B-Horizon  (1) The lower soil zone which is enriched by the deposition or precipitation of material from the overlying zone, or A-Horizon.  (2) A mineral horizon of a soil, below the A-horizon, sometimes called the Zone of Accumulation and characterized by one or more of the following conditions: an illuvial accumulation of humus or silicate clay, iron, or aluminum; a residual accumulation of sesquioxides or silicate clays; darker, stronger, or redder coloring due to the presence of sesquioxides; a blockly or prismatic structure.  Constitutes part of the Zone of Eluviation.
Babble  To make a continuous low, murmuring sound, as flowing water.
BAC  See Biological Activated Carbon (BAC) Process.
Backbar Channel  A channel formed behind a bar connected to the main channel but usually at a higher bed elevation than the man channel.  Backbar channels may or may not contain flowing or standing water.
Backfill, or Backfilling  process of filling the notches carved in the earth from strip mining in order to restore the original slope.  This is intended to reduce soil erosion and allow for the reestablishment of vegetation.
Backflow  (1) The backing up of water through a conduit or channel in the direction opposite to normal flow.  (2) The undesirable flow of water from a plumbing system back into the community potable water supply (3) A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one.  Backflow prevention assemblies prevent contamination and are required by city and state laws.  Also referred to as Back Siphonage.
Backflow Preventer  A device that allows liquids to flow in only one direction in a pipe.  Backflow preventers are used on sewer popes to prevent a reverse flow during flooding situations.  Also referred to as a Check Valve.
Back Lands  Generally refers to lands lying back from and not contiguous to a highway or water course.
Back Pressure  A pressure that can cause water to Backflow into the water supply when a user's waste water system is at a higher pressure than the public system.
Back Siphonage  A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one.  Also referred to as Backflow.
Back Swamp  Marshy area of a flood plain at some distance from and lower than the banks of a river confined by natural levees.
Backrush  The seaward return of water after the landward motion of a wave.  Also referred to as Backwash.
Backset  An eddy or countercurrent in water.
Backshore  The part of a shore between the Foreshore and the landward edge that is above high water except in the most severe storms.
Backslope  The slope component that is the steepest, straight then concave, or merely concave middle portion of an erosional slope.
Backwash  (1) A backward flow or water, also referred to as Backrush.  (2) (Water Quality) The reversal of flow through a rapid sand filter to wash clogging material out of the filtering medium and reduce conditions causing loss of head (pressure).
Backwashing  In a wastewater or water treatment facility, the flow of clean water in a direction opposite (upward) to the normal flow of raw water through rapid sand filters in order to clean them.
Backwater  (1) A small, generally shallow body of water attached to the main channel, with little or no current of its own.  (2) Water backed up or retarded in its course as compared with its normal or natural condition of flow.  In Stream Gaging, a rise in Stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below.  The difference between the observed stage and that indicated by the Stage-Discharge Relation, is reported as backwater.
Backwater Curve  The longitudinal profile of the water surface in an open channel where the water surface is raised above its normal level by a natural or artificial obstruction.  The term is sometimes used in a generic sense to denote all water surface profiles, or profiles where the water is flowing at depths greater than critical.
Backwater Effect  The rise in surface elevation of flowing water upstream from and as a result of an obstruction to flow such as a narrow bridge opening, buildings or fill material that limits the area through which the water must flow.  In stream gaging, a rise in stage produced by a temporary obstruction such as ice or weeds, or by the flooding of the stream below.  The difference between the observed stage and that indicated by the stage-discharge relation is reported as backwater.  Also referred to as heading up.
Backwater Flooding  Flooding caused by a restriction or blocking of flow downstream.  Examples include a narrowing of the channel, logjam, ice jam, high flow in a downstream confluence stream, or high tide blocking high river flows from entering estuaries.
Backwater Pools  A pool type formed by an eddy along channel margins downstream from obstructions such as bars, rootwads, or boulders, or resulting from backflooding upstream from an obstructional blockage.  Backwater pools are sometimes separated from the channel by sand or gravel bars.
Bacteria (Singular: Bacterium)  (1) Microscopic one-celled organisms which live everywhere and perform a variety of functions.  While decomposing organic matter in water, bacteria can greatly reduce the amount of oxygen in the water.  They also can make water unsafe to drink.  (2) Microscopic unicellular organisms, typically spherical, rod-like, or spiral and threadlike in shape, often clumped into colonies.  Some bacteria cause disease, while others perform an essential role in nature in the recycling of materials, for example, decomposing organic matter into a form available for reuse by plants.  Some forms of bacteria are used to stabilize organic wastes in wastewater treatment plants, oil spills, or other pollutants.  Disease-causing forms of bacteria are termed "pathogenic."  Some forms of bacteria harmful to man include:
(1)  Total Coliform Bacteria - A particular group of bacteria that are used as indicators of possible sewage pollution.  They are characterized as aerobic or facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria which ferment lactose with gas formation within 48 hours at 3?C.  In the laboratory these bacteria are defined as all the organisms that produce colonies with a golden-green metallic sheen within 24 hours when incubated at 35?C plus or minus 1.0?C on M-Endo medium (nutrient medium for bacterial growth).  Their concentrations are expressed as numbers of colonies per 100 milliliter (ml)l of sample.
(2)  Fecal Coliform Bacteria - Bacteria that are present in the intestine or feces of warm-blooded animals.  They are often used as indicators of the sanitary quality of the water.  In the laboratory they are defined as all the organisms that produce blue colonies within 24 hours when incubated at 44.5?C plus or minus 0.2?C on M-FC medium (nutrient medium for bacterial growth).  Their concentrations are expressed as numbers of colonies per 100 ml of sample.
