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Mississippi River
Introduction
The Mississippi River, derived from the old
Ojibwe word misi-ziibi meaning 'big river' (gichiziibi in the modern language), is the secondlongest river in the United States; the longest is
the Missouri River, which flows into the
Mississippi. Taken together, they form the largest
river system in North America. If measured from
the head of the Missouri, the length of the
Missouri/Mississippi combination is
approximately 6,270 km (3,900 miles) long.
Mississippi delta from space
The Mississippi River has the third largest
drainage basin in the world, exceeded in
size only by the watersheds of the Amazon
River and Congo River. It drains 41
percent of the 48 contiguous states of the
United States. The basin covers more than
1,245,000 square miles (3,225,000 km²),
including all or parts of 31 states and two
Canadian provinces.
The Mississippi drains most of the area
between the Rocky Mountains and the
Appalachian Mountains, except for the
area drained by the Great Lakes. It runs
through, or borders, ten states in the
United States ,for example, Minnesota,
Wisconsin, Iowa, Illinois, Missouri,
Kentucky, Arkansas, Tennessee, Mississippi
and Louisiana.
The river is divided into the upper Mississippi,
further divided into three sections: the from its
source south to the Ohio River, and the lower
Mississippi, from the Ohio to its mouth near New
Orleans. The upper Mississippi is headwaters,
from the source to Saint Anthony Falls; a series
of man-made lakes between Minneapolis and St.
Louis; and the middle Mississippi, a relatively
free-flowing river downstream of the confluence
with the Missouri River at St. Louis.
Speed
At the headwaters of the Mississippi, the
average surface speed of the water is near
1.2 miles per hour - roughly one-third as
fast as people walk. At New Orleans, on
2/24/2003, the speed of the river was 3
miles per hour.
Width
At Lake Itasca, the river is between 20-30
feet wide, the narrowest stretch for its
entire length.
The Mississippi is more than four miles
wide at Lake Onalaska. Near LaCrosse,
Wisconsin, Mississippi water held behind
Lock and Dam #7 and water held back by
damming the Black River combine to form
this broad reach of the Mississippi River
Depth
At its headwaters, the Mississippi is less
than 3 feet deep. The river's deepest
section is between Governor Nicholls
Wharf and Algiers Point in New Orleans
where it is 200 feet deep.
Elevation
The elevation of the Mississippi at Lake
Itasca is 1,475 feet above sea level. It
drops to 0 feet above sea level at the Gulf
of Mexico. More than half of that drop in
elevation occurs within the state of
Minnesota.
Sediment Load
The Mississippi carries an average of
436,000 tons of sediment each day. Over
the course of a year, it moves an average
of 159 million tons of sediment. Averages
have ranged from 1,576,000 tons per day
in 1951 to 219,000 in 1988.
Volume
At Lake Itasca, the average flow rate is 6
cubic feet per second.
At Upper St. Anthony's Falls, the
northernmost Lock and Dam, the average
flow rate is 12,000 cubic ft/second.
At New Orleans, the average flow rate is
600,000 cubic feet per second
Wildlife
The Mississippi River and its floodplain are home
to a diverse population of living things:
At least 260 species of fishes, 25% of all fish
species in North America; Forty percent of the
nation's migratory waterfowl use the river
corridor during their Spring and Fall migration;
Sixty percent of all North American birds (326
species) use the Mississippi River Basin as their
migratory flyway;
The Upper Mississippi is host to more than 50
species of mammals;
At least 145 species of amphibians and reptiles
inhabit the Upper Mississippi River environs.
The source of the Mississippi River
on the edge of Lake Itasca
Impacts of flooding in
Mississippi
Introduction
• A flood is defined as the temporary overflow of
a river onto adjacent lands not normally covered
by water. The most devastating flood in U.S.
history occurred in the summer of 1993.
1. The Mississippi River at St. Louis, Missouri, was
above flood stage for 144 days between April 1
and September 30, 1993.
2. Approximately 3 billion cubic meters of water
overflowed from the river channel onto the
floodplain downstream from St. Louis.
3. All large Midwestern streams flooded including the
Mississippi, Missouri, Kansas, Illinois, Des Moines and
Wisconsin rivers.
