Urban development assessment in flood hazard areas using integrated HEC-RAS, SCS, and FAHP models: a case study of Pardisan Settlement, Qom

Alluvial fan surfaces present unique challenges for urban development due to their susceptibility to flooding and other environmental hazards. This study focuses on the Pardisan settlement in Qom, which houses over 200,000 residents and is particularly prone to flood risks due to its geographical characteristics. The primary aim of this research is to identify and manage areas within Pardisan that are optimal for safe and sustainable urban expansion. To address this goal, we utilized a comprehensive methodology that includes flood risk modeling with HEC-RAS 6, using the Soil Conservation Service (SCS) method for a hypothetical 100-year flood event. Additionally, we incorporated 13 development criteria, developed from expert consultations, to assess land suitability for urban development. These criteria were analyzed using the Analytic Hierarchy Process (AHP) combined with Fuzzy logic, facilitating a nuanced comparison of potential sites for expansion. Our findings reveal that, despite existing watershed management and road infrastructure adjustments, current settlement areas in Pardisan remain vulnerable to flooding. The research highlights deficiencies in current flood prevention measures and underscores the need for enhanced strategies and further studies. Flood modeling showed that major infrastructures, such as bridges in the eastern sector of the settlement, are likely to withstand a 100-year flood, whereas smaller railway bridges require ongoing monitoring to manage debris accumulation. Furthermore, the channel within Pardisan is inadequate for managing the water flow and sediment from such a flood event, and upstream dams do not sufficiently address the volume and sedimentation challenges posed by potential floods. The outcomes of the AHP-Fuzzy model identified the southeast section of Pardisan as the most suitable area for future urban development. This recommendation is based on a thorough evaluation of the specified criteria, pointing to significant potential for targeted, optimal urban expansion in this region.