Buffalo, N.Y. -- Dead zones in critical waterways, accelerated
loss of arable land and massive famines. They're all caused by the
24 billion tons of soil that are lost every year to erosion, a
phenomenon that costs the world as much as $40 billion
But predicting where erosion occurs, and thus how to prevent it,
is a serious challenge.
That's why University at Buffalo geographer Sean Bennett has
constructed various systems to model it, with assistance from UB's
machine shop. His methods range from the deceptively low-tech, like
simulating rainstorms over sandboxes to the high-tech, such as the
use of particle image velocimetry (PIV) in large, re-circulating
flumes to study how water and grains of sand interact.
The purpose of his work is both exceedingly practical -- geared
toward helping farmers learn how to best prevent erosion -- and
fundamental, to better understand how planetary surfaces evolve
"We have feet in two domains," he explains, "we're studying
processes similar to those that created Niagara Falls; at the same
time, we're studying how these processes degrade soil resources
The UB research is helping scientists better understand some of
the key triggers of erosion, the complex formation of channels on
the landscape, called rills and gullies.
"Rills and gullies are the dominant erosion processes on
agricultural landscapes today and the main contributor to soil
loss," says Bennett, PhD, UB professor of geography in the College
of Arts and Sciences and an active researcher in the UB 2020
Strategic Strength in Extreme Events.
Rills and gullies also are a primary cause behind excess
sediment and nutrients in waterways, which transports soil and
chemicals further downstream.
Bennett says that these high nutrient loadings of nitrogen and
phosphorus from eroding agricultural areas destroy aquatic
resources, causing unmitigated growth of aquatic algae, depletion
of dissolved oxygen and the creation of "dead zones" in places like
the Gulf of Mexico.
Ironically, past research by Bennett demonstrated that when
farmers till fields to remove rills and gullies, they actually end
up accelerating erosion.
"Our numerical model showed that you could reduce soil losses by
400 percent if you adopt a no-till farming practice," says Bennett.
"This is because the gullies grow to some maximum size on the
landscape during a growing season. If farmers repair them by
tilling the soil each spring, the practice actually causes much
greater soil loss over the long term."
Bennett's physical model showed similar phenomena.
"Our laboratory landscape showed the same thing," he says,
"rills grow and evolve in time and space, erosional processes get
arrested and reach an endpoint. After that, they don't produce much
To model how rills and gullies form, Bennett and his students
built a rainfall soil erosion facility, erecting a 30-foot by
8-foot flume containing eight tons of soil, which allowed them to
monitor their simulated landscape, looking for disturbances in the
soil and the creation of rills and gullies.
Using digital cameras positioned directly above the flume, they
developed digital elevation models of the topography across the
flume, at millimeter-scale accuracy.
"Each set of images represents how the topography evolved at a
discrete space and time during the simulated storm," says
The images reveal at what point during the rainfall and runoff,
phenomena called headcuts -- small intense areas of localized
erosion -- begin to carve deep channels into the soil.
"If we can predict where and when these headcuts occur, and
develop technology that allows us to control them, then we can
greatly improve soil resource management," says Bennett.
Such technologies include runoff diversions, grass barriers and
The images also revealed with startling clarity the fractal
patterns that the simulated storm created in the landscape.
"Fractal organization is one of the most compelling ideas in
science," says Bennett."While I always knew that landscapes had
fractal characteristics, I never saw it demonstrated so clearly as
when I saw these treelike patterns in the images we took of our
To study sediment transport processes in rivers and how
particles interact with the turbulent flow, Bennett designed a
30-foot by 2-foot flume channel, which was constructed by the UB
In one experiment, the researchers fill the channel with sand
and water, flatten the bed, and then turn on the centrifugal pump
to initiate sediment movement.
"Once the flow reaches a certain velocity, the entire bed erupts
into ripples, created by the instability between the fast-moving
fluid overlying the slow-moving sediment," Bennett explains.
"The PIV system can provide us with high-quality images and data
right at the bed surface while these bedforms are being created,"
he continues. "By examining the physics of sediment transport in
this way, we can develop improved models for flow and transport in
rivers, allowing us to better manage our river systems and aquatic
Bennett hopes to use these flumes and equipment to expand his
research on the interactions between vegetation and river function
and form. Such interactions are critical to the process of
restoring and stabilizing degraded streams, a primary thrust of the
National Science Foundation-funded "Ecosystem Restoration Through
Interdisciplinary Exchange" graduate training program at UB, in
which Bennett participates through research and training.
His work is funded by the U.S. Department of Agriculture and the
National Science Foundation.
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York system and its largest and most comprehensive campus. UB's
more than 28,000 students pursue their academic interests through
more than 300 undergraduate, graduate and professional degree
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the Association of American Universities.