models, including the irrotational and conduction solutions, and qualitatively discusses the potential importance of the convection model.
The focus of the study is on the temporal evolution of vertical velocity profiles influenced by waves and wave-induced currents, exploring how these profiles change under varying relative water depths (kh)
and wave steepness (ka). Additionally, the temporal evolution of vorticity profiles is examined to identify the underlying mechanisms driving these changes.
To extract the net Lagrangian drift from particle tracking data, three averaging methods—time-averaging, wave-by-wave, and low-pass filtering—are compared. The wave-by-wave method is found to be the most suitable for this study.
The velocity profile transitions from an initially irrotational state, characterized by uniform motion near the surface, to a more complex structure resembling the conduction solution as vorticity diffuses. However, the observed profiles do not quantitatively align with the conduction solution. After approximately 60 minutes, the profile stabilizes but continues to exhibit discrepancies from both the irrotational and conduction models. At equilibrium, while the velocity profiles qualitatively align with the theoretical predictions of the conduction solution, significant quantitative differences remain, particularly in surface drift velocities an the negative peak velocity in the middle of the water column.
The study also shows that as wave steepness increases, deviations from theoretical predictions grow, indicating that higher steepness disrupts the assumptions underlying the conduction solution, leading to greater discrepancies between observed and predicted velocities. The evolution of the velocity profile is further explained through vorticity transport, where a more uniform vorticity distribution is observed compared to predictions from the conduction solution. This complex behavior is influenced by factors such as sidewall interactions and vorticity convection along the direction of wave propagation. ...
The focus of the study is on the temporal evolution of vertical velocity profiles influenced by waves and wave-induced currents, exploring how these profiles change under varying relative water depths (kh)
and wave steepness (ka). Additionally, the temporal evolution of vorticity profiles is examined to identify the underlying mechanisms driving these changes.
To extract the net Lagrangian drift from particle tracking data, three averaging methods—time-averaging, wave-by-wave, and low-pass filtering—are compared. The wave-by-wave method is found to be the most suitable for this study.
The velocity profile transitions from an initially irrotational state, characterized by uniform motion near the surface, to a more complex structure resembling the conduction solution as vorticity diffuses. However, the observed profiles do not quantitatively align with the conduction solution. After approximately 60 minutes, the profile stabilizes but continues to exhibit discrepancies from both the irrotational and conduction models. At equilibrium, while the velocity profiles qualitatively align with the theoretical predictions of the conduction solution, significant quantitative differences remain, particularly in surface drift velocities an the negative peak velocity in the middle of the water column.
The study also shows that as wave steepness increases, deviations from theoretical predictions grow, indicating that higher steepness disrupts the assumptions underlying the conduction solution, leading to greater discrepancies between observed and predicted velocities. The evolution of the velocity profile is further explained through vorticity transport, where a more uniform vorticity distribution is observed compared to predictions from the conduction solution. This complex behavior is influenced by factors such as sidewall interactions and vorticity convection along the direction of wave propagation. ...
This thesis presents a comprehensive study of Lagrangian and Eulerian mass transport in a wave flume experiment, aiming to improve understanding of mass transport mechanisms and their role in wave-current interactions. This has important implications for nearshore particle transport and pollutant dispersion. The research utilizes state-of-the-art Particle Tracking Velocimetry (PTV) to directly measure the Lagrangian velocity of individual particles, providing higher temporal resolution and precision in capturing unsteady flow phenomena compared to traditional methods. The study compares experimental mass transport data with existing mathematical models, including the irrotational and conduction solutions, and qualitatively discusses the potential importance of the convection model.
The focus of the study is on the temporal evolution of vertical velocity profiles influenced by waves and wave-induced currents, exploring how these profiles change under varying relative water depths (kh)
and wave steepness (ka). Additionally, the temporal evolution of vorticity profiles is examined to identify the underlying mechanisms driving these changes.
To extract the net Lagrangian drift from particle tracking data, three averaging methods—time-averaging, wave-by-wave, and low-pass filtering—are compared. The wave-by-wave method is found to be the most suitable for this study.
The velocity profile transitions from an initially irrotational state, characterized by uniform motion near the surface, to a more complex structure resembling the conduction solution as vorticity diffuses. However, the observed profiles do not quantitatively align with the conduction solution. After approximately 60 minutes, the profile stabilizes but continues to exhibit discrepancies from both the irrotational and conduction models. At equilibrium, while the velocity profiles qualitatively align with the theoretical predictions of the conduction solution, significant quantitative differences remain, particularly in surface drift velocities an the negative peak velocity in the middle of the water column.
The study also shows that as wave steepness increases, deviations from theoretical predictions grow, indicating that higher steepness disrupts the assumptions underlying the conduction solution, leading to greater discrepancies between observed and predicted velocities. The evolution of the velocity profile is further explained through vorticity transport, where a more uniform vorticity distribution is observed compared to predictions from the conduction solution. This complex behavior is influenced by factors such as sidewall interactions and vorticity convection along the direction of wave propagation.
The focus of the study is on the temporal evolution of vertical velocity profiles influenced by waves and wave-induced currents, exploring how these profiles change under varying relative water depths (kh)
and wave steepness (ka). Additionally, the temporal evolution of vorticity profiles is examined to identify the underlying mechanisms driving these changes.
To extract the net Lagrangian drift from particle tracking data, three averaging methods—time-averaging, wave-by-wave, and low-pass filtering—are compared. The wave-by-wave method is found to be the most suitable for this study.
The velocity profile transitions from an initially irrotational state, characterized by uniform motion near the surface, to a more complex structure resembling the conduction solution as vorticity diffuses. However, the observed profiles do not quantitatively align with the conduction solution. After approximately 60 minutes, the profile stabilizes but continues to exhibit discrepancies from both the irrotational and conduction models. At equilibrium, while the velocity profiles qualitatively align with the theoretical predictions of the conduction solution, significant quantitative differences remain, particularly in surface drift velocities an the negative peak velocity in the middle of the water column.
The study also shows that as wave steepness increases, deviations from theoretical predictions grow, indicating that higher steepness disrupts the assumptions underlying the conduction solution, leading to greater discrepancies between observed and predicted velocities. The evolution of the velocity profile is further explained through vorticity transport, where a more uniform vorticity distribution is observed compared to predictions from the conduction solution. This complex behavior is influenced by factors such as sidewall interactions and vorticity convection along the direction of wave propagation.
Climate change is adding more and more pressure to the water systems. The area which is protected by the storm surge barrier of Ramspol have high probability of flooding for climate projections in 2050 and 2100.
Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions.
In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied.
The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.
...
Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions.
In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied.
The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.
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Climate change is adding more and more pressure to the water systems. The area which is protected by the storm surge barrier of Ramspol have high probability of flooding for climate projections in 2050 and 2100.
Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions.
In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied.
The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.
Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions.
In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied.
The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.
Master thesis
(2023)
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I. de Vries, O.A.C. Hoes, Anne van der Heijden, R. Uijlenhoet, W.S.J. Uijttewaal
Polders water canals are sometimes exposed to brackish seepage from the nearby saline sea (salinization). This is a problem because the canal water is used to irrigate crops. A characteristic of water is that less dense (fresh) water floats on top of dense (saline) water. In lakes and oceans, it is common that water layers with various densities flow on top of each other (stratification). However, this has not been observed yet on a small scale, such as in polder water canals. It is assumed that, with a traditional weir, fresh water is discharged, and saline water stays behind. To encounter this, a modified weir is developed. It uses an underflow gate in front of the traditional weir to discharge the bottom water out of the canal. This research aimed to investigate if stratification happens in polder water canals and to explore how a modified weir can be implemented. The Negenboerenpolder in Groningen (the Netherlands) served as an example. Multiple methods are used because of the broad and practical nature of the problem. First, field measurements in the Negenboerenpolder demonstrated stratification in polder water canals. At multiple locations in the polder, the Electrical Conductivity (EC) is measured over the depth or continuously measured at two depths. Secondly, flume experiments gave information about the experimental procedure and implementation of a modified weir. Thirdly, 2D simulations of a modified weir are done in ANSYS Fluent, a Computation Fluid Dynamics (CFD) software. The simulations suggest that a modified weir works as expected, but the model is not completely representative. Observations are that such a weir is more effective in discharging brackish water with a low flow velocity and a larger distance between the underflow gate and the weir. Implementation advice for a modified weir is also included in this research. To conclude, this research implies that a modified weir can be used to discharge brackish water, but the design and implementation need to be done carefully. Recommendations for future research are to experiment with a modified weir in a polder and to build a 3D CFD model to investigate the flow around the underflow gate.
