EFFECT OF DEPTH OF IMPERVIOUS LAYER AND ADSORPTION ON SOLUTE TRANSPORT IN TILE-DRAINED IRRIGATED LANDS

A two-dimensional finite element model of solute transport in a tile-d rained soil-aquifer system was applied to study the effect of the dept h of impervious layer and adsorption on salt distribution in the soil and groundwater, and the salinity of drainage effluent. The model cons iders steady state water flow in the unsaturated and saturated zones, and includes the effect of convective transport, dispersion and linear adsorption. The results indicate that though the depth of the impervi ous layer has little effect on salt distribution in the unsaturated zo ne, it significantly influences the quality of the drainage effluent. Further, it was found that during the initial years of reclamation of a highly saline soil with subsurface drainage, the effect of adsorptio n is more pronounced in the unsaturated zone than in the saturated zon e and the movement of adsorbing solute species is retarded for a longe r time in the groundwater than in the soil.