Chain of Rocks Lock and Dam, also known as Locks No. 27, is a

lock Lock(s) or Locked may refer to: Common meanings *Lock and key, a mechanical device used to secure items of importance *Lock (water navigation), a device for boats to transit between different levels of water, as in a canal Arts and entertainme ...

situated at the southern end of Chouteau Island near

St. Louis, Missouri St. Louis ( , sometimes referred to as St. Louis City, Saint Louis or STL) is an Independent city (United States), independent city in the U.S. state of Missouri. It lies near the confluence of the Mississippi River, Mississippi and the Miss ...

, on the Upper

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

. Its associated dam is just downstream of the Chain of Rocks Bridge, and the lock is located over southeast on the Chain of Rocks canal. The canal and locks allow river traffic to bypass a portion of the river that is unnavigable in low water due to an anticlinal exposure of

bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

in the river—a "chain of rocks". The canal, main lock, and auxiliary lock were built in the late 1940s and early 1950s to allow a by-pass of the Chain of Rocks lying in the main channel of the Mississippi River. This stretch of river in low water seasons was treacherous for commercial tow boats and barges, often requiring them to wait several days for the river to rise. The dam for lock 27 is atypical for the Mississippi, being a

weir A weir or low-head dam is a barrier across the width of a river that alters the flow characteristics of water and usually results in a change in the height of the water level. Weirs are also used to control the flow of water for outlets of l ...

made of tons of rock laid in the Mississippi to create a small pool elevation upstream from the Chain of Rocks. The drop at Locks 27 can vary from a few feet to over a ten-foot drop depending on the river stage. The Chain of Rocks Lock is operated by the St. Louis District of the

U.S. Army Corps of Engineers The United States Army Corps of Engineers (USACE) is the military engineering branch of the United States Army. A direct reporting unit (DRU), it has three primary mission areas: Engineer Regiment, military construction, and civil wor ...

. Locks No. 27 are the southernmost locks on the

and they are the only Locks south of the confluence of the Mississippi River and

Missouri River The Missouri River is a river in the Central United States, Central and Mountain states, Mountain West regions of the United States. The nation's longest, it rises in the eastern Centennial Mountains of the Bitterroot Range of the Rocky Moun ...

. As such, the Locks move more cargo than any other navigation structure on the Mississippi River.

September 2012 shutdown

An accident caused the lock to be shut down on September 15, 2012. Over four dozen towboats, and over four hundred barges, were stranded when the lock was shut down. A large, rock-filled steel cell—used to help align barges prior to transiting the lock—split causing the channel to be blocked with rock. The cause of the incident was attributed to exceptionally low water levels. The steel cell has armored sections, to protect it from impacts and abrasion from the heavy barges. But the water had fallen so low that barges were impacting an unarmored portion of the shaft.

Gallery

File:Chain of Rocks Canal and Locks.jpg, The Chain of Rocks Canal and Locks in Madison County, Illinois File:Dam -27.JPG, This low water dam across the Mississippi maintains a minimum pool level upstream of the locks. File:Chain_of_rocks_lock_aerial.png, Chain of Rocks locks File:Lock and dam 27.png, Annual tonnage through lock

References

External links

Chain of Rocks Lock and Dam - U.S. Army Corps of Engineers
* {{authority control Dams on the Mississippi River Historic American Engineering Record in Illinois Historic American Engineering Record in Missouri Locks of Illinois Mississippi River locks Mississippi Valley Division Rock-filled dams Transport infrastructure completed in 1953 Transportation buildings and structures in Madison County, Illinois

September 2012 shutdown

Gallery

See also

References

External links