Academic literature on the topic 'Swash groundwater'

Coastal flooding is a growing socioeconomic and humanitarian hazard (e.g., Nicholls, 2010). Increased beach groundwater levels may inundate low-lying areas and simultaneously propagate swash impacts onto higher beach and backshore elevations. Generally, coastal flood modeling and risk assessment characterize only surface flows, neglecting beach groundwater and swash zone processes such as infiltration and porous media flow. Numerous studies have considered the effects of swash on groundwater (e.g., Gourlay, 1992). Infiltration leads to reduced wave runup (Pintado-Patino et al., 2015) and is promoted by low beach groundwater levels (Bakhtyar et al., 2011), suggesting that beach groundwater plays a critical role in infiltration/exfiltration processes. Notably, the impacts of beach groundwater on swash flows and subsequent consequences on coastal flooding have not been explored. Coastal flooding from wave overtopping is expected to occur around the maximum tide. However, recent field observations suggest maximum overtopping lags behind high tide and is in phase with maximum groundwater levels. In this study, a turbulence and depth resolving numerical model is developed to examine the interaction between beach groundwater and wave overtopping processes.

Coastal aquifers are highly dynamic groundwater systems. Sea level rise will cause a rise in coastal groundwater tables resulting in increased risk of shallow or emergent groundwater (Befus et al., 2020). Marine water level fluctuations cause the beach groundwater table to oscillate over a relatively large range. Understanding these oscillations is crucial, as shallow (i.e., high) water tables may impact subsurface infrastructure, mobilize sediment, and increase liquefaction risks. Although the impacts of tides and wave setup on coastal water tables have been studied (e.g., Nielsen, 1990; Housego et al, 2021), the cumulative impacts of wave runup, partially saturated flow, complex beach topography, and dual tidal forcing for bay-backed regions have not been explored. This work numerically models beach water table fluctuations which are compared to in-situ swash and beach groundwater observations at Cardiff State Beach in Encinitas, CA.

This research work is aimed at developing a coupled surface-groundwater flow model which can be used to simulate both surface and groundwater flow at the swash zone. The coupled model is then used to investigate the effects of seepage on swash hydrodynamics as well as morphodynamics. The surface flow model was originally developed by Briganti et al. (2012), which solved a system of equations consisting of the Nonlinear Shallow Water Equations and the bed-evolution (Exner) equation with bed shear stress computed using a boundary layer model without seepage developed in Briganti et al. (2011). In this work, a groundwater flow model which solves Laplace's equation following the approach of Li and Barry (2000) is incorporated into the surface flow model, which allows computation of seepage into the bed (infiltration) and out of it (exfiltration). The seepage is then included into the boundary layer models to incorporate the effects of seepage on the bed shear stress. To assess the performance of the surface flow model, dam-break cases are simulated and compared against analytical and quasi-analytical solutions from literature. Firstly, the dam-break case on a fixed bed is simulated and compared against Ritter solution (Stoker, 1957) and then the dam-break case on a mobile bed is verified against Zhu (2012)'s quasi-analytical Riemann solver. Both models show good agreement with their respective reference results. Subsequently, the verification of the groundwater flow model is conducted by simulating phreatic surface flow through a rectangular dam and comparing the results against those of Kazemzadeh-Parsi and Daneshmand (2012). Next, the coupled surface-groundwater flow model is validated by reproducing surface and groundwater flow in the prototype-scale BARDEX II experiment. Firstly, the groundwater flow cases (higher and lower lagoon levels than the initial sea level) without surface water waves are simulated. The comparison of time-averaged numerical phreatic surface elevations against the experimental data shows excellent agreement. Next, the surface water waves are included and the simulations are repeated for the previous two cases. The groundwater comparisons again yield good agreement and the hydrodynamics of the surface waves show reasonably close agreement. Increase in exfiltration is observed to result in an increase in boundary layer thickness, which subsequently results in smaller velocity gradients and a decrease in bed shear stress using exfiltration included BBL model of Cheng and Chiew (1998). Conversely, the increase in infiltration causes a decrease in boundary layer thickness, which results in an increase in bed shear stress using infiltration included BBL model of Chen and Chiew (2004). The model results also show that the boundary layer effect by infiltration is opposed by the 'continuity effect' in the swash zone (Baldock and Nielsen, 2009). The model results show that an increase in infiltration rates is observed to increase slip velocity, and also compares well against the empirical equation derived in Chen and Chiew (2004). Furthermore, the rate of increase (decrease) of bed shear stress due to infiltration (exfiltration) compares favourably against the empirical trend line of Nielsen et al. (2001) and experimental data of Conley (1993). Additionally, the boundary layer model bed shear stress is compared against single swash event bed shear stress results from Kikkert et al. (2013) experiment and shows reasonably good agreement. The boundary layer models can be used to account for seepage effects on bed shear stressfor a larger range of ventilation parameters than Nielsen et al. (2001), which would improve morphodynamical modelling on permeable beds in the swash zone. Finally, the performance of the coupled surface-groundwater model is further investigated by simulating the BARDEX II experiment with a mobile bed. The swash zone water depth compares well with the BARDEX II experimental results. Although the corresponding dataset for velocity is shown to be rather unreliable during backwash, during uprush, the comparison is very close. Using both Meyer-Peter-Müller (MPM) and Grass sediment transport models, similar morphodynamical patterns are observed. The bed change comparisons against experimental results show that the model predicts the same order as well as the same pattern of erosion. However, deposition in the upper swash zone is not predicted by the model which could be due to the presence of significant amounts of suspended sediment which would lead to onshore sediment transport (Pritchard and Hogg, 2005, Zhu and Dodd, 2015) which is not accounted for in the simplified numerical model. The model is shown to be robust and flexible and it is capable of simulating both surface and groundwater flow simultaneously on fixed or evolving bed.

