Developing Flood Extent Map by using Numerical Models and Determination of Areas under Flood Risk: Türkköse Stream Case

Due to rapid and unplanned urbanization, natural disasters such as rising floods affect the daily life. In order to prevent losses and minimize damages, it is necessary to model the streams passing through urban areas and to establish flood extent maps. In addition, the generated flood extent maps should be updated taking into account the changes in land use occurring in urban areas. Moreover, new settlements near the streams should be made by considering the flood extent maps. Moreover, existing residential areas near the streams should also be resettled to safe areas, taking into account flood extent maps. In this context, studies on the calculation of flood flows and the development of flood extent maps are of vital importance. In this study, the hydrological model of the Sazlıdere Watershed in Istanbul and the hydraulic model of the Türkköse Stream, which is the main stream within the basin boundaries, were generated. In the study, watershed area, slope and boundary, elevation map, land use, soil type and stream routes were modeled by using the WMS software program. The HEC-HMS software program for hydrological model and the HEC-RAS software program for hydraulic model were used. The hydrological model was calibrated by using rainfall and flow rate data previously measured in the watershed. Finally, flood extent maps generated on the main stream and side branches on the watershed were obtained by using heavy rainfall between 03 and 05 July 2005. The floods in the model were examined and it was observed that the depth of the water in the areas close to the downstream of the main stream could be around 8 m. In addition, it was determined from the model results that the water depths in the main stream and on the side branch passing through the settlement areas were 6 m and 4 m, respectively, and the flood extent widths were 260 m and 240 m, respectively. Thus, the flood analysis of the Türkköse Stream was carried out with the described model and the areas affected by the flood in the settlement area were determined.