gabion A rectangular basket or mattress made of steel wire in a hexagonal mesh. Gabions are generally subdivided into equal-sized cells that are wired together and filled with stones, forming a large, heavy mass used for shore protection.

gage Also gauge. 1)A device for indicating the magnitude or position of a thing in specific units, when such magnitude or position undergoes change. For example: the elevation of a water surface, the velocity of flowing water, the pressure of water, the amount or intensity of precipitation, the depth of snowfall, etc. 2)The act or operation of registering or measuring the magnitude or position of a thing when these characteristics are undergoing change. 3) The operation, including both field and office work, of measuring the discharge of a stream of water in a waterway. 4) Tidal gauge.

gage datum The arbitrary "zero plane" from which all stage measurements are taken from. Usually set below the natural bottom of the channel so all stage height readings will be greater than zero.

gage height The water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term stage, although gage height is more appropriate when used with a reading on a gage.

gage pressure The pressure within a closed container or pipe as measured with a gage. In contrast, absolute pressure is the sum of the atmospheric pressure (14.7 lbs/sq ft) plus pressure within a vessel (as measured by a gage). Most pressure gages read in gage pressure or psig (pounds per square inch gage pressure).

gage zero Same as gage datum.

gaging station A particular site on a stream, canal, lake or reservoir where systematic observations of gage height or discharge are obtained.

gale warning A warning of 1-minute sustained surface winds in the range 39 to 54 mph (34 to 47 knots) inclusive, either predicted or occurring not directly associated with tropical cyclones.

galleria A fringe of forest along a river especially in tropical grassland or savannah areas.

gallery 1) 2) A passageway within the body of a dam or abutment. 3) 4)

galvanic Pertaining to an effect caused by the cell—often dissimilar metal contact that results in electrolytic potential.

galvanic cell An electrolytic cell capable of producing electrical energy by electrochemical action. The decomposition of materials in the cell causes an electric (electron) current to flow from cathode to anode.

galvanic corrosion Corrosion that is increased because of the current caused by a galvanic cell (sometimes called couple action)

galvanic series A list of metals and alloys presented in the order of their tendency to corrode (or go into solution). Also called the electromotive series. This is a practical application of the theoretical electrochemical series.

galactose A carbohydrate (monosaccharide) which, along with glucose, is one of the sugars formed from the hydrolysis of lactose.

galvanize To coat a metal (especially iron or steel) with zinc. Galvanization is the process of coating metal with zinc.

game Wild animals, usually mammals or birds, hunted for sport or food and subject to legal regulations.

game fish Species like trout, salmon, or bass, caught for sport. Many of them show more sensitivity to environmental change than rough fish.

gamma logging A borehole logging technique that measures the natural gamma radiation emitted by the formation of rocks. It is used to delineate subsurface rock types, their positions, and thicknesses.

gamma ray High energy, shot wavelength electromagnetic radiation emitted from the nucleus. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Gamma rays are very penetrating and are best stopped or shielded against by dense materials such as lead or uranium. Gamma rays are similar to X-rays, but are usually more energetic.

garbage Animal and vegetable waste resulting from the handling, storage, sale, preparation, cooking, and serving of foods.

garnet A group of hard, reddish, glassy, mineral sands made up of silicates of base metals (calcium, magnesium, iron, and manganese). Garnet has a higher density than sand.

gas A state of matter characterized by a very low density and viscosity (relative to liquids and solids); comparatively great expansion and contraction occur with changes in temperature and pressure; ability to diffuse readily into other gases; and ability to occupy with almost complete uniformity the whole of any container.

gas chromatograph/mass spectrometer Highly sophisticated analytical instrument that identifies the molecular composition and concentrations of various chemicals in water and soil samples.

gasification Conversion of solid material such as coal into a gas for use as a fuel.

gasohol Mixture of gasoline and ethanol derived from fermented agricultural products containing at least nine percent ethanol. Gasohol emissions contain less carbon monoxide than those from gasoline.

gasoline volatility The property of gasoline whereby it evaporates into a vapor. Gasoline vapor is a volatile organic compound.

gas purged pressure gauge A type of analog tide gauge in which gas, usually nitrogen, is emitted from a submerged tube at a constant rate. Fluctuations in hydrostatic pressure due to changes in tidal height modify the emission rate for recording. Same as bubbler tide gauge.

gastroenteritis An inflammation of the stomach and intestine resulting in diarrhea, with vomiting and cramps when irritation is excessive. When caused by an infectious agent, it is often associated with fever.

