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

lock Lock(s) 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 entertainment * ''Lock ...

situated at the southern end of

Chouteau Island Chouteau Island ( ), situated approximately due north of the Gateway Arch in St. Louis, Missouri, and approximately south of the confluence of the Missouri River and Mississippi River, is one of a cluster of three islands: Chouteau Island, Gaba ...

near

St. Louis St. Louis () is the second-largest city in Missouri, United States. It sits near the confluence of the Mississippi and the Missouri Rivers. In 2020, the city proper had a population of 301,578, while the bi-state metropolitan area, which e ...

Missouri Missouri is a state in the Midwestern region of the United States. Ranking 21st in land area, it is bordered by eight states (tied for the most with Tennessee): Iowa to the north, Illinois, Kentucky and Tennessee to the east, Arkansas t ...

on the Upper

Mississippi River The Mississippi River is the second-longest river and chief river of the second-largest drainage system in North America, second only to the Hudson Bay drainage system. From its traditional source of Lake Itasca in northern Minnesota, it fl ...

. Its associated dam is just downstream of the

Chain of Rocks Bridge The old Chain of Rocks Bridge spans the Mississippi River on the north edge of St. Louis, Missouri. The eastern end of the bridge is on Chouteau Island (part of Madison, Illinois), while the western end is on the Missouri shoreline. Its most ...

, 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 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 river 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 , colors = , anniversaries = 16 June (Organization Day) , battles = , battles_label = Wars , website = , commander1 = ...

. 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. 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

towboat A pusher, pusher craft, pusher boat, pusher tug, or towboat, is a boat designed for pushing barges or car floats. In the United States, the industries that use these vessels refer to them as towboats. These vessels are characterized by a squar ...

s, 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