Whether babbling peacefully across a sun-drenched meadow or raging as a torrent down a rocky canyon, water provides a vital lifeline to all living things. Although often depicted as a placid pond, water remains one of the most primitive and first-harnessed powers in the history of mankind. The desire to harness and control water isn’t even a strictly human invention: that lowly water rodent, the beaver builds debris dams to create deeper pools for housing purposes. Early man no doubt first gained the idea of dam building from watching these busy creatures control their environment.
Man has been building dams since prehistoric times. Often, early dams collected scarce rainfall in arid regions and facilitated the growth of agriculture. Dams could trap a trickle of water from a seasonal stream to provide irrigation in even desert regions. Dam and canal irrigation methods were common in ancient Egypt and allowed the development of an advanced civilization. All over the world, evidence of dam-building occurs early in the area’s settlement history. The earliest known dam with archeological evidence is the Jawa Dam in Jordan, built around 2500 B.C.
Dams were also used very early in flood control: one example is the extensive system of dikes that protected reclaimed lands from the North Sea in the Netherlands. These dikes, or levees, are simply earthen dams that physically wall off a body of water from newly-productive farm lands. Dikes and levees are also found worldwide, although usually on a lesser scale than are seen in the Netherlands. Most of the world’s major river systems have had their banks fortified by the use of levees meant to control flooding during periods of high water. What most people think of as true dams, however, are those built across a valley or depression to limit the flow of a river or stream.
Dams of various types also gave rise to some of the earliest forms of power: several methods of channeling the power from rushing water was used to pump water into irrigation canals. By the time of the Han Dynasty (200+ BC) water mills for the grinding of grain into flour were in wide usage. The use of dams to consolidate and strengthen the flow of water for milling was used all over the world. This original power-source, along with it’s early wind energy counterpart, prompted the spread of settled civilizations who could control their environment to create a permanent food source via irrigation, flood control and milling.
Controlled water and the attendant power provided was so widely used that a great many place names from all over Europe and the Americas have some variation of the local word for ‘dam’ in their name. In North America, this use of dams and milling power is easily documented as written records are available from the frontiers of the day (although Native Americans used a simple form of damming to produce weirs for fishing purposes, there is little evidence that they used water for a power source). Settlement expansion progressed rapidly as enterprising businessmen built rudimentary dams in remote regions to power grist mills for flour-a staple needed for settlement. It wasn’t long before hydro power was being used to support manufacturing. The Northeastern United States was quickly supplied with dams for industry; entire cities sprang up where rushing streams could be dammed and corralled for power to drive machinery. In some places, so many dams were built for mechanical power that there was little remaining of the original river.
Several excellent museums exist, both in the United States and in Europe, with exhibits based on the ingenious uses to which water power was applied. From the simplest primitive waterwheel to such ‘modern’ power generation methods as pressurized hydraulics and compressed air hydropower – all are preserved to delight the mechanical minded visitor. After the electric generator was developed in the late 19th century, hydro power drove the engines of the industrial revolution and electrified the streets, businesses and homes of the civilized world.
One of the original forms of ‘green energy’, hydro power still supplies much of the world’s electricity in countries such as France, Germany,India, China, Spain, Canada and the United States. By the 1920s, 40% of United States electrical power was produced by hydroelectric. A well-known project in the United States is the series of dams built by the Tennessee Valley Authority in the Southeast. The US Army Corps of Engineers. Bureau of Reclamation and the Bonneville Power Administration built dams for flooding control, irrigation and power generation across the Great Plains and the West. The famed recreational reservoirs of the Southeast and the West, such as Kentucky Lake, Lake Powell and Lake Mead, along with nearly every other reservoir in the western states were created by these projects. The majority of these reservoirs were created to alleviate flooding as well as generate power.
Many of these ‘project’ dams have extensive data websites which provide information on water storage capacity and megawatt output. Storage and flood control dam reservoirs are seldom full; excess capacity is built in to contain seasonal run-off from surrounding mountains, both to protect property and to harness water for later use. Persons looking for information regarding water volumes and sizes are often confused because widely varying figures are often quoted within the official information. Most dam reservoirs will list a figure for a ‘dead pool’ (water below the dam outlet that does not drain naturally), a ‘conservation pool’( sometimes referred to as ‘full pool’ – the water conserved for municipal uses, irrigation, recreation and power generation) and ‘flood storage’ pool (the maximum amount of water the reservoir can hold during seasonal flooding). These widely-varying numbers lead to most arguments regarding the size of reservoirs, with both sides certain their particular ‘lake’ is the largest.
Hydroelectric power is generated in a variety of ways: Conventional generation uses the rushing water through a designated flume or pipe to turn turbines to generate electricity. Some dam-generated hydropower plants also use the Pumped Storage method of pumping water mechanically across turbines to generate power. Pumped storage is sometimes used with a series of dammed reservoirs, where excess power is used during time of low-demand to pump water into a higher-elevation reservoir for later re-use. Run-of-River generation is used in small-dam configurations to produce smaller amounts of electricity where there isn’t the storage space of a large reservoir. The largest hydropower facilities are in the Gigawatt range (one billion watts) and produce nearly double the output of the world’s largest nuclear power facilities. Three dam/hydroelectric generating systems exist that produce over 10 GW – in China, Brazil and Venezuela.
Increasingly, dams and the reservoirs they create are important sources of wildlife habitat. Although there is a widespread movement to remove dams in much of the world, on the premise that a naturally-flowing river provides a more natural environment for fish and aquatic creatures, dams are being built in other places specifically to provide habitat. In the arid Western states, reservoirs offer scarce wetlands and feeding areas to migratory birds and local wildlife. In other places, dams that have been in place for well over 100 years have afforded mature wetlands with entire populations of birds, waterfowl, fish, mollusks, mammals, reptiles, amphibians, native grasses and rare bog plants. The small lakes and ponds offer valued recreational and fishing lands and increase property values. Removing dams in these situations would destroy already mature and populated wetland habitat for dubious reasons.
Given the need for renewable and clean energy, producing hydroelectric power from these smaller dams may provide the best of all solutions. It is time to examine the re-activation of the many de-commissioned hydro-electric dams to provide the clean, home-grown energy the country needs.
For more information, see:
Mohamed Bazza “overview of the hystory of water resources and irrigation management in the near east region” ww.fao.org/world/regional/…/HYSTORY-OF-WATER-RESOURCES.pdf
US Army Corps of Engineers Lakes Gateway
http://corpslakes.usace.army.mil/visitors/
Tennessee Valley Authority History: From The New Deal To A New Century
http://www.tva.com/abouttva/history.htm
Bureau of Reclamation Dams
http://www.usbr.gov/projects/dams.jsp
China Completes Three Gorges Dam
http://www.cbsnews.com/stories/2006/05/20/world/main1638180.shtml
Is It Worth A Dam
http://ehp.niehs.nih.gov/qa/105-10focus/focus.html
Hydropower Revisited
www.cleanenergyresourceteams.org/files/CERTsManualCh5.pdf
