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Researcher Feature: Dr. Sarah V. McKnight

Dr. Sarah McKnight is currently an Assistant Professor of Hydrogeology at the Department of Geology and Environmental Sciences at the University of Dayton. She recently graduated with a PhD from the Department of Geosciences at the University of Massachusetts Amherst. She received a B.A. at Mount Holyoke College and M.S. at UMass Amherst. Her research uses numerical simulations and remote sensing techniques to study density-driven flow dynamics of brine-rich groundwater in arid basins, and resulting geochemical and surface water interactions. Her current work focuses on field sites in the Altiplano-Puna region, but previous work has taken her to the Ruby Mountains in northwestern Utah and parts of the Middle East including Jordan and Palestine/Israel.


How would you explain your research to your family/4th grader/12-year-old?

My work focuses on using different modeling techniques to better understand how groundwater is moving through deserts. You can’t see water flowing through the ground, but if you know the physics behind groundwater flow, you can calculate how much water is moving and how fast it moves through the ground to match what we see above the ground. A lot of interesting things happen in deserts like groundwater in valley floors tends to get saltier. Since salty water is heavier, any less salty or fresher water will flow over and above the salty water, so you can have groundwater flowing very differently in different parts of the same aquifer depending on the water chemistry. So modeling water flow through these kinds of systems is really important for better understanding these water resources for all the communities, economies, and ecosystems that rely on them.

Give us an elevator pitch of your last paper.

The most recent paper focused on characterizing the inflow and outflow dynamics of surface water bodies that lie next to salt flats and are important for sustaining ecosystems in arid environments. Through lumped parameter modeling, I was able to estimate how inflow would change over time following extremely large rain events that have been increasingly occurring in the Altiplano-Puna region of South America. Modeling results suggest that post-precipitation groundwater recharge is crucial for long-term changes in surface water inundation. However, local groundwater fluctuations don’t capture this kind of long-term recharge, which suggests that groundwater recharge occurs elsewhere and likely in the higher-elevation, upgradient areas of the aquifer where more precipitation occurs.

How did you end up in the field of Hydrology?

When I was doing a Fulbright Fellowship in Jordan, where I was studying the historical seismicity of the Dead Sea Transform fault, I was lucky enough to go on side projects with my advisor. He is a geophysicist, and he was involved in doing surveys that helped characterize aquifers all around the country. Those projects, coupled with the experience of living in Jordan which is the world’s most water-poor country, made me really curious about how groundwater flows through the subsurface, especially in arid regions.

Which part of your work do you feel is the most rewarding?

There are so many parts of this work that feel rewarding. I would say one is engaging with students who are curious about better understanding hydrogeology. Another part is just the process of learning through modeling, and how much you can learn simply by building a model.

Share a funny story from the field or the lab.

I’ve been lucky to go on a lot of different field excursions, one including work near Crested Butte, Colorado, where we were using drone imagery to map out the temperature for identifying sources of groundwater discharge to a pristine alpine stream. After our mapping was complete, I hiked all around the basin to pick up the orange cones we had hammered down into the ground and geo-tagged as waypoints for stitching our imagery together. Scrambling down a hill, out of the silence I suddenly hear that unmistakable rattling sound! I run in the opposite direction, and catching sight of my colleague in the distance, I start shouting about rattlesnakes, and hearing him shout a sort of incredulous, “Really?” I say “Yes, really,” getting flustered, when suddenly, I hear another rattling directly in front of me, which makes me freeze. That’s when I realized that in my hurry, I had kicked a pine cone, and the way these pine cones rolled down the slurry of alluvial debris sounded very similar to a rattlesnake’s warning. We laughed about my moment of panic afterward, and I learned to keep an eye on what my feet were kicking up during off-trail hikes like that one.

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