(3)  Fecal Streptococcal Bacteria - Bacteria found also in the intestine of warm-blooded animals.  Their presence in water is considered to verify fecal pollution.  They are characterized as gram-positive, cocci bacteria which are capable of growth in brain-heart infusion broth.  In the laboratory they are defined as all the organisms that produce colonies which produce red or pink colonies within 24 hours at 35?C plus or minus 1.0?C on KF-streptococcus medium (nutrient medium for bacterial growth).  Their concentrations are expressed as numbers of colonies per 100 ml of sample.
Bacterial Plate Count  A system used to quantify the number of bacteria in a sample of solid or liquid material by measuring the growth of bacterium into full colonies.
Bactericidal  Able to kill bacteria.
Bacteriostatic  A substance that inhibits bacterial growth but is not necessarily lethal.
Badlands  Barren land characterized by roughly eroded ridges, peaks, and mesas.
Baffle  A flat board or plate, deflector, guide, or similar device constructed or placed in flowing water or slurry systems to cause more uniform flow velocities to absorb energy and to divert, guide, or agitate liquids.
Bag of Waters  The double-walled fluid-filled sac that encloses and protects the fetus in the womb and that breaks releasing its fluid during the birth process
Bail  To remove water, as from the bottom of a boat or other vessel.
Bailer  An instrument such as a long pipe with a valve at the lower end used to extract a water sample from a groundwater well.  Also used to remove slurry from the bottom or side of a well as it is being drilled.
Bajada  (1) A long outwash detrital (sedimentary) slope at the base of a mountain range.  (2) A broad, continuous alluvial slope or gently inclined detrital surface, extending along and from the base of a mountain range out into and around an inland basin, formed by the lateral coalescence of a series of separate but confluent alluvial fans, and having an undulating character due to the convexities of the component fans.  It occurs most commonly in semiarid and desert regions, as in the southwestern United States.  A bajada is a surface of deposition, as contrasted a pediment (a surface of erosion that resembles a bajada in surface form), and its top often merges with a pediment.
Balanced Operation  Operation of a canal system where the water supply exactly matches the total flow demand.
Balanced Groundwater Scenario (BGS)  A term referring to the development of a scenario exploring changes in cropping patterns such that long-term ground water withdrawals do not exceed long-term groundwater recharge rates.  Also see Agricultural Restructuring Scenario (ARS), Ground Water Overdraft, and Ground Water Mining.
Ball Cock  A self-regulating device controlling the supply of water in a tank, cistern, or toilet by means of a float connected to a valve that opens or closes with a change in water level.
Ball Valve  A valve regulated by the position of a free-floating ball that moves in response to fluid or mechanical pressure.
Ballast  Heavy material, often seawater, placed in the hold of a ship to gain stability.  Periodic discharges of this ballast water from oil tankers constitute a significant portion of the oil introduced into the oceans of the world each year.
Ballena  A major landform comprising distinctively round topped ridgeline remnants of fan alluvium.  The ridge's broadly rounded shoulders meet from either side to form a narrow crest and merge smoothly with the concave backslopes.  In ideal examples, the slightly concave footslopes of adjacent ballenas merge to form a smoothly rounded drainageway.
Bank, and Banks  The slope of land adjoining a body of water, especially adjoining a river, lake, or a channel.  With respect to flowing waters, banks are either right or left as viewed facing in the direction of the flow.  As Banks, a large elevated area of a sea floor.
Bank and Channel Stabilization  Implementation of structural features along a streambank to prevent or reduce bank erosion and channel degradation.
Bankfull Channel  The stream channel that is formed by the dominant discharge, also referred to as the active channel, which meanders across the floodplain as it forms pools, riffles, and point bars.
Bankfull Discharge  See Dominant Discharge.
Bankfull Stage  The stage at which a stream first begins overflows its natural banks.  More precisely, an established river stage at a given location along a river which is intended  to represent the maximum safe water level that will not overflow the river banks or cause any significant damage within the river reach.  Bankfull stage is a hydraulic term, whereas Flood Stage implies resultant damage.
Banking (Water)  See Water Banking.
Bank Storage  The water absorbed into the banks of a stream, lake, or reservoir, when the stage rises above the water table in the bank formations, then returns to the channel as effluent seepage when the stage falls below the water table.  Bank storage may be returned in whole or in part as seepage back to the water body when the level of the surface water returns to a lower level.
Baptism  (1) A Christian sacrament marked by ritual use of water and admitting the recipient to the Christian community; (2) A non-Christian rite using water for ritual purification.
Bar  (1) A sand or gravel deposit found on the bed of a stream that is often exposed during low-water periods.  (2) An elongated landform generated by waves and currents, usually running parallel to the shore, composed predominantly of unconsolidated sand, gravel, stones, cobbles, or rubble and with water on two sides.  (3) A component landform comprised of elongate, commonly curving, low ridges of well sorted sand and gravel that stand above the general level of a Bolson floor and were built by the wave action of a Pleistocene lake.  (4) A unit of pressure equal to 106 dynes per cm2, 100 kilopascals, or 29.53 inches of mercury.
Barothermograph  An instrument which records simultaneous barometric pressure and temperature on the same chart.
Bar Racks  (Water Quality) The closely spaced rods, often in the form of a screen, that remove large solids from the wastewater entering a sewage treatment plant.
Bar Screen  (Water Quality) In wastewater treatment, a device used to remove large solid materials.
Barrage  An artificial obstruction, such as a dam or an irrigation channel, built in a watercourse to increase its depth or to divert its flow either for navigation or irrigation.  Sometimes the purpose is to control peak flow for later release.
Barrel  (1) A measure of liquid volume (conventionally) equal to 42 U.S. gallons (34.9723 Imperial gallons), or 158.9873 liters.  (2) Any of various units of volume or capacity.  In the U.S. Customary System, it varies, as a liquid measure, from 31 to 42 U.S. gallons (approximately 120 to 159 liters) as established by law or usage.
