Building the World

WATER: Paleo Valleys – potential solution to floods (and droughts)


“Among the Sierra Nevada, California” painted by Albert Bierstadt, 1868. Courtesy of Smithsonian American Art Museum: #1977.107.1. Wikimedia pubic domain. Included with appreciation.

Is there a hidden resource, beneath the land, that can ease water problems – both drought and flood? Maybe the answer could be paleo valleys. California found three paleo valleys, one in Sacramento. More await. There has never been a better time for this discovery.

“Sacramento Rice Fields” by photographer Mark Miller, 2014. Creative commons 3.0. Included with appreciation.

California has recently suffered storms and resulting floods imperiling 90% of the state. But the paradox is that California also needs the water. But when drought parches the land, and wildfires burn not just buildings but vegetation that formerly held water with root systems, parched land cannot absorb too much water at once. Yet, recently, California has endured such downpours that flooding is inevitable.

“California Total Precipitation 26 December 2022 to 11 January 2023,” by Weather Prediction Center, 11 January 2023. Public Domain. Included with appreciation, and concern.


According to the Pacific Institute in Oakland, letting the rivers hold more water may be the answer to problems at both ends of the spectrum.  Peter Gleick, Pacific Institute’s co-founder, stated that we must “capture more of these flood flows, store it underground in these aquifers.” (Marsh 2023)

“California Water System” graphic by Shannon1, based on DEMIS data, 2010. Creative Commons 3.0. Included with appreciation.

There are two possible solutions, among some others, to deal with extreme flooding and water retention: levees and paleo valleys.

“Sacramento River broken levee.” U.S. Army Corps of Engineers, 1997. Wikimedia public domain. Included with appreciation.

“Levée” is a French term meaning “raised.” The term was first used in New Orlean in 1672. Some natural levees are cliffs or hills, but most are engineered and built. And that means costs, maintenance, repair. Original levees built in California may have to be moved back. Costs estimates are $20 billion. California already has levees, but these structures were designed and built for an earlier time. Today’s virulent storms are more than current levees can handle. California’s Central Valley, where 25% of American produce is grown in a vast agricultural system, relies on levees. But the same area offers another option, now hidden.

“Hanging Valley (a paleo canyon) near Red Rock.” by Greg Willis, 2009. Creative commons 2.0. Included with appreciation.

Paleo valleys. In ancient times, during the ice age, glaciers streamed along the Sierra Nevada mountains into California’s Central Valley. As the glaciers retreated, their powerful melt dragged rock and bits of gravel into the valley. When the glacial rivers dried up, the valleys remained. The depth, width, and terrain of these “paleo valleys” makes them perfect for soaking up today’s floodwaters from storms that are becoming more powerful and releasing more and more water. As a bonus – an important one –  these paleo valleys can absorb 60 times more water than the clay soil of most of the Central Valley. According to Professors Graham Fogg, University of California, Davis, and Rosemary Knight, Stanford, California should use paleo valleys for flood water retention, aquifer recharge, and water renewal. The water storage area is vast, already there, and can be identified by airborne electromagnetic imaging (AEM). There is a technical name for paleo valleys: incised valley fill (IVF). (Knight 2022)

Paleo Valleys used to look like this, but now they are underground and must be located. Image: “Glacial Valley – Stryn, Norway.” by TravelOtter, 2004. Creative Commons 2.0. Included with appreciation.

In both cases, levees or paleo valleys, land will need to be used, perhaps acquired by eminent domain, and involving settlements with land owners. Property owners will not be happy. Neither will governments who will see increased building costs and decreased tax revenues.  Insurance will play an important role: insurance companies will not authorize rebuilding if future flood damage is probable. But while levees will keep the water back, unless they are redesigned, they will not serve the dual purpose of restoring groundwater, increasingly precious in a period of drought. The Colorado River can do only so much.

Could paleo valleys become preserves? Image: “Yellowstone National Park” by Henry Wellge, 1905. wikimedia public domain. Included with appreciation.

Levees will continue to be an important defense against inundations. But paleo valleys may be an additional solution to California’s water challenges: absorbing flood water and replenishing underground aquifers. We are just beginning this exploration: a system of paleo valleys has been found in Southeastern Brazil, and in the Himalayas. Where else may we find these hidden resources? How can we preserve and use them in a new era of climate change? Think of paleo valleys as Nature’s infrastructure.

Flavelle, Christopher and Raymond Zhong. “Weeks of Storms Test California’s Approach to Taming Nature.” 5 January 2023; updated 11 January 2023. The New York Times.

Gies, Erica. “Hidden ‘Paleo Valleys’ Could Help California Survive Droughts.” 18 November 2022. Scientific American.

Gies, Erica. Water Always Wins: Thriving in an Age of Drought and Deluge. Chicago: University of Chicago Press, 2022.

Knight, Rosemary, et al., “Airborne geophysical method images fast paths for managed recharge of California’s groundwater.” 2 December 2022. Environmental Research Letters, Volume 17, Number 2.

Marsh, René. “California’s dilemma: How do you harness an epic amount of rain in a water-scarce state” Let it flood, scientists say.” 10 January 2023. CNN.

Mount, Jeffrey. “The High Cost of Fixing Levees.” 23 February 2017. Public Policy Institute of California (PPIC).

Pacific Institute.

Building the World Blog by Kathleen Lusk Brooke and Zoe G. Quinn is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Un

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