Canal & River Locks
Page 6: History & Development
Dams and weirs
In ancient times river transport was common, but rivers were often too shallow to carry anything but the smallest boats. Ancient people discovered that rivers could be made to carry larger boats by making dams to raise the water level. The water behind the dam deepened until it spilled over the top creating a weir. The water was then deep enough to carry larger boats. This dam building was repeated along the river, until there were "steps" of deep water.
This however created the problem of how to get the boats between these "steps" of water. An early and crude way of doing this was by means of a flash lock. A flash lock consisted essentially of a small opening in the dam, which could be quickly opened and closed. On the Thames in England, this was closed with vertical posts (known as rimers) against which boards were placed to block the gap.
When the gap was opened, a torrent of water would spill out, cattying a "downstream" boat with it, or allowing an "upstream" boat to be manhauled through against the flow. When the boat was through, the opening would be quickly closed again. The "gate" could also be opened to release a 'flash' downstream to enable grounded boats to get off shoals, hence the name.
This system was used extensively in Ancient China and in many other parts of the world. But this method was dangerous, many boats were sunk by the torrent of water.
A more sophisticated device was the staunch or water gate, consisting of a gate (or pair of mitred gates) which could be closed (and held shut by water pressure) when the river was low, in order to float vessels over upstream shallows at times of low water. However, the whole upstream head of water had to be drained (by some auxiliary method approaching modern sluices) before the a boat could pass. Accordingly they were not used where the obstacle to be passed was a mill weir.
The natural extension of the Staunch was to provide an upper gate (or pair of gates) to form an intermediate "pound" which was all that need be emptied when a boat passed through. This is a pound lock, the type of lock seen today: known in Medieval Europe, but first used on the Grand Canal in China long before that...
The Songshi or History of the Song Dynasty, volume 307, biography 66, records how Qiao Weiyue, a high-ranking tax administrator, was frustrated at the frequent losses incurred when his grain barges were wrecked on the West River near Huai’an in Jiangsu. The soldiers at one double slipway, he discovered, had plotted with bandits to wreck heavy imperial barges so that they could steal the spilled grain. In 984 Qiao installed a pair of sluice-gates two hundred and fifty feet apart, the entire structure roofed over like a building. By siting two staunch gates so close by one another, Qiao had created a short stretch of canal, effectively a pound-lock, filled from the canal above by raising individual wooden baulks in the top gate and emptied into the canal below by lowering baulks in the top gate and raising ones in the lower.
Page 1 - Introduction & use of locks...Go
Page 2 - Basic construction and operation...Go
Page 3 - Details & Terminology...Go
Page 4 - Variations...Go
Page 5 - Illustrations...Go
Page 6 - History & Development...(Current page)
Page 7 - Use of water...Go
Page 8 - Alternatives...Go