In addition to reducing the Mississippi River

In addition to reducing the Mississippi River crest downstream, this diversion is also reducing the chances of a channel change by reducing stress on the other elements of the control system.Some geologists have noted that the possibility for course change into the Atchafalaya also exists in the area immediately north of the Old River Control Structure. Sony VAIO VGN-AW11M/H Battery

Army Corps of Engineers geologist Fred Smith once stated, "The Mississippi wants to go west. 1973 was a forty-year flood. The big one lies out there somewhere—when the structures can't release all the floodwaters and the levee is going to have to give way. That is when the river's going to jump its banks and try to break through." Sony VAIO VGN-AW11S/B Battery

If the main channel of the lower Mississippi River changes permanently to the Old River and Atchafalaya River channels in the Atchafalaya Basin, thus bypassing Baton Rouge and New Orleans, the ecological and economic consequences for Louisiana, the region, the nation, and international commerce would be immense. Sony VAIO VGN-AW11XU/Q Battery

Sedimentation and erosion patterns would quickly change greatly, including development of a new river channel and delta, as well as a new pattern offloodplains, natural levees, and backswamps. Changes to salinity of coastal waters (less saline near new delta, more saline near the present delta) would affectmarine life, fisheries, beaches, and coastal marshes. Sony VAIO VGN-AW11Z/B Battery

The abandoned river channel would eventually fill and revegetate, probably with a major influx of invasive non-native species. On the other hand, the low-lying outer parts of the present delta, lacking replenishment, would mostly soon erode away. Over time, the new channel would itself develop meanders and cutoffs, eventually leading to formation of new oxbow lakes. Sony VAIO VGN-AW120J/H Battery

Human society would also be greatly altered locally, with broader consequences nationally and globally. Transportation by road, rail, sea, and river barge would all be dramatically affected, and various sizable new bridges would be urgently needed. Sony VAIO VGN-AW150Y/H Battery

Existing port facilities may have to be relocated or replaced, and channel alterations would be needed to maintain any substantial degree of commercial shipping on either the new or the old channel of the Mississippi. Power lines, pipelines, and fiber-optic and other communications lines would be similarly disrupted, and housing, Sony VAIO VGN-AW160J/Q Battery

agriculture, forestry, petroleum-production facilities, and other land uses would be suddenly altered, as would patterns of recreational activities. Morgan City in particular would be quite heavily impacted. Values of many properties would be greatly altered, some increasing, some decreasing, and ownership claims would need to be resolved for the newly exposed land of the old riverbed. Sony VAIO VGN-AW170Y/Q Battery

Another possible course change for the Mississippi River is a diversion into Lake Pontchartrain near New Orleans, Louisiana. This route is currently controlled by the Bonnet Carré Spillway, built to reduce flooding in New Orleans. However, the spillway and an imperfect natural levee about 4–6 meters (12 to 20 feet) Sony VAIO VGN-AW180Y/Q Battery

high are all that prevents the Mississippi from taking a new, shorter course through Lake Pontchartrain to the Gulf of Mexico.^[32] Diversion of the Mississippi's main channel through Lake Pontchartrain would have generally similar consequences to an Atchafalaya diversion, Sony VAIO VGN-AW190JAH Battery

but to a lesser extent, since the present river channel would remain in use past Baton Rouge and into the New Orleans area. Following a Lake Pontchartrain diversion, the Mississippi's new delta would develop offshore of southern Mississippi.

The New Madrid Seismic Zone, along the Mississippi River near New Madrid, Missouri, Sony VAIO VGN-AW190NAB Battery

between Memphis and St. Louis, is related to an aulacogen (failed rift) that formed at the same time as the Gulf of Mexico. This area is still quite active seismically. Four great earthquakes in 1811 and 1812, estimated at approximately 8 on the Richter magnitude scale, Sony VAIO VGN-AW190NBB Battery

had tremendous local effects in the then sparsely settled area, and were felt in many other places in the midwestern and eastern U.S. These earthquakes created Reelfoot Lake in Tennessee from the altered landscape near the river, and temporarily reversed the direction of flow of the Mississippi itself. Sony VAIO VGN-AW190NCB Battery

The Mississippi River runs through or along 10 states, from Minnesota to Louisiana, and was used to define portions of these states' borders, with Wisconsin,Illinois, Kentucky, Tennessee, and Mississippi along the east side of the river, and Iowa, Missouri, and Arkansas along its west side. Sony VAIO VGN-AW190YAB Battery

Substantial parts of both Minnesota and Louisiana are on either side of the river, although the Mississippi defines part of the boundary of each of these states.

