The integration of GIS and hydrological modelling appears to be an essential approach for efficient management of water resources, especially in contexts where data is scarce. The objective of this study is to carry out a hydrological modelling of rain-flow in the basin of ‘cedar isser’ by integrating the HEC-HMS model and the GIS. This approach will simulate the basin’s hydrological response to various rainfall events. To assess the flood risk of this river, the HEC-HMS model was combined with the HEC-GeoHMS extension in ArcGIS. Based on 23-year rainfall data and the HEC-HMS hydrological model, we simulated a 24-hour rain corresponding to a 100-year return period. Runoff volume was estimated using the Curve Number (SCS-CN) method., then converted to a flood hydrogram using the SCS unit hydrogram method. This approach has made it possible to simulate the excess of rainwater and its runoff path through the watershed. The results indicate that the fast and intense flows of the centenary flood of the river of ‘cedra isser’ is 698.9 m3/s with 60.96mm loss volume; The results showed that the observed and simulated hydrographs were highly correlated with a coefficient of 0.879 ,The performance of the model was evaluated using an NSE coefficient that equals 0.816, Results indicate that the model is suitable for hydrological needs simulations in the cedar isser basin,This study contributes to better management of water resources for the purpose of flood control.