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The aim of the present investigation is to clarify the role and evaluate the importance of air entrainment in the swash zone by carrying out a set of detailed laboratory experiments. Experiments involved generating a single, highly repeatable, large-scale, bore-driven swash event on a sand-rough impermeable beach with slope 1:10. Measurements that yield the characteristics of the entrained air, including the void fractions, bubble size and bed-parallel bubble velocity, and the hydrodynamics are obtained at five cross-shore locations in the swash zone using an optical probe and a combined PIV/LIF system. The results show that two distinct bubble clouds enter the swash zone, the first is the result of local entrainment at the wave tip and the second are the remaining bubbles of the air that is entrained at the second plunge point of wave breaking before the wave starts climbing the beach. The void fractions are up to 0.20 and bubble size up to 20 mm which are similar to air entrainment after wave breaking in the surf zone and deep water. Local entrainment of air continues in the swash zone, but void fractions decrease rapidly with distance up the slope and no air is present after flow reversal. Energy dissipation in the swash zone attributable to entrained air is at least of order 1% of the total energy dissipation. This is smaller than in the surf zone or deep water because of the smaller volume of entrained air and the greater total energy dissipation in the swash zone.

To determine the feasibility of using a dam-break generated flow from the sea into a storm-drain to aid in the regeneration of iron particles that control the production of H2S in the storm-drain, a laboratory experimental investigation is carried out to measure the regeneration potential and the detailed hydrodynamics of the dam-break generated flow that causes the regeneration. The experiments are carried out using a reservoir of essentially infinite size, the sea, and a channel of limited width and adverse slope 1:20, the storm-drain. The regeneration experiments confirmed the ability of the dam-break generated flow to aid in the regeneration of the iron particles, however the regeneration potential varies from good to poor with distance away from the gate into the channel. The detailed measurements of the hydrodynamics highlighted that the dam-break generated flow from an infinite reservoir diverges little during the first uprush, has much smaller velocities during the first backwash and includes significant free surface waves. An initially wet channel bed reduces the flux into the channel. Close to the gate the flow depth increases more quickly but the velocity, and therefore the regeneration potential, is smaller.

This paper examines the numerical prediction of the sediment transport and bed evolution for a single swash event on a coarse sediment beach. In these conditions bed load is the dominant mode of sediment transport. Laboratory experiments of a single bore-driven swash event are simulated numerically using a fully-coupled model that solves the system of Non Linear Shallow Water Equations and the Exner sediment conservation formula. The analysis focuses on two aspects: the optimal choice of parameters for the Meyer-Peter and Muller sediment transport formula and the model used for computing the shear stress. The methods tested for the bed shear stress are the momentum integral method and the Chezy formulation in which the friction factor is computed using two different formulae. Infiltration into the beach and its effects on the shear stress and sediment transport are also modelled. Results show that the basic Meyer-Peter and Muller sediment transport formula provides good results in the run-up. On the other hand, the sediment transport in the early stage of the backwash is overestimated. A reduction of the sediment mobility constant in the formula in the backwash marginally improves the results. However, the causes of the overestimation of the sediment transport at the early stage of the backwash is the overestimation of the shear stress, while at later stages there are several contributions that are identified, i.e. modelling of the sediment transport and infiltration. It is also suggested that the Meyer-Peter and Muller sediment transport formula might not capture the complexity of the processes involved during the backwash. The comparison of the methods for the estimate of the bed shear stress show that comparable results can be obtained using the momentum integral method and the Chezy formulation with time and space varying friction factor. The resulting bed evolution is also described. In the predicted final profile, deposition is found in the upper part of the beach and erosion in the lower part. A bed step is formed just below the position of the initial shoreline. This feature is determined by the onset of a hydraulic jump during the backwash.

Experimental measurements are obtained to investigate the detailed hydrodynamics of wave–wave interactions in the swash-zone. Two bores are generated using a double dam-break mechanism and interact on a 1:10 impermeable rough slope. Measurements of the hydrodynamics are obtained via acoustic displacement sensors and a combined particle image velocimetry and laser induced fluorescent system. Two types of interactions are investigated: wave capture, with the second bore reaching the first one during the uprush, and weak wave–backwash interactions when interaction happens during the backwash of the first wave. The relative strength of the bores at the initial shoreline and time between their arrivals determines the initial type of interaction, however the type as well as the intensity of the interaction may vary throughout the swash-zone for the same swash event. During wave capture and weak wave–backwash interactions, the fluid of the first bore is advected upwards, then mixed with the fluid of the second bore by intense shearing and highly turbulent vortices generated at the front of the second bore because of the relative velocity differences between the two bores. The details of the hydrodynamics during interaction confirm the potential of swash–swash interactions to suspend sediment and transport it shoreward or interrupt seaward sediment transport.