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Polders water canals are sometimes exposed to brackish seepage from the nearby saline sea (salinization). This is a problem because the canal water is used to irrigate crops. A characteristic of water is that less dense (fresh) water floats on top of dense (saline) water. In lakes and oceans, it is common that water layers with various densities flow on top of each other (stratification). However, this has not been observed yet on a small scale, such as in polder water canals. It is assumed that, with a traditional weir, fresh water is discharged, and saline water stays behind. To encounter this, a modified weir is developed. It uses an underflow gate in front of the traditional weir to discharge the bottom water out of the canal. This research aimed to investigate if stratification happens in polder water canals and to explore how a modified weir can be implemented. The Negenboerenpolder in Groningen (the Netherlands) served as an example. Multiple methods are used because of the broad and practical nature of the problem. First, field measurements in the Negenboerenpolder demonstrated stratification in polder water canals. At multiple locations in the polder, the Electrical Conductivity (EC) is measured over the depth or continuously measured at two depths. Secondly, flume experiments gave information about the experimental procedure and implementation of a modified weir. Thirdly, 2D simulations of a modified weir are done in ANSYS Fluent, a Computation Fluid Dynamics (CFD) software. The simulations suggest that a modified weir works as expected, but the model is not completely representative. Observations are that such a weir is more effective in discharging brackish water with a low flow velocity and a larger distance between the underflow gate and the weir. Implementation advice for a modified weir is also included in this research. To conclude, this research implies that a modified weir can be used to discharge brackish water, but the design and implementation need to be done carefully. Recommendations for future research are to experiment with a modified weir in a polder and to build a 3D CFD model to investigate the flow around the underflow gate.
Accumulations of floating debris at culverts and inverted siphons cause partial blockage of the hydraulic structure’s inlet, leading to an increase in head loss that is also referred to as backwater rise. This effect is of high importance in flood management, because backwater rise associated with floating debris accumulations can cause or intensify flooding in the area upstream of the hydraulic structure, yet it is often not adequately addressed in practice or in design guidelines due to a lack of fundamental understanding. A prime example of this was observed at the Geul inverted siphon located near the village of Bunde in the south of Limburg, the Netherlands. During the 2021 floods the inverted siphon experienced a reduction in conveyance capacity due to accumulation of large wood at its inlet, intensifying flooding of nearby villages.
This thesis studied the development of floating debris accumulations at fully submerged and outlet-controlled culverts and inverted siphons, and analysed the effect that floating debris accumulations have on backwater rise. Experiments were performed in a flume under varying conditions of Froude number and submergence rate, achieved by adjusting the upstream flow depth compared to the culvert’s height. The scale model was representative of inverted siphons typical of the Limburg province. Upstream and downstream water levels were measured after addition of fixed batches of debris to the flume. The debris mixture consisted of six size classes of natural wood and was based on logs observed at the Geul inverted siphon. A grate was placed at the culvert’s inlet to prevent logs from passing through. In addition, flow velocities were measured at various locations using Laser Doppler Anemometry.
Based on visual observations and a feasibility study three mechanisms were proposed that describe the development of floating debris accumulations, and the feasibility of these mechanisms was confirmed in preliminary analyses. Furthermore, the experimental results were analysed to determine the influence on backwater rise of canopy drag due to skin friction within and below the accumulation, as well as form drag due to partial blockage of the inlet. It was found that in all cases inlet blockage was the dominant cause of head loss. Using this knowledge a theoretical framework based on a momentum balance equation was derived that relates the inlet blockage ratio to backwater rise, separating the contributions of the grate and debris. A regression analysis was then performed to obtain a design equation for the inlet blockage ratio caused by debris. In conclusion, this thesis provides improved understanding of the development of floating debris accumulations and their influence on backwater rise at submerged culverts and inverted siphons. The results enable more accurate predictions of water levels that can occur during floods and thus offer a solid foundation for flood management strategies. ...
This thesis studied the development of floating debris accumulations at fully submerged and outlet-controlled culverts and inverted siphons, and analysed the effect that floating debris accumulations have on backwater rise. Experiments were performed in a flume under varying conditions of Froude number and submergence rate, achieved by adjusting the upstream flow depth compared to the culvert’s height. The scale model was representative of inverted siphons typical of the Limburg province. Upstream and downstream water levels were measured after addition of fixed batches of debris to the flume. The debris mixture consisted of six size classes of natural wood and was based on logs observed at the Geul inverted siphon. A grate was placed at the culvert’s inlet to prevent logs from passing through. In addition, flow velocities were measured at various locations using Laser Doppler Anemometry.
Based on visual observations and a feasibility study three mechanisms were proposed that describe the development of floating debris accumulations, and the feasibility of these mechanisms was confirmed in preliminary analyses. Furthermore, the experimental results were analysed to determine the influence on backwater rise of canopy drag due to skin friction within and below the accumulation, as well as form drag due to partial blockage of the inlet. It was found that in all cases inlet blockage was the dominant cause of head loss. Using this knowledge a theoretical framework based on a momentum balance equation was derived that relates the inlet blockage ratio to backwater rise, separating the contributions of the grate and debris. A regression analysis was then performed to obtain a design equation for the inlet blockage ratio caused by debris. In conclusion, this thesis provides improved understanding of the development of floating debris accumulations and their influence on backwater rise at submerged culverts and inverted siphons. The results enable more accurate predictions of water levels that can occur during floods and thus offer a solid foundation for flood management strategies. ...
Accumulations of floating debris at culverts and inverted siphons cause partial blockage of the hydraulic structure’s inlet, leading to an increase in head loss that is also referred to as backwater rise. This effect is of high importance in flood management, because backwater rise associated with floating debris accumulations can cause or intensify flooding in the area upstream of the hydraulic structure, yet it is often not adequately addressed in practice or in design guidelines due to a lack of fundamental understanding. A prime example of this was observed at the Geul inverted siphon located near the village of Bunde in the south of Limburg, the Netherlands. During the 2021 floods the inverted siphon experienced a reduction in conveyance capacity due to accumulation of large wood at its inlet, intensifying flooding of nearby villages.
This thesis studied the development of floating debris accumulations at fully submerged and outlet-controlled culverts and inverted siphons, and analysed the effect that floating debris accumulations have on backwater rise. Experiments were performed in a flume under varying conditions of Froude number and submergence rate, achieved by adjusting the upstream flow depth compared to the culvert’s height. The scale model was representative of inverted siphons typical of the Limburg province. Upstream and downstream water levels were measured after addition of fixed batches of debris to the flume. The debris mixture consisted of six size classes of natural wood and was based on logs observed at the Geul inverted siphon. A grate was placed at the culvert’s inlet to prevent logs from passing through. In addition, flow velocities were measured at various locations using Laser Doppler Anemometry.
Based on visual observations and a feasibility study three mechanisms were proposed that describe the development of floating debris accumulations, and the feasibility of these mechanisms was confirmed in preliminary analyses. Furthermore, the experimental results were analysed to determine the influence on backwater rise of canopy drag due to skin friction within and below the accumulation, as well as form drag due to partial blockage of the inlet. It was found that in all cases inlet blockage was the dominant cause of head loss. Using this knowledge a theoretical framework based on a momentum balance equation was derived that relates the inlet blockage ratio to backwater rise, separating the contributions of the grate and debris. A regression analysis was then performed to obtain a design equation for the inlet blockage ratio caused by debris. In conclusion, this thesis provides improved understanding of the development of floating debris accumulations and their influence on backwater rise at submerged culverts and inverted siphons. The results enable more accurate predictions of water levels that can occur during floods and thus offer a solid foundation for flood management strategies.
This thesis studied the development of floating debris accumulations at fully submerged and outlet-controlled culverts and inverted siphons, and analysed the effect that floating debris accumulations have on backwater rise. Experiments were performed in a flume under varying conditions of Froude number and submergence rate, achieved by adjusting the upstream flow depth compared to the culvert’s height. The scale model was representative of inverted siphons typical of the Limburg province. Upstream and downstream water levels were measured after addition of fixed batches of debris to the flume. The debris mixture consisted of six size classes of natural wood and was based on logs observed at the Geul inverted siphon. A grate was placed at the culvert’s inlet to prevent logs from passing through. In addition, flow velocities were measured at various locations using Laser Doppler Anemometry.
