Using SEEP / W Numerical Model to Simulate Drain Installation Depth Effects on Drain Water Salinity Improvement

Drian installation depth is one of the most important challenges in drainage network design and construction. Deep drain installation leads to increase inflow volume to the drain and causes to decrease drain water quality. In the other hand, deep drains washes deeper soil profile and discharges traped salts in lower layers to final outlet. The objective of this study was to find the optimum drain installation depth to reduce drain volume and improve drain water quality. To do this, a laboratory investigation was carried out as well as numerical simulation. Drainage pipes were installed in 0.25, 0.5 and 0.85 m depth within a sand box filled with three silty clay soil layers with initial salinity of 12.7, 31.2 and 67.5 dS/m, respectively from top to bottom. Drain outflow volume and water quality from the sand tank were measured. The laboratory test was simulated using SEEP/W software and the results showed that a deeper soil profile has been leached by increasing drain installation depth, and streamlines flew to a deeper layer and then moved back to the drain pipes. In addition, drain outflow rate was computed using the software. The results showed that the outflow rate increases with drain depth. So, it could be concluded that reduction in drain depth leads to inprove drain water quality and decrease in drainage volume.