Theme 2-13-Drain spacing computation in sloping lands - an analytical approach

Abstract

Subsurface drainage seems to be one of the feasible solutions to solve the problem of waterlogging and salinity, because by providing adequate drainage, both the excess water and harmful salts can be appropriately removed from the root zone. In the present study analytical solution of Boussinesq equation linearized by Baumann's method, incorporating constant or depth dependent evapotranspiration has been obtained to describe spatial and temporal variation of water table between two parallel drains overlying a sloping impermeable barrier. Adopting the practically feasible unsteady state drainage design criteria which stipulates that water table should be lowered by 30 cm in 2 days, once the water table reaches the soil surface, the drain spacings were computed. A computer program was written in FORTRAN 77 to compute the position of maximum water table heights, transient falling water tables for a given spacing, and drain spacing from the implicit analytical solution. Effect of slope of impermeable barrier, various rates of evapotranspiration and values of reduction factor on falling water tables and drain spacing has also been studied and dis-cussed with the help of a numerical example.