Dams

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 to