عنوان مقاله [English]
A study was done to determine the optimum dimensions of Gorgan city drainage network using model SWMM. In this study, to calibrate the model, four rainfall events, were used and the speed of the corresponding runoffs in the chosen sub basin were recorded. In this study, Nash-Sutcliff, square root of error and bias error were used as model performance indices in the estimating peak discharge and flow volume. The model calibration results showed that the simulated peak discharge and flow volume are in good correspondence with the observed values and the calibration results were used for the optimum values of parameters. To evaluate and test model validation, two rainfall events, were used. The evaluation results were confirmed the efficiency and accuracy of the model, so that the model performance indices were acceptable in both cases. After evaluating model performance, design rainfall with return period was calculated and model with design return period was performed in respect to the optimal parameters and dimensions of the drainage network. Peak discharge passing through the channels was identified based on design rainfall intensities. The adequacy of existing network to carry runoff with design return period was assessed with regard to model results based on presence or absence of added load and flood conditions at the nodes and channels. According to the model results, 40.1, 30.6 and 12.5 percent of drainage network channels possess critical and flood conditions in 2, 5 and 10 return periods respectively.