A - apparent trace.

A&E (A/E) - architectural and engineering.

AAC - All American Canal.

AAHU - average annual habitat units.

AAM - annual arithmetic mean.

AAR - alkali-aggregate reaction.

AB - Assembly Bill.

ABC - Association of Boards of Certification.

Aberrant. Atypical, departing from the normal type or structure.

Abiotic. The absence of living organisms.

Abrasion. Wearing away of surfaces by friction.

Absolute pressure. Atmospheric pressure plus gauge pressure.

Absorbed dose. The amount of a chemical that enters the body of an exposed organism.

Absorbed water. Water held mechanically in a soil or rock mass and having physical properties not substantially different from ordinary water at the same temperature and pressure. See adsorbed water.

Absorption. Taking in of fluids or other substances through, or as if through, cells or tissues. The uptake of water or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in the soil). Should not be confused with adsorption.

Absorption factor. The fraction of a chemical making contact with an organism that is absorbed by the organism.

Abutment. That part of the valley wall against which the dam is constructed. The part of a dam that contacts the riverbank. A structure that supports the ends of a dam or bridge. An artificial abutment is sometimes constructed, as a concrete gravity section, to take the thrust of an arch dam where there is no suitable natural abutment. Action or place of abutting; the part of a structure that is the terminal point or receives thrust or pressure. Defined in terms of left and right as looking away from the reservoir, looking downstream (i.e., left abutment, right abutment).

ac - acre.

Acceleration. In terms of flow, acceleration is the time rate of change of the velocity vector, either of magnitude or direction or both.

Accelerogram. The record from an accelerometer showing acceleration as a function of time.

Acceptable daily intake (ADI). Estimate of the largest amount of a chemical to which a person can be exposed on a daily basis that is not anticipated to result in adverse effects (usually expressed in mg/kg/day). The daily exposure level which, during an entire lifetime of a human, appears to be without appreciable risk on the basis of all facts known at the time. See RFD.

Access charge. A charge levied on a power supplied, or its customer, for access to a utility's transmission or distribution system. It is a charge for the right to send electricity over another's wires.

Access control point. A location staffed to restrict entry of unauthorized personnel into a risk area during emergency and/or disaster events. Access control is normally performed just outside of the risk area and involves use of vehicles, barricades, or other measures to deny access to a particular area.

Access shaft. Concrete portion of an outlet works between the shaft house and the gate chamber. The access shaft provides vertical access to the gates.

Accident assessment. The evaluation of the nature, severity, and impact of an accident. Dam operating personnel are primarily responsible for accident assessment for incidents at Reclamation dams.

Acclimation. Adjustment of an organism to a new habitat or environment.

Accretion. Process of growth whereby material is added to the outside of nonliving matter. The gradual increase in flow of a stream attributable to seepage, ground water discharge, or tributary inflow.

Accuracy. How closely an instrument measures the true or actual value of the process variable being measured or sensed.

ACEC - area of critical environmental concern.

ACER - Assistant Commissioner - Engineering and Research.

ACES - Automated Coastal Engineering System.

ac-ft - acre-foot, acre-feet.

ACGIH - American Conference of Government Industrial Hygienists.

ACHP - Advisory Council on Historic Preservation.

Acid. A substance that has a pH value between 0 and 7. ACID - Anderson-Cottonwood Irrigation District.

Acid rain. Precipitation which has been rendered acidic by airborne pollutants.

Acidic. The condition of water or soil which contains a sufficient amount of acid substances to lower the pH below 7.0.

Acidified. The addition of an acid (usually nitric or sulfuric) to a sample to lower the pH below 2.0.

ACR - alkali-carbonate reaction.

Acre (ac). Unit for measuring land, equal to 43,560 sq. ft., 4840 sq. yds., or 160 sq. rds.

Acre-foot (ac-ft). A term used in measuring the volume or amount of water needed to cover 1 acre (43,560 square feet) 1 foot deep (325,851 gallons or 1,233.5 cubic meters).

ACRM - Assistant Commissioner-Resources Management.

Activated carbon. Adsorptive particles or granules of carbon usually obtained by heating carbon (such as wood). These particles or granules have a high capacity to selectively remove certain trace and soluble materials from water.

Active capacity. The reservoir capacity normally usable for storage and regulation of reservoir inflows to meet established reservoir operating requirements. It extends from the highest of either the top of exclusive flood control capacity, the top of joint use capacity, or the top of active conservation capacity, to the top of inactive capacity. It is also the total capacity less the sum of the inactive and dead capacities. The reservoir capacity that can be used for irrigation, power, municipal and industrial use, fish and wildlife, recreation, water quality, and other purposes.

Active conservation capacity (active storage). The reservoir capacity assigned to regulate reservoir inflow for irrigation, power, municipal and industrial use, fish and wildlife, navigation, recreation, water quality, and other purposes. It does not include exclusive flood control or joint use capacity. It extends from the top of the active conservation capacity to the top of the inactive capacity (or dead capacity where there is no inactive capacity).

Active earth pressure. The minimum value of earth pressure. This condition exists when a soil mass is permitted to yield sufficiently to cause its internal shearing resistance along a potential failure surface to be completely mobilized.

Active fault. A fault which, because of its present tectonic setting, can undergo movement from time to time in the immediate geologic future. A fault, which has moved during the recent geologic past (Quarternary) and, thus, may move again. It may or may not generate earthquakes. See capable fault.

Active transport. An energy-expending mechanism by which a cell moves a chemical across the cell membrane from a point of lower concentration to a point of higher concentration, against the diffusion gradient.

Activity. The ratio of the plasticity index to the percent by dry mass of soil particles finer than 0.002 mm (2 microns) in size.

ACTS - Action Correspondence Tracking System.

Acute. Occurring over a short period of time; used to describe brief exposures and effects which appear promptly after exposure.

Acute exposure. A single exposure to a toxic substance which results in severe biological harm or death. Acute exposures are usually characterized as lasting no longer than a day.

Acute toxicity. The ability of a substance to cause poisonous effects resulting in severe biological harm or death soon after a single exposure or dose. Also, any severe poisonous effect resulting from a single short-term exposure to a toxic substance.

ACWA - Association of California Water Agencies.

Adaptation. Adjustment to environmental conditions.

Additive effect. Combined effect of two or more chemicals equal to the sum of their individual effects.

Adhesion. Shearing resistance between soil and another material under zero externally applied pressure.

ADI - acceptable daily intake.

Adit. A nearly horizontal underground excavation in an abutment having an opening in only one end. An opening in the face of a dam for access to galleries or operating chambers.

ADMS - Accessibility Data Management System.

ADP - automated data processing.

ADR - alternative dispute resolution.

Adsorbate. The material being removed by the adsorption process.

Adsorbed water. Water in a soil or rock mass, held by physico-chemical forces, having physical properties substantially different from absorbed water or chemically combined water, at the same temperature and pressure.

Adsorbent. The material (for example activated carbon) that is responsible for removing the undesirable substance in the adsorption process.

Adsorption. The process by which chemicals are held on the surface of a mineral or soil particle. The adherence of a gas, liquid, or dissolved material on the surface of a solid. An increase in concentration of gas or solute at the interface of a two-phase system. Should not be confused with absorption.

ADSS - Advanced Decision Support System.

ADT - average daily traffic.

Advanced Decision Support System (ADSS). Computer software designed to provide easy access to and allow efficient use of methods of analysis and information management.

Advisory Council on Historic Preservation (ACHP). Executive agency responsible for ensuring requirements of National Historic Preservation Act and 36 CFR Part 800 are met. Visit the Advisory Council on Historic Preservation web site.

AEB - Elephant Butte Power and Storage Division (Truth or Consequences, NM).

Aeolian (eolian). Materials carried, deposited, produced, or eroded by the wind.

Aeolian deposits. Wind-deposited material such as dune sands and loess deposits.

Aerate. To impregnate with gas, usually air.

Aeration. The process of adding air to water by either passing air through water or passing water through air.

Aerial cover. Ground area circumscribed by the perimeter of the branches and leaves of a given plant or group of plants (generally used as a measure of relative density).

Aerobic. A condition in which free (atmospheric) or dissolved oxygen is present in water. The opposite of anaerobic.

af - acre-feet.

Affected environment. Existing biological, physical, social, and economic conditions of an area subject to change, both directly and indirectly, as the result of a proposed human action. Also, the chapter in an environmental impact statement describing current environmental conditions.