In all of these cases, the middle of the riverbed at the time the borders were established was used as the line to define the borders between adjacent states. Sony VAIO VGN-AW190YBB Battery

In various areas, the river has since shifted, but the state borders have not changed, still following the former bed of the Mississippi River as of their establishment, leaving several small isolated areas of one state across the new river channel, contiguous with the adjacent state. Sony VAIO VGN-AW190YCB Battery

Also, due to a meander in the river, a small part of western Kentucky is contiguous with Tennessee, but isolated from the rest of its state.

The first bridge across the Mississippi River was built in 1855. It spanned the river in Minneapolis, Minnesota where the current Hennepin Avenue Bridge is located. Sony VAIO VGN-AW190YDB Battery

No highway or railroad tunnels cross under the Mississippi River.

The first railroad bridge across the Mississippi was built in 1856. It spanned the river between the Rock Island Arsenal inIllinois and Davenport, Iowa. Steamboat captains of the day, fearful of competition from the railroads, considered the new bridge "a hazard to navigation". Sony VAIO VGN-AW220J/B Battery

Two weeks after the bridge opened, the steamboat Effie Afton rammed part of the bridge, catching it on fire. Legal proceedings ensued, with Abraham Lincoln defending the railroad. The lawsuit went to the Supreme Court of the United States and was eventually ruled in favor of the railroad. Sony VAIO VGN-AW230J/H Battery

Below is a general overview of selected Mississippi bridges which have notable engineering or landmark significance, with their cities or locations. They are sequenced from the Upper Mississippi's source to the Lower Mississippi's mouth.

A clear channel is needed for the barges and other vessels that make the main stem Mississippi one of the great commercialwaterways of the world. Sony VAIO VGN-AW235J/B Battery

The task of maintaining a navigation channel is the responsibility of the United States Army Corps of Engineers, which was established in 1802. Earlier projects began as early as 1829 to remove snags, close off secondary channels and excavate rocks and sandbars.Steamboats entered trade in the 1820s, so the period 1830 – 1850 became the golden age of steamboats. Sony VAIO VGN-AW290JFQ Battery

As there were few roads or rails in the lands of the Louisiana Purchase, river traffic was an ideal solution. Cotton, timber and food came down the river, as did Appalachian coal. The port of New Orleans boomed as it was the trans-shipment point to deep sea ocean vessels. Sony VAIO VGN-AW41JF Battery

As a result, the image of the twin stacked, wedding cake Mississippi steamer entered into American mythology. Steamers worked the entire route from the trickles of Montana, to the Ohio river; down the Missouri and Tennessee, to the main channel of the Mississippi. Only with the arrival of the railroads in the 1880s did steamboat traffic diminish. Sony VAIO VGN-AW41JF/H Battery

Steamboats remained a feature until the 1920s. Most have been superseded by pusher tugs. A few survive as icons—the Delta Queen and the River Queen for instance.A series of 29 locks and dams on the upper Mississippi, most of which were built in the 1930s, is designed primarily to maintain a 9 feet (2.7 m) deep channel for commercial barge traffic. Sony VAIO VGN-AW41MF Battery

The lakes formed are also used for recreational boating and fishing. The dams make the river deeper and wider but do not stop it. No flood control is intended. During periods of high flow, the gates, some of which are submersible, are completely opened and the dams simply cease to function. Sony VAIO VGN-AW41MF/H Battery

Below St. Louis, the Mississippi is relatively free-flowing, although it is constrained by numerous levees and directed by numerous wing dams.In 1829, there were surveys of the two major obstacles on the upper Mississippi, the Des Moines Rapids and the Rock Island Rapids, where the river was shallow and the riverbed was rock. Sony VAIO VGN-AW41XH Battery

The Des Moines Rapids were about 11 mi (18 km) long and just above the mouth of the Des Moines River at Keokuk, Iowa. The Rock Island Rapids were between Rock Island and Moline, Illinois. Both rapids were considered virtually impassable.

