Dusek J., Dohnal M., Vogel T. (2009), Numerical analysis of ponded infiltration experiment under different experimental conditions, Soil and Water Research, 4, S22-S27.
Abstract
One of the most important properties, affecting the flow regime in the soil profile, is the topsoil saturated hydraulic conductivity (Ks). The laboratory-determined Ks often fails to characterise properly the respective field value; the Ks lab estimation requires labour intensive sampling and fixing procedures, difficult to follow in highly structured and stony soils. Thus, simple single- or double-ring ponded infiltration experiments are frequently performed in situ to obtain the field scale information required. In the present study, several important factors, affecting the infiltration rate during the infiltration experiments, are analysed using three-dimensional axisymmetric finite-element model S2D. The examined factors include: (1) the diameter of the infiltration ring, (2) the depth of water in the ring, (3) the depth of the ring insertion under the soil surface, (4) the size and the shape of the finite-element mesh near the ring wall, and (5) the double- vs. single-ring setup. The analysis suggests that the depth of the ring insertion significantly influences the infiltration rate. The simulated infiltration rates also exhibit high sensitivity to the shape of the finite-element mesh near the ring wall. The steady-state infiltration rate, even when considering a double-ring experiment, is significantly higher than the topsoil saturated hydraulic conductivity. The change of the water depth in the outer ring has only a small impact on the infiltration rate in the inner ring.
Abstract
The main objective of this study is to assess the effect of hysteresis of soil hydraulic properties on model predictions of soil water movement in a variably saturated soil. The model predictions are generated by the S1D model, which is based on numerical solution of one-dimensional Richards’ equation. The analysis is made for a loamy sand soil located in a small headwater catchment. The model is used to simulate the development of soil water pressure during three successive vegetation seasons. Three major simulation scenarios are formulated: the first scenario assumes no hysteresis in soil hydraulic properties, the second scenario involves a predefined hypothetical hysteresis, while the third scenario is based on optimized hysteresis, determined through the inverse modeling procedure. The analysis of the simulation results suggests that, in our case, ignoring hysteresis does not lead to any significant deviation of the model predictions from the observed soil water system responses.
Abstract
This paper focuses on numerical modelling of soil water movement in response to the root water uptake that is driven by transpiration. The flow of water in a lysimeter, installed at a grass covered hillslope site in a small headwater catchment, is analysed by means of numerical simulation. The lysimeter system provides a well defined control volume with boundary fluxes measured and soil water pressure continuously monitored. The evapotranspiration intensity is estimated by the Penman-Monteith method and compared with the measured lysimeter soil water loss and the simulated root water uptake. Variably saturated flow of water in the lysimeter is simulated using one-dimensional dual-permeability model based on the numerical solution of the Richards’ equation. The availability of water for the root water uptake is determined by the evaluation of the plant water stress function, integrated in the soil water flow model. Different lower boundary conditions are tested to compare the soil water dynamics inside and outside the lysimeter. Special attention is paid to the possible influence of the preferential flow effects on the lysimeter soil water balance. The adopted modelling approach provides a useful and flexible framework for numerical analysis of soil water dynamics in response to the plant transpiration.