An analytical solution for bi-level drainage design in the presence of evapotranspiration

The linearized Boussinesq equation incorporating the effect of evapotranspi ration with appropriate initial and boundary conditions was solved analytic ally to predict a fall in the water table in a bi-level drainage system. It was assumed that the evapotranspiration rate decreases linearly with a red uction in the elevation of the water table above the drains. A special case of this solution (i.e. with no evapotranspiration) was verified by compari son with an independent and accepted analytical method, and almost: identic al values of spatial and temporal distribution of water table heights were obtained. The effects of various parameters like evapotranspiration rate an d depth-dependent reduction factor on spacing between bi-level and level dr ains were also studied. Results suggested that inclusion of evapotranspirat ion in the analytical solution for bi-level drainage design in arid and sem i-arid regions is useful and makes a significant difference in spacing. We conclude that in a bi-level drainage system spacing between two drains can be increased by 9.61-13.75% fur soils having a hydraulic conductivity of 3 m/day, if the contribution of evapotranspiration at a rate of 8 mm/day in l owering the water table is taken into account. (C) 2000 Elsevier Science B. V. All rights reserved.