Changing Nature

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Changing Natures Course

• Tracy Morris
• David Trombley

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A War of Two Rivers

• Atchafalaya
• Controls Louisianas crawfish crop
• Basin encompasses over 370,000 acres of fresh
  marsh, bottomland hardwoods, cypress swamps, and
  open water (the largest wetland in the US)

• Mississippi
• Drains 41 of the contiguous US
• Basin covers more than 1,245,000 square miles
• Lower alluvial valley is a flat plain of 35,000
  square miles

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Map of Southern Louisiana Today

• The Old River connects the Mississippi to the
  Atchafalaya.
• The Atchafalaya runs a much shorter course to the
  Gulf of Mexico.
• Commerce has depended on the Mississippi for 200
  years.

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How It All Began

• 1831- Old River created by steamboat captain to
  shorten his upriver trip
• Old River flow slowed as the upper portion filled
  with silt
• 1839 State of Louisiana began to clear 30 mile
  logjam on Atchafalaya River
• Flow in Atchafalaya began increasing

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If It Did Switch Course?

• New Orleans ranks number 1 in the United States
  in tonnage of goods shipped through its port
• The Mississippi River is associated with 40 of
  the tidal wetlands in the contiguous United
  States
• Riverside development along Atchafalaya would be
  inundated

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Change Isnt Always Good

• Businessmen quickly realized that they needed the
  Mississippi to remain a navigable river
• In 1927, a 100-year flood gave us a second reason
  to control the flow

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The Flood of 1927

• Inundated 16.5 million acres in 7 States
• Destroyed 102 million of crops
• 160,000 homes
• 40,000 buildings
• Killed 500 people
• Prompted Congress to pass Flood Control Act
  of 1928

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Flood Control

• Corps accepted over 300 proposals
• Winning proposal had three facets

• Incorporate floodways to divert peak flow
• Create backwater areas
• Design all works on basis of a great hypothetical
  flood

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Slowly but Surely

• 1953- Mississippi River Commission recommended an
  Old River Control Structure
• 1954- Corps engineers designed a lock, a dam over
  the Lower Old River and two control structures
  Overbank and Low Sill
• 1955- Construction began

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Old River Control Structure

• Completed in 1962
• Kept Acadiana from flooding
• Keep enough water in Mississippi so big ships can
  navigate to New Orleans
• Composed of dams, weirs, and levees
• Designed to allow 30 of the Mississippi to flow
  down Atchafalaya under normal times

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Old River Control Structure

• Without control structure, the straighter shorter
  Atchafalaya would capture the mainstream of the
  Mississippi

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Old River Control StructureLow Sill Structure

• Made of eleven gates
• 44 ft wide
• Total length 566 ft
• Maximum water height allowed in forebay
• 69.8 ft above sea level
• Designed to withstand a 37 foot difference in
  water levels between Mississippi an Atchafalaya
• Can only maintain 22 ft

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Old River Control StructureOverbank Structure

• Contains 73 bays
• Each 44 ft wide
• Total length 3,356 ft

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Old River Control StructureAuxiliary Control
Structure

• Completed in 1986
• Total of 6 gates
• 62 ft wide
• Total length 442 ft

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Old River Control StructureNavigation Lock

• Allows travel between Mississippi, Red and
  Atchafalaya rivers
• 75 ft wide
• 1,185 ft long
• Floor 11 ft below sea level

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Other Control Structures

• Bonnet Carre Spillway
• Built 1937
• Diverted water to Lake Pontchartrain

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References

• 1927 Flood Pictures http//www.riddlelawoffice.or
  g/1927Flood.shtml
• http//www.mvd.usace.army.mil/offices/pa/brochures
  /mrtbrochure.pdf
• http//www.biology.lsu.edu/webfac/cramcharan/Louis
  iana.html
• http//www.theadvertiser.com/news/html/BF4039D3-B1
  D9-497C-AB63-F8CB394C2B9F.shtml
• http//www.tulane.edu/bfleury/envirobio/enviroweb
  /FloodControl.htm
• Pictures of control structure
  http//www.msstate.edu/dept/geosciences/CT/TIG/WEB
  SITES/LOCAL/Spring2002/Cathrine_Duex/OldRiverContr
  ol.html
• http//www.dnr.state.la.us/sec/execdiv/pubinf
  o/newsr/archive/ crawfish.ssi
• http//www.lacoast.gov/cwppra/projects/atchaf
  alaya/

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Questions?
Questions?