Bartlett Decree (Nevada)  The Bartlett Decree was issued on January 2, 1931 by Judge George A. Bartlett  and adjudicated water rights along the Humboldt River and its tributaries.  In addition to adjudicating the river system's water rights, this decree also recognized that the s
Basalt  (Geology) A dark volcanic rock composed of microscopic grains of augite, feldspar, and olivine.  Some basalts have many holes that give the rock a swiss-cheese-like appearance.  As the lava cools, gases escape, leaving holes of different sizes.
Basalt Aquifers  Aquifers found in basalt rock in areas of past volcanic activity, particularly in the Pacific Northwest region of the United States and in Hawaii.
Base  (1) Any of various typically water-soluble and bitter tasting compounds that in solution have a pH greater than 7, are capable of reacting with an acid to form a salt, and are molecules or ions able to take up a proton from an acid or able to give up an unshared pair of electrons to an acid.  (2) Chemicals that release hydroxide ions (OH-) in solution.  Such solutions have a soapy feel, neutralize acids, and conduct electricity.
Base Flood (100-Year Flood)  The flood having a 1 percent average probability of being equaled or exceeded in a given year at a designated location.  It may occur in any year or even in successive years if the hydrologic conditions are conducive for flooding.  Also see Hundred-Year Flood, X-Year Flood, and X-Year Flood, Y-Duration Rain.
Base Flood (FEMA)  A term used in the National Flood Insurance Program (Federal Emergency Management Agency) to indicate the minimum size flood to be used by a community as a basis for its floodplain management regulations; presently required by regulation to be that flood which has a one-percent chance of being equaled or exceeded in any given year.  Also known as a 100-Year Flood or One-Percent Chance Flood.
Base Flood Elevation (BFE)  (1) The height in relation to mean sea level (MSL) expected to be reached by the waters of the Base Flood at specific points in the floodplain of Riverine areas.  (2) The elevation for which there is a one-percent chance in any given year that flood levels will equal or exceed it.  (3) The elevation shown on the Flood Insurance Rate Map (FIRM) for Zones AE, AH, A1-A30, AR, AR/A, AR/AE, AR/A1-A30, AR/AH, AR/AO, V1-V30, and VE that indicates the water surface elevation resulting from a flood that has a 1-percent or greater chance of being equaled or exceeded in any given year.  The BFE is generally based on statistical analysis of stream flow records for the watershed and rainfall and runoff characteristics in the general region of the watershed, and application of hydraulic backwater models.
Base Floodplain  The floodplain that would be inundated by a One-Percent Chance Flood (100-Year Flood).
Base Flow  (1) The flow that a perennially flowing stream reduces to during the dry season.  It is supported by groundwater seepage into the channel.  (2) The fair-weather or sustained flow of streams; that part of stream discharge not attributable to direct runoff from precipitation, snowmelt, or a spring.  Discharge entering streams channels as effluent from the groundwater reservoir.  (3) The volume of flow in a stream channel that is not derived from surface run-off.  Base flow is characterized by los flow regime (frequency, magnitude, and duration daily, seasonally, and yearly), by minimum low flow events and in context of the size and complexity of the stream and its channel.
Base Level  (1) The elevation to which a stream-channel profile has developed.  (2) The lowest level to which a land surface can be reduced by the action of running water.
Base Period  A period of time specified for the selection of data for analysis.  The base period should be sufficiently long to contain data representative of the averages and deviations from the averages that must be expected in other periods of similar and greater length.  For example, the U.S. Weather Bureau computes values of average, heavy, and light monthly precipitation from data observed during the base period of 1931-1960.  For ground-water studies, the base period should both begin and end at the conclusion of a dry trend so that the difference between the amount of water in transit in the soil at the ends of the base period is minimal.
Base Runoff  Sustained or fair weather runoff.  In most streams, base runoff is composed largely of ground-water effluent.  The term base flow is often used in the same sense as base runoff.  However, the distinction is the same as that between streamflow and runoff.  When the concept in the terms base flow and base runoff is that of the natural flow in a stream, base runoff is the more appropriate term.
Base Width  (1) The time interval between the beginning and end of the direct runoff produced by a storm.  (2) The time period covered by a Unit Hydrograph.
Baseline  The condition that would prevail if no action were taken.
Baseline (Data)  A quantitative level or value from which other data and observations of a comparable nature are referenced.  Information accumulated concerning the state of a system, process, or activity before the initiation of actions that may result in changes.
Basic  Describing a solution, sediment, or other material that has a pH greater than 7.0.
Basic Hydrologic Data  Includes inventories of features of land and water that vary only from place to place (e.g., topographic and geologic maps), and records of processes that vary with both place and time (e.g., records of precipitation, streamflow, ground-water, and quality-of-water analyses).  Basic Hydrologic Information is a broader term that includes surveys of the water resources of particular areas and a study of their physical and related economic processes, interrelations and mechanisms.
Basin  (1) (Hydrology) A geographic area drained by a single major stream; consists of a drainage system comprised of streams and often natural or man-made lakes.  Also referred to as Drainage Basin, Watershed, or Hydrographic Region.  See Basins (Nevada).  (2) (Irrigation) A level plot or field, surrounded by dikes, which may be flood irrigated.  (3) (Erosion Control) A catchment constructed to contain and slow runoff to permit the settling and collection of soil materials transported by overland and rill runoff flows.  (4) (Nautical) A naturally or artificially enclosed harbor for small craft, such as a yacht basin.
Basin and Range (Nevada)  A region of north-trending mountains ranges and valleys encompassing western Utah and essentially all of Nevada.  This geologic territory includes virtually all of the Great Basin and extends south and east through Arizona, New Mexico, and Texas all the way into Mexico.  The Basin and Range can be differentiated from its surrounding geologic regions by its uplifted and tilted ranges separated by broad elongated basins.  The Great Basin forms a unique part of this geologic region in as much as this hydrologic area has no drainage to the ocean.
