ConsenCIS DotNet Home: New Orleans: Geography:

10,000 Years at the Mouth of the River


   Topics
GeographyHeadlinesInfrastructureKatrinaNeighborhoodsPeopleRecreation
Location of the delta over time
Location of the delta over time


10,000 years ago the most recent Ice Age still held huge amounts of water in the ice caps so sea levels were much lower and the mouth of the river was far to the south, out in what is now the Gulf.

As the ice melted the sea level rose and finally stabilized about 5,000 years ago. The mouth of the Mississippi retreated northward and established a delta south of Baton Rouge, far to the west of its current location. Since then the river's course has changed about every 500-1,000 years establishing seven distinct lobes of high land and creating lakes Maurepas and Pontchartrain.

New Orleans is built on three of these lobes. The Metairie and Gentilly ridges across the center of the city are what remains of the natural levee created 2,000 years ago when the river bed was two miles north of its current position.  Click on the image to see an expanded view.

The Times Picayune animation called The Rise and Disapperance of Southeast Louisiana captures the story in words and images. Turn your volume up.

  • Damaged Delta : Over the past 285 years and particularly since 1900 the river has been under tight control. Levees, diversions, channel engineering, jetties and even more levees all the way to the head of passes near the mouth of the river have prevented flooding. :: Continue reading...
  • Gulf Dead Zone : At the beginning of every summer a phenomenal algae (phytoplankton) bloom in the Gulf just off the mouth of the Mississippi creates an area of low oxygen. Fish flee the "dead zone" in search of more hospitable waters. Other organisms are trapped and die. As Fall arrives the bloom stops and gradually life returns. :: Continue reading...

  • Unstable Equilibrium?
    As silt flows into an area and builds new land, the river's path to the Gulf changes to avoid the new high ground. At the same time land away from the mouth, deprived of the freshwater and silt that built it, slowly subsides. Over time the river shifts to the course that offers the least resistance (steepest path, fewest obstacles). As the course approaches a tipping point, an event like a hurricane can accelerate the process causing the course to shift dramatically. (It looks like a hose spraying water out its nozzle and flopping back and forth across an area nearly 200 miles wide.)

    In the 1950's it became apparent that the River was about to change its course into the Atchafalaya basin. The Corps reacted by building the Old River Structure, a series of gates and flood control structures to keep the river in place and control the flow into the Atchafalaya.

    It's a lot of water
    The Mississippi River drains 1/3rd of the United States. The 250 Mississippi tributaries include the Missouri , Ohio, Arkansas, Tennessee, Yazoo and Red Rivers which combine to drain land from Pennsylvania to Idaho. As the rivers come together the flow increases to a maximum of 3 million cubic feet per second in the lower basin. That's a lot of water. It's enough to fill the 24 mile wide Lake Pontchartrain just to the north of New Orleans in 18 hours. It would fill the Louisiana Superdome in 42 seconds. It could flood the entire 1200 square miles of southeast Louisiana wetlands with running fresh water and silt to a depth of 3 feet and keep it flooded for two months in the Spring. The river is 2000 feet wide and 200 feet deep as it flows past New Orleans at about 5 miles per hour.


    Geological Time 300 Years of flooding


    Created : 5/10/2006 6:43:57 AM Updated: 6/16/2007 4:51:36 AM

      f1 f3

    Web Application Byf3 ConsenCIS

     

    sitemap

    1042

     

    Notes regarding this page
    • Subnotes