The risk of flooding near the Sacramento-San Joaquin Delta is likely to increase substantially over the next century if a new levee system is not implemented, according to a report released Friday by the California Department of Water Resources.
The department's Delta Risk Management Strategy Phase 1 report assessed major risks to the Delta levees from earthquakes, high water conditions, climate change, dry weather events, and a combination of these factors.
Phase 2 of the risk management project will evaluate long-term options to reduce the risks and consequences of levee failures. The second phase is expected to be available for public review in the fall.
The report released Friday concluded "the Delta Region as it exists Friday is unsustainable."
According to a previous report, an earthquake with a magnitude of 6.7 or greater has a 62 percent probability of occurring in the vicinity of the Delta Region by 2032.
If a major earthquake occurs, levees would fail and as many as 20 islands in the region could be flooded simultaneously, according to the report released Friday.
Winter storms causing high-water conditions are the most common cause of levee failures in the region, and the report estimated about 140 levee failures would occur in the next century due to storms if no new changes were implemented.
Much of the land in the Delta Region is below sea level and many of the region's 1,330 miles of levees were built at least 100 years ago without using modern engineering practices, according to the department.