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2015 URBAN WATER MANAGEMENT PLAN <br />Delta levee failure: The levees are vulnerable to failure because most original levees were simply <br />built with soils dredged from nearby channels and were not engineered. A breach of one or more <br />levees and island flooding could affect Delta water quality and SWP operations for several months. <br />When islands are flooded, DWR may need to drastically decrease or even cease SWP Delta exports <br />to evaluate damage caused by salinity in the Delta. <br />The Delta Risk Management Strategy addresses the problem of Delta levee failure and evaluates <br />alternatives to reduce the risk to the Delta. Four scenarios were developed to represent a range of <br />possible risk reduction strategies (Department of Water Resources, The State Water Project Final <br />Delivery Capability Report 2015, July 2015). They are: <br />• Trial Scenario 1 Improved Levees: This scenario looks at improving the reliability of Delta levees <br />against flood- induced failures by providing up to 100 -year flood protection. The report found that <br />improved levees would not reduce the risk of potential water export interruptions, nor would it change <br />the seismic risk of most levees. <br />• Trial Scenario 2 Armored Pathway. This scenario looks at improving the reliability of water <br />conveyance by creating a route through the Delta that has high reliability and the ability to minimize <br />saltwater intrusion into the south Delta. The report found that this scenario would have the joint <br />benefit of reducing the likelihood of levee failures from flood events and earthquakes, and of <br />significantly reducing the likelihood of export disruptions. <br />• Trial Scenario 3 isolated Conveyance: This scenario looks to provide high reliability for conveyance <br />of export water by building an isolated conveyance facility on the east side of the Delta. The effects of <br />this scenario are similar to those for Trial Scenario 2 but with the added consequence of seismic risk <br />of levee failure on islands that are not part of the isolated conveyance facility. <br />• Trial Scenario 4 Dual Conveyance: This scenario is a combination of Scenarios 2 and 3 as it looks <br />to improve reliability and flexibility for conveyance of export water by constructing an isolated <br />conveyance facility and through -Delta conveyance. It would mitigate the vulnerability of water exports <br />associated with Delta levee failure and offer flexibility in water exports from the Delta and the isolated <br />conveyance facility. However, seismic risk would not be reduced on islands not part of the export <br />conveyance system or infrastructure pathway. <br />DWR has altered the SWP operations to accommodate species of fish listed under the Biops, and these <br />changes have adversely impacted SWP deliveries. DWR's Water Allocation Analysis indicated that export <br />restrictions are currently reducing deliveries to Metropolitan as much as 150 TAF to 200 TAF under <br />median hydrologic conditions. <br />Operational constraints likely will continue until a long -term solution to the problems in the Bay -Delta is <br />identified and implemented. New biological opinions for listed species under the Federal ESA or by the <br />California Department of Fish and Game's issuance of incidental take authorizations under the Federal <br />ESA and California ESA might further adversely affect SWP and CVP operations. Additionally, new <br />litigation, listings of additional species or new regulatory requirements could further adversely affect SWP <br />operations in the future by requiring additional export reductions, releases of additional water from <br />storage or other operational changes impacting water supply operations. <br />arcadis.rom� w� 3-7 <br />