New Drainage Formulas Considering Delayed Gravity Response and Evaporation from Shallow Water Table
Drainage formulas usually can be classified into two categories: steady flow formulas for the cases of long lasting rainfall or closely spaced drains and nonsteady flow ones for the cases of short period rainfall and irrigation water infiltration. In the latter cases the specific yield and evaporation from water table are the important parameters involved in the drainage formulas. As shown by W. Zhang and Y. Zhang (1982) the drain-able porosity for a certain soil is a function of rate of drawdown and initial depth to ground water table, as well as intensity of evaporation. The formulas for water table draw-down with delayed gravity response have been developed by Neuman (1982) on the basis of 2-D flow equations.
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