Carl

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.

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.

Overflow dams are designed to carry water which flow over their

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.

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.

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. 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.

But perhaps it is the plans for the Amazon Basin in Brazil that

shows