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The Great Flood

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The map on the right shows rainfall in Iowa over a two-day period. ... Nearly fifty people died as a result of the flooding, 26,000 were evacuated and ... – PowerPoint PPT presentation

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Title: The Great Flood


1
The Great Flood
  • Mississippi River
  • Summer 1993

2
What is a flood?
  • 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.

3
Overview
  • The Mississippi River at St. Louis, Missouri, was
    above flood stage for 144 days between April 1
    and September 30, 1993.
  • Approximately 3 billion cubic meters of water
    overflowed from the river channel onto the
    floodplain downstream from St. Louis.

4
Overview
  • All large Midwestern streams flooded including
    the Mississippi, Missouri, Kansas, Illinois, Des
    Moines and Wisconsin rivers.
  • 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).

5
U.S. After the Flood
6
Reasons for the Flooding
7
Four reasons for flooding
  • 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

8
Rainfall for that area
9
Four reasons for flooding
  • 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

10
Reason for flooding
  • 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.

11
Prevention
  • 1. Build levees or floodwalls to contain rising
    stream levels
  • 2. Build reservoirs on tributary streams to store
    floodwaters for later release.

12
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.

13
Consequences of the flood
14
Des Moines Iowa
  • 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.

15
Farmland
  • 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.

16
Barge problems
  • The Mississippi River itself is a crucial part of
    the Midwests economic infrastructure.
  • Barge traffic normally moves goods through a
    system of 29 locks between Minneapolis and St.
    Louis.
  • Barges carry 20 of the nations 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

17
Road Damage
  • Hundreds of miles of roads built on the flat,
    wide floodplain were closed.
  • Flooding is estimated to have cost 500 million
    in road damage.

18
Mississippi Before (1988)
19
Mississippi (1993)
20
The Whole Picture
21
What it actually looked like there
22
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23
Humans altering the area?
24
Damage it did
  • Real pictures of the damage water can do to an
    area

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