To investigate the feasibility of suspending sediments in storm-drains in coastal cities using tidal energy, numerical and physical experiments are carried out to understand the behaviour of a dam-break generated flow from an infinite reservoir (the sea) into a positively inclined channel of limited width (the storm-drain). The numerical results are obtained using LES as these yield the most accurate predictions of the results from the physical experiments. The hydrodynamics of the flow inside the channel are controlled by the large volume of water in the reservoir and cross waves are generated in the channel due to its limited width. On relatively steep slopes, the bed shear stress results indicate that sediment suspension is likely to occur under the leading edge of the flow while on mild slopes suspension of sediments may occur over a great distance into the channel and for a long duration after the initial dam-break.

Experimental measurements and numerical simulations are carried out to determine the hydrodynamics induced by suspended canopies of limited width and height for canopies with six different densities and canopy element arrangements and two different upstream velocities. Measurements of velocity are obtained using acoustic Doppler velocimetry and the drag force via a load cell. Numerical simulation results using OpenFOAM agree very well with the experimental data and are used to investigate the generated flow fields in detail. The bulk features of the flow are similar to those of other canopies, including emergent and submerged canopies, but the finite dimensions of the canopy results in flow patterns that differ from suspended canopies of essentially infinite width. The detailed hydrodynamics of the flow are controlled by the blockage of the suspended canopy which depends both on the canopy density and the lateral spacing between consecutive longitudinal rows of canopy elements. Increased flow blockage results in increases in the drag coefficient from 0.72 to 1.4, reduction in the flow rate inside the canopy from 58 to 98 % (of the diverted flow, 20–43 % is diverted below the canopy) and increases in the steady wake zone length from 0.6 to 4 times the canopy length. Flow blockage has relatively little effect on the length of the upstream adjustment and total wake zones at 1.09 and 7 times the canopy length respectively. The flow also depends only weakly on the upstream velocity.

An experimental investigation is carried out to determine the trajectory, spread, dilution and cross-sectional flow structures of non-buoyant oblique jets released in a moving ambient, covering initial discharge angles from 10 to 90°. For each angle, measurements of the side view and plan view integrated concentration fields are obtained. The double-Gaussian assumption is used to characterize the cross-sectional concentration profiles, which gradually change from the axi-symmetric Gaussian of the weak-jet region to the double-vortex pair structure of the momentum puff region. In the weakly-advected region, the spread is similar to that of the jet in a stagnant ambient, while in the strongly-advected region a new spread relationship is obtained based on the double-Gaussian assumption. The spread relationships are used in an existing integral model, resulting in predictions for the trajectory and dilution that are a good match for the experimental data in the weakly- and strongly-advected regions.

A renewable granular iron-based technology for hydrogen sulfide removal from sediment and water in box culverts and storm drains is discussed. Iron granules, including granular ferric hydroxide (GFH), granular ferric oxide (GFO) and rusted waste iron crusts (RWIC) embedded in the sediment phase removed aqueous hydrogen sulfide formed from sedimentary biological sulfate reduction. The exhausted iron granules were exposed to dissolved oxygen and this regeneration process recovered the sulfide removal capacities of the granules. The recovery is likely attributable to the oxidation of the ferrous iron precipitates film and the formation of new reactive ferric iron surface sites on the iron granules and sand particles. GFH and RWIC showed larger sulfide removal capacities in the sediment phase than GFO, likely due to the less ordered crystal structures on their surfaces. This study demonstrates that the iron granules are able to remove hydrogen sulfide from sediment and water in box culverts and storm drains and they have the potential to be regenerated and reused by contacting with dissolved oxygen.

