The Importance of Flood Risk Management In California’s Central Valley

(3BL Media/JustMeans) The Central Valley is California’s heartland, a 400- mile long place full of farmland. It has some of the fastest growing cities within our most populous state, and two of them, Stockton and Sacramento, are vulnerable to major flood events.

One of the worst floods in California history—and the worst flood on record in the Central Valley—occurred in January 1997. Over 30 levees ruptured and 300,000 square miles in the Central Valley were flooded. It was “one of the most extensive and costly floods in the state’s history,” according to a 2007 study by the California Department of Water Resources.

Many experts think that a large flood event in the Central Valley will re-occur. The cost of direct flood damages in the state’s capital city, Sacramento, a city of 495,234, could be greater than $25 billion. Experts predict that a large flood event in the Central Valley could be double the size of the earlier flood. “Climate change is increasing the probability of these large events happening,” John Cain, Director of Conservation for California Flood Management, American Rivers, told Just Means.

“When floods happen in the Central Valley, it's usually wintertime,” Cain explained. “Unlike the flooding you see in New Orleans or Houston, the idea of wading flood water is not something that could happen here easily because we're talking about water temperatures that are 50 degrees. So, hypothermia would set in quite early. Some of the communities in the Sacramento and Stockton area would flood to depths of 10 to 20 feet. Loss of life would be much higher."

Many of the levees that protect flood plains in the Central Valley are good at preventing smaller floods that happen every five to 10 years, but they are "going to be overwhelmed by the large floods,” said Cain. “When the large floods happen, the levees are prone to break unexpectedly and catastrophically, causing a Ninth Ward sort of event. We have quite a bit of urbanized communities behind these levees.”

The Central Valley Flood Protection Board has adopted a new flood plan to help protect over a million people who live at risk of devastating floods and $70 billion in homes, businesses and infrastructure. The new plans calls for an expansion of floodways and the creation of a new flood bypass at Paradise Cut on the Lower San Joaquin River to protect the cities of Stockton, Lathrop, and Manteca. The new bypass would lower peak flood stage along 30 miles of the river, and peak stage reduction of 2.5 feet at the I-5 bridge where thousands of new houses have been built.

While it is not possible to eliminate all flood risks, there are many things that can be done to reduce the risk or manage floods, as Cain pointed out. The new plan calls for the implementation of multi-benefit flood management projects designed to reduce flood risk and help fish and wildlife habitat. Multi-benefits projects allow upstream dam operators to contain more water in reservoirs. For salmon, multi-benefit projects increase floodplain habitat known to produce larger and healthier juvenile salmon.

"There's a big emphasis on multi-benefit flood management projects,” Cain said. What is great about them, he added, is the investment put into flood risk reduction “pays off in many other ways to improve our quality of life."

Photo: American Rivers