Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers chance viewing of river cutoff forming provides rare insight

22.09.2011
For University of Illinois river researchers, new insight into river cutoffs was a case of being in the right place at the right time.

Geography professor Bruce Rhoads and geology professor Jim Best were conducting research where the Wabash River meets the Ohio River in the summer of 2008 when they heard about a new channel that had just formed, cutting off a bend in the winding Wabash just upstream from the confluence. That serendipity gave the researchers a rare view of a dynamic, little-understood river process that changed the local landscape and deposited so much sediment into the river system that it closed the Ohio River.

“It was fortunate to be there right when it was beginning to happen, because these are hard-to-predict, unusual events, particularly on large rivers,” Rhoads said.

While cutoffs are common in meandering rivers, or rivers that wander across their floodplains, the conditions surrounding cutoff events are poorly understood. Most cutoffs are discovered long after they first develop. The Illinois team’s quick response to the 2008 Wabash cutoff, and witnessing of a second cutoff in the same bend a year later, allowed them to monitor the huge amounts of sediment the cutoffs released into the river. The researchers published their findings in the journal Nature Geoscience.

“Cutoffs occur in just about every meandering river on the face of the earth,” said Jessica Zinger, a graduate student and lead author of the paper. “Although it’s unusual to capture one like this, they are ubiquitous events, so it’s important to understand what happens when these cutoffs occur, why they occur when they do, and how they evolve after they occur.”

The two cutoffs, both 1 kilometer long, delivered about 6 million tons of sediment from the floodplain into the river – equivalent to 6.4 percent of the total annual sediment load of the entire Mississippi River basin (which the Wabash contributes to) – in a matter of days. It would take nearly 250 years of bank erosion to displace the same amount of sediment along the bend, had the cutoff not occurred. Such sediment pulses, as they are known, are more often associated with mountain rivers, rather than the relatively level landscape of rural Illinois.

“The first kilometer-long channel was cut in eight days, which is a phenomenal rate of erosion,” Best said. “There were banks collapsing, sediment moving; it’s probably one of the most dynamic river environments you’ll ever see, and you don’t expect that in lowland, flat-grade rivers.”

The researchers found that, after each cutoff, the majority of the sediment was deposited locally. In particular, a large percentage of the sediment accumulated where the Wabash joins the Ohio River. The new layer of sediment, up to 7 meters thick, raised the bed of the Ohio River and required dredging so that barges could continue to use the river.

The Wabash River study demonstrated that cutoffs can have large, immediate effects on sediment transport and deposition in a river – processes not accounted for in current models of meandering rivers.

“If we look at river systems and their role in the landscape, one of their most fundamental roles from a geoscience perspective is that they transport sediment from the land surfaces to ocean basins,” Rhoads said. “What has not been recognized is that these cutoff events can actually deliver large amounts of sediment to the river very rapidly. Then, the question is, since cutoffs are ubiquitous along a lot of meandering rivers, could this be something that we have not recognized fully as a major sediment delivery mechanism for all meandering rivers?”

The researchers plan to continue monitoring the cutoff and the areas just upstream and downstream to document how the cutoffs contribute to the river’s evolution. They anticipate that the river will abandon the bend and the first cutoff as more water is directed through the second cutoff, a more direct route for the river to flow. The abandoned bend will become a new wetland area, shaping the local ecology. The researchers will continue to measure and model changes in flow velocity, sediment transport and morphology in the river as the cutoff channel widens, providing valuable insight into cutoff effects and perhaps contributing to a model that could predict where such sediment pulses could occur.

“Our study brings attention to a whole range of elements – the basic science, the local effects, the ecological effects, the commercial effects – all from this one mechanism of channel change,” s said. “A lot of the meandering models that are out there treat cutoffs very schematically and they don’t deal with the processes that are occurring once a cutoff develops. I think that our work could really make people rethink that aspect of modeling the long-term evolution of meander bends.”

The National Science Foundation supported this work.

Liz Ahlberg | University of Illinois
Further information:
http://www.illinois.edu

More articles from Earth Sciences:

nachricht New research calculates capacity of North American forests to sequester carbon
16.07.2018 | University of California - Santa Cruz

nachricht Scientists discover Earth's youngest banded iron formation in western China
12.07.2018 | University of Alberta

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

Im Focus: Chemical reactions in the light of ultrashort X-ray pulses from free-electron lasers

Ultra-short, high-intensity X-ray flashes open the door to the foundations of chemical reactions. Free-electron lasers generate these kinds of pulses, but there is a catch: the pulses vary in duration and energy. An international research team has now presented a solution: Using a ring of 16 detectors and a circularly polarized laser beam, they can determine both factors with attosecond accuracy.

Free-electron lasers (FELs) generate extremely short and intense X-ray flashes. Researchers can use these flashes to resolve structures with diameters on the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

Microscopic trampoline may help create networks of quantum computers

17.07.2018 | Information Technology

In borophene, boundaries are no barrier

17.07.2018 | Materials Sciences

The role of Sodium for the Enhancement of Solar Cells

17.07.2018 | Power and Electrical Engineering

VideoLinks
Science & Research
Overview of more VideoLinks >>>