Fast paths: Harnessing geophysical imaging to recharge groundwater

Supported by a Sustainability Accelerator Seed Grant, geophysicist Rosemary Knight and her team, including Meredith Goebel and Seogi Kang, use electromagnetic imaging and years of data gathered in California fields to create mapping software that highlights what they call “fast paths.” Fast paths are areas of coarser sediments where water spread on the ground surface can easily move underground. They’ve built an intuitive web-based application and offer an online training course to help users make the most of their one-of-a-kind system.

What is the sustainability problem you are working on?

Rosemary Knight: The water we’re pulling out of our groundwater systems is exceeding the water we’re putting in. This has many negative consequences. First, and most obvious, we’re depleting our groundwater supply. Wells are going dry. This is of particular concern in underserved communities in California where people rely on shallow domestic wells. Depletion of groundwater also has an impact on the connected rivers, lakes, and wetlands. These are critical habitats for many species – fish, migratory birds, others. And, last but not least, removal of groundwater causes the aquifers to compact and the surface to drop, often unevenly. California now needs an estimated $2 billion to repair broken canals that move water from the north of California to the south. 

We want to help people actively manage the recharge of groundwater. Natural recharge occurs by rainfall and snowmelt percolating down below the ground surface. But natural recharge is not keeping up with outflows. Our system helps water managers direct excess surface water to places most suitable for recharging groundwater. 

What did your Accelerator Grant allow you to do that you couldn’t before?

Knight: The Accelerator Grant provided us the funding to work with a great team of software developers at Curvenote, a private company that creates scientific publishing infrastructure and writing tools, to build a web-based application so that others can use the results of our research to find fast paths for recharge. We have been using electromagnetic geophysical imaging methods that can remotely see below the ground surface, measuring the electrical resistivity to map the types of sediments to a depth of about 300 meters. There is a helicopter-deployed method that gives us large, basin-scale coverage. There’s also a towable system that does the same thing only at smaller scales and only to depths of about 50 meters, but it allows you to take a closer look at a specific area where you’re considering a recharge site. Our software then helps identify sites that have interconnected, permeable pathways of geological material – sand and gravel usually – allowing water to move rapidly below ground. We call them “fast paths.” The geophysical imaging will show you, sand and gravel over here, clay and fine-grained sediments over here, allowing us to locate the easiest pathway for water to go from the ground surface to the water table at every point.

Seogi Kang: We’ve been researching this over about eight years and now we’ve created a web-based application that farmers, water managers, and other interested people can use to access these geophysical data of the soil makeup to produce maps of fast paths in their area. The application brings up a map of California. You select your area of interest. Our Fast Path App converts electrical resistivity to an image of the subsurface based on the percent of coarse-grained material that is present. And the seed grant allowed us to pay for the back-end and front-end code development.

Meredith Goebel: The grant also allowed me to work very closely with the Stanford Center for Professional Development to create an online course to help people use and understand the system. It’s an eight-hour online course. I focused on developing the educational materials. Our goal is to put the application in as many hands as possible so anyone can use it. And through the Center for Professional Development, the Accelerator seed grant allowed us to build this course to give people the background information they need to make informed decisions.

What makes you excited about this project?

Knight: I have a sign over my door that says, “Knowledge into action.” And that’s what we do: We take the results of our research, and we think about how we can package it in a way that it can be used by the greatest number of people possible – water managers, landowners, community members – to address critical groundwater issues. I always use the analogy with medical imaging. Medical imaging came along at the start of the 20th century. It revolutionized managing human health in the same way we believe that geophysical imaging can revolutionize managing the health of our groundwater systems. And we just need to be advancing adoption by getting tools into people’s hands. Now we’re going global. Next week, I’m talking to someone from Zimbabwe one morning and someone from India another. To me, it’s this wonderful intersection of a compelling problem that needs a solution and geophysical imaging, which I love. Years ago I came across a quote: “What is vocation? You are called to work in a place where your great gladness and the world’s great hunger meet.” I think I’ve found that.

Goebel: For me I get excited being able to see the impact. The science itself is exciting, but it’s even more exciting when you see someone make an informed decision using your work and to think: “The world is better because we did that.”

Kang: I think on my end, seeing how to formulate these types of problems in a technical form and then developing software, data, and a platform that realizes this idea is exciting. I’m a geophysicist, but on the more computational side. My motivation is to address real needs and practical problems using mathematics, physics, and computation. This was actually a perfect project for me to realize how we could translate scientific knowledge into a really useful product. 

Rosemary Knight is the The George L. Harrington Professor in the Stanford Doerr School of Sustainability and Professor of Geophysics.