Evaluation of DRAINMOD-S in Simulating Drainage Water Salinity of Subsurface Drains

After installing subsurface drainage system, quality of drainage water in saline lands continuously changes, starting from the beginning of irrigation and drainage network operation, until reaching a more or less equilibrium state. Reaching a state of equilibrium in areas with saline groundwater may take several years. In this regard, field experiments are useful but they also have significant limitations. As an alternative, simulation models are among the methods that greatly eliminate these limitations. Therefore, in this research, the performance of DRAINMOD-S model was evaluated in simulation of drainage volume, drainage water salinity, and water table fluctuations. To validate the results of the model, data collected in the 2007-2008 cropping year from ARC18-18 farm was used in the research site of Sugarcane Research Center (Amir Kabir Agro Industrial Development Unit of Sugarcane Development Company, Khuzestan Province). This information included meteorological and soil data, drainage outflow, irrigation water salinity, water salinity within piezometers, and drainage water salinity. After statistical analysis and calculating the root mean square error (RMSE) and standard error (SE), the fits between the measured and simulated values of drainage water salinity, groundwater salinity, water table fluctuations and drainage discharge were investigated. The RMSE statistical index was 4.76 dS /m for drainage water salinity, 0.82 dS/m for groundwater salinity, 21.2 cm for groundwater surface and 2.1 L/s for the drain discharge, which indicated a fairly good accuracy compared with actual conditions. The results showed that the model was capable of simulating the water level fluctuations, drainage outflow and its salinity in Khuzestan region with saline and shallow groundwater table.