In this study, a two-dimensional numerical model for subsurface flow has been developed for the analysis of unsteady flow for subsurface drains. The governing equation is the two-dimensional Richard’s equation in the mixed form. A strongly implicit finite-difference scheme has been used to solve the governing equation.

The model has been validated using the available analytical results of the one side drains. Validation of the model indicates good agreement between the results. It has been used to simulate a hypothetical case of subsurface drains with parallel drains. The present numerical model can be used to simulate the unsteady subsurface drainage problem having a side drain and parallel drains at both sides.

In areas with periodic irrigations or high intensity rainfall, the assumption of a steady recharge is no longer justified. Under these conditions, unsteady state solution of the flow problem must be applied. Therefore, knowledge of the water table and its fluctuations in the irrigated areas is essential in assessing the possibilities of waterlogging. In case a barrier is to be constructed to keep the polluted water on one side and fresh water on another, a lateral drainage can serve the purpose. The analysis of unsteady flow to subsurface drains has been carried out keeping this in view.

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