Based on visual observations and a feasibility study three mechanisms were proposed that describe the development of floating debris accumulations, and the feasibility of these mechanisms was confirmed in preliminary analyses. Furthermore, the experimental results were analysed to determine the influence on backwater rise of canopy drag due to skin friction within and below the accumulation, as well as form drag due to partial blockage of the inlet. It was found that in all cases inlet blockage was the dominant cause of head loss. Using this knowledge a theoretical framework based on a momentum balance equation was derived that relates the inlet blockage ratio to backwater rise, separating the contributions of the grate and debris. A regression analysis was then performed to obtain a design equation for the inlet blockage ratio caused by debris. In conclusion, this thesis provides improved understanding of the development of floating debris accumulations and their influence on backwater rise at submerged culverts and inverted siphons. The results enable more accurate predictions of water levels that can occur during floods and thus offer a solid foundation for flood management strategies.
Master thesis
(2022)
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E. te Velde, W.S.J. Uijttewaal, B. Hofland, J.C. Winterwerp, A. Gijón Mancheño, Tom Wilms
Mangroves trap sediment and are the first coastal defence line for many coastal areas. Unfortunately, mangrove coasts worldwide are eroding due to deforestation, exposing local communities to flood hazards. In Demak, Indonesia, a Building with Nature approach was chosen to counteract erosion. Permeable dams were built on the foreshore to attenuate waves and restore the sediment balance. The dams have increased the bed level locally and mangroves expand after construction. A new project called MuMaCo (Mussels as Mangrove facilitators for Coastal defence) is launched to integrate mussel aquaculture into the mangrove rehabilitation project in Demak. Mussels increase the roughness and diameter of the bamboo poles, which could increase their wave attenuation capacity. Moreover, mussel culture gives the local communities an economic incentive to sustain the structures. This thesis describes and quantifies how mussels' growth influences the forces acting on bamboo poles. Small-scale experiments are performed in the wave flume of the Delft University of Technology on a scale of 1:3 and 1:6. Physical models were used for experiments with steady flow and waves. The steady flow experiments cover a range of Reynolds (Re) numbers between 10^3 and 10^4 to seek the drag crisis. Single mussel covered cylinders for both scales are compared to smooth cylinders and cylinders with an equivalent diameter. For the wave experiments, cnoidal waves with Keulegan-Carpenter ($KC$) numbers ranging from 3 to 113 that correspond with measured waves in Demak are chosen. Moreover, only mussel covered cylinders are compared to a smooth cylinder for a scale of 1:6. During the experiments, the flow velocity, force, and surface elevation are measured, and the drag and inertia coefficients are obtained with the help of the Morison equation. The drag coefficient shows a clear relationship with the Reynolds numbers for steady flow. Although the drag coefficients display the same qualitative behavior as in other studies in the literature, the drag coefficients of the smooth cylinder are more than 40 % larger than in the literature. This is probably due to large variations in the offset of the velocity meters (EMS) during the experiments. The large mussels show higher drag coefficients than the smooth cylinder. For the wave experiments, the drag coefficients show good correspondence to other studies in the literature, but the inertia coefficients are a factor two larger than expected for smooth cylinders. Treating the peak and trough of the cnoidal wave as individual sinusoidal waves shows similar results and suggest that cnoidal waves can be represented by KC numbers, as it is done for linear waves. The best fit to the literature values was found by solving the Morison equation with the measured force with the depth-integrated velocity squared and acceleration from the Fenton theory. This suggests that the results of the wave experiments have been uncertain due to inaccuracies in the EMS recordings. This thesis presents a method to schematize mussels for laboratory experiments and provides a qualitative comparison of the forces acting on poles with and without mussels
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Mangroves trap sediment and are the first coastal defence line for many coastal areas. Unfortunately, mangrove coasts worldwide are eroding due to deforestation, exposing local communities to flood hazards. In Demak, Indonesia, a Building with Nature approach was chosen to counteract erosion. Permeable dams were built on the foreshore to attenuate waves and restore the sediment balance. The dams have increased the bed level locally and mangroves expand after construction. A new project called MuMaCo (Mussels as Mangrove facilitators for Coastal defence) is launched to integrate mussel aquaculture into the mangrove rehabilitation project in Demak. Mussels increase the roughness and diameter of the bamboo poles, which could increase their wave attenuation capacity. Moreover, mussel culture gives the local communities an economic incentive to sustain the structures. This thesis describes and quantifies how mussels' growth influences the forces acting on bamboo poles. Small-scale experiments are performed in the wave flume of the Delft University of Technology on a scale of 1:3 and 1:6. Physical models were used for experiments with steady flow and waves. The steady flow experiments cover a range of Reynolds (Re) numbers between 10^3 and 10^4 to seek the drag crisis. Single mussel covered cylinders for both scales are compared to smooth cylinders and cylinders with an equivalent diameter. For the wave experiments, cnoidal waves with Keulegan-Carpenter ($KC$) numbers ranging from 3 to 113 that correspond with measured waves in Demak are chosen. Moreover, only mussel covered cylinders are compared to a smooth cylinder for a scale of 1:6. During the experiments, the flow velocity, force, and surface elevation are measured, and the drag and inertia coefficients are obtained with the help of the Morison equation. The drag coefficient shows a clear relationship with the Reynolds numbers for steady flow. Although the drag coefficients display the same qualitative behavior as in other studies in the literature, the drag coefficients of the smooth cylinder are more than 40 % larger than in the literature. This is probably due to large variations in the offset of the velocity meters (EMS) during the experiments. The large mussels show higher drag coefficients than the smooth cylinder. For the wave experiments, the drag coefficients show good correspondence to other studies in the literature, but the inertia coefficients are a factor two larger than expected for smooth cylinders. Treating the peak and trough of the cnoidal wave as individual sinusoidal waves shows similar results and suggest that cnoidal waves can be represented by KC numbers, as it is done for linear waves. The best fit to the literature values was found by solving the Morison equation with the measured force with the depth-integrated velocity squared and acceleration from the Fenton theory. This suggests that the results of the wave experiments have been uncertain due to inaccuracies in the EMS recordings. This thesis presents a method to schematize mussels for laboratory experiments and provides a qualitative comparison of the forces acting on poles with and without mussels
On the Taylor column driven motion of a buoyant sphere in a free-surface vortex core
An experimental study
Master thesis
(2022)
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C. van Nieuwenhuizen, B. Hofland, W.S.J. Uijttewaal, W. Bakker, S.P.A. Duinmeijer, F.H.L.R. Clemens
The added drag on a buoyant body traveling in a solid-body rotation flow has been rigorously studied over the last century with G.I. Taylor being the first one to describe it in 1922, a hundred years ago. A recent publication by Duinmeijer (2021) investigated the capacity of free-surface vortices to transport solids as a practical application to avoid solids accumulation in wastewater pump sumps. In that research, the assumption was made that a Taylor column exists upstream and downstream of the solids body, aiding the downward motion in the vortex core. This has however never been experimentally confirmed for free-surface vortex flows. The goal of this research is to experimentally check whether or not the Taylor-column induced drag force is the main mechanism for the downward motion of buoyant particles in a free surface vortex core. An experimental set-up consisting of a 600 x 1000mm (diameter x height) Perspex tank is used, in which controlled vortices can be generated. A novel combination of Laser Doppler Velocimetry (LDV) and Particle Tracking Velocimetry (PTV) is deployed simultaneously to obtain synchronised data of both the flow velocities and particle motion. The LDV device measures the tangential and axial flow components in a small measurement volume. Many point-measurements along a horizontal line through the vortex enable us to create the tangential and axial velocity profiles. A deconvolution process is applied on the LDV data to account for the spatial averaging effect of the LDV measurement volume and the wandering of the vortex core. The PTV system is used to determine the particle location over time, from which the velocity is obtained. For simplicity, only one type of particle - a buoyant sphere of 25 mm in diameter - is considered in this study. To obtain repeatability of the experiments, a particle dropping device is introduced to insert the sphere in the vortex core without entrapping air. A PID control system is added to the set-up to keep the discharge through the system constant. The first part of this research focusses on the performance of the measurement system, where the measurements of the flow characteristics of the free-surface vortex in the absence of a buoyant particle are compared to the results obtained by Duinmeijer (2020), repeating one of the experiments from that thesis without a buoyant particle. The tangential velocities measured with LDV, coincide well with the tangential velocity profiles found during PIV measurements by Duinmeijer. The axial velocity profiles however do not agree. Duinmeijer measured maximum axial velocities around the vortex core radius where in this thesis an axial velocity profile with two maxima is found; one in the vortex centre and one at 60-70% of the vortex core radius. Several additional experiments were performed to rule out possible causes for this difference, from which it is concluded that the axial velocity is non-zero in the vortex centre. The second part of the thesis focusses on the characteristics of the flow in the vortex core in the presence of a buoyant sphere. With the synchronized deployment of the LDV and PTV-system, the flow mechanics and the motion of the buoyant sphere can be simultaneously characterized. Such that the influence of the sphere's presence on the tangential and axial velocity components is quantified. New findings were obtained from these measurements, with the most striking one being a significant difference that is observed in the tangential velocities of the flow just above and below the buoyant sphere. Although this effect is described in theory e.g. by Moore and Saffman and Maxworthy (1970; 1968), it has not been measured before in any lab experiment before and therefore it was not expected to be observed so clearly during the experiments. The clear tangential velocity discrepancy experimentally confirms the presence of the Taylor column above and below the sphere.
