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sur le développement des zones arides et semi-arides

Titre : Long term convective saline plume development beneath an evaporating salt lake : experiment and computation

Auteur : Taylor, James Hiron

Université de soutenance : Australian National University

Grade : Doctor of Philosophy (PhD) 1997

Résumé partiel
Long term convective saline plume development beneath evaporating salt lakes is not well understood. It is of importance because of the use of evaporating salt lakes as disposal basins for pumped saline groundwater in the Murray-Darling Basin and because of the amount of salt trapped beneath some salt lakes. Evaporation results in highly concentrated brines that can potentially move downward, through the lake beds, at faster rates than anticipated. These brines may interact with surrounding groundwater, recycling salt back into the regional groundwater systems of the Basin. This study approaches the problem in two ways. Firstly, experiments in HeleShaw cells, were performed using a schlieren system to visualise density-driven flow for homogeneous and heterogeneous porous media. The Hele-Shaw cell is a twodimensional analogue of a porous medium and was used to represent an evaporating salt lake in two dimensions. In the homogeneous case, experiments confirmed that two flow features seen by Wooding et. al. (1997a) in the short term were also present at long times. In addition, two previously unreported flow features were observed. The continued development of convective saline fingers at the evaporation boundary at times well after the completion of initial finger development was observed. The convective fingers continued to be produced as long as inflow was present. Also, the convecting saline fingers were advected horizontally along the evaporation boundary as they developed. In a natural salt lake system, this would correspond to the horizontal motion of the vertically convecting saline plumes from the lake margin towards the centre of the lake. The two new flow features observed here were the presence of a wavelike disturbance in the boundary layer prior to the onset of instability that traveled from the cell wall to the interior evaporation point and a transient period in the Hele-Shaw cell that involved the production of two or more recirculating convective cells beneath the evaporation boundary prior to the development of the long term cell behaviour. In the heterogeneous case flow behaviour was observed to be qualitatively similar to the homogeneous case except significant horizontal motion of the fingers occurred at the interface between permeability regions.

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