Estimating Soil Hydraulic Parameters By Using Green and Ampt Infiltration Equation

Infiltration is the process of water movement from the ground surface into the soil and is an important process in the hydrological cycle. In this study, a mathematical equation of the upward-advancing wet front is derived from the Green and Ampt infiltration model, and a new method is proposed to estimate the values of soil hydraulic parameters such as unsaturated hydraulic conductivity ($K$) and the capillary pressure head (${\Psi }_f$). In the proposed method, these parameters are estimated from the advancing wet front data or infiltration test data under constant head. Experiments in which water flow is entered into the unsaturated soil column from beneath under constant head and the advancing wet front is recorded with the time are conducted on the five uniform sandy soils for different values of the saturation ratio (Sr). Results indicated that hydraulic parameters of unsaturated soils are not constant values. With increasing soil water content, $K$ is decreased from $1.69K_s$ at $\mathrm{Sr}=0\%$ to $K_s$ at $\mathrm{Sr}=100\%$. But the value of ${\Psi }_f$ is first decreased and then increased until reaching zero at $\mathrm{Sr}=100\%$.