TR(BR)-2/98-99 : Analysis of unsteady flow for subsurface drains

Abstract

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. A knowledge of the water table and its fluctuations in the irrigated area is therefore essential in assessing the possibilities of water logging. Even if any barrier is to be constructed to keep the polluted water one side and fresh water in another side in that case also a lateral drainage can serve the purpose. Keeping this in view, the analysis of unsteady flow to subsurface drains has been carried out.

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 Richards equation in the mixed form. A strongly implicit finite-difference scheme has been used to solve the governing equation. The present model has been validated using the available analytical results for one side drain. The model 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 one side drain and parallel drains (drain at both sides).