Lower Mississippi River
Encyclopedia
The Lower Mississippi River is the portion of the Mississippi River
downstream of Cairo
, Illinois
. From the confluence
of the Ohio River
and Upper Mississippi River
at Cairo, the Lower flows just under 1600 kilometers (1000 mi) to the Gulf of Mexico
. It is the most heavily travelled component of the Mississippi River System
.
Unlike on the upper rivers, there are no locks or dams
on the Lower Mississippi. The river is, however, constrained by levees and dikes to control flooding and secure a navigation channel for barges. The Old River Control Structure
, the Bonnet Carré Spillway
, the Mississippi River – Gulf Outlet Canal and other man-made structures on the lower reaches of the river seek to manipulate the flow of water in the vicinity of New Orleans.
The political and engineering focus in the 20th century was to separate the Lower Mississippi River from its floodplain
. Levees and channelization—along with substantial loss of bottomland forests to agriculture in the alluvial valley—have resulted in a loss of wildlife and fish habitat, decreased water quality, and an expansion of the hypoxic zone in the Gulf of Mexico
. Agricultural runoff
has resulted in increased turbidity
, silt
ation, pollution from pesticides, toxicity
to aquatic organisms, oxygen depletion and eutrophication
.
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...
downstream of Cairo
Cairo, Illinois
Cairo is the southernmost city in the U.S. state of Illinois. It is the county seat of Alexander County. Cairo is located at the confluence of the Mississippi and Ohio rivers. The rivers converge at Fort Defiance State Park, an American Civil War fort that was commanded by General Ulysses S. Grant...
, Illinois
Illinois
Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...
. From the confluence
Confluence (geography)
In geography, a confluence is the meeting of two or more bodies of water. It usually refers to the point where two streams flow together, merging into a single stream...
of the Ohio River
Ohio River
The Ohio River is the largest tributary, by volume, of the Mississippi River. At the confluence, the Ohio is even bigger than the Mississippi and, thus, is hydrologically the main stream of the whole river system, including the Allegheny River further upstream...
and Upper Mississippi River
Upper 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 to Cairo, where it is joined by the Ohio River to form the Lower Mississippi...
at Cairo, the Lower flows just under 1600 kilometers (1000 mi) to the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. It is the most heavily travelled component of the Mississippi River System
Mississippi River System
The Mississippi River System, also referred to as the Western Rivers, is a mostly riverine network which includes the Mississippi River and connecting waterways....
.
Unlike on the upper rivers, there are no locks or dams
DAMS
Driot-Arnoux Motorsport is a racing team from France, involved in many areas of motorsports. DAMS was founded in 1988 by Jean-Paul Driot and former Formula One driver René Arnoux. It is headquartered near Le Mans, only 2 km from the Bugatti Circuit.- History :The year after its foundation,...
on the Lower Mississippi. The river is, however, constrained by levees and dikes to control flooding and secure a navigation channel for barges. The Old River Control Structure
Old River Control Structure
The Old River Control Structure is a floodgate system located in a branch of the Mississippi River in central Louisiana. It regulates the flow of water leaving the Mississippi into the Atchafalaya River, thereby preventing the Mississippi river from changing course. Completed in 1963, the...
, the Bonnet Carré Spillway
Bonnet Carré Spillway
The Bonnet Carré Spillway is a flood control operation in the Lower Mississippi Valley. Located in St. Charles Parish, Louisiana - about west of New Orleans - it allows floodwaters from the Mississippi River to flow into Lake Pontchartrain and thence into the Gulf of Mexico...
, the Mississippi River – Gulf Outlet Canal and other man-made structures on the lower reaches of the river seek to manipulate the flow of water in the vicinity of New Orleans.
The political and engineering focus in the 20th century was to separate the Lower Mississippi River from its floodplain
Floodplain
A floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
. Levees and channelization—along with substantial loss of bottomland forests to agriculture in the alluvial valley—have resulted in a loss of wildlife and fish habitat, decreased water quality, and an expansion of the hypoxic zone in the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. Agricultural runoff
Surface runoff
Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...
has resulted in increased turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
, silt
Silt
Silt is granular material of a size somewhere between sand and clay whose mineral origin is quartz and feldspar. Silt may occur as a soil or as suspended sediment in a surface water body...
ation, pollution from pesticides, toxicity
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
to aquatic organisms, oxygen depletion and eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
.
See also
- List of crossings of the Lower Mississippi River
- 2011 Mississippi River floods2011 Mississippi River floodsThe Mississippi River floods in April and May 2011 were among the largest and most damaging recorded along the U.S. waterway in the past century, comparable in extent to the major floods of 1927 and 1993. In April 2011, two major storm systems deposited record levels of rainfall on the Mississippi...