Flood, levee, and erosion control glossary - G
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Gabion
A rectangular or cylindrical wire mesh cage filled with rock or broken pieces
of concrete and used as a protecting apron, revetment, retaining wall, etc.,
against erosion.
Photo courtesy of USDA NRCS.
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Photo of a gabion. |
Gabion Basket
Rectangular wire mesh box that is filled with rocks. Often Gabion Baskets are
used to create durable embankments that allow water percolation. Gabion Baskets
can be stacked like bricks to build embankments of varying heights. Over time
the wire is expected to rust away, leaving a durable rock embankment.
Photo courtesy of USDA NRCS.
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Photo of gabion baskets. |
Gage or Gauge
A vertical measuring device to determine the
height of a river above its bottom or some fixed point. Device for registering
precipitation, water level, discharge, velocity, pressure, temperature, etc.
Gaging Station
A selected section of a stream channel
equipped with a gage, recorder, or other facilities for determining stream
discharge.
General Permit
An NPDES permit issued under 40 CFR 122.28
that authorizes a category of discharges under the CWA within a geographical
area. A general permit is not specifically tailored for an individual
discharge.
Geographic Information System (GIS)
A computerized system
designed to collect, manage, and analyze large volumes of spatially referenced
and associated attribute data. System that links
spatial information such as satellite images and maps with alphanumeric
information to produce a geographically referenced database. A collection of
computer hardware, software, and geographic data designed to capture, store,
update, manipulate, analyze, and display geographically referenced data.
Geologic Erosion
The erosion process on a given land form that is not associated with the activities of man.
Geomembrane
An impervious thin sheet of rubber or plastic
material that functions as a barrier for liquid or vapor. See Geotextile.
Geotextile
Textile made from synthetic fibers, usually
nonbiodegradable. Geotextiles can be woven or nonwoven and have varying degrees
of porosity. They are used as moisture barriers, for separation or
reinforcement of soils, for filtration, and for drainage.
Geo-Textile Fabric
Woven, non-woven, or knitted fabric
that is water permeable and usually non-biodegradable that is used to separate,
filter, and reinforce aggregate.
GIS
Abbreviation for Geographic Information System. See Geomembrane.
Global Positioning System (GPS)
Network of satellites that
emit continuous location-finding radio signals; GPS receivers use the signals
from multiple satellites to determine their exact three-dimensional coordinates
(latitude, longitude, and height).
GPO
Abbreviation for Government Printing Office.
Grade
(1) The slope of a road, channel or natural ground
or any surface prepared for the support of construction like paving. (2) To
finish the surface of a roadbed, top of embankment, or bottom of excavation.
Grade Control Structures
Any of several types of structures used to control channel gradient (see stabilizer, drop structure, and flume).
Gradient
A measure of the earth surface slope relating
changes in horizontal distance to changes in vertical elevation.
Gradually Varied Flow
Depth of flow changes gradually over
the channel length.
Grass
A member of the botanical family Gramineae,
characterized by bladelike leaves arranged on the culm or stem in two ranks.
Grassed Channel (Waterway)
A natural or constructed
waterway, usually broad and shallow, covered with erosion resistant grasses,
used to conduct surface water from land.
Grassed
Waterway
Natural or constructed watercourse or outlet that is shaped
or graded and established in suitable vegetation for the disposal of runoff
water without erosion.
Photo courtesy of USDA NRCS.
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Photo of a grassed waterway. |
Gravel
Soil particles ranging from 1/5 inch to 3 inches in
diameter.
Greenbelt
Strip of trees and shrubs growing parallel to a
stream that prevents overuse of the top bank area by people, animals, and
machinery; retards rainfall runoff down the bank slope; and provides a root
system that binds soil particles together.
Grey Water
Domestic wastewater other than that containing
human excrete such as sink drainage, washing machine discharge, or bath water.
Groin
A shore protection structure (usually perpendicular to the shoreline) built to
trap littoral drift or retard erosion of the shore.
Photo courtesy of USDA NRCS.
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Photo of groin, a shore protection structure. |
Groin Bay
The beach compartment between two groins.
Groin Field
(NAVFAC DM-26.3) A series of groins acting together to protect a section of beach.
Groin System
A series of groins acting together to protect a section of beach. Commonly called a groin field.
Gross Erosion
The total of all sheet, gully, and channe1 erosion in a drainable basin, usually expressed in units of weight.
Ground Cover
Typically a low-lying plant or grass that
will spread outward, eventually covering all surrounding bare soil keeping it
from being blown or washed away.
Ground Water
Subsurface water in the zone of saturation.
Ground Water Table
The free surface of the ground water,
that surface subject to atmospheric pressure under the ground, generally rising
and falling with the season, the rate of withdrawal, the rate of restoration,
and other conditions. It is seldom static.
Groundwater
Water found under the earth's surface, and
especially in the saturated zone.
Ground-Water Discharge
Ground water entering near coastal
waters which have been contaminated by land- fill leachate, deep well injection
of hazardous wastes, septic tanks, etc.
Groundwater Flow
Water that moves through the subsurface
soil and rocks.
Groundwater Recharge
The infiltration of water into the
earth. It may increase the total amount of water stored underground or only
replenish supplies depleted through pumping or natural discharge.
Groundwater Table
The depth below the surface where the
soil is saturated (the open spaces between the individual soil particles are
filled with water). Above the groundwater table and below the ground surface
the soil either has no water between the particles or is partially saturated.
Grouting
The practice of filling the holes in concrete
blocks with concrete to increase the strength of a concrete block floodwall.
Gully
A channel or miniature valley cut by concentrated
runoff but through which water commonly flows only during and immediately after
heavy rains or during the melting of snow. The gullies may be branching or
linear, rather long, narrow, and of uniform width. The difference between gully
and rill is the depth. A gully is sufficiently deep that it would not be
obliterated by tillage operations. A rill of lesser depth can be smoothed by
regular tillage equipment. A channel caused by the concentrated flow of surface
and stormwater runoff over unprotected erodible land.
Gully Erosion
An advanced form of rill erosion, in which large channels are incised into
the soil by water runoff.
Photo courtesy of USDA NRCS.
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Photo of gully erosion. |
Gullying
Formation of ditches or hollows worn by running
water.
Gut
A tidal stream connecting two larger waterways.
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