Week Three – Rivers

Today my whole family got to take a drive that I would always try to do on my why home from college.  When driving from Mankato, MN to Tomah, WI, I would go straight east to Winona and take highway 14 down the Mississippi River.  My favorite time of year to do this was during the fall season when the leaves were turning colors.

As we took the drive I got to explain details about the Mississippi and how we would boat, swim, duck hunt, and fish on the Mississippi during the summers.  I told the girls that the Mississippi is 2,350 miles long and begins at Lake Itasca and goes into the Gulf of Mexico (NPS, 2017).  I explained that every river is a drain for a drainage basin and that a drainage basin is basically all the land sloped into the river.  Since the Mississippi is considered the third largest river system in the world, can you imagine the size of the drainage basin that is covers (Lutgens & Tarbuck, 2015) (p. 342 – 343).  The girls could not comprehend what exactly the basin was, so I had to compare it to Lake Nacimiento in CA.  I asked them if they remember all the hills around Lake Nacimiento and when we saw it raining how we could see the water draining into the river, well that is the same principle, it is just on a bigger scale.  In fact, the Mississippi drainage basin covers about 1.2 million square miles or all or part of 31 states and two Canadian Provinces (NPS, 2017).  If you were to look at the river from space it would look like a tree.  This is because so many tributary streams feed the Mississippi that from far away it takes on a dendritic pattern or tree pattern.  This varies from other patterns that are more radial, rectangular, or trellis (Lutgens & Tarbuck, 2015) (p. 343 – 344). 

When the girls asked about how much water the river holds, I told them it is between 20 and 30 feet at its narrowest and over 11 miles at its widest.  The water travels down the river around 1.2 and 3 miles per hour in normal conditions and it takes about 3 months for the water to make its way from the start of the river to the end (mouth).  All these dimensions result in about 593,003 cubic feet of water per second going into its base level, the Gulf of Mexico (NPS, 2017).  I tried to explain that precipitation, gradient of the river, shape of the channel, depth of resistive channel properties all affect the amount of water discharge that a river will have and that these figures are estimates on a so called normal day.  Overall the river has a very laminar flow that means it is a slow-moving river that flows pretty straight within the rivers alluvial channel (Lutgens & Tarbuck, 2015) (p. 344 – 345).  However, there is always a chance of flooding and with a river this size there can be serious consequences when it floods.

So, I said can you imagine how much sediment is carried by the river and they had no idea what I was talking about.  So, I explained that sediment or small pieces of dirt that are dissolved or suspended within the water that mostly come from the headwater, but some can come from side banks (abrasion), and the river bed (quarrying).  This dirt gets transported down the river by water and then ends up getting placed at the mouth of the river because its speed slows down when it hits the ocean and all the dirt settles and forms a delta going into the Gulf of Mexico.  My daughter joked we could probably put a house on the delta, and I told her it would probably take thousands of years before it would be solid enough to build a house on.  This movement of sediment from all parts of the river is what makes the river a constant changing thing and can result in new paths and joining of other rivers (Lutgens & Tarbuck, 2015) (p. 347 – 350).  Sometime man-made devices are used to control the river’s course.  In the Mississippi this is done with a series of locks and dams.

When we got to Lacrosse, WI we got to witness a barge go through the lock and dam on the border of MN and WI.  This lock and dam is labeled number 7 and watching a barge go through is an impressive feat.  From Minneapolis to the Gulf of Mexico the Mississippi has 39 locks and dams.  The reason for these locks and dams is to change the makeup of the river and sort of flatten out the rate the water drops to make sure the water is at a deep enough level, so the large and heavy cargo ships can navigate the river (KCRG-TV9 News Staff, 2017).

Mississippi River tributary structure (American Rivers, n.d.).

 

#7 Barge area where water level is lowered and raised (Weeks, 2017).

#7 lock and dam on Mississippi (Weeks, 2017).

                                                                            References

American Rivers. (n.d.). Mississippi River. Retrieved from https://www.americanrivers.org/river/mississippi-river/

KCRG-TV9 News Staff. (2017). How Mississippi Lock and Dams Work. Retrieved from

          http://www.kcrg.com/content/news/How-Mississippi-Lock-and-Dams-Work-428373923.html

Lutgens, F. & Tarbuck, E. (2015). Essentials of Geology (12^th ed.). Upper Saddle River, NJ: Pearson Education, Inc.

NPS. (2017). Mississippi River Facts. Retrieved from https://www.nps.gov/miss/riverfacts.html

Weeks, J. (2017). Lock & Dam # 7 Mississippi River Lock & Dam La Crescent, Minnesota. Retrieved from http://www.johnweeks.com/river_mississippi/pagesL/missLD07.html