By Julia Munemo Photo by Brad Wakoff
A photo of volunteers clearing debris out buckets of debris from streams in Hopkins Forest.
Volunteers spent a day in August clearing tons of sediment out of the weirs of Hopkins Forest’s Birch Brook.

Marco Vallejos ’20 was working as a lab assistant for the geosciences department a few summers ago when he was recruited to help out with Weir Day. He joined 20 other Williams volunteers—students, faculty and staff—on a hot August day, hiking into Hopkins Memorial Forest carrying shovels, buckets and spring scales to clear tons of sediment out of the weirs of the Birch Brook.

The weirs are low dams with a v-notch in their center. Built in 1936 by the Civilian Conservation Corps to help measure the flow of water, they are still in use today. But so much sediment accumulates around them over the course of a year that the instruments used to measure the water get buried. So volunteers gather for Weir Day each summer to clean them out.

Vallejos enjoyed his experience both for the camaraderie and because it clarified his academic path. “Spending a few hours knee-deep in cold water on a hot summer day with a shovel in hand cannot be beat,” he says. “I spent the day talking with upperclassmen and professors, and those conversations swayed me into a geosciences major even more than my summer lab work.”

The volunteers’ efforts help keep the 2,600-acre reserve pristine and maintain its relatively undisturbed ecosystems. Faculty and students use Hopkins Forest as a laboratory to conduct research of all kinds, from studies about the population dynamics of the invasive garlic mustard plant to understanding the migration patterns of Northern Saw-whet Owls.

Emeritus professor of geosciences David Dethier has used the forest for his research in hydrology, geomorphology and geochemistry for more than 30 years. He was instrumental in starting Weir Day, and he and his colleague Jay Racela, who supervises the Environmental Analysis Lab, keep track of the data that come from the work clearing, sorting and weighing sediment.

Typically the volunteers remove about four metric tons of rocks and organic material. Storms and other factors can increase the amount of sediment; in 2013, volunteers needed two days to clear out what turned out to be 25 metric tons.

Recently Dethier and Racela collaborated with Scott Weiman ’14, who participated in Weir Day as a student and now manages a lab at the NASA Goddard Space Flight Center. They studied three decades of chemical data collected at Hopkins Forest’s weirs and weather stations. “Our work shows that the Clean Air Act is having results,” Dethier says. “While acid rain did have an impact on the streams, recovery is now taking place.” The team will publish its work in the journal Hydrological Processes this winter.

Morgan Dauk ’21, who plans to major in biology and environmental studies, volunteered for Weir Day this past summer. “I felt the experience is likely similar to what I will encounter in a research-based career path someday,” she says.

Adds Vallejos, who has volunteered every year since he was first recruited, “Weir Day provides a respite to a summer filled with academia. It should not be missed.”