Biseau salé | EPFL Graph Search

Un biseau salé (ou une intrusion salée) est l'intrusion d'eau saumâtre ou salée dans une masse d'eau. L'eau salée étant plus lourde et visqueuse que l'eau douce. S'il y a déséquilibre, l'eau salée (plus dense) peut « repousser » vers l'intérieur des terres la nappe d'eau douce. Théoriquement, en raison d'une différence importante de densité, après un temps d'équilibrage, ces deux masses d'eau peuvent ne pas se mélanger (en l'absence de mouvements des masses d'eau ou de mélanges d'origine géothermique, le mélange peut se faire par dispersion/diffusion, lequel peut être freiné dans certains substrats, dans le calcaire peu faillé par exemple). Près de la côte, des mouvements épisodiques ou saisonniers (par exemple induit par une marée ou par les pompages, ou par un afflux d'eau d'origine pluviale ou de fonte de neige ou glacier) peuvent également mélanger ces eaux et/ou déplacer le biseau salé, en pouvant poser problème quand l'eau salée menace une nappe phréatique (souterraine ou sup

Thermohaline Flow in Seawater Intrusion in Shallow Coastal Aquifers

David Andrew Barry, Chenming Zhang

Temperature and salinity, with largely different diffusivities, make a perfect couple that drives thermohaline flow (double diffusive convection where heat and salt are the two main concerned properties) in porous media wherever their gradients co-exist. Studies of double diffusion convection have revealed various flow regimes generated by instable and even stable vertical stratification of heat and salt including diffusive, finger, and mixed flow regimes. In the context of seawater intrusion in shallow coastal aquifers, however, temperature and salinity gradients present more likely horizontal than vertical. Moreover, while salinity gradient is apparently seaward, the direction of temperature gradient may vary over the seasons. In such cases, understanding on how thermohaline flow exhibit and influence the overall state of seawater intrusion in near-shore aquifers remains largely deficient. In this study, we examine the occurrence and characteristics of thermohaline flow in seawater intrusion in coastal aquifers under various scenarios of salinity and temperature distribution by laboratory experiments and numerical simulation. Its effects on solute transport and saltwater circulation are also investigated.

2018

Seawater intrusion processes, investigation and management: Recent advances and future challenges

David Andrew Barry

Seawater intrusion (SI) is a global issue, exacerbated by increasing demands for freshwater in coastal zones and predisposed to the influences of rising sea levels and changing climates. This review presents the state of knowledge in SI research, compares classes of methods for assessing and managing SI, and suggests areas for future research. We subdivide SI research into categories relating to processes, measurement, prediction and management. Considerable research effort spanning more than 50 years has provided an extensive array of field, laboratory and computer-based techniques for SI investigation. Despite this, knowledge gaps exist in SI process understanding, in particular associated with transient SI processes and timeframes, and the characterization and prediction of freshwater-saltwater interfaces over regional scales and in highly heterogeneous and dynamic settings. Multidisciplinary research is warranted to evaluate interactions between SI and submarine groundwater discharge, ecosystem health and unsaturated zone processes. Recent advances in numerical simulation, calibration and optimization techniques require rigorous field-scale application to contemporary issues of climate change, sea-level rise, and socioeconomic and ecological factors that are inseparable elements of SI management. The number of well-characterized examples of SI is small, and this has impeded understanding of field-scale processes, such as those controlling mixing zones, saltwater upconing, heterogeneity effects and other factors. Current SI process understanding is based mainly on numerical simulation and laboratory sand-tank experimentation to unravel the combined effects of tides, surface water groundwater interaction, heterogeneity, pumping and density contrasts. The research effort would benefit from intensive measurement campaigns to delineate accurately interfaces and their movement in response to real-world coastal aquifer stresses, encompassing a range of geological and hydrological settings.

Elsevier2013

Effects of temperature on tidally influenced coastal unconfined aquifers

David Andrew Barry, Li Pu, Chenming Zhang

Aquifer-ocean temperature contrasts are common worldwide. Their effects on flow and salinity distributions in unconfined coastal aquifers are, however, poorly understood. Based on laboratory experiments and numerical simulations, we examined the responses of flow processes in tidally influenced aquifers to aquifer-ocean temperature differences. The extent of seawater intrusion and seawater circulation were found to vary with the aquifer-ocean temperature contrast. Compared with the isothermal case, an increase of up to 40% of the tide-induced seawater circulation rate in the intertidal zone was observed when seawater is warmer than groundwater. In contrast, saltwater circulation in the lower saltwater wedge declines notably no matter whether the seawater is warmer or colder than groundwater. As the seawater temperature rises, the contribution of tide-induced circulation to the overall increase of submarine groundwater discharge becomes more important compared with that of density-driven seawater circulation. Both the upper saline plume and the freshwater discharge zone expand significantly with warmer seawater whereas the lower saltwater wedge contracts.

2020

Seawater intrusion processes, investigation and management: Recent advances and future challenges

David Andrew Barry

Elsevier2013