The last part of the thesis is dedicated to quantifying the Taylor column induced drag force, derived from the tangential velocity difference of the flow above and below the particle. This difference in tangential velocities induces a pressure difference over the particle leading to a downward pointing force. The magnitude of this force is shown to be 75±17% of the total drag on the particle, making the Taylor column induced drag the main downward transport mechanism for the buoyant sphere in the free-surface vortex core given the conditions used in this experimental set-up.
It is recommended to investigate further the effect of the vortex core radius/particle characteristic length ratio on the Taylor column induced drag. The axial free-surface vortex flow is not radially uniform, with a region of high axial flow around the core radius. This axial flow being pushed into a Ekman layer on the sphere surface is generating the pressure difference over the particle and thus the downward force. It is therefore suspected that vortex core/particle size ratio strongly influences the Taylor column induced drag magnitude and thus be researched further. ...
The last part of the thesis is dedicated to quantifying the Taylor column induced drag force, derived from the tangential velocity difference of the flow above and below the particle. This difference in tangential velocities induces a pressure difference over the particle leading to a downward pointing force. The magnitude of this force is shown to be 75±17% of the total drag on the particle, making the Taylor column induced drag the main downward transport mechanism for the buoyant sphere in the free-surface vortex core given the conditions used in this experimental set-up.
It is recommended to investigate further the effect of the vortex core radius/particle characteristic length ratio on the Taylor column induced drag. The axial free-surface vortex flow is not radially uniform, with a region of high axial flow around the core radius. This axial flow being pushed into a Ekman layer on the sphere surface is generating the pressure difference over the particle and thus the downward force. It is therefore suspected that vortex core/particle size ratio strongly influences the Taylor column induced drag magnitude and thus be researched further. ...
The added drag on a buoyant body traveling in a solid-body rotation flow has been rigorously studied over the last century with G.I. Taylor being the first one to describe it in 1922, a hundred years ago. A recent publication by Duinmeijer (2021) investigated the capacity of free-surface vortices to transport solids as a practical application to avoid solids accumulation in wastewater pump sumps. In that research, the assumption was made that a Taylor column exists upstream and downstream of the solids body, aiding the downward motion in the vortex core. This has however never been experimentally confirmed for free-surface vortex flows. The goal of this research is to experimentally check whether or not the Taylor-column induced drag force is the main mechanism for the downward motion of buoyant particles in a free surface vortex core. An experimental set-up consisting of a 600 x 1000mm (diameter x height) Perspex tank is used, in which controlled vortices can be generated. A novel combination of Laser Doppler Velocimetry (LDV) and Particle Tracking Velocimetry (PTV) is deployed simultaneously to obtain synchronised data of both the flow velocities and particle motion. The LDV device measures the tangential and axial flow components in a small measurement volume. Many point-measurements along a horizontal line through the vortex enable us to create the tangential and axial velocity profiles. A deconvolution process is applied on the LDV data to account for the spatial averaging effect of the LDV measurement volume and the wandering of the vortex core. The PTV system is used to determine the particle location over time, from which the velocity is obtained. For simplicity, only one type of particle - a buoyant sphere of 25 mm in diameter - is considered in this study. To obtain repeatability of the experiments, a particle dropping device is introduced to insert the sphere in the vortex core without entrapping air. A PID control system is added to the set-up to keep the discharge through the system constant. The first part of this research focusses on the performance of the measurement system, where the measurements of the flow characteristics of the free-surface vortex in the absence of a buoyant particle are compared to the results obtained by Duinmeijer (2020), repeating one of the experiments from that thesis without a buoyant particle. The tangential velocities measured with LDV, coincide well with the tangential velocity profiles found during PIV measurements by Duinmeijer. The axial velocity profiles however do not agree. Duinmeijer measured maximum axial velocities around the vortex core radius where in this thesis an axial velocity profile with two maxima is found; one in the vortex centre and one at 60-70% of the vortex core radius. Several additional experiments were performed to rule out possible causes for this difference, from which it is concluded that the axial velocity is non-zero in the vortex centre. The second part of the thesis focusses on the characteristics of the flow in the vortex core in the presence of a buoyant sphere. With the synchronized deployment of the LDV and PTV-system, the flow mechanics and the motion of the buoyant sphere can be simultaneously characterized. Such that the influence of the sphere's presence on the tangential and axial velocity components is quantified. New findings were obtained from these measurements, with the most striking one being a significant difference that is observed in the tangential velocities of the flow just above and below the buoyant sphere. Although this effect is described in theory e.g. by Moore and Saffman and Maxworthy (1970; 1968), it has not been measured before in any lab experiment before and therefore it was not expected to be observed so clearly during the experiments. The clear tangential velocity discrepancy experimentally confirms the presence of the Taylor column above and below the sphere.
The last part of the thesis is dedicated to quantifying the Taylor column induced drag force, derived from the tangential velocity difference of the flow above and below the particle. This difference in tangential velocities induces a pressure difference over the particle leading to a downward pointing force. The magnitude of this force is shown to be 75±17% of the total drag on the particle, making the Taylor column induced drag the main downward transport mechanism for the buoyant sphere in the free-surface vortex core given the conditions used in this experimental set-up.
It is recommended to investigate further the effect of the vortex core radius/particle characteristic length ratio on the Taylor column induced drag. The axial free-surface vortex flow is not radially uniform, with a region of high axial flow around the core radius. This axial flow being pushed into a Ekman layer on the sphere surface is generating the pressure difference over the particle and thus the downward force. It is therefore suspected that vortex core/particle size ratio strongly influences the Taylor column induced drag magnitude and thus be researched further.
The last part of the thesis is dedicated to quantifying the Taylor column induced drag force, derived from the tangential velocity difference of the flow above and below the particle. This difference in tangential velocities induces a pressure difference over the particle leading to a downward pointing force. The magnitude of this force is shown to be 75±17% of the total drag on the particle, making the Taylor column induced drag the main downward transport mechanism for the buoyant sphere in the free-surface vortex core given the conditions used in this experimental set-up.
It is recommended to investigate further the effect of the vortex core radius/particle characteristic length ratio on the Taylor column induced drag. The axial free-surface vortex flow is not radially uniform, with a region of high axial flow around the core radius. This axial flow being pushed into a Ekman layer on the sphere surface is generating the pressure difference over the particle and thus the downward force. It is therefore suspected that vortex core/particle size ratio strongly influences the Taylor column induced drag magnitude and thus be researched further.
Assessing the functional performance of the Meuse river
The impact of bed developments and an altering discharge regime on future river functioning
Master thesis
(2020)
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Marijn de Rooij, Astrid Blom, Wim Uijttewaal, Olivier Hoes, S. van Vuren, Richard E. Jorissen, Wout van Dijk
The Meuse river facilitates important socio-economic functions. In the light of Integrated River Management (IRM), the question rises whether these functions can be facilitated in future decades (until 2050) as well. The riverbed is expected to degrade over the coming decades, just like in the past century. On top of that, the discharge regime will alter because of climate change. This research studies the impact of bed degradation and altering discharge regimes on the river functioning regarding navigation and flood safety. This is done by linking hydraulic river conditions to functional performance indicators.