The paper reports on dambreak-type swash experiments in which intra-swash hydrodynamics and sediment flux are measured for swash on a coarse sand beach and a gravel beach. Flow velocity and depth are measured using PIV and LIF respectively; the intra-swash sediment flux is measured using sediment traps. Comparison of measured hydrodynamics with the immobile, permeable bed experiments of Kikkert et al. (2013) indicates that bed mobility impacts on the swash hydrodynamics, reducing the maximum run-up by approximately 8% for both beaches, compared to the maximum run-up on the corresponding immobile beach. The measured intra swash sediment flux at a given location is characterised by high flux at the moment of bore arrival, followed by rapid decay during uprush, becoming zero at some time before flow reversal. For the gravel beach, the backwash sediment flux is negligibly small, while for the sand beach the backwash flux increases slowly as the flow accelerates down the beach, and peaks at about the time of maximum backwash velocity. Intra-swash sediment flux calculated using the Meyer-Peter and Müller bed load transport formula, with measured hydrodynamics as input and bed shear stress estimated using both the Swart and Colebrook formulae, is within a factor 2 of the measured intra-swash flux. The agreement between the calculated and measured flux is better for the sand beach than for the gravel beach, and better for uprush than for backwash. For the sand beach there is good agreement between calculated and measured total uprush and total backwash sediment volumes. The agreement is less good for the gravel beach, for which calculated and measured uprush volumes show a similar trend but the calculated backwash volumes over-estimate the (negligible) volumes observed in the experiments.

A detailed experimental investigation of the hydrodynamics of large-scale, bore-driven swash on impermeable, rough beach slopes is described. The experiments were carried out on 1:10 impermeable, rough slopes with three different surface roughnesses based on 1.3 mm sand, 5.4 mm gravel and 8.4 mm gravel. The large-scale discrete swash event was produced by the collapse of a dambreak-generated bore on the beach. Simultaneous depths and velocities were measured using LIF, Laser-induced fluorescence, and PIV, particle image velocimetry, respectively, yielding better resolution of the hydrodynamics than previous studies. Depth time-series, instantaneous velocity profiles, depth-averaged velocities, instantaneous turbulent kinetic energy profiles, depth-averaged turbulent kinetic energy, Reynolds stress profiles and bed shear stresses are presented for five cross-shore measurement locations in the swash. The measurements resolve the backwash shoreline position, and the late backwash period when depths are shallow and velocities are high. The detailed data can be used to test and develop advanced numerical models for bore-driven waves on rough slopes.

Depth-averaged equations describing turbulent free-surface flows are usually derived assuming that the free surface is constant over a statistical ensemble of realizations. This work presents the d...

Details of an experimental investigation into the behaviour of discharges with three-dimensional (3D) trajectories are presented. A light attenuation technique is employed to track the position of peak concentrations in the flow and the transition from weakly to strongly advected behaviour can be clearly observed: two peaks are evident at a given cross-section in the strongly advected region, whereas only a single peak occurs at cross-sections in the weakly advected region. Length scales, based on dominant momentum fluxes in the weakly and strongly advected regions, can be employed to locate the transitions between these distinctly different flow forms. Coefficients for these length scales have been determined based on numerous studies of discharges following an essentially 2D path. Length scale estimates, based on the 2D path coefficients, and the measured transition locations from the present study indicate that the transition to strongly advected behaviour can be delayed significantly, if the discharge...

We present the results of a preliminary experimental investigation into the behaviour of non-buoyant oblique discharges in a moving ambient fluid. Light Attenuation techniques are employed to measure trajectory, spread and integrated dilution data. A series of experiments have been conducted where the angle between the discharge direction and that of the ambient motion varied from 0 to 90 degrees. The experiments confirm that the nature of the discharge in the strongly advected region is only a function of this discharge angle. For angles less than or equal to 20 ° trends in the data obtained in the strongly advected region resemble that of a Gaussian weak-jet. For discharge angles of 40 ° and above the variation in strongly advected data was consistent with that of an advected line momentum puff, where the local tracer and velocity fields resemble those of a vortex pair. However, for flows released at discharge angles between 20 ° and 40 ° , the formation of a Gaussian weak-jet or an advected line momentum puff could not be clearly identified in the strongly advected region. A conceptual model based on a set of analytical solutions is outlined and this provides the basis for interpreting the experimental data. Lagrangian integral numerical models are also developed to aid in the interpretation of the data.

Analytical solutions are developed to predict the behavior of inclined negatively buoyant discharges and these solutions are compared with data from previous studies and from experiments described here, where light attenuation and laser-induced fluorescence techniques are employed to study these flows. Comparisons show that the analytical solutions provide reasonable predictions of the flow’s path for initial discharge angles ranging from 0 to 75° and initial Froude numbers ranging from 14 to 99. The solutions also predict the maximum height of the outer edge of the jet with reasonable accuracy, and thus the outer spread of the jet is well predicted. However, the inner spread is underestimated and minimum dilution predictions are shown to be conservative by approximately 18% at the centerline maximum height and 34% at the return or impact point. Predictions from the CorJet and VisJet numerical models are also shown to be conservative.

