Kwan said that Seven Oaks was one of his first assignments after he joined the Army Corps: He got to see it go from a sketch to a fully operating dam. But he didn’t register any emotion when confronted with the probability that it would fail in a repeat of 1862. Instead, he shifted to talking about the dam-break analysis that the Army Corps had done and the inundation map it prepared. He’s an engineer, after all.
From the top of Seven Oaks, you can see the crowded valley below, home to more than four million people. If you keep following the Santa Ana, you’ll reach the hills above Anaheim and Orange County, home to millions more. The wave running down the river following a dam breach would remain high all the way to those hills. Nearly a mile from the dam, it would still be 69 feet from top to bottom. By the time it got to the San Bernardino airport, an hour later, it would have spread out and slowed down, at merely 30 feet tall.
The inundation map shows all that would be caught in its path. Red dots for fire stations, purple dots for police stations, green squares for schools: Highland Grove Elementary, Cypress Elementary, Lankershim Elementary, Warm Springs Elementary, Bing Wong Elementary, Monterey Elementary, H. Frank Dominguez Elementary, Urbita Elementary, Woodrow Wilson Elementary, Patricia Beatty Elementary, Fremont Elementary, Ina Arbuckle Elementary, West Riverside Elementary.
Houses would be knocked off their foundations, warehouses would crumple, commercial jets would be tossed about. Much of the infrastructure along the river, bridges, highways and railroads, would be washed away. Thousands of people would have minutes to evacuate. The death toll would be far higher than that of an ordinary flood. If the surge found a flaw in Prado Dam, which sits above Orange County, all of Anaheim would be added to the inundation zone, Disneyland included, before the water met the sea.
In 1986, during one of the worst floods Northern California experienced in the 20th century, Mike Dettinger was stranded on Point Reyes with a colleague and both their families, including Dettinger’s 9-month-old daughter. “We were a bunch of groundwater hydrologists, and we knew there was a storm coming in but really had no sense of how bad it was going to be,” he told me. They ended up driving their Cadillac across a flooded road and losing control of it. The two families spent the next night sleeping in a fire station and the one after that in the manager’s office of a local motel.