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Modeling Sediment in San Francisco Bay's Tidal Marshes

Modeling Sediment in San Francisco Bay's Tidal Marshes

It’s a bright December day on the breezy, northern side of the Exploratorium’s Pier 15. Despite the cool temperatures, two kids are experimenting with water, mud, and sand pumped up from the Bay below.

A woman and two boys interact with the Sediment Trapping exhibit, a flume flowing with Bay water and sediment.

They’re at a new outdoor exhibit called Trapping Sediment, where Bay water and sediments flow gently down a sloping flume table. 

A young boy using the Trapping Sediment exhibit prepares to adjust an array of artificial plant stems.

After sloshing things around a bit, one boy carefully places a set of artificial plants into the stream. He stares transfixed as sparkling grains of sediment tumble down the stream, glinting in the sunlight. The plants slow down the water nearby, causing sediment to build up in tiny, muddy shoals. It’s a pretty good model of the processes happening in tidal marshes along the shores of San Francisco Bay.

The new exhibit grew out of a collaboration between the Exploratorium’s Studio for Public Spaces and the research group of Laurel Larsen, a UC Berkeley assistant professor of physical geography. UC Berkeley environmental engineering graduate student Madeline Foster-Martinez also played a key role in the collaboration.

Professor Laurel Larson stands in front of a sediment research flume in her lab at UC Berkeley, while lab manager Aaron Hurst stands on top of it.

Larsen's grant from the National Science Foundation funded both the exhibit and a research-grade flume for the lab (above, with Larsen, left and former Lab Manager Aaron Hurst). Her team is using the flume to study the things that help sediment get deposited around plant stems in marshes. They’re especially curious about the role of biofilms—the goopy, bacteria-filled gunk that coats the surfaces of many aquatic plants.

Researchers in Laurel Larson's lab wearing waders work at their research apparatus among the wetlands of Louisiana's Wax Lake Delta.

Larsen's team also studies sediment dynamics in real estuaries, like the Wax Lake Delta in Louisiana (above), using field flumes to isolate a small section of the marsh. 

An aerial view of a former salt pond in southern San Francisco Bay, converted into a tidal marshland filled with green plants and meandering waterways.

Studying sediment build-up is important for estuaries like San Francisco Bay, where wetlands managers are trying to preserve existing tidal marshes, and rebuild marshes that once lined the Bay’s shores, such as the salt ponds in the South Bay (above). Tidal marshes help protect shorelines against erosion from waves and storm surges. And as sea levels rise due to climate change, marshes may gradually shift inland, helping to protect nearby urban landscapes.

Like wetland scientists, visitors to the Sediment Trapping exhibit can experiment with ways to keep sediment in a marsh. They can arrange artificial plants in different patterns to see which one traps sediment most effectively.

Perhaps playing in the mud will inspire the next generation of wetlands researchers. Larsen remembers how she spent her time in Florida as a child: “playing around outside, mostly in water, reading, and solving puzzles.” And, she likes to point out, these are all important parts of her job as a scientist today.

The Exploratorium exhibit development team for this project included Maz Kattuah, Steve Gennrich, Shawn Lani, Sue Pomon, Kevin Boyd, Eileen Campbell, and Susan Schwartzenberg.

Photo credits: Steve Gennrich; Amy Snyder; Environmental Systems Dynamics Laboratory; Laurel Larsen; and Cris Benton.