Sewer authorities in the US are constructing tunnels to control Combined Sewer Overflow (CSO) to meet regulatory requirements. This paper focuses on the design solutions for drop structures that convey an extreme variation of flow. The Doan Valley Storage Tunnel in Cleveland Ohio conveys dry and wet weather flows with a series of dual purpose conveyance and CSO storage tunnels. Baffled drop structures with dry weather drop pipes were designed to address this uncommon flow variation. This paper summarizes the design approach including numerical and physical modeling, air entrainment, energy dissipation, and structural systems for these unique drop shafts.
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