gas/vapor toxicity An indication of the likelihood of adverse health effects when the time weighted average threshold limit value (TWA-TLV) is approached or exceeded.

gate A device in which a leaf or member is moved across the waterway from an external position to control or stop flow. There are many different kinds of gates used on a dam. Some of the more common types are bulkhead, crest (or spillway), emergency, fixed wheel, flap, flood, guard, outlet, radial, regulating, and slide gates.

gate valve A valve regulating fluid flow through a channel by the position of a movable plate in the channel’s cross section.

gauge, pipe A number that defines the thickness of the sheet used to make steel pipe. The larger the number, the thinner the pipe wall.

gavage Type of exposure in which a substance is administered to an animal through a stomach tube.

gene The basic unit of heredity, which plays a part in the expression of a specific characteristic. The expression of a gene is the mechanism by which the genetic information that it contains is transcribed and translated to obtain a protein. A gene is a part of the dna molecule that directs the synthesis of a specific polypeptide chain. It is composed of many codons. When the gene is considered as a unit of function in this way, the term cistron is often used.

general corrosion Corrosion in an uniform manner.

general permit A permit applicable to a class or category of dischargers.

general reporting facility A facility having one or more hazardous chemicals above the 10,000 pound threshold for planning quantities. Such facilities must file MSDS and emergency inventory information with the SERC and LEPC and local fire departments.

generating force mechanism An action causing wave formation such as gravitational attraction.

generator 1) A treatment works that produces residuals and sludge that is subject to further management. 2) A facility or mobile source that emits pollutants into the air or releases hazardous waste into water or soil. 3) Any person, by site, whose act or process produces regulated waste or whose first act causes such waste to become subject to regulation. In a case where more than one person (e.g., doctors with separate medical practices) is located in the same building, each business entity is a separate generator.

genetics The study of heredity or inherited features in individuals or populations.

gene transfer The use of genetic or physical manipulation to introduce foreign genes into a host cells to achieve desired characteristics in progeny.

genetic engineering A technique used to modify the genetic information in a living cell, reprogramming it for a desired purpose (such as the production of a substance it would not naturally produce).

genome All the genes carried by a cell.

genus A category of biological classification ranking between the family and species.

geodetic datum See National Geodetic Vertical Datum of 1929. geodetic head

geographic information system (gis) A computerized graphics and database system designed for storing, manipulating, analyzing, and displaying data in a geographical context.

geohydrology That branch of hydrology relating to subsurface, or subterranean waters.

geologic log A detailed description of all underground features discovered during the drilling of a well (depth, thickness, and type of formation).

geologic structure The form, symmetry, and geometry of geologic units. Structural geology may include the study of folds, faults, and joints, as well as the mechanical properties of rocks.

geologic cross section Method of extrapolating surface geologic observations to the relationships of geologic units under the surface. A cross section is a two-dimensional presentation of a study area and can be either of large or small scale.

geophysical log A record of the structure and composition of the earth encountered when drilling a well or similar type of test hole or boring.

geophysical methods Means of obtaining data on subsurface conditions. Includes use of electromagnetics, ground-penetrating radar, electrical resistivity, magnetics, seismic refraction and reflection, gravity, and borehole measuring techniques.

geophysics The study of the physical characteristics and properties of the earth; including geodesy, seismology, meteorology, oceanography, atmospheric electricity, terrestrial magnetism, and tidal phenomena.

geopotential The unit of geopotential difference, equal to the gravity potential of 1 meter squared per second squared, m² / s², or 1 joule per kilogram, J / kg.

geopotential anomaly The excess in geopotential difference over the standard geopotential difference [at a standard specific volume at 35 parts per thousand (°/..) and 0 degrees C] between isobaric surfaces. See geopotential and geopotential topography.

geopotential difference The work per unit mass gained or required in moving a unit mass vertically from one geopotential surface to another. See geopotential, geopotential anomaly, and geopotential topography.

geopotential (equipotential) surface A surface that is everywhere normal to the acceleration of gravity.

geopotential topography The topography of an equiscalar (usually isobaric) surface in terms of geopotential difference. As depicted on maps, isopleths are formed by the intersection of the isobaric surface with a series of geopotential surfaces. Thus, the field of isopleths represents variations in the geopotential anomaly of the isobaric surface above a chosen reference isobaric surface (such as a level of no motion).

