Environmental Engineering Reference
In-Depth Information
Herbaceous:
Non-woody type of vegetation, usually lacking permanent strong
stems, such as grasses, cereals, and canola (rape).
High-speed shaft:
Transmits force from the gearbox to the generator.
High-temperature collector:
A solar thermal collector designed to operate at a
temperature of 180°F or higher.
Historic conditions:
The composition, structure, and functioning of ecosystems
resulting from natural processes that we believe, based on sound profes-
sional judgment, were present prior to substantial human-related changes
to the landscape.
Holding pond:
A structure built to contain large volumes of liquid waste to ensure
that it meets environmental requirements prior to release.
Horizontal axis wind turbine:
The most common type of wind turbine where the
axis of rotation is oriented horizontally.
Horsepower:
A unit for measuring the rate of work (or power) equivalent to 33,000
foot-pounds per minute or 746 watts.
Hot dry rock (HDR):
Subsurface geologic formations of abnormally high heat con-
tent that contain little or no water.
Hub:
The center part of the rotor assembly, which connects the blades to the low-
speed shaft.
Hub height:
In a horizontal-axis wind turbine, the distance from the turbine plat-
form to the rotor shaft.
Hydraulic fracturing:
Fracturing of rock at depth with fluid pressure. Hydraulic
fracturing at depth may be accomplished by pumping water into a well at
very high pressures. Under natural conditions, vapor pressure may rise high
enough to cause fracturing in a process known as hydrothermal brecciation.
Hydraulic head:
The distance between the respective elevations of the upstream
water surface (headwater) above and the downstream surface water (tailwa-
ter) below a hydroelectric power plant.
Hydraulic stimulation:
A stimulation technique performed using fluid.
Hydrocarbon:
An organic chemical compound of hydrogen and carbon in the gas-
eous, liquid, or solid phase. The molecular structure of hydrocarbon com-
pounds varies from the simplest (methane, a constituent of natural gas) to
the heavy and very complex.
Hydroelectric power:
The use of flowing water to produce electrical energy.
Hydrogen:
The lightest of all gases, occurring chiefly in combination with oxygen in
water; exists also in acids, bases, alcohols, petroleum, and other hydrocarbons.
Hydrokinetic energy:
The energy possessed by a body of water because of its
motion (kinetic energy = 1/2 mass × velocity
2
).
Hydrologic or flow regime:
Characteristic fluctuations in river flows.
Hydrology:
The science of waters of the Earth: their occurrences, distributions,
and circulations; their physical and chemical properties; and their reactions
with the environment, including living beings.
Hydrolysis:
Decomposition of a chemical compound by reaction with water.
Hydrostatic energy:
The energy possessed by a body because of its position or loca-
tion at an elevation or height above a reference or datum (potential energy
= mass × gravity × height).