Basin Fill  Unconsolidated material such as sand, gravel, and silt eroded from surrounding mountains and deposited in a valley.
Basin Floor  A generic term for the nearly level, lowermost major physiographic part of intermontane basins, i.e., of both Bolsons and semi-bolsons.  The floor includes all of the alluvial, eolian, and erosional landforms below the piedmont slope.
Basin-Floor Remnant  A flattish topped, erosional remnant of any former landform of a basin floor that has been dissected following the incision of an axial stream.
Basin Lag  (1) The time from the centroid (centermost point in time based on total period rainfall) of rainfall to the hydrograph peak.  (2) The time from the centroid of rainfall to the centroid of the Unit Hydrograph.
Basin Management (of Water)  Also referred to as Water or Watershed Management, it is the analysis, protection, development, operation, or maintenance of the land, vegetation, and water resources of a drainage basin for the conservation of all its resources for the benefit of man.  Basin management for water production is concerned with the quality, quantity, and timing of the water which is produced.
Basin of Origin  The area (hydrographic region or area) from in surface waters naturally occur or from which groundwater is removed.
Basin Yields  The amount of water which will flow from a drainage or catchment area in a given storm.
Basins (Nevada)  The U.S. Geological Survey (USGS) and the Nevada Division of Water Resources, Department of Conservation and Natural Resources, have divided the state into discrete hydrologic units for water planning and management purposes.  These have been identified as 232 Hydrographic Areas (256 areas and sub-areas, combined) within 14 major Hydrographic Regions or Basins.  These 14 Nevada Hydrographic Regions (Basins), along with the approximate surface areas (Nevada only), counties of coverage, extension into adjoining states, and number of hydrographic areas and sub-areas are:
(1)  Northwest Region - Covers 3,052 square miles (7,905 square kilometers or 1,953,280 acres) of northern Washoe and Humboldt counties and encompasses 16 hydrographic areas; also extends into the State of California to the west and the State of Oregon to the north;
(2)  Black Rock Desert Region - Covers 8,632 square miles (22,357 square kilometers or 5,524,480 acres) of parts of Washoe, Humboldt, and Pershing counties and includes 17 valleys (hydrographic areas), two of which are divided into two hydrographic sub-areas each; also extends into the State of California to the west and the State of Oregon to the north;
(3)  Snake River Basin - Covers 5,230 square miles (13,546 square kilometers or 3,347,200 acres) in parts of Elko and Humboldt counties to include eight hydrographic areas; also extends into the states of Oregon and Idaho to the north and the State of Utah to the east;
(4)  Humboldt River Basin - Covers over 16,843 square miles (43,623 square kilometers or 10,779,520 acres) in parts of eight counties - Elko, White Pine, Eureka, Humboldt, Lander, Nye, Pershing, and Churchill - and the largest stream (Humboldt River) wholly within Nevada.  This basin contains 34 hydrographic areas and one hydrographic sub-area; this basin is one of only two that are wholly contained within the State of Nevada;
(5)  West Central Region - Covers 1,656 square miles (4,289 square kilometers or 1,059,840 acres) and includes parts of Pershing, Lyon, and Churchill counties and comprises five hydrographic areas; this basin is one of only two that are wholly contained within the State of Nevada;
(6)  Truckee River Basin - Encompasses 2,300 square miles (5,957 square kilometers or 1,472,000 acres) containing parts of Washoe, Pershing, Churchill, Lyon, Douglas, Carson City, and Storey counties comprising 12 hydrographic areas; has its origin to the west in the State of California;
(7)  Western Region - Covers 602 square miles (1,559 square kilometers or 385,280 acres) and is wholly contained in Washoe County and contains nine valleys (hydrographic areas) one of which is divided into two sub-areas and another divided into one hydrographic sub-area; also extends to the west into the State of California;
(8)  Carson River Basin - Covers 3,519 square miles (9,114 square kilometers or 2,252,160 acres) and includes parts of six counties - Douglas, Carson City, Lyon, Storey, Churchill, and Pershing - containing five hydrographic areas and one hydrographic sub-area along the Carson River and its tributaries; has its origin to the west in the State of California;
(9)  Walker River Basin - Covers 3,046 square miles (7,889 square kilometers or 1,949,440 acres) of Mineral, Lyon, and Douglas counties (and a very small portion of Churchill County) including five hydrographic areas, one of which has been divided into three hydrographic sub-areas; has its origin to the west in the State of California;
(10)  Central Region - By far the largest hydrographic region in Nevada covering 46,783 square miles (121,167 square kilometers or 29,941,120 acres) in 13 counties - Nye, Elko, White Pine, Lincoln, Clark, Humboldt, Pershing, Churchill, Lander, Eureka, Lyon, Mineral, and Esmeralda.  This region includes 78 valleys (hydrographic areas), 10 of which are divided into two hydrographic sub-areas and one into three hydrographic sub-areas; extends to the south and west into the State of California;
(11)  Great Salt Lake Basin - Covers 3,807 square miles (9,860 square kilometers or 2,436,480 acres) of the easternmost portions of Elko, White Pine, and Lincoln counties.  It consists of eight hydrographic areas, one of which is divided into four hydrographic sub-areas; extends to the east into the State of Utah;
(12)  Escalante Desert Basin - This basin covers a large area in Utah but only a very small part of it is in Lincoln County - 106 square miles (275 square kilometers or 67,480 acres) - and is made up of only one hydrographic area; extends to the east into the State of Utah;
(13)  Colorado River Basin - Covers 12,376 square miles (32,054 square kilometers or 7,920,640 acres) including parts of Clark, Lincoln, Nye, and White Pine counties and is divided into 27 hydrographic areas; extends to the south into the State of California, borders the Colorado River to the east and south, and extends into the states of Arizona and Utah to the east;
(14)  Death Valley Basin - Covers 2,593 square miles (6,716 square kilometers or 1,659,520 acres) of Nye and Esmeralda counties including eight hydrographic areas, one of which has been divided into two hydrographic sub-areas; extends into the State of California to the south and west.
