Floodplain
The valley you overlook
at the posted coordinates (the "GZ") is a classic
floodplain.
Floodplains are a natural feature of rivers. They are the
mostly flat land adjacent to the river and form due to the actions
of the river. Rivers erode their own banks and redeposit the eroded
material downstream. Material is added to the floodplain during
floods, a process called overbank deposition. The material that
underlies floodplains is a mixture of thick layers of sand and thin
layers of mud.
The floodplain during its formation is marked by
meandering streams, ox-bow lakes and bayous, marshes or stagnant
pools, and is occasionally completely covered with water. When the
drainage system has ceased to act or is entirely diverted for any
reason, the floodplain may become a level area of great fertility,
similar in appearance to the floor of an old lake. The floodplain
differs, however, because it is not altogether flat. It has a
gentle slope down-stream, and often, for a distance, from the side
towards the center
Floodplains in their natural form are beneficial for a
number of reasons: a) reducing the number and severity of floods,
b) minimizing non-point source water pollution, c) filtering storm
water, d) providing habitat for plants and animals, and e)
aesthetic beauty and outdoor recreation benefits.
During high water events, some of the water is absorbed by
the floodplain, helping to keep the river from overflowing. The
absorbed water can then be returned to the stream during times of
low water. If a high water event is large enough, water will
overflow the channel of the river and flow onto and spread over the
floodplain, which slows the flow of the water. Reduced water flow
can help prevent severe erosion and flooding
downstream.
Floodplains are also home to many types of plants and
animals and may also have forests and wetlands on or adjacent to
them. These river edges provide habitat for insects, birds,
reptiles, amphibians, and mammals. The vegetation also helps filter
contaminants out of the water flowing into the river. Additionally,
vegetated floodplains provide shade for the adjacent rivers and
streams, increasing dissolved oxygen levels and consequently
improving habitat for aquatic plants and animals.
Flood Plain
History
The flood plain
currently has the Great Miami River flowing through it, but it was
also contained 2 other rivers. Before the most recent set of
glaciers this valley contained the Teays river - which actually
flowed north. After some early glaciers the beginnings of the
Ohio river flowed through this valley, not its current track south
of where you stand. For more info on this river history visit
my other earthcache in Ault Park that overlooks the other end of
what is called "The Deep Stage Ohio River" http://coord.info/GC36J9G. This ancient rivers helped form the valley that
contains the floodplain. As stated above the flat plain is
formed by periodic floods that deposit sediment ("alluvium")
carried in the water left when the water recedes. If you
follow the trail west to N 39.1179, W 84.8168 you
will overlook a valley that contains many features of a floodplain:
an oxbow lake and meander scars shown in the diagram
below. For more info on the oxbow lake visit the
earthcache http://coord.info/GC26AZM . The river used to be much closer to
what is now Lawrenceburg, Indiana. That was still the
main channel in 1847. Sometime before 1900 the meander was
cut off and it became a meander scar. The most recent change
in the floodplain occurred when the Ohio river backed up behind the
newly constructed Markland dam (built between 1959 and 1964).
The mouth of the Great Miami River was flooded a few miles upriver
and water reentered the meander scar, partially flooding it.
The Great Miami River itself has been changed over time. It
not longer floods as strongly as it used
to.
In March 1913, the citizens of
the Miami Valley witnessed a natural disaster unparalleled in the
region's history. Within a three-day period, eight to 11 inches of
rain fell throughout the Great Miami River Watershed. This
rainfall, coupled ground already saturated from the melting of snow
and ice of a hard winter, produced more than 90-percent runoff, and
caused the Great Miami River and its tributary streams to overflow.
Every city along the river was inundated with
floodwaters.
More than 360
people lost their lives. Property damage exceeded $100 million
(that’s more than $2 billion in today’s dollars). The
amount of water that passed through the river channel in Dayton
equaled the amount of water that flows over Niagara Falls in a
four-day period.
In the wake of
the tragedy, the citizens of the Miami Valley — who had lost
virtually everything — rallied to initiate plans for the
prevention of future flooding. Some 23,000 citizens contributed
more than $2 million to begin a comprehensive flood protection
program on a valley-wide basis. The main feature of this plan are 5
dams that are used to moderate the flow of water through the
river. This also moderates the flooding somewhat at the end
of the river where you are standing.
Tale of Two
Rivers
Ohio
river can be seen looking south from the second waypoint. N
39.1179, W
84.8168. Note the differences between the two river and
valleys. Below is a chart that categorizes rivers by channel,
slope, and meander.
The
graphic depicting the stream channel classification system
developed by Dave Rosgen. Courtesy of Dave Rosgen, Wildland
Hydrology, 2003. Adapted by Steve Adams.
One of the ways to better understand
streams is a classification system developed by Dave
Rosgen, (1994) . This system helps us predict the
form and shape of a stream when faced with changes in the
hydrologic regime and the bankfull discharge, loss of stream length
due to straightening, or increases in sediment
supply.
To log this
earthcache please email me the answers to these
questions:
1) What human activity
can be observed on the floodplain? Why is the floodplain a
good place for this?
2) Compare
and contrast the Great Miami River and valley and the Ohio river to
the south. Consider the chart above and list the river type
(AA through G) you think best represents the Great Miami River at
this location.
3) What river(s) carved
out the 1.5 mile wide valley to see looking from the GZ towards the
I-275 highway (and deposited much of the alluvium that makes up the
floodplain floor?
Optional: a
photo of yourself or gps with the floodplain behind
you.