Gustaaf Adriaan Kikkert

Subsurface processes generated by bore‐driven swash on coarse‐grained beaches

[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.

Removal of aqueous hydrogen sulfide by granular ferric hydroxide—kinetics, capacity and reuse

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 latters 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.

Buoyant jets with three-dimensional trajectories

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 discharged fluid follows a 3D path. This delay has significant implications for the dilution rates of the effluent.

Hydrogen sulfide removal from sediment and water in box culverts/storm drains by iron-based granules

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.

RADINS equations for aerated shallow water flows over rough beds

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 derivation of the Reynolds-Averaged-Depth-Integrated Navier–Stokes (RADINS) equations obtained if this assumption is removed. These equations are applied to transient turbulent open-channel flow over a rough bed with an aerated free surface containing air bubbles. The RADINS equations contain terms which explicitly include the contribution of turbulent free-surface fluctuations to the large-scale volume and momentum transfer. These terms are evaluated in a laboratory experiment which involves a turbulent bore climbing up a rough slope. The new RADINS equations are compared with the conventional depth-integrated-Reynolds-averaged Navier–Stokes (DIRANS) equations. The RADINS and DIRANS equations are identical only for flows with negligible depth fluctuations. If this condition is not satisfied, the equations are different and the terms in the RADINS equations have a clearer physical meaning.

Behaviour of oblique jets released in a moving ambient

ABSTRACT 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.

Laboratory study investigating the regeneration potential of iron particles by and the hydrodynamics of a dam-break generated flow from an infinite reservoir into a channel with an adverse slope

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.