Diagnosing Tunnel Hydraulic Behavior in San Francisco

During large wet weather events reports of spouting and other hydraulic issues in the Richmond Transport/Storage Tunnel (RMT) area have been received by the City of San Francisco. Analyses were undertaken to identify the cause of these issues and develop remedial measures. The analyses included i) simulations using the San Francisco Public Utilities Commission (SFPUC)’s Hydraulic and Hydrologic Model of the collection system, ii) surge modeling using the Transient Analysis Program (TAP) (Applied Science Inc., 2010) model, and iii) analyses of air flow in the system and associated venting needs. The analyses showed that a bore (moving hydraulic jump) develops in the tunnel system during large wet weather events, but was not the cause of the hydraulic phenomena that were reported. Rather, the issues appear to be the result of insufficient air conveyance and venting capacity. Recommendations were developed and are being evaluated by the SFPUC.