Predicting wetting front advance in soils using simple laboratory derived hydraulic parameters

An approximate simulation of wetting front advance or leaching time is often the necessary and sufficient information required to optimize irrigation strategies or wastewater land treatment systems. For such simulations, we show that only three physically comprehensible and easily measured parameters are necessary, namely the saturated hydraulic conductivity, and the slope and the intercept of the soil-water potential plotted against the natural logarithm to the soil-water content. We derived the new 3-parameter simulation model from a fully linear flow model based on the Richards equation with the additional assumption of zero conductivity at zero soil-water content. A simple analytical solution for water infiltration during saturation at the soil surface, based on the 3-parameter model, gave results that compared well with measured wetting front advances in three Danish loamy and coarse sands and, also, with semi-analytical and numerical solutions from literature. Less agreement between predicted and measured wetting front advance was observed during infiltration into an initially dry forest soil due to extreme soil-water repellency. The presented derivation procedure assuming linear water flow seems promising for obtaining simple, approximate analytical solutions for unsaturated flow problems.