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 phenomenainorder tomanagedrain effluent,especially whenitis supposedtodischargeintotheenvironment.Inthis paper,thesystem 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 valuesindeterminingaccuracyofsimulated water table level,drainagedischarge,and salinityof drainwaterare14.4cm, 0.43 L=s,and 2.8 dS=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 drainagewater andalso topreventenvironmentaldamage
