Environmental Engineering Reference
In-Depth Information
•
Develop new tools to improve water use efficiency and operations optimiza-
tion within hydropower units, plants, and river systems with multiple hydro-
power facilities.
•
Identify improved practices that can be applied at hydropower plants to
mitigate for environmental effects of hydro development and operation.
H
ydropower
g
eneratIon
: d
IssoLved
o
xygen
C
onCerns
The benefits derived from the use of hydropower include: (1) it is a clean fuel source;
(2) it is a fuel source that is domestically supplied; (3) it relies on the water cycle and
thus is a renewable power source; (4) it is generally available as needed; (5) it creates
reservoirs that offer a variety of recreational opportunities, such as fishing, swim-
ming, and boating; and (6) it creates a supply of water where needed and assists in
flood control. Many of these benefits are well known and often taken for granted.
Coins are two sided, of course; that is, the good side of anything is generally
accompanied by a bad side. Many view this to be the case with hydropower. The bad
side or disadvantages of hydropower include the impact on fish populations, such
as salmon, when the fish cannot migrate upstream past impoundment dams to their
spawning grounds or migrate downstream to the ocean. Hydropower can also be
impacted by drought, because when water is not available the plant cannot produce
electricity. Hydropower plants also compete with other uses for the land.
Other lesser known negatives of hydropower plants concern their impact on water
low and quality; hydropower plants can cause low water levels that impact riparian
habitats. Water quality is also affected by hydropower plants. Low dissolved oxygen
(DO) levels in the water, which are harmful to riparian habitats, can result when
reservoirs stratify; that is, they develop layers of water of different temperatures (see
Figure 4.10
)
. Stratification can affect the water temperature, thus causing changes
in dissolved oxygen levels, nutrient levels, productivity, and the bioavailability of
heavy metals. During the summer, the natural process of stratification can divide a
reservoir into distinct vertical strata, such as a warm, well-mixed upper layer (epi-
limnion) over a cooler, relativity stagnant lower layer (hypolimnion). Plant and ani-
mal respiration, bacterial decomposition of organic matter, and chemical oxidation
can all act to progressively remove dissolved oxygen from hypolimnetic waters. This
decrease in hypolimnetic dissolved oxygen is not generally offset by the renewal
mechanisms of atmospheric diffusion, circulation, and photosynthesis that operate
Epilimnion (warm; oxygenated)
Metalimnion
Hypolimnion (cool; low oxygen)
FIGURE 4.10
Thermal stratification of a hydropower reservoir.
