## 1 Introduction
The most widely used software for flood risk modeling are HEC-RAS, FLO-2D, SRH-2D, IBER, MIKE SHE, TUFLOW, River-Flow2D, and LISFLOOD-FP [37; 38]. The HEC-RAS 6.5 software developed by the U.S. Army Corps of Engineers (USACE) in Washington, DC, USA is capable of performing one-dimensional steady flow and one- and two-dimensional unsteady flow calculations, sediment transport/mobile bed calculations, modeling of past floods, determination of flood-prone areas, and generation of different hydrological development scenarios [38; 39; 40; 41]. The software is used in various studies due to its features such as data entry/editing, hydraulic analysis (river analysis, flood/inundation analysis, etc. ), data storage and management, reporting, and graphical presentation of analysis results [42]. In this study, the HEC-RAS 6.5 software, which is a free open-source software that is most frequently used in flood risk mapping studies [37; 43; 44; 45; 46; 47], was used. HEC-RAS 6.5 software was chosen not only because of its widespread use in flood risk modeling but also because of its functional features and efficiency in terms of data processing [48]. The 1D modeling of the software is frequently used in studies because it offers user-friendly features for researchers, does not require expertise, produces fast results, and works with minimum input data [49]. This model, which is one-dimensional and assumes constant velocity and water level along the cross-section, gives remarkable results for the flow in the channel [50; 51]. Although HEC-RAS 1D can accurately calculate channel processes, 2D is a superior choice for the evaluation of flood wave dynamics in the floodplain, when the capacity of the channel is exceeded and the flow is spread over a wide area [52; 53; 54]. However, the HEC-RAS 1D model has some limitations. One-dimensional modeling has less detail compared to 2D and may not represent flood dynamics and relief at a high level [44]. While 1D modeling is sufficient for modeling the main river system, 2D modeling is more advantageous in areas requiring higher hydrodynamic accuracy, and combined 1D/2D modeling is more advantageous in larger river systems [54]. Moreover, if the flow path of the water is not known completely or the flow path is changing, 2D modeling gives more accurate results. Although HEC-RAS 2D and combined 1D/2D have been revealed to perform better than 1D when using high spatial resolution topographic data [54], the availability of high spatial resolution satellite data (LIDAR, DEM, etc.) is limited in developing countries such as Turkiye due to its high cost. Taking all these into account, although HEC-RAS 2D and combined HEC-RAS 1D/2D models have performed better in modeling flood processes and flooding than HEC-RAS 1D, HEC-RAS 1D can be used efficiently in terms of computation-time-cost, especially in developing countries where severe floods have the potential to cause devastating damages [48]. Therefore, more case studies around the world are still needed to use and evaluate the HEC-RAS 1D model [52]. The study was carried out in the Bogacay sub-basin, which flows into the Mediterranean Sea in Antalya, one of the most important tourism centers of Turkiye. The Bogacay River meets the sea with the confluence of two main streams in the city by affecting/being affected by various ecosystems along its route. The fact that there are many recorded flood catastrophes in the area, especially the catastrophic impacts of the floods in 2003 and 2006, and the high probability of recurrence have been important factors in determining this area as a study area. The study aims to create flood simulations in the Bogacay sub-basin and evaluate the possible impacts of these flood simulations on landscape composition. Initially, the natural threshold boundaries of the Bogacay sub-basin were determined using a geographic information system (GIS).