LITITZ, Pa. — Dorothy J. Merritts, a geology professor at Franklin & Marshall College in Lancaster, Pa., was not looking to turn hydrology on its ear when she started scouting possible research sites for her students a few years ago.
But when she examined photographs of the steep, silty banks of the West Branch of Little Conestoga Creek, something did not look right. The silt was laminated, deposited in layers. She asked a colleague, Robert C. Walter, an expert on sediment, for his opinion.
“Those are not stream sediments,” he told her. “Those are pond sediments.” In short, the streamscape was not what she thought.
That observation led the two scientists to collaborate on a research project on the region’s waterways. As they reported this year in the journal Science, their work challenges much of the conventional wisdom about how streams in the region formed and evolved. The scientists say 18th- and 19th-century dams and millponds, built by the thousands, altered the water flow in the region in a way not previously understood.Continue reading the main story
They say that is why efforts to restore degraded streams there often fail. Not everyone agrees, but their findings contribute to a growing debate over river and stream restoration, a big business with increasing popularity but patchy success.
Many hydrologists and geologists say people embark on projects without fully understanding the waterways they want to restore and without paying enough attention to what happens after a project is finished.
In part because most projects are local and small scale, it is hard to say exactly how much Americans spend each year to restore rivers and streams. A group of academic researchers and government scientists, writing in Science in 2005, put the figure at well over $1 billion, for thousands of projects. Efforts are under way to bring more academic rigor to the business.
For example, the National Science Foundation is supporting construction of a large model streambed in Minneapolis, where researchers will be able to test ideas. Meanwhile, though, “an awful lot of stream restoration, if not the vast majority of it, has no empirical basis,” said William E. Dietrich, a geomorphologist at University of California, Berkeley, who studies rivers and streams. “It is being done intuitively, by looks, without strong evidence. The demand is in front of the knowledge.”
Property owners and local and state agencies restore streams for many reasons, like repairing damage from bridge and dam construction or runoff from farms, subdivisions and parking lots. The damage is visible in reduced water quality, damage to habitats, declines in fish, reduced recreational and aesthetic value and other problems.
Some projects use bulldozers to reshape waterways. Others rely on boulders, rock-filled metal baskets called gabions or concrete and other armor to hold rivers in place. Unfortunately, “we have not done enough monitoring to know what works and what doesn’t,” said Chris Conrad, an environmental engineer for the United States Geological Survey, voicing a widely held view.
“Most agencies want to spend the money making things happen and not spend the money finding out if they work,” Dr. Dietrich said.
David R. Montgomery, a geomorphologist at the University of Washington, agreed. Monitoring “involves a lot of people and thought and expertise,” he said. “And you don’t have any new projects to show for it.”
As a result, the academic and government scientists said in their report, “Many opportunities to learn from successes and failures, and thus to improve future practice, are being lost.”
Nowadays, Dr. Montgomery said, most people agree that the best approach is to create landforms and water flows that streams can maintain naturally. “But how you translate that into action and at this stream rather than that stream really requires a lot of work to figure out,” he said. With an ailing waterway, he said, “sometimes there’s a clear line between the symptoms and the cause, and sometimes there’s not.”
Project failure comes in many forms. Often, Dr. Dietrich said, people design projects in hopes of creating “a meandering channel with relatively low banks that look nice.” Then, he said, “a large storm can come through and completely wipe it out,” leaving shallow channels traveling around sandbars in multiple threads, what geologists call a braided channel.
“In most of those cases,” he added, “the restorer has taken a system that is naturally braided and forced it into a form. The channel simple defeated it by being its natural dynamic self.”
At other failed sites, restorers install boulders or other stabilizing armor only to see the water shift around it, leaving piles of rubble midstream. In the Pacific Northwest, people tried to improve stream flow by removing bank side logs and branches only to realize that the debris provided important fish habitat. “We are now spending millions of dollars to compensate for all the wood we took out earlier,” Dr. Dietrich said.
In Pennsylvania, Dr. Merritts and Dr. Walter say, efforts to restore stream flow by removing dams ignored not just the sediment piled up behind them, but also the original landscape, in many cases not meandering streambeds but swampy valleys over which shallow water flowed in sheets.
