Permeable Beach Research Articles

Numerical Study of Swash Driven by a Breaking Wave Over a Permeable Sandy Beach

We present a new methodology that is able to resolve wavefield and bottom boundary layer processes throughout the water column over a permeable beach. An Eulerian two-phase model for sediment phase, SedFoam, and a surface wave solver, InterFoam/olaFlow, are integrated in the OpenFOAM framework. The new model, called SedWaveFoam, is validated with two laboratory datasets for swash driven by a plunging solitary wave over a permeable and immobile sandy beach. Results demonstrate that surface elevation and depth-averaged velocity are well predicted during uprush. To better match the model results with the measured data during backwash, sand beds with different porosities are tested. It is suggested that significant vertical pore pressure gradient can be induced due to infiltration and exfiltration processes that affects stabilizing force of sand particles.

Incompressible SPH simulation of solitary wave propagation on permeable beaches

Wave propagation on uniformly sloped beaches is a canonical coastal engineering topic that has been studied extensively in the past few decades. However, most of these studies treat beaches as solid boundaries even though they are often made of porous materials, such as sediment and vegetation. Permeable beaches struck by tsunami-like waves have not been adequately investigated. It is expected that the degree of permeability plays a crucial role in mitigating the impact of the wave. This study examines solitary wave run-ups on sandy beaches using an incompressible smoothed particle hydrodynamics (ISPH) model. The permeability of the beach is considered to be directly related to the diameter of its constituent sand particles. To obtain a satisfactory pressure field, which cannot be achieved using the original ISPH algorithm, the source term of the pressure Poisson equation has been modified based on a higher-order source-term expression. Flows within the porous medium are computed in the same framework as those outside the porous medium. In the current model, no transition zone is needed at the boundary of the porous structure. The wave-attenuation effect of the porous medium is discussed, with a particular focus on the relationship between the run-up height and grainsize.

Decomposition of sediment-oil-agglomerates in a Gulf of Mexico sandy beach

Sediment-oil-agglomerates (SOA) are one of the most common forms of contamination impacting shores after a major oil spill; and following the Deepwater Horizon (DWH) accident, large numbers of SOAs were buried in the sandy beaches of the northeastern Gulf of Mexico. SOAs provide a source of toxic oil compounds, and although SOAs can persist for many years, their long-term fate was unknown. Here we report the results of a 3-year in-situ experiment that quantified the degradation of standardized SOAs buried in the upper 50 cm of a North Florida sandy beach. Time series of hydrocarbon mass, carbon content, n-alkanes, PAHs, and fluorescence indicate that the decomposition of golf-ball-size DWH-SOAs embedded in beach sand takes at least 32 years, while SOA degradation without sediment contact would require more than 100 years. SOA alkane and PAH decay rates within the sediment were similar to those at the beach surface. The porous structure of the SOAs kept their cores oxygen-replete. The results reveal that SOAs buried deep in beach sands can be decomposed through relatively rapid aerobic microbial oil degradation in the tidally ventilated permeable beach sand, emphasizing the role of the sandy beach as an aerobic biocatalytical reactor at the land-ocean interface.

A comparison between water circulation and terrestrially-driven dissolved silica fluxes to the Mediterranean Sea traced using radium isotopes

