Integrated plan combining house-level I/I mitigation program and GI technology to avoid street flooding - Case study: Newton-Bedford blueprint Columbus

The integrated plan program by the City of Columbus “Blueprint Columbus” is designed to mitigate sanitary sewage overflow(SSO), manhole flooding (MH Flooding) and incidents of sewage water backing up into properties’ basements (WIB). The mitigation technology selected by the City is source reduction for the Inflow and Infiltration I/I. This is being achieved through comprehensive application of three mitigation technologies; lining sewer mains and lateral house connections, roofs drainage redirection to the street, and storm water sump pumps installation. The City started applying the mitigation program since January 2016. The plan is also designed to encompass additional benefits to improve neighborhood quality of Blueprint Columbus areas by placing and maintaining a green infrastructure program (GI), including GI units along major streets and designing neighborhood parks with subsurface stormwater storage. These stormwater control structures are sized to mitigate the potential street flooding expected because of the I/I reduction. It is also designed to provide water quality volume (WQv) control and targeting at least 20% total suspended soil (TSS) reduction in the stormwater before it is collected in the storm collection system to the receiving waters.

The house-based collection system hydrologic and hydraulics model (H/H model) approach by Dr. Hazem Gheith is used to plan the integrated plan program. The approach splits the I/I into its source components; house foundation, lateral house connections and main sewers. The approach tracks the groundwater fluctuation at these sources, and calculates their impact on the I/I hydrograph. This split allows improved quantification of I/I through the roof drainage redirection away from the house’ perimeter, storm sump pump foundation drainage, lining both the lateral house connections and main sewers. The approach also allows the usage and application of a user defined present effectiveness of technology application at a house level and investigate its impact on meeting the proposed level of service (LOS) for SSO, MH flooding and WIB. As the H/H model is used to track the sanitary system LOS, the modeling approach also quantifies the additional street flow because of the I/I reduction activities, which allows adequate planning to avoid additional street flooding.

Effective placement and sizing of the GI program as to mitigate the storm collection system deficiency and to track water quality improvement require confidence in modeling the surface stormwater flooding and routing conditions. The City of Columbus produced a Stormwater Modeling Manual for Blueprint Columbus in which the modeling approach is enhanced with the addition of street channels, the incidental street ponding and the limitation of the storm inlets. LiDAR data is used to obtain the street cross channel section and the ARCGIS Sink Analysis is used to identify the streets incidental ponds and their attribute. Field investigation is performed to obtain storm inlets configuration. The updated model platform is used to calculate the street stormwater flow at a high level as well as the expected street flooding spread. This in turns allowed for effective planning for the GIs to mitigate the additional ponding and flooding spread, as well as planning a WQv and 20% TSS removal targets.

This presentation details the steps taken to plan and implement the Blueprint Columbus program to the Miller/Kelton study area. The presentation will detail the I/I modeling approach, the procedure to predict I/I removal and the impact of the street channels, incidental ponds and storm inlets on planning and placing the proposed GI program.