Windblown
soils called loess were created at the end of
the last Ice Age nearly 18,000 years ago. These
soils, consisting of lightweight particles and
ground as fine as flour by the glaciers, are
highly susceptible to water erosion. Twenty-two
counties in western Iowa contain deposits of
loess between 13 and 200 feet thick.
Streams seek
an energy equilibrium, or the
point at which erosion happens
as fast as deposition. If there
is too much energy in the stream
system, the streams will erode,
whereas if there is too little
energy in the system the streams
will deposit sediment. If the
slope of a stream changes, the
behavior of the stream will
change until it gets back to its
energy equilibrium.
In the early part of the 20th
century a movement to straighten western Iowa
streams began in earnest. Channelizing the
streams brought more land into farming. But,
little did they know the effect this would have
in the future.
Channelization
caused the stream slope
to increase. Think of
slope, or grade, like
this. It is the
horizontal distance a
stream flows divided by
the vertical distance it
drops. When the streams
were channelized, the
meandering, longer path
of streams was changed
to a straight, shorter
path. However, the
streams were still
dropping the same
elevation as before.
Thus, the slope
increased.
 Well,
increased slopes cause
higher velocities, or
more energy. The streams
had two choices at this
point to reduce their
energy. They could begin
meandering again or
downcut into their
channels. Coupled with
the high erodibility of
the loess soils, the
streams downcut quickly,
creating ever-deepening
"canyons" out of
once-peaceful streams.
Streams
that
were
once
jumped
by a
young
farm boy
now
measure
100 to
150 feet
from
bank to
bank.
Streams
that in
1930
measured
no more
than
three
feet
deep now
reach
depths
of 30
feet or
more.
Degradation
of
western
Iowa
streams
has
caused
more
than
$1.1
billion
in
damages
to
public
and
private
infrastructure.
Stabilization
of these
seriously
degrading
tributaries
of the
Missouri
River
continues
to be
one of
the most
challenging
problems
facing
western
Iowa.
In 1992,
Hungry
Canyons
Alliance,
a
non-profit
corporation,
was
formed
to
research
and
implement
solutions
to the
problem
of
stream
channel
erosion
in the
deep
loess
soils
region
of
western
Iowa.
Members
of the
Alliance
represent
the 22
counties
in the
region
and
include
county
engineers,
landowners,
county
Boards
of
Supervisors,
and Soil
and
Water
Conservation
Districts.
The
Hungry
Canyons
Alliance
addresses
the
severe
loss of
land and
damage
to
infrastructure
caused
by
stream
channel
erosion
in the
22
county
area of
the deep
loess
soils
region
of
western
Iowa.
Significant
stream
channel
erosion
(channel
deepening
and
widening)
has been
identified
on 155
streams
in the
region,
causing
damage
to
bridges,
pipelines,
telephone
lines,
and loss
of
agricultural
land
through
land
voiding.
Bank
stabilization,
upland
conservation
treatments
and land
use have
all
played
important
roles in
inhibiting
soil
erosion
in
streams.
However,
the
effects
of these
efforts
are
short-term
if the
bed of
the
stream
remains
unstable.
A long
term and
low
maintenance
approach
to
stream
stabilization
must
include
some
form of
grade
control.
Hungry
Canyons
Alliance
structures
work by
using a
raised
weir
section
that
decreases
stream
energy
and
grade,
prevents
downcutting,
creates
an
upstream
backwater
condition,
traps
sediments
upstream,
and
reduces
downstream
sediment
flow.
Today,
157
structures
for
grade
control
on
degrading
streams
have
been
included
in the
Hungry
Canyons
Alliance
cost
share
program.
Installation
of
Hungry
Canyons
Alliance
streambed
stabilization
structures
has
protected
nearly
$40
million
in Iowa
property
including
bridges,
roads,
utilities,
and
farmland.
Since
1992,
$11.1
million
in
federal
and
state
funds
have
been
used for
Hungry
Canyons
structures.
Counties
have
contributed
nearly
$4
million
toward
the cost
of these
structures.
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