Environmental Engineering Reference
In-Depth Information
D
Dam:
A physical barrier constructed across a river or waterway to control the flow of
or raise the level of water. The purpose of construction may be for flood con-
trol, irrigation needs, hydroelectric power production, or recreation usage.
Daylighting:
The use of direct, diffuse, or reflected sunlight to provide supplemental
lighting for building interiors.
Daylighting controls:
A system of sensors that assesses the amount of daylight and
controls lighting or shading devices to maintain a specified lighting level.
The sensors are sometimes referred to as
photocells
.
d.b.h.:
The diameter measured at approximately breast height (usually 4.5 feet above
the ground), commonly used by foresters to describe tree size.
DC:
Direct current.
Deadweight tons:
The lifting capacity of a ship expressed in long tons (2.240 lb),
including cargo, commodities, and crew.
Decatherm:
Ten therms or 1,000,000 Btu.
Decontamination:
Removal of unwanted radioactive or hazardous contamination
by a chemical or mechanical process.
Deepest total depth:
The deepest total depth of a given well is the distance from
a surface reference point (usually the Kelly bushing; also called the
drive
bushing
) to the point of deepest penetration measured along the wellbore. If
a well is drilled from a platform or barge over water, the depth of the water
is included in the total length of the wellbore.
Defoliator:
An agent that damages trees by destroying leaves or needles.
Deforestation:
The net removal of trees from forested land.
Degasification system:
The methods employed for removing methane from a coal
seam that could not otherwise be removed by standard ventilation fans and
thus would pose a substantial hazard to coal miners. These systems may be
used prior to mining or during mining activities.
Degradable organic carbon:
The portion of organic carbon present in such solid
waste as paper, food waste, and yard waste that is susceptible to biochemi-
cal decomposition.
Degradation:
The loss of native species and processes due to human activities such
that only certain components of the original biodiversity persist, often
including significantly altered natural communities.
Demand indicator:
A measure of the number of energy-consuming units, or the
amount of service or output, for which energy inputs are required.
Demonstrated resources:
Same qualifications as identified resources, but include
measured and indicated degrees of geologic assurance and exclude the
inferred.
Demurrage:
The charge paid to a vessel owner or operator for detention of a ves-
sel at a port beyond the time allowed, usually 72 hours, for loading and
unloading.
Densification:
A mechanical process to compress biomass (usually wood waste) into
pellets, briquettes, cubes, or densified logs.
