Hydraulic Parameters in Heterogeneous Soils: Temporal Vs. Spatial Variability.

This study investigates effective soil hydraulic properties applicable to transient infiltration in heterogeneous soils. The main idea is to utilize time frame dependent-effective hydraulic parameters to effectively represent spatially variable infiltration processes. Specifically, the objectives are to investigate: 1) how the effective hydraulic parameters are sensitive to the process time frame, and 2) how hydraulic parameter variability and correlation impact the effective hydraulic parameters.  The heterogeneous landscape is represented by a series of vertically homogeneous parallel columns. The optimal effective hydraulic parameters are then calculated with an inverse procedure that minimized the difference between average cumulative infiltration and cumulative infiltration based on a single set of effective parameters. The sensitivity of the effective hydraulic parameters to the time frame of infiltration is examined. We further investigate the influence of various factors on the effective hydraulic parameters, such as hydraulic parameter correlation, surface ponding depth, groundwater table depth, local-scale hydraulic parameter sampling population, and hydraulic parameter variance. Results illustrate that the effective hydraulic parameter values may need to be adjusted as time evolves.  During the initial stage of infiltration, the effective parameters may vary significantly with time. At later stages, the effective parameters reached asymptotic and constant values, thus reflecting better applicability of the effective parameter concept. A more pronounced transition between infiltration types would make it more difficult to use the effective homogeneous medium idea, in which case effective hydraulic parameters are more difficult to define for the heterogeneous soils.