Simulation of Drainage Water Quantity and Quality Using System Dynamics

The quantity and quality of drainage water in areas with shallow and saline groundwater changes over time until it reaches a balance. The balance time is fairly long and depends on the characteristics of the shallow aquifer. Therefore, it is very important to simulate such phenomena in order to manage drain effluent, especially when it is supposed to discharge into the environment. In this paper, the system dynamics technique was used to simulate the performance of a drainage system in the unsteady state condition. The study used the system dynamic programming tool Vensim. The model developed in this study is capable of predicting many hydrological variables such as water table fluctuation, drainage discharge, and the salinity of drain water and ground water. The model was validated using data collected at a tile-drained experimental site irrigated with shallow ground water located in the Khuzestan province of Iran. The results show that the standard error values in determining accuracy of simulated water table level, drainage discharge, and salinity of drain water are 14.4 cm, $0.43\mathrm{L}/\mathrm{s}$, and $2.8\mathrm{dS}/\mathrm{m}$, respectively. A sensitivity analysis was done to determine the response of simulated results to changes in model parameters. The results indicated a good agreement between the observed and simulated variables, and the model can be used to manage and control saline drainage water and also to prevent environmental damage.