AFO - Auburn-Folsom Office (Auburn, CA).

AFRP - Anadromous Fish Restoration Program.

Afterbay (tailrace). The body of water immediately downstream from a powerplant or pumping plant. A reservoir or pool that regulates fluctuating discharges from a hydroelectric power plant or a pumping plant.

Afterbay dam (reregulating dam). A dam located downstream from a large hydroelectric powerplant used to regulate discharges downstream. See regulating dam.

afy (af/yr) - acre-feet per year.

ag - agriculture. AG - association of governments.

AGC - automatic generation control.

Age tank (day tank). A tank used to store a chemical solution of known concentration for feed to a chemical feeder.

Aggradation. Geologic process wherein streambeds, floodplains, sandbars, and the bottom of water bodies are raised in elevation by the deposition of sediment; the opposite of degradation.

Aggregate. Crushed rock or gravel screened to sizes for use in road surfaces, concrete, or bituminous mixes. A mass or cluster of soil particles, often having a characteristic shape.

AGM - annual geometric mean.

Agricultural drainage. The process of directing excess water away from root zones by natural or artificial means, such as by using a system of pipes and drains placed below ground surface level (also called subsurface drainage). The water drained away from irrigated farmland.

Agrochemical. Synthetic chemicals (pesticides and fertilizers) used in agricultural production.

AHS - Archaeological and Historical Services.

AIPC - American Indian Program Council.

Air quality. Measure of the health-related and visual characteristics of the air, often derived from quantitative measurements of the concentrations of specific injurious or contaminating substances.

Air release valve. A valve, usually manually operated, which is used to release air from a pipe or fitting.

Air slaking. The process of breaking up or sloughing when an indurated soil is exposed to air.

Air-space ratio. Ratio of volume of water that can be drained from a saturated soil or rock under the action of force of gravity to total volume of voids.

Air-void ratio. The ratio of the volume of airspace to the total volume of voids in a soil mass.

Air waves. Air borne vibrations caused by explosions.

AIRFA - American Indian Religious Freedom Act.

AIS - Automated Information System.

AISC - American Institute of Steel Construction.

aka - also known as.

ALB - Albuquerque Projects Office (Albuquerque, NM).

ALC - agency location code.

Alert (Automated Local Evaluation in Real Time). A flood warning system consisting of remote sensors, data transmission by radio, and a computer software package developed by the National Weather Service (NWS). Also, a generic term used for a decision making software package.

Alevin. A young fish which has not yet absorbed its yolk sac.

Algae. Simple plants containing chlorophyll; most live submerged in water. Microscopic plants which contain chlorophyll and live floating or suspended in water. They also may be attached to structures, rocks or other submerged surfaces. They are food for fish and small aquatic animals. Excess algal growths can impart tastes and odors to potable water. Algae produce oxygen during sunlight hours and use oxygen during the night hours. Their biological activities appreciably affect the pH and dissolved oxygen of the water.

Algae bloom. A heavy growth of algae in and on a body of water as a result of high phosphate concentration from farm fertilizers and detergents.

Algal bloom. Rapid and flourishing growth of algae. Sudden, massive growths of microscopic and macroscopic plant life, such as green or bluegreen algae, which develop in lakes and reservoirs.

Algicide. Any substance or chemical specifically formulated to kill or control algae.

Aliquot. Portion of a sample.

Alkali. A soluble salt obtained from the ashes of plants. A substance having marked basic properties. Various soluble salts, principally of sodium, potassium, magnesium, and calcium, that have the property of combining with acids to form neutral salts and may be used in chemical water treatment processes.

Alkali-aggregate reaction (AAR). A deterioration of concrete by which the alkali in the cement paste in the concrete reacts chemically with the silica or carbonate present in some aggregates. In the presence of free moisture, the gel (product of the reaction) will expand and manifest into cracking and differential movement in structures as well as other deleterious effects such as reduction in freeze-thaw durability and compressive and tensile strength. Three forms of alkali-aggregate reaction have been identified, see alkali-silica reaction, the slow/late-expanding type of reaction referred to as alkali-silicate reaction, and the alkali-carbonate reaction. Visit the Alkali-Aggregate Reactions database.

Alkali-carbonate reaction (ACR). Reaction of alkalis which occurs between certain argillaceous dolomitic limestones and the alkaline pore solution in the concrete and causes expansion and extensive cracking. Expansive dolomite limestones are characterized by a matrix of fine calcite and clay minerals with scattered dolomite rhobohedra. This reaction usually occurs early and structures may show cracking within 5 years after construction. See alkali-aggregate reaction.

Alkaline. Having a pH of 7.0 or above. The condition of water or soil which contains a sufficient amount of alkali substances to raise the pH above 7.0. The quality of being bitter due to alkaline content.

Alkali-silica reaction (ASR). Reaction of alkalis with aggregate with various forms of poorly crystalline reactive silica: opal, chert, flint and chalcedony and also tridymite, crystoblite and volcanic glasses. Aggregate containing such materials (e.g., some cherty gravels) may cause deterioration of concrete when present in amounts of 1% to 5%. Concrete made of these aggregates is characterized by the early onset of a relatively rapid expansion. Cracking of structures is often observed within 10 years of construction. See alkali-aggregate reaction.

Alkali-silicate/silica reaction (ASSR). Reaction of alkalis with strained quartz is thought to be one reactive component of aggregates causing this reaction. A wide variety of quartz-bearing rocks have been found to be reactive including graywackes, argillites, quartzwackes, quartzarenites, quartzites, hornfels, quartz biotite, gneiss, granite, phyllite, arkose and sandstone. This type of reaction is characterized by a delayed onset of expansion and cracking may not become evident for up to 20 years after construction. See alkali-aggregate reaction.

Allelopathy. Influence of plants upon each other caused by products of metabolism, e.g., creosote bushes produce a toxic substance which inhibits the growth of other plants in the immediate vicinity.

Allochthonous. Exotic species of a given area. Also refers to deposits of material that originated elsewhere, e.g., drifted plant material on the bottom of a lake.

Allopatric. Having separate and mutually exclusive areas of geographical distribution.

Allowable bearing capacity. The maximum pressure that can be permitted on foundation soil, giving consideration to all pertinent factors, with adequate safety against rupture of the soil mass or movement of the foundation of such magnitude that the structure is impaired.

Allowable pile bearing load. The maximum load that can be permitted on a pile with adequate safety against movement of such magnitude that the structure is endangered.

Alluvial. Related to, composed of, or found in alluvium. Sedimentary material transported and deposited by the action of flowing water, such as in a riverbed, flood plain, or delta.

Alluvial fan. A large fan-shaped accumulation of sediment deposited by streams where they emerge at the front of a mountain range.

Alluvium. Material transported and deposited by flowing water, such as clay, silt, sand, and gravel. Soil, the constituents of which have been transported in suspension by flowing water and subsequently deposited by sedimentation. A stratified bed of sand, gravel, silt, and clay deposited by flowing water.

ALP - Animas-La Plata Project.

Alternating current (AC). An electric current that reverses its direction (positive/negative values) at regular intervals. See direct current.

Alternatives. Courses of action that may meet the objectives of a proposal at varying levels of accomplishment, including the most likely future conditions without the project or action.

Alum - ammonium sulfate.

AM - area manager.

AMA - adaptive management area.

Ambient. Surrounding natural conditions or environment at a given place and time. Environmental or surrounding conditions.

Ambient temperature. Temperature of the surrounding air (or other medium).

Ambursen dam. A buttress dam in which the upstream part is a relatively thin flat slab usually made of reinforced concrete.

AMCR - alternative management control review.

Ammonium. One form of nitrogen that is usable by plants.

amp - ampere. AMP - Adaptive Management Plan.

Amperage. The strength of an electric current measured in amperes. The amount of electric current flow, similar to the flow of water in gallons per minute (gpm).

Ampere (amp). A unit of electric current or rate of flow of electrons. One volt across 1 ohm of resistance causes a current flow of 1 ampere.

Amperometric. Based on the electric current that flows between two electrodes in a solution.

Amphibian. Vertebrate animals that have life stages both in water and on land (e.g., salamanders, frogs, and toads). Animals capable of living either in water or land.

Amplification. Modification of the input bedrock ground motion by the overlying unconsolidation materials. Amplification causes the amplitude of the surface ground motion to be increased in some range of frequencies and decreased in others. Amplification is a function of the shear wave velocity and damping of the unconsolidated materials, its thickness and geometry, and the strain level of the input rock motion.

