Analysis of the Impact of Effective Hydraulic Properties on the Modelling of Heterogeneous Water Flow.

Defining soil hydraulic properties is an important part of using deterministic models for modelling water flow and solute transport in soils. Since hydraulic properties can vary across scales and over space, the most accurate representation of a real soil can be difficult to quantify. Simplified assumptions of the hydraulic properties, called effective hydraulic properties, are often used in modelling applications. The estimation of these hydraulic properties can be done in multiple ways including direct measurements, pedotransfer functions, scaling techniques and inverse modelling. In order to test the effects that different definitions of hydraulic properties have on heterogeneous outflow a modelling exercise was performed in HYDRUS-3D that simulated a previous flow experiment conducted on an undisturbed soil lysimeter in the lab. Spatially-varied outflow was collected from the bottom of the column in 150 outflow cells while multiple flow rates of water were applied to the top of the column over the course of 41 days. While the flow experiment was running periodic measurements of three-dimensional Electrical Resistivity Tomography (ERT) were collected and later used to define the heterogeneous geometry of the model domain. After the completion of the flow experiment 30 core samples of 8 cm diameter x 5 cm height were collected form the lysimeter and hydraulic properties were estimated based on both measurements and inverse modelling. Pedotransfer functions and Miller-Miller scaling techniques were also used to estimate hydraulic properties for each of the 30 core samples based on their particle size distributions. Each set of effective hydraulic properties was used in the HYDRUS model and spatial outflow was calculated. The spatial outflow from the model was then compared to the measured outflows from the column experiment for validation.