Upper Mississippi River

From Wikipedia, the free encyclopedia

See also: Mississippi River

The Upper Mississippi River is the portion of the Mississippi River upstream of Cairo, Illinois, United States. From the headwaters at Lake Itasca, Minnesota, the river flows approximately 2000 kilometers (1250 mi) to Cairo, where it is joined by the Ohio River to form the Lower Mississippi River.^[4][5]

[edit] History

In terms of geologic and hydrographic history, the Upper Mississippi is a portion of the now-extinct Glacial River Warren which carved the valley of the Minnesota River, permitting the immense Glacial Lake Agassiz to join the world's oceans at the Gulf of Mexico. The collapse of ice dams holding back Glacial Lake Duluth and Glacial Lake Grantsburg carved out the Dalles of the Saint Croix River.

The Driftless Area is a portion of North America left unglaciated at that ice age's height, hence not smoothed out or covered over by previous geological processes.

Inasmuch as the Wisconsin glaciation formed lobes that met (and blocked) where the Mississippi now flows, and given that huge amounts of glacial meltwater were flowing into the Driftless Area, and that there is no lakebed, it is assumed that there were instances of ice dams bursting. Considering the history of Glacial Lake Missoula, something like this is believed to have happened.

[edit] Characteristics

The Upper Mississippi is a gorge with high limestone bluffs carved from water paths over time. Unlike the wide lower portion, the Upper Mississippi river is relatively narrow. The states of Minnesota, Wisconsin and Iowa, along with the Federal government, have preserved certain areas of the land along this reach of the river.

Unlike the Lower Mississippi, the upper river is a series of pools created by a system of 29 locks and dams. The structures were authorized by Congress in the 1930s, and most were completed by 1940.^[6] A primary reason for damming the river is to facilitate barge transportation. The dams regulate water levels for the Upper River, and play a major part in regulating levels on the Lower Mississippi.

[edit] Ecology

On the upper reaches near the Minnesota-Wisconsin border, the river's floodplain is between 1.5 and 5 kilometers (between 1 and 3 mi) wide. South of St. Louis, Missouri, the alluvial floodplain is approximately 80 kilometers (50 mi) wide. Major tributaries to the Upper Mississippi River include the Missouri, Illinois, Minnesota, St. Croix, Black, and Kaskaskia Rivers.^[7]

The Upper Mississippi provides habitat for more than 125 fish species and 30 species of freshwater mussels. Three national wildlife refuges along the river cover a total of 465 square kilometers (285,000 ac). The largest of them, the Upper Mississippi River National Wildlife and Fish Refuge, is over 420 kilometers (260 mi) long, reaching from the Alma, Wisconsin area down to Rock Island, Illinois. The refuge consists of blufflands, marshes, bottom-land forest, islands, channels, backwater lakes and sloughs.^[8][7]It is part of the Mississippi Flyway.

Most of the Upper Mississippi River, though, is not clean enough to allow fish consumption or swimming. Fertilizers and animal and human waste have contributed to high levels of nitrogen and phosphorus throughout the river basin. These nutrients initiate a chemical reaction which reduces the amount of oxygen dissolved in the water, which in turn affects a number of riverine species. The phenomenon also contributes to a hypoxic "dead zone" in the Gulf of Mexico.^[9]

[edit] Navigation

Main article: List of locks and dams of the Upper Mississippi River

Navigation locks allow towboats, barges, and other vessels to transit the dams. Approximately 1350 kilometers (850 mi), from the head of navigation near Minneapolis-St. Paul down to Cairo, has been made suitable for commercial navigation with a depth of 2.75 meters (9 ft).^[7] The agriculture and barge transportation industries have lobbied in the late 20th and early 21st centuries for a multi-billion dollar project to replace the aging lock and dam system. Some environmental groups and advocates of budgetary restraint argue that the project lacks economic justification.^[10]

Each lock & dam complex creates a pool upstream of it. There are 29 locks on the Upper Mississippi maintained by the U.S. Army Corps of Engineers—from Upper St. Anthony Falls upstream to Chain of Rocks downstream. The locks provide a collective 123 meters (404 ft) of lift.^[11] Note that there is a Lock 5 as well as a Lock 5A. Note also that there is no Lock 23.^[12]

[edit] List of pools and locks

[edit] References

1. ^ General Information about the Mississippi River. U.S. National Park Service. Retrieved on 2006-04-01.
2. ^ Background on Upper Mississippi River Basin. EPA: Mississippi River Basin & Gulf of Mexico Hypoxia. Retrieved on 2006-04-01.
3. ^ Wlosinski, Joseph, et al. Habitat Changes in the Upper Mississippi River Floodplain. National Biological Service: Our Living Resources. Retrieved on 2006-04-01.
4. ^ Old Man River: History along the Mississippi. Herbert Hoover Presidential Library. Retrieved on 2006-03-12.
5. ^ Upper Mississippi River Region. Rock Island District Engineers. Retrieved on 2006-03-12.
6. ^ About the Upper Mississippi River System. USGS Upper Midwest Environmental Sciences Center. Retrieved on 2006-03-13.
7. ^ ^{a b c} Basin Facts. Upper Mississippi River Basin Association. Retrieved on 2006-04-01.
8. ^ About the refuges. Friends of the Upper Mississippi River Refuges. Retrieved on 2006-04-01.
9. ^ Army Corps Reform: The Mississippi River. American Rivers. Retrieved on 2006-04-02.
10. ^ Marcia Zarley Taylor (08 March 2006). River debate continues. AgWeb. Retrieved on 2006-03-13.
11. ^ U.S. Waterway System Facts, December 2005 (PDF). USACE Navigation Data Center. Retrieved on 2006-04-27.
12. ^ Operation & Maintenance of Navigation Installations (OMNI) Reports. Rock Island District Engineers. Retrieved on 2006-04-27.

[edit] See also

• List of crossings of the Upper Mississippi River
• List of locks and dams of the Upper Mississippi River