4. Seventeen thousand square miles of land were
covered by floodwaters in a region covering all or
parts of nine states (North Dakota, South Dakota,
Nebraska, Kansas, Missouri, Iowa, Wisconsin,
Minnesota, Illinois).
Causes of Flooding
There were four principal reasons why flooding was so
extensive:
• The region received higher than normal precipitation
•
during the first half of 1993. Much of the area received
over 150% of normal rainfall and parts of North Dakota,
Kansas, and Iowa received more than double their
typical rainfall.;
Individual storms frequently dumped large volumes of
precipitation that could not be accommodated by local
streams. The map on the right shows rainfall in Iowa
over a two-day period. Over six inches of rain fell in
parts of southern Iowa;
• The ground was saturated because of cooler than
•
normal conditions during the previous year (less
evaporation) so less rainfall was absorbed by soils
and more ran-off into streams;
The river system had been altered over the previous
century by the draining of riverine wetlands and the
construction of levees.
Weather Conditions
• The abnormal rainfall was attributed to a weather
system formed when warm moist air from the Gulf of
Mexico collided with cold, dry air from Canada over the
Midwest. When the warm Gulf air cooled it lost the
moisture it carried as rain. Normally this rainfall would
have been distributed throughout the northeastern
states but a stalled high-pressure system over the
southeast blocked the flow of the jet-stream bringing a
constant stream of storms over the Midwest. For nearly
two months (June, July) weather patterns in the U.S.
were dominated by this stationary high-pressure system
(see diagram below).
Mississippi River System
• The Mississippi River is divided
into two parts. The Upper
Mississippi runs from it source
to Thebes, southern Illinois,
where the Ohio river meets the
Mississippi. The Lower
Mississippi runs downstream
from Thebes to the Gulf of
Mexico. Flooding was confined
to the Upper Mississippi
because the river channel
widens considerably south of
Thebes, and the Lower
Mississippi received lower than
average inflow from tributaries.
Discharge increases steadily downstream as more tributaries
add water to the river. The map on the left shows the
locations of four gaging stations and the graph above
illustrates how discharge increases on the river between
its source and St. Louis. The large increase near St. Louis
is caused by the addition of the flow of the Missouri
River. Click here to go to a satellite view of flooding on
the Mississippi and Missouri Rivers near St. Louis.
Modification of the
Mississippi River
• The Mississippi River is one of the most heavily
engineered natural features in the U.S. The character of
the floodplain has changed to accommodate agriculture
and urbanization. Approximately 80% of the original
wetlands along the river were drained since the 1940’s.
Wetlands act as natural storage reservoirs for
floodwaters. They absorb water during heavy
precipitation and release it slowly thus reducing run-off
to streams and decreasing flood volumes. The river
channel itself has been artificially constrained by levees
and floodwalls. These structures serve to increase the
volume of water that can be held in the channel and
thus increase the size of the flooded area if the levee
breaks.
Upper Mississippi River in
July, 1992
Upper Mississippi River in July,
1993
Two satellite views of the Mississippi River (Lake Michigan is on the right) show the change in size
of the river related to the 1993 flood. Larger views of both images can be viewed at the
Federal Goernment’s SAST (Scientific Assessment and Strategy Team) site.
We can either attempt to stop natural hazards from
occurring (prevention) or recognize that they will happen
and modify our life styles to deal with them (adjustment).
Prevention
• There are two principal ways that engineers have attempted to
•
control the flow of rivers in the Mississippi River basin: 1. Build
levees or floodwalls to contain rising stream levels; 2. Build
reservoirs on tributary streams to store floodwaters for later
release. Steps taken to adjust to flood events include: 1.
Purchasing flood insurance though the National Flood Insurance
Program; 2. Seek assistance from the Federal Emergency
Management Agency (FEMA) following a flood event.
The U.S. Army Corps of Engineers were given directions to
construct flood control structures (dams, reservoirs, levees) on
the Mississippi River following flood events in the 1930’s.
Levees may fail because the flood water rises over the top of
the structure or the levee collapses under the weight of the
water. Levees and floodwalls protect people on the floodplain
from most floods. However, they may not protect against the
largest floods with recurrence intervals of more than 100 years.
