Glossary “Water Management”

A B C D E—F G—H I—K L—M N—O P Q—R S—T U—V W—Z

A

A-HORIZON — The uppermost zone in the Soil Profile, from which soluble Salts and Colloids are leached, and in which organic matter has accumulated. Generally this represents the most fertile soil layer. Along with the B-Horizon, this layer constitutes part of the Zone of Eluviation.

ABANDONED WATER RIGHT — A water right which has not been put to Beneficial Use for generally five or more years, in which the owner of the water right states that the water right will not be used, or takes such actions that would prevent the water from being beneficially used. Compare to Forfeited Water Right.

ABANDONED WELL — A well which is no longer used or a well removed from service; a well whose use has been permanently discontinued or which is in a state of such disrepair that it cannot be used for its intended purpose. Generally, abandoned wells will be filled with concrete or cement grout to protect groundwater from waste and contamination.

ABANDONMENT — Failure to put a water right to Beneficial Use for generally five or more years, in which the owner of the water right states that the water right will not be used, or takes such actions that would prevent the water from being beneficially used. Also see Abandoned Water Right.

ABANDONMENT OF A DAM — In a legal sense, abandonment is most precisely described as transfer of all rights, title and interest in a dam to the current property owner. Abandonment may also involve the slow but resolute erosion of rights to a dam by non-use, physical destruction, lack of maintenance or intent of same. In this latter instance the final determination of legal abandonment can only be decided by the court holding jurisdiction.

ABSORPTION — (1) The entrance of water into the soil or rocks by all natural processes, including the infiltration of precipitation or snowmelt, gravity flow of streams into the valley alluvium into sinkholes or other large openings, and the movement of atmospheric moisture. (2) The uptake of water or dissolved chemicals by a cell or an organism (as tree roots absorb dissolved nutrients in soil). (3) More generally, the process by which substances in gaseous, liquid, or solid form dissolve or mix with other substances. Not to be confused with Adsorption.

ABSOLUTE HUMIDITY — The actual weight of water vapor contained in a unit volume of the atmosphere, usually expressed in grams of water per kilogram of air. Compare to Relative Humidity.

ABUTMENT (of a Dam) — The part of a valley side wall against which a dam is constructed. 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. Right and left abutments are designated as one looks downstream.

ACRE FOOT — The volume of water required to cover one acre of land to a depth of one foot (43,560 cubic feet or 325,851 gallons).

ADEQUATE-SIZE FARM — A farm with resources and productivity sufficient to generate enough income to (a) provide an acceptable level of family living; (b) pay current operating expenses and interest on loans; and (c) allow for capital growth to keep pace with technological growth.

ADMINISTERED GROUNDWATER BASIN — A groundwater basin (watershed, area, or sub-area) which, in the interest of public welfare, is monitored by an appropriate agency to insure adequate water resources for prescribed uses. Quite often, such basins will have Preferred Uses designated for future development to insure that the basin's Perennial Yield is not exceeded. Also referred to as Designated Groundwater Basin.

AERATION (UNSATURATED) ZONE — The zone between the land surface and the water table which characteristically contains liquid water under less than atmospheric pressure and water vapor and air or other gases at atmospheric pressure. The term Unsaturated Zone is now generally applied.

AFFLUENT (Lake) — A tributary or feeder stream. Streams receiving the run-off from the watershed and flowing into the lake are its affluents; analogous to the affluent of a river. The analogy can be very close where a lake has large inflowing and outflowing streams and is located in a valley or elongated basin. In usage, the term may have the same meaning as influent; although where the reference is to a single inflowing stream, the word influent appears to be the preferred one.

AFFLUENT (Stream) — A stream or river that flows into a larger one; a Tributary.

AFFORESTATION — The artificial establishment of forest crops by planting or sowing on land that has not previously, or recently, grown trees

AFLOAT — Floating on water.

AFTERBAY — The tail race or reservoir of a hydroelectric power plant at the outlet of the turbines used to regulate the flow below the plant; may refer to a short stretch of stream or conduit, or to a pond or reservoir.

AGE (of Groundwater) — An approximation of the time between the water's penetration of the land surface at one location and its later presence at another location.

AGGRADATION — (1) The build-up of sediments at the headwaters of a lake or reservoir or at a point where streamflow slows to the point that it will drop part or all of its sediment load. (2) Modification of the earth's surface in the direction of uniformity of grade or slope, by Deposition, as in a river bed.

AGGRADING — The building up of a stream channel which is flowing too slowly to carry its sediment load.

AGGRESSIVE WATER — Water which is soft and acidic and can corrode plumbing, piping, and appliances.

AGRIBUSINESS — The sum of all operations involved in the production, storage, processing, and wholesale marketing of agricultural products.

AGRICULTURAL — Having to do with farming or farms.