The circulation of seawater through permeable coastal sediments is increasingly recognized as an important source of nutrients, including dissolved silica (DSi), to the coastal ocean. Here, we utilized a Ra isotope (223Ra, 224Raex, 228Ra) mass balance to quantify DSi fluxes driven by water circulation to a small shallow coastal lagoon (La Palme; French Mediterranean) during June 2016, as compared to karstic groundwater spring inputs. The DSi flux driven by lagoon water circulation (derived from 224Raex) was approximately one order of magnitude greater (1900 ± 1700 mol d−1) than the DSi load of the karstic groundwater spring (250 ± 50 mol d−1) and greater than molecular diffusion (970 ± 750 mol d−1). Lagoon water circulation was a negligible source of 228Ra, indicating that circulation-driven DSi inputs occur over a time-scale of days. Offshore transects were studied to quantify fluxes of marine-derived submarine groundwater discharge (SGD) from the permeable sandy coastline adjacent to the lagoon, into the Mediterranean Sea. Surface water transects revealed near-shore enrichments of Ra and DSi, attributed to wave-setup and water exchange through the permeable beach between the lagoon and the sea. Upscaling over the 9.5 km stretch of sandy beaches results in a marine SGD-driven DSi flux of 2.3 ± 1.3 × 104 mol d−1, similar in magnitude to the Têt river during November 2016 (3.3 ± 2.4 × 104 mol d−1), the largest river in the region. A positive relationship between DSi and 224Raex in lagoon water and seawater, but not 228Ra, suggests that 224Raex and DSi enrichments are derived from a similar source, the sediment (i.e. lithogenic particle dissolution), operating on short time-scales. A marine SGD-driven DSi flux to the Gulf of Lions (3.8 ± 2.2 × 105 mol d−1) is likely continuous over time. The relatively constant DSi inputs from water circulation for the shallow lagoons and beaches along the French Mediterranean Sea may sustain primary production in the coastal zone. In comparison, terrestrial groundwater and rivers supply temporally variable nutrient (N, P, Si) inputs via changes in regional precipitation, runoff and aquifer storage.

Fully integrated modeling of surface water and groundwater in coastal areas

This paper presents an improved model based on a three-dimensional non-hydrostatic wave model NHWAVE to simulate the interactions between the surface water and the groundwater affected by tides or waves in coastal areas. With the model, both the surface water flow and the groundwater flow are calculated based on the well-balanced Volume-averaged Reynolds-averaged Navier-Stokes equations. The spatially varying porosity and hydraulic conductivity are used to identifiy the domains for the surface water and the groundwater. The model is calibrated and validated using a wide range of laboratory measurements reported in the literature, involving the tide propagation through a sandy embankment, the tide-induced groundwater table fluctuation in a sandy beach, and the wave setup in a sloping sandy beach. The interactions between the surface water and the groundwater are analyzed and the influencing factors on the groundwater flow are discussed. The phase lag between the surface water elevation and the groundwater table fluctuation is mainly influenced by the hydraulic conductivity of the porous media. The wave attenuation in the groundwater is proportional to its propagation distance. The computed wave setup elevationin the permeable beach is smaller than in the impermeable beach. It is shown that the fully integrated model is capable of simulating the interactions between the surface water and the groundwater affected by tides or waves in coastal areas. It can be an efficient tool to study the tide and wave dynamics in the permeable sandy beach.

Numerical simulation for sediment transport using MPS-DEM coupling model

Interactions between the uprush and backwash waves around a swash zone cause a complex water surface with wave breaking. Infiltration and exfiltration on a permeable beach face produce significant effects on the bottom shear stress. Abrupt changes of the bottom shear stress induced by uprush waves onto a dry bed have a significant impact on the estimation of sediment flux. In order to simulate, with a high degree of accuracy, a violent flow with wave breaking and complex moving bed boundaries along the on-off shore direction, wave motions are solved by using an enhanced particle method based on the MPS (Moving Particle Semi-implicit) method, while the DEM (Discrete Element Method) is used for a movable bed simulation. Consequently, the high potential of a MPS-DEM coupling model to simulate the swash beach process is clearly demonstrated by comparison with previous experimental results. Furthermore, the significance of the seepage flow in the swash beach process is shown with referring the Nielsen's modified Shields number.

