Many people have

already dammed a small stream using sticks and

mud by the time they become adults. Humans

have used dams since early civilization, because

four-thousand years ago they became aware that

floods and droughts affected their well-being and

so they began to build dams to protect themselves

from these effects.1 The basic principles of dams

still apply today as they did before; a dam must

prevent water from being passed. Since then,

people have been continuing to build and perfect

these structures, not knowing the full intensity of

their side effects. The hindering effects of dams on

humans and their environment heavily outweigh the

beneficial ones. The paragraphs below will prove

that the construction and presence of dams always

has and will continue to leave devastating effects

on the environment around them. Firstly, to

understand the thesis people must know what

dams are. A dam is a barrier built across a water

course to hold back or control water flow. Dams

are classified as either storage, diversion or

detention. As you could probably notice from it's

name, storage dams are created to collect or hold

water for periods of time when there is a surplus

supply. The water is then used when there is a

lack of supply. For example many small dams

impound water in the spring, for use in the summer

dry months. Storage dams also supply a water

supply, or an improved habitat for fish and wildlife;

they may store water for hydroelectricity as well.2

A diversion dam is a generation of a commonly

constructed dam which is built to provide sufficient

water pressure for pushing water into ditches,

canals or other systems. These dams, which are

normally shorter than storage dams are used for

irrigation developments and for diversion the of

water from a stream to a reservoir. Diversion

dams are mainly built to lessen the effects of floods

and to trap sediment.3 Overflow dams are

designed to carry water which flow over thier

crests, because of this they must be made of

materials which do not erode. Non- overflow

dams are built not to be overtopped, and they may

include earth or rock in their body. Often, two

types of these dams are combined to form a

composite structure consisting of for example an

overflow concrete gravity dam, the water that

overflows into dikes of earthfill construction.4 A

dam's primary function is to trap water for

irrigation. Dams help to decrease the severity of

droughts, increase agricultural production, and

create new lands for agricultural use. Farmland,

however, has it's price; river bottomlands flooded,

defacing the fertility of the soil. This agricultural

land may also result in a loss of natural artifacts.

Recently in Tasmania where has been pressure

from the government to abandon the Franklin

project which would consume up to 530 sq miles

of land listed on the UN World Heritage register.

In the land losses whole communties must leave

everything and start again elsewhere.5 The

James's Bay Hydroelectric project, hailed to be

one of the most ambitious North American

undertaking of dams was another example of the

lands that may be lost. The 12.7 billion scheme

was to generate 3 160 megawatts of electricity a

day, this power output would be enough to serve

a city of 700 000! One of the largest problems

with this dam, is that it would be built on a region

that meant a lot to 10 500 Cree and 7 000 Inuit.

Lands that their ancestors have hunted and lived

on for more than 5 000 years will be flooded

along with 90% of their trapping lines.6 If this

happened these people must resettle, find a new

way of life and face the destruction of a piece of

their heritage if this project is approved. When a

dam is being constructed, the river where it is

supposed to be built on must be drained. This kills

much of the life and disrupts the ecosystem and

peaceful being of all the aquatic and terrestrial

animals around it. At fisheries there is a large

impact on the fish. The famous Columbia River

saw it's stock of salmon drop considerably after

the dams were built, although there were fish

ladders built. The salmon were unable to swim

upstream when it was time for breeding as they

usually did.7 But perhaps it is the plans for the

Amazon Basin in Brazil that shows us how large

the side-effects can be. In the city Surinam, in

northern Brazil, Lake Brokopondo was created in

1864 swamping about 580 square miles of virgin

rainforest. Foul smelling gas called hydrogen

sulfide was produced as the trees decomposed.

The turbine casings were attacked by the acidic

water and the decay of water allowed a chance

for hyacinths to float on the surface. This did not

allow the light