Evaluation of Factors Affecting the Fresh and Saline Water Mixing Zone Features in The Irrigated Lands With Shallow and Saline Ground Water

Irrigated lands of Khuzestan are lands with shallow and saline groundwater, in which water losses of deep percolation during irrigation cause that irrigation water, because of the density difference, floats to the top of saline aquifer creating a fresh and saline water mixing zone. In new drainage issues such as reducing the depth of drain insertion aimed to an optimum use of water, dynamic studies on this region and evaluation of factors affecting its features are necessary. In the present study, two farms of sugarcane in south Khuzestan with two different drainage depths were selected. During the study, for each farm, installing pisometers at various depths and different distances from drain collector, the water level inside the pisometers and groundwater salinity were measured. Results indicated that by starting a heavy irrigation, hydraulic load is increased and hydraulic load variance between bottom layer (4 and 5 m) to the surface one ( 1 and 1.3 m) creates a vertical flow of saline water. As well, by reducing the drain insertion depth and increasing the distance from drain collector, in addition of the increase of hydraulic load to 10-15 cm, mixing zone`s thickness increases to 1 m and the mean salinity line in this region reduces to 5-10 percent. But, as well, this region`s features depend on the depth of impermeable layer and existence of sand lenses, as with low depth of impermeable layer and existence of sand lenses, because of the hydraulic load`s lack of increase, mixing zone`s thickness, is reduced and the salinity is highly increased.