Impact of soil heterogeneity on the water budget of the unsaturated zone

The impact of soil heterogeneity on the spatially average water budget of the unsaturated zone is investigated using a framework of analytical solutions. This framework was previously shown to adequately represent the long-term average water budget as well as its transient evolution. Nine combinations of three climate and three soil types are considered, covering a wide range of different conditions. In highly conductive soils, where evapotranspiration is limited by percolation through the lower boundary, heterogeneity increases the spatially average evapotranspiration relative to the uniform (scaled average) soil. In contrast, for less conductive soils the decreasing infiltration rates due to soil heterogeneity cause evapotranspiration to become smaller. Formally derived “equivalent” parameters, which are intended to capture the effect of soil heterogeneity by means of one set of soil hydraulic parameters, are shown to depend not only on the spatially heterogeneous parameters, but on climate as well. Moreover, the “equivalent” parameters derived for the long-term average water budgets are not valid for transient behavior.

[1]  R. Bras.  Hydrology : an introduction to hydrologic science , 1990 .

[2]  J. Stricker,et al.  An Analytical Framework for the Water Budget of the Unsaturated Zone , 1996 .

[3]  D. R. Nielsen,et al.  Scaling Field-Measured Soil Hydraulic Properties Using a Similar Media Concept , 1977 .

[4]  Peter S. Eagleson,et al.  Climate, soil, and vegetation: 2. The distribution of annual precipitation derived from observed storm sequences , 1978 .

[5]  R. J. Luxmoore,et al.  Soil spatial variability and its consequences on simulated water balance , 1979 .

[6]  Rao S. Govindaraju,et al.  Spatial averaging of unsaturated flow equations under infiltration conditions over areally heterogeneous fields: 1. Development of models , 1994 .

[7]  R. H. Brooks,et al.  Properties of Porous Media Affecting Fluid Flow , 1966 .

[8]  Rao S. Govindaraju,et al.  Spatial averaging of unsaturated flow equations under infiltration conditions over areally heterogeneous fields 2. Numerical simulations , 1994 .

[9]  E. E. Miller,et al.  Physical Theory for Capillary Flow Phenomena , 1956 .

[10]  Walter J. Rawls,et al.  Variation within Texture Classes of Soil Water Parameters , 1980 .

[11]  Peter S. Eagleson,et al.  Climate, soil, and vegetation: 1. Introduction to water balance dynamics , 1978 .

[12]  Peter S. Eagleson,et al.  Climatology of Station Storm Rainfall in the Continental United States: Parameters of the Bartlett-Lewis and Poisson Rectangular Pulses Models , 1992 .

[13]  Peter S. Eagleson,et al.  Effects of spatial variability on annual average water balance , 1987 .

[14]  Gedeon Dagan,et al.  Unsaturated flow in spatially variable fields: 2. Application of water flow models to various fields , 1983 .

[15]  Jan W. Hopmans,et al.  Stochastic analysis of soil water regime in a watershed , 1989 .

[16]  J. Parlange,et al.  A parameter‐efficient hydrologic infiltration model , 1978 .

[17]  J. Stricker,et al.  INFLUENCE OF SPATIALLY VARIABLE SOIL HYDRAULIC PROPERTIES AND RAINFALL INTENSITY ON THE WATER BUDGET , 1996 .

[18]  David Russo,et al.  Soil Hydraulic Properties as Stochastic Processes: I. An Analysis of Field Spatial Variability , 1981 .

[19]  Gedeon Dagan,et al.  Unsaturated flow in spatially variable fields: 1. Derivation of models of infiltration and redistribution , 1983 .

[20]  Roger David Braddock,et al.  THE THREE‐PARAMETER INFILTRATION EQUATION , 1982 .