The head of navigation is the farthest point above the
mouth of a river that can be navigated by
ships
A ship is a large vessel that travels the world's oceans and other navigable waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, ...
. Determining the head of navigation can be subjective on many streams, as the point may vary greatly with the size or the
draft
Draft, the draft, or draught may refer to:
Watercraft dimensions
* Draft (hull), the distance from waterline to keel of a vessel
* Draft (sail), degree of curvature in a sail
* Air draft, distance from waterline to the highest point on a v ...
of the ship being contemplated for navigation and the seasonal water level. On others, it is quite objective, being caused by a
waterfall
A waterfall is any point in a river or stream where water flows over a vertical drop or a series of steep drops. Waterfalls also occur where meltwater drops over the edge
of a tabular iceberg or ice shelf.
Waterfalls can be formed in seve ...
, a low bridge that is not a
drawbridge
A drawbridge or draw-bridge is a type of moveable bridge typically at the entrance to a castle or tower surrounded by a moat. In some forms of English, including American English, the word ''drawbridge'' commonly refers to all types of moveable b ...
, or a
dam without navigation
locks. Several rivers in a region may have their heads of navigation along a line called the
fall line
A fall line (or fall zone) is the area where an upland region and a coastal plain meet and is noticeable especially the place rivers cross it, with resulting rapids or waterfalls. The uplands are relatively hard crystalline basement rock, and the ...
.
Longer rivers such as the
River Thames
The River Thames ( ), known alternatively in parts as the The Isis, River Isis, is a river that flows through southern England including London. At , it is the longest river entirely in England and the Longest rivers of the United Kingdom, s ...
may have several heads of navigation depending on the size of the vessel. In the case of the Thames, that includes
London Bridge
The name "London Bridge" refers to several historic crossings that have spanned the River Thames between the City of London and Southwark in central London since Roman Britain, Roman times. The current crossing, which opened to traffic in 197 ...
, which historically served as the head of navigation for tall ships;
Osney Bridge in
Oxford
Oxford () is a City status in the United Kingdom, cathedral city and non-metropolitan district in Oxfordshire, England, of which it is the county town.
The city is home to the University of Oxford, the List of oldest universities in continuou ...
, which has the lowest headroom of any bridge on the Thames that generally restricts navigation to smaller vessels such as
narrowboat
A narrowboat is a particular type of Barge, canal boat, built to fit the narrow History of the British canal system, locks of the United Kingdom. The UK's canal system provided a nationwide transport network during the Industrial Revolution, b ...
s and
cabin cruisers, and the long reach above
St John's Lock, the first lock downstream of the
river’s source, on the outskirts of
Lechlade, where the river can become treacherously narrow and shallow for anything but small motorboats and human-powered vessels.
In the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
, the entirety of a navigable waterway up to the head of navigation is subject to federal jurisdiction. The government recognizes that the "upper limit" of navigability will "often be the same point traditionally recognized as the head of navigation" but may under some circumstances lie "yet farther upstream."
[33 CFR § 329.11(b).]
References
{{Water-transport-stub
Nautical terminology