Modeling of Transient Two Dimensional Flow in Saturated-Unsaturated Porous Media

We study the transient two-dimensional flow problems related to the recharge of groundwater using an approach based on the physics of water transfer in the whole domain, including both the saturated and the unsaturated zones. Such a domain is limited by the soil surface and by the lower impervious boundary of the aquifer. The flow problem is solved using a numerical iterative procedure based on the alternate directions implicit finite differences method. To simulate the water transfer in an unsaturatedsaturated porous medium, we developed a mathematical model based on a single flow equation used for both zones. To this end, the unsaturated and saturated zones are regarded as only one continuum and the Richards equation is used for both zones. The simulated results were validated by the calculation of the mass balance, then on values obtained by an experimental model of 160 cm length and 50 cm in height. The numerical model reproduces in a satisfactory way the experimental results giving the spacetime evolution of the level of water table

ETUDE EXPERIMENTALE ET MODELISATION NUMÉRIQUE DES TRANSFERTS HYDRIQUES ET DE SOLUTE DANS UN MILIEU POREUX NON SATURE-SATURE

In this work, a mathematical modeling tool was developped to simulate in a simple and fast way, and with an acceptable precision, the water and solute transfers in unsaturated-saturated porous medium. The resolution of this problem in unstationary mode, is based on the use of an mathematical formulation which consists in considering as a single continuum the saturated and the unsaturated zones. The modeling tool is based on two numerical methods: the alternate directions implicit method (ADI) and the finite elements method (finite elements code Freefem++). This code was adapted to the equations used in this study, namely: Richards’ equation to study the water flow in the unsaturated zone, the diffusivity equation expressed in a linear and nonlinear form for the groundwater flow and the transport equation of advection-dispersion type to study the solute transfer. The advantage of the Freefem++ code is that it generates selfadapting grids. This is interesting to analyse the transfers at singular zones, in particular at the capillary fringe. Experiments were carried out on a laboratory physical model, consisting in a sand filled tank of 160 cm length and 50 cm in height. This experimental model enabled to follow the spacetime evolution of the water-table and the propagation of a tracer (Fluorescein) from the infiltration strip to the discharge system of the model. The modeling tool was validated using experimental data measured on the small-scale physical model and some results taken from the literature. It allowed to predict with an excellent precision the water-table position and the propagation of the non-reactive solute in both unsaturated and saturated compartments. A comparative study between the two numerical methods was carried out and showed that even if the finite differences method provides satisfactory results, the use of the finite elements Freefem++ code presents a light advantage and provides slightly more accurate result

Etude expérimentale et numérique des transferts hydriques et de soluté dans un milieu poreux non saturé-saturé

POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Experimental monitoring and numerical study of pesticide (carbofuran) transfer in an agricultural soil at a field site

We studied the transport of a pesticide at field scale, namely carbofuran molecule which is known for its high mobility, especially in sandy soils with high hydraulic conductivity and low organic matter. To add to our knowledge of the future of this high-mobility molecule in this type of soils, we developed a mechanistic numerical model allowing the simulation of hydric and solute transfers (bromide and carbofuran) in the soil. We carried out this study in an agricultural plot in the region of Mnasra in Morocco. Confrontation of the measured and simulated values allowed the calibration of the parameters of hydric transfer and carbofuran. The developed model accurately reproduces the measured values. Despite a weak irrigation and precipitation regime, carbofuran was practically leached beyond the root zone. Prospective simulations show that under a more important irrigation regime, carbofuran reaches 100cm depth, whereas it does not exceed 60cm under a deficit regime.Peer ReviewedPostprint (published version

Experimental monitoring and numerical study of pesticide (carbofuran) transfer in an agricultural soil at a field site

We studied the transport of a pesticide at field scale, namely carbofuran molecule which is known for its high mobility, especially in sandy soils with high hydraulic conductivity and low organic matter. To add to our knowledge of the future of this high-mobility molecule in this type of soils, we developed a mechanistic numerical model allowing the simulation of hydric and solute transfers (bromide and carbofuran) in the soil. We carried out this study in an agricultural plot in the region of Mnasra in Morocco. Confrontation of the measured and simulated values allowed the calibration of the parameters of hydric transfer and carbofuran. The developed model accurately reproduces the measured values. Despite a weak irrigation and precipitation regime, carbofuran was practically leached beyond the root zone. Prospective simulations show that under a more important irrigation regime, carbofuran reaches 100cm depth, whereas it does not exceed 60cm under a deficit regime.Peer Reviewe