ANDREA SEABROOK, host:
Time now for Science Out of the Box. This week: how the urge to return a landscape to its pristine state can be misguided.
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Billions of dollars have gone to restoring degraded American rivers to what's supposed to be their natural form. Often, the goal is to recreate a river that curves back and forth, winding beautifully. But according to a new study, the idea that a meandering river is natural maybe flawed.
NPR's John Nielsen met the authors of the new study near a winding creek in rural Pennsylvania.
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Mr. ROBERT WALTER (Geologist): We're along the banks of the Little Conestoga Creek, which flows into the main Conestoga. Now, we're going to walk along the right bank of the stream.
JOHN NIELSEN: Geologist Robert Walter used to think the Little Conestoga was about as natural as the creek can get. It's beautiful, it's tree lined and it wind past tall soil embankment that look like they've been around for thousands of years. In short, this is just the kind of stream that river restoration experts like to use as a model in this part of the East.
But then, about five years ago, geologist Dorothy Merritts, who is married to Robert Walter, started finding strange objects. There are even some of the tall banks that lined its stream.
For example, stumps from giant swamp trees cut by European settlers.
Professor DOROTHY MERRITTS (Earth and Environment, Franklin & Marshall College; Geologist): We also find log roads that early settlers built to get across these marshy bottomlands. They would cut down some of the younger trees' tall, straight trunks and lay them out in a row and lash them all together.
NIELSEN: Those finds made it look like Little Conestoga Creek had changed a lot over the past few hundred years. To find out more, Robert Walter took a bunch of soil samples and then ran tests that were designed to tell him whether the riverbanks were really as ancient as they looked.
He says it turns out that there is nothing at all ancient about big dirt embankments like the one we are now facing.
Prof. WALTERS: Everything that you see basically from my ankles to about 20 feet above it was deposited between 1730 and 1850, about 120 years.
NIELSEN: In other words, whatever the stream used to look like is now buried under 20 feet of mud. And in retrospect, Walter thinks it's obvious where all this mud came from. Three hundred years ago, they started washing down off of deforested hillsides and farm fields, he says. Then, it started pooling up behind small dams colonists had built to cover local grist mills.
He found one of those early dams nearby. A winding creek flowed over the top of it then fell 10 feet into some rocks.
Prof. WALTERS: What they did initially was probably filled a timber-crib structure and maybe fill that with sediment. And then as time went on, they reinforced it with limestone, the Conestoga limestone.
NIELSEN: Walter says more than 60,000 of these dams were turning Eastern Rivers into mill ponds by the end of the 1840s. But by the beginning of the 1900s, most of the ponds behind the dams were full of mud, and the dams themselves were abandoned or destroyed.
In the journal Science, Walter and Dorothy Merritts argued that this is when a lot of supposedly natural winding rivers actually got their start, by cutting deep channels down through the leftover mud.
Walter and Merritts teach geology at Franklin and Marshall College in Lancaster, Pennsylvania. They say the story of what happened at Little Conestoga Creek shows how quickly people can forget what natural landscapes used to look like.
Other river experts, like David Montgomery of the University of Washington, say the study is also a cautionary tale for everyone involved in the art of river restoration. He says the basic message of this paper is that if you want to put Humpty Dumpty back together again, you need to know exactly what he looked like in the first place.
Prof. DAVID MONTGOMERY (Geomorphology, University of Washington): If you are trying to restore rivers to benefit fish and other organisms in those rivers, if you're not just trying to make them look pretty — the best model for that is the system in which they evolved and thrived.
NIELSEN: Back in Pennsylvania, Robert Walter says the landscape under the Little Conestoga was probably full of swampy streams that split off into lots of little twisted channels. He says wetlands like this were probably found all over the East Coast at one time. Excavating them will not be easy.
John Nielsen, NPR News, Washington.
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In recent years, billions of dollars have been spent restoring American rivers to their so-called "natural" state. Now researchers say those restorations may be a waste of time and money, since the rivers may never have been naturally curvy to start with.
Billions of dollars have been spent in the United States on river restoration projects.
In many cases, the goal of these projects is a so-called "natural" river that curves broadly back and forth across a landscape.
But if a new paper in the journal Science is correct, there's not much that's natural about some of the curving rivers used as models for this restoration work.
The authors of the paper say that's because many eastern U.S. rivers weren't created by the forces of nature, but by Colonial farmers who built thousands of small dams across wetland areas in New England and the Middle Atlantic States. Geologists Robert Walter and Dorothy Merritts of Franklin and Marshall University in Lancaster, Pa., wrote the paper.
Walter says they first began to wonder five years ago whether winding creeks in the area were really all that natural. Merritts and some of her graduate students started pulling strange objects out of the bottoms of ancient-looking dirt embankments near the edges of the creeks.
"We found the stumps of giant trees that had been sawed down by European settlers," she says. "We found Indian artifacts and logged roads that the early settlers used to get across some of these marshy bottomlands."
Those finds made it look like the creeks had changed a lot over the past few hundred years. They also raised questions about whether the dirt embankments were really all that ancient.
These questions were answered by geologist Robert Walter, who is married to Merritts. He says tests on soil samples taken from the flood plain that surrounded the creeks showed that the riverbanks were hundreds, not thousands of years old.
Standing at the foot of a 20-foot tall embankment, he says, "basically everything you see above my ankles was deposited from 1730 to 1850 — 120 years."
In other words, the stream that had been here when European farmers first arrived is now buried underneath roughly 20 feet of mud. In retrospect, Walter says it's obvious where the mud came from.
He thinks it started washing down out of deforested areas and farm fields roughly 300 years ago. Then it started pooling up behind small dams the colonists built all over the region. More than 60,000 of these dams had been built by the end of the 1840s, Walter says, and, at one point, giant mill ponds formed behind all of them.
Eroded soils had filled most of these ponds to the brim by the start of the 1900s, Walter says. When that happened, the dams were abandoned and many were destroyed.
In the Science paper, Walter and Merritts argue that this is when many of the so-called "natural" winding rivers in the East took shape, as they cut deep channels through the leftover mud. They say that's why topographic photos of the region show that many flood plains look a little bit like giant staircases.
"Long flat stretches mark the locations of the filled-in mill ponds," Merritts says. "The sharp drops are where the dams were."
Merritts and Walter say their paper shows how quickly people can forget what natural landscapes used to look like.
David Montgomery, a geologist at the University of Washington, says the paper is also a cautionary tale for everyone involved in river restoration projects.
For example, says Montgomery, "if you are trying to restore rivers in a way that will benefit fish and other organisms — if you're not just trying to make them look pretty — the best model for that is the system in which they evolved and thrived."
Basically, if you want to put Humpty Dumpty back together again, you need to know exactly what he looked like in the first place.
Merritts and Walter say it's likely that the landscape underneath a lot of winding rivers was dominated by broad wetlands full of tangled water channels. Walter says those broad wetlands are now all but nonexistent in the East. Whether they will be restored on a large scale is an open question, he says.