Macroscopic and microscopic capillary length and time scales from field infiltration

Estimates of characteristic times to approach steady state flow in multidimensional infiltration in the landscape depend on the magnitude and character of the capillary length scale λc and the associated capillary time scale tc. Here we derive relationships between λc and tc and readily measured field properties sorptivity S and hydraulic conductivity K or S at two supply heads. We explore the relations between λc and tc and other macroscopic and microscopic length, potential, and time scales. In addition, we show that the microscopic characteristic length λm associated with λc gives physically plausible estimates of flow-weighted mean pore dimensions. We contrast values of λc, tc, and λm for undisturbed field soils with those of repacked materials for water supply potentials close to zero. Large λm for the undisturbed surface soils are attributed to preferential flow. Data from here and elsewhere reveal no apparent trend of λc with soil texture, with most λc of the order of 100 mm. We suggest that the characteristic size of devices used to determine hydraulic properties of field soils should be greater than or equal to λc for representative measurements. The geometric mean time of approach to steady state flow when water is supplied at potentials near or greater than zero is found to be 1.7 hours. This value together with published results suggest that the time of approach to steady state flow from multidimensional cavities is of the order of 1 hour for many field situations.

[1]  Brent Clothier,et al.  Measurement of Sorptivity and Soil Water Diffusivity in the Field , 1981 .

[2]  D. Smiles,et al.  Solute Transport During Absorption of Water by Soil: Laboratory Studies and Their Practical Implications , 1978 .

[3]  E. G. Youngs,et al.  Scaling of infiltration behavior in dissimilar porous materials , 1981 .

[4]  J. Philip Linearized unsteady multidimensional infiltration , 1986 .

[5]  S. Zegelin,et al.  Design for a Field Sprinkler Infiltrometer 1 , 1982 .

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

[7]  J. R. Philip,et al.  Reply To “Comments on Steady Infiltration from Spherical Cavities , 1985 .

[8]  M. Sharma,et al.  Spatial variability of infiltration in a watershed , 1980 .

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

[10]  J. Philip Sorption and infiltration in heterogeneous media , 1967 .

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

[12]  Van Genuchten,et al.  A closed-form equation for predicting the hydraulic conductivity of unsaturated soils , 1980 .

[13]  W. Green,et al.  Studies on Soil Phyics. , 1911, The Journal of Agricultural Science.

[14]  D. R. Nielsen,et al.  Scaling of Horizontal Infiltration into Homogeneous Soils , 1972 .

[15]  J. Philip,et al.  THE THEORY OF INFILTRATION: 6 EFFECT OF WATER DEPTH OVER SOIL , 1958 .

[16]  W. R. Gardner,et al.  Comparison of Empirical Relationships between Pressure Head and Hydraulic Conductivity and Some Observations on Radially Symmetric Flow , 1971 .

[17]  P. Carman,et al.  Permeability of saturated sands, soils and clays , 1939, The Journal of Agricultural Science.

[18]  W. R. Gardner,et al.  Solutions and Tests of the Diffusion Equation for the Movement of Water in Soil1 , 1958 .

[19]  I. White,et al.  Use of Sorptivity to Determine Field Soil Hydraulic Properties1 , 1987 .

[20]  D. Farrell,et al.  Determination of Wetting Front Suction in the Green-Ampt Equation1 , 1974 .

[21]  J. Philip ON SOLVING THE UNSATURATED FLOW EQUATION: 1. THE FLUX‐CONCENTRATION RELATION , 1973 .

[22]  Herman Bouwer,et al.  Rapid field measurement of air entry value and hydraulic conductivity of soil as significant parameters in flow system analysis , 1966 .

[23]  D. Smiles,et al.  Absorption of water by soil: some effects of a saturated zone. , 1980 .

[24]  J. Philip,et al.  Theory of Infiltration , 1969 .

[25]  Janice L. Stolzy,et al.  Effects of spatial variability of soil hydraulic properties in water budget modeling , 1977 .

[26]  W. Green Studies in soil physics : I. The flow of air and water through soils , 1911 .

[27]  D. Elrick,et al.  IN SITU MEASUREMENT OF FIELD‐SATURATED HYDRAULIC CONDUCTIVITY, SORPTIVITY, AND THE α‐PARAMETER USING THE GUELPH PERMEAMETER , 1985 .

[28]  John Knight,et al.  ON SOLVING THE UNSATURATED FLOW EQUATION: 3. NEW QUASI‐ANALYTICAL TECHNIQUE , 1974 .

[29]  T. Talsma In situ measurement of sorptivity , 1969 .

[30]  Herman Bouwer,et al.  Unsaturated flow in ground-water hydraulics , 1964 .

[31]  J. Philip,et al.  The Theory of Infiltration , 1958 .

[32]  T. Talsma Re-evaluation of the Well Permeameter as a Field Method for Measuring Hydraulic Conductivity , 1987 .

[33]  Brent Clothier,et al.  Measuring saturated hydraulic conductivity and sorptivity using twin rings , 1982 .

[34]  J. Philip,et al.  THE THEORY OF INFILTRATION: 4. SORPTIVITY AND ALGEBRAIC INFILTRATION EQUATIONS , 1957 .

[35]  S. P. Neuman,et al.  Vadose zone permeability tests: unsteady flow. , 1983 .