Process-based model for nearshore hydrodynamics, sediment transport and morphological evolution in the surf and swash zones

Barry

Brovelli

2012

Coastal Engineering

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A comprehensive two-dimensional (cross-shore) process-based numerical model of nearshore hydrodynamics (based on the Navier-Stokes equations, k-ε turbulence closure and the Volume-Of-Fluid method), beach morphology, and variable-density groundwater flow (SEAWAT-2000) was developed. This model, which was applied at the field scale, relaxes simplifications in existing models that do not include such detailed mechanistic descriptions. Numerical experiments were conducted to investigate the effects of varying aquifer, beach and wave characteristics (e.g., inland groundwater head, sand grain size, different wave heights and periods) on the coupled system. Spilling and plunging breakers on dissipative and intermediate beaches were simulated. For a given set of boundary conditions, the model was run for 1 y without the hydrodynamic sub-model to achieve a realistic salt-/freshwater interface. Then, the hydrodynamic component was run for 15 min and the model results analyzed. The main features considered were groundwater circulation, saltwater wedge position, in/exfiltration across the beach face, and beach morphology. The predictions of the numerical model agree well with existing understanding and experimental measurements. For an inland watertable that is lower than the still water level (SWL), such that the groundwater flow is mainly landward, on both coarse and fine sand beaches the addition of wave motion moves the saltwater wedge further landward. For an inland watertable that is higher than the SWL, the opposite behavior occurred. The numerical experiments showed that more sediment transport takes place on intermediate beaches than on dissipative beaches. In addition, beach profile variations are greater under plunging breakers, while coarse sand beaches are steeper than fine sand beaches for the same wave conditions. There is a strong correlation between in/exfiltration and beach face deposition/erosion for the coarse beaches, while in/exfiltration has a slight effect on sediment transport for fine beaches. The model is capable of simulating the short-term evolution of foreshore profile changes, and beach 3 watertable and saltwater wedge movement due to interactions between wave motion and coastal groundwater. IntroductionMost previous investigations concerned with modeling of interactions between ocean water and coastal groundwater focused on tide-induced watertable fluctuations, neglecting high-frequency wave-induced oscillations and variable-density groundwater flow (e.g., Teo et al., 2003;Brovelli et al., 2007;Robinson et al., 2007bRobinson et al., , 2009Slooten et al., 2010;Li et al., , 2007Xin et al., 2010). However, given the interplay of mechanisms inherent in coastal processes -mixing of fresh-and seawater driven by waves, sediment transport and beach profile changes -it is not possible to extrapolate readily existing results to realistic coastal zone behavior.Waves in the nearshore zone are an important forcing on sediments and groundwater behavior. While waves induce instantaneous pore wat...

Section: Introductionmentioning

confidence: 99%

Numerical experiments on interactions between wave motion and variable-density coastal aquifers

Barry

Brovelli

2012

Coastal Engineering

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“…The governing equations were discretized using standard finite-difference methods with Cartesian coordinates, while a staggered grid was used for the calculation domain. The time step was determined 10 by iteration until computational stability was achieved (Bakhtyar et al, 2008(Bakhtyar et al, , 2009. Stability was controlled mainly by the local Courant number.…”

Section: Numerical Modelmentioning

confidence: 99%

Experiments and numerical modeling of baffle configuration effects on the performance of sedimentation tanks

FiroozabadiB.

2013

Can. J. Civ. Eng.

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Abstract:The hydraulic efficiency of sedimentation basins is reduced by short-circuiting, circulation zones and bottom particle-laden jets. Baffles are used to improve sediment tank performance. In this study, laboratory experiments were used to examine the hydrodynamics of several baffleconfigurations. An accompanying numerical analysis was performed based on the 2D ReynoldsAveraged Navier-Stokes equations along with the k-ε turbulence closure model. The numerical model was supplemented with the Volume-Of-Fluid technique (VOF), and the advection-diffusion equation to simulate the dynamics of particle-laden flow. Model predictions compared well with the experimental data. An empirical function was constructed to indicate the location and amount of sediment collected in the tank. Hydraulic performance was determined for given baffle locations and heights. The results revealed that, for the laboratory setup, a baffle half way along its length decreases its performance, while a baffle much closer to its inlet and with height 25 ~ 30% of water depth improves efficiency.

“…The model has not been validated against experimental data for the conditions considered in this manuscript since suitable data sets are not available. But, the predictive capabilities of the each sub-module have been tested previously (i.e., [12,17,37,38]) and good agreement was found considering different conditions. Thus, we believe that the model used in this study is to some extent validated.…”

Section: Introductionmentioning

confidence: 99%

Transport of variable-density solute plumes in beach aquifers in response to oceanic forcing

Advances in Water Resources

Brovelli

Barry

et al. 2013

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A comprehensive numerical study was undertaken to investigate transport of a variabledensity, conservative solute plume in an unconfined coastal aquifer subject to high and low frequency oceanic forcing. The model combined variable-density saturated flow for groundwater and solute transport, and wave hydrodynamics from a 2D Navier-Stokes solver. A sinusoidal tidal signal was specified by implementing time-varying heads at the seaward boundary. The solute plume behavior was investigated under different oceanic forcing conditions: no forcing, waves, tide, and combined waves and tide. For each forcing condition, four different injected solute densities (freshwater, brackish water, seawater, brine) were used to investigate the effects of density on the transport of the injected plume beneath and across the beach face. The plume's low-order spatial moments were computed, viz., mass, centroid, variance and aspect ratio. The results confirmed that both tide-and wave-forcing produce an upper saline plume beneath the beach face in addition to the classical saltwater wedge. For the no-forcing and tide-only cases (during rising tides), an additional small circulation cell below the beach face was observed. Oceanic forcing affects strongly the solute plume's flow path, residence time and discharge rate across the beach face, as well as its spreading. For the same oceanic forcing, solute plumes with different densities follow different trajectories from the source to the discharge location (beach face). The residence time and plume spreading increased with plume density. It was concluded that simulations that neglect the effect of waves or tides cannot reproduce accurately solute plume dispersion and also, in the case of coasts with small waves or tides, the solute residence time in the aquifer.