Study of using multi-step falling-head infiltration to estimate hydraulic conductivity at various depths

Most infiltration methods measure the saturated hydraulic conductivity (K _s) of the unsaturated zone at only one depth at or near the surface. The proposed model is extended the falling-head infiltration theory to a multi-step falling-head infiltration test (MSFIT) for estimating K _s at various depths in a one-dimensional saturated vertical flowdomain. Water content sensors at various depths are required to add to the MSFIT. The resolution of the MSFIT is determined by the number of steps and the change of the ponded water head. The MSFIT is performed in three independent laboratory two-layer sand columns. The estimated hydraulic conductivity shows a consistent decrease in three independent laboratory sand column tests and is in agreement with the value obtained from twelve core samples using the constant-head method. The proposed MSFIT is simple, flexible, and versatile for obtaining hydraulic conductivity at various depths for one-dimensional saturated vertical flow domains.