...
...
The Meuse river facilitates important socio-economic functions. In the light of Integrated River Management (IRM), the question rises whether these functions can be facilitated in future decades (until 2050) as well. The riverbed is expected to degrade over the coming decades, just like in the past century. On top of that, the discharge regime will alter because of climate change. This research studies the impact of bed degradation and altering discharge regimes on the river functioning regarding navigation and flood safety. This is done by linking hydraulic river conditions to functional performance indicators.
Modelling of hydrodynamic and erosion processes at vegetated lake shores
Development of a process-based tool for the design of the protection of a lake shore with reed-like vegetation
Master thesis
(2020)
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K. van Batenburg, W.S.J. Uijttewaal, P.M.J. Herman, A. Gijón Mancheño, Tom Wilms
In recent years, the interest in integrating shore protection with the local ecosystems has increased. In comparison with the traditional reinforced embankments, integrated shores form a gradual transition from land to water where shore vegetation can establish itself. These nature-friendly shores have a positive impact upon the water quality, flora and fauna and the amenities of the shore. Some of the benefits of vegetation are its capability of reducing the hydrodynamic loads on the shore and its ability to increase the soil strength against erosion. Both effects have been investigated in detail in previous research and have been implemented for coastal protection designs in sandy coastal settings. But a designing tool for cohesive shorelines in lake environments is still missing. In this research, the different aspects important for the erosion of a vegetated cohesive shoreline are studied and the first steps towards a process-based design tool are taken. The model results show that the dominant processes for erosion can be found at the point of wave breaking and at the start of the run-up, as both combinations give the highest induced bed shear stresses. This can be used for a strategic placement of vegetation to dampen the wave impact and reinforce the soil through the roots. There are situations in which a partially vegetated shore is sufficient to withstand the daily wave attack. This allows the vegetation to grow naturally to full strength, which is required in a storm situation. In this way a financial benefit can be reached as well as a healthier vegetated shore, as a large part of the vegetation has grown naturally.
...
In recent years, the interest in integrating shore protection with the local ecosystems has increased. In comparison with the traditional reinforced embankments, integrated shores form a gradual transition from land to water where shore vegetation can establish itself. These nature-friendly shores have a positive impact upon the water quality, flora and fauna and the amenities of the shore. Some of the benefits of vegetation are its capability of reducing the hydrodynamic loads on the shore and its ability to increase the soil strength against erosion. Both effects have been investigated in detail in previous research and have been implemented for coastal protection designs in sandy coastal settings. But a designing tool for cohesive shorelines in lake environments is still missing. In this research, the different aspects important for the erosion of a vegetated cohesive shoreline are studied and the first steps towards a process-based design tool are taken. The model results show that the dominant processes for erosion can be found at the point of wave breaking and at the start of the run-up, as both combinations give the highest induced bed shear stresses. This can be used for a strategic placement of vegetation to dampen the wave impact and reinforce the soil through the roots. There are situations in which a partially vegetated shore is sufficient to withstand the daily wave attack. This allows the vegetation to grow naturally to full strength, which is required in a storm situation. In this way a financial benefit can be reached as well as a healthier vegetated shore, as a large part of the vegetation has grown naturally.
Determining the mechanisms causing the hydraulic damping during ship berthing
Comprehending the water cushion effect
Master thesis
(2020)
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Iris Heemskerk, Erik Broos, Wim Uijttewaal, Robert Jan Labeur, Perry Groenewegen, Wim van Buuren
When a large ship enters a port the vessel is navigated by the pilots instead of the captain due to safety reasons. The final part of the berthing manoeuver is the most critical and consists of the vessel moving laterally towards the quay wall. At this point the vessel does not use its own propulsion force anymore but is pushed by the tugboats. During this lateral berthing manoeuver a resistance force can be noticed counteracting the lateral manoeuver to the quay which acts as hydraulic damping. A large force is needed to overcome this hydraulic damping which is known as the water cushion effect. There are a handful of circumstances that are suspected to enhance the effect of hydraulic damping, but a substantiated conclusion is not yet drawn. To determine the mechanisms causing the hydraulic damping during ship berthing, field experiments in the Port of Rotterdam are carried out and analysed. In addition, a one-dimensional theoretical model is developed to simulate the field experiments and investigate the flow behaviour around a berthing ship.
...
When a large ship enters a port the vessel is navigated by the pilots instead of the captain due to safety reasons. The final part of the berthing manoeuver is the most critical and consists of the vessel moving laterally towards the quay wall. At this point the vessel does not use its own propulsion force anymore but is pushed by the tugboats. During this lateral berthing manoeuver a resistance force can be noticed counteracting the lateral manoeuver to the quay which acts as hydraulic damping. A large force is needed to overcome this hydraulic damping which is known as the water cushion effect. There are a handful of circumstances that are suspected to enhance the effect of hydraulic damping, but a substantiated conclusion is not yet drawn. To determine the mechanisms causing the hydraulic damping during ship berthing, field experiments in the Port of Rotterdam are carried out and analysed. In addition, a one-dimensional theoretical model is developed to simulate the field experiments and investigate the flow behaviour around a berthing ship.
Master thesis
(2020)
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Tim Ruwiel, Alessandro Antonini, Wim Uijttewaal, Danny Janssen, Bas Reedijk, Michael van de Koppel
XblocPlus is a single layer armour unit that is recently developed by BAM Infraconsult. It is the successor of the Xbloc. An important advantage of the XblocPlus is the relatively high construction speed compared to the Xbloc. The increased construction speed is caused by the possibility to place XblocPlus in a uniform pattern and the relatively large surface area that can be covered with a small number of blocks. A disadvantage of XblocPlus is the limited block stability at the top armour rows of a low crested structure. The limited stability is caused by the reduced interlocking capacity of the blocks on the top armour row. In previously performed studies, a back support is placed behind the blocks to stabilise the top armour row on the front slope. The back support of a concrete element significantly improves the stability of these armour blocks. However, at normative wave conditions, the stability of the top armour row on the front slope is still insufficient to meet the target stability (Ns,c = 3.0). The stability of the top row on the rear slope is not investigated in other studies. Consequently, no conclusions can be drawn about the stability of the crest blocks on the rear slope. In this study, physical model tests in a wave flume were performed to assess the effect of crest modifications on the stability of the top armour rows on the front and rear slope. The main objective of this study is to design a stable breakwater crest that has the best hydraulic performance with respect to the economically most feasible breakwater dimensions. After an exploratory study into the meaning of the main objective, it can be concluded that a relative crest width of 1 is desirable. The relative crest width is determined as the ratio between the crest width (B) and the significant wave height Hs. The principle of previous studies is used to set a reference situation. This crest configuration contains a concrete element between the top armour rows that functions as a support. This is a rather wide structure with a relative crest width equal to 2.7. After testing the reference situation, the top row on the front slope turned out to be normative for the crest stability. The found stability at failure coincides with the stability found in previous studies. The blocks on the top row of the rear slope remained stable. Also after reduction of the crest width to a relative crest width of 1.9, the crest blocks on the rear slope remained stable while the crest blocks on the front slope failed. It can be concluded that the blocks on the top row of the front slope are normative for the crest stability. The weight of these blocks is too limited to meet the target stability. By application of modified XblocPlus blocks is attempted to obtain stable blocks on both top rows. The adjusted blocks are much bulkier and consequently heavier than the original XblocPlus blocks. The blocks shape is modified in such a way that the crest blocks on the front and rear slope can be placed back to back without the support of a crest element. As a result, the relative crest width is reduced to 1.1. Several variants of modified crest blocks are tested to acquire information about the stabilising effect of the applied modifications. Modified blocks with an increased permeability, an increased interlocking capacity and a relatively large resistance against rotational instability were tested. Overall, the bulky block shape, the block's permeability, and the interlocking generated by the almost vertical back of a block, appear to be very important for the crest stability. The acquired information of this first test series is used as a foundation for further optimisation of the permeable block. An attempt to optimise the modified block is done by reducing the volume at places that have the least impact on the block stability. Application of measures that streamline the block shape in flow direction and further increase the block’s permeability were applied in this optimisation phase. Finally, a block with a 44% larger volume than the original XblocPlus block is obtained that meets the target stability of Ns = 3.0.
