The Formation and Control of Surges and Geysers in Tunnel Systems

Deep tunnel systems have become more popular over the last two decades for the control of combined sewer overflows (CSO). Advancements in tunneling construction equipment and technologies over the past several years have resulted in tunnels being a cost-effective control measure. The construction of tunnels also involves relatively small levels of near surface disruptions to the impacted community when compared to other end of pipe treatment and storage control facilities. Furthermore, a tunnel system has the ability to share capture volume amongst multiple overflow locations as compared to other end of pipe treatment options. However, a design concern with storage tunnels is that the filling of these systems can create dynamic flow surges which need to be addressed to limit geysering, damage to control structures, and impacts on upstream collection systems. This paper reviews surge issues related to the design of deep tunnel systems and how the use of unsteady flow surge modeling software can be used in the tunnel design process to address undesirable impacts. Specific examples are provided from the involvement of the authors in the preliminary design of the Joint Regional Tunnel (JRT) in Southeast Michigan.