AMR - acquisition management review.

AMWUA - Arizona Municipal Water Users Association.

Anadromous. Fish that migrate from salt water to freshwater to breed. Going up rivers to spawn.

Anaerobic. A condition in which free (atmospheric) or dissolved oxygen is not present in water. The opposite of aerobic.

Anchor block. See thrust block.

Ancillary services. Other energy-related services that are required to control system frequency, to meet changing scheduling requirements, to react to changing loads and unexpected contingencies, and to ensure system stability (i.e. preventing blackouts).

Andesite. Fine-grained, medium gray volcanic rock of intermediate composition between rhyolite and basalt.

Angle of external friction (angle of wall friction). Angle between the abscissa and the tangent of the curve representing the relationship of shearing resistance to normal stress acting between soil and surface of another material.

Angle of internal friction (angle of shear resistance). The angle between the axis of normal stress and the tangent to the Mohr envelope at a point representing a given failure-stress condition for solid material.

Angle of obliquity. The angle between the direction of the resultant stress or force acting on a given plane and the normal to that plane.

Angle of repose. Angle between the horizontal and the maximum slope that a particular soil or geologic material assumes through natural processes. For dry granular soils, the effect of the height of slope is negligible; for cohesive soils, the effect of height of slope is so great that the angle of repose is meaningless.

Angle of wall friction. Angle between the abscissa and the tangent of the curve representing the relationship of shearing resistance to normal stress acting between soil and surface of another material.

Angler-day. The time spent fishing by one person for any part of a day.

Anion. A negatively charged ion in an electrolyte solution, attracted to the anode under the influence of a difference in electrical potential. See cation.

Anisotropic mass. A mass having different properties in different directions at any given point.

Anisotropy. Flow conditions vary with direction. Most aquifers are anisotropic.

Annex (functional). An emergency operations plan element that describes the jurisdiction's plan for functioning in that component area of activity during emergencies.

Annual energy cost. Variable costs relating to energy production in a year, usually espressed in mills per kilowatt-hour.

Annual failure probability. The probability of the load multiplied by the probability of failure.

Annual inspection (AI). Annual inspections of a dam and appurtenant facilities are conducted by the local operating office. These examinations address both O&M and dam safety issues and use an "Annual Inspection Checklist" to aid in the examination and formal documentation of the inspection.

Annual load factor. This factor is equal to energy generated in a year divided by the product of the peak demand for that year and the number of total hours in a year.

Annual operating cost. This is a general term which is sometimes called annual operating expense and includes all annual operation and maintenance expense, wheeling, purchased power, etc.

Annual work plan. Annual budget document that describes proposed work to be performed at a specific Bureau of Reclamation project, and details the amount of funds required.

Annualized loss of life. The sum of the probability of dam failure multiplied by the annual probability of the loading and the estimated number of lives that would be lost (consequences) for each dam failure scenario under a particular loading category (i.e. (probability of failure)(probability of load)(potential loss of life)).

Annular. Ring-shaped.

Annular space. A ring-shaped space located between two circular objects, such as two pipes.

Anode. The positive pole or electrode of an electrolytic system. The anode attracts negatively charged particles or ions (anions). See cathode.

Anoxic. Without oxygen.

ANSI - American National Standards Institute.

Antecedent flood. A flood or series of floods assumed to occur prior to the occurrence of an inflow design flood (IDF).

Anthropogenic. Human-created.

Anticline. A fold in rocks that curves upward in a convex way. Upward fold in rock layers that creates an arched or domelike uplift of sedimentary layers. See syncline.

AO - area office.

AOP - annual operating plan.

AP - analysis plan.

APCD - Air Pollution Control District.

APE - area of potential effect.

APO - Arizona Projects Office.

Appendix. An emergency operations plan element attached to a functional annex to provide information on special approaches or requirements generated by unique characteristics of specified hazards of particular concern to the jurisdiction.

Application efficiency. The ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied, expressed as a percent.

Applied water (delivered water). Water delivered to a user. Applied water may be used for either inside uses or outside watering. It does not include precipitation or distribution losses. It may apply to metered or unmetered deliveries.

Appraisal estimate. An estimate used in an appraisal study as an aid in selecting the most economical plan by comparing alternative features or for determinimg whether more detailed investigations of a potential project are economically justified. Used to obtain approximate costs in a short period of time with inadequate data. Not to be used for project authorization.

Appraisal level of detail. The level of detail necessary to facilitate making decisions on whether or not to proceed with a detailed study and evaluation of any alternative.

Appraisal study (appraisal report). A study incorporating an appraisal level of detail.

Approach channel. The channel upstream from that portion of the spillway having a concrete lining or concrete structure. Channel upstream from intake structure of an outlet works. Channel is generally unlined, excavated in rock or soil, with or without riprap, soil cement or other types of erosion protection.

Appropriation. Amount of water legally set apart or assigned to a particular purpose or use.

Appropriative. Water rights to or ownership of a water supply which is acquired for the beneficial use of water by following a specific legal procedure.

Appurtentant structures. Outlet works, spillways, bridges, drain systems, tunnels, towers, etc.

Apron (fore apron). A section of concrete or riprap constructed upstream or downstream from a control structure to prevent undercutting of the structure. A short ramp with a slight pitch. A floor or lining of concrete, timber, or other suitable material at the toe of a dam, discharge side of a spillway, a chute, or other discharge structure, to protect the waterway from erosion from falling water or turbulent flow.

AQIA - air quality impact analysis.

AQMD - Air Quality Management District.

AQMP - Air Quality Management Plan.

Aquatic. Living, growing, or occurring in or on the water.

Aquatic algae. Microscopic plants that grow in sunlit water containing phosphates, nitrates, and other nutrients.

Aqueduct. Man-made canal or pipeline used to transport water.

Aqueous. Something made up of, similar to, or containing water; watery.

Aquiclude. A layer of clay which limits the movement of ground water.

Aquifer. A water-bearing stratum of permeable rock, sand, or gravel. A water-bearing formation that provides a ground water reservoir. Underground water-bearing geologic formation or structure. A geologic formation, group of formations, or part of a formation that stores and transmits water and yields significant quantities of water to wells and springs. A natural underground layer of porous, water-bearing materials (sand, gravel) usually capable of yielding a large amount or supply of water.

Arable. Suitable for farming. Having soil or topographic features suitable for cultivation.

Arable land. Land which when farmed in adequate size units for the prevailing climatic and economic setting, and provided with the essential on-farm improvements of removing vegetation, leveling, soil reclamation, drainage, and irrigation related facilities, will generate sufficient income under irrigation to pay all farm production expenses; provide a reasonable return to the farm family's labor, management, and capital; and at least pay the operation, maintenance, and replacement costs of associated irrigation and drainage facilities.

ARAR - applicable or relevant and appropriate requirement.

Arch dam. A concrete or masonry dam which is curved upstream in plan so as to transmit the major part of the water load to the abutments and to keep the dam in compression. A solid concrete dam curved upstream in plan. An arch dam is most likely used in a narrow site with steep walls of sound rock. See thin arch dam, medium-thick arch dam, thick arch dam, arch-buttress dam, arch-gravity dam, constant angle arch dam, constant radius arch dam, double curvature arch dam, and multiple arch dam.

Arch-buttress dam (or curved buttress dam). A buttress dam which is curved in plan.

Arch-gravity dam. An arch dam which is only slightly thinner than a gravity dam.

Archaic. In American archeology, a cultural stage following the earliest known human occupation in the New World (about 5,500 B.C. to A.D. 100). This stage was characterized by a generalized hunting and gathering lifestyle and seasonal movement to take advantage of a variety of resources.

Archeology. Study of human cultures through the recovery and analysis of their material relics.

Archimedean screw. An ancient water-raising device attributed to Archimedes, made up of a spiral tube coiled about a shaft or of a large screw in a cylinder, revolved by hand. A pump consisting of an inclined, revolving, corkscrew-shaped shaft tightly enclosed in a pipe.

Arching. The transfer of stress from a yielding part of a soil or rock mass to adjoining less-yielding or restrained parts of the mass.

Area-capacity table. A table giving reservoir storage capacity, and sometimes surface areas, in terms of elevation increments.

Area of influence of a well. Area surrounding a well within which the piezometric surface has been lowered when pumping has produced a maximum steady rate of flow.