The morphodynamics of a steeply sloping gravel beach in the south western UK (tanβ = 0.15–0.2; d50 = 6 mm; ξb = 1–4) were measured during low energy wind-wave conditions (Hb < 0.5 m). Measurements of water depth, groundwater-level, waves and currents, concurrent with observations of morphological change and swash sediment loads, were successfully obtained over two spring-to-neap tidal cycles and used to investigate the short-term evolution of gravel beach morphology. Incident frequency motions dominated the hydrodynamics since wave transformation was concentrated at the base of the beach. Subharmonic energy was of secondary importance at most, never exceeding 15% of the total energy. Standing edge waves were generally absent since the lack of swell waves limited their forcing, and there was c. 50% reflection of the gravity-band energy.

Les écoulements en milieux poreux non-saturés sont modélisés par l'équation de Richards qui est une équation non-linéaire parabolique dégénérée. Ses limites et les défis que soulèvent sa résolution numérique sont présentés. L'obtention de résultats robustes, précis et efficaces est difficile en particulier à cause des fronts de saturation raides et dynamiques induits par les propriétés hydrauliques non-linéaires. L'équation de Richards est discrétisée par une méthode de Galerkine discontinue en espace et des formules de différentiation rétrograde en temps. Le schéma numérique résultant est conservatif, d'ordre élevé et très flexible. Ainsi, des conditions aux limites complexes sont facilement intégrées comme la condition de suintement ou un forçage dynamique. De plus, une stratégie adaptative est proposée. Un pas de temps adaptatif rend la convergence non-linéaire robuste et un raffinement de maillage adaptatif basée sur des blocs est utilisée pour atteindre la précision requise efficacement. Un indicateur d'erreur a posteriori approprié aide le maillage à capturer les fronts de saturation raides qui sont également mieux approximés par une discontinuité introduite dans la solution grâce à une méthode de Galerkine discontinue pondérée. L'approche est validée par divers cas-tests et un benchmark 2D. Les simulations numériques sont comparées à des expériences de laboratoire de recharge/drainage de nappe et une expérience à grande échelle d'humidification, suite à la mise en eau du barrage multi-matériaux de La Verne. Ce cas exigeant montre les potentialités de la stratégie développée dans cette thèse. Enfin, des applications sont menées pour simuler les écoulements souterrains sous la zone de jet de rive de plages sableuses en comparaison avec des observations expérimentales
Flows in unsaturated porous media are modelled by the Richards' equation which is a degenerate parabolic nonlinear equation. Its limitations and the challenges raised by its numerical solution are laid out. Getting robust, accurate and cost-effective results is difficult in particular because of moving sharp wetting fronts due to the nonlinear hydraulic properties. Richards' equation is discretized by a discontinuous Galerkin method in space and backward differentiation formulas in time. The resulting numerical scheme is conservative, high-order and very flexible. Thereby, complex boundary conditions are included easily such as seepage condition or dynamic forcing. Moreover, an adaptive strategy is proposed. Adaptive time stepping makes nonlinear convergence robust and a block-based adaptive mesh refinement is used to reach required accuracy cost-effectively. A suitable a posteriori error indicator helps the mesh to capture sharp wetting fronts which are also better approximated by a discontinuity introduced in the solution thanks to a weighted discontinuous Galerkin method. The approach is checked through various test-cases and a 2D benchmark. Numerical simulations are compared with laboratory experiments of water table recharge/drainage and a largescale experiment of wetting, following reservoir impoundment of the multi-materials La Verne dam. This demanding case shows the potentiality of the strategy developed in this thesis. Finally, applications are handled to simulate groundwater flows under the swash zone of sandy beaches in comparison with experimental observations

