Creating flood risk map of Giresun Aksu River by using hec-ras

Floods are one of the most common natural disasters in Türkiye and around the world. Climate change due to global warming, problems in riverbed sections, the diversity and intensity of human activities in river basins especially in cities are some of the events that cause floods. In Giresun, which is one of the places where floods and overflow events are most common in our country due to its climatic conditions and geomorphological characteristics, urbanization without considering flood and overflow risks causes great loss of life and property. Due to the serious loss of life and property it causes, it is of great importance to determine in advance the areas that may be at risk from floods and to calculate the damages they may cause. While flood risk maps reveal what kind of damage the region will suffer from a possible flood disaster and what precautions should be taken, they also provide information for the correct preparation of construction plans and land use. Within the scope of the thesis, flood risk analysis was carried according to the return periods of 100, 200, and 500 years using Geographic Information Systems (GIS), Digital Elevation Model (DEM) and a hydraulic analysis program HEC-RAS, in the Aksu, Çaykara and Küçükköy neighbourhoods including the Etbaşoğlu bridge which are located in the Giresun Aksu River basin. According to the analysis results, the precautions to be taken and the necessary solutions were presented. Return periods were calculated by SCS unit hydrograph method, Snyder unit hydrograph method and flood frequency analysis. For flood frequency analysis, the most used probability distributions in the literature, Lognormal (Log-N), 3-Parameter LN (3P-LN), General Extreme Value (GED), Gumbel and log-Pearson type 3 (LP-3), were used. It was determined that the most appropriate probability distribution for frequency analysis was LP-3. In this study, the values obtained from the Snyder unit hydrograph method were used for the return periods of 100 and 200 years, while the values obtained from the frequency analysis and SCS unit hydrograph methods were used in addition to the Snyder unit hydrograph method for the return period of 500 year. As a result of the flood risk analysis, the status of the floodplains formed according to different return periods was determined and the Etbaşoğlu bridge was examined according to two different scenarios in the hydraulic model created. According to the first scenario, in which the existing flood protection wall is not taken into consideration, it was determined that flood waters flooded the land for approximately 150 m from the bridge abutment on the right bank, while in the second scenario, in which the flood protection wall was considered, it was determined that discharges up to peak discharge of Q500 did not damage the bridge.