Groundwater flow due to a nonlinear wave set-up on a permeable beach

Water flow through the beach body plays an important role in the biological status of the organisms inhabiting the beach sand. For tideless seas, the groundwater flow in shallow water is governed entirely by the surface wave dynamics on the beach. As waves propagate towards the shore, they become steeper owing to the decreasing water depth and at some depth, the waves lose their stability and start to break. When waves break, their energy is dissipated and the spatial changes of the radiation stress give rise to changes in the mean sea level, known as the set-up. The mean shore pressure gradient due to the wave set-up drives the groundwater circulation within the beach zone. This paper discusses the circulation of groundwater resulting from a nonlinear set-up. The circulation of flow is compared with the classic Longuet-Higgins (1983) solution and the time series of the set-up is considered for a 24h storm. Water infiltrates into the coastal aquifer on the upper part of the beach near the maximum run-up and exfiltration occurs on the lower part of the beach face near the breaking point.

Groundwater flow due to a nonlinear wave set-up on a permeable beach

Groundwater flow due to a nonlinear wave set-up on a permeable beach

A survey of deepwater horizon (DWH) oil-degrading bacteria from the Eastern oyster biome and its surrounding environment.

The deepwater horizon (DWH) accident led to the release of an estimated 794,936,474 L of crude oil into the northern Gulf of Mexico over an 85 day period in 2010, resulting in the contamination of the Gulf of Mexico waters, sediments, permeable beach sands, coastal wetlands, and marine life. This study examines the potential response of the Eastern oyster’s microbiome to hydrocarbon contamination and compares it with the bacterial community responses observed from the overlaying water column (WC) and the oyster bed sediments. For this purpose, microcosms seeded with DWH crude oil were established and inoculated separately with oyster tissue (OT), mantle fluid (MF), overlaying WC, and sediments (S) collected from Apalachicola Bay, FL, USA. Shifts in the microbial community structure in the amended microcosms was monitored over a 3-month period using automated ribosomal intergenic spacer region analysis, which showed that the microbiome of the OT and MF were more similar to the sediment communities than those present in the overlaying WC. This pattern remained largely consistent, regardless of the concentration of crude oil or the enrichment period. Additionally, 72 oil-degrading bacteria were isolated from the microcosms containing OT, MF, WC, and S and identified using 16S ribosomal RNA gene sequencing and compared by principal component analysis, which clearly showed that the WC isolates were different to those identified from the sediment. Conversely, the OT and MF isolates clustered together; a strong indication that the oyster microbiome is uniquely structured relative to its surrounding environment. When selected isolates from the OT, MF, WC, and S were assessed for their oil-degrading potential, we found that the DWH oil was biodegraded between 12 and 42%, under the existing conditions.

Experimental study of bore-driven swash hydrodynamics on permeable rough slopes

A detailed experimental investigation of the hydrodynamics of large-scale, bore-driven swash on steep permeable, rough beaches is described. The experiments were carried out on two permeable, but fixed rough beaches, made of 1.3mm sand and 8.4mm gravel, respectively. The large-scale discrete swash event was produced by the collapse of a dam break-generated bore on the beach. Simultaneous depths and velocities were measured using laser-induced fluorescence (LIF), and particle image velocimetry (PIV), respectively. Depth time series, instantaneous velocity profiles, depth-averaged velocities, instantaneous turbulent kinetic energy profiles, depth-averaged turbulent kinetic energy, turbulent shear stress profiles and bed shear stresses are presented for several cross-shore measurement locations in the swash. The effect of beach permeability is investigated by comparing new experimental results with previously published data for impermeable beaches with identical surface roughness (Kikkert et al., 2012). The detailed data can be used to test and develop advanced numerical models for bore-driven swash on rough permeable beaches.

