The use of numerical groundwater model to improve effectiveness of subsurface drainage system in irrigated field

The research demonstrates that Three-Dimensional Variable-Density Groundwater Flowmodels such as the SEAWAT model can be effectively used for design of subsurfacedrainage systems for controlling salt concentration in the root zone on salt affectedirrigated land. The SEAWAT model was used to optimize subsurface drainage design toensure that the salt concentration of the groundwater at the base of the root zone does notexceed pre determined levels instead of the conventional approach of maintaining thegroundwater at a predetermined water table level. The study was carried out on aconceptual uniform homogenous block of irrigated flat field of shallow water table depthof 0.5 m and salt concentration of 7200 mg/l with impermeable layer at 20 m deep andimpermeable field boundaries. Using the model, spacings were designed to be used asdesign criteria for subsurface drainage system to maintain salt concentrations of 6000,5000 and 4000 mg/l at the base of the root zone and water table depth of 0.8 m from thesoil surface. The results showed that over a wide range of irrigation water quality andaquifer hydraulic conductivity the optimum drain spacing using SEAWAT was,depending on irrigation water quality and aquifer hydraulic conductivity, wider bybetween 3 and 50 % and the amount of drain discharge reduced by 1 and 27 % thanwould be recommended using conventional design equations.It was concluded that Three-Dimensional Variable-Density Groundwater Flowmodels are better for designing effective drainage systems than Conventional drainspacing design equations such as Hooghoudt