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School of Environment and Natural Resources


Ohio State Study: What Happens to a River When a Dam Comes Down?

April 8, 2014
This article was originally published on the CFAES website on April 7, 2014, and was written by Kurt Knebusch.
COLUMBUS, Ohio -- Tear down a dam and a river will change. But just how much? And what will it do to what lives in the river?
To find out, scientists in Ohio State University’s College of Food, Agricultural, and Environmental Sciences are looking no farther than their own backyard.
Mazeika Sullivan and Kristin Jaeger, assistant professors in the College's School of Environment and Natural Resources, are studying the effects of dam removal at two former dams in Columbus: the Fifth Avenue dam on the Olentangy River, which flows through Ohio State’s campus, and the Main Street dam on the Scioto River some five miles south downtown.
“There’s a growing trend toward using dam removal to restore rivers, but studies documenting both short- and longer-term river responses to dam removal are limited,” Sullivan said. “This work links exciting basic science questions with outstanding opportunities for applications to river management and conservation.”
The study’s findings should improve future dam removals, he said, especially in similar urbanized areas, by giving a clearer idea of what to expect and whether a project’s goals will be met.
Jaeger, shown here sampling sediment at a site not part of the study, specializes in
the morphology of rivers and streams -- the shape of their channels and how they
respond to changes. (Photo: K. D. Chamberlain.)
Government agencies are increasingly tearing down unneeded dams, aiming to improve water quality, fish and wildlife habitat, and recreation safety and access in rivers.
The researchers are documenting the exact physical changes seen at the sites, especially in terms of channel shape, water flow, and features like pools and riffles. Then they’re trying to show the changes’ effects on the fish, birds, insects and others that call the rivers home.
They’re also looking at changes in the rivers’ ecosystem processes, such as sediment transport, contaminant buildup, and the flow of energy and carbon in food webs between creatures in the water and on land.
Sullivan is an ecologist who studies riparian ecosystems -- how communities of living things in and along rivers interact with their environment.
Ohio State's Jared Shaffer, a research associate with the study, uses an acoustic
Doppler profiler last summer on the Olentangy River. The device gives detailed
data on the shape of the river bottom and on the river's currents and flow.
(Photo: Kristin Jaeger.)
Jaeger’s interests lie in stream morphology -- the shape of a stream or river channel and its responses to changes, whether changes due to nature or people.
By combining their different disciplines, they hope to see the wider ripples that come from freeing up a river.
A slow, deep, stagnant pool will be gone from where the dam was, for example. New pools and riffles will form. The current will mostly be faster. The river’s width will grow and shrink in more direct response to rain and snow.
Those and other features should have strong impacts on biological communities, Sullivan said.
The study will survey the numbers and diversity of aquatic organisms at both sites,
including insects and fish. Shown here is a smallmouth bass, a popular game fish
that lives in both rivers. (Photo: Eric Engbretson, U.S. Fish and Wildlife Service.)
“We’re hoping to show those connections, between changes in the river and changes in the aquatic communities, and how they play out over time,” said Jaeger.
A National Science Foundation (NSF) rapid-response grant partly funds their research.
Workers demolished the Fifth Avenue dam in 2012 as part of Columbus’s Lower Olentangy Ecosystem Restoration Project.
The Main Street dam was partially brought down in fall 2013 as a step in the city’s Scioto Greenways plan.
City and state officials said neither dam was needed anymore. Both dams were lowhead dams, which are usually less than about 15 feet high.
Jaeger is using a high-tech tool called an acoustic Doppler profiler to survey the sites about every three months. The device uses sound waves to get high-resolution topographic data about the shape of the streambed. It also provides high-resolution “velocity profiles” -- cross-sections of the channel showing the speed and direction of the flow.
A scene last summer on the Olentangy River shows new riffles near the dam removal
site. Riffles are areas of faster flow that aerate the water, a step toward better water
quality. They also diversity the habitat for aquatic organisms. (Photo: Kristin Jaeger.)
Sullivan is collecting and identifying aquatic invertebrates, such as caddisflies and mayflies. He’s seining and electrofishing to see what types of fish are there, from darters to bass and in between.
He’s also sampling streamside spiders and, using mist nets, is surveying the sites’ bird life. Are tree swallows and other aerial insectivores -- birds that eat insects caught on the wing -- finding more or less food to eat? Is the quality of their food resources changing? The answers may benefit conservation efforts, as aerial insectivores are currently seeing widespread population drops.
Tissue or blood samples taken from the organisms will let him test for stable isotopes -- a way to trace food-web connections -- and for contaminants, such as heavy metals and PCBs, which can build up in sediments behind dams.
The study also will survey “aerial insectivores” at the sites -- birds, like this tree swallow,
that eat insects caught on the wing. As a group, aerial insectivores are seeing steep
drops in population. (Photo: Tachycineta bicolor by Bear Golden Retriever licensed
under CC BY 2.0 via Wikimedia Commons.)
Key to the research is that Sullivan has done similar surveys since before the dams fell, part of another study on how changes in urban land use affect several aspects of rivers.
“Thus we have a three-year ecological data set of pre-dam-removal river conditions, which enables us to explicitly test the effects of dam removal. This isn’t common in other (dam removal) studies,” he said.
The control site -- the “before” in the before-and-after study -- is a dammed section of the Olentangy River next to Ohio State’s Wilma H. Shiermeier Olentangy River Wetland Research Park. The park, just north of the university’s campus, also provides newly renovated wet lab space for some of the work.
Part of the research also will compare active versus passive restoration after a dam is removed. Are steps such as regrading the riverbed and replanting bankside vegetation necessary? Are they cost-effective? Or does it work just as well to let nature take its course?
More than 60 dams have been removed from Ohio rivers and streams since the 1970s, according to an Ohio Department of Natural Resources website. About a third have come down in the past 10 years.
Sullivan said estimates done in the year 2000 showed that Ohio had nearly 4,800 dams of all sizes, and the U.S. about 75,000, with a big majority of both being small or lowhead dams.
“We’ve had a profound effect on rivers with our land uses and with our physical engineering of the river channel," said Jaeger. "We’ve really altered and constrained a lot of river processes, such as the downstream flux of sediments and river connectivity with the adjacent floodplain, that may have cascading effects into ecosystem processes.
“It’s still a relatively new science, but we’re coming to understand the consequences of human impacts that limit river processes,” she said.
“We can’t necessarily undo all our activities, but through projects like this one, hopefully we can better manage our rivers and watersheds to benefit the ecosystems they support.”
In addition to the NSF grant, Jaeger and Sullivan have jointly received a grant from the National Institutes for Water Resources to support their research. Sullivan also has gotten grants from the Ohio Water Development Authority and the Ohio Department of Natural Resources’ Division of Wildlife to support the work.
Both scientists hold appointments with the college’s research arm, the Ohio Agricultural Research and Development Center.