Environmental Engineering Reference
In-Depth Information
Hydrograph:
Graph showing variation of water elevation, velocity, stream-
flow, or other property of water with respect to time.
Hydrologic cycle:
Literally, the water-earth cycle; the movement of water in
all three physical forms through the various environmental media
(air, water, biota, soil).
Hydrology:
The science that deals with water as it occurs in the atmosphere,
on the surface of the ground, and underground.
Hydrostatic pressure:
The pressure exerted by water at any given point in a
body of water at rest.
Hygroscopic:
Refers to a substance that readily absorbs moisture.
I
Impermeability:
The incapacity of a rock to transmit a fluid.
Index of Biotic Integrity (IBI):
An aggregated number, or index, based on
several attributes or metrics of a fish community that provides an
assessment of biological conditions.
Indicator sites:
Stream sampling sites located at outlets of drainage basins
with relatively homogeneous land use and physiographic condi-
tions; most indicator-site basins have drainage areas ranging from
20 to 200 square miles.
Infiltration:
The downward movement of water from the atmosphere into
soil or porous rock.
Influent:
Water flowing into a reservoir, basin, or treatment plant.
Inorganic:
Containing no carbon; matter other than plant or animal.
Inorganic chemical:
A chemical substance of mineral origin not having car-
bon in its molecular structure.
Inorganic soil:
Soil with less than 20% organic matter in the upper 16 inches.
Instantaneous discharge:
The volume of water that passes a point at a par-
ticular instant of time.
Instream use:
Water use taking place within the stream channel for such
purposes as hydroelectric power generation, navigation, water qual-
ity improvement, fish propagation, and recreation. Sometimes called
nonwithdrawal use
or
in-channel use
.
Intermittent stream:
A stream that flows only when it receives water from
rainfall runoff or springs, or from some surface source such as melt-
i ing s now.
Internal drainage:
Surface drainage whereby the water does not reach the
ocean, such as drainage toward the lowermost or central part of an
interior basin or closed depression.
Intertidal:
Alternately flooded and exposed by tides.
Intolerant organisms:
Organisms that are not adaptable to human alterations
to the environment and decline in numbers where alterations occur.
Invertebrate:
An animal having no backbone or spinal column.
Ion:
A positively or negatively charged atom or group of atoms.
