Applying Flood Risk Resiliency Analysis to a Regional Stormwater Management Program

The Northeast Ohio Regional Sewer District (District) services more than one million residents across 60 communities within the Greater Cleveland area and began implementing a Regional Stormwater Management Program (RSMP) starting in 2016.

Utilizing SWMM models, the District applies asset management principles to assign flood risks to each stormwater asset along their regional stormwater system (RSS), as well as any building, transportation, or utility (BTU) along the RSS. The District defines an asset’s probable annual risk (PAR) as an asset’s flood risk multiplied by the design storm’s annual probability, then sums the PAR score for each of the modeled design storms, which was previously presented at ICWMM in 2022. This presentation builds upon the original PAR tool presentation to further support an RSMP.

Applying different variations of rainfall totals, storm durations, and rainfall distribution types under a series of stormwater model simulations, then post-processing the results with our PAR tool helps identify how resilient stormwater management systems are to heavy rainfall and high intensity storms. The model results can be easily and consistently organized, symbolized, and presented in a simple flood risk matrix, which allows for a quick assessment and comparison of the flood risk resiliency of a particular subwatershed or region across a stormwater service area to identify areas of vulnerability by storm type. Outcomes of the flood risk resiliency analysis can support defining advanced flood warning rules, recommending field monitoring equipment, and prioritizing advanced stormwater planning, design, or construction projects.

Case studies and lessons learned will be shared on how applying a range of different types of storm events and utilizing the PAR score helps assess the resiliency of stormwater systems under both existing conditions and potential impacts due to climate change.