The HEC-HMS hydrological model performance in the rainfall-runoff process simulation for the upstream watersheds of Gonbad, Iran

Large flood events occurrence such as the 18 March 2019 flood event in the city of Gonbad in Golestan Province has been often associated with socioeconomic and ecologic damages. The aim of this research is to simulate flood hydrograph using the HEC-HMS hydrological model and to evaluate model performance at the Arazkuseh Watershed outlet, located in the vicinity of Gonbad, and also for the upstream tributaries namely the Minodasht and the Nodeh Khandooz Watersheds. The HEC-HMS model was run by applying the SCS-Curve Number, the SCS-Unit Hydrograph, and the Muskingum-Cunge methods. The parameters of CN, initial abstraction, lag time, and the Manning's roughness coefficient were calibrated for the river gauge stations. The averaged calibrated parameters were used to validate the model at the gauge stations. The sensitivity analysis indicates that CN has the greatest influence on the model performance. The shapes of the simulated hydrographs in the validation stage show that the model underestimates the peak flows for the Arazkuseh Station. Whereas, the statistical indices of NSE, R2 and KGE for the validated hydrographs at the Arazkuseh Station were 0.81, 0.89 and 0.67, for the Nodeh Station were 0.85, 0.91 and 0.74, and for the Lazoreh Station identified as 0.62, 0.72 and 0.61, respectively. The analysis indicates the acceptable performance of the model. Considering the performance of the HEC-HMS model for the Arazkuseh Watershed and its upstream tributaries, the model can be used to predict the hydrological impacts of applying flood risk reduction scenarios in the upstream watersheds of Gonbad.