Arid. A term describing a climate or region in which precipitation is so deficient in quantity or occurs so infrequently that intensive agricultural production is not possible without irrigation.

Armoring. See riprap.

ARMS - Automated Records Management System.

ARP - address resolution protocol.

Arroyo. A gully or channel cut by an intermittent stream. A water-carved channel or gulley in an arid area, usually rather small in cross section with steep banks, dry much of the time due to infrequent rainfall and the depth of the cut which does not penetrate below the level of permanent ground water.

Artesian well. Water held under pressure in porous rock or soil confined by impermeable geologic formations. An artesian well is free flowing. See confined aquifer.

Artifact. Any human-made or used object, intact or in pieces, 50 years or older. Artifacts are protected by the Archaeological Resources Protection Act of 1979.

Artificial drains. Man-made or constructed drains.

Artificial recharge. Addition of surface water to a ground water reservoir by human activity, such as putting surface water into spreading basins. See ground water recharge, and recharge basin.

ARTS - Automated Resources Training System.

ARWRI - American River Water Resources Investigation.

AS - assistant secretary.

ASAP - as soon as possible.

ASC - Administrative Service Center.

ASCC - Alaskan System Coordination Council (part of NERC).

ASCE - American Society of Civil Engineers.

ASCII - American Standard Code for Information Interchange.

ASCMP - Administrative Support Career Management Program.

ASCS - Agricultural Stabilization and Conservation Service.

ASR - Alkali-silica reaction.

ASSE - American Society of Safety Engineers.

Associated facility. A term used by Reclamation to describe those facilities examined by the respective regional or area office. These facilities include most carriage, distribution, and drainage systems, small diversion works, small pumping plants and powerplants, open and closed conduits, tunnels, siphons, small regulating reservoirs, waterways, and class B bridges.

Association of Boards of Certification (ABC). An international organization representing over 150 boards which certify the operators of waterworks and waste water facilities. For more information, visit the ABC website.

ASSR - alkali-silicate/silica reaction.

ASTM - American Society for Testing and Materials.

ASTS - above ground storage tanks.

Asymmetric. Not similar in size, shape, form or arrangement of parts on opposite sides of a line, point or plane.

ATF - Austin Field Office (Austin, TX).

At-rest earth pressure. The value of the earth pressure when the soil mass is in its natural state without having been permitted to yield or without having been compressed.

Atmospheric pressure. Pressure of air enveloping the earth, averaged as 14.7 psi at sea level, or 29.92 inches of mercury as measured by a standard barometer.

Attenuation. Decrease in amplitude of the seismic waves with distance due to geometric spreading, energy absorption and scattering.

Atterberg limits (consistency limits). The boundaries (determined by laboratory tests) of moisture content in a soil between the liquid state and plastic state (known as liquid limit), between the plastic state and the semisolid state (known as the plastic limit), and between the semisolid state and the solid state (known as the shrinkage limit).

Attribute survey. Survey to determine the important components of the recreational experience.

ATV - all-terrain vehicle.

Atypical. Not typical.

Auger. A rotating drill having a screw thread that carries cuttings away from the face.

AUM - animal unit months.

AUO - administratively uncontrollable overtime.

Author's signature. This is the signature of the person or persons with primary responsibility for writing the document. Signature of the document by the author(s) signifies that a draft document was provided to team members and that they had an opportunity to comment on the draft. The author's signature also implies that comments were considered and that any critical issues or influencing factors were incorporated into the document.

Authorization. An act by the Congress of the United States which authorizes use of public funds to carry out a prescribed action.

Authorized Reclamation project. A congressionally approved Bureau of Reclamation project that has been authorized for specific purposes.

Automatic generation control (AGC). Computerized power system regulation to maintain scheduled generation within a prescribed area in response to changes in transmission system operational characteristics. The function of dedicated generating capacity changing moment to moment to follow the loads in a defined control.

Auxiliary equipment. Accessory equipment necessary for the operation of a generating station.

Auxiliary spillway. A spillway, usually located in a saddle or depression in the reservoir rim which leads to a natural or excavated waterway, located away from the dam which permits the planned release of excess flood flow beyond the capacity of the service spillway. A control structure is seldom furnished. The crest is set at the maximum water surface elevation for a 100-year flood or some other specific frequency flood. The auxiliary spillway thus has only infrequent use. Any secondary spillway which is designed to be operated very infrequently and possibly in anticipation of some degree of structural damage or erosion to the spillway during operation.

AVADS - Automated Vacancy Announcement Distribution System.

Available capacity. The amount of water held in the soil that is available to the plants. See water holding capacity.

Average. The arithmetic mean. The sum of the values divided by the number of values.

Average annual runoff. For a specified area, the average value of annual runoff amounts calculated for a selected period of record that represents average hydrologic conditions.

Average degree of consolidation. The ratio of the total volume change in a soil mass at a given time to the total volume change anticipated in the soil mass due to primary consolidation.

Average energy. The total power generation produced by a powerplant during all of the years of its actual or simulated operation divided by the number of years of actual or simulated operation.

Average year water demand. Demand for water under average hydrologic conditions for a defined level of development.

Average year supply. The average annual supply of a water development system over a long period.

Avian. Having to do with birds.

Avoirdupois weight. An English and American system of weights based on a pound of 16 ounces.

AWARDS - Agricultural Water Resources Decision Support.

AWOL - absence without leave.

AWTR - Advanced Water Treatment Research.

AWWA - American Water Works Association.

Axis. A straight line around which a shaft or body revolves.

Axis of dam. A vertical plane or curved surface, appearing as a line in plan or cross section, to which horizontal dimensions can be referred.

Axis of dam (concrete). A vertical reference surface coincident with the upstream face at the top of the dam.

BA - biological assessment.

Back pressure. A pressure that can cause water to backflow into the water supply when a user's water system is at a higher pressure than the public water system.

Backfill. Material used in refilling excavation, or the process of such refilling. Material used to fill an excavated trench.

Backfill concrete. Concrete used in refilling excavation in lieu of earth material.

Backflow. A reverse flow condition, created by a difference in water pressures, which causes water to flow back into the distribution system.

Backfurrow. The first cut of a plow, from which the slice is laid on undisturbed soil.

Backsiphonage. A form of backflow caused by a negative or below atmospheric pressure within a water system.

Backwater. A small, generally shallow body of water with little or no current of its own. Stagnant water in a small stream or inlet. Water moved backward or held back by a dam, tide, etc.

BACT - best available control technology.

BADA - Bay Area Dischargers Association.

Baffle. A flat board or plate, deflector, guide or similar device constructed or placed in flowing water to cause more uniform flow velocities, to absorb energy, and to divert, guide, or agitate the flow.

Baffle block (dentate). One of a series of upright obstructions designed to dissipate energy as in the case of a stilling basin or drop structure. A block, usually of concrete, constructed in a channel or stilling basin to dissipate the energy of water flowing at high velocity.

Bailer. A 10- to 20-foot-long pipe equipped with a valve at the lower end. A bailer is used to remove slurry from the bottom or the side of a well as it is being drilled.

Balanced head condition. The condition in which the water pressure on the upstream and downstream sides of an object are equal (such as an emergency or regulating gate).

Ball-milling. The repeated churning action of cobbles, gravel, and sand caused by the force of water in a stilling basin or other structure by which severe concrete abrasion can occur.

Bank full. 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.

Bank storage. Water that has inflitrated from a reservoir into the surrounding land where it remains in storage until water level in the reservoir is lowered.

Barrage (gate-structure dam). A barrier built across a river, comprising a series of gates which when fully open allow the flood to pass without appreciably increasing the flood level upstream of the barrage.

Barrel. A volumetric unit of measure for crude oil and petroleum products equivalent to 42 U.S. gallons.

Basalt. Fine-grained, dark-colored volcanic rock rich in iron-bearing minerals.

Bascule gate. See flap gate.

Base. A substance that has a pH value between 7 and 14.

Base course. A layer of specified or selected material of planned thickness constructed on the subgrade or subbase for the purpose of serving one or more functions such as distributing load, providing drainage, minimizing frost action, etc.

Base exchange. The physicochemical process whereby one species of ions adsorbed on soil particles is replaced by another species.

Base flood. The flood having a one percent chance of being equalled or exceeded in any given year. This term is used in the National Flood Insurance Program (NFIP) to indicate the minimum level of flooding to be used by a community in its flood plain management regulations.

