Laboratory Experiments of Drainage, Imbibition and Infiltration under Artificial Rainfall Characterized by Image Analysis Method and Numerical Simulations

Belfort Belfort,Weill Weill,Lehmann Lehmann,Fahs Fahs

doi:10.3390/w11112232

Abstract

Two laboratory experiments consisting of drainage/imbibition and rainfall were carried out to study flow in variably saturated porous media and to test the ability of a new measurement method. 2D maps of water content are obtained through a non-invasive image analysis method based on photographs. This method requires classical image analysis steps, i.e., normalization, filtering, background subtraction, scaling and calibration. The procedure was applied and validated for a large experimental tank of internal dimensions 180 cm long, 120 cm wide and 4 cm deep that had been homogenously packed with monodisperse quartz sand. The calibration curve relating water content and reflected light intensities was established during the main monitoring phase of each experiment, making this procedure very advantageous. Direct measurements carried out during the water flow experiments correspond to water content, pressure head, temperature, and cumulative outflow. Additionally, a great advantage of the proposed method is that it does not require any tracer or dye to be injected into the flow tank. The accuracy and other benefits of our approach were also assessed using numerical simulations with state-of-the-art computational code that solves Richards’ equation.

Highlights

The vadose zone (VZ), situated between the soil surface and the groundwater table, supports many processes linked to the hydrological cycle
The quantification of water dynamics in porous media is important to assess the effects of water management actions dealing with agricultural irrigation or water supply plans
The water content, and by extension the saturation of the media, is a key variable involved in the characterization and modelling of flow in the VZ

Summary

Introduction

The vadose zone (VZ), situated between the soil surface and the groundwater table, supports many processes linked to the hydrological cycle. The disciplines of soil physics, hydrology and agronomy study the VZ mainly through the lens of water flow and distribution. The water content, and by extension the saturation of the media, is a key variable involved in the characterization and modelling of flow in the VZ. The relationships between pressure head, water content, and hydraulic conductivity have been widely studied with respect to the water retention curve or soil water characteristic curve [7,8]. Water content is involved in the transport of solutes and pollutants (evaluation of pollution of groundwater reservoir, salinization, etc.), or in chemical reactions and

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