Groundwater fluxes and flow paths within coastal barriers: Observations from a large-scale laboratory experiment (BARDEX II)

The dynamics of groundwater at the beach face land�ocean boundary have important implications to the exchange of water, nutrients, and pollutants between the ocean and coastal aquifers, and more subtly, varying groundwater levels may induce differing morphological response at the beach face. As a component of the multi-institution Barrier Dynamics Experiment (BARDEX II), groundwater fluxes and flow paths within a prototype-scale sandy barrier are quantified and reported at the three fundamental spatio-temporal scales (individual waves, the beach face, and total barrier), under controlled wave and water level conditions. A particular feature of the experimental programme was the inclusion of a back-barrier �lagoon�, that via a pump system and an intermediate water reservoir enabled the forcing of contrasting hydraulic gradients across the barrier. It was observed that the groundwater level, flow paths, and fluxes within the beach face region of the sand barrier were predominantly controlled by the action of waves at the beach face, regardless of the overall seaward- or landward-directed barrier-scale hydraulic gradients. In the presence of waves, all tests undertaken to complete this study developed a seaward gradient in this zone under the influence of waves. As a further result of wave forcing at the beach face boundary, localised groundwater flow divides were observed to develop, further partitioning the circulation and flow paths of groundwater within the prototype-scale sand barrier

Influence of Waves on Groundwater Flows and Geochemistry in a Sandy Nearshore Aquifer: A Combined Field and Modelling Study

Waves are known to influence the flux of pollutants to coastal waters via groundwater discharge. This study combines field measurements with numerical groundwater modelling to evaluate the influence of a period of intensified wave conditions (wave event) on nearshore groundwater flows and geochemistry in a sandy freshwater beach. Comprehensive vertical nested pressure transducer data obtained over a 2.5 day isolated wave event reveal the development of transient groundwater flow recirculations through the nearshore aquifer combined with enhanced water exchange across the sediment-water interface (i.e., beach face). The wave-induced groundwater flows were simulated in FEFLOW using a phase-averaged wave setup approach to represent waves acting on the sediment-water interface. The time-varying measured and simulated hydraulic gradients match well indicating that consideration of wave setup alone, rather than instantaneous (phase-resolved) wave effects, is able to adequately capture wave-induced perturbations in nearshore groundwater flows. Additionally, the impact of the wave-induced groundwater flows on geochemical conditions near the sediment-water interface is illustrated by redox and pH fluctuations over the wave event. The observed fluctuations may considerably impact the fate of reactive pollutants discharging and also recirculating through a nearshore aquifer. In addition to the importance of the phase-averaged effect of waves, the phase-resolved effects of waves also need to be understood to better predict the fate of chemical and microbial constituents close to the sediment-water interface. Additional high frequency field measurements indicate that the phase-resolved effects of waves account for considerably larger fluxes of water and associated constituents exchanged across the sediment-water interface than the phase-averaged flux. Despite the large magnitude, the flux generated by phase-resolved wave effects is rapidly reversing in direction and thus is not expected to considerably influence dissolved constituents due to its short residence time, estimated to be between \u3c 1 and 70 seconds. However, the exchange of particulates may be important as their transport is strongly governed by attachment and detachment processes. It is proposed that the rapid water exchange processes near the sediment-water interface control the fate and transport of particulate organic matter and fecal bacteria and thus are important for regulating nutrient and microbial coastal water quality

Cross-shore morphodynamics of coarse grained beaches and beach/structure interaction: Numerical modelling and large scale measurements

