عنوان مقاله [English]
At designing stage of subsurface drainage systems, the direction of surface irrigation is considered perpendicular to the orientation of drain pipes. However in practice, irrigation might be conducted alongside the subsurface drains for executive reasons. The purpose of this study is to simulate and compare the performance of subsurface drainage along and perpendicular to the irrigation by the DRAINMOD model. Therefore, measured data from 4 experimental units (including water table and drains discharge) in one of the irrigation and drainage projects in Mian-Aab plain of Khuzestan province was utilized. Irrigation was perpendicular to subsurface drains in 2 units (each unit contains 5 lines of subsurface drains) and parallel in the others. To compare the observations and results of the model, operation of the model in simulating water table in both treatments were calibrated and validated. Root Mean Squared Error (RMSE) in the calibration and validation periods for treatment in which drainage is perpendicular to irrigation was respectively 10.25 and 12.97, and in treatment with parallel drains to the irrigation direction was 13.04 and 13.87. These values represent success of the model in simulation of water table in both treatments. Since, irrigation is conducted based on allocated water rights in the experimental units with deficit irrigation conditions; possibility of full irrigation in the units is investigated at irrigation efficiency of 33%, 40% and 45% by the model. The results of simulation showed that drains can successfully control water table at irrigation efficiency of 45% and full irrigation might be possible in this irrigation efficiency.