University of Birjand-Research Group of Drought and Climate Change Journal of Drought and Climate change Research 3092-6076 3 4 2026 02 20 Urban Flood Risk Mapping with Coupling Storm and Sanitary Analysis Software (ASSA) and HEC-RAS Model, Case Study of Ladan Urban Watercourse, Mashhad, Iran Urban Flood Risk Mapping with Coupling Storm and Sanitary Analysis Software (ASSA) and HEC-RAS Model, Case Study of Ladan Urban Watercourse, Mashhad, Iran 23 44 3643 10.22077/jdcr.2025.9632.1150 FA Reyhaneh Khashavarz Ph.D. Student, University of Tehran, Kish International Campus, Kish, Iran. Bahram Malek Mohammadi Faculty Member, Department of Environmental Engineering, University of Tehran, Tehran, Iran. Mohammad Nik Sokhan Professor, Faculty of Environmental, University of Tehran, Iran. Keivan Bina Assistant, Department of Civil Engineering, Engineering Faculty & Disaster Risk Reduction Research Group, Khayyam University, Mashhad, Iran. 0000-0002-5726-4045 Journal Article 2025 06 23 Flooding is among the most destructive natural hazards, causing significant human and economic losses. Urban flood risk zoning offers an effective approach to mitigating such damages by identifying vulnerable areas and assessing hazard intensity, thereby enabling proactive planning and management. This study aimed to perform flood risk mapping of the Ladan watercourse in 9rd District of Mashhad city, Iran, through hydraulic and hydrological modeling. The analysis employed Storm and Sanitary Analysis (ASSA) and HEC-RAS 6.2 software. Rainfall–runoff modeling was based on a uniform rainfall pattern, while hydraulic simulations were conducted for return periods of 25, 50, and 100 years. Flood hazard zoning for the 100-year flood was prepared in accordance with Iranian Guideline for flood hazard mapping (Code 821), in which the product of flow depth and velocity (V×D) was considered as the flood hazard index. The findings revealed that the Ladan watercourse can convey floods with return periods of 25 and 50 years. However, during the 100-year flood, specifically, the initial 200 meters of the channel were identified as critical zones where overtopping and road inundation are likely to occur.<br /><br />The outcomes of this research highlight the importance of flood risk zoning in supporting sustainable urban planning and flood management. The results provide a practical basis for prioritizing vulnerable zones and guide the development of preventive strategies and flood control structures. Flooding is among the most destructive natural hazards, causing significant human and economic losses. Urban flood risk zoning offers an effective approach to mitigating such damages by identifying vulnerable areas and assessing hazard intensity, thereby enabling proactive planning and management. This study aimed to perform flood risk mapping of the Ladan watercourse in 9rd District of Mashhad city, Iran, through hydraulic and hydrological modeling. The analysis employed Storm and Sanitary Analysis (ASSA) and HEC-RAS 6.2 software. Rainfall–runoff modeling was based on a uniform rainfall pattern, while hydraulic simulations were conducted for return periods of 25, 50, and 100 years. Flood hazard zoning for the 100-year flood was prepared in accordance with Iranian Guideline for flood hazard mapping (Code 821), in which the product of flow depth and velocity (V×D) was considered as the flood hazard index. The findings revealed that the Ladan watercourse can convey floods with return periods of 25 and 50 years. However, during the 100-year flood, specifically, the initial 200 meters of the channel were identified as critical zones where overtopping and road inundation are likely to occur.<br /><br />The outcomes of this research highlight the importance of flood risk zoning in supporting sustainable urban planning and flood management. The results provide a practical basis for prioritizing vulnerable zones and guide the development of preventive strategies and flood control structures. https://jdcr.birjand.ac.ir/article_3643_7ae11af20803185120e83d3ce4fb4ed7.pdf