Urban Storm Water Management and Flooding under Extreme Precipitation Events in Seattle

Floods are extreme hydroclimate events that have severe impacts on the environment and humanity. Urban flood events can be particularly impactful, yet for the major of U.S. cities, our understanding of the extensiveness and severity of potential flooding remains incomplete. In this presentation, we will demonstrate methodologies to characterize flood generation and flood hazard mapping during a given storm period in southwestern part of Seattle, Washington State We simulate precipitation-runoff-drainage flow to understand how extreme precipitation events cause flood hazard through overtopping of river banks and overflow from manholes. In addition to using the standard hydrology and hydraulics models, we have developed and tested a new and efficient methodology to map the manhole flooding extent and recession. The models are calibrated and validated using existing flow data and flood maps and multiple model evaluation techniques. The results show that most of the flood hazard is caused due to excess precipitation generated flood near the riverine system and inability of the existing drainage system to accommodate such floods as most of the drainage system in Seattle were designed for low intensity and longer duration rainfall events.