Numerical simulation of three-dimensional breaking waves on a gravel slope using a two-phase flow Navier–Stokes model

Wave breaking is mainly a three-dimensional flow problem characterized by wave energy dissipation due to turbulence. The understanding of the wave breaking mechanism on a beach is essential in studying coastal processes. The complexity of the wave-induced turbulence flow is also increased by the presence of a two-phase flow, which introduces buoyancy effects. In this work a set of numerical experiments is carried out on wave breaking on a gravel slope. The influence of a one-phase and two-phase flow and the permeability effect of the beach are investigated numerically by means of a Navier–Stokes model known as IH-3VOF, which considers the volume-averaged Reynolds-averaged Navier–Stokes (VARANS) equations (del Jesus, 2011 [3]) to characterize the flow within the porous media. The accuracy of the VARANS equations is demonstrated by means of comparisons with laboratory data. The results are found to be within a 2% error in terms of wave height prior to the broken wave, and up to a 10% error after then, and in the order of 0.20 s in the time domain for the worst case. A further analysis of wave evolution on a permeable beach with alongshore variation of porosity is studied. Three-dimensional wave breaking and post-breaking wave transformations alongshore are analysed according to porosity values.

Wave-induced water table fluctuations, sediment transport and beach profile change: Modeling and comparison with large-scale laboratory experiments

Coastal groundwater systems can have a considerable impact on sediment transport and foreshore evolution in the surf and swash zones. Process-based modeling of wave motion on a permeable beach taking into account wave-aquifer interactions was conducted to investigate the effects of the unconfined coastal aquifer on beach profile evolution, and wave shoaling on the water table. The simulation first dealt with wave breaking and wave runup/rundown in the surf and swash zones. Nearshore hydrodynamics and wave propagation in the cross-shore direction were simulated by solving numerically the two-dimensional Navier–Stokes equations with a k–ε turbulence closure model and the Volume-Of-Fluid technique. The hydrodynamic model was coupled to a groundwater flow model based on SEAWAT-2000, the latter describing groundwater flow in the unconfined coastal aquifer. The combined model enables the simulation of wave-induced water table fluctuations and the effects of infiltration/exfiltration on nearshore sediment transport. Numerical results of the coupled ocean/aquifer simulations were found to compare well with experimental measurements. Wave breaking and infiltration/exfiltration increase the hydraulic gradient across the beachface and enhance groundwater circulation inside the porous medium. The large hydraulic head gradient in the surf zone leads to infiltration across the beachface before the breaking point, with exfiltration taking place below the breaking point. In the swash zone, infiltration occurs at the upper part of the beach and exfiltration at the lower part. The simulations confirm that beaches with a low water table tend to be accreted while those with a high water table tend to be eroded.

Laboratory investigation on tsunami run-up

Experimental investigations of tsunami run-up and erosion area on permeable slope beaches were carried out in a laboratory channel. A natural sandy beach was configured with a diameter of 0.35 mm and specific gravity of 2.63. The slope of the beach was 1:5. Furthermore, different types of armor units, the diameter and specific gravity of which varied in the range of 10–13.8 mm and 2.318–2.289, respectively, were placed on permeable slope beaches. Experiments for impermeable beaches were performed for comparison with previous investigations and it is seen that the results agree with each other. Tsunami run-up heights were investigated for permeable (armored and not armored) beaches and empirical formulas for were suggested. From the results of these experiments it was observed that armor units causes a decrease about 50% in run-up height. In addition to these, coastal profile changes formed by tsunami was examined and an empirical formula giving dimensionless erosion area parameter for without armor area is suggested. Also the relation between run-up height and erosion area is expressed with a formula.

波による海浜地形変化と透過性斜面内の流れ場に関する研究

Beach profile change has been investigated in relation to velocity field inside and outside of permeable beach. Velocity field on shore and swash zone has been obtained by conducting numerical simulations and model experiments. In the experiments, water surface change has been measured using run-up gage covered with finewire mesh and compared to verify the numerical simulation results. Infiltration flow has been found to play an important role on sediment transport. It is also revealed that sediment transport and formation process of gravel beach can be well explained by considering of kinetics on beach.

