Water wheels

Left, an overshot waterwheel in Poland, right, an undershot waterwheel, Den Gamle By, Denmark.

The water wheel was the start of a whole, and rather serious set of simple machines, devices that used power. The water wheel gave more power more cheaply (once a mill was built), it helped feed a lot of people, but more importantly, it set people to thinking about the mechanical works of a mill.

Water mills probably started in Greece, some time before 80 BCE, because that was when a Greek poet called Antipater of Thessalonika mentioned young women being relieved of the work of operating a hand-mill, now water had taken over the hard work.

Soon, waterwheels began to spread into other areas where there was plenty of rainfall, all year round, places where slaves were hard to get. It was the first labour-saving device. The water wheel may have got its start, though, as a device used to raise water from a river to fields, high above the river bank, and that requires some explanation.

Today, if a moored paddle steamer sits in a current and the paddle wheel is disconnected from the engine, the wheel will turn. Something similar would happen to a water-raising wheel (usually powered by humans, working it as a treadmeill) when it sits in the current of the river. This is the simplest of water wheels, the undershot wheel, where water passes under the wheel, making it turn.

Then there is the more efficient overshot wheel where water drops onto the front side of the wheel and carries the front of the wheel down. Both the undershot and overshot wheel need at least two gear wheels to transfer the rotation through 90°.

Waterwheels were not as good at gathering energy as the efficient turbines in modern hydroelectric stations. Still, when there were no animals to feed, all you had to do was have a big enough mill, and enough fall to get enough energy from it.

This was a special problem with overshot wheels, where mill owners needed to take water out of the river, somewhere upstream, and run it through a channel that wound around the contours on a gentler gradient than the river bed.

Sometimes this would be helped out by a weir or a dam that raised the water level, but if there were several mills along a river, they would sooner or later start to interfere with each other. The Domesday Book was completed in England in 1086. This inventory of what the Normans had taken when they invaded England listed 5624 waterwheels in England, about one for every 50 households.

Bread was a staple food, and so mills were needed, all over the country. The Domesday book also records two mills in Somerset which paid their rent, before 1086, with blooms of iron, which makes it fairly clear that those mills were being used to forge iron. 

Cistercian abbeys in 12^th century France commonly used waterwheel power to grind grain, to sieve flour, to full cloth and to tan leather.

At other times, water power crushed olives and operated bellows for forges and the fires used to brew beer. A paper mill powered by water existed in Spain in 1238, and seven such mills were to be found in Italy by 1268. Paper was made by pounding linen, either by hand, or by foot, or by water power. Guess which one was more popular with the workers?

Water power was easier. when you could get it. In France, a tributary of the Seine River, the Robec, had two mills in the 10^th century, four in the 11^th, ten in the 13^th and twelve at the start of the 14^th century. Before long, the medieval world was running out of space for mills, and disputes began to break out as dams and weirs grew higher, backing water up to the next dam upstream, reducing the fall at the upper dam.

At peak times, the Garonne River at Toulouse in France has a flow of up to 9000 tons of water a second, about a fifth of a cubic mile or 780 megalitres of water a day. Damming something like that meant driving thousands of 6-metre oak logs into the river bed in two rows and then filling the gap between with rocks, gravel, oil and wood to make a water-tight wall.

There were three Garonne dams: Château-Narbonnais, La Daurade and Le Bazacle, and between 1278 and 1408, various acts of dam-raising led to lawsuits and orders to demolish dam extensions and pay damages that were mostly ignored. By 1408, the La Daurade company had ceased to exist, its last shares snapped up by the shareholders of Le Bazacle, ending the dispute.

In later times, windmills took over part of the task, simply because they could be located where there was no reliable flow of water, but windmills were not as powerful. The early Industrial Revolution grew up near rivers, but with time, the waterwheels were replaced by steam engines. The world was ready for them, because the mechanical skills needed to build and fix mills driven by water and wind were very much the skills needed to make early steam engines.