Study area Samsun/Atakum province is almost under threat of flooding in each year. In this region, the main reason of devastating flood is the influence of the Degirmen stream especially during March, April, and July and due to seasonal rainfall, which eventually makes the district vulnerable to flooding. In addition, the human-based constructions and the collapse of water retaining structures are among the main causes of flooding. In this study flood risks of Samsun Degirmen stream determinate by MIKE 11 and GIS.  Numerical model selection for studies provides advantages in developing and changing the solutions with time. The flood modeling studies include the following steps: digitization of topographical data and preparation of digital elevation model using ArcGIS, simulation of flood discharges of different return periods using a hydraulic model (MIKE 11), and preparation of flood risk maps by integrating the results of first two steps. Hydrological models were also created corresponding to 100 and 500-year return period floods. A 1D hydrodynamic model was created with MIKE powered by DHI software; MIKE 11. The flood inundation maps demonstrated that some areas, from the upstream to downstream of the Degirmen stream basin, is affected by 100 and 500-year return period events