The Yuba City Basin (sometimes called the Sutter Basin) is a flat plain below the elevation of high flows in the surrounding Sacramento, Feather, Yuba and Bear Rivers.
"Every winter and spring, rainfall and melting snow result in often-destructive stream flows coming off the mountains into the rivers. Before we began building levees and dams, Sierra runoff would form deep pools on much of the Valley floor, taking months to drain into San Francisco Bay."
— David Kennedy, water engineer and former head of the State Department of Water Resources.
The first organized responses to seasonal floods were simple dirt levees, generally built by farmers to protect their crops and farm properties. The early settler's levees were often no more than berms of loose dirt, sometimes built over old lake beds. Today's levees are frequently built on top of those older leaky foundations of porous, unstable and sandy soils.
After major floods in the early part of the 20th century, the US Army Corps of Engineers constructed a comprehensive and connected set of levees and bypasses (or overflow channels) to contain the river runoff. Eventually, dams were also built that act as shock absorbers, storing sudden storm water surges to avoid overtopping levees.
Despite efforts to ward off inundation, levee breaches in 1917, 1955, 1986 and 1997 have resulted in major flooding that have affected the region, resulting in dozens of deaths and millions of dollars in property damage.
After Hurricane Katrina, national scrutiny of areas behind levees
Many Central Valley levees are now under scrutiny. Some leak and slump because of water pressure forcing water through the levee; others fail because of seepage underneath because the levees were originally built on sandy, porous soils. New federal rules will call for upgrading, and may mandate flood insurance and land use controls.
California weather is changing, perhaps as a result of global climate change. More precipitation is falling in the mountains as rain, and less as snow pack. This change will increase the stress on the region's flood control system.
Levee restoration proposal to be discussed on April 23
Earlier this year, staff of the Sutter Butte Flood Control Agency proposed looking at whether the Agency should begin levee rehabilitation efforts along a stretch of west Feather River levees from Yuba City north to the Thermalito Afterbay. They believe that this effort would provide significant protections against catastrophic flooding. This work, called the Early Implementation Project (or EIP for short) would take place before the US Army Corps of Engineers completes a comprehensive multi-year parallel effort called the Feasibility Study.
