The Nightmare of Locks

26 February 2010, 22:00

A Flash Lock is effectively a weir with a single gate to allow boats to navigate beyond the structure. Originally very simple structures allowing boards to be dropped into place across the water to build up depth later versions used movable gates. Flash locks did exist on river navigations in the early days but were replaced with pound locks as soon as it became practical to do so. Flash locks are extremely difficult to navigate and inherently dangerous, often resulting in damage to vessels and injury to their crews.


Flash lock on the River Thames

Map of a flash lock - very, very few survive today



When closed the gates allowed the stretch of river behind them to fill with water. As there was only a single gate without any method of containing the water, once the gate was opened the water would rush out down to the lower level of the river on the other side gradually depleting the water level upstream.

Boats would literally have to ride the rush of water to move to the next level, an extremely difficult manoeuvre if you’re having to haul a barge upstream against the flow of water with only horse or human power to do so, although winches were later installed to aid the process. Flash locks were also called Navigation Weirs and Staunches.

If boat was fortunate, it could just about manage and fight the strong flow of water through the flash lock gate and pull itself upriver. If not so lucky, it could be overwhelmed by water and its passengers drowned and consigned to an early watery grave. Nedless to say, flash locks were replaced in the 18th century by the modern chamber lock, still the most common type of lock in use today.

Imagine a journey through a huge flash lock...


Flash locks were often built directly into weirs

5 Comments

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Elat 27 February 2010 @ 16:32 That looks like something on the river moy.

JupiterKid 2 March 2010 @ 02:57 The weir you mean? I'm not sure of any surviving flash locks in Ireland. The first Shannon navigation works in the late 17th and early 18th century had a series of flash locks but these were seen as dangerous and unreliable. Maybe someone could do a historical project on identifying, mapping and surveying any surviving flash locks (or their remains on Irish waterways today.

Elat 2 March 2010 @ 18:02 like totally!

JupiterKid 2 March 2010 @ 21:43 Ooh thank you Elat! You're the only poster who seems to care about this blog. I think I'll have to sex it up a but...

Elat 3 March 2010 @ 16:04 sex it up a bit? aw bless!