A Simplified Falling‐Head Technique for Rapid Determination of Field‐Saturated Hydraulic Conductivity

Simplified measurements of the field‐saturated hydraulic conductivity, K fs , require short duration experiments, small water volumes, and easily transportable equipment. A simplified falling‐head (SFH) technique for the rapid determination of K fs has been developed and tested. The technique consists in applying a small volume of water on a soil surface, confined by a ring inserted a short distance into the soil, and then measuring the time from the application of water to the instant at which the surface area is no longer covered by water. A measurement of the initial and field‐saturated soil water contents, and an estimate of the α* parameter of the Gardner's exponential model are then used to calculate K fs using a simple solution that includes gravity. The K fs of both repacked and undisturbed soil cores was determined in the laboratory by the SFH and the early time constant‐head (ECH) techniques. The SFH and (constant‐head) pressure infiltrometer (PI) techniques were then compared in the field. The maximum discrepancy between the mean K fs results obtained within an experiment was of a factor of approximately two. This difference is negligible in most practical applications and it was concluded that the SFH technique compared favorably with the ECH technique in the laboratory and to the PI technique in the field. The SFH technique appears promising for determining K fs in a relatively short period of time without the need for extensive instrumentation or analytical methodology, and therefore it appears suitable for detailed field measurements over large areas.