1.2.4 INTRODUCTION TO RESERVOIRS History of Reservoirs
The first archeological evidence of dams (and reservoirs) is dated to approximately 3000 BC.
These structures were constructed in the region recognized today as Jordan. A similar body of evidence
and history of earthen and stone dams and reservoirs is found for other regions such as Europe, other
parts of the Middle East, Southeast Asia, China, and Central America. These early reservoirs were
constructed for the purposes of irrigation and water supply. This technology was a logical development
where human needs for water surpassed naturally occurring supplies.
Hydropower from dams dates to antiquity. Watermills using flowing water were used to turn
grinding stones in the first century BC. This technology was used widely and water power was crucial
to industry early in the industrial revolution. Later, electricity generated from hydropower was able to
export the energy of water motion to locations greatly removed from the stream.
As development continued and as population densities increased, the impact of floods on local
and regional economies was greater and greater. Dams served dual purposes of providing protection
from flooding as well as electrical power. Regional development was stimulated through large dam
construction programs such as administered by the Tennessee Valley Authority.
In areas where farming was limited by water availability, dams and reservoirs provided water
for irrigation. This was more prevalent in the western states of the U.S.A. The first very large dam
project was Hoover Dam which was begun in 1931 and , when completed, was the largest dam in the
world. Today, much larger dams have been completed and are planned all around the world.
The reasons for building reservoirs are several but not numerous. The reasons usually include
flood protection, hydropower, water supply, irrigation, recreation, and wildlife habitat. Often in this
country, a reservoir authorized for one set of purposes may eventually offer other economic
opportunities as well. Most recently, because dam and lake construction is costly and controversial,
dams have been authorized for multiple and sometimes conflicting purposes.
The economic benefit of reservoirs is also not constant. Local and regional development around
and near reservoirs can greatly increase the economic interest for recreation. If sufficient change occurs,
the authorized purpose may be modified. In 1997, Glen Canyon dam began experimental non-power
releases to simulate the flooding that occurred seasonally in the river prior to its construction. If the
benefits to habitat and recreation are proven sufficient, this operation may become normal. Elsewhere, a
dam may be removed if sufficient economic purpose is discovered. These decisions are all important to
aquatic habitats and water quality because they determine operational schedules and patterns of water


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