In 1848, the Illinois and Michigan Canal was built to connect the Mississippi River to Lake Michigan via the Illinois River near Peru, Illinois. Sony VAIO VGN-AW41XH/Q Battery

The canal allowed shipping between these important waterways. In 1900, the canal was replaced by theChicago Sanitary and Ship Canal. The second canal, in addition to shipping, also allowed Chicago to address specific health issues (typhoid fever, cholera and other waterborne diseases) by sending its waste down the Illinois and Mississippi river systems rather than polluting its water source of Lake Michigan. Sony VAIO VGN-AW41ZF Battery

The Corps of Engineers recommended the excavation of a 5 ft (1.5 m) deep channel at the Des Moines Rapids, but work did not begin until after Lieutenant Robert E. Lee endorsed the project in 1837. The Corps later also began excavating the Rock Island Rapids. Sony VAIO VGN-AW41ZF/B Battery

By 1866, it had become evident that excavation was impractical, and it was decided to build a canal around the Des Moines Rapids. The canal opened in 1877, but the Rock Island Rapids remained an obstacle. In 1878, Congress authorized the Corps to establish a 4.5-foot (1.4 m) Sony VAIO VGN-AW50DB/H Battery

deep channel to be obtained by building wing dams which direct the river to a narrow channel causing it to cut a deeper channel, by closing secondary channels and by dredging. The channel project was complete when the Moline Lock, which bypassed the Rock Island Rapids, opened in 1907. Sony VAIO VGN-AW51JGB Battery

To improve navigation between St. Paul, Minnesota, and Prairie du Chien, Wisconsin, the Corps constructed several dams on lakes in the headwaters area, including Lake Winnibigoshish and Lake Pokegama. The dams, which were built beginning in the 1880s, stored spring run-off which was released during low water to help maintain channel depth. Sony VAIO VGN-AW52JGB Battery

In 1907, Congress authorized a 6-foot (1.8 m) deep channel project on the Mississippi, which was not complete when it was abandoned in the late 1920s in favor of the 9 feet (2.7 m) deep channel project.In 1913, construction was complete on a dam at Keokuk, Iowa, the first dam below St. Anthony Falls. Sony VAIO VGN-AW53FB Battery

Built by a private power company to generate electricity, the Keokuk dam was one of the largest hydro-electric plants in the world at the time. The dam also eliminated the Des Moines Rapids. Lock and Dam No. 1 was completed in Minneapolis, Minnesota in 1917. Lock and Dam No. 2, near Hastings, Minnesota was completed in 1930. Sony VAIO VGN-AW70B/Q Battery

Prior to the Great Mississippi Flood of 1927, the Corps' primary strategy was to close off as many side channels as possible to increase the flow in the main river. It was thought that the river's velocity would scour off bottom sediments, deepening the river and decreasing the possibility of flooding. Sony VAIO VGN-AW71JB Battery

The 1927 flood proved this to be so wrong that communities threatened by the flood began to create their own levee breaks to relieve the force of the rising river.The Rivers and Harbors Act of 1930 authorized the 9 feet (2.7 m) channel project, which called for a navigation channel 9 ft (2.7 m) deep and 400 ft (120 m) wide to accommodate multiple-barge tows. Sony VAIO VGN-AW72JB Battery

This was achieved by a series of locks and dams, and by dredging. Twenty-three new locks and dams were built on the upper Mississippi in the 1930s in addition to the three already in existence.Until the 1950s, there was no dam below Lock and Dam 26 at Alton, Illinois. Sony VAIO VGN-AW73FB Battery

Chain of Rocks Lock (Lock and Dam No. 27), which consists of a low-water dam and an 8.4 mi (13.5 km) long canal, was added in 1953, just below the confluence with the Missouri River, primarily to bypass a series of rock ledges at St. Louis. It also serves to protect the St. Louis city water intakes during times of low water. Sony VAIO VGN-AW80NS Battery