To Flow or Not to Flow: 45mgd Bypass Flow Management Strategy for a 96-inch Sewer Rehabilitation

King County needed to rehabilitate approximately 1,100 meters (3,700 LF) of severely corroded 2,400 mm (96 in) diameter reinforced concrete pipe located in Renton, WA. During design of the project, Carollo completed a Flow Bypass Study to analyze existing flows in the interceptor and to develop a plan to bypass up to 173,000 m3/d (45 mgd) during low-flow summer months. The resulting bypass plan included provisions in the design that allowed for working under live flow conditions while providing the capability to remove all essential personnel and equipment during emergency high flow conditions. The bypass plan also included the preparation of a flow management plan that included coordination efforts of three wastewater treatment plants and two offsite operations groups, in addition to the project team to manage flows entering the project area. This paper reviews the risk management aspects addressed in preparing the bypass plan, including the flow analysis and flow management plan.