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Flashcards in Mississppi Deck (19)
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1

How long is the Mississippi?

The Mississippi is about 3,800 km long from its source in Lake Itasca to the Gulf of Mexico.

2

Mississippi What area does the Mississippi drain?

The river drains a huge area of the United States, about 3,256,000 km between the Rockies and the Appalachians.

3

Mississippi How is rich soil a cause of flooding?

The rich soil and the abundant wildlife attracted settlers and therefore the flood plain soon became densely settled and towns and cities developed.

4

Mississippi When does the upper Mississippi and its tributaries reach maximum flow?

The upper Mississippi and its tributaries reach maximum flow between March and June; floods develop when melting snows are followed by early summer rains.

5

Mississippi Why does excess water not get absorbed?

 Because people have settled on the flood plain, wetlands have been drained and areas of forest that once absorbed excess rainwater have been cleared.

6

Mississippi What increases the speed and force of water flows across the land.

 Rivers have been channelled and land uses developed which also increase the speed and force of water flows across the land.

7

Mississippi How has the catastrophe of floods increased?

In the past, only occasional farmhouses were destroyed by floods, but now they affect valuable transport infrastructure and more valuable property.

8

What are the two most commonly used methods of flood control along the Mississippi?

The two most commonly used methods of flood control along the Mississippi and its tributaries are reservoirs and levees.

9

Within urban areas what are some additional methods of flood control along the Mississippi?

Within urban areas there are additional measures, including concrete walls, flood-gates to protect particular areas, drainage channels and pumping stations.

10

Describe the use of reservoirs along the Mississippi.

Flood control reservoirs are built well upstream of the main waterway, on the tributaries. The Upper Mississippi has 20 major flood control reservoirs They can occur naturally, but most of those in the Mississippi basin have been enlarged artificially Flood reservoirs were stated as being particularly effective combined with levees

11

What maintains the navigability of the Mississippi after floods?

Dredging is also carried out, particularly after severe floods, to maintain navigability and to reduce river levels.

12

When have the levees been breached?

In 1993, as had occurred in 1927 and 1974, inhabitants along the Mississippi were shocked when the protective network of levees was over-topped or breached and the waters unleashed on to the towns and farmland along its edge.

13

What methods have been suggested for reducing flooding along the Mississippi after the over topping of the levees?

Such events have prompted researchers since 1974 to ask to what extent levees and other human modifications to the river system have actually worsened the threat to humans and property when the inevitable large floods occur. It has been suggested that levees and other channelled structures put in place over the last century or so have systematically confined the flow of flood waters and forced flood stages to grow higher and higher for the same discharge.

14

What was the conclusion of the the way to prevent flooding along the Mississippi?

Following the 1993 floods, the Army Corps of Engineers suggested that levee removal would not have a significant impact on lowering flood stages. Raising levees would not be very cost effective and could have adverse environmental effects.

15

Describe a major flood along the mississippi, in the 90's.

1993

  • 72, 000 homes flooded ($12 billion property damage)
  • 6200 families evacuated
  • disease threat (stagnant water = rats)
  • collapse of electrical lines caused a power loss
  • 6 million acres of farmland floodex $2.6 billion crop losses 

16

Describe a major flood along the mississippi, in the 21st century. 

​2011

  • More than 21,000 homes and businesses and 1.2 million acres of agricultural land were affected, and more than 43,000 people felt some effects.
  • 392 killed across the 7 states 
  • delay in river barge traffic transporting a huge amount of crops. 
  • riverboat cruises closed for 6-8 weeks ($14 million losses) 
  • polluted water ntered Gulf of Mexico contributiong to 'dead zones' of the aquatic life (no O2).

17

How has development affected flooding on the Mississippi? 

  • Urbanisation (memphis) causing surface run-off and storm drains
  • Deforestation (no longer intercepts and absorbes water)
  • Wing dams were created to prevent sediment build up to deepen river for shipping increasing velocity and quantity. 
  • Channelistaion (St louis) for transport efficiency
  • Levees 1993 - overflowed due to channelled structure confining flow of flood water - moves faster

18

How has development along the Mississppi affected flooding? 

  • Missouri has 105 dams 
  • Strengthened levees (up to 15 m high, 3000 km worth) 
  • straightened course (1750 km of artificial cannels) 
  • Afforestation opn water sheds and valley sides (tennesse river)
  • Diversonary spillage - The Bonnet Carré Spillway is a flood control operation in the Lower Mississippi Valley. It allows floodwaters from the Mississippi River to flow into Lake Pontchartrain and thence into the Gulf of Mexico.
  • Flood controll reserviors (20 at upper mississippi controlled by US Army Corps of Engineers)
  • Floodwater released after a flood to prepare for flood water the same season. 

19