The Flood That Could Drown California

Back in late 1861 and early 1862, much of the state of California was flooded by rainfalls of biblical proportions. The new state capital, Sacramento, was under 15 feet of water and the Central Valley became a lake. Meteorologists labelled it as a thousand-year flood, but more recent research has found that such floods happened every couple of hundred years, and the floods of 1861-2 were not even the largest on record. 

It's been 160 years since the last big flood so the state may be coming due for another one. What happened then and what such a flood would mean today is the subject of a long article in Mother Jones. It would be, by far, the biggest weather catastrophe in US history.

Apart from economic losses, “the evolution of a modern society creates new risks from natural disasters,” Jones told me. She cited electric power grids, which didn’t exist in mid-19th-century California. A hundred years ago, when electrification was taking off, extended power outages caused inconveniences. Now, loss of electricity can mean death for vulnerable populations (think hospitals, nursing homes, and prisons). Another example is the intensification of farming. When a few hundred thousand cattle roamed the sparsely populated Central Valley in 1861, their drowning posed relatively limited biohazard risks, although, according to one contemporary account, in post-flood Sacramento, there were a “good many drowned hogs and cattle lying around loose in the streets.”

Today, however, several million cows are packed into massive feedlots in the southern Central Valley, their waste often concentrated in open-air liquid manure lagoons, ready to be swept away and blended into a fecal slurry. Low-lying Tulare County houses nearly 500,000 dairy cows, with 258 operations holding on average 1,800 cattle each. Mature modern dairy cows are massive creatures, weighing around 1,500 pounds each and standing nearly 5 feet tall at the front shoulder. Imagine trying to quickly move such beasts by the thousands out of the path of a flood—and the consequences of failing to do so.

A massive flood could severely pollute soil and groundwater in the Central Valley, and not just from rotting livestock carcasses and millions of tons of concentrated manure. In a 2015 paper, a team of USGS researchers tried to sum up the myriad toxic substances that would be stirred up and spread around by massive storms and floods. The cities of 160 years ago could not boast municipal wastewater facilities, which filter pathogens and pollutants in human sewage, nor municipal dumps, which concentrate often-toxic garbage. In the region’s teeming twenty-first-century urban areas, those vital sanitation services would become major threats. The report projects that a toxic soup of “petroleum, mercury, asbestos, persistent organic pollutants, molds, and soil-borne or sewage-borne pathogens” would spread across much of the valley, as would concentrated animal manure, fertilizer, pesticides, and other industrial chemicals.