The effect of soil suction on evaporative fluxes from soil surfaces

Abstract

This paper presents a theoretical approach in which a Dalton-type mass transfer equation is used to predict the evaporative fluxes from nonvegetated soil surfaces. Soil evaporation tests were conducted in the laboratory on three different soil samples of Beaver Creek sand, Custom silt, and Regina clay. The soil surfaces were saturated and allowed to evaporate to a completely air-dried state. The actual evaporation rate for each soil surface was measured along with the potential evaporation rate for an adjacent water surface. The ratio of actual evaporation to potential evaporation or normalized soil evaporation was then evaluated with respect to drying time, soil-water content, and soil suction. The value of the normalized soil evaporation was found to be approximately equal to unity for all soils until the total suction in the soil surfaces reached approximately 3000 kPa. The rate of actual soil evaporation was observed to decline when the total suction exceeded 3000 kPa. A relationship between the actual evaporation rate and total suction was found to exist for all three soil types which appears to be unique and independent of soil texture, drying time, and water content.Résumé : Cet article présente une approche théorique dans laquelle une équation de transfert de masse de type Dalton a été utilisée pour prédire les flux d'évaporation des surfaces de sol non couvertes de végétation. Des essais d'évaporation des sols ont été faits en laboratoire sur trois échantillons de sols différents, soit un sable de Beaver Creek, un silt Custom, et une argile de Regina. Les surfaces du sol ont été saturées et soumises à une évaporation jusqu'à un état de sècheresse complète à l'air. La vitesse réelle d'évaporation pour chaque surface de sol a été mesurée en même temps que la vitesse d'évaporation potentielle d'une surface d'eau adjacente. Le rapport de l'évaporation réelle sur l'évaporation potentielle, ou l'évaporation normalisée du sol, était alors évalué par rapport au temps de séchage, de la teneur en eau et de la succion du sol. L'on a trouvé que la valeur de l'évaporation normalisée du sol était approximativement égale à l'unité pour tous les sols jusqu'a ce que la succion totale dans les surfaces de sol atteignent approximativement 3000 kPa. L'on a observé que la vitesse de l'évaporation réelle du sol diminue lorsque la succion totale dépasse 3000 kPa. Il existe une relation entre la vitesse d'évaporation réelle et la succion totale pour les trois types de sol qui semble être unique et indépendante de la texture du sol, du temps de séchage, et de la teneur en eau.

Estimating hydraulic conductivity of internal drainage for layered soils in situ

“…Despite small differences in θ s between sandy and clay textured horizons, θ r showed remarkable variability with change in clay content with a range of 0.19 to 0.26 mm mm −1 observed for a clay content range of 35 to 48 %. These findings are similar to those made from sandy and clayey horizons by various authors (Wilson et al, 1997;Wildenchild et al, 2001;Fraenkel, 2008;Chimungu, 2009). Sandy soils are well known for their large volume of macro-pores that drain readily at near saturation as a result of the small air-entry value that was approximated at −1 kPa.…”

In situ unsaturated zone water stable isotope (<sup>2</sup>H and <sup>18</sup>O) measurements in semi-arid environments: a soil water balance

“…As discussed earlier, diurnal temperature and humidity cycles could cause not only condensation in the upper part of the soil profile but also higher enrichment during the daytime as compared to the conditions during the night, when the soil is colder than atmospheric vapor. Further, the interaction between soil water potential and water vapor might be driven by relative humidity (Wilson et al, 1997), but its effect on isotope fractionation is not well understood and will be a challenge for future research (Soderberg et al, 2012). The investigation of such processes using in situ approaches for stable isotope analysis seem to be promising in this regard, since the composition of vapor can be measured in the field.…”

Physically based approaches incorporating evaporation for early warning predictions of rainfall-induced landslides

“…-vapor pressure ( ) or, alternatively, vapor water flux ( ) ; the boundary value problem was addressed by quantifying the former from air relative humidity and air temperature records; provides the ratio ( ) ( 0 ) ⁄ , while provides 15 the partial pressure of the vapor phase in saturated conditions ( 0 ) using the Tetens equation (Tetens, 1930); -temperature is assumed to equal air temperature measured two meters above the surface of the ground, in line with the approach followed by Wilson et al (1997).…”