Editorial: Restore California’s floodplains to capture more stormwater

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

You can read the answer in the landscape of the central valley. To the eye it is almost flat, covered by layers of gravel, silt and clay washed from the mountains by rain and melting snow over the eons. Amid the flatness, gradual slopes extend down the middle of the valley, where the Sacramento River forms a water vein to the north and the San Joaquin River does the same in the middle. Once—prior to the late 19th century, when newcomers began draining the land and diverting water from the wetlands to agricultural fields—the southern portion of the valley was home to the largest freshwater lake by area west of the Mississippi River.

Many of California’s smaller valleys also have rivers, including the Salinas, which are often almost dry but flood their banks in wet years like this, more from torrential rain than from snowmelt.

That’s where the water flows: into the valley floors, where it causes the rivers to swell in flood years until they burst their banks and endanger communities like Pajaro and the people in it.

During the great flood of 1861-62, water covered the entire Central Valley. It would have been possible to sail north past the flooded Capitol in Sacramento from what wasn’t Bakersfield yet, almost to where Redding now sits.

In drier times, however, those same flat floodplains looked particularly attractive to farmers and builders, so now the valley floors are being cultivated and developed. But in wet years like this, all the rain and melted snow still need a place to go and pay no attention to human development. It’s still looking for the deepest ground, and it will find it. A quick glance at a satellite photograph of the snow-capped Sierra makes it clear: no number of dams can hold back all that water, no number of reservoirs can contain it.

The solution is shockingly simple, relatively inexpensive – compared to the cost of catastrophic flooding – and surprisingly uncontroversial. We just haven’t done it to the extent required.

California needs to restore its flood plains. Not the whole valley floors and not like in the pre-development period. But many more acres of land need to be set aside for flooding.

Restoring flood plains requires delineating low-lying inland areas to allow water to pool away from homes and critical infrastructure. It’s as easy as moving dams. Rather than building them higher and higher to force the rushing water into the sea, levees set back from the riverbanks give the water a place to slow, settle, and seep into the ground, safely away from human activity settlement and commercial investment.

There are several benefits. The first, of course, is the protection of life and property, as flood water is given a place other than city streets to pool. In addition, water that settles over floodplains seeps into the ground and, where geology permits, replenishes groundwater that has been dangerously depleted by agricultural overpumping.

And restoring floodplains restores seasonal wetlands, which is good for the entire natural web that holds California together — including native plants that are less likely to burn during fire season than invasive species, fish that regain their spawning habitat, migratory birds, the nesting grounds find mammals that can once again wander across the valley.

In dry seasons, restored flood plains can be wildlife sanctuaries. But they can also be soccer fields, golf courses or even arable land for annual crops like tomatoes or melons. Just no houses or perennials like almonds.

Some homes are already standing where floodwaters can naturally accumulate, and that poses a dilemma. Do we protect them from flooding at all costs, or do we leave them to it? The questions are the same as with homes destroyed by wildfires and whether it is society’s duty to protect people who choose to rebuild in an area threatened by fire, flood or other foreseeable disasters. There is no consensus. As with coastal neighborhoods threatened by rising sea levels, in some cases the prudent and inexpensive step will be a controlled retreat from riverbeds that could flood, even if they are dry most years.

All that is missing to restore the flood plains is the will and enough money to buy land, usually farmland, that has become too expensive to continue farming. Gov. Gavin Newsom is touting his decision to use some of this year’s plentiful rain to replenish groundwater. But he also eliminated most of the funding for floodplain restoration from his proposed budget for the third straight year.

In years like this, when the state seems to have more water than money, a floodplain restoration advocate’s mind may turn to voting. A well-crafted binding measure could give a serious boost to the necessary restoration efforts. Even if the state is threatened by flooding today, a bond could easily end up on the ballot in a parched year when atmospheric rivers, historic snowpacks and flooded highways are long forgotten. But whether it’s a budget allocation or a bond, let’s try to remember: There will be even wetter winters, and restored floodplains can protect homes and stockpile water for use in bone-dry summers.