Base flood plain. The flood plain innundated by the 100-year flood.

Base flow. Ground water inflow to the river. Portion of stream discharge that is derived from natural storage.

Base safety condition (BSC). The level of loading above which a dam failure does not contribute an incremental loss of life.

Base width or thickness. The maximum thickness or width of a dam measured horizontally between upstream and downstream faces and normal to the axis or centerline crest of the dam, but excluding projections for outlets or other appurtenant structures. The base thickness of the crown cantilever of an arch dam. In general, the term thickness is used for gravity or arch dams, and width is used for other dams.

Baseline (condition or alternative). Conditions that would prevail if no actions were taken. See future without.

Baseline profile. Used for a survey of the environmental conditions and organisms existing in a region prior to unnatural disturbances.

Baseload. Minimum load in a power system over a given period of time. The minimum constant amount of load connected to the power system over a given time period, usually on a monthly, seasonal, or yearly basis.

Baseloading. Running water through a powerplant at a roughly steady rate, thereby producing power at a steady rate.

Baseload plant. Powerplant normally operated to carry baseload; consequently, it operates essentially at a constant load. A plant, usually housing high-efficiency steam-electric units, which is normally operated to take all or part of the minimum load of a system, and which consequently produces electricity at an essentially constant rate and runs continuously. These units are operated to maximize system mechanical and thermal efficiency and minimize system operating costs.

BASIC - Beginner's All-purpose Symbolic Instruction Code.

Basin runoff model. Any one of the computer programs that mathematically models basin characteristics to forecast reservoir inflow from rainfall and/or streamflow data.

Basin States - Arizona, California, Colorado, New Mexico, Utah, Wyoming.

BAT - best available treatment technologies.

Batter. Inclination from the vertical. A pile driven at an angle to widen the area of support and to resist thrust.

Bay - San Francisco Bay.

Bay-Delta - Sacramento/San Joaquin River Delta and San Francisco Bay.

B/C - benefit-cost ratio.

BCD - Black Canyon Dam (Emmett, ID).

BCO - Bend Construction Office (Bend, OR).

BCPA - Boulder Canyon Project Act (1928).

BDAC - Bay-Delta Advisory Council.

BDD - business decision document.

BEA - U.S. Bureau of Economic Analysis.

Beaching. The action of water waves by which beach materials settle into the water because of removal of finer materials.

Bear-trap gate. Any of a family of crest gates consisting of two leaves, an upstream leaf hinged and sealed at the upstream edge and a downstream leaf hinged and sealed on its downstream edge. The two leaves have a sliding seal at their juncture. When lowered the leaves are in a horizontal position. Gate is raised by admitting water from the forebay into the space beneath the leaves. Probably the first gate operated on the principal of application of headwater pressure.

Bed elevation. Height of streambed above a specified level.

Bed layer. The flow layer, several grain diameters thick (usually taken as two grain diameters thick), immediately above the bed.

Bed load. Sediment that moves by rolling or sliding along the bed and is essentially in contact with the streambed in the bed layer.

Bed-load discharge. The quantity of bed load passing a cross section of a stream in a unit of time.

Bed material. Unconsolidated material, or sediment mixture, of which a streambed is composed.

Bed-material discharge. That part of the total sediment discharge which is composed of grain sizes found in the bed. The bed-material discharge is assumed equal to the transport capability of the flow.

Bedding. Ground, or layer of such, for support purposes on which pipe is laid. Soil placed beneath and beside a pipe to support the load on the pipe.

Bedding plane. A separation or weakness between two layers of rock, caused by changes during the building up of the rock-forming material.

Bedload. Coarse sediments carried along near the bottom of a river.

Bedrock. The solid rock at the surface or underlying other surface materials. Rock of relatively great thickness and extent in its native location. A general term for any solid rock, not exhibiting soil-like properties, that underlies soil or other unconsolidated surficial materials. As distinguished from boulders. The consolidated body of natural solid mineral matter which underlies the overburden soils. The solid rock that underlies all soil, sand, clay, gravel, and other loose materials on the earth's surface. Any sedimentary, igneous, or metamorphic material represented as a unit in geology; being a sound and solid mass, layer, or ledge of mineral matter; and with shear wave velocities greater than 2500 feet per second.

Behavior. Reaction of an animal to its environment.

Bell. An expanded, or enlarged, end of a pipe section, into which the next pipe fits. See spigot.

Bench. A working level or step in a cut.

Bench mark (BM). A permanent or temporary monument of known elevation above sea level, used for vertical control at a construction site. A point of known or assumed elevation used as a reference in determining other elevations. A permanent reference point (elevation) used in a survey.

Bend. A change of direction in piping.

Benefit-cost ratio (B/C). The ratio of the present value of project benefits to the present value of the project costs, used in economic analysis.

Beneficial use. Water loss through use for the betterment of society, e.g. irrigation or municipal use. See consumptive use.

Beneficiary. Any individual, entity, or governmental agency (local, State, or Federal) that benefits from a Reclamation project.

Benthic. Bottom of rivers, lakes, or oceans; organisms that live on the bottom of water bodies. Bottom- or depth-inhabiting.

Benthos. Organisms living in or on the bottom of a lake, pond, ocean, stream, etc.

Bentonitic clay (bentonite). A clay with a high content of the mineral montmorillonite, usually characterized by high swelling on wetting and shrinkage on drying.

Berm. A horizontal strip or shelf built into an embankment or cut to break the continuity of the slope, usually for the purpose of reducing erosion or to increase the thickness of the embankment at a point of change in a slope or defined water surface elevation. A horizontal step in the sloping profile of an embankment dam. A shelf that breaks the continuity of a slope, or artificial ridge of earth. A ledge or shoulder, as along the edge of a road or canal. An artificial ridge of earth.

BEST - budget estimate system tools.

Best gate. The gate opening where the peak efficiency of a turbine occurs at a particular head.

BFO - Blythe Field Office (Blyth, CA).

BIA - U.S. Bureau of Indian Affairs.

Biennial. Plant which produces seeds during its second year and then dies.

Binder (soil binder). Portion of soil passing a No. 40 (0.425 mm) United States Standard sieve.

Binomial. Scientific name of plants or animals which has two parts: a genus and a species name.

Bioaccumulation. The intake and retention of nonfood substances by a living organism from its environment, resulting in a build-up of the substances in the organism.

Bioassay. Test which determines the effect of a chemical on a living organism.

Bioassimilation. The accumulation of a substance within a habitat.

Biological diversity. Number and kinds of organisms per unit area or volume; the composition of species in a given area at a given time.

Biological growth. The activity and growth of any and all living organisms.

Biological magnification (biomagnification). Step by step concentration of substances in successive levels of food chains. The enhancement of a substance (usually a contaminant) in a food web such that the organisms eventually contain higher concentrations of the substance than their food sources.

Biological Opinion (BO). Document stating the U.S. Fish and Wildlife Service (FWS) and the National Marine Fisheries Service (NMFS) opinion 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 processes. Processes characteristic of, or resulting from, the activities of living organisms.

Biology. The scientific study of life.

Biomass. Total mass or amount of living organisms in a particular area or environment.

Biosphere. Portion of the solid and liquid earth where organisms live.

Biota. Plant and animal life of a region.

Biotic potential. Inherent capacity of an organism to reproduce and survive, which is pitted against limiting influences of the environment.

Biotic pyramid. Set of all food chains or hierarchic arrangements of organisms as eaters and eaten in a prescribed area when tabulated by numbers or by biomasses, usually takes the form of an inverted pyramid.

Biotope. Smallest geographical unit of a habitat, characterized by a high degree of uniformity in the environment and its plant and animal life, e.g., a decaying stump.

Biotype. Genetically homogeneous population composed only of closely similar individuals; a genotypic race or group of organisms.

BIP - Budget Input Program.

Bituminous. Containing asphalt or tar.

Black water. Liquid and solid human body waste and the carriage water generated through toilet usage.

Blackout. The disconnection of the source of electricity from all the electrical loads in a certain geographical area brought about by an emergency forced outage or other fault in the generation, transmission, or distribution system serving the area. See brownout.

Blade. Usually a part of an excavator which digs and pushes dirt but does not carry it.

Blast. To loosen or move rock or soil by means of explosives or an explosion.

Blasting mats. A blanket usually composed of woven cable or interlocked rings placed over a blast to reduce flyrock.

