Transient water-table recession in drained lands modeled using HYDRUS and compared with theoretical analyses assuming a succession of momentarily steady states

The transient water-table recession in lands drained by parallel lines of ditches extending down to a horizontal floor was numerically modeled for sand and silty clay when the ditch-water level was dropped from an initial equilibrium level to zero. For initially surface-ponded conditions, numerical results agreed well with analytical recessions that assumed the water table behaved as a succession of momentarily steady states and the specific yield to be that for equilibrium soil-water profiles above the water table. They also agreed for sand, but agreed less for silty clay when the initial water table was at depth. The agreement found between the modeled and analytical results for this simple situation gives confidence in the use of similar analyses in modeling the water-table movement in drained lands subject to more complicated hydrological conditions.