Floodplain residents may experience a false sense of security
that can lead to more extensive development of flood prone
lands (the "levee effect").
Over 9,300 km of levees were damaged following the 1993 flood.
Only 17% of federal levees were damaged, but up to 77% of
locally constructed levees failed. Most levee breaks occurred south
of St. Louis.
St. Louis was protected by a massive floodwall. The wall
developed a leak but held up over the length of the flood. Over 50
propane tanks containing over a million gallons of gas in south St.
Louis presented the threat of a massive explosion. A levee break
south of the city allowed the river level to drop around St. Louis
and reduced pressure on the propane tanks. Many of the smaller
levees in rural areas failed.
• Large dams and
reservoirs on the
Mississippi River would
hinder transportation.
Therefore, the majority of
flood control structures in
the Upper Mississippi
River basin are located in
the Missouri River basin.
The Missouri basin can be
further subdivided and
most of the dams are
located in a southern
sub-basin, the Kansas
River basin.
Approximately 85% of
stream flow in the Kansas
basin is controlled, i.e. it
flows through dams.
Locations of dams on tributary
streams in the Kansas River
basin.
Adjustment
• Approximately 10% of Midwest residents who lived in
flood-prone areas had flood insurance prior to the 1993
floods. Over eleven million buildings are located in floodprone areas in the U.S. but only 19% purchased flood
insurance.
• FEMA was created in 1979 to provide financial assistance
to people and areas affected by natural disasters. Over
400 counties in the flood region were declared disaster
areas, making them eligible for disaster relief. Not all
areas affected by flooding are declared disaster areas.
Residents who don't buy flood insurance must gamble
that they will receive disaster aid from FEMA to help
cover clean up costs.
People and the Flood
•
Nearly fifty people died as a result of the flooding,
26,000 were evacuated and over 56,000 homes were
damaged. Economic losses that are directly attributable
to the flooding totaled $10-12 billion. Indirect losses in
the form of lost wages and production can not be
accurately calculated.
Further consequences of flooding:
1. Economic and Social aspect
2. Psychological aspect
3. Political aspect
Economic and Social aspect
• The greatest economic losses occurred in cities on the
•
floodplain. Des Moines, Iowa, located in the center of the
flood region, became the largest U.S. city to lose its water
supply when its water treatment plant flooded. More than
250,000 people lost drinking water for 19 hot summer days.
Water pipes, contaminated by floodwaters carrying sewage
and agricultural chemicals, had to be flushed out before the
municipal water supply was reconnected. Economic losses in
Des Moines totaled approximately $716 million.
The flooding submerged eight million acres of farmland.
Production of corn and soybeans were down 5-9% as a
result and corn prices rose by $0.15 per bushel. Floods
deposited thick layers of sand in some fields. The U.S. Soil
Conservation Service spent $25 million to buy flood-prone
farmlands for conversion to natural conditions (e.g.
wetlands). Conversion of natural lands to farmlands has
resulted in greater run-off and exaggerated the effects of
flooding. Modern farming methods leave plant residue on
the surface and reduce run-off.
• The Mississippi River itself is a crucial part of the
Midwest’s economic infrastructure. Barge traffic normally
moves goods through a system of 29 locks between
Minneapolis and St. Louis. Barges carry 20% of the
nation’s coal, a third of its petroleum, and half it
exported grain. Barge traffic was halted for two months;
carriers lost an estimated $1 million per day. Some
power plants along the river saw their coal stocks
dwindle from a two-month supply to enough to last just
20 days.
• Hundreds of miles of roads built on the flat, wide
floodplain were closed. Flooding is estimated to have
cost $500 million in road damage
• Many facilities were damaged, reconstruction is
necessary. This may stop the development of the society.
Psychological aspect
• People are suffer from
fear. They lost their
homes, properties and
families. They were
psychologically seriously
hurt. They lost their
relatives and these are a
treasure of priceless
worth and irrecoverable.
Political aspect
• The government rule will
become unstable. They
cannot provide a good
prevention system for the
flooding and made the
society suffer from serious
destruction. People blamed
the government. The
government need to carry
out relief work immediately
to appease the victims of a
natural disaster.