BLM - U.S. Bureau of Land Management.

Blockloading. Providing a consistent amount of electrical power in a stated period of time.

Blue tops. Grade stakes whose tops indicate finish grade level.

BMP - best management practices.

BO - Biological Opinion.

BOD - biochemical oxygen demand.

BOM - U.S. Bureau of Mines.

BON - basis of negotiation.

Bonnet. The upper portion or the cover of a gate valve body.

Bonneville Power Administration (BPA). One of five federal power marketing administrations that sell low cost electric power produced by federal hydro electric dams to agricultural and municipal users. The Bonneville Power Administration serves Idaho, Oregon, and Washington as well as parts of Nevada and Wyoming.

Books. See publications.

BOR - U.S. Bureau of Reclamation.

Borderline soils. Soils that have the characteristics of two of the classification groups in the Unified Soil Classification System.

Boring. Rotary drilling.

Borrow. Material excavated from one area to be used as fill material in another area.

Borrow areas. Generally, surface areas, that contain borrow pits. The area from which material for an embankment is excavated.

Borrow pits. Specific site(s) within a borrow area from which material is excavated for use.

Boulder. A rock fragment, usually rounded by weathering or abrasion, with an average dimension of 12 inches or more: will not pass a 12-inch screen. A particle of rock that will not pass a 12-inch (300-mm) square opening. A rock which is too heavy to be lifted readily by hand.

Boulder clay. A geological term used to designate glacial drift that has not been subjected to the sorting action of water and therefore contains particles from boulders to clay sizes.

Box girder. A hollow steel beam with a square or rectangular cross section.

BPA - Bonneville Power Administration, blanket purchase agreement.

Brackish. Mixed fresh and salt waters. Water containing too much salt to be useful to people but less salt than ocean water.

BRAIN - Bureau of Reclamation Acquisition Information Network.

Brake horsepower. The brake horsepower of a pump is the actual motor input horsepower required to produce the hydraulic horsepower from a pump (flow and head) taking into account the losses incurred within the pump due to friction, leakage, etc. Brake horsepower is the ratio of hydraulic horsepower to pump efficiency.

Branch. An addition to the main pipe in a piping system.

BRC - Budget Review Committee, Bureau Procurement Chief.

BRD - USGS Biological Resources Division (formerly NBS).

Breach. A gap, rift, hole, or rupture in a dam; providing a break; allowing water stored behind a dam to flow through in an uncontrolled and unplanned manner. An eroded opening through a dam which drains the reservoir. A controlled breach is a constructed opening. An uncontrolled breach is an unintentional opening which allows uncontrolled discharge from the reservoir.

Breach hydrograph. A flood hydrograph resulting from a dam breach.

Breccia (volcanic breccia). Conglomerate-like rock made up of angular pieces of volcanic rock usually bound in volcanic ash.

Brecciated. A rock made up of highly angular, coarse fragments.

Breeding density. Density of sexually mature organisms in a given area during the breeding period.

Breeding potential. Maximum rate of increase in numbers of individuals of a species or population under optimum conditions.

Breeding rate. Actual rate of increase of new individuals in a given population; the breeding potential minus limiting factors.

Bridge, Class A. A bridge located on a Federal-aid highway. Examination of this type of bridge is required every 2 years with an in-depth examination every 6 years.

Bridge, Class B. A bridge not located on a Federal-aid highway that is used by the public. Examination of this type of bridge is required every 3 years.

Bridge, Class C. A bridge not located on a Federal-aid highway that can be designated as being a private or operating bridge and could be gated or closed to the public, if desired.

British thermal units (Btu). Quantity of heat required to raise the temperature of one avoirdupois pound of water 1 degree F at or near 39.2 degrees F. A standard unit for measuring the quantity of heat required to raise the temperature of 1 pound of water by 1 degree Fahrenheit.

BRM - business reply mail.

Broad-crested weir. An overflow structure on which the nappe is supported for an appreciable length in the direction of flow. See weir.

Brownout. The partial reduction of electrical voltages. A brownout results in lights dimming and motor-driven devices slowing down. See blackout.

BSC - base safety condition.

BSO - Business Services Office.

BTU - British Thermal Units.

Bucket. A part of an excavator which digs, lifts, and carries dirt.

Budget Review Committee (BRC). An ad hoc committee of representatives from each Region, the Reclamation Service Center, and the Washington Office, coordinates Reclamation budget activities through the formulation phase.

BUDS - business utilization development specialist.

Buffer strips (filter strips, vegetated filter strips, grassed buffers). Strips of grass or other close-growing vegetation that separates a waterway (ditch, stream, creek) from an intensive land use area (subdivision, farm).

Built environment. Human- modified environment, e.g. buildings, roads, and cities. See cultural resource.

Bulkhead. A one-piece fabricated steel unit which is lowered into guides and seals against a frame to close a water passage in a dam, conduit, spillway, etc. An object used to isolate a portion of a waterway for examination, maintenance, or repair. A wall or partition erected to resist ground or water pressure.

Bulkhead gate. A gate used either for temporary closure of a channel or conduit before dewatering it for inspection or maintenance or for closure against flowing water when the head difference is small (e.g., for diversion tunnel closure).

Bulking. The increase in volume of a material due to manipulation. Rock bulks upon being excavated; damp sand bulks if loosely deposited, as by dumping, because the apparent cohesion prevents movement of the soil particles to form a reduced volume.

Bureau of Indian Affairs (BIA). The Bureau of Indian Affairs' mission is to enhance the quality of life, to promote economic opportunity, and to carry out the responsibility to protect and improve the trust assets of American Indians, Indian tribes, and Alaska Natives. BIA is an agency within the U.S. Department of the Interior.

Bureau of Land Management (BLM). The Bureau of Land Management, an agency within the U.S. Department of the Interior, administers 264 million acres of America's public lands, located primarily in 12 Western States. The BLM sustains the health, diversity, and productivity of the public lands for the use and enjoyment of present and future generations.

Bureau of Reclamation (USBR, Reclamation, BOR). The mission of the Bureau of Reclamation is to manage, develop, and protect water and related resources in an environmentally and economically sound manner in the interest of the American public.

Burden. In blasting, the distance between the free face and the first row of holes or the distance between rows of holes parallel to the face. Apparent burden is the burden as outlined by the delay pattern.

Bus (buswork). A conductor, or group of conductors, that serve as a common connection for two or more electrical circuits. In powerplants, buswork comprises the three rigid single-phase connectors that interconnect the generator and the step-up transformer(s).

Busbar. A heavy metal conductor used to carry a large current.

Butt joint (open joint). In pipe, flat ends that meet but do not overlap.

Butterfly valve. A valve designed for quick closure that consists of a circular leaf, slightly convex in form, mounted on a transverse shaft carried by two bearings.

Buttress dam. A dam consisting of a watertight upstream part (such as a concrete sloping slab) supported at intervals on the downstream side by a series of buttresses (walls normal to the axis of the dam). Buttress dams can take many forms. See arch-buttress dam, flat slab or slab and buttress dam, massive head buttress dam, multiple arch dam, and solid head buttress dam.

BW - body weight.

°C - degrees Celsius.

Cairn. A pile of stones used as a marker.

Caisson. A box or chamber used in construction work under water. A structure or chamber which is usually sunk or lowered by digging from the inside. Used to gain access to the bottom of a stream or other body of water.

Calcite. Light-colored mineral composed of calcium carbonate that often fills veins in igneous rocks and forms the sedimentary rock limestone.

Caldera (crater). Large circular depression formed by explosion or collapse of a volcano.

Camber. The extra height added to the crest of embankment dams to ensure that the freeboard will not be diminished by foundation settlement or embankment consolidation. The amount of camber is different for each dam and is dependent on the amount of foundation settlement and embankment expected to occur.

Canal. A channel, usually open, that conveys water by gravity to farms, municipalities, etc.

Canal headworks. The beginning of a canal.

Canal prism. The shape of the canal as seen in cross section.

Candidate species. Plant or animal species that are candidates for designation as endangered (in danger of becoming extinct) or threatened (likely to become endangered), but is undergoing status review by the U.S. Fish and Wildlife Service (FWS).

Capability. The maximum load that a generating unit, generating station, or other electrical apparatus can carry under specified conditions for a given period of time without exceeding approved limits of temperature and stress.

Capable fault. An active fault that is judged capable of producing macro-earthquakes and exhibits one or more of the following characteristics:

(1) Movement at or near the ground surface at least once within the past 35,000 years.

