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Most models for subsurface drainage in flat lands are based on the Boussinesq equation. This paper compares a semianalytical model called SIDRA, which assumes a constant water-table shape during the period of water table recession, to a model called SLOP, which is based on a numerical solution to the Boussinesq equation. Solutions were obtained for both steady-state and transient drainage events on flat lands and for drainage under steady-state recharge on sloping lands. The two models were in excellent agreement for steady-state and transient drainage on flat lands. Differences in the shape factors calculated from the two models were always less than 4%. The implicit solutions in SIDRA were also in good agreement with SLOP for sloping lands. The numerical solutions in SLOP were reliable for low slopes but were unstable for conditions in which the streamlines cannot be considered horizontal.