Geoscience Reference
In-Depth Information
Medieval watermills typically powered their wheels by using a dam or weir to concentrate
the falling water and pond a reserve supply. These modifications to rivers became increas-
ingly common all over Europe, and by the end of the Middle Ages, in the mid-15th century,
watermills were in use on a huge number of rivers and streams. The importance of water
power continued into the Industrial Revolution, when a series of inventions transformed
the manufacture of cotton in England and gave rise to a new mode of production: the fact-
ory system. The early textile factories were built to produce cloth using machines driven
by waterwheels, so they were often called mills.
The supremacy of running water was soon superseded by steam power generated by burn-
ing charcoal, coal, and later oil and gas, although rivers have continued to play a role in
industrial power generation. All thermal electric generating stations, whether the source of
heat they use is fossil fuels, nuclear, or geothermal, convert water - or some other fluid
- into steam to drive electricity-generating turbines. The steam has to be condensed in a
cooling system in order to be recycled through the turbines, and large quantities of water
are also required for this purpose. Much of this water is drawn from rivers, along with lakes
and aquifers and the oceans.
The energy potential of water moving in rivers has re-emerged in the modern era with the
advent of hydroelectricity generation. Hydropower is the only renewable resource used on
a large scale for electricity generation, and about one-third of all countries rely on hydro-
power for more than half their electricity. Globally, hydropower provides about 20% of the
world's total electricity supply. Most large hydroelectric stations rely on a dam to supply a
reliable flow of water to turn their turbines, but small 'run of river' hydroelectric stations
do not need such obstacles to the natural flow of the river. Countries with abundant rainfall
and mountainous terrain have developed hydropower to become their foremost supply of
electricity. Norway is an interesting example. Its rivers provide more than enough hydro-
electricity for its own needs so the country has become an exporter of hydropower.
