UM-44 : User's manual for design of drainage system for steady and unsteady state

Abstract

Using Dupuit (1863) Forchheimer (1930) assumptions Donman has derived equation for drain spacing for steady state condition of discharge. The similar equation using eauivalent depth (d) in place of depth to impervious laver (D) has been obtained by Hooahout for steady state condition of recharge.

The Boussinesq-equation which describes the position of water table under non steady state of recharge, has been solved by Glover Glover assumed an initial horizontal around water table as a result of an instantaneous recharge of rainfall or irriaation. Dumm solved the same equation for the initial water table corresponding to the shape of Fourth degree parabola. This equation which is known as Glover Dumm equation was modified by placing d in place of D to account for flow converaence in the vicinity of drains. This substitution also made the equation applicable to pipe drainage.

The Boussinesq-equation was further solved in this report for the constant and continuous recharge, constant recharge during a restricted period and intermittent recharge conditions. Computer programs are prepared for steady and unsteady state condition using Hooghouts and Glover, Dumm, Glover Dumm and Modified Glover Dumm equations respectively. Separate programs are also prepared for the condition of constant and continuous recharge, constant recharge during a restricted period and intermittent recharge. The computer program developed are interactive type and can be easily used by field engineers.