Coastal defence systems are implemented in many countries for the stability of coastlines and prevention of erosion and flooding. The maintenance of such schemes includes the use of 'soft' engineering techniques, which require accurate predictions of sediment transport and profile change. This thesis describes the development of a numerical model for coarse-grained crossshore transport for use in such schemes. The model combines a hydrodynamic model based on weakly non-linear Boussinesq equations, coupled to a sediment transport module and a morphology change module. Studies have been performed on the hydrodynamic and sediment models to assess the performance of the components for this purpose. The 1-D Boussinesq model has been validated with physical wave flume data. The model is shown to provide good predictions for shoaling and breaking waves near the coastline, and is also shown to provide good predictions for the properties of a reflected wave field. The model is then used to perfonn a study on the nature of wave shoaling and reflection with regard to the velocity field, and the development of the velocity skewness pattern is discussed. Recent sediment transport formulae have been reviewed, and a bed-load sediment transport model has been developed. A model for differential transport of different grain sized niaterial has also been introduced. Developed from a river sediment model, this is able to predict sorting of grain sizes over the cross-shore profile. Results of the combined model are shown for natural plane beaches, and for beaches coupled with sea walls. The model predicts reduced erosion patterns for irregular wave fields compared to regular waves, and for mixed sediment composition sea beds compared to homogeneous sea beds. These findings show agreement with features found in previous physical studies. A series of sensitivity studjes has also been performed with respect to hydrodynamic and sediment properties. The model shows a high degree of sensitivity for the profile changes to these parameters. The ability of the model to show predictions for an evolving beach profile subject to tidal water depth variation is also introduced

Transport of terrigenous sediment and horseshoe crab eggs in the swash zone of an estuarine foreshore in Delaware Bay, New Jersey, USA

Identification of processes responsible for egg exhumation and transport in the swash zone is paramount to conservation of species that use the intertidal foreshore. One example where the understanding of these processes is critical to egg exhumation, transport and deposition is in Delaware Bay, USA. Beaches in Delaware Bay provide foraging grounds to many shorebird species that migrate thousands of miles from Central and South America to feed on nutrient rich horseshoe crab eggs during their peak spawning season. Eggs laid at depth by horseshoe crabs are exhumed and transported by bioturbation, wave and swash processes and made available to foraging shorebirds. The objectives of this dissertation are to: (1) compare differences in the significance of wave and swash processes to horseshoe crab egg exhumation and transport on the mid - foreshore relative to the upper foreshore in the absence of spawning; (2) compare how horseshoe crab eggs are mobilized relative to sediment; and (3) evaluate the processes responsible for textural changes of sediment in transport. The study was conducted on a steep, predominantly sandy foreshore on the New Jersey shoreline of Delaware Bay. Instrumented wave (height and period) and swash (depth, duration, velocity, width) measurements were gathered on October 12 and October 14, 2007 during spring tidal conditions. Dyed horseshoe crab eggs and sediment were injected at a location on the mid-foreshore that were influenced by wave breaking and swash flows and at a location on the upper foreshore that was influenced by swash flows alone. Total load traps were used to measure textural changes in sediment and quantities of egg and sediment tracer transported over individual swash events during the rising, high and falling tide. Sediment on the foreshore comprised medium to coarse sands with a gravel fraction of granules and pebbles. The proportion of gravel within the foreshore prior to trapping was low. An increase in the percent gravel transported was observed in the swash approaching the time of high water. Results suggest that as the energy under incident waves increase with tidal rise, the quantities of gravel mined out from the bed also increase and are incorporated into the beach step. Plunging waves breaking over the step suspend gravel and transport it up the foreshore in the swash. The lag in the rate of step migration relative to migration of the breaker zone during the falling tide increases the likelihood of mining gravel from the step and transporting it downslope in the backwash. Results from the tracer experiments reveal that wave breaking is the primary mechanism that accounts for the greater quantities of sediment and eggs trapped from the mid-foreshore in the uprush relative to the backwash despite offshore directed flows during the tidal cycle when wave heights ranged from 0.43-0.64 m. Low quantities of eggs and sediment entrained from the upper foreshore are a function of the decreasing swash depths and flow velocities approaching the uprush limit. Waves did not activate sediment on the mid-foreshore to depths where crabs would generally lay eggs and subsequent spawning would be required to make these eggs available to shorebirds. Data reveal that higher wave heights ranging from 0.65-1.1 m representing storm conditions resulted in accretion across the foreshore, and no eggs were released from the mid or upper foreshore

