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Evaporation and Salt Movement in Soils in the Presence of Water Table¹

ABSTRACT

Evaporation from homogeneous and stratified columns, in the presence of shallow water table, at steady state, was examined. Soils from Syria and Egypt were used. Their hydraulic conductivity-moisture tension curves were determined and fitted to smooth curves represented by Gardner's empirical formula. Solutions obtained by Gardner for the steady flow equations were modified for the boundary conditions of the top and bottom layers then reduced to a dimensionless form with two variables, the relative flux density, and the relative tension at the interface. The resulting equations were used to calculate the evaporation rates. Salt profiles near the surface, at different evaporation rates, were also studied.

In case of homogeneous soil columns the calculated values gave close estimates of the measured evaporation rates. However, the ratio of the calculated to measured rates was 1.3 to 1.6 for stratified columns.

The salt profiles in the top dry layer indicated the polyphasic nature of water movement in this zone. The observed increase in the dispersion coefficient with the solution velocity was more pronounced in soils of wider range of pore size.

¹ Contribution from Dep. of Soils and Water Science, College of Agriculture, Alexandria Univ., Alexandria, Egypt.

² Assistant Professor and Graduate Student, respectively, at the Dep. of Soils and Water Science, College of Agriculture, Alexandria Univ., Alexandria, Egypt.

Received for publication August 13, 1975. Accepted for publication December 28, 1976.