.
Hydroelectricity
Environmental Costs of
Hydroelectricity
Frederic Beaudry
Hydroelectricity
is a significant source of power in many regions of the globe, providing 24% of
the global electricity needs.
Brazil and Norway rely almost exclusively on hydropower.
In the United States, 7 to 12% of all electricity is produced by
hydropower; the states which depend the most on it are Washington, Oregon,
California, and New York.
Hydropower vs. Hydroelectricity
Hydropower is when water is used to activate moving parts, which in
turn may operate a mill, an irrigation system, or an electric turbine (in which
case we can use the term hydroelectricity).
Most commonly, hydroelectricity is produced when water is held back by
a dam, led down a penstock through a turbine, and then released in the river
below. The water is both pushed by pressure from the reservoir above and pulled
by gravity, and that energy spins a turbine coupled to a generator producing
electricity.
The rarer run-of-the-river hydroelectric plants also have a dam, but
no reservoir behind it; turbines are moved by the river water flowing past them
at the natural flow rate.
Ultimately, the generation of electricity relies on the natural water
cycle to refill the reservoir, making it a renewable process with no input of
fossil fuel needed.
Our use of fossil fuels is associated with a multitude of
environmental problems: for example, the extraction of oil from tar sands
produces air pollution; fracking for natural gas is associated with water
pollution; and the burning of fossil fuels produces climate change –inducing
greenhouse gas emissions.
We therefore look to sources of renewable energy as clean alternatives
to fossil fuels.
However, like all sources of energy, renewable or not, there are
environmental costs associated with hydroelectricity.
Here is a review of some of those costs, along with some benefits.
Costs
· Barrier to Fish. Many migratory fish species swim
up and down rivers to complete their life cycle. Anadromous fish, like salmon,
shad, or Atlantic sturgeon, go upriver to spawn, and young fish swim down river
to reach the sea. Catadromous fish, like the American eel, live in the rivers
until they swim out to the ocean to breed, and the young eels (elvers) come
back to freshwater after they hatch. Dams obviously block the passage of these
fish. Some dams are equipped with fish ladders or other devices to let them
pass unharmed. The effectiveness of these structures is quite variable, but
improving.
· Changes in Flood Regime. Dams can buffer large,
sudden volumes of water following spring melt of heavy rains. That can be a
good thing for downstream communities (see Benefits below), but it also starves
the river from a periodic influx of sediment, and prevents the natural high
flows from regular re-countering of the river bed, which renews habitat for
aquatic life. To recreate these ecological processes, authorities periodically
release large volumes of water down the Colorado River, with positive effects
on the native vegetation alongside the river.
· Temperature and Oxygen Modulation. Depending on
the design of the dam, water released downstream often comes from the deeper
parts of the reservoir. That water is therefore much the same cold temperature
throughout the year. This has negative impacts on aquatic life adapted to wide
seasonal variations in water temperature. Similarly, low oxygen levels in
released water can kill aquatic life downstream, but the problem can be
mitigated by mixing air into the water at the outlet.
· Evaporation. Reservoirs increase a river’s surface
area, thus increasing the amount of water lost to evaporation. In hot, sunny
regions the losses are staggering: more water is loss from reservoir
evaporation than is used for domestic consumption. When water evaporates,
dissolved salts are left behind, increasing salinity levels downstream and
harming aquatic life.
· Mercury Pollution. Mercury is deposited on
vegetation long distances downwind from coal-burning power plants. When new
reservoirs are created, the mercury found in the now submerged vegetation is
released, and converted by bacteria into methylmercury. This methylmercury
becomes increasingly concentrated as it moves up the food chain (a process
called bio-magnification). Consumers of predatory fish, including humans, are
then exposed to dangerous concentrations of the toxic compound.
· Methane Emissions. Reservoirs often become
saturated with nutrients coming from decomposing vegetation or nearby
agricultural fields. These nutrients are consumed by algae and microorganisms
which in turn release large amounts of methane, a powerful greenhouse gas. This
problem has of yet not been studied enough to understand its true extent.
Benefits
· Flood control. Reservoir levels can be lowered in
anticipation of heavy rain or snowmelt, buffering the communities downstream
from dangerous river levels.
· Recreation. Large reservoirs are often used for
recreational activities like fishing and boating.
· Alternative to Fossil Fuels. Producing
hydroelectricity releases a lower net amount of greenhouse gases than fossil
fuels. As part of a portfolio of energy sources, hydroelectricity allows
greater reliance on domestic energy, as opposed to fossil fuels mined overseas,
in locations with less stringent environmental regulations.
Some Solutions
Because the economic benefits of older dams wane while the
environmental costs mount, we have seen any increase in dam decommissioning and
removal.
These dam removals are spectacular, but most importantly they allow
scientists to observe how natural processes are restored along the rivers.
Much of the environmental problems described here are associated with
large-scale hydroelectric projects.
There is a multitude of very small scale projects (often called “micro
hydro”) where judiciously placed small turbines use low-volume streams to
produce electricity for a single home or a neighborhood.
These projects have little environmental impact if properly designed.
Frederic Beaudry is an associate
professor of environmental science and a wildlife biologist with interests in a
broad range of environmental issues.
Experience
Dr. Beaudry teaches courses in environmental
sciences at Alfred University, New
York. Prior to teaching, he worked as a wildlife biologist focusing on the
ecology and conservation of birds and turtles. He has authored several
scientific papers on land use and conservation. His current research examines
land use changes and their effects on bird and amphibian communities.
Education
Dr. Beaudry has a BS in Biology from the
Université du Québec à Rimouski, a master's degree in Natural Resources from
Humboldt State University, and a PhD in Wildlife Ecology from the University of
Maine. He conducted postdoctoral research at the University of
Wisconsin-Madison.
Frederic Beaudry
"Strong science has greatly developed our
understanding of environmental issues in the last decade. I am hoping to
connect readers with sound information about new developments affecting our
air, water, soil, and biodiversity. We are in charge of our health, that of our
land, and of the plants and animals that depend on it."
https://www.thoughtco.com/environmental-costs-of-hydroelectricity-1204183
https://www.thoughtco.com/environmental-costs-of-hydroelectricity-1204183
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