(A listing of Nevada's Hydrographic Regions, Areas and Sub-Areas is presented in Appendix A-1 (hydrographic regions, areas and sub-areas), Appendix A-2 (listed sequentially by area number) Appendix A-3 (listed alphabetically by area name), and Appendix A-4 (listed alphabetically by principal Nevada county(ies) in which located).)
Bath  The act of soaking or cleansing a body, as in water or steam.  Also, the water used for such cleansing.
Bathe  (1) To take a bath or go into the water for swimming or other recreation.  (2) To become immersed in or as if in liquid; to seem to wash or pour over; suffuse.
Batholith  A mass of Igneous rock that forms intrusively and can rise to the surface.
Bathing Water  Water in swimming pools or natural fresh or marine waters used for swimming.
Bathometer  An instrument used to measure the depth of water.
Bathtub Effect  The accumulation of Leachate in a landfill containing a good liner, but not equipped with a leachate collection and removal system.
Bathyal Zone  The ocean stratum beneath the Euphotic Zone and above the Abyssal Zone, or to the bottom of the Continental Shelf.  The density of life in this zone depends on organic material settling from the euphotic zone and is generally inversely proportional to the depth.
Bathymetric Map  A map showing the depth of water in lakes, streams, or oceans.
Bathymetry  (1) The measurement of the depth of large bodies of water.  (2) The measurement of water depth at various places in a body of water.  Also the information derived from such measurements.
Bathyscaphe  A free-diving, self-contained deep-sea research vessel consisting essentially of a large flotation hull with a crewed observation capsule fixed to its underside, capable of reaching depths of 10 kilometers (6.2 miles) or more.
Bathysphere  A reinforced spherical deep-diving chamber in which persons are lowered by a cable to study the oceans.  The bathysphere, limited to depths of about 900 meters (3,000 feet), has been supplanted by the safer and more navigable Bathyscaphe.
Bathythermograph  An instrument designed to record water temperature as a function of depth.
Baumé  Being, calibrated in accordance with, or according to either of two arbitrary hydrometer scales for liquids lighter than water or for liquids heavier than water that indicate specific gravity in degrees.
Bay  A part of a sea or lake, indenting the shoreline; a wide inlet not so large as a Gulf.
Bay-Delta (California)  Refers to the region encompassing the Sacramento-San Joaquin river delta system forming a basically delta or triangular structure extending from south Sacramento in the north to below Stockton in the south to the San Francisco Bay in the west.  The Bay-D
Bayesian Inference  (Statistics) Bayes' theorem recognizes that a decision maker usually has some expectation (an a priori model) of what will occur even before acquiring information, and provides a procedure for using new evidence to produce a revised a posteriori estimate of probability.  Also see Statistical Inference and Classical Inference.
Bayou  In general, a creek, secondary watercourse, or minor river, tributary to another river or other body of water.  A term regularly used in the lower Mississippi River basin and in the Gulf-coast region of the United States to denote a large stream or creek, or small river, characterized by a slow or imperceptible current through alluvial lowlands or swamps.  May also refer to an estuarial creek or inlet on the Gulf coast; a small bay, open cove, or harbor; also, a lagoon, lake or bay, as in a sea marsh or among salt-marsh islands.
Beach  (1)  A sloping landform on the shore of larger water bodies, generated by waves and currents and extending from the water to a distinct break in landform or substrate type (e.g., a foredune, cliff, or bank.)  (2)  A generic term for offshore bars, barrier bars, and beach terraces.  (3) To run a ship up onto a beach or shore.
Beach Erosion  The carrying away of beach materials by wave action, tidal currents, or littoral currents, or by wind.
Beach Plain  A major landform of Bolson floors comprised of numerous, closely spaced offshore bars and intervening lagoons built by a receding Pleistocene lake.
Beach, Public  Beach dedicated by a governmental body to the common use of the public, which the unorganized public an each of its members have a right to use while it remains so designated.
Beach Terrace  A component landform occurring on the lower piedmont slope that consists of a wave-cut scarp and a wave-built terrace of well sorted sand and gravel marking a still-stand of a Pleistocene lake.
Bead  A small, round object, especially a drop of moisture, as beads of sweat.
Beaufort's Scale  (Meteorology) A scale devised by Sir F. Beaufort, Royal Navy, in 1805, in which the strength of the wind is indicated by numbers from 0 to 12.  The corresponding terms are:  calm (0), light air (1), light breeze (2), gentle breeze (3), moderate breeze (4), fresh breeze (5), strong breeze (6), moderate gale (7), fresh gale (8), strong gale (9), whole gale (10), storm (11), hurricane (12).  Also see Wind Scale.
Bed  (1) The bottom of a body of water, such as a stream.  (2) An underwater or intertidal area in which a particular organism is established in large numbers.  (3) (Geology) A rock mass of large horizontal extent bounded, especially above, by physically different material (as in Bedrock).
Bedew  To wet with or as if with Dew.
Bed Load  (1) Sediment particles up to rock, which slide and roll along the bottom of the streambed.  (2) Material in movement along a stream bottom, or, if wind is the moving agent, along the surface.  (3) The sediment that is transported in a stream by rolling, sliding, or skipping along or very close to the bed.  In USGS reports, bed load is considered to consist of particles in transit from the bed to an elevation equal to the top of the bed-load sample nozzle (usually within 0.25 feet of the streambed).  Contrast with material carried in Suspension or Solution.
Bed Load Discharge  The quantity of sediment, typically measured in tons per day, that is moving as bed load, reported as dry weight, that passes a cross section in a given time.
Bed Material  The sediment mixture of which a streambed, lake, pond, reservoir, or estuary bottom is composed.
