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Accueil du site → Doctorat → Royaume-Uni → 1998 → Recharge processes under arid and semi-arid conditions : laboratory experiments and modelling (BL)

Cranfield University (1998)

Recharge processes under arid and semi-arid conditions : laboratory experiments and modelling (BL)

Parehkar, M

Titre : Recharge processes under arid and semi-arid conditions : laboratory experiments and modelling (BL)

Auteur : Parehkar, M

Université de soutenance : Cranfield University

Grade : Doctor of Philosophy (PhD) 1998

Résumé
In this research, a link was made between soil physical and hydrogeological methods of estimating ground water recharge. An experimental methodology was developed in order to study the flow processes which occur in the unsaturated zone of natural formations. Sand columns with heights of 4000 mm and low soil moisture contents were set up in the laboratory. Comprehensive measurements of soil hydraulic properties were made in the laboratory. Three phenomena were observed in the laboratory column experiments. (i) the water, which was already present in the soil profile (as old water), is pushed in front of the newly applied water even in a profile with low soil moisture content. This is because the soil water is still moving downwards even after a long period of gravity drainage ; the initial condition prior to application of new water is one of slow downward movement (not equilibrium). (ii) Movement of infiltrating rainwater from large to small pores, which are filled with water (water-filled pores), results in a downward displacement of soil moisture present in the soil profile. (iii) There is a rapid, but relatively small, rise in the water table before the wetting front reaches the zone of rapidly changing soil water content just above the capillary fringe. The LEACHM model was used to simulate the above-mentioned phenomena. This model solves the Richards’ and Convection-Diffusion equations by a finite difference technique. Parameters used by the model were all measured in the laboratory : parameter values were not changed in a conventional calibration process. The water retention function in the model was modified and the model was altered to include hysteresis. After tests with and without modifications, the original model was found to be able to reproduce the laboratory observations of water and solute movement. The model generated predictions that the water (and consequently the solutes) would move faster with than without the inclusion of hysteresis.

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