geospatial Refers to the geographic location and characteristics of natural or constructed features and boundaries on the Earth.

geostationary orbit An earth orbit located directly above the equator, approximately 22,300 miles above the surface. Satellites in this orbit rotate at the same relative speed as the earth itself. This allows earth antennas to remain fixed.

geostationary orbiting environmental satellite (GOES) A series of artificial satellites orbiting 22,300 miles (35,900 km) above the earth's surface that remains above the same locations on the earth. DCPs transmit river and rainfall data to the GOES for relay to a ground-receive site in Wallops Island, VA.

geostrophic flow A solution of the relative hydrodynamic equations of motion in which it is assumed that the horizontal component of the Coriolis force is balanced by the horizontal component of the pressure gradient force.

germicide A substance formulated to kill potentially disease causing microorganisms. The germicidal properties of chlorine make it an effective disinfectant.

Giardia lamblia A pathogenic protozoa excreted by animals and whose cysts can infect humans causing the enteric disease, giardiasis. Giardia is highly resistant to chlorination.

giardiasis Intestinal disease caused by the infestation of Giardia flagellates.

GIS (Geographic Information System) A computerized data base/mapping system that may be used to store, retrieve, and analyze information, such as soil and hydro geologic data, based on geographic location.

glade An open space in a woods or forest.

globe valve A type of stemmed valve that is used for flow control. The valve has a globe shaped plug that rises or falls vertically when the stem handwheel is rotated.

globulin A family of proteins found in abundance in plasma. They include the gamma globulins, which in turn include the various antibody molecules produced by the immune system.

glovebag A polyethylene or polyvinyl chloride bag-like enclosure affixed around an asbestos-containing source (most often thermal system insulation) permitting the material to be removed while minimizing release of airborne fibers in the surrounding atmosphere.

glucose A simple sugar, c₆h₁₂o₆.

glycoprotein Protein to which groups of sugars become attached. Human blood group proteins, cell wall proteins and some hormones are examples of glycoproteins.

glycosylation The covalent attachment of sugars to an amino acid in the protein portion of a glycoprotein.

GOES DCS (Data Collection System) A satellite-based, data collection system that collects a variety of environmental data from locations in the western hemisphere. The system is a data relay network for more than 10,000 DCPs which transmits data to one of two GOES satellites (East and West). These data are relayed to a ground station located at Wallops Island, VA. The data are then relayed over to Silver Springs, MD, where the data is then distributed to appropriate recipients.

gopher A menu-based system for exploring the Internet. Users locate resources by selecting resources from menus.

gooseneck A portion of a service connection between the distribution system water main and a meter. Sometimes called a pigtail.

governmental entity The Commonwealth, a town, city, county, service authority, sanitary district or any other governmental body established under state law, including departments, divisions, boards, or commissions.

GPR (Ground Penetrating Radar) A surface geophysical technique based upon the transmission of repetitive pulses of electromagnetic waves into the ground. Some of the radiated energy is reflected back to the surface and the reflected signal is captured and processed. GPR is useful for defining the boundaries of buried trenches and other subsurface installations.

grab sample A single sample collected from a volume of matter or fluid at a particular time and place which represents the composition of the sampled volume only at that time and place.

grade 1) The elevation of the invert of the bottom of a pipeline, canal, culvert, or similar conduit. 2) The inclination or slope of a pipeline, conduit, stream channel, or natural ground surface; usually expressed in terms of the ratio or percentage of number of units of vertical rise or fall per unit of horizontal distance. A 0.5 percent grade would be a drop of one-half foot per hundred feet of pipe.

gradient The rate of change in value of a physical or chemical parameter per unit change in position. For example, hydraulic gradient is equal to the difference in head measured at two points (usually wells) divided by the distance separating the two points. The dimensions of head and distance are both lengths, therefore the gradient is expressed as a dimensionless ratio (L/L).

gradient flow A solution of the relative hydrodynamic equations of motion in which only the horizontal Coriolis, pressure gradient, and centrifugal forces are considered.

grain 1) A portion of a solid metal (usually a fraction of an inch in size) in which the atoms are arranged in an orderly pattern. The irregular junction of two adjacent grains is known as a grain boundary. 2) A unit of weight, 1/7000th of a pound.

grain loading The rate at which particles are emitted from a pollution source. Measurement is made by the number of grains per cubic foot of gas emitted.

gram A unit of mass equivalent to one milliliter of water at 4 degrees Celsius. 1/454 of a pound.

