Digging in the desert

Geosciences student Garth Llewellyn once spent three weeks in Egypt digging for water in the sand—a seemingly futile task. "The locals say that it last rained for 15 minutes...two years ago," he says.

However, flooding is a problem for Elizabeth Walters, a Penn State art historian who is leading the excavation of Hierakonpolis—one of the most important archaeological sites for understanding the foundations of ancient Egyptian society. Water runoff from the irrigation of nearby sugar cane fields is preventing Walters and her team from uncovering deeply buried temple ruins.

"The runoff is ruining the stratigraphy of the site," says Llewellyn. "As soon as Elizabeth digs below the water table, the ground becomes a slurry."

Llewellyn is part of a team of geoscientists helping Walters figure out how to "dewater" Hierakonpolis. "Burying a sump pump in the ground just isn’t economically feasible," he says, "We’re trying to characterize the nature of the water flow and find out if the water table is really rising."

The team of geoscientists—led by Penn State professors Duff Gold, Richard Parizek, and Shelton Alexander—is using seismic information to model the groundwater flow under the archaeological site. Seismic waves move through different materials, such as sand and water, at different velocities. The reflection and refraction of the waves allows researchers to map the water table.

"We found anomalies in the seismic data suggesting that there was unsaturated sand above and below a pool of water," says Llewellyn. "That could mean that a perched water layer is located above the water table." Perhaps, he explains, the water table is not permanently rising; rather, it could be rising with the runoff then falling, leaving a pool of water perched on an impermeable layer in the ground.

Another student recorded the seismic data a year before Llewellyn’s trip to Egypt. When he arrived in the desert in February 2001, Llewellyn’s job was to dig holes and log the layers of material in the ground: soil, saturated sand, clay, water, and unsaturated sand.

"In my undergraduate thesis I’ll compare the seismic data to the holes to help characterize the area that showed the seismic anomalies," says Llewellyn.

Garth Llewellyn was an undergraduate student in the Department of Geosciences in the College of Earth and Mineral Sciences at Penn State.