Biomedical Engineering Reference
In-Depth Information
of riverbeds and loss of riverbanks. Since turbine gates are often opened intermittently, rapid
or even daily fluctuations in river flow are observed. For example, in the Grand Canyon, the
daily cyclic flow variation caused by Glen Canyon Dam was found to be contributing to
erosion of sand bars. Dissolved oxygen content of the water may change from pre-construc-
tion conditions. Depending on the location, water exiting from turbines is typically much
warmer than the pre-dam water, which can change aquatic faunal populations, including
endangered species, and prevent natural freezing processes from occurring. Some hydroelec-
tric projects also use canals to divert a river at a shallower gradient to increase the head of the
scheme. In some cases, the entire river may be diverted leaving a dry riverbed.
The ecological and “local” climate change can bring changes that may or may not be
wanted, especially during the transition from one sustainable state (before water storage)
to another sustainable state (when storage reached steady state). The reservoirs of hydro-
power plants in tropical regions may produce substantial amounts of methane. This is due
to plant material in flooded areas decaying in an anaerobic environment and forming
methane, a very potent GHG. According to the 2010 World Commission on Dams report,
where the reservoir is large compared to the generating capacity (less than 100 W/m 2 of
surface area) and no clearing of the forests in the area was undertaken prior to impoundment
of the reservoir, GHG emissions from the reservoir may be higher than those of a conventional
oil-fired thermal generation plant. Although these emissions represent carbon already in the
biosphere, not fossil deposits that had been sequestered from the carbon cycle, there is
a greater amount of methane due to anaerobic decay, causing greater damage than would
otherwise have occurred had the forest decayed naturally.
In boreal reservoirs of Canada and Northern Europe, however, GHG emissions are typi-
cally only 2% e 8% of any kind of conventional fossil-fuel thermal generation. The carbon
emission due to reservoir displacing vegetation land can be significantly reduced with
proper management. A new class of underwater logging operation that targets drowned
forests can mitigate the effect of forest decay.
In 2007, International Rivers accused hydropower firms for cheating with fake carbon
credits under the Clean Development Mechanism (CDM), for hydropower projects already
finished or under construction at the moment they applied to join the CDM. These carbon
credits d of hydropower projects under the CDM in developing countries d can be sold to
companies and governments in developed countries, in order to comply with the Kyoto
protocol.
To embrace the change in sustainable state, there is a need to relocate the people living
where the reservoirs are planned. Change of sustainable state is not a process that can be
implemented without sacrifice. With any change, there are permanent losses of values. In
February 2008, it was estimated that 40 e 80 million people worldwide had been physically
displaced as a direct result of dam construction. In many cases, no amount of compensation
can replace ancestral and cultural attachments to places that have spiritual value to the dis-
placed population. Additionally, historically and culturally important sites can be flooded
and lost. Such problems have arisen at the Aswan Dam in Egypt between 1960 and 1980,
the Three Gorges Dam in China, the Clyde Dam in New Zealand, and the Ilisu Dam in
Turkey.
Colossal industrial accidents are rare and could bring noticeable harm to humanity. The
most damaging of all is a dam failure. Dam failures have accounted for the most serious
Search WWH ::




Custom Search