(This article was published in the March, 2009, Facets of Freshwater, the Freshwater Society’s newsletter. Read it here, or go to www.freshwater.org.)
This summer, there are going to be some big floods in Minneapolis.
The floods won’t inundate Hennepin Avenue, they won’t seep into the IDS Crystal Court or the Metrodome and they won’t displace residents of any of the city’s neighborhoods.
In fact, the floods won’t be real floods at all. They will be a carefully planned experiment in which torrents of water – each the equivalent of a once-in-50-years flood – will be sent rushing through the floodplain of the small artificial stream that is the heart of the University of Minnesota’s new Outdoor StreamLab.
The fake floods, nine-hour events intended to allow researchers to observe and precisely measure how engineered structures and vegetation such as sedges and rushes stabilize stream banks and prevent the loss of soil to high water, are an example of the controlled experiments the Outdoor StreamLab makes possible.
“What we have is an opportunity to change the stream, manipulate what’s entering the system, and see how it affects the water, sediment, and organisms within the stream,” said Anne Lightbody, a university research fellow who is director of the lab.
The $500,000 artificial stream cutting through an artificial flood plain has been used by researchers since last summer. It is across the Mississippi River from Downtown Minneapolis, a little way upstream from the Stone Arch Bridge. Water from the Mississippi is diverted into the stream through two 18-inch pipes.
Despite its relatively small size – 130 feet by 60 feet, about one-sixth the size of a football field – the StreamLab stream lab is, by far, the largest such facility in the United States. It is a dramatic improvement on the indoor flumes and basins that researchers long have used to model stream behavior in the university’s nearby St. Anthony Falls Laboratory.
“Everything we do here is trying to build small-scale models of natural phenomena,” said Fotis Sotiropoulos, the director of the St. Anthony Falls Lab. “The indoor lab is very useful and serves its purpose, but it has limitations.”
The outdoor lab is operated as a partnership between the St. Anthony Falls Lab and the National Center for Earth Surface Dynamics, a multi-university consortium sponsored by the National Science Foundation and housed at the St. Anthony Falls Lab.
The stream in the Outdoor SteamLab is about 9 feet wide and about a foot deep in its quiet pools, a few inches deep where it flows over rocks and gravel. It allows experiments that mimic creeks and streams. Eventually, Sotiropoulos hopes, the partners will build a bigger, much longer, artificial stream adjacent to the current one that would allow researchers to conduct experiments more applicable to large rivers.
For now, though, the researchers using the Outdoor StreamLab are reveling in their ability to manipulate the flow and environment of the artificial stream for experiments.
Lightbody is leading research on the impact of sediment pollution on aquatic insects.
Last summer, researchers introduced about a ton each of sand, clay and top soil into the stream – an attempt to replicate the kind of sedimentation that would accompany an intense storm. Then they captured and counted the insect species floating in the water and clinging to rocks in the shallows, upstream and downstream of the sedimentation.
Another research project is attempting to measure the extent to which nitrogen, a common pollutant, is removed from stream water when water flows out of the stream, into the sub-surface water table and then back again into the stream.
Still another research project looked at the way sediment moved within the stream. The stream was constructed with a flat bottom, but over a short time that changed. To the delight of the researchers, the artificial flow created sand bars on the inside of bends and deep pools on the outside, the same behavior as a natural stream.
“The river is continually moving sediment, and the question of how much it is moving and where it is putting it is important in streams of all sizes,” Lightbody said.