page_title: Lock (water navigation)
section_title: Flood gates
hierarchical_section_title: Lock (water navigation) / Special cases / Flood gates
caption_attribution_description: English: Stop gate on C &amp; O Canal, above lock 16, at 13.74 miles near Great Falls, Maryland, USA. According to Thomas Hahn's Towpath Guide (p. 40), this was constructed in 1852 to control flood damage esp. in the Widewater area.
context_page_description: 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 level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is the chamber itself that rises and falls.
  Locks are used to make a river more easily navigable, or to allow a canal to cross land that is not level. Later canals used more and larger locks to allow a more direct route to be taken.
  Since 2016, the largest lock worldwide is the Kieldrecht Lock in the Port of Antwerp, Belgium.
context_section_description: A flood gate or "stop gate" is the cheaper equivalent of a flood lock. Only one set of gates exist, and so when the river is higher than the canal, the gates are closed and navigation ceases. These are quite common in the French inland waterways system. Flood gates may also be used to sub-divide long canal pounds or protect, in case of bank collapse, the surrounding area if this is lower than the water level of the canal. They are commonly found at the ends of long embankments and at aqueducts. These gates are often overlooked because they lack balance beams and are only a little higher than normal canal level.
caption: Flood gate or Stop gate (American usage) on Chesapeake and Ohio Canal. When a flood threatened, boards were put in the lock to divert waters from the canal to the Potomac river. Note winch house on top for the boards.
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