This study investigates the mechanisms and impacts of flash flooding in Semel City in the Kurdistan Region - Iraq, focusing on hydro-meteorological factors and the effects of urbanization. Flash floods pose significant challenges due to their rapid onset and limited response time, resulting in extensive economic and human losses. The research utilizes advanced tools like geo-informatics techniques, such as remote sensing, to analyze morphometric characteristics of sub-watersheds, such as elongation ratio (0.74), bifurcation ratio (2–3.6), low drainage density (1.10), and time of concentration (12 minutes) for each Runoff accumulation in the sub-watershed outlet. Key findings highlight inadequate culvert capacity and urbanization as major contributors to flood risks. In this study, sizing of Flash floods for highways is proposed using the Rainfall depth to derive the volume-duration frequency curve, and then the rainfall volume is determined. However, the runoff volume was calculated based on a catchment area of 17.7 km². Recommendations include improving culvert designs, enhancing land-use management, and integrating geomorphological and hydrological parameters for effective flood mitigation strategies. The study highlights the importance of proactive planning and sustainable watershed management practices in safeguarding lives and infrastructure in vulnerable regions.