SACRAMENTO-SAN JOAQUIN DELTA LEVEE SYSTEM: RISKS AND REHABILITATION
California’s Central Valley, one of the nation’s highly productive agricultural regions, is drained by the Sacramento River flowing from the north and the San Joaquin River flowing from the south. These rivers converge in the Sacramento-San Joaquin Delta before flowing to Suisun Bay and eventually to the San Francisco Bay and the Pacific Ocean. The Delta region comprises about 738,000 acres of land in six counties. Once dominated by islands, wetlands, and riparian forests, the Delta has been completely reconfigured for agriculture. Beginning in the 1850s, levees were constructed along the Sacramento and San Joaquin Rivers, and many of their tributaries, to make the land usable for both human settlement and agriculture (Kelley, 1989).
The Central Valley today has one of the nation’s most extensive levee systems, with approximately 1600 miles of federal levees and an equal length of nonfederal levees. The Delta region includes approximately 1100 miles of levees, of which 385 levee miles are incorporated into federal flood control projects, mostly along the main-stem Sacramento and San Joaquin Rivers. The 700-plus miles of nonfederal levees, many of which line not rivers but rather channels and prevent tidal inflows, generally do not meet the same design standards as the federal levees (USACE, 2006). Unlike river levees, which experience only periodic water loading during floods, many Delta levees have constant water loading. The aging Delta levee system is fragile and undergoing failure (USACE, 2006; Mayer, 2010). Performance is
recommendations by a specially convened independent, external review panel (ASDSO, 2001). A “risk informed” management approach has been adopted and is being implemented (see USACE, 2012d). The Corps Dam Safety Program is important in the context of this report and its emphasis on setting priorities for infrastructure investments. The Corps is using a risk-based approach to assess the risk status of dams and to prioritize dam safety investments for the dams in need of life-safety risk-reduction actions.
Within its dam safety program activities, the Corps has conducted a screening of all of its nearly 700 dams to identify and classify its highest risk dams in need of urgent and compelling action (USACE, 2012c). The Corps’ Dam Safety Action Classification (DSAC) program is intended to provide consistent and systematic guidelines for appropriate actions to address dam safety issues and of an urgent and compelling situation requiring immediate action for unsafe