Water Drainage in Layered Soils. Laboratory Experiments and Numerical Simulation

Abstract

Experimental results during first and second drainage in a vertical column of saturated layered soil were compared to those predicted from simulation. The sample was composed of a sandyloam soil overlying a fine sand. The soil water content was measured by using gamma-ray absorption method (Am-241) and the water pressure through tensiometers, arranged vertically along the column and connected to pressure transducers. From the evaluation of moisture and pressure versus time, the characteristic curves Psi(theta) of the layers were obtained and approximated by van Genuchten's analytical equation. The relationship K(theta) between hydraulic conductivity and moisture was estimated by van Genuchten's prediction model. Psi(theta) and K(theta) equations were used as inputs in the numerical model. The drainage of water was simulated by Richard's partial differential equation, which was solved with the finite differences computational scheme type Laasonen. The upper and lower boundary conditions were zero flux and a periodically changing head respectively. Numerical results show a good agreement with experimental data, with small deviations for certain hours.