When people think of natural disasters in California, they typically think about earthquakes. Yet the natural disaster residents are most likely to face involves flooding, not fault lines. In fact, all 58 counties in the state have declared a state of emergency at least three times since 1950. Floods also affect every Californian because flood management projects and damages are paid with public funds.

California Flooding Overview

During heavy rains in California, large rivers as well as smaller streams and creeks can become dangerous. Additionally, the Central Valley, bordered by the Sierra Nevada on the east and the Coast Range on the west, is similar to a large bowl that collects most of California’s rainfall.

Flooding in California is not only caused by hard rains. On a sunny day in 2004 a levee in the Sacramento-San Joaquin Delta crumbled and sent surging river water into Upper and Lower Jones Tract west of Stockton. Total costs related to the levee break were estimated at about $90 million, including millions of dollars in direct flood fighting and levee-repair costs, and millions more in losses of crops and property.

In the Delta, there are approximately 1,100 miles of levees protecting 700,000 acres of lowland. In the Suisun Marsh, there are approximately 230 miles of levees protecting over 50,000 acres of marsh land. Even so, in 2008 the state’s Delta Risk Management Strategy found a better than 60 percent chance that an earthquake or major flooding in the Delta will cause multiple levees to fail simultaneously in the next half century.

Upstream dams have done much to reduce flooding risks in California, but whether downstream levees can provide adequate protection in some areas is a big concern. These concerns deepened in 2005, after the destruction of New Orleans by Hurricane Katrina brought new attention to levees throughout the United States, including California.

The city of Sacramento, located on the American River and close to the Folsom River, only has about a 100-year level of flood protection – a 1 percent chance of a flood disaster occurring each year. In other words, a homeowner in such an area has a one-in-four chance that a flood of that magnitude will occur sometime during a typical 30-year mortgage. This is much less protection than most major cities in the United States. Elsewhere, in 2005 the Department of Water Resources warned that the Central Valley’s flood protection system is “deteriorating and, in some places, literally washing away.”

California Flooding Challenges

Flood management is inextricably intertwined with politics, economics and values. Meanwhile, historic floodplains have been heavily developed for agricultural, commercial and residential use.

The effects of climate change further complicate flood risk management in California. Precipitation and runoff patterns are changing, which could impact the timing and magnitude of flows. Expected impacts include more precipitation falling as rain rather than snow. An earlier melt to the winter snowpack is also expected. The California Climate Change Center says more coastal floods are expected due to increasingly severe winter storms, rising sea levels and high tides. In turn these severe weather events are expected to cause more frequent and more severe flooding, erosion and damage to structures along the coast.

California’s flood protection system is facing unprecedented challenges, including increasing floodplain development, rising flood peaks, higher costs that delay fixing problem levee sites, the need for environmental protection and greater state liability for levee breaches.

In response, there are multi-fold efforts underway to staunch the flow of food risks. Through DWR’s FloodSAFE California Initiative local, regional, state, tribal and federal officials have teamed up to create sustainable, integrated flood management and emergency response systems throughout the state. Goals include providing 200-year level of protection to all urban areas in the Sacramento-San Joaquin Valley by the end of 2025. And in 2006, California voters approved Proposition 1E and Proposition 84, which provided a $4 billion general obligation bond to pay for work including levee repairs in the Delta and Central Valley, improved flood protection for cities and stormwater flood projects.

In 2012, California legislators passed the comprehensive Central Valley Flood Protection Plan. The Flood Plan is a 25-year, $17 billion blueprint that includes the acquisition of as much as 40,000 acres of land to accommodate flood waters as they drain from the Sacramento and San Joaquin River watersheds. It is based on “broad management actions to improve the flood management system, policies, and institutions at a system-wide level, while enabling flexibility in addressing changing needs and funding scenarios,” according to DWR.