Bedrock  (Geology) The solid rock beneath the soil (Zone of Aeration or Zone of Saturation) and superficial rock.  A general term for solid rock that lies beneath soil, loose sediments, or other unconsolidated material.
Bedscarp (Nick Point)  An abrupt change in grade in the bottom of a stream channel that moves progressively upstream; the change in grade forms a waterfall.  Also, the location where a streambed is actively eroding downward to a new base level.
Bed Slope  The inclination of the channel bottom.
Beheaded Stream  The lower section of a stream that has lost its upper portion through diversion or Stream Piracy.
Bell  A hollow, usually inverted vessel, such as one used for diving deep below the surface of a body of water.
Belt of Soil Moisture  Subdivision of the Zone of Aeration.  Belt from which water may be used by plants or withdrawn by soil evaporation.  Some of the water passes down into the intermediate belt, where it may be held by molecular attraction against the influence of gravity.
Bench Flume  A flume built on constructed benches or terraces along hillsides or around mountain slopes when the ground is too rough or too steep to permit the use of an excavated canal.
Bench Land (Soils)  A general term describing porous and coarse-textured (sandy-gravelly) well-drained soils, overlying a deep water table (if occurring), that exhibits relatively low water holding capacity and rapid infiltration of irrigation water.
Bench Lands (Nevada)  The U.S. Department of the Interior, Bureau of Reclamation criteria (revised 1992) has defined Bottom Land for Nevada's Newlands Irrigation Project, located in Churchill County, Nevada, as "those lands with a five-foot soil profile having a holding capac
Benchmark  Data used as a base for comparative purposes with comparable data.
Beneficial Use (of Water)  (1) The amount of water necessary when reasonable intelligence and diligence are used for a stated purpose.  (2) A use of water resulting in appreciable gain or benefit to the user, consistent with state law, which varies from one state to another.  Most states recognize the following uses as beneficial:
(1)  domestic and municipal uses;
(2)  industrial uses;
(3)  irrigation;
(4)  mining;
(5)  hydroelectric power;
(6)  navigation;
(7)  recreation;
(8)  stock raising;
(9)  public parks;
(10)  wildlife and game preserves.
(3) The cardinal principle of the (Prior) Appropriation Doctrine.  A use of water that is, in general, productive of public benefit, and which promotes the peace, health, safety and welfare of the people of the State.  A certificated water right is obtain
Benefit-Cost Ratio  (1) The relationship of the economic benefits of an action to its total costs.  (2) An economic indicator of the efficiency of a proposed project, computed by dividing benefits by costs; usually, both the benefits and the cost are discounted, so that the ratio reflects efficiency in terms of the present value of future benefits and costs.
Benthic  (1) The bottom of lakes or oceans.  See Benthic Region.  (2) Referring to organisms that live on the bottom of water bodies.  See Benthic Invertebrates and Benthic Organisms.
Benthic Invertebrates  Aquatic animals without backbones that dwell on or in the bottom sediments of fresh or salt water.  Examples are clams, crayfish, and a wide variety of worms.
Benthic Organisms  Those organisms living at or near the bottom of a body of water.  They include a number of types of organisms, such as bacteria, fungi, insect larvae and nymphs, snails, clams, and crayfish.  They are useful as indicators of water quality.  See Indicator Species.  Also see Benthic Invertebrates.
Benthic Region  The bottom of a body of water, supporting the Benthos.
Benthos  (1) All the plant and animals living on or closely associated with the bottom of a body of water.  (2) Organisms living within a streams's substrate.
Bentonite  A clay material that swells as it dries, filling gaps and sealing itself against a well casing.  It is commonly used to seal abandoned dewatering wells at mines.  Concrete, by contrast, shrinks as it cures, and can therefore leave gaps around a wellhead casing that can allow contaminated water from the surface to penetrated into the well.
Berg  A mass of floating or stationary ice; and Iceberg.
Bernoulli Effect  The phenomenon of internal pressure reduction with increased stream velocity in a fluid.  Named after Daniel Bernoulli.
Bernoulli's Equation  Under conditions of steady flow of water, the sum of the velocity head, the pressure head, and the head due to elevation at any given point is equal to the sum of these heads at any other point plus or minus the head losses between the points due to friction or other causes.
Berm  (1) A narrow ledge or path as at the top or bottom of a slope, stream bank, or along a beach.  (2) (Dam) A horizontal step or bench in the upstream or downstream face of an Embankment Dam.
Best Available Demonstrated Technology (BADT)  The level of effluent limitation technology required by the 1972 Clean Water Act (CWA) to be used in setting new source performance standards for new industrial direct dischargers of water pollutants.
Best Available Technology Economically Achievable (BAT)  A national goal under the Water Pollution Control Act of 1972 (Public Law 92-500, commonly referred to as the Clean Water Act) which provides that industry shall use the best treatment technically and economically achievable for a category or class of point sources.  Under this concept, pollution control will consider such factors as the age of the facilities and equipment involved, processes employed, engineering aspects of the control techniques, process changes, cost of the reductions, and environmental impacts other than water quality, including energy requirements.
Best Conventional Control Technology (BCT)  The level of water pollution control technology required of existing dischargers for the treatment of conventional pollutants by the 1977 Clean Water Act (CWA).
Best Management Practices (BMP)  (1) A generally accepted practice for some aspect of natural resources management, such as water conservation measures, drainage management measures, or erosion control measures.  Typically incorporates conservation criteria.  (2) A set of field activities that provide the most effective means for reducing pollution from a nonpoint source.  (3) Accepted methods for controlling Non-Point Source (NPS) Pollution as defined by the 1977 Clean Water Act (CWA); may include one or more conservation practices.  Also refers to water conservation techniques of proven value.  See, for example, Best Management Practices (BMP) - Urban Water Use.