Mean concentration fields of strongly advected non-buoyant discharges are characterised with a double-Gaussian assumption. Comparisons with experimental data show that the approximation provides a reasonable representation of the cross-sectional profiles. The self-similarity of these profiles enables their form to be represented by two additional parameters, one describing the relative separation of the peaks and the other the ratio of the cross-sectional spreads. Values for these additional parameters are determined from experimental data. This systematic approach to characterising the strongly advected flows provides a consistent framework for determining spreading rates and concentration ratios, such as the peak to centreline maximum and the peak to top hat. The double-Gaussian framework also provides a basis for comparisons with the CorJet and VisJet numerical models. In addition the double-Gaussian assumption is employed to interpret data obtained using the Light Attenuation technique. This is a relatively simple measuring system, which provides depth integrated concentration information. The data obtained using this technique is shown to be generally consistent with that from previous studies.

Aqueous hydrogen sulfide causes a number of sulfide-related problems in sediment/aqueous environments. This paper investigates the use, regeneration and reuse of granular ferric hydroxide (GFH) for removal of aqueous hydrogen sulfide in batch experiments simulating water environments. The sulfide removal by GFH can be described by pseudo-first-order reaction kinetics with respect to dissolved sulfide concentrations and the removal rate was proportional to the GFH dosage. The sulfide removal rate almost tripled as pH decreased from 9.0 to 7.2. An increasing ionic strength (in NaCl solution) and the presence of SO4(2-) in simulated seawater decreased the removal rate while Ca(2+) and Mg(2+) in seawater hardly had any influence. The aqueous sulfide was mainly oxidized to elemental sulfur with the concurrent reduction of solid Fe(III) to Fe(II). The accumulation of the products (elemental sulfur, iron sulfide and surface-associated Fe(II)) on the surface of GFH eventually led to the latter's exhaustion. By mixing with water containing dissolved oxygen, the exhausted GFH was able to recover with the simultaneous oxidation of Fe(II) to ferric (hydr)oxides and of solid sulfide to elemental sulfur and sulfur of higher valence states. The recovery in removal capacity could be attributed to the formation of amorphous or less ordered ferric (hydr)oxides on the GFH surface and the reduction in GFH granule size. This study suggests that GFH is a promising renewable material for removal of aqueous hydrogen sulfide in sediment/aqueous systems.

[1] Large‐scale laboratory experiments presented in this paper involved bore‐driven swash on permeable immobile coarse‐grained beaches. Two different sediments were used (d50 = 1.5 and 8.5 mm) resulting in different beach permeability and surface roughness. The experiments yielded detailed measurements of swash depth and velocities, wetting front, pressure, and groundwater levels across the swash zone. This paper is focused on the processes occurring within the beach. The measurements provide the shape of the wetting front and the groundwater table and reveal the behavior of air in the unsaturated region of the beach. Air is initially at atmospheric pressure, but the pressure builds up when air becomes encapsulated between the saturated region formed below the swash and the groundwater table. For the 1.5 mm beach, entrapped air significantly affected the water exchange between the swash and the subsurface. The considerable buildup of interstitial air pressure reduced vertical hydraulic gradients and thus infiltration rates. At the lower end of the beach the hydraulic gradients even became negative, indicating flow reversal and exfiltration. In contrast, for the 8.5 mm beach the rate of infiltration was only slightly affected by the buildup of pore‐air pressure. The vertical hydraulic gradients were more than twice the magnitude of those within the 1.5 mm beach. The results presented in the paper clarify the mechanisms that drive and impede the water exchange between the surface and subsurface flow. In particular, infiltration into the initially unsaturated part of the beach and the resulting air entrapment play a significant role in swash and similar flows.

The current study reports the results from a new laboratory experimental investigation, carried out to improve understanding and modeling of the internal kinematics of swash interactions, and its role on beach face morphology. Two typical types of swash interactions, wave capture interaction and backwash interaction (Erikson et al., 2005), were observed in detail by conducting large-scale dam-break experiments in a flume with two adjacent reservoirs and a fixed coarse-sand beach. The experiments were designed to enable detailed measurements of swash depths, velocity fields and turbulent quantities at different locations across the swash zone to be obtained.