After dams were built — as many as 8,000 in Pennsylvania — water accumulated in millponds, and the sediment it carried settled to the bottom. When waterpower fell out of favor in the late 19th and early 20th centuries, the dams deteriorated until they failed or were removed.
Freed to flow more swiftly, streams began incising channels through the beds of silt. The fine material eroded rapidly, sending tons of sediment — much of it carrying agricultural chemicals like nitrogen and phosphorous — downstream to the Susquehanna River and, ultimately, Chesapeake Bay.
One day recently, Dr. Walter and Dr. Merritts visited restoration sites in the Lancaster region. On one stream, a property owner had planted trees to stabilize stream banks. But the trees had to send roots through almost five feet of accumulated sediment before reaching the water table, a feat most were unable to accomplish before dying of thirst.
Dr. Merritts and Dr. Walter recommend simply removing the sediment and exposing the valley floor, as was done in a restoration project near Lititz, Pa. The project, financed by the State of Pennsylvania, working with LandStudies Inc., a restoration concern, involved removing up to 25,000 to 30,000 cubic yards of silt, enough to fill thousands of dump trucks. Luckily, said Ward Oberholtzer, a partner in LandStudies, it was easy to dispose of because farmers love to spread it on their fields.
And because there are no boulders or other armor involved, he said, “cost-wise we compete pretty well.”
When the work was done, a result was a shallow sheet of water moving over a graveled bed. The water was lined with native plants like sedges, vervain and verbena, sprouted from seeds buried under the silt for more than 100 years. One spot was deepened to create a cool refuge for fish, and nearby, dozens shimmered in the water.
But an approach that works in one place may fail in another. And some critics say restoration to some pristine ideal is simply impractical. Perhaps the most prominent is David L. Rosgen, a hydrologist who runs Wildland Hydrology, a consultancy in Fort Collins, Colo., that designs restoration projects and offers courses on his restoration theories.
“It is impossible to try to restore streams to some condition that is totally different, before we showed up, before we caused disequilibrium,” he said in an interview. “You know how many valleys have aggraded because of those old mill dams? You are talking about hundreds of millions of cubic yards of sediment.”
Dr. Rosgen devised a system that classifies rivers and streams, and prescribes restoration remedies according to several qualities, including water flow, channel characteristics and sediment load, and takes into account how human activity affects the landscape. By now, he said, more than 14,000 people from state and federal agencies and conservation groups have taken his courses and many have used his ideas to good effect.
But he, too, has his critics. Dr. Montgomery called Dr. Rosgen’s classification “a very clever system” but said it was wrong to think that “just by knowing what channel type you have you would know what to do.”
But there is not a great deal of other guidance. Some geologists point to a 1992 report by the National Research Council, the research arm of the National Academy of Sciences, that emphasizes understanding underlying natural conditions and the importance of monitoring.
Among other agencies, the federal Fish and Wildlife Service cites the Rosgen system, as does the North Carolina State University Stream Restoration Program. Overall, though, “The strategy is still largely a ‘kick it and see’ approach,” Dr. Dietrich of Berkeley said. “We don’t know whether any of this stuff that’s being done is worth it.”
He said he hoped better answers would emerge from the National Center for Earth Surface Dynamics, a research center supported by the National Science Foundation and based at the St. Anthony Falls Laboratory, on the Mississippi River, in Minneapolis. Scientists and engineers at the lab, which is affiliated with the University of Minnesota, use computers to model stream and river behavior, including sediment movement, channel and floodplain dynamics and dam removal.
The lab is also working on what Dr. Dietrich described as “the first major, outdoor, to-scale experimental facility to do experiments on a large enough scale to figure out how to bring a scientific basis to stream restoration.”
This “outdoor streamlab” relies on bypasses once used to send river water around falls, and researchers hope that it will let them try building restoration projects “to the scale of small, real channels” and test the results, Dr. Dietrich said . Researchers are lining up to use it. Dr. Dietrich said he hoped work at the lab and elsewhere would help make river and stream restoration “a predictive science — you do the following things, you get the following things.”
The problem is complex, he said, but the demand for answers is increasing. For scientists who study waterways, he said, “these are exciting times.”
A picture caption on Tuesday with an article about stream restoration misspelled the surname of a researcher. She is Dorothy Merritts, not Merrits. And the picture credit misstated the surname of the photographer. He is Robert Walter, not Walker.