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

Abstract

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.