Optimizing green/gray solutions to control stormwater flooding – Blueprint Columbus case study

The City of Columbus is implementing an integrated planning project “Blueprint Columbus” to meet the wet weather management goals and storm water regulations. A combination of Rain Driven Inflow and Infiltration (RDII) reduction and Green Infrastructure (GI) control measures will address the sanitary sewer overflows, water-in-basement occurrences, and provide storm water quality and quantity control. Since RDII reduction will increase the storm water runoff, careful consideration is required to ensure improvements to one collection system will not be in the expense of the other. Additionally, water quality improvements is desired since the removed RDII flow used to go through full treatment and now is captured and redirected to receiving waters.

Two pilot areas are studied to determine the required amount of Stormwater improvements. These areas are Weisheimer and Chatham Rd sub-watersheds, located in Clintonville north of the City’s downtown. Both areas are approximately 30 acres in size, and sewer rehabilitation projects are planned for both areas to reduce RDII. However, the storm collection systems for both pilot areas also have significant flooding issues. A SWMM model for the two areas predicted street flooding will occur every 5 months and every 1.5 years for the Weisheimer and Chatham Rd sub-watersheds, respectively.

This presentation quantifies the impact of RDII reduction on the storm water collection system. It also discusses how GI technologies could mitigate this impact and what would be the associated benefits and cost. The presentation will also provide findings on how GI and gray combination could increase the LOS for the stormwater systems in each pilot area and at what cost while meeting the storm water quality regulation. Detailed modeling for the watersheds surface runoff allowed for educated understanding of the current stormwater level of service and for quantifying the impact of different GI configuration on improving the stormwater conveyance ability.