2006 Water Comprehensive Plan - City of Bellevue

• If improvements to increase the water system’s ability to transfer flow from the EastOperating Area to the West Operating Area (discussed in the Storage Analysis section ofthis chapter) are constructed, surplus inlet capacity in the East Operating Area wouldbecome available to the West Operating Area. This surplus capacity could be used to deferthe need for inlet capacity improvements in the West Operating Area beyond 2018.OverviewVULNERABILITY ANALYSISThe primary focus of vulnerability analysis for Bellevue’s water system is the determination ofoperational capabilities following loss of a major facility which might result from an emergencysuch as an earthquake or from planned or emergency maintenance activities. Analysis of systemvulnerability was performed as part of the storage and inlet capacity analysis described above.System vulnerability was evaluated under build-out demand conditions.Under most operational scenarios, system adjustments can be made to accommodate the loss ofa single pump station, reservoir, or transmission line through redundant facilities inherent inBellevue’s distribution system.System analysis was conducted to simulate the loss of major facilities followed by a reduction ofdemand from MDD to ADD after 24 hours, presuming this will be the result of publicnotifications and it is consistent with the Water Shortage Contingency Plan. This demandreduction reflects the City’s actual experience during past emergencies. The results of thisanalysis indicated the system could maintain system pressures above 30 psi during a 72 hourduration simulation. There is sufficient redundancy of major facilities to adequately meet thecustomers need under ADD conditions. The vulnerability analysis conducted for this plan didnot include any manual operational changes that could be made to further mitigated the loss of amajor facility and is therefore a conservative assessment. System vulnerability should beconsidered when analyzing and evaluating any improvement to the water system.8-16