Outline 15 The Mississippi River PDF

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STEPHANIE WELCH...

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ESSC 101 Lecture Outline 15 The Mississippi River Chapter 10 

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Flooding When water levels rise and overtop the banks of a river. It is a natural process of all rivers. Without flooding, sediment would not be deposited o Recurrence Intervals: 100 yr., 500 yr., etc. The Mississippi River It has a drainage basin in 31 states and 2 Canadian provinces. o Development of South Louisiana over 65 million years Cretaceous period to tertiary period. Meteorite collided into Gulf of Mexico and debris covered sunlight which made the dinosaurs become extinct. Rocky Mountains formed as a result of pieces of pacific plate subducting under western US and the low angle allowed for them to form. 60 million years – Rocky Mountains have formed which is the western edge of the Mississippi river divide (the east side was already there [Appalachian]) 50-40 million years ago – Rocky Mountains continue to form. Appalachian Mountains were slowly eroding down. 25 million years ago – still same thing 15 million years ago – Mississippi River could start to form 8 million years ago – first Mississippi River delta in south La started to take form about 10 million years ago. Without the Mississippi River, our state would stop around the Shreveport area. 3 million years ago – rivers build out modern south La. 100,000 years ago – ice age was completed. Continental shelf is result of raised sea level beyond the real coastline. Within the last 10,000 years, the Mississippi River has taken different paths across south La. The joint of its change is “the ankle of the boot”, corner of Mississippi. The river has continued to change courses because the river will build up sediment until the river switches path entirely into the Gulf of Mexico or the path of least resistance: straighter, steeper path o Recent Avulsions of the Mississippi River

1,000 years ago, the red and mississippi river paralleled each other and ran into gulf of mexico. Mississippi River changed over time, the

meanderloops flowed into the path of the red river making it a tributary and distrubutary of mississippi river. Red river flowed into mississippi river and then into the atchafalaya river. In 1831, shreve’s cut eliminated turnbull’s bend entirely; it formed what would have occurred naturally. The red river and atchafalaya river are now distributaries of mississippi river and are intrical parts of the system. By 1950, the mississippi river started to flow in its currrent way. o The Great Flood and Modern Engineering of the River 1927 was the great flood of Mississippi river (500 year) and was the most destructive river flood in the history of US. Tremendous rainfall caused rivers to swell and almost caused catastrophic floods in New Orleans, but it went down. After the flood waters started to fall, big banks created the Caernarvon diversion: blew the levees after the receded flood waters which flooded thousands of acres of farm lands. Led to the Flood Act of 1928 and construction of several safeguards against future floods, particularly in the vulnerable areas of Baton Rouge and New Orleans.  Lower River Controls Increase in water started to flow into the atchafalaya river. By 1990, it was determined that the Mississippi River could change its course entirely. The old river control structure was completed in 1963; it controls the amount of water that flows from the mississippi river to the atchafalaya river. It takes 30% of water from the mississippi river through the complex and into the atchafalaya river losing more coastline. During the May 2011 Flood, the Morganza Spillway, the Old River Control Structure, and the Bonnet Carre Spillway was opened as controls on the Mississippi River.

o Future of the Mississippi River and Coastal Louisiana Mississippi river ends at English turn, which banishes the lower part of river. Freshwater diversions would allow for the sediment in the river to be deposited across south La. Managing deltas is a big part of trying to maintain current coastline of Louisiana.

This picture wants to keep the current path of river. The old river control allows 30% water flow through atchafalaya basin which would build up the delta there which is important for maintaining that part of the coastline. Continuing to allow it flow past Baton Rouge and New Orleans will let the sediment migrate into separate freshwater diversions. Sediment will follow and allow for those coastal communities to become uplifted. Every diversion would have its own mini delta of Mississippi river and allow for sediment to come through for the areas with land lost enough to maintain the coastline....