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.
