The Changing Courses of the Mississippi River

The Louisiana coast has been built over the last 7,000 years by the Mississippi River changing course and creating six different delta complexes. Before the extensive levee system that “trained” our river to stay in one place, the Mississippi changed course about once every 1,000 years.

The Mississippi River will always take the most direct path to the Gulf of Mexico—generally the route with the steepest gradient. As it occupies a course, it begins to deposit sediment along its route to the ocean. This decreases the slope of the river channel over time, and eventually, this path will no longer be the most efficient. At this point, the river will avulse (change course), occupying another path which has a steeper channel. The river will begin to divert increasingly more of its water and sediment down the other channel, until eventually the old channel is completely abandoned.

The modern Mississippi Delta is overdue for an avulsion. In a natural system, the Mississippi River would have overtaken the Atchafalaya River channel due to its more efficient gradient. Engineering efforts, through levees and diversion structures such as Old River Control Structure, enable us to prevent a course change. Despite our ability to control the river’s physical path, it is difficult to ensure that the amount of water and sediment traveling down the channel won’t decrease over time, since the system naturally began allowing more water and sediment to travel down the Atchafalaya and less down the Mississippi.

Our Bird’s Foot delta remains in the same physical location, but due to the natural “delta cycle” (tendency to abandon one delta and relocate to another), the Bird’s Foot is not the healthy prograding (building) delta that it once was. Instead, the delta is retreating over time.


Understanding a graph of NOAA Weather Observatory Data

Wind Speed (m/s)

Wind Direction (Degree)

1.    What does the red line on this graph indicate? _____________________________ 

2.    What unit is used to measure wind speed? ____________ 

3.    On this graph, what unit is used to measure time? ____________ 

4.    On what dates was this data collected? __________________________________ 

5.    On what day(s) was the wind speed the highest? ____________________
On what day(s) was the wind speed the highest? ____________________

6.    What do the small blue dots and arrows mean? _____________________________
    ___________________________________________________________________

7.    On what days was the wind gusting mostly to the north (the arrows would be pointing toward the top of the graph)? _____________________________________ ___________________________________________________________________

8.    On what days was the wind gusting mostly to the south (the arrows would be pointing toward the bottom of the graph)? __________________________________ ___________________________________________________________________

9.    What might be responsible for the shift in the wind pattern?  What is your evidence?
___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________


Understanding a graph of NOAA Weather Observatory Data

Barometric Pressure (mbar)

1.    What does the blue line on this graph indicate? _____________________________ 

2.    What unit is used to measure barometric pressure? ____________ 

3.    On this graph, what unit is used to measure time? ____________ 

4.    On what dates was this data collected? __________________________________ 

5.    At Point A on the graph, what was the barometric pressure at the observatory? ____
At Point B on the graph, what was the barometric pressure at the observatory? ____

6.    Draw a vertical line in this graph that will divide this graph into two pieces.  Each piece should have similar characteristics.

7.    What is similar in the pattern of barometric pressure on the left hand side of your vertical line? ________________________________________________________ ___________________________________________________________________

8.    What is similar in the pattern of barometric pressure on the right hand side of your vertical line? ________________________________________________________ ___________________________________________________________________

9.    What might be responsible for the shift from the pattern on the left to the pattern on the right?  What is your evidence?
___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________


Data Sources

 

Water Level, Velocity, Turbidity, and Temperature Data

Time: 2015-2-14 to 2015-2-20

Station: The Wax Lake Delta Sensor Database, Mike3

 

Wind speed, Air Pressure, and Air Temperature Data

Time: 2015-2-14 to 2015-2-20

Station: NOAA Tide and Currents, 8764227 LAWMA, Amerada Pass, LA

 

Water Salinity, Level, and Temperature Data

Time: 2015-2-14 to 2015-2-20

Station: CPRA-CIMS, CRMS0479


Data Stations

Click here to find out more about data stations.