(2) Macroseismicity (3.5 magnitude Richter or greater) instrumentally determined with records of sufficient precision to demonstrate a direct relationship with the fault.

(3) A structural relationship to a capable fault such that movement on one fault could be reasonably expected to cause movement on the other.

(4) Established patterns of microseismicity that define a fault, with historic macroseismicity that can reasonably be associated with that fault.

Capacity. In power terminology, the load for which a generator, transmission line, or system is rated, expressed in kilowatts. The amount of electric power delivered or required for which a generator, turbine, transformer, transmission circuit, station, or system is rated by the manufacturer. The maximum load that a machine, station, or system can carry under existing service conditions. Equivalent terms: peak capability, peak generation, firm peak load, carrying capability. In transmission, the maximum load a transmission line is capable of carrying. See excess capacity and peaking capacity. Also refers to powerplant generation capability under specific operating conditions and the amount of marketable resource under such conditions.

Capillary action (capillarity). The rise or movement of water in the interstices of a soil or rock due to capillary forces. The process by which water rises through rock, sediment or soil caused by the cohesion between water molecules and an adhesion between water and other materials that pulls the water upward. A property of surface tension that draws water upwards. See capillary movement.

Capillary attraction (capillary force). The tendency of water to move into fine spaces, as between soil particles, regardless of gravity.

Capillary forces. The molecular forces which cause the movement of water through very small spaces.

Capillary fringe zone. The zone above the free water elevation in which water is held by capillary action. The porous material just above the water table which may hold water by capillarity in the smaller void spaces.

Capillary head. The potential, expressed in head of water, that causes the water to flow by capillary action.

Capillary migration (capillary flow). The movement of water by capillary action.

Capillary movement. Movement of underground water in response to capillary attraction. See capillary action.

Capillary rise. The height above a free water elevation to which water will rise by capillary action.

Capillary water. Underground water held above the water table by capillary attraction. Water subject to the influence of capillary action.

Capital costs. Costs (usually long-term debt) of financing construction and equipment. Capital costs are usually fixed, one-time expenses which are independent of the amount of water produced. All the implements, equipment, machinery and inventory used in the production of goods and services.

Capital investment. A general term used to identify any money amount which is to be considered as an investment as opposed to an annual expense. Can be either interest bearing or non interest bearing.

Carnivore. Any flesh-eating or predatory organism.

Carry over. The quantity of water which continues past an inlet.

Cartography. Art and science of graphically representing the features of the Earth's surface; synonymous with map making.

Casing. A pipe lining for a drilled hole. The material that is installed in wells to prevent the collapse of the walls of the bore hole, to prevent pollutants from entering the well, and to house the pump and pipes.

Catastrophe. A sudden and great disaster causing misfortune, destruction, or irreplaceable loss extensive enough to cripple activities in an area.

Catch. At a recreational fishery, refers to the number of fish captured, whether they are kept or released.

Catchment basin. Unit watershed; an area from which all the drainage water passes into one stream or other body of water.

Cathode. The negative pole or electrode of an electrolytic cell or system. The cathode attracts positively charged particles or ions (cations). See anode.

Cathodic protection. An electrical system for prevention of rust, corrosion, and pitting of metal surfaces which are in contact with water or soil. A low-voltage current is made to flow through a liquid (water) or a soil in contact with the metal in such a manner that the external electromotive force renders the metal structure cathodic. This concentrates corrosion on auxiliary anodic parts which are deliberately allowed to corrode instead of letting the structure corrode.

Cation. A positively charged ion in an electrolyte solution, attracted to the cathode under the influence of a difference in electrical potential. See anion.

Caulk. The material used to seal joints.

Cavitation. The formation of partial vacuums in fast-flowing water caused by subatmospheric pressures immediately downstream from an obstruction or offset. Usually accompanied by noise and vibration. The formation of voids or cavities caused in a liquid due to turbulence or temperature which causes the pressure in local zones of the liquid to fall below the vapor pressure. This happens on the backside of ship propellers, water turbines, blades in pumps, in high-velocity flow lines, and similar locations, depending on the design of equipment and degree of turbulence. The formation and collapse of a gas pocket or bubble on the blade of an impeller or the gate of a valve. The collapse of this gas pocket or bubble drives water into the impeller or gate with a terrific force that can cause pitting on the impeller or gate surface. Cavitation is accompanied by loud noises that sound like someone is pounding on the impeller or gate with a hammer. The attack on surfaces caused by subatmospheric pressures immediately downstream from an obstruction or offset. Usually accompanied by noise and vibration.

Cavitation damage. Damage caused when partial vacuums formed in a liquid by a swiftly moving solid body (e.g. a propeller) pit and wear away solid surfaces (e.g. metal or concrete). The attack on surfaces caused by the implosion of bubbles of water vapor.

Cellular gravity dam. See hollow gravity dam.

Celsius (C), (°C). Unit of temperature. Degrees Celsius equals (5/9)x(degrees Fahrenheit-32).

Central flyway. An important international migration route for many birds.

Centrifugal pump. A pump that moves water by centrifugal force developed by rapid rotation of an impeller. A pump consisting of an impeller fixed on a rotating shaft that is enclosed in a casing, and having an inlet and discharge connection. As the rotating impeller whirls the water around, centrifugal force builds up enough pressure to force the water through the discharge outlet. The rotating impeller imparts energy to the water.

Certification signature. Certification signatures are those of the persons who co-facilitated the risk analysis. These signatures signify that Reclamation methodology, processes, and requirements were followed. In addition, these signatures verify that qualifications of the persons making various probability estimates were appropriate. The purpose of endorsing qualifications is to reduce the potential for inappropriate estimates, or conflicts, arising from limited qualifications that might result in total rejection of risk analysis findings. Certification signatures also signify that the spirit of the risk analysis and team dynamics are represented by the document. In other words, any divergent views, critical issues or significant influencing factors have been captured. This is a check of the author's responsibility to fully capture and represent the team's thinking.

Certified water right. A State-issued document that serves as legal evidence that an approved application has been physically developed and the water put to beneficial use. The certificate establishes: priority date, type of beneficial use, and the maximum amount of water that can be used. Verification must be provided to the State through a survey conducted by an approved water-rights examiner. Even certified rights are subject to occasional review to ensure continued beneficial use.

Chamfer. To bevel or slope an edge or corner.

Channel. Natural or artificial watercourse of perceptible extent, with a definite bed and banks to confine and conduct continuously or periodically flowing water. Rivers and streams. A general term for any natural or artificial facility for conveying water.

Channel margin deposits. Narrow sand deposits which line channel banks.

Check dam. A small dam designed to retard the flow of water and sediment in a channel, used especially to control soil erosion. Small barrier constructed in a gully or other small watercourse to decrease flow velocity, minimize channel scour, and promote deposition of sediment.

Check structure. A structure used to regulate the upstream water surface and control the downstream flow in a canal.

Check valve. Any device which will allow fluid or air to pass through it in only one direction. A special valve with a hinged disc or flap that opens in the direction of normal flow and is forced shut when flows attempt to go in the reverse or opposite direction of normal flow. A device preventing backflow in pipes. Water can flow readily in one direction but any reversal of the flow causes the check valve to close.

Checked signature. Checked signatures verify that all probability estimates, inputs and outputs and their distributions, were entered correctly into event trees, and that any other calculations, figures, or tables have been checked. This includes "back-of-the-envelope" calculations performed during the risk analysis but not documented in any place but the report. In addition, the accuracy of computer spreadsheets have been checked.

Chimney drain. A vertical or inclined layer of pervious material in an embankment to facilitate and control drainage of the embankment fill.

Chironomid. Group of two-winged flying insects who live their larval stage underwater and emerge to fly about as adults.

Chipping. Loosening of shallow rock by light blasting or air hammers.

Chisel plowing. Cropland preparation by a special implement (chisel) that avoids complete inversion of the soil (as occurs with conventional moldboard plowing). Chisel plowing can leave a protective cover of crop residues on the soil surface that helps prevent erosion and improve infiltration.

Chlorination. The application of chlorine to water, generally for the purpose of disinfection, but frequently for accomplishing other biological or chemical results (aiding coagulation and controlling tastes and odors).

Chute. Portion of spillway between the gate or crest structure and the terminal structure, where open- channel flow conditions will exist. A conduit for conveying free-flowing materials at high velocity to lower elevations.

