ASCE OC EWRI: Exploring Multi-Benefit Approaches to California’s Flood Risk
The Orange County chapter of the Environmental & Water Resources Institute (OC EWRI) recently hosted a presentation exploring how California can address increasingly complex flood risks while also creating environmental and community benefits. The presentation, “Multi-benefit Adaptation to California’s Ultrahazardous Flood Risk,” was led by Brett F. Sanders, Ph.D., of the University of California, Irvine, and examined opportunities and challenges associated with adapting California’s flood management systems.
The presentation highlighted how California’s historical reliance on single-purpose flood control infrastructure has contributed to a range of sustainability challenges, including poor stormwater capture, water quality impacts, loss of biodiversity and fish habitat, sediment management costs and reduced recreational and community benefits. At the same time, flood risk remains significant. The presentation noted that in Los Angeles County alone, more than 425,000 people and approximately $56 billion in property could be exposed to flooding greater than one foot.
Sanders discussed research using the Parallel Raster Inundation Model (PRIMo), a high-speed flood modeling tool developed to evaluate flood hazards and potential adaptation strategies. The model incorporates factors including rainfall, reservoirs, levees, storm drains, infiltration and impervious surfaces to better understand how different approaches affect flood exposure. Modeling of the February 2024 atmospheric river event demonstrated the importance of considering the timing and duration of rainfall when evaluating flood risk.
A key finding was that **not all nature-based solutions have the same effect on flood risk**. Watershed naturalization—such as reducing impervious surfaces—was found to reduce flood exposure, while channel naturalization could increase exposure by reducing channel conveyance. Channel widening could substantially reduce flood exposure, but the approach could also result in significant displacement of people and property.
The presentation ultimately proposed an adaptation pathway that combines watershed and channel naturalization while monitoring changes in flood peaks over time. The research found that reducing imperviousness can provide a roughly one-to-one reduction in flood exposure, while flood exposure is highly sensitive to increases in precipitation. These findings underscore the importance of designing future flood management projects to achieve multiple benefits while carefully evaluating their potential impacts on flood risk.
The presentation provided OC EWRI members with an important perspective on the intersection of flood protection, climate adaptation, watershed management and environmental sustainability—and the need to consider these objectives together when planning California’s next generation of water infrastructure.
About the Author:
Ben Smith oversees OCWD's recharge basins and wetlands while keeping billions of gallons in check. With master’s degrees in Civil Engineering and Public Administration, he’s proven qualified to make water nerdy.
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