Restore California’s floodplains to protect human life

The southern Sierra Nevada is covered with the deepest snowpack in recorded history, and the rest of the range is not far behind. When all that snow melts, where will it go?

You can read the answer in the landscape of the Central Valley. To the eye it is nearly flat, covered by layers of gravel, silt and clay washed from the mountains over the eons by rain and melting snow. Amid the flatness are gradual slopes down to the valley’s center, where the Sacramento River creates a watery vein in the north and the San Joaquin River does the same in the middle. Once — before the late 19th century, when newcomers began to drain the land and channel the water from wetlands into farm fields — the southern part of the valley held the largest freshwater lake, by surface area, west of the Mississippi.

Many smaller California valleys likewise feature rivers, including the Salinas, that are often nearly dry but flood their banks in wet years like this one because of torrential rain rather than snowmelt.

That’s where the water goes: to the valley floors, swelling the rivers in flood years until they overflow their banks, imperiling communities like Pajaro and the people in them.

During the Great Flood of 1861-62, water covered the entire Central Valley. It would have been possible to sail from what was not yet Bakersfield, north past the flooded Capitol in Sacramento, almost to where Redding now sits.

In drier times, though, those same flat floodplains looked especially attractive to farmers and builders, so now the valley floors are cultivated and developed. But in wet years like this one, all that rain, as well as the melted snow, still needs a place to go, and it doesn’t pay any attention to human development. It still seeks the lowest ground, and it will find it. A quick look at a satellite photo of the snow-covered Sierra makes it plain: No number of dams can hold all that water back, no number of reservoirs can lock it up.

The solution is shockingly simple, relatively cheap — compared with the cost of cataclysmic floods — and surprisingly non-controversial. We just haven’t yet done it on the scale that’s needed.

California needs to restore its floodplains. Not the whole valley floors, and not as they were in the pre-development era. But it needs to have many more acres of land reserved for floodwater.

Restoring floodplains requires setting aside low-lying inland areas for water to accumulate away from homes and critical infrastructure. It’s as easy as moving levees. Instead of building them ever taller, to hustle rushing water out to sea, levees set back from riverbanks give the water a place to slow down, settle and seep into the ground, safely away from human habitation and commercial investment.

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