Water mass balance in the case of vertical infiltration

Water movement in the unsaturated zone is an important hydrological process. Richard’s
equation is windily used to describe both soil water infiltration and soil water absorption.
Various methods have been developed to solve Richard’s equation. Wang et al. (2003)
have developed an algebraic model for the description of soil water infiltration, based on
Parlange’s solution of Richard’s equation and on soil retention curve and hydraulic
conductivity equation given by Brooks and Corey. Their model utilizes experimental
measurements of the cumulative infiltration volume and the wetting front distance as
functions of time in order to describe soil water infiltration. The objective of this paper is to
test the accuracy of the Wang et al. algebraic model for the one-dimensional (vertical) soil
water infiltration. A vertical infiltration experiment was conducted on a sandy soil, for the
measurement of the cumulative infiltration volume and the wetting front distance. Soil
water content was determined at selected times and positions, using gamma ray
absorption. Additionally the hydraulic conductivity K(θ) and the soil retention curve Ψ(θ)
were determined. The algebraic model developed by Wang et al., was found simple to
use since the required data are the cumulative infiltration (F), the wetting front distance
(zf) and the initial and saturated soil water content (θi and θs respectively). The results
show a fair agreement between calculated and measured values on soil water content
profiles, hydraulic conductivity and on the water mass balance.