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April 2015 P R A C T I C A L W I N E R Y & V I N E YA R D 73 B O O K E X C E R P T The delta was once a 700,000-acre net- work of wetlands and channels, with sea- sonally shifting river inflows, and host to millions of migrating birds and fish as well as animals such as elk and grizzlies. During the Gold Rush, however, the del- ta's natural wetlands were drained and converted to farmland to feed the grow- ing population in San Francisco. Islands in the delta were formed, protected by levees built by farmers, Chinese labor- ers and miners, using wheelbarrows, picks and shovels. These earthen levees confi ned river flows to the channels, so that the wetlands on the newly isolated islands no longer received sediments or nutrients. Over time, the sediment debris on the wetlands that had accumulated over cen- turies dried, oxidized, and decomposed. Winds blew the dried peats away, caus- ing the islands to subside by up to 25 feet below sea level. The levees separate the channeled waterways through the delta from these now-sunken "islands." In recent years, over half a million homes have been built on these islands in the delta, yet many of the new occupants are unaware of the substantial flood risks. As the levees continue to age, they are becoming more prone to failure during floods and even earthquakes. In 2004, a 350-foot section of a levee 10 miles west of Stockton collapsed, flooding a 12,000- acre island called the Upper and Lower Jones Tracts (see photo on page 70). As discussed in chapter 12, a breach in a levee in the delta also has the potential of allowing seawater to intrude into the freshwater supply that is pumped to resi- dents in Southern California as well as to farmers in the San Joaquin Valley. California's capital city of Sacramento, located just north of the delta along the Sacramento River and just downstream of the Folsom Reservoir, is also at the mercy of levees that are over a century old. This city, which was under 10 to 20 feet of water in the 1861– 62 flood written about in chapter 2, has the lowest level of flood protection for an urban area anywhere in the United States, despite its dramatic flood history. With flood pro- tection well below that of New Orleans, a large flood in the Sacramento region could result in tens of billions of dollars in damage and put thousands of lives at risk. An atmospheric river "superstorm" Recent research shows that atmospheric river storms have produced the larg- est historical floods along the Pacific Coast states of California, Oregon and Washington. As the global climate warms over the next century, larger and warmer atmospheric river storms (and extended storm seasons) are predicted. From a flood-risk perspective, this is bad news. The U.S. Geological Survey has pub- lished a new emergency-preparedness scenario called "ARkStorm" (standing for Atmospheric River 1000 Storm). This scenario assesses the extent of damage that would result if a hypothetical series of atmospheric river storms, analogous to those that struck in 1861– 62, slammed the West Coast today. The ARkStorm sce- nario shows that flood control systems would be overwhelmed, and Sacramento, as well as the expanding cities and pop- ulations in California's Central Valley, delta, and other low-lying regions, would be almost entirely underwater in a "Hurricane Katrina-like" disaster. The ARkStorm scenario also indicates that hurricane-force winds would strike the coast, in some places reaching 125 miles per hour. As slopes and hillsides become quickly saturated, the ensuing landslides and mudflows would cause widespread damage to roads and property. This sce-