Evaluation of DRAINMOD Model for Predicting Water Table Depth and Drain Discharge in Subsurface-Drained Paddy Fields

In this research, the applicability of DRAINMOD model for simulating water table fluctuations and subsurface drain discharge variations was evaluated at the consolidated paddy fields of Sari Agricultural Sciences and Natural Resources University. During free drainage period of a canola season (November 28, 2011- April 2, 2012), water table depths and subsurface drain discharges were measured in three subsurface drainage systems including drainage system with drain depth of 0.9 m and drain spacing of 30 m (0.9L30), drain depth of 0.65 m and drain spacing of 30 m (D0.65L30), and drain depth of 0.65 m and drain spacing of 15 m (D0.65L15). The reliability of the model was tested using the statistics including model efficiency (EF), percent error (PE), coefficient of determination (R2), root mean square error (RMSE) and mean deviation (AD). Mean values of measured and simulated water table depths in the calibration treatment (D0.65L15) were both 32.4 cm. For validation treatments, such values were, respectively, 24.1 and 14.1 cm for D0.65L15and 2.1 and 19.7 cm for D0.9L30. EF, PE, R2, RMSE and AD values for predicted drainage discharges ranged from 5.1 to -1.3, 9.1 to 21.6, 0.2 to 0.35, 0.08 to 0.11 and 0.07 to 0.1, respectively. Comparison of measured values with the simulation results showed that DRAINMOD model can be used as a practical tool for predicting the general pattern of water table and drain discharge variations in the study area.