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
Oasis of life in the ice-covered central Arctic
24.10.2016 | Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung
Receding glaciers in Bolivia leave communities at risk
20.10.2016 | European Geosciences Union
Terahertz excitation of selected crystal vibrations leads to an effective magnetic field that drives coherent spin motion
Controlling functional properties by light is one of the grand goals in modern condensed matter physics and materials science. A new study now demonstrates how...
Researchers from the Institute for Quantum Computing (IQC) at the University of Waterloo led the development of a new extensible wiring technique capable of controlling superconducting quantum bits, representing a significant step towards to the realization of a scalable quantum computer.
"The quantum socket is a wiring method that uses three-dimensional wires based on spring-loaded pins to address individual qubits," said Jeremy Béjanin, a PhD...
In a paper in Scientific Reports, a research team at Worcester Polytechnic Institute describes a novel light-activated phenomenon that could become the basis for applications as diverse as microscopic robotic grippers and more efficient solar cells.
A research team at Worcester Polytechnic Institute (WPI) has developed a revolutionary, light-activated semiconductor nanocomposite material that can be used...
By forcefully embedding two silicon atoms in a diamond matrix, Sandia researchers have demonstrated for the first time on a single chip all the components needed to create a quantum bridge to link quantum computers together.
"People have already built small quantum computers," says Sandia researcher Ryan Camacho. "Maybe the first useful one won't be a single giant quantum computer...
COMPAMED has become the leading international marketplace for suppliers of medical manufacturing. The trade fair, which takes place every November and is co-located to MEDICA in Dusseldorf, has been steadily growing over the past years and shows that medical technology remains a rapidly growing market.
In 2016, the joint pavilion by the IVAM Microtechnology Network, the Product Market “High-tech for Medical Devices”, will be located in Hall 8a again and will...
14.10.2016 | Event News
14.10.2016 | Event News
12.10.2016 | Event News
24.10.2016 | Earth Sciences
24.10.2016 | Life Sciences
24.10.2016 | Physics and Astronomy