gram stain A differential stain by which bacteria can be divided into gram-positive or gram-negative groups, depending upon whether they retain or lose the primary stain (crystal violet) when exposed to treatment with a de-colorizing agent.

grandfathering Also grandparenting. 1) A pre-existing noncompliance situation that is not subject to enforcement action. 2) Acceptance by the state of data collected 3 years prior to the beginning of an initial compliance period to satisfy a system's initial sampling requirements. Grandfathering of data enables an eligible system to sample at repeat frequencies that are generally lower than initial frequencies.

grand jury A jury of inquiry composed of 23 citizens whose duty is to determine, in the case of proposed felony charges, if there is sufficient evidence to warrant a trial.

grandparenting See grandfathering.

granular activated carbon treatment A filtering system composed of porous crystalline carbon particles with the smallest dimension larger than 0.1 mm (GAC) often used in small water systems and individual homes to remove organics. GAC can be highly effective in removing elevated levels of radon from water.

graph A way to show quantitative data visually, using a system of coordinates.

graphitization (graphite corrosion) 1) Corrosion of gray cast iron in which the metallic constituents are converted to corrosion products, leaving the graphite flakes intact. 2) Graphitization is also used in a metallurgical sense to mean the decomposition of iron carbide to form iron and graphite.

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.

grassland An area in which grasses are the major plants; trees and shrubs are largely absent.

gravimetric A means of measuring unknown concentrations of water quality indicators in a sample by weighing a precipitate or residue of the sample.

gravitational tide Same as equilibrium tide.

gravity dam A concrete structure proportioned so that its own weight provides the major resistance to the forces exerted on it.

gray (Gy) The absorbed radiation dose unit of the international system of units. One gray equals 100 rad.

gray water, graywater A domestic wastewater fraction of sewage that does not contain significant amounts of human wastes, such as sink drainage or washing machine discharge.

gravity wave A wave for which the restoring force is gravity. See forced wave.

great diurnal range (Gt) The difference in height between mean higher high water and mean lower low water. The expression may also be used in its contracted form, diurnal range.

great tropic range (Gc) The difference in height between tropic higher high water and tropic lower low water. The expression may also be used in its contracted form, tropic range.

greenbelt A plot of vegetated land separating or surrounding areas of intensive residential or industrial use and devoted to recreational or park uses.

greenhouse effect The warming of the earth’s surface resulting from the capacity of the atmosphere to transmit short-wave energy (visible and ultra-violet light) to the earth’s surface and to absorb and retain heat radiating from the surface; carbon dioxide and water vapor in the atmosphere both contribute to the effect.

Greenwich argument Equilibrium argument computed for the meridian of Greenwich.

Greenwich interval An interval referred to the transit of the Moon over the meridian of Greenwich as distinguish from the local interval which is referred to the Moon's transit over the local meridian.

Greenwich Mean Time (GMT) The name of the twenty-four hour time scale that is used throughout the scientific and military communities. Standard Time begins at Greenwich, England, which is the Prime Meridian of Longitude. The globe is divided into twenty-four (24) time zones of 15 degrees of arc, or one hour in time apart. To the east of this meridian, time zones are numbered 1 to 12 and prefixed with a minus (-), while to the west, the time zones are also numbered 1 through 12 but prefixed with a plus (+). Other names for this time measurement are Universal Time Coordinate (UTC) and Zulu (Z).

Gregorian calendar The modern calendar in which every year divisible by 4 (excepting century years) and every century year divisible by 400 are bissextile (or leap) years with 366 days. All other years are common years with 365 days. The average length of this year is, therefore, 365.242,5 days which agrees very closely with the length of the tropical year (the period of changes in the seasons).

grinder pump A mechanical device that shreds wastewater borne solids and raises the fluid to a higher elevation through pressure sewers.

grit The heavy, mineral material present in wastewater, such as sand, eggshells, gravel, and cinders.

grit removal A process that reduces the flow velocity (by enlarging the channel) to allow the heavier grit to settle to the bottom of the channel where it can be removed.

grit washer

groin or groyne A low wall built out into the sea, perpendicular to the coastline, to resist the travel of sand and shingle along a beach or to minimize erosion by the sea.

gross alpha particle activity The total radioactivity due to alpha particle emission as inferred from measurements on a dry sample.

gross beta particle activity The total radioactivity due to beta particle emission as inferred from measurements on a dry sample.

gross income The gains from the deposition of assets, profits, personal compensation, rents, interest, and dividends before deductions of any costs are made over a specified accounting period.

ground cover Plants grown to keep soil from eroding.

grounded ice Ice which has run aground or is contact with the ground underneath it.

ground receive sites A satellite dish and associated computer which receives signals from the GOES satellite, decodes the information, and transmits it to a another site for further processing. The GOES satellite ground-receive site is located at Wallops Island, VA; and the information is relayed to a mainframe computer at NWS Headquarters for processing.

groundwater The supply of fresh water found beneath the earth's surface, usually in aquifers, which is often used for supplying wells and springs. Because groundwater is a major source of drinking water, there is growing concern over areas where leaching agricultural or industrial pollutants or substances from leaking underground storage tanks are contaminating groundwater.

groundwater discharge Groundwater entering near coastal waters that has been contaminated by landfill leachate, deep-well injection of hazardous wastes, septic tanks, etc.

groundwater divide A line on a water table where on either side of which the water table slopes downward. It is analogous to a drainage divide between two drainage basins on a land surface.

groundwater hydrology The branch of hydrology that specializes in groundwater, its occurrence and movements, its replenishment and depletion, the properties of rocks that control groundwater movement and storage, and the methods of investigation and utilization of groundwater flow.

groundwater storagegroundwater system A system that uses water extracted from the ground (i.e., a well or spring).

groundwater under the direct influence of surface water Groundwater under the direct influence of surface water. Any water beneath the surface of the ground with: 1) significant occurrence of insects or other macroorgansims, algae, or large-diameter pathogens, such as Giardia lamblia, or 2) significant and relatively rapid shifts in water characteristics, such as turbidity, temperature, conductivity, or pH which closely correlate to climatological or surface water conditions. Direct influence must be determined for individual sources in accordance with criteria established by the state, in accordance with 12 VAC 5-590-430.

groundwater vulnerability The degree to which groundwater in the area surrounding a well is sensitive to pesticide infiltration, based on an assessment of the hydrogeological makeup of an aquifer, such as depth of the water table, soil properties, and groundwater recharge rates.

groundwater withdrawal Removal of water from an aquifer by pumping.

grout A watery mixture of cement (and commonly bentonite) without aggregate that is used to seal the annular space around well casings to prevent infiltration of water or short-circuiting of vapor flow.

grower A firm or individual that raises livestock, raw agricultural products, or aquacultural products for sale (farms, feedlots, dairy farms, and botanicals).

growing season The number of consecutive days where the temperature has not gone below an index temperature for specific vegetation. If vegetation is more resistant to cold temperatures the index temperature would be lower. The index temperatures used in growing season analysis usually include 24, 28, and 32 degrees Fahrenheit.

growing season period The period of time, beginning date and ending date, that defines the period that the temperature has not dropped belowthe index temperature.

growth curve Representation, in graph form, of the growth (in phases) of bacteria in a culture medium.

guarantee A promise to provide municipal bondholders with full and timely payment of principal and interest on the municipal debt obligation to the limit of the guarantee in the event of default by the municipality.

Guiana Current An Atlantic Ocean current setting northwestward along the north-east coast of South America.

Guinea Current An Atlantic Ocean current setting eastward along the west central coast of Africa. A continuation of the Equatorial Counter Current of the Atlantic Ocean.

gulder Local name given to the double low water occurring along a coast. See double tide.

Gulf Coast Low Water Datum (GCLWD) A tidal datum. GCLWD is defined as mean lower low water when the type of tide is mixed and mean low water (now mean lower low water) when the type of tide is diurnal.

Gulf Coast Low Water Datum line The line on a chart or map which represents the intersection of the land with the water surface at the elevation of Gulf Coast Low Water Datum.

Gulf Stream A North Atlantic Ocean current setting northeastward off the east coast of the United States. A segment of the Gulf Stream System, the Gulf Stream extends from the region off Cape Hatteras to an area southeast of the Grand Banks at about latitude 40° north, longitude 50° west. It continues the flow of the Florida Current to the North Atlantic Current.

Gulf Stream System The continuous current system composed of the Florida Current, Gulf Stream, and North Atlantic Current.

gully erosion Severe erosion in which trenches are cut to a depth greater than 30 centimeters. Generally, ditches deep enough to cross with farm equipment are considered gullies.

GWUDISW See groundwater under the direct influence of surface water.

gyre A circular or spiral pattern of oceanic or atmospheric circulation.