Esna, Egypt - 10 January 2008
Two barrage bridges straddle the Nile at this point: one built by the British in 1906, and the "Electricity Bridge" built in the 1990s. Navigation – particularly, Nile cruisers ferrying tourists from Luxor to Aswan, 155 km further upstream – can be held up for hours while vessels negotiate their way through the lock system.
The two main points of interest in Esna are its lively tourist-oriented souk, which fills a couple of streets leading inland from the corniche. The other is the temple of Esna. The temple, which has only been partially excavated, is about 200 meters from the river and some 9 meters below street level.
A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber whose water level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is the chamber itself (usually then called a caisson) that rises and falls.
Locks are used to make a river more easily navigable, or to allow a canal to take a reasonably direct line across country that is not level.
The term airlock was coined for a similar device used to allow persons to pass to and from a location in which a particular atmosphere is maintained, such as underwater, in space, or in a clean room.
A lock is required when a stretch of river is made navigable by bypassing an obstruction such as a rapid, dam, or mill weir — because of the change in river level across the obstacle.
The lowest lock on a navigable river separates the tidal and non-tidal stretches. Sometimes a river is made entirely non-tidal by constructing a sea lock directly into the estuary.
In more advanced river navigations, more locks are required.
Where a longer cut bypasses a circuitous stretch of river, the upstream end of the cut will often be protected by a flood lock.
The longer the cut, the greater the difference in river level between start and end of the cut, so that a very long cut will need additional locks along its length. At this point, the cut is, in effect, a canal.
Early completely artificial canals, across fairly flat countryside, would get round a small hill or depression by simply detouring (contouring) around it. As engineers became more ambitious in the types of country they felt they could overcome, locks became essential to effect the necessary changes in water level without detours that would be completely uneconomic both in building costs and journey time. Later still, as construction techniques improved, engineers became more willing to barge directly through and across obstacles by constructing long tunnels, cuttings, aqueducts or embankments, or to construct even more technical devices such as inclined planes or boat lifts. However, locks continued to be built to supplement these solutions, and are an essential part of even the most modern navigable waterways.
Two barrage bridges straddle the Nile at this point: one built by the British in 1906, and the "Electricity Bridge" built in the 1990s. Navigation – particularly, Nile cruisers ferrying tourists from Luxor to Aswan, 155 km further upstream – can be held up for hours while vessels negotiate their way through the lock system.
The two main points of interest in Esna are its lively tourist-oriented souk, which fills a couple of streets leading inland from the corniche. The other is the temple of Esna. The temple, which has only been partially excavated, is about 200 meters from the river and some 9 meters below street level.
A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterways. The distinguishing feature of a lock is a fixed chamber whose water level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is the chamber itself (usually then called a caisson) that rises and falls.
Locks are used to make a river more easily navigable, or to allow a canal to take a reasonably direct line across country that is not level.
The term airlock was coined for a similar device used to allow persons to pass to and from a location in which a particular atmosphere is maintained, such as underwater, in space, or in a clean room.
A lock is required when a stretch of river is made navigable by bypassing an obstruction such as a rapid, dam, or mill weir — because of the change in river level across the obstacle.
The lowest lock on a navigable river separates the tidal and non-tidal stretches. Sometimes a river is made entirely non-tidal by constructing a sea lock directly into the estuary.
In more advanced river navigations, more locks are required.
Where a longer cut bypasses a circuitous stretch of river, the upstream end of the cut will often be protected by a flood lock.
The longer the cut, the greater the difference in river level between start and end of the cut, so that a very long cut will need additional locks along its length. At this point, the cut is, in effect, a canal.
Early completely artificial canals, across fairly flat countryside, would get round a small hill or depression by simply detouring (contouring) around it. As engineers became more ambitious in the types of country they felt they could overcome, locks became essential to effect the necessary changes in water level without detours that would be completely uneconomic both in building costs and journey time. Later still, as construction techniques improved, engineers became more willing to barge directly through and across obstacles by constructing long tunnels, cuttings, aqueducts or embankments, or to construct even more technical devices such as inclined planes or boat lifts. However, locks continued to be built to supplement these solutions, and are an essential part of even the most modern navigable waterways.
More on Wikipedia: http://en.wikipedia.org/wiki/Lock_%28water_transport%29
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