The Flexible Tolerance Method for Estimating Hydrologic Parameters in the Root Zone

Abstract

In this study, a constrained minimization method, the flexible tolerance method, was used to solve the optimization problems for determining hydrologic parameters in the root zone: water uptake rate, spatial root distribution, infiltration rate, and evaporation. Synthetic soil moisture data were first generated using the Richards' equation and its associated initial and boundary conditions, and these data were then used for the inverse analyses. The results of inverse simulation indicate the following. If the soil moisture data contain no noise, the rate of estimated water uptake and spatial root distribution parameters are equal to the true values without using constraints. If there is noise in the observed data, constraints must be used to improve the quality of the estimate results. In the estimation of rainfall infiltration and surface evaporation, interpolation methods should be used to reduce the number of unknowns. A fewer number of variables can improve the quality of inversely estimated parameters. Simultaneous estimation of spatial root distribution and water uptake rate or estimation of evaporation and water uptake rate is possible. The method was used to estimate the water uptake rate, spatial root distribution, infiltration rate, and evaporation using long‐term soil moisture data collected from Nebraska's Sand Hills.

Spatial trends in saturated hydraulic conductivity of vegetated dunes in the Nebraska Sand Hills: Effects of depth and topography

“…Using the model of hydraulic conductivity profile by Beven and Kirkby (1979), where K fs decreases exponentially with depth, Chen and Hu (2004) found K fs decreased by a factor of 5.2 over depths up to 100 cm. In another study, Chen and Yin (2006) calibrated hydraulic parameters in the vadose zone in the NSH by applying inverse numerical modeling to long-term soil moisture observations. Their method resulted in a threefold increase in K fs from the soil surface to 100 cm depth.…”