AGRICULTURAL CAPABILITY — Determines, given the ideal state, what a given area of land is capable of producing in terms of agricultural production and output.

AGRICULTURAL DRAINAGE — (1) The process of directing excess water away from the root zones of plants by natural or artificial means, such as by using a system of pipes and drains placed below ground surface level. Also referred to as Subsurface Drainage. (2) The water drained away from irrigated farmland.

AGRICULTURAL ECONOMICS — The application of economic principles to the Agribusiness sector of the economy.

AGRICULTURAL LAND — Land in farms regularly used for agricultural production; all land devoted to crop or livestock enterprises, for example, farmstead lands, drainage and irrigation ditches, water supply, cropland, and grazing land.

AGRICULTURAL LEVEE — A levee that protects agricultural areas where the degree of protection is usually less than that of a flood control levee.

AGRICULTURAL POLLUTION — Liquid and solid wastes from all types of farming, including runoff from pesticides, fertilizers, and feedlots; erosion and dust from plowing; animal manure and carcasses; and crop residues and debris.

AGRICULTURAL RESTRUCTURING SCENARIO (ARS) — A term used to describe the sensitivity of agricultural water demand and farm marketing revenues to changes in certain cropping patterns.

AGRICULTURAL RUNOFF — The runoff into surface waters of herbicides, fungicides, insecticides, and the nitrate and phosphate components of fertilizers and animal wastes from agricultural land and operations. Considered a Non-Point Source (NPS) of water pollution.

AGRICULTURAL SUITABILITY — Determines how suitable a given area of land is, in it's present state, for agricultural purposes.

AGRICULTURAL USE — The use of any tract of land for the production of animal or vegetable life; uses include, but are not limited to, the pasturing, grazing, and watering of livestock and the cropping, cultivation, and harvesting of plants.

AGRICULTURAL WATER USE — Includes water used for irrigation and non-irrigation purposes. Irrigation water use includes the artificial application of water on lands to promote the growth of crops and pasture, or to maintain vegetative growth in recreational lands, parks, and golf courses. Non-irrigation water use includes water used for livestock, which includes water for stock watering, feedlots, and dairy operations, and fish farming and other farm needs.

AGRO-ECOSYSTEM — Land used for crops, pasture, and livestock; the adjacent uncultivated land that supports other vegetation and wildlife; and the associated atmosphere, the underlying soils, ground and surface waters, irrigation channels, and drainage networks.

AGROINDUSTRIAL — Of or relating to production (as of power for industry and water for irrigation) for both industrial and agricultural purposes.

AIR STRIPPING — (Water Quality) A process for the removal of organic contaminants from groundwater. The groundwater flows downward inside a tower filled with materials (the packing) over a large surface area. Air is introduced at the bottom of the tower and is forced upward past the falling water. Individual organic contaminants are transferred from the water to the air, according to the gas and water equilibrium concentration values of each contaminant. Also referred to as Packed Tower Aeration.

AIR VENT (of a Dam) — A pipe designed to provide air to the outlet conduit to reduce turbulence and prevent negative pressures during the release of water. Extra air is usually necessary downstream of constrictions.

ALKALI — Any strongly basic (high pH) substance capable of neutralizing an acid, such as soda, potash, etc., that is soluble in water and increases the pH of a solution greater than 7.0. Also refers to soluble salts in soil, surface water, or groundwater.

ALKALI LAKES — Those containing water very highly impregnated with alkalies. The "alkali" may be sodium carbonate or sodium sulfate and potassium carbonate but includes other alkaline compounds as well. Restricted to arid and semi-arid regions. See: Potash lakes and Soda lakes.

ALKALINE — Sometimes water or soils contain an amount of Alkali substances sufficient to raise the pH value above 7.0 and be harmful to the growth of crops. Generally, the term alkaline is applied to water with a pH greater than 7.4.

ALKALINITY — The capacity of water for neutralizing an acid solution. Alkalinity of natural waters is due primarily to the presence of hydroxides, bicarbonates, carbonates and occasionally borates, silicates and phosphates. It is expressed in units of milligrams per liter (mg/l) of CaCO3 (calcium carbonate) or as microequivalents per liter (µeq/l) 20 µeq/l = 1 mg/l of CaCO₃. A solution having a pH below 4.5 contains no alkalinity. Low alkalinity is the main indicator of susceptibility to acid rain. Increasing alkalinity is often related to increased algal productivity. Lakes with watersheds that have sedimentary carbonate rocks are high in dissolved carbonates (hard-water lakes). Whereas lakes in granite or igneous rocks are low in dissolved carbonates (soft water lakes).

ALLUVIAL — An adjective referring to soil or earth material which has been deposited by running water, as in a riverbed, flood plain, or delta.

ALLUVIAL DAM LAKES — Numerous basins which are the sites of both existing and extinct lakes in the arid regions of western U. S. were formed