Surf zone dynamics simulated by a Boussinesq type model. Part I. Model description and cross-shore motion of regular waves

This is the first of three papers on the modelling of various types of surf zone phenomena. In this first paper, part I, the model is presented and its basic features are studied for the case of regular waves. The model is based on two-dimensional equations of the Boussinesq type and it features improved linear dispersion characteristics, possibility of wave breaking, and a moving boundary at the shoreline. The moving shoreline is treated numerically by replacing the solid beach by a permeable beach characterized by an extremely small porosity. Run-up of nonbreaking waves is verified against the analytical solution for nonlinear shallow water waves. The inclusion of wave breaking is based on the surface roller concept for spilling breakers using a geometrical determination of the instantaneous roller thickness at each point and modelling the effect of wave breaking by an additional convective momentum term. This is a function of the local wave celerity, which is determined interactively. The model is applied to cross-shore motions of regular waves including various types of breaking on plane sloping beaches and over submerged bars. Model results comprise time series of surface elevations and the spatial variation of phase-averaged quantities such as the wave height, the crest and trough elevations, the mean water level, and the depth-averaged undertow. Comparisons with physical experiments are presented. The phaseaveraged balance of the individual terms in the momentum and energy equation is determined by time-integration and quantities such as the cross-sectional roller area, the radiation stress, the energy flux and the energy dissipation are studied and discussed with reference to conventional phase-averaged wave models. The companion papers present cross-shore motions of breaking irregular waves, swash oscillations and surf beats (part II) and nearshore circulations induced by breaking of unidirectional and multidirectional waves (part III).

Nutrient Retention Time in High‐Permeability, Oil‐Fouled Beach

Following the grounding of the \IExxon Valdez\N in March 1989, many beaches in the Alaskan waters were fouled with oil. One of these was Kittiwake Beach of Knight Island in Prince William Sound. The U.S. Environmental Protection Agency initiated a research project to evaluate the application of nutrients to the surface of the beach to stimulate biodegradation of the surficial and infiltrated oil by indigenous microbial populations. Nutrients were dissolved in seawater and applied by sprinklers to study plots along the beach. As part of this project, a preliminary, simplified model of the beach hydraulics is developed to describe the advective fate of the applied nutrients. The retention time of nutrients in the beach is estimated to be on the order of 12 h (one tidal cycle) for the application method used. Simulations indicate that application of nutrients through a trench or subsurface drain placed above the high-tide level, rather than directly on the beach by sprinklers, would result in significantly longer retention times. Design guidance for future remediation is provided to ensure nutrient coverage of the entire oiled profile of a permeable beach.

Interim guidance for prediction of wave run-up on beaches

A method of predicting wind wave run-up (for any desired quantile or statistic value) on smooth linear mild slopes has been presented. The method is based on a re-analysis of an extensive laboratory measurement run-up data base of Mase [(1989), Random wave run-up height on gentle slopes. J. WatWay, Port, Coastal, Ocean Engng Div., ASCE 115, 649–661] and Mase and Iwagaki [(1984), Run-up of random waves on gentle slopes. Proceedings of the 19th Coastal Engineering Conference, ASCE, pp. 593–609]. The predictive run-up measurement equation is based on a modified dimensionless form of the Hunt [(1959), Design of seawalls and breakwaters. Proc. J. WatWay Harbour Div., ASCE, 85, 123–152] formula with a linear intercept term (which appears to be due to mild slope wave set-up). Values of the slope coefficient in the run-up predictive equation are based on the Rayleigh probability distribution in accordance with findings from the present re-analysis of the Mase data set. Run-up prediction for a given quantile or statistic value is then found utilizing the slope coefficient based on Rayleigh theory combined with the predictive linear equation found herein for the average run-up height R mean in a stationary wave train. In the case of rough slopes and permeable beaches, it is obvious that the true run-up would be reduced from the predicted values of run-up given by the smooth slope method provided herein. At present the extent of such reduction is a matter of speculation. As an interim measure, it is recommended that conservative design practice be followed by using the run-up values predicted via the method given herein unless sufficient justification for run-up reduction based on laboratory or field findings can be provided.