...
XblocPlus is a single layer armour unit that is recently developed by BAM Infraconsult. It is the successor of the Xbloc. An important advantage of the XblocPlus is the relatively high construction speed compared to the Xbloc. The increased construction speed is caused by the possibility to place XblocPlus in a uniform pattern and the relatively large surface area that can be covered with a small number of blocks. A disadvantage of XblocPlus is the limited block stability at the top armour rows of a low crested structure. The limited stability is caused by the reduced interlocking capacity of the blocks on the top armour row. In previously performed studies, a back support is placed behind the blocks to stabilise the top armour row on the front slope. The back support of a concrete element significantly improves the stability of these armour blocks. However, at normative wave conditions, the stability of the top armour row on the front slope is still insufficient to meet the target stability (Ns,c = 3.0). The stability of the top row on the rear slope is not investigated in other studies. Consequently, no conclusions can be drawn about the stability of the crest blocks on the rear slope. In this study, physical model tests in a wave flume were performed to assess the effect of crest modifications on the stability of the top armour rows on the front and rear slope. The main objective of this study is to design a stable breakwater crest that has the best hydraulic performance with respect to the economically most feasible breakwater dimensions. After an exploratory study into the meaning of the main objective, it can be concluded that a relative crest width of 1 is desirable. The relative crest width is determined as the ratio between the crest width (B) and the significant wave height Hs. The principle of previous studies is used to set a reference situation. This crest configuration contains a concrete element between the top armour rows that functions as a support. This is a rather wide structure with a relative crest width equal to 2.7. After testing the reference situation, the top row on the front slope turned out to be normative for the crest stability. The found stability at failure coincides with the stability found in previous studies. The blocks on the top row of the rear slope remained stable. Also after reduction of the crest width to a relative crest width of 1.9, the crest blocks on the rear slope remained stable while the crest blocks on the front slope failed. It can be concluded that the blocks on the top row of the front slope are normative for the crest stability. The weight of these blocks is too limited to meet the target stability. By application of modified XblocPlus blocks is attempted to obtain stable blocks on both top rows. The adjusted blocks are much bulkier and consequently heavier than the original XblocPlus blocks. The blocks shape is modified in such a way that the crest blocks on the front and rear slope can be placed back to back without the support of a crest element. As a result, the relative crest width is reduced to 1.1. Several variants of modified crest blocks are tested to acquire information about the stabilising effect of the applied modifications. Modified blocks with an increased permeability, an increased interlocking capacity and a relatively large resistance against rotational instability were tested. Overall, the bulky block shape, the block's permeability, and the interlocking generated by the almost vertical back of a block, appear to be very important for the crest stability. The acquired information of this first test series is used as a foundation for further optimisation of the permeable block. An attempt to optimise the modified block is done by reducing the volume at places that have the least impact on the block stability. Application of measures that streamline the block shape in flow direction and further increase the block’s permeability were applied in this optimisation phase. Finally, a block with a 44% larger volume than the original XblocPlus block is obtained that meets the target stability of Ns = 3.0.
Assessing the impact of plastic waste accumulation on flood events with citizen observations
A case study in Kumasi, Ghana
Master thesis
(2020)
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Jacintha Tjia, Marie-claire ten Veldhuis, Nick van de Giesen, Hessel Winsemius, Wim Uijttewaal
This research assesses the impact of plastic waste accumulation on flood events with citizen observations in Kumasi, Ghana. In Kumasi, the fastest growing city in Ghana, flooding events have become more intense due to rapid urbanisation and land use intensification. Additionally, rapid population growth, urbanisation and lack of organised waste collection, brings along tonnes of solid (plastic) waste on the streets, riverbeds and -ways. Plastic waste creates blockages in drains and rivers, which causes flooding of open areas, streets and houses. To what degree plastic waste accumulation aggrevates flooding in Kumasi remains poorly understood. Therefore, this study investigates to what extent plastic accumulation impacts flood severity, in response to rainfall events in the city of Kumasi, Ghana. This is done by modelling different rainfall scenarios in a 1D-2D model developed with the software HEC-RAS. This model was forced with static and dynamic data available from open source databases and collected during fieldwork. Data collection took place during six consecutive weeks in May-June 2019 and consists of bathymetry and discharge measurements, a flood- and plastic waste survey performed together with citizens. The impact can be determined using different model scenarios varying in rainfall magnitude and in obstruction of riverways, serving as plastic accumulation. Flood severity was analysed in terms of extent, depth, velocity, local hydraulic impact and flow distribution. The model has been validated with two events, one during which velocity and stage was measured, which results in the same order of magnitude, modelled slightly lower than measured in the field. The second event was a historic rainfall event, which could be validated with community reported flood depths. From this validation it became clear the flood extent of the event was underestimated and depths close to the streams were overestimated. The results show that the selected rainfall events without blockage cover the studied area between 11-25% with water depths higher than 10 cm. The inundated areas are adjacent to the river streams and inundate flat and low lying areas. Comparing this to the scenarios where bridges where obstructed to 33% and 67% individually, the total inundated area remains more or less the same, varying between 0-3% in inundated area compared to the scenario without blockage. However, in terms of flood distribution, areas around the blocked bridge are impacted more, thus inundation areas shift within the observed study area. Comparing this to the rest of the area, upstream or downstream less flooded areas arise, making the change in total flood extent only change slightly. Furthermore, the two bridges that are obstructed have different impact on the flow in the study area, as the scenarios of obstructing the second bridge with 33% produce a numerical instability and therefore incorrect results. From the plastic waste survey it followed that plastic waste is very much abundant in the study area, thus the occurrence of plastic accumulation at the bottleneck locations seem inevitable. The results of this research have shown the main contribution to flooding is flow from upstream areas exceeding river capacity, while local blockages mainly aggravate flooding around the blocked locations.
...
This research assesses the impact of plastic waste accumulation on flood events with citizen observations in Kumasi, Ghana. In Kumasi, the fastest growing city in Ghana, flooding events have become more intense due to rapid urbanisation and land use intensification. Additionally, rapid population growth, urbanisation and lack of organised waste collection, brings along tonnes of solid (plastic) waste on the streets, riverbeds and -ways. Plastic waste creates blockages in drains and rivers, which causes flooding of open areas, streets and houses. To what degree plastic waste accumulation aggrevates flooding in Kumasi remains poorly understood. Therefore, this study investigates to what extent plastic accumulation impacts flood severity, in response to rainfall events in the city of Kumasi, Ghana. This is done by modelling different rainfall scenarios in a 1D-2D model developed with the software HEC-RAS. This model was forced with static and dynamic data available from open source databases and collected during fieldwork. Data collection took place during six consecutive weeks in May-June 2019 and consists of bathymetry and discharge measurements, a flood- and plastic waste survey performed together with citizens. The impact can be determined using different model scenarios varying in rainfall magnitude and in obstruction of riverways, serving as plastic accumulation. Flood severity was analysed in terms of extent, depth, velocity, local hydraulic impact and flow distribution. The model has been validated with two events, one during which velocity and stage was measured, which results in the same order of magnitude, modelled slightly lower than measured in the field. The second event was a historic rainfall event, which could be validated with community reported flood depths. From this validation it became clear the flood extent of the event was underestimated and depths close to the streams were overestimated. The results show that the selected rainfall events without blockage cover the studied area between 11-25% with water depths higher than 10 cm. The inundated areas are adjacent to the river streams and inundate flat and low lying areas. Comparing this to the scenarios where bridges where obstructed to 33% and 67% individually, the total inundated area remains more or less the same, varying between 0-3% in inundated area compared to the scenario without blockage. However, in terms of flood distribution, areas around the blocked bridge are impacted more, thus inundation areas shift within the observed study area. Comparing this to the rest of the area, upstream or downstream less flooded areas arise, making the change in total flood extent only change slightly. Furthermore, the two bridges that are obstructed have different impact on the flow in the study area, as the scenarios of obstructing the second bridge with 33% produce a numerical instability and therefore incorrect results. From the plastic waste survey it followed that plastic waste is very much abundant in the study area, thus the occurrence of plastic accumulation at the bottleneck locations seem inevitable. The results of this research have shown the main contribution to flooding is flow from upstream areas exceeding river capacity, while local blockages mainly aggravate flooding around the blocked locations.
Damping of ship-induced primary waves
Damping ship-induced primary waves in rivers by modifying groynes with the aim of increasing fauna habitat quality
Master thesis
(2020)
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R. Pasman, J.D. Bricker, R.M.J. Schielen, E. Mosselman, W.S.J. Uijttewaal, A.J. van der Hout, Freek Huthoff
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.
...
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.
Below the surface
A laboratorial research to the vertical distribution of buoyant plastics in rivers
Rivers are identified as main sources of plastic litter in oceans. About 65% of the plastic litter is buoyant in fresh waters, meaning it has the capability to float, making transport over rivers relatively easy. A better understanding of how plastic litter is transported via rivers is crucial. Both for quantification and mitigation of the plastic problem. Most research on quantification of the plastic flux is based on surface-measurements only, up till about 50 cm water-depth. Thereby, most cleaning strategies focus on skimming only the surface. This research investigates the distribution of buoyant plastic litter over the water depth in rivers. Given the wide use of marginal buoyant plastics, it is hypothesized that a significant share of the plastic in rivers is transported below the first 50 cm surface-water, due to the mixing ability of turbulent flow. In such case, a great share of the plastic litter is overlooked in both flux estimates and riverine removal strategies. The question arises: How is plastic distributed over the water depth in rivers and how is this distribution related to prevailing flow conditions? The research is based on four pillars: Knowledge on the hydraulic plastic parameters (1), in combination with experimental observations (2), might lead to an explanation of the distribution with a theoretical approximation (3), based on existing literature from neighboring research fields. Lastly, manipulation (4) of this plastic distribution by hydraulic interventions is investigated. With this research, a first insight is created on the vertical behavior of plastic in relation to the flow conditions. This study shows that marginal buoyant plastics can be sensitive to turbulent motions in flow and a significant amount of plastic might be transported below the surface. In order to create a complete picture of the behavior of different kinds of plastic in stream flows, more extensive research is needed.
...
Rivers are identified as main sources of plastic litter in oceans. About 65% of the plastic litter is buoyant in fresh waters, meaning it has the capability to float, making transport over rivers relatively easy. A better understanding of how plastic litter is transported via rivers is crucial. Both for quantification and mitigation of the plastic problem. Most research on quantification of the plastic flux is based on surface-measurements only, up till about 50 cm water-depth. Thereby, most cleaning strategies focus on skimming only the surface. This research investigates the distribution of buoyant plastic litter over the water depth in rivers. Given the wide use of marginal buoyant plastics, it is hypothesized that a significant share of the plastic in rivers is transported below the first 50 cm surface-water, due to the mixing ability of turbulent flow. In such case, a great share of the plastic litter is overlooked in both flux estimates and riverine removal strategies. The question arises: How is plastic distributed over the water depth in rivers and how is this distribution related to prevailing flow conditions? The research is based on four pillars: Knowledge on the hydraulic plastic parameters (1), in combination with experimental observations (2), might lead to an explanation of the distribution with a theoretical approximation (3), based on existing literature from neighboring research fields. Lastly, manipulation (4) of this plastic distribution by hydraulic interventions is investigated. With this research, a first insight is created on the vertical behavior of plastic in relation to the flow conditions. This study shows that marginal buoyant plastics can be sensitive to turbulent motions in flow and a significant amount of plastic might be transported below the surface. In order to create a complete picture of the behavior of different kinds of plastic in stream flows, more extensive research is needed.
Modelling forces on buoyant macro plastics and their cross-sectional distribution in rivers
Simplified modelling of buoyant macro plastics according to cornerstones in behavior and particle response times in a range of riverine environments to set-up efficient monitoring campaigns and help select locations for efficient plastic removal.
Master thesis
(2019)
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Thomas van Welsenes, Wim Uijttewaal, Jeremy Bricker, Erik Mosselman, Frans Buschman
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.
...
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.
Master thesis
(2019)
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Lina Nikolaidou, Wim Uijttewaal, Bas Hofland, Jeremy Bricker, Tom O'Mahoney, Niels G. Jacobsen
Granular bed protections are a common measure to mitigate scour of the sand bed around hydraulic structures. In view of marching towards cost-effective solutions to tackle erosion-related problems, it is important to accurately predict the loads exerted on the bed and come up with the needed rock grading. To that end, a 3-D eddy resolving modelling technique could help in formulation of a new stability formula, based on extreme local flow conditions It is the aim of this thesis to build a hydrodynamic numerical tool, able to predict governing mechanisms in stone stability. Special attention is paid on the way of representing a rough boundary and predicting wall and free turbulence. That being said, a Wall-Modelled Large Eddy Simulation (WMLES) is suggested and is build using the open-source CFD toolbox OpenFOAM. Firstly, simple open channel flow case simulations are set-up, to evaluate the performance of rough wall functions in the LES environment. Secondly, a backwards facing step kind of flow from the experimental study of Jongeling et. al (2003) is simulated and the performance of the numerical model is evaluated based on the experimental results. Finally, the suitability of this method for the target applications of this study is discussed, including a comparison with previous numerical studies of this research area.
...
Granular bed protections are a common measure to mitigate scour of the sand bed around hydraulic structures. In view of marching towards cost-effective solutions to tackle erosion-related problems, it is important to accurately predict the loads exerted on the bed and come up with the needed rock grading. To that end, a 3-D eddy resolving modelling technique could help in formulation of a new stability formula, based on extreme local flow conditions It is the aim of this thesis to build a hydrodynamic numerical tool, able to predict governing mechanisms in stone stability. Special attention is paid on the way of representing a rough boundary and predicting wall and free turbulence. That being said, a Wall-Modelled Large Eddy Simulation (WMLES) is suggested and is build using the open-source CFD toolbox OpenFOAM. Firstly, simple open channel flow case simulations are set-up, to evaluate the performance of rough wall functions in the LES environment. Secondly, a backwards facing step kind of flow from the experimental study of Jongeling et. al (2003) is simulated and the performance of the numerical model is evaluated based on the experimental results. Finally, the suitability of this method for the target applications of this study is discussed, including a comparison with previous numerical studies of this research area.
Rocking of single layer armour units
Rocking revisited 3
Master thesis
(2019)
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Ganga Caldera, Bas Hofland, Wim Uijttewaal, Alessandro Antonini, Markus Muttray, Cock van der Lem, Marcel van Gent
After the failure of several large breakwaters in late 1970’s and early 1980’s where the role of rocking and breakage of armour became apparent, the importance of understanding this rocking phenomenon is given a great emphasis. Single layer randomly placed armour units are widely used in breakwater designs as they are more economical due to the less volume requirement. But these single layer units have a much more “brittle” behaviour and strength of the units becomes a critical factor. As the stresses developed after the impact is difficult to measure directly in the scale models, currently percentage rocking is used as a design criterion. But a clear relationship between this quantity and breakage has not been identified. Even though the single layer armour unit types are widely used the knowledge on the rocking behaviour of this type of units are limited. Therefore, to get a better insight into the rocking behaviour of single layer armour units a previously proposed technique of instrumented unit with embedded sensor was adopted. This technique was found to be promising in detecting the rocking motion in standalone mode. However, one issue of that technique was relatively lower sampling frequency. Because of that, enough data could not be captured to resolve the rocking motion in time very accurately.
Therefore, in this report the measurements with standalone IMU sensor embedded in 3D printed model armour unit has been developed further. Firstly , different techniques were adopted to get the optimum sampling frequency and sampling frequency was increased from 25 Hz to 100 Hz.
This report includes further details on the processing method and obtained results after performing the 2D physical model testings. It is the first time that stand alone rocking motions are reported for single layer armour units. By increasing the sampling frequency from25 Hz to 100 Hz, rocking events can now be resolved in time by 5-10 measurements points. Gyroscope data and accelerometer data were combined to separate the linear acceleration from raw accelerometer data. Upward and downward rotational motions were distinguished, and impact velocities were calculated based on both accelerometer and gyroscope. By analyzing the data it was observed that the angle of rotation during the rocking event is small and usually unit returns to its original position after a full rotation. ...
Therefore, in this report the measurements with standalone IMU sensor embedded in 3D printed model armour unit has been developed further. Firstly , different techniques were adopted to get the optimum sampling frequency and sampling frequency was increased from 25 Hz to 100 Hz.
This report includes further details on the processing method and obtained results after performing the 2D physical model testings. It is the first time that stand alone rocking motions are reported for single layer armour units. By increasing the sampling frequency from25 Hz to 100 Hz, rocking events can now be resolved in time by 5-10 measurements points. Gyroscope data and accelerometer data were combined to separate the linear acceleration from raw accelerometer data. Upward and downward rotational motions were distinguished, and impact velocities were calculated based on both accelerometer and gyroscope. By analyzing the data it was observed that the angle of rotation during the rocking event is small and usually unit returns to its original position after a full rotation. ...
After the failure of several large breakwaters in late 1970’s and early 1980’s where the role of rocking and breakage of armour became apparent, the importance of understanding this rocking phenomenon is given a great emphasis. Single layer randomly placed armour units are widely used in breakwater designs as they are more economical due to the less volume requirement. But these single layer units have a much more “brittle” behaviour and strength of the units becomes a critical factor. As the stresses developed after the impact is difficult to measure directly in the scale models, currently percentage rocking is used as a design criterion. But a clear relationship between this quantity and breakage has not been identified. Even though the single layer armour unit types are widely used the knowledge on the rocking behaviour of this type of units are limited. Therefore, to get a better insight into the rocking behaviour of single layer armour units a previously proposed technique of instrumented unit with embedded sensor was adopted. This technique was found to be promising in detecting the rocking motion in standalone mode. However, one issue of that technique was relatively lower sampling frequency. Because of that, enough data could not be captured to resolve the rocking motion in time very accurately.
Therefore, in this report the measurements with standalone IMU sensor embedded in 3D printed model armour unit has been developed further. Firstly , different techniques were adopted to get the optimum sampling frequency and sampling frequency was increased from 25 Hz to 100 Hz.
This report includes further details on the processing method and obtained results after performing the 2D physical model testings. It is the first time that stand alone rocking motions are reported for single layer armour units. By increasing the sampling frequency from25 Hz to 100 Hz, rocking events can now be resolved in time by 5-10 measurements points. Gyroscope data and accelerometer data were combined to separate the linear acceleration from raw accelerometer data. Upward and downward rotational motions were distinguished, and impact velocities were calculated based on both accelerometer and gyroscope. By analyzing the data it was observed that the angle of rotation during the rocking event is small and usually unit returns to its original position after a full rotation.
Therefore, in this report the measurements with standalone IMU sensor embedded in 3D printed model armour unit has been developed further. Firstly , different techniques were adopted to get the optimum sampling frequency and sampling frequency was increased from 25 Hz to 100 Hz.
This report includes further details on the processing method and obtained results after performing the 2D physical model testings. It is the first time that stand alone rocking motions are reported for single layer armour units. By increasing the sampling frequency from25 Hz to 100 Hz, rocking events can now be resolved in time by 5-10 measurements points. Gyroscope data and accelerometer data were combined to separate the linear acceleration from raw accelerometer data. Upward and downward rotational motions were distinguished, and impact velocities were calculated based on both accelerometer and gyroscope. By analyzing the data it was observed that the angle of rotation during the rocking event is small and usually unit returns to its original position after a full rotation.
Coastal structures with horizontal overhangs are built due to design constraints, but wave loadings substantially increase under these confined geometries. Vertical structure elements, such as steel gates, are vulnerable to damage caused by impulsive wave impacts, potentially exposing the coastal zone to flooding and erosion. Existing formulas to determine impulsive loadings in engineering practice are limited to purely vertical structures. Research has shown that openings along the surface of structures relieve wave impact pressures, but there are currently no design methods available to quantify this pressure release. The stochastic nature of impulsive impacts and uncertain influence of air adds to the problem complexity. This study aims to investigate the influence of ventilations to reduce wave impact loadings on vertical structures with horizontal overhangs, applying a theoretical pressure-impulse approach and computational fluid dynamics. In this study, the pressure-impulse model is implemented for experimental cases in two and three dimensions using a finite difference numerical scheme and validated against semi-analytical solutions with high accuracy. Boundary conditions are modified to include and assess the influence of venting holes on the pressure-impulse contours. To achieve the largest efficiency in the reduction of pressure-impulses, rectangular ventilations are located at the critical corner between vertical wall and overhang and spaced across the structure width. Based on physical model dimensions, the open source CFD software OpenFOAM is also employed to simulate standing wave impacts on structures. Waves are generated in the CFD model using the waves2Foam toolbox, in conjunction with the OceanWave3D utility. Convergence of the CFD model is achieved by gradually refining the mesh near the wave impact region. Validation between simulated and experimental total wave forces on the vertical wall shows very good agreement for both overhang sizes considered. The distribution of first impact pressure-impulses along the vertical structure show similar trends among the pressure-impulse theory and CFD models. While large discrepancies are observed for predicted maximum pressure-impulses, the relative error of total impulse at wall between both models is low. From both CFD and pressure-impulse model results, empirical relations are derived between relative venting area and total impulse release. The assumption adopted in the theory of zero pressure-impulse at the venting position is not reproduced in CFD results, which leads to overestimation of the impact mitigation effects of ventilations using the pressure-impulse theory. This divergence in the venting boundary condition is possibly linked to the omission of convective acceleration terms in the pressure-impulse model. Two ventilation design methods for vertical structures with overhangs subject to wave impacts are proposed based on the research conducted in this study. The first design method employs the derived empirical relations, standing wave theories and theoretical pressure distributions to determine the total impulse affecting the structure. The second design method applies the splitting approach of measured impulsive forces with low-pass filters to calculate the total impulse, requiring numerical or physical modelling. Further research is needed to support the models with small and large scale experiments using ventilations and expand the validity range of the results.
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Coastal structures with horizontal overhangs are built due to design constraints, but wave loadings substantially increase under these confined geometries. Vertical structure elements, such as steel gates, are vulnerable to damage caused by impulsive wave impacts, potentially exposing the coastal zone to flooding and erosion. Existing formulas to determine impulsive loadings in engineering practice are limited to purely vertical structures. Research has shown that openings along the surface of structures relieve wave impact pressures, but there are currently no design methods available to quantify this pressure release. The stochastic nature of impulsive impacts and uncertain influence of air adds to the problem complexity. This study aims to investigate the influence of ventilations to reduce wave impact loadings on vertical structures with horizontal overhangs, applying a theoretical pressure-impulse approach and computational fluid dynamics. In this study, the pressure-impulse model is implemented for experimental cases in two and three dimensions using a finite difference numerical scheme and validated against semi-analytical solutions with high accuracy. Boundary conditions are modified to include and assess the influence of venting holes on the pressure-impulse contours. To achieve the largest efficiency in the reduction of pressure-impulses, rectangular ventilations are located at the critical corner between vertical wall and overhang and spaced across the structure width. Based on physical model dimensions, the open source CFD software OpenFOAM is also employed to simulate standing wave impacts on structures. Waves are generated in the CFD model using the waves2Foam toolbox, in conjunction with the OceanWave3D utility. Convergence of the CFD model is achieved by gradually refining the mesh near the wave impact region. Validation between simulated and experimental total wave forces on the vertical wall shows very good agreement for both overhang sizes considered. The distribution of first impact pressure-impulses along the vertical structure show similar trends among the pressure-impulse theory and CFD models. While large discrepancies are observed for predicted maximum pressure-impulses, the relative error of total impulse at wall between both models is low. From both CFD and pressure-impulse model results, empirical relations are derived between relative venting area and total impulse release. The assumption adopted in the theory of zero pressure-impulse at the venting position is not reproduced in CFD results, which leads to overestimation of the impact mitigation effects of ventilations using the pressure-impulse theory. This divergence in the venting boundary condition is possibly linked to the omission of convective acceleration terms in the pressure-impulse model. Two ventilation design methods for vertical structures with overhangs subject to wave impacts are proposed based on the research conducted in this study. The first design method employs the derived empirical relations, standing wave theories and theoretical pressure distributions to determine the total impulse affecting the structure. The second design method applies the splitting approach of measured impulsive forces with low-pass filters to calculate the total impulse, requiring numerical or physical modelling. Further research is needed to support the models with small and large scale experiments using ventilations and expand the validity range of the results.