Using Paleo Valleys to Recharge Aquifers, with Dr. Rosemary Knight
For a transcript, please visit https://climatebreak.org/using-paleo-valleys-to-recharge-aquifers-with-dr-rosemary-knight/ How can insights from geophysics help us to make better use of rainwater? Geophysicists, like Stanford’s Dr. Rosemary Knight, can identify ancient, buried riverbeds called paleo valleys. We spoke with her about how such geologic structures can help us recharge aquifers deep below the Earth’s surface.
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Show Notes
What are Paleo Valleys?
Paleo Valleys were created at the end of the last ice age by melting glaciers that carved into the sediments deposited in the Central Valley. When the glaciers receded, high-velocity meltwater carried sediments and grain material into the valley. These sediments are extremely porous, and the permeability means they can absorb 60 times more water than surrounding clay. Because of this, they provide a pathway that can draw surface water hundreds of meters down to aquifers, which also hold water in soil.
Using Paleo Valleys
Paleo valleys can greatly benefit aquifer recharge. Because of the high permeability, paleo valleys can hold large quantities of water and provide a direct route for water to the aquifers. As the result of drought and pumping from aquifers, California groundwater is significantly depleted. Paleo valleys can help replenish the groundwater. In addition, paleo valleys can store excess water during storms, which can then help replenish groundwater. Thus, identifying and enhancing paleo valleys could increase our capacity to hold and store water below ground in California.
Challenges in Locating Valleys
In the Sierra Nevada Mountains, each of the major rivers draining watersheds are likely to have associated paleo valleys. However, locating these paleo valleys has proved challenging for scientists and researchers. Finding the valleys requires substantial soil testing, and it has taken scientists longer than anticipated to uncover just a few of the paleo valleys suspected to exist.
That is where airborne electromagnetic imaging (AEM) comes in. This technology uses electromagnetic pulses and responses (usually from airplane overflights) to distinguish the soil types in these regions. This method has been used to visualize and more easily identify paleo valleys in the Sierras and the Central Valley. Rosemary Knight and her team have been using this technique to map out optimal locations where the subsurface provides a good storage capacity. These results have helped Knight create a three-dimensional map showing the makeup of the land, essential to identifying paleo valleys.
About Our Guest
Dr. Rosemary Knight is a geophysics professor at the Stanford Doerr School of Sustainability. Her research focuses on developing geophysical methods for imaging. She specifically uses electromagnetic methods to explore how the movement of water in the subsurface is distributed, and what processes cause this. She has conducted many studies and published multiple papers on modeling these land characteristics, and her developments have revolutionized the ability to identify subsurfaces.
Further Reading
- Airborne geophysical method images fast paths for managed recharge of California's groundwater (Knight et al. 2022).
- How CA's ancient hidden waterways could be key to recharging state's depleted groundwater
- Capturing the Flood in California’s Ancient Underground Waterways
- What is Airborne Electromagnetics?
For a transcript, please visit https://climatebreak.org/using-paleo-valleys-to-recharge-aquifers-with-dr-rosemary-knight/