The Northeast Ohio Regional Sewer District’s (NEORSD) Project Clean Lake is a 25-year program established to reduce combined sewer overflows (CSOs) impacting Lake Erie and its tributary waterways to meet their Consent Decree requirements. The Doan Valley Storage Tunnel (DVT) is one of seven storage tunnels in NEORSD’s Project Clean Lake program that will store and convey wet weather flows. Flow discharged from the DVT will be conveyed to the Easterly Wastewater Treatment Plant before discharge to Lake Erie. With a storage volume of 18 million gallons (MG), the DVT system is under construction to provide relief to the Doan Valley Interceptor (DVI) by reducing overflows to the Doan Brook, and providing additional capacity to improve the service level of the DVI. Wade Trim, in a joint venture with McMillen Jacobs Associates, is providing design and construction phase professional services for the DVT system and local system control improvements.

Design for this 3.7-mile rock tunnel system, located in Cleveland’s bustling University Circle, optimized the alignment to minimize community impacts and constructability risks while hydraulically managing both dry and wet weather flows. Major components include the 18-foot-diameter storage tunnel, two 8.5-foot-diameter consolidation conveyance tunnels, five drop shafts, six diversion structures, and an emergency overflow.

A four-month flow monitoring program and extensive hydraulic modeling were conducted to support design activities. Key flow management challenges included balancing existing interceptor and new tunnel performance to achieve optimal CSO control, design of baffled drop shafts to handle dry and wet weather flows at deeper shafts with larger flow, and surge modeling to develop operational protocols to protect the tunnel during large events. Mixed-regime transient modeling was performed for the tunnel systems to account for the dynamic-filling nature of the tunnels and to develop operational protocols to protect the tunnel system for large storm events. Computational fluid dynamics (CFD) modeling was used for key hydraulic structures.

Anticipated to be operational in 2021, the DVT system will help control CSOs at 11 locations along Doan Brook – from Shaker Heights to Lake Erie – and prevent 365 MG of CSO from reaching the environment in a typical year.