A control lock, guard lock or stop lock differs from a normal

canal lock A lock is a device used for raising and lowering boats, ships and other watercraft between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber in which the water ...

in that its primary purpose is controlling variances in water level rather than raising or lowering vessels. A control lock may also be known as a tide lock where it is used to control seawater entering into a body of fresh water.

Examples

The T. J. O’Brien Lock and Dam at

Chicago, Illinois (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = Country , subdivision_name ...

is a guard lock that controls the outflow of water from

Lake Michigan Lake Michigan is one of the five Great Lakes of North America. It is the second-largest of the Great Lakes by volume () and the third-largest by surface area (), after Lake Superior and Lake Huron. To the east, its basin is conjoined with that o ...

into the

Illinois Waterway The Illinois Waterway system consists of of navigable water from the mouth of the Calumet River at Chicago to the mouth of the Illinois River at Grafton, Illinois. Based primarily on the Illinois River, it is a system of rivers, lakes, and cana ...

while locking vessels through between the waterway and Lake Michigan. Lock 8 near the south end of the

Welland Canal The Welland Canal is a ship canal in Ontario, Canada, connecting Lake Ontario and Lake Erie. It forms a key section of the St. Lawrence Seaway and Great Lakes Waterway. Traversing the Niagara Peninsula from Port Weller in St. Catharines ...

Port Colborne, Ontario Port Colborne is a city in Ontario, Canada that is located on Lake Erie, at the southern end of the Welland Canal, in the Niagara Region of Southern Ontario. The original settlement, known as Gravelly Bay, dates from 1832 and was renamed after ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by to ...

is a guard lock. Due to the large expanse of shallow water in

Lake Erie Lake Erie ( "eerie") is the fourth largest lake by surface area of the five Great Lakes in North America and the eleventh-largest globally. It is the southernmost, shallowest, and smallest by volume of the Great Lakes and therefore also ha ...

, changes in wind direction and force create water level changes as great as 11 feet (3.4 m) at Port Colborne. Lock 8 controls the water level in the canal, keeping it independent of the fluctuations of Lake Erie, but allows ships to enter Lake Erie regardless of its level.

References

{{DEFAULTSORT:Control Lock Locks (water navigation)