As Gurgaon expands horizontally and vertically, it continues to transition from farms to urban villages to a concrete maze. This photographic project documents the growth of Gurgaon a city recently developed near India's capital, Delhi. It is a booming financial and industrial center, home to most Multinational Corporations (MNCs) and has third highest per-capita income in India. As its advocates often like to point out, Delhi’s booming neighbor has 1,100 high-rises, at least 30 malls and thousands of small and big industries. On the other hand, as its detractors unfailingly like to note, the dust bowl’s population has grown two and a half fold, it has 12-hour power blackouts, and its groundwater would probably not last beyond this decade. Gurgaon's transformation began sometime around 1996, with the advent of Genpact, then a business unit of General Electric. Other multinational companies followed it slowly thereafter. It helped that the city was a few kilometers away from Delhi. Two decades on, Gurgaon is already "on its deathbed." From 0.8 million in 2001, the city is expected to reach a population of 6.9 million in 2031. It is speckled with glass buildings with curtain walls, and swish apartment blocks with Greco-Roman influences, but there is little water or power for them. These numbers alone don’t capture the lived reality of Gurgaon, though. The skyline that its older residents were accustomed to has completely disappeared. And yet on the periphery, one sees the "Unfinished City" growing. The landscapes and flora shouting; their sentiments brutalized by evictions and concrete. Slaughtered farms now seem witness to monstrosity with desolate faces and fading memories. Set in 2014 the project explores the ephemerality of Gurgaon’s glamor and defective town planning. Families had been displaced, laborers’ children were growing up on heaps of cement, and farmlands had turned into things of memories.

Synthetic Aperture Radar Interferometry (InSAR) is a remote sensing technique very effective for the measure of smalldisplacements of the Earth’s surface over large areas at a very low cost as compared with conventional geodetictechniques. Advanced InSAR time series algorithms for monitoring and investigating surface displacement on Earth arebased on conventional radar interferometry. These techniques allow us to measure deformation with uncertainties of 1mm/year, interpreting time series of interferometric phases at coherent point scatterers (PS) without the need for humanor special equipment presence on the site. By applying InSAR processing techniques to a series of radar images over thesame region, it is possible to detect line-of-sight (LOS) displacements of infrastructures on the ground and therefore identifyabnormal or excessive movement indicating potential problems requiring detailed ground investigation. A major advantageof this technology is that a single radar image can cover a major area of up to 100 km by 100 km or more as, for example,Sentinel-1 C-band satellites data cover a 250 km wide swath. Therefore, all engineering infrastructures in the area, suchas dams, dikes, bridges, ports, etc. subject to terrain deformation by volcanos, landslides, subsidence due to groundwater,gas, or oil withdrawal could be monitored, reducing operating costs effectively. In this sense, the free and open accessCopernicus Sentinel-1 data with currently up to 6-days revisit time open new opportunities for a near real-time landmonitoring. In addition, the new generation of high-resolution radar imagery acquired by SAR sensors such as TerraSARX,COSMO-SkyMed, and PAZ, and the development of multi-interferogram techniques has enhanced our capabilities inrecent years in using InSAR as deformation monitoring tool. In this paper, we address the applicability of using spaceborneSAR sensors for monitoring infrastructures in geomatics engineering and present several cases studies carried out by ourgroup related to anthropogenic and natural hazards, as well as monitoring of critical infrastructures.