Pro/Con Arguments
• Like almost all complex environmental
issues, there are pro and con arguments
to this issue. There are both positive and
negative human and environmental
consequences to attempts to manage the
Midwest's rivers.
Pro Arguments
• 1. Maintenance of a Navigation Channel
– Major rivers of the Mississippi River system are vital
routes for barge traffic. To maintain and improve
navigation, the Army Corps of Engineers has
straightened, shortened, and deepened parts of the
river via dredging and construction of locks and dams.
Sandbars, snags, and navigation hazards are regularly
removed and the Corps has an extensive network of
navigation buoys on the rivers. Use of the rivers as
routes for barge traffic is essential to the commerce
and economy of the Midwest.
• 2. Flood Protection
– People, property, businesses, industry, and
agricultural crops are at risk from the inevitable floods
along the rivers. The Army Corps of Engineers has
developed a monumental network of levees, dikes,
berms, and floodwalls along the banks of the rivers
intended to protect humans and human structures
and enterprises from the threats of floods. These
flood protection measures have been highly
successful in the smaller, more frequent floods, but
may actually exacerbate the very large, less frequent
floods (see below).
• 3. Enhanced Utilization of Floodplains
– The extensive levee system along more than 3,000
miles of Midwest rivers has allowed greater human
utilization of floodplain lands adjacent to the rivers.
This land has been developed for agricultural,
industrial, commercial, and residential purposes.
Without the levee system, many of these areas, often
wetlands, would have been less suitable for human
development. Also without the levee system, these
areas would have been subject to frequent flooding.
This third benefit also has negative consequences, as
described below.
Con Arguments
• 1. Reduced Alluvial Soil Deposition
– The fertility of floodplain soils is due in large
part to deposition of new soils by periodic
floods. Since the levee system prevents rivers
from spreading out over floodplains and
depositing their sediment load, deposition of
fertile new soil is blocked.
• 2. Human Developments in Natural Floodplains
– Human habitation and development in floodprone areas are invitations to disaster. The
levee and floodwall system along Midwest
rivers has encouraged development in
floodplains and often provided a false sense
of security. When floods do top or break
levees in developed areas, the resultant
damage is severe and costly.
• 3. Loss of Wetland and Riparian Ecosystems
– Until fairly recently, wetlands were regarded as
useless lands. Most of the former wetland areas of
the Mississippi River system have been drained,
developed, and protected by levees. Wetlands are
now recognized as biologically rich areas worthy of
preservation. Riparian ecosystems are those natural
areas immediately adjacent to rivers. Like wetlands,
riparian zones are ecologically valuable. With human
development and levee construction, much of the
riparian areas along Midwest rivers have been lost or
altered.
• 4. Exacerbation of Major Floods
– While the levee system has been effective in
containing small floods, the levees may actually
increase the severity of major floods. Levees prevent
the rivers from spreading out over their natural
floodplains. If a river spreads out over a large
floodplain area, then the height of the water's rise
during a flood is relatively small. However, if a river is
not allowed to spread out over a floodplain, then the
water will rise much higher in the artificially narrowed
river channel. Higher water levels may top existing
levees, resulting in flooding and calls for ever-higher
levees.
• 5. Enhanced Soil Erosion and Sediment Load
– Natural riparian zones help to trap soil eroding from
lands adjacent to rivers. Loss of natural riparian zones
results in more soil entering riverways by erosion. The
amount of sediment a river carries is proportional to
water velocity in the river. Because major rivers of the
Midwest have been straightened, deepened, and
artificially confined to narrow channels, water velocity
and hence sediment load have increased. More and
more precious topsoil from Midwest farms is being
carried out into the Gulf of Mexico.
• 6. Adverse Impacts on Aquatic Life
– Dredging of major rivers of the Midwest is
commonplace to maintain the rivers as navigation
channels. Dredging severely impacts benthic, or
bottom-dwelling, species. Species found in the water
column are adversely affected by the increased
turbidity resulting from greater sediment loads found
in the rivers. Loss of riparian and wetland areas and
chemical and nutrient pollution have also adversely
impacted the biota of Midwest rivers. The overall
effect of these human-related changes has been to
decrease the biological richness of aquatic
ecosystems in the Mississippi River system.
END
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