This EarthCache is
located on the Cannon River in Goodhue County, just east of
beautiful downtown Cannon Falls, and requires you to take a little
trip downstream.
This riverbound EarthCache
adventure will take you on a caching journey down the Cannon River,
highlighting one of the fluvial features which has sculpted this
scenic waterway.
The Cannon River flows from Shields Lake
near
Faribault, Minnesota to Red Wing, Minnesota, where it joins
the
Mississippi River. The Cannon River Watershed drains 1,460
square
miles of land in southeastern Minnesota. The main waterways,
the
Cannon and Straight Rivers, run continuously for nearly 150
miles
east to the Mississippi River. The region varies from bluffs in
the
east to lakes in the west, with the vast majority of the land
used
for agriculture.
Bounded by rolling hills, bluffs, farmland, and
woods in its
upper reaches, the Cannon enters a broad gorge below Cannon
Falls,
where it is flanked by bluffs up to 300 feet (100 m) high.
The
Cannon River is comprised of a variety of sedimentary rocks.
The
river valley created by cutting through these rocks revealed
rock
outcrops of St. Peter Sandstone, the Prairie du Chien Group
of
dolomites and sandstone, and near the river's mouth, Jordan
Sandstone and the St. Lawrence and Franconia formations.
Just downstream of the falls in downtown Cannon
Falls, the
Cannon River is enters the “Driftless Area” of
Minnesota. This is the region which remained untouched by the
glaciars during the last ice age advance, allowing the river
to
carve a very impressive canyon. The upper region of the river
is
bounded by it’s glacial history displaying an
impressive
topography of terminal moraines, eskers and glacial till, and
is
not within the boundaries of the Driftless Area.
As you travel downstream, please take the time to
notice how the
river has etched a deeper and deeper path into the bluffs and
bedrock. This trip will introduce you to the differences in
the
course a river can follow. A flowing body of water can run
straight, it can bend a little and create a sinuous route, or
it
can bend repeatedly, and create a meander.
A meander in general is a bend in a sinuous
watercourse. A
meander is formed when the moving water in a river erodes the
outer
banks and widens its valley. A stream of any volume may assume
a
meandering course, alternatively eroding sediments from the
outside
of a bend and depositing them on the inside. The result is a
snaking pattern as the stream meanders back and forth across
its
down-valley axis.
Most meanders occur in the region of a river
channel with
shallow gradients, a well-developed floodplain, and cohesive
floodplain material. Erosion is greater on the outside of the
bend
where velocity is greatest. Deposition of sediment occurs on
the
inner edge because the river, moving slowly, cannot carry its
sediment load, creating a slip-off slope called a point bar.
The
faster moving current on the outside bend has more erosive
ability
and the meander tends to grow in the direction of the outside
bend,
forming a small cliff called a cut bank. This can be seen in
areas
where willows grow on the banks of rivers; on the inside of
meanders, willows are often far from the bank, whilst on the
outside of the bend, the roots of the willows are often exposed
and
undercut, eventually leading the trees to fall into the river.
This
demonstrates the river's movement. Slumping usually occurs on
the
concave sides of the banks resulting in mass movements such
as
slides.
The meander ratio or sinuosity index is a means
of quantifying
how much a river or stream meanders (how much its course
deviates
from the shortest possible path). It is calculated as the length
of
the stream divided by the length of the valley. A perfectly
straight river would have a meander ratio of 1 (it would be
the
same length as its valley), while the higher this ratio is above
1,
the more the river meanders.
The sinuosity index has been used to separate
single channel
rivers into three general classes: straight (SI 1.5)
The channel sinuosity index is the channel length
(the actual
distance traveled/paddled down the river from the Starting point
to
the Ending point (waypoint 1) divided by the valley length
(straight line distance from the Starting point to Ending
point
(waypoint 1) and are calculated from a map or from an aerial
as
shown in the satellite view or topo map of this area of the
Cannon
River.
Sinuosity Index has a non-mathematical utility
where rivers and
streams can be placed in categories; for example, when the
index
displays a ratio of 1 to 1.4 the river or stream is sinuous, but
if
the ratio is 1.5 and 4, then the river or stream is meandering.
To complete this EarthCache, you are going
to
estimate the Sinuosity Index of a portion of the Cannon
River,
starting on the river, near the posted coordinates.
A. Step 1: Determine the Channel Length.
Take
note of your odometer reading on your gps at this point, and
take
the final reading of your odometer at Waypoint 2. This number
is
the “Channel Length.”
B. Step 2: Determine the Valley Length.
Valley
Length = Straight line distance measured from the Starting point
to
Waypoint 1 + the Straight Line distance measured from Waypoint 1
to
Waypoint 2.
C. Step 3: Calculate the Channel Sinuosity
Index.
Channel Length divided by Valley Length = the Sinuosity Index
(ratio). Then determine if you have just “meandered down
the
river” or just done a “sinus wave.”
The logging
requirements
are as follows:
E-mail me (do NOT post in your log):
1) The distance you traveled.
2) Your distance from the starting coordinates.
3) Your calculated sinuosity index.
4) How you would classify this portion of the river.
OPTIONAL: Post a photo of yourself and/or team at
any
interesting point along your river journey between the
Starting
point and the Ending point.
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