Hybrid Finite Analytic Solution for Computation of Spacing between Drains in Sloping Lands

Rise in groundwater and salinity levels causes water congestion and soil salinization in the root zone of the crop, which adversely affects the growth and development process of plants, leading to reduced production. Thus, water table and salinity should not be allowed to encroach and occupy root zone longer than the crop tolerance period, and a suitable technique should be adopted for its control. Subsurface drainage seems a feasible alternative to overcome such a problem. In the present study, hybrid finite analytic solution of a one-dimensional Boussinesq equation incorporating evapotranspiration has been obtained to describe spatial and temporal variation of water table between two drains in a sloping unconfined aquifer. Assuming the unsteady state drainage criteria of a 30 cm fall of water table within 2 days once it has reached near the land surface, the spacing between two drains has been computed, and the effect of slope of the impermeable barrier, evapotranspiration (ET), depth dependent reduction factor on spacing, and water table fall has been studied and discussed with the help of a numerical example. It was observed that consideration of ET and the slope of the impermeable barrier results in an increase in spacing between two drains and economizes the design. Fall of water table in the midregion computed by hybrid finite analytic solution is faster than the fall computed by existing analytical solution. Similarly, spacing between drains computed by hybrid finite analytic solution is more than the spacing computed by the existing analytical solution.