Unique Solution: Bending Weir Solves Overflow and Basement Flooding Problem

The City of Columbus, Ohio entered into a Consent Order with the Ohio EPA regarding Combined Sewer Overflows. The Cherry Street/Fourth Street Stream Inflow Redirection project was one of several projects set to be completed as part of the City’s Wet Weather Management Plan. The City must mitigate the overflow from the “Typical Year Storm” (TYS) to reduce the Combined Sewer Overflow (CSO) contribution from the project sewershed. Additionally, the City required this flow must be mitigated without causing or worsening Water-In-Basement (WIB) flooding complaints in the project area. Downtown Columbus is an area known for the density of existing utilities. Additionally, narrow rights-of-way combined with buildings that encroach on the right-of-way make finding locations for new utilities difficult. Traffic wasalso a concern for this project as Fourth Street is currently the only arterial road that provides access to Interstate71 northbound from the downtown area. With the WWMP-prescribed inflow redirection alternative proving to be less than desirable in meeting the project goals, an out-of-the-box solution was necessary. Ultimately, a bending weir was utilizedin a custom concrete structure to direct overflow to the storm sewer system with minimal increase in the hydraulic gradeline (HGL) of the combined sewer. Typically, a weir is used to increase storage in a pipe, thus reducing overflow frequency and volume. In our case, the bending weir is utilized to keep the hydraulic grade line at a more consistent elevation for flows up to a 2.4 cubic meters per second (m3/s) (54.9 mgd) overflow rate. This application of a bending weir allows the City to meet their requirements of the consent order with regard to CSO control and timeline constraints without negatively impacting the sewer system downstream.