The southern Sierra Nevada is covered in the deepest snow pack on record, and the rest of the range isn’t far behind. If 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 with layers of gravel, silt and clay that have been washed away from the mountains by rain and melting snow over the centuries. Amidst the flatness there are gradual slopes to the center of the valley where the Sacramento River forms a water vein in the north and the San Joaquin River does the same in the middle. At one time—before the late 1800s, when newcomers began draining the land and diverting water from the wetlands to farmland—the southern part of the valley was home to the largest freshwater lake by area west of the River Mississippi.
Similarly, many of California’s smaller valleys have rivers, including the Salinas, which often run almost dry, but in wet years when they burst their banks due to torrential rain rather than slush.
That’s where the water flows: into the bottom of the valleys, which in years of flooding swell the rivers until they overflow their banks, endangering communities like Pajaro and the people in them.
During the Great Flood of 1861-1862, water covered the entire Central Valley. It would have been possible to sail north past the flooded Capitol in Sacramento from what was not yet Bakersfield, almost to where Redding now sits.
In drier times, however, these flat floodplains seemed particularly attractive to farmers and builders, so the valleys were now cultivated and developed. But in wet years like this, all that rain and melted snow still needs a place to go, and it doesn’t matter to human development. It’s still looking for the deepest ground, and it will find it. A quick glance at a satellite image of the snow-capped Sierra makes it clear: no dam can hold back all that water, no reservoir can hold 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 necessary.
California needs to restore its floodplains. Not all of the valley floors and not like in the pre-development period. But it would have to reserve many more acres of land for flooding.
To restore floodplains, inland low-lying areas must be demarcated so water can flow away from homes and critical infrastructure. It’s as easy as switching banks. Instead of building them higher and higher to drive the rushing water out to sea, levees set back from the banks of the river provide a place for them to slow down, settle and seep into the ground, safely away from human habitation and commercial activity. investments.
There are several benefits. The first, of course, is the protection of life and property, as floodwaters find another place to collect than in the city streets. In addition, water that settles over floodplains seeps into the ground and, where geology allows, replenishes groundwater that has been dangerously depleted by agricultural overpumping.
And floodplain restoration restores seasonal wetlands, which benefits the entire natural web that holds California together — including native plants that are less likely to burn during the fire season than invasive species, fish that regain their spawning habitat, migratory birds, the breeding grounds that find mammals that back through the valley.
In dry seasons, restored floodplains can be nature reserves. But it can also be football fields, golf courses, even arable land for annual plants such as tomatoes or melons. Just no houses or perennials like almonds.
Some homes are already standing where the floodwaters naturally collect, posing a dilemma. Do we protect them against floods at all costs or do we allow them? The questions are the same as for homes destroyed by wildfires and whether it is society’s duty to protect people who choose to rebuild in an area at risk of fire, flood or other foreseeable disaster. There is no consensus. As with coastal areas threatened by rising sea levels, the prudent and inexpensive step would in some cases be controlled withdrawal from riverbeds, which can flood even when dry most years.
The only thing missing from floodplain restoration is the will and enough money to buy land, mostly farmland, which has become too expensive to continue farming. Gov. Gavin Newsom is expressing his decision to use some of this year’s heavy rainfall to replenish groundwater. But it also cut most of the funding for floodplain restoration from the proposed budget for the third consecutive year.
In years like this, when the state seems to have more water than money, a proponent of floodplain restoration can vote. A well-designed retention measure can give a serious boost to the necessary recovery efforts. Even if the state is threatened by flooding today, a bond could easily end up on the ballot in a dry year in which atmospheric rivers, historic snowdrifts and flooded highways are long forgotten. But whether it’s a budget allocation or a bond, let’s try to remember: There will be wetter winters yet, and restored floodplains can protect homes and collect water for use in bone-dry summers.
Source: LA Times