University of California

Movement of water through soil as influenced by osmotic pressure and temperature gradients


J. Letey

Author Affiliations

J. Letey was Professor of Soil Physics and Soil Physicist in the Experiment Station, Riverside.

Publication Information

Hilgardia 39(14):405-418. DOI:10.3733/hilg.v39n14p405. November 1968.

PDF of full article, Cite this article


The equation used to describe steady-state water flow through a soil in response to hydraulic pressure (or suction in unsaturated soil), osmotic pressure, and temperature gradients is Jv = Lvv grad P + LvD grad ? - Lvq grad T. Published research results indicate that Lvq is relatively independent of suction when suctions are greater than about 0.06 bar, becomes quite small when suctions are lower than 0.06 bar, and increases in a predictable manner as the average temperature increases. A value of 3.0 × 10-3 cm2deg-1hr-1 is suggested for Lvq for estimates of water flow in response to temperature gradients. LvD can be considered to be zero for suctions less than about 0.25 bar except under conditions of very high clay content. The value of LvD is not likely to be greater than 10 per cent of Lvv (3 per cent is suggested for approximate calculations) at suctions between 0.25 and 1 bar. LvD would more nearly equal Lvv at greater suctions, but no data are available on this relationship at higher suctions. The suggested values of Lvq and LvD are based on relatively few data and are to be considered as approximate. Additional data are required for more specific values for these coefficients.

Literature Cited

Mahmoud H., Taylor S. A. ABd-EL-AZiz. Simultaneous flow of water and salt through unsaturated porous media. I. Rate equations. Soil Sci. Am. Proc. 1965. 29(2):141-43. DOI: 10.2136/sssaj1965.03615995002900020010x [CrossRef]

Gary J. W. Onsager’s relation and the non-isothermal diffusion of water vapor. Jour. Phys. Chem. 1963. 67(1):126-29. DOI: 10.1021/j100795a030 [CrossRef]

Gary J. W. An evaporation experiment and its irreversible thermodynamics. Int. Jour. Heat Mass Transfer. 1964. 7(5):531-38. DOI: 10.1016/0017-9310(64)90050-X [CrossRef]

Gary J. W. Water flux in moist soil: thermal versus suction gradients. Soil Sci. 1965. 100(3):168-75. DOI: 10.1097/00010694-196509000-00004 [CrossRef]

Cary J. W., Taylor S. A. The interaction of the simultaneous diffusions of heat and water vapor. Soil Sci. Soc. Am. Proc. 1962a. 26(5):413-16. DOI: 10.2136/sssaj1962.03615995002600050004x [CrossRef]

Cary J. W., Taylor S. A. Thermally driven liquid and vapor phase transfer of water and energy in soil. Soil Sci. Soc. Am. Proc. 1962b. 26(5):417-20. DOI: 10.2136/sssaj1962.03615995002600050005x [CrossRef]

Hanks R. J., Gardner H. R., Fairbourn M. L. Evaporation of water from soils as influenced by drying with wind or radiation. Soil Sci. Soc. Am. Proc. 1967. 31(5):593-98. DOI: 10.2136/sssaj1967.03615995003100050001x [CrossRef]

Katchalsky A., Curran PEter F. Nonequilibrium thermodynamics in biophysics. 1965. Cambridge, Mass: Harvard University Press. 263p.

Kemper W. D., Evans N. A. Movement of water as affected by free energy and pressure gradients. III. Restriction of solutes by membranes. Soil Sci. Soc. Am. Proc. 1963. 27(4):485-90. DOI: 10.2136/sssaj1963.03615995002700050007x [CrossRef]

Kemper W. D., Rollins J. B. Osmotic efficiency coefficients across compacted clays. Soil Sci. Soc. Am. Proc. 1966. 30(5):529-34. DOI: 10.2136/sssaj1966.03615995003000050005x [CrossRef]

Letey J., Kemper W. D. Flow of water and dissolved salts through clay mineral strata—Theory and experimental data. Amer. Assoc. Petroleum Geologists Monogr. 1968.

Letey J., Kemper W. D., Noonan L. The effect of osmotic pressure gradients on water movement in unsaturated soil. Soil Sci. Soc. Am. Proc. 1968.

Weeks L. V., Richards S. J., Letey J. Water and salt transfer in soil resulting from thermal gradients. Soil Sci. Soc. Am. Proc. 1968. 32(2):193-97. DOI: 10.2136/sssaj1968.03615995003200020014x [CrossRef]

Letey J. 1968. Movement of water through soil as influenced by osmotic pressure and temperature gradients. Hilgardia 39(14):405-418. DOI:10.3733/hilg.v39n14p405
Webmaster Email: wsuckow@ucanr.edu