A new study from K-State researchers documents the extensive
environmental damage that dredging causes to the Kansas River. Listen to these
preliminary findings (and remember to email your public comment by December
- The scientists have documented riverbed incision in dredged
reaches, which is most likely also causing excessive bank erosion both upstream
and downstream of dredge sites.
- Private in-channel dredging operations on sand bed rivers
like the Kansas River cause deepening and widening of the channel and
accelerate erosion of the banks. As a result, dredging lowers the water level
of the river and the adjacent water table in the floodplain.
- This creates the risk for harm to public river uses (such as
water treatment facilities, municipal wells, bridge footings, etc.) as well as
to fish communities throughout the watershed, including endangered species.
The Army Corps of Engineers is considering a proposal from
five private dredging companies to increase dredging on the Kaw close to 50%,
from 2.2 million tons to 3.2 million tons. Make your comments by this Friday, December 9, 2011. It’s easy - see instructions and a
Personal comments are always preferred but just making a
comment is the most important action – you can even add personal comments to
the sample letter. Make it your holiday gift to the Kaw!
MORE ON THE STUDY:
nonprofit conservation group Friends of the Kaw (FOK) recently interviewed
Daniels for its public comment to the U.S. Army Corps of Engineers. The study was
funded by the Kansas Department of Wildlife and Parks (KDWP) and carried out by
Kansas State University researchers Melinda Daniels and Craig Paukert. The
final study results will be released in late December.
“If you take 3.2 million tons from the river bottom, then
the river will take 3.2 million tons from the riverbanks, trying to balance the
sediment load in the system,” Daniels said. “That’s the simple physics of how
water works in river channels to transport sediment. Any riparian owner should
be worried, particularly farmers with unforested river banks next to their
fields. So should anyone with a water intake pipe or a creek in their
backyard. The effects of
in-channel dredging will propagate both upstream and downstream from the dredge
site until a hard control point, like a dam or a bedrock outcrop, is
reached. That means up tributary
streams as well as the main river.”
Daniels surveyed major dredge holes on the Kansas River with
a sophisticated new measuring technology, an acoustic Doppler instrument that
mapped river channel topography and measured water velocity. The researchers
discovered that while the Kansas River averages four to five feet deep, active
dredge holes can measure up to forty feet deep.
The researchers also discovered that these deep dredge holes
can migrate up and down river - sometimes very rapidly, depending on water
conditions. Even during small flow increases, researchers documented the
upslope lip of a dredge hole traveling upstream.
“People used to think the dredge holes just filled up, but
now we know they don’t. The holes first cause erosion upstream and downstream
and then eventually do fill in, but not before causing a net loss of sediment
from the bed and banks of the channel, meaning the channel does not simply go
back to its original state,” Daniels said. “If there’s no bedrock, or physical
structure like the Bowersock Dam to stop them, those dredge holes cause channel
erosion that will keep on going through the entire river network. Their effects
can even travel up the tributaries.” Unless a bridge footing or other
engineering infrastructure in the river is armored, then the migrating hole
could erode that physical structure as well.
The technical term for this river phenomenon is a “migrating
head cut.” Here’s how it works:
The Kansas River is a sand bed river. Sand is a light
sediment, and water transports it easily. When dredgers excavate into the
riverbed, that hole creates a steep wall (or head cut) where the river depth
suddenly increases. Water rushes rapidly over that wall, gaining speed and
picking up sand from the upstream edge.
At the same time, some sand falls into the hole. The water passing over
the hole then picks up new sediment downstream, causing erosion there as
well. The hole starts to expand,
both upstream and downstream.
Part of the dredging proposal before the Army Corps is to
re-open a closed dredge site above Topeka. The Army Corps previously shut down
the site, operated by Meier’s Ready Mix, due to unacceptable bed
“Whatever happens above Topeka will eventually migrate
upstream through the entire network, stopping only at the bases of Tuttle Creek
and Milford and other dams,” said Daniels. “It could happen quickly, within one
to two years. Dredging incisions set up cascading environmental effects – bed
degradation, riverbanks become unstable and steep from accelerated erosion,
etc. Change happens very quickly on a sand bed river.”
Over time, repeated dredging deepens and widens the river by
removing sediment from the system. The result is that the river bottom lowers,
too, along with the water level. This can leave the intakes for water treatment
plants stranded. Dredging on the
Missouri River has been scaled back recently because of similar problems
propagating into the lower Kansas River and other tributaries to the Missouri.
When the river deepens, the water table in the floodplain
lowers. Daniels said that this creates the potential for less water storage,
which could affect the many municipal wells along the river. A lower water
table also affects river vegetation and forests. For example, the cottonwood –
the state tree of Kansas – can’t survive unless its roots can reach a good
The deep dredge holes may affect fish populations, too. “The river’s physical habitat is
significantly different between dredged and un-dredged areas,” noted Daniels.
However, dredging’s most major environmental impacts for
fish are not limited to the Kaw. Since migrating head cuts can also affect
river tributaries, Daniels said the K-State study raises questions about risks
to the habitat of endangered species (like the Topeka Shiner) that live in
these smaller streams.
Daniels said that knowledge of the environmental impacts of
dredging is incomplete without studying dredging’s impacts on the entire Kansas
“We need a new environmental impact study that considers the
impacts of dredging on fish that live in the tributaries as well,” said
Daniels. Right now, the U.S. Army Corps of Engineers is depending on an
environmental impact statement (EIS) dating from 1991.
Before Daniels and Paukert carried out their study, the
effect of sand and gravel dredging on the Kansas River had not been seriously
studied. This study was the first time such sophisticated measuring technology
has been used.
“The Army Corps has studied similar conditions with sand
dredging on the Missouri River,” said Daniels. “They are aware of the problems,
and if dredging is a problem for the Missouri River, then it’s going to be a
problem for the Kansas River.
Simply shifting the problem from the Missouri to the Kansas is not a
How fast will the dredge holes move? Water movement on the
Kaw is greatly influenced by how much water the Army Corps releases from
upstream reservoirs. Extreme rains plus reservoir releases can add a lot of
extra velocity to the Kansas River system. In some circumstances, this may mean
the dredge holes have the potential for very rapid movement.
Daniels is seeking additional funding for a second phase of
the study, to model dredge hole migrations under different flow regimes.
You can help.
Send a public comment to the Army Corps on the dredging
proposal by emailing email@example.com by December 9, 2011.
More information and public comment template can be found at Friends of the Kaw's web site