Best Management Practices (BMP)-Urban Water Use  Water conservation measures that generally meet one of two criteria:  (1) Constitutes an established and generally accepted practice among water purveyors that provides for the more efficient use of existing water supplies or contributes towards the conservation of water; or (2) Practices which provide sufficient data to clearly indicate their value, are technically and economically reasonable, are environmentally and socially acceptable, are reasonably capable of being implemented by water purveyors and users, and for which significant conservation or conservation-related benefits can be achieved.  See Appendix C-1, Best Management Practices - Urban Water Use, for a more complete itemization of BMPs and Potential BMPs.
Best Practicable Control Technology (BPT)  A national goal under the Water Pollution Control Act of 1972 (Public Law 92-500, or the Clean Water Act) which provides that industry shall use the best treatment practices practical, with due consideration to cost, age of the plant and equipment, and other factors.
Bias  An error in data gathering or analysis caused by faulty program design, mistakes on the part of personnel, or limitations imposed by available instrumentation or data sources.
Bicarbonate  (Water Quality) A compound containing the HCO3- group, for example, sodium bicarbonate (NaHCO3), which ionizes in solution (water) to produce HCO3-.  Also see Carbonate and Carbonate Buffer System.
Biennial Plant  A plant that lives for two years, producing vegetative growth the first year, usually blooming and fruiting in the second year, and then dying.
Bifurcate  Dividing structure which splits the flow of water.
Bilge Water  Water that collects and stagnates in the bilge or bottom-most areas of a ship.
Billabong  (Australian) (1) A dead-end channel extending from the main stream of a river.  (2) A streambed filled with water only in the rainy season.  (3) A stagnant pool or backwater.
Billow  A large wave or swell of water.
Bimodal Distribution  (Statistics) A collection of observations with a large number of values centered (as in a Normal Distribution) around each of two points.  For example, in a sampling of the heights of a population, the sample results would tend to be concentrated around an average heights for males and a second average height for females.
Bioaccumulants  Substances that increase in concentration in living organisms as they take in contaminated air, water, or food because the substances are very slowly metabolized or excreted.  Also see Biological Magnification.
Bioaccumulation  The increase in concentration of a chemical in organisms that reside in environments contaminated with low concentrations of various organic compounds.  Also used to describe the progressive increase in the amount of a chemical in an organism resulting from rates of absorption of a substance in excess of its metabolism and excretion.
Bioassay  A method for quantitatively determining the concentration of a substance by its effects on the growth of a suitable animal, plant, or microorganism under controlled conditions.
Biochemical Oxidation  The process by which bacteria and other microorganisms feed on complex organic materials and decompose them.  Self-purification of waterways and activated sludge and trickling filter wastewater treatment processes depend on this principle.
Biochemical Oxygen Demand (BOD)  (1) A measure of the quantity of dissolved oxygen, in milligrams per liter, necessary for the decomposition of organic matter by microorganisms, such as bacteria.  (2) A measure of the amount of oxygen removed from aquatic environments by aerobic micro-organisms for their metabolic requirements.  Measurement of BOD is used to determine the level of organic pollution of a stream or lake.  The greater the BOD, the greater the degree of water pollution.  Also referred to as Biological Oxygen Demand (BOD).
Biochemical Oxygen Demand (BOD) Loading  (Water Quality) The BOD content, commonly expressed in pounds/day, of wastewater passing into a waste treatment system or a body of water.  The greater the BOD content, the greater the degree of pollution.
Biocide  A chemical substance that kills living organisms.  Typically used to include materials that can kill desirable as well as undesirable organisms.
Bioclimatic Zones  Also referred to as Biomes, these constitute the earth's ten zones differentiated by climate, soil, water, and plant and animal life.  See Biome.
Biocoenosis  A community of animal and plant life.
Bioconcentration  (1) The process by which an individual organism directly concentrates a substance from the surrounding air, water, or soil.  (2) The increase in concentration of a chemical in an organism resulting from absorption levels exceeding the rate of metabolism and excretion.
Bioconcentration Factor (BCF)  Used to describe the accumulation of chemicals in aquatic organisms that live in contaminated environments.  Also see Bioconcentration.
Bioconcentration Potential (BCP)  The maximum concentration of a chemical in an organism resulting from the rate of absorption equaling the rate of metabolism and excretion.
Bioconversion  The conversion of organic materials, such as plant or animal waste, into usable products or energy sources by biological processes or agents, such as certain microorganisms.
Biodegradable  Capable of being decomposed by biological agents or microorganisms, especially bacteria.  The property of a substance that permits it to be broken down by micro-organisms into simple, stable compounds such as carbon dioxide and water.
Biodegradation  The metabolic breakdown of materials into simpler components by living organisms.  A more specific form of Biotransformation.
Biodenitrification  The controlled use of microbes, usually bacteria, to reduce level of nitrates (NO3-) and thereby reclaim contaminated water or wastewater.  The process consists of several stages to decompose the nitrates first into nitrites and then into nitrogen gas, N2.  Upon entering the treatment process, sodium sulfite (Na2SO3) is added as a reducing agent to the wastewater to remove the oxygen from the water.  To break down the nitrates, the bacteria must have a carbon food source and typically ethanol is added for the bacteria to feed on.  In order to survive, however, the bacteria need oxygen which they obtain by breaking down the nitrate ions, first to nitrite and then to harmless nitrogen gas.  Also referred to as Endogenous Respiration.
Biodisc  (Water Quality) A large rotating cylinder possessing surface features that allow for the growth of attached microorganisms.  The cylinder revolves and contacts the wastewater along one side while the other side is exposed to air, thereby maximizing the oxygenation of the water and stimulating decomposition of dissolved or suspended organic material.