BEACHES: PROFILES, PROCESSES AND PERMEABILITY

Equilibrium beach profiles have been investigated in the laboratory for two beach materials, 0.22 mm marine sand and 1.55 mm crushed coal. Analysis of the results confirms that the dimensionless fall velocity H0/Tw is an important parameter influencing both surf zone hydraulics and the form of the resulting equilibrium profile. Beach permeability also significantly influences the hydraulics within the beach face and it has been found that both H0/Tw and the parameter wf/w, the ratio of the fluidizing velocity to the fall velocity, influence the form of the equilibrium profiles of permeable beaches.

Erosion susceptibility of the Virginia Chesapeake Bay shoreline

This study defines the susceptibility of differing shoreline types in the Virginia Chesapeake Bay to erosion. There is a high variability of the coastal environments in this area influenced by: (1) the relict Pleistocene high-order dendritic drainage system, resulting in a large diversity of shore orientations; (2) the moderate, but highly variable wave energy in the Bay system and highly variable submergence rates, resulting in a spectrum of shoreline transformation from primary to secondary types; (3) exposures of coastal plain sediments of widely varying composition and volume; and (4) diverse salt marsh development. Eighty percent of the shore is composed of three morphologically distinct beach environments, each reflecting different susceptibilities to erosion: (1) Permeable beaches, composed entirely of sand-sized material, comprise 59% of the beaches (mean erosion = 0.85 m/yr) and have the largest vertical and horizontal dimensions. This provides the largest vertical buffer to the effects of storm surge and waves. (2) Impermeable beaches, composed of a veneer of sand overlying impermeable, pre-Holocene sediments, comprise 24% of the beaches. The combined influence of low swash infiltration, low beach elevation and groundwater effects result in the highest mean erosion (1.14 m/yr). (3) Marsh barrier beaches (17%), composed of a veneer of sand overlying peat, contains a resistant rhizome framework, resulting in the least erodable beach environment (0.66 m/yr). Marsh margins, the remaining 20% of the shoreline, are the least erodable shore environment (0.54 m/yr). There is a large variability in the local subsidence rates along the shoreline. The subsidence highs correspond to the areas with largest nearshore terraces and the main concentrations of salt marsh development. A balance in the shore stability exists as a result of salt marsh development: The marsh retards shore erosion, yet it occurs at the areas of highest local submergence where the highest shoreline retreat is expected.

Comparison of Recent Shoreline Sedimentation with Stratigraphy of Upper Cretaceous Oil Fields, Rocky Mountain Area: ABSTRACT

The recognition of the shoreline of a marine basin is one of the most important tasks facing the stratigrapher. Determining the position and trend of the shoreline aids in lithofacies studies and is the basis for the art of paleogeography. An important depositional feature of some modern shorelines is the barrier island on which barrier bar sands are accumulating. The barrier bar deposit is characterized by a narrow linear, well sorted porous and permeable sandstone, beach structures and littoral fauna on one flank, beach ridges, eolian deposits, and other minor features. Sedimentation along the central Georgia coast illustrates the factors which disrupt normal barrier island development and cause abrupt termination of barrier bars. A knowledge of these factors is importa t to the trend-pursuing petroleum geologists. By using lithologic and biologic criteria developed from Recent sediment studies, barrier bar sands can be demonstrated as common shoreline deposits in the Cretaceous of the Rocky Mountains. These sands are important petroleum reservoirs and are prime targets in the search for stratigraphic traps. Surface and subsurface studies indicate that the newly found petroleum accumulations on the Wamsutter arch, southern Wyoming, are in barrier bar sands of Late Cretaceous age. The trend of these shoreline deposits is nearly perpendicular to the axis of the broad east-plunging anticline. The updip permeability seal on the trap is the change from barrier bar sands to impermeable swamp and lagoonal sediments. Because barrier bar sands represent less than 1 per cent of the Cretaceous strata, they are elusive targets in petroleum exploration. End_of_Article - Last_Page 381------------