Effect of Drain Diameter, Openings and Envelopes on Water Table Drawdown

Abstract

ABSTRACT NUMERICAL solutions to the Richards equation for saturated and unsaturated flow to parallel drains were used to determine the effects of drain tube diameter, openings and envelopes on water table draw-down. Conventional drain tubes with a finite number of openings in the walls were represented as completely open tubes with an effective radius, re. The effect of drain tube size and the use of envelopes on water table drawdown was determined for different soils, drain spacingS and profile depths. It was concluded that envelopes will allow an increase in drain spacing without reducing the design drawdown rate. However the allow-able spacing increase is smaller than previously reported in the literature. The midpoint drawdown rate was found to be relatively insensitive to changes of one or two sizes in the drain tube diameter. Finally it was shown that the effect of drain tube diameter on drainage rates is dependent on drain spacing and profile depth as well as hydraulic properties of the soil.