Cipolletti weir (trapezoidal weir). A contracted weir of trapezoidal shape in which the sides of the notch are given a slope of 1 horizontal to 4 vertical.

Circle of influence. The circular outer edge of a depression produced in the water table by the pumping of water from a well. See cone of influence.

Circuit. The complete path of an electric current, including the generating apparatus or other source; or, a specific segment or section of the complete path.

Circuit breaker. A safety device in an electrical circuit that automatically shuts off the circuit when it becomes overloaded. The device can be manually reset.

Circuit mile. For single circuit electric power transmission lines, circuit miles are equal to geographic miles or pole miles. For double circuit transmission lines, the number of circuit miles is twice the structure, pole, or geographic miles.

Cirque. Bowl-like depression carved into a mountaintop by ice at the head of a glacier.

Cistern. A small tank (usually covered) or a storage facility used to store water for a home or farm. Often used to store rain water.

Civil Defense Agency. State and/or local agency responsible for emergency operations, planning, mitigation, preparedness, response, and recovery for all hazards. Usually, the more current term of emergency management agency is used.

Cladophora. Filamentous green alga.

Clam shell gate. High pressure regulating gate consisting of two curved leaves which open and close over the end of a conduit. Used for free discharge into air with minimal cavitation damage.

Class (pipe and fittings). The working pressure rating of a specific pipe for use in water distribution systems which includes allowances for surges. This term is used for cast iron, ductile iron, asbestos cement, and some plastic pipe.

Clay. Fine-grained soil or the fine-grained portion of soil that can be made to exhibit plasticity (putty-like properties) within a range of moisture contents, and that exhibits considerable strength when air-dry. Plastic soil which passes a No. 200 (0.075 mm) United States Standard sieve.

Clay size. That portion of the soil finer than 0.002 mm (0.005 mm in some cases).

Clean Water Act. See Federal Water Pollution Control Act of 1948.

Clearance. A procedure used to establish, under tightly controlled discipline, a safe environment for maintenance, repair, or inspection. It includes systematically isolating pertinent equipment from all sources of hazardous energy (hydraulic, electrical, mechanical, pneumatic, chemical, etc.) and attaching safety tags or locks to the appropriate controls. Also, it includes a written statement that documents isolation of the equipment (also referred to as lockout or tagout).

Clearing. The removal of all vegetation such as trees, shrubs, brush, stumps, exposed roots, down timber, branches, grass, and weeds. The removal of all rubbish and all other objectionable material. See grubbing.

Climate. Average conditions of the weather over a number of years. See macroclimate and microclimate.

Climatic year. Continuous 12-month period during which a complete climactic cycle occurs.

Coarse gravel protection. Gravel generally placed in a layer upon a finished surface to protect the finished surface from deterioration or erosion.

Coaster gate. A rectangular gate similar in construction and appearance to the tractor gate except sealing is accomplished in much the same way as a ring seal gate.

Coating. The protective material applied to the outer surface of a material, frequently metalwork.

Cobble (cobblestone). A rock fragment, usually rounded or semirounded, with an average dimension between 3 to 12 inches; will pass a 12-inch screen, but not a 3-inch screen. A particle of rock that will pass a 12-inch (300-mm) square opening and be retained on a 3-inch (75-mm) U.S.A. Standard sieve.

Coefficient of compressibility. The slope of a one-dimensional compression curve relating void ratio to effective stress.

Coefficient of consolidation. A coefficient that relates the change in excess pore pressure with time to the excess pore pressure diffusion in the soil mass in terms of soil mass and pore fluid characteristics.

Cofferdam. A temporary structure enclosing all or part of the construction area so that construction can proceed in the dry. A diversion cofferdam diverts a river into a pipe, channel or tunnel. A temporary barrier, usually an earthen dike, constructed around a worksite in a reservoir or on a stream, so the worksite can be dewatered or the water level controlled. See dam.

Cogenerator. A generating facility that produces electricity and another form of useful thermal energy (such as heat or steam), used for industrial, commercial, heating, or cooling purposes. To receive status as a qualifying facility (QF) under the Public Utility Regulatory Policies Act (PURPA), the facility must produce electric energy and "another form of useful thermal energy through the sequential use of energy," and meet certain ownership, operating, and efficiency criteria established by the Federal Energy Regulatory Commission (FERC). (See the Code of Federal Regulations, Title 18, Part 292.)

Cohesion. The mutual attraction of soil particles due to molecular and capillary forces in the presence of water. Cohesion is high in clay (especially dry) but of little significance in silt or sand. The ability of a substance to stick to itself and pull itself together. Molecular attraction which holds two particles together.

Cohesionless materials (cohesionless soil). Soil materials that when unconfined have little or no strength when air-dried and that have little or no cohesion when submerged. Soil that has little tendency to stick together whether wet or dry, such as sands and gravels.

Cohesive soil. Predominantly clay and silt soil, fine-grained particles, that sticks together whether wet or dry. A soil that, when unconfined, has considerable strength when air-dried, and that has significant cohesion when submerged.

Cold joint. An unplanned joint resulting when a concrete surface hardens before the next batch is placed against it. Fresh concrete placed on harden concrete.

Cold-water fishery. Water or water system which has an environment suitable for salmonoid fishes.

Coliform. Organisms common to the intestinal tract of humans and animals; the organisms' presence in waste water is an indicator of pollution.

Collar. The open end of a drill hole.

Collaring. Starting a drill hole. When the hole is deep enough to hold the bit from slipping out of it, it is said to be collared.

Colloidal particles. Soil particles that are so small that the surface activity has an appreciable influence on the properties of the aggregate. Particles smaller than 0.001 mm.

Colloidal suspension. A method of sediment transport in which water turbulence (movement) supports the weight of the sediment particles, thereby keeping them from settling out or being deposited.

Colluvium. A general term applied to loose and incoherent deposits, usually at the foot of a slope and brought there chiefly by gravity.

Combined cycle plant. A plant which achieves higher efficiency by employing two cycles in tandem. For example, heat rejected from a gas-fired turbine is used to generate steam to operate a steam turbine.

Commercial operation. Commercial operation begins when control of the loading of the generator is turned over to the system dispatcher.

Commercial river trip. Trips organized by boating companies that conduct tours for paying passengers or customers.

Commercial user day. Amount of commercial use within a 24-hour period or any portion thereof.

Commercial water use. Water for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions.

Common excavation. All materials excavated not considered as rock. Boulders or detached pieces of solid rock less than 1 cubic yard in volume are classified as common excavation. See excavation.

Common material. All earth materials which do not fall under the definition of rock.

Community. All members of a specified group of species present in a specific area at a specific time; a group of people that see themselves as a unit.

Community cohesion. Ability of a community to have a unified response when facing a problem; e.g., an external threat to their sustainability.

Compacted backfill. Backfill which has been reduced to bulk by rolling, tamping, or soaking.

Compacted embankment. Embankment which has been reduced in bulk by rolling, tapping, or soaking.

Compaction. To make soil dense by mechanical manipulation. Mechanical action which increases the density by reducing the voids in a material. See dumped, dynamic compaction, jetting, ponding, puddling, rolling, saturation, sluicing, surface vibration, and tamping.

Compaction curve (Proctor curve, moisture-density curve). The curve showing the relationship between the dry density (dry unit weight) and the moisture content of a soil for a given compactive effort.

Compaction test. A laboratory compacting procedure whereby a soil at a known moisture content is placed in a specified manner into a mold of given dimensions, subjected to a compactive effort of controlled magnitude, and the resulting dry unit weight determined. The procedure is repeated for various moisture contents sufficient to establish a relation between moisture content and dry unit weight.

Composite power value. The value of power including both a capacity and energy component, usually expressed in mills per kilowatt-hour.

Comprehensive Facility Review (CFR). A review performed on a high- or significant-hazard dam every 6 years, which includes a field examination and a state-of-the-art review of a structure's design assumptions, construction practices, and integrity under various loading conditions. A detailed examination performed on dams with a senior dam engineer. Comprehensive facility reviews are designed to gather together appropriate technical disciplines for a brief, but intensive assessment of a dam's performance history, the dam safety analyses that have been performed to date, and the current condition of the dam and damsite. The comprehensive facility review covers both O&M and dam safety issues. Comprehensive facility reviews are generally followed every 3 years by a periodic facility review.

Compressibility. Property of a soil descri