Groundwater dynamics in subterranean estuaries of coastal unconfined aquifers: Controls on submarine groundwater discharge and chemical inputs to the ocean

Sustainable coastal resource management requires sound understanding of interactions between coastal unconfined aquifers and the ocean as these interactions influence the flux of chemicals to the coastal ocean and the availability of fresh groundwater resources. The importance of submarine groundwater discharge in delivering chemical fluxes to the coastal ocean and the critical role of the subterranean estuary (STE) in regulating these fluxes is well recognized. STEs are complex and dynamic systems exposed to various physical, hydrological, geological, and chemical conditions that act on disparate spatial and temporal scales. This paper provides a review of the effect of factors that influence flow and salt transport in STEs, evaluates current understanding on the interactions between these influences, and synthesizes understanding of drivers of nutrient, carbon, greenhouse gas, metal and organic contaminant fluxes to the ocean. Based on this review, key research needs are identified. While the effects of density and tides are well understood, episodic and longer-period forces as well as the interactions between multiple influences remain poorly understood. Many studies continue to focus on idealized nearshore aquifer systems and future work needs to consider real world complexities such as geological heterogeneities, and non-uniform and evolving alongshore and cross-shore morphology. There is also a significant need for multidisciplinary research to unravel the interactions between physical and biogeochemical processes in the STE, as most existing studies treat these processes in isolation. Better understanding of this complex and dynamic system can improve sustainable management of coastal water resources under the influence of anthropogenic pressures and climate change

Embracing Insecurity: Harm Reduction Through a No-Fault Approach to Consumer Data Breach Litigation

The lack of a clear remedy for data subjects whose private information has been compromised in data breaches prompts expensive and exploratory litigation that encounters difficulties with the unique set of risks posed by the data economy. Examining the market forces and risk environments posed by the data economy yields the conclusion that vulnerability is a guaranteed feature and investments in cybersecurity go largely unrewarded. The importance of data to our economy requires that the benefit of potential solutions to data subjects be weighed against the potential costs of burdening innovation. This Note proposes that the ideal solution should prioritize harm reduction by implementing a no-fault resolution system to provide an efficient remedy for compromised data subjects and a safe harbor-based compliance program to improve cybersecurity without hampering the direction of innovation

Studies of flow and scalar distribution in two large industrial environments.

Available from British Library Document Supply Centre-DSC:DXN037619 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Combining Shamir & Additive Secret Sharing to Improve Efficiency of SMC Primitives Against Malicious Adversaries

Secure multi-party computation provides a wide array of protocols for mutually distrustful parties be able to securely evaluate functions of private inputs. Within recent years, many such protocols have been proposed representing a plethora of strategies to securely and efficiently handle such computation. These protocols have become increasingly efficient, but their performance still is impractical in many settings. We propose new approaches to some of these problems which are either more efficient than previous works within the same security models or offer better security guarantees with comparable efficiency. The goals of this research are to improve efficiency and security of secure multi-party protocols and explore the application of such approaches to novel threat scenarios. Some of the novel optimizations employed are dynamically switching domains of shared secrets, asymmetric computations, and advantageous functional transformations, among others. Specifically, this work presents a novel combination of Shamir and Additive secret sharing to be used in parallel which allows for the transformation of efficient protocols secure against passive adversaries to be secure against active adversaries. From this set of primitives we propose the construction of a comparison protocol which can be implemented under that approach with a complexity which is more efficient than other recent works for common domains of interest. Finally, we present a system which addresses a critical security threat for the protection and obfuscation of information which may be of high consequence.Comment: arXiv admin note: text overlap with arXiv:1810.0157