Environmental Impact of Dams

Ben Warren
James Kulinski
Dan Lawlor
PE = mgh
P = energy/time
P = mgh/t = m/t * g * h
Ø = flow rate in kg/sec
Ø = 1 kg/s
g = 9.8
h = 90 m
P=1kg/s *
9.8m/s *
= 882 J/s = 882 W
The Water Wheel
The Water Wheel
Efficiency ~ 60%
882 W * .60 =
529.2 W
This is only
converted into
Efficiency ~
80 %
882 W * .80 =
705.6 W
Efficiency ~
80 %
882 W * .80 =
705.6 W
Almost 50%
more efficient
than water
Environmental Impact of Dams
Fragmentation of Ecosystems
A hydroelectric dam disrupts the natural flow of
Flooding upstream of the dam can submerge
large areas of the landscape, displacing landdwelling species.
Decreased flow downstream of the dam can dry
out river banks and tributaries, displacing
aquatic species.
Dams can interrupt the migratory routes of fish.
Salmon have been most notably affected – the
adults are often unable to travel upstream, and
the young are often caught in the turbines
traveling downstream.
The larger the dam, the greater the threat to
animal populations.
Thus, large dams must be constructed with greater
caution than smaller 'micro-hydroelectric' dams,
which impact the environment much less.
To mitigate the impact to fish migration, systems
like the 'fish ladder' pictured below have
become much more common.
A more subtle threat is posed by the 'scouring'
of riverbanks downstream from the dam.
Dams tend to filter the sediment out of the water,
which besides posing a threat to the dam's integrity,
also creates a flow of dissolute water that sucks
sediment from the banks downstream.
Dams will periodically need to purge, resulting in
small controlled floods, which also take sediment
from the river downstream.
Depending upon the composition of the river, this
can be more or less of a problem. Rivers with
delicate systems of sandbars can erode and widen
at a very destructive rate.
An eroded riverbank in the Hinboun river in Laos,
downstream from the “Nam Theun 2” dam.
Human Impact
The geographical changes resulting from large
dams can have complicated political effects.
The 'Three Gorges' Dam on China's Yangtze River is
the world's largest electrical generation plant of any
It is 185 metres tall, and 2,335 metres long. It
generates 80 Terawatt-hours of electricity a year!
The Three Gorges Dam brought water levels up by as
many as 100 meters in its flood basin, and has
displaced as many as 1,300 archeological and
historical sites. Many of these are some of the oldest
and most academically rich in the world.
The Three Gorges also displaced a large portion of
the local population. However, since the dam
provided them with cheap energy, reactions have
been mixed.
Other Human Impacts
The construction of a single dam upstream can
have drastic effects on an entire river.
These effects can cross over political boundaries.
Egypt's Aswan Dam has lowered the level of the
Nile in several of the countries downstream.

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