Flood modeling in Samsun Engiz Stream: Evaluation of the adequacy of river sections with HEC-RAS

Floods pose a significant threat to communities, particularly in Turkey's Central Black Sea Region, where they cause widespread economic, social, and environmental damage. The Ondokuzmayis district of Samsun has been especially vulnerable to recurrent flooding, emphasizing the need for precise risk assessments and effective flood management strategies. In this study, the flood modelling of Engiz Stream, located in the Ondokuzmayis district of Samsun, was conducted using one-dimensional modeling due to its speed, low computational cost and ease of implementation. Hydraulic modeling was performed in HEC-RAS using flow data from Ballıca Station on Engiz Stream and statistical distributions from the EasyFit software library. In the study, flow rates for 25, 50, 100, and 500-year flood return periods (Q25: 431 m³/s, Q50: 479.87 m³/s, Q100: 531.75 m³/s, Q500: 665.37 m³/s) were calculated, and the flow was modeled using a 5-meter resolution digital surface model. The modeling results indicated that while the cross-sections in urban areas were adequate, the river cross-sections in the agricultural areas where the river flows into the Black Sea were insufficient for the Q25 flow rate and beyond.