Biodiversity  (1) The variety of life and its processes.  Biodiversity includes the diversity of landscapes, communities, and populations (genetic variation).  Also called Biological Diversity or Biotic Diversity.  (2) Refers to the variety and variability of life, in
(1)  Genes - Genetic diversity encompasses the variety of genetically coded characteristics of plant and animal populations;
(2)  Populations - Groups of individuals of a species that interbreed or interact socially in an area;
(3)  Species - The level at which most organisms are recognizable as distinct from all others;
(4)  Natural Communities - Groups of species that typically occur in recognizable units, such as redwood forests, coastal sage scrub, or oak woodlands.  A natural community includes all the vegetation and animal life, and their interactions within that community; and
(5)  Ecosystems - A collection of natural communities.  An ecosystem can be as small as a rotting log or a puddle of water, but current management efforts typically focus on larger landscape units, such as a mountain range, a river basin, or a watershed.
Biofouling  The gradual accumulation of waterborne organisms (as bacteria and protozoa) on the surfaces of engineering structures in water that contributes to corrosion of the structures and to a decrease in the efficiency of moving parts.
Biogas  Methane gas produced during the Anaerobic decomposition of the remains of plants or animal wastes by bacteria.
Biogenic  Used to describe changes in the environment resulting from the activities of living organisms.
Biogeochemical Cycling  The flow of chemical substances to and from the major environmental reservoirs:  Atmosphere, Hydrosphere, Lithosphere, and Biosphere.  As chemicals move in the cycle, they often change chemical form, usually existing in a characteristic form in each reservoir.  As an example, carbon (in the lithosphere) exists mainly as carbon dioxide in the atmosphere, carbonic acid, bicarbonate, or the carbonate ion when dissolved in water (hydrosphere), and as more complex organic compounds in animals and plants (biosphere).
Biogeochemistry  The study of the transformation and movement of chemical materials to and from the Lithosphere, the Atmosphere, the Hydrosphere, and the bodies of living organisms (the Biosphere).
Biogeography  The study of the geographic distribution of organisms.
Bioindicator  A living organism that denotes the presence of a specific environmental condition.  For example, the presence of coliform bacteria identifies water that is contaminated with human fecal material.
Biological Activated Carbon (BAC) Process  The combination of Ozonation and Granular Activated Carbon (GAC) for the removal of dissolved organics, particularly Dissolved Organic Carbon (DOC) from drinking water.  This water treatment method has seen more widespread use in Europe primarily due to:  (1) the generally poorer quality of surface waters there; (2) the greater concern and more stringent standards for chlorination byproducts; and (3) the strict aesthetic demand of European consumers.  Also referred to as the Biologically Enhanced Activated Carbon Process.
Biological Additives  Cultures of bacteria, enzymes, or nutrients that are introduced into an oil discharge or other wastes to promote decomposition.
Biological Community  All of the living things in a given environment.
Biological Control  The direct human introduction of living organisms - predators, parasites, or pathogens - to eliminate or control undesirable species.  The practice is usually considered an ecologically sound alternative to the application of chemical pesticides.
Biological Diversity  The number and kinds of organisms per unit area of volume; the composition of species in a given area at a given time.
Biological Magnification  Refers to the process whereby certain substances such as pesticides or heavy metals move up the food chain, work their way into rivers or lakes, and are eaten by aquatic organisms such as fish, which in turn are eaten by large birds, animals or humans.  The substances become concentrated in tissues or internal organs as they move up the chain.  Also see Bioaccumulants and Bioaccumulation.
Biological Opinion  A document which states the opinion of the U.S. Fish and Wildlife Service (USFWS) as to whether a federal action is likely to jeopardize the continued existence of a threatened or endangered species or result in the destruction or adverse modification of critical habitat.
Biological Oxidation  Decomposition of complex organic materials by microorganisms.  Occurs in the self-purification of water bodies and in activated sludge wastewater treatment processes.
Biological Oxygen Demand (BOD)  (1) The amount of oxygen required to stabilize decomposable matter by aerobic action.  (2) (Water Quality) An indirect measure of the concentration of biologically degradable material present in organic wastes.  It usually reflects the amount of oxygen consumed in five days by biological processes breaking down organic waste.  Also see BOD5.  Also referred to as Biochemical Oxygen Demand (BOD).
Biological Processes  Processes characteristic of, ore resulting from, the activities of living organisms.
Biological Treatment  A treatment technology that uses bacteria to consume organic wastes.
Biological Wastewater Treatment  The use of bacteria to degrade and decompose organic materials in wastewater.
Biology  (1) The science of life and of living organisms, including their structure, function, growth, origin, evolution, and distribution.  It includes Botany and Zoology and all their subdivisions.  (2) The life processes or characteristic phenomena of a group or category of living organisms.  (3) The plant and animal life of a specific area or region.
Biomagnification  The process by which a substance is passed up the food chain resulting in an especially high level of the substance at upper levels of the food chain.  A biological process wherein a contaminant's concentration increases at each level up the food chain, including humans.  Thus, the availability of such contaminants, even in the seemingly insignificant parts per trillion range, often are ecologically important.
Biomass  (1) The total mass of living matter within a given unit of environmental area, typically expressed as mass per unit area or volume of habitat.  (2) Plant material, vegetation, or agricultural waste used as a fuel or energy source.  Some methods of determining biomass in a sample include:
(1)  Ash Mass - The mass or amount of residue present after the residue from the dry mass determination has been ashed in a muffle furnace at a temperature of 500?C for 1 hour.  The ash mass values of zooplankton and phytoplankton are expressed in grams per cubic meter (g/m3), and periphyton and benthic organisms in grams per square mile (g/mi2).
(2)  Dry Mass - The mass of residue present after drying in an oven at 105?C for zooplankton and periphyton, until the mass remains unchanged.  This mass represents the total organic matter, ash and sediment, in the sample.  Dry-mass values are expressed in the same units as ash mass.
(3)  Organic Mass or Volatile Mass - Refers to the mass of a living substance as the difference between t