Friday, January 25, 2008

Natural Rivers

After thousands of years of human habitation and rearrangement of the land to better serve human needs and interests, it is very difficult to actually determine what is really natural and what is not (very true of our rivers and Parkway).

Study: Are River Restoration Efforts Misguided?
by John Nielsen
All Things Considered, January 19, 2008 •

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 300years 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.