Dams are important water infrastructure whose main purposes can be compromised by sedimentation. This causes loss of storage volume, affecting river sediment fluxes and morphology. However, sediment management strategies can be implemented to reduce these impacts. Our goal is to characterize and quantify key processes of an idealized and reduced physical model of water injection dredging, applicable as a sediment management technique. Three sets of experiments were conducted, varying the following parameters: (a) jet discharge; (b) jet angle; (c) bed angle. The spatio-temporal evolution of the main physical processes (scour hole formation, sediment suspension development, and downstream deposition) was analyzed using images of profiles acquired during the experiments. We identified two distinct transport modes depending on how the jet flow connects with the turbidity current, each associated with different stages of scour hole development. In our experiments, the bed-perpendicular component of the exit velocity (momentum) of the jet is the primary driver of the morphological evolution. We demonstrate self-similarity in the longitudinal profiles of the scour hole and downstream deposit. Finally, we discuss practical implications of this study, such as the net displacement of the material, scaling, and limitations. This research contributes to the development of innovative sediment management strategies for water reservoirs and other hydraulic structures.

In river systems, transported suspended sediment interacts with in-channel and riparian vegetation. The involved physical processes are complex and still poorly reproduced by numerical models. This study compares the performance of background horizontal eddy viscosity models in reproducing flow fields and suspended sediment transport processes inside partially vegetated flows. Particularly, we selected an experiment with a partly-vegetated flume which we numerically replicated with the Delft 3D-2DH model. We applied three existing horizontal eddy viscosity approaches: constant value, Elder model and hybrid model. Besides, we represented the vegetation by using Baptist formulation. The results show that the Elder viscosity model reproduces the explicit development of vortices along the flume, while all three viscosity models show an underestimate of the sediment deposition in the vegetated area and an overestimation of sediment deposition in the non-vegetated area. Further investigation is needed to reproduce the experimental introduction of the sediment and to link transversal suspended sediment dynamics with the resolved dynamics in numerical models.

Compound weirs have been used as adjustable structures to divert flow, for example, through river branches at the river bifurcations. For this purpose, a wide variety of weir configurations can be used including asymmetric configurations that have not been studied in the literature yet. A proper one-dimensional representation of flow over these structures is needed as the effect they have on the river are generally added as subgrid energy losses to the river hydrodynamic models. In this study, an experimental study was conducted to estimate the correct representation of compound weirs at varying weir configurations and flow conditions. In the experimental campaign, eight weir configurations were used with six discharge values. Upstream flow depths at each case were recorded and their relationship with the flow rate and weir configuration was analyzed. A 1D model was proposed to estimate flow rates when the upstream flow depths are known. The proposed correction to the well-known Kindsvater and Carter approach was applied to modify the discharge coefficient when nonuniform geometries are used that cause horizontal flow contraction. To estimate and validate the proposed correction, additional numerical simulations using computational fluid dynamics (CFD) were conducted to estimate the detailed flow field upstream of the nonuniform weirs. Surface particle image velocimetry (SPIV) measurements were also conducted to validate the CFD model. The corrected 1D model predicted the flow rates at 48 cases covering uniform to highly nonuniform weir geometries with a maximum of 9.7% and a mean of 2.45% deviation from the measurements. Additional tests on the performance of the proposed model validated its effectiveness in various nonuniform geometries at low flows. However, when substantial changes are made to the geometry, such as the removal of buttresses, the model may require calibration to maintain its accuracy.

Tidal stream turbines are becoming an affordable option for harvesting sustainable energy in coastal areas. They can be retrofitted in barrages, providing an integral solution for flood protection and emission-free power generation, within environmental constraints. To optimize the turbine-barrage configuration with respect to these objectives, simulation tools are needed to predict the efficiency of the turbines as well as their impact on the adjacent tidal system. These tools should be based on an accurate representation of the underlying flow processes, which cover a wide range of spatial scales — from meters at the barrage and turbines to tenths of kilometers in the tidal basin. This article presents the development of such a tool by linking an analytical model for turbine fences in barrage gates to a regional flow model. The turbine model is validated with experimental data, and data from a thoroughly monitored tidal energy pilot project. Simulations reveal how clustering the turbines in small arrays can increase their efficiency, owing to array blockage effects, with only little effect on the tidal exchange. We also demonstrate the potential of using turbine fences to manipulate the tidal jet, issued from the barrage, with benefits for coastal — and wildlife protection in the basin. The presented research helps understanding how turbine fences in barrages can be configured with high energy yield and calculated impact to the environment.

Knowledge of plastic debris transport mechanism in open waters and its interaction with hydraulic structures (i.e. accumulation and clogging) is of paramount importance for effective waste-removal strategies and sustainable management of plastic debris. To the author’s best knowledge, current models for prediction of plastic debris transport assume a highly simplified geometry, while making use of parameterization of the physical processes, therefore pointing out the need for further research. Herein, the effect of shape and buoyancy on the motion of a single particle was studied employing point-particle approach while the background flow is solved using RANS approach. It is observed that the particles with the same amount of plastic mass but different shape and density showed substantially different behaviors, resulting in different trajectories. Since parametrization and point-particle approach were used, even if the particle size is larger than the mesh size, these preliminary results showed that further validation is required for prediction of accurate trajectory by means of resolved-particle approach.

Marine biofouling is a major concern in the operational performance of submerged floating tunnels (SFTs). The objective of this research is to extend hydrodynamic conditions in experiments and numerically investigate the effects of marine fouling on the hydrodynamic behavior of SFTs, including flow characteristics and forces on the SFT subject to waves. A sensitivity analysis of roughness parameters including different roughness heights and roughness coverage ratios is carried out. Additionally, the hydrodynamic forces of a roughened SFT with a circular shape and a newly designed parametric shape are compared.

The modelling of complex free surface flows is challenging due to the mobility and deformability of the interface and air entrainment characteristics, which are highly affected by turbulence. With the framework of Reynolds averaged Navier–Stokes (RANS) models and the volume of fluid (VOF) method, turbulence quantities at the air–water interface tend to be over-estimated. In this study, interfacial turbulence treatment methods including the buoyancy modification model based on the simple gradient diffusion hypothesis (SGDH) and Egorov’s turbulence damping model are investigated. Furthermore, due to the unconditionally unstable characteristics of the standard k-ε turbulence model, the stabilized k-ε turbulence model is applied as a comparison. The turbulence attenuation performance using different interfacial turbulence treatment methods in the vicinity of the interface is compared and discussed for stratified flows and free overflow weirs for aerated and non-aerated nappe scenarios. The turbulence quantities and free surface profile under different flow conditions are validated against experimental data and an analytical model. The results show that for free surface waves, both the SGDH model and the turbulence damping model give strong improvements in turbulence production compared with the standard k-ε model. The SGDH model augments the turbulence kinetic energy (TKE) in the unstable stratification, leading to unphysical behaviour for the partially dispersed and separated flow.

Marine biofouling is a major concern in the operational performance of submerged floating tunnels (SFTs). The objective of this research is to investigate the effects of marine fouling (represented by surface roughness) on the hydrodynamic behavior of SFTs, including the hydrodynamic forces on the SFT subject to current-only, wave-only, and combined current-wave flow conditions. The effects of increased surface roughness induced by marine fouling on the dynamic response of an SFT are characterized by hydrodynamic force coefficients, including drag and inertia coefficients. At the Water Lab of Delft University of Technology (TU Delft), experiments have been performed in a wave-current flume to compare the SFTs’ behaviors as affected by different roughness characteristics. In addition, a parametric cross-section for an SFT is presented, and the hydrodynamic performance associated with surface roughness effects on the parametric shape and circular SFT cross-section shape are compared. The results show that the parametric shape can effectively reduce the drag coefficient (C_d) under current-only conditions and lower the inertia coefficient (C_m) when waves are present. As roughness height and coverage ratio increase, C_d generally increases while C_m decreases. However, small differences in C_d and C_m can be observed with regard to roughness parameters for wave-only conditions. The Morison coefficients adapted for a marine-fouled SFT measured in the experiments are compared to predictions from engineering standards and are recommended for engineering practice.

The effects of surface roughness as induced by marine fouling on the hydrodynamic forces on a submerged floating tunnel (SFT) are experimentally and numerically investigated in detail at Reynolds numbers Re = 8.125 × 10³–5.25 × 10⁴. A sensitivity analysis to different roughness parameters including roughness height, skewness, coverage ratio, and spatial arrangement is performed. In addition, an optimized parametric cross-section for an SFT is proposed, and the hydrodynamic performance of the parametric shape and circular SFT cross-section shape with roughness elements is compared. The pressure distribution along the SFT, flow separation and wake characteristics are analyzed to provide a systematic insight into the fundamental mechanism relating the roughness parameters and flow around an SFT. In order to better understand the nonlinear relationships among structural geometry, roughness parameters, flow states, and structural response, an artificial intelligence method using Random Forest (RF) for feature importance ranking is applied. The results show that with the parametric shape, the hydrodynamic forces on the fouled SFT can be effectively mitigated. The roughness height and coverage ratio affect the equivalent blockage and hence, change flow separation and recirculation length in the wake. Lower skewness of the roughness elements can increase the critical Re by changing the relative roughness parameter. Horizontal arrangement of the roughness elements on an SFT generally results in the largest hydrodynamic forces, compared to staggered and vertical distributions. Throughout the feature importance ranking, the flow regime is found to be the most important feature of the hydrodynamics of the SFT. In addition, the SFT cross-section shape and roughness coverage ratio play a dominant role.

Gas-mixing is commonly applied in anaerobic digesters, yet the resulting flow and hydraulic mixing are difficult to evaluate because of limited full-scale experimental data and uncertainties in integrating sludge rheological data. This study used computational fluid dynamics (CFD) to assess the impact of treated sludge rheology on flow and mixing characterisation in a full-scale biogas-mixed digester. The CFD model, which was firstly validated using a lab-scale setup, showed that flow and mixing predictions depended on the rheological properties, especially at low shear rates. The predicted dominant shear rate was out of the effective shear-rate range of the Ostwald model, leading to flow and mixing performance overestimation. The results indicated that there are limitations in applying the Ostwald model and the conventional approaches for determining dead-zone. The Herschel-Bulkley model was more appropriate for the prevailing low shear rates and predicted large viscosity gradients in the digester, indicating two distinct compartments with different flow and mixing behaviour based on the gas-sparging height: a plug-flow compartment with dominant vertical convection above, and a dead-zone compartment with considerable segregation below. The results showed that the applied gas-sparging induced insufficient flow and mixing, but contributed to the well-functioning of the digester. To correctly assess flow and mixing, the applied rheological data should be in agreement with the type of sludge that is treated in the digester. Our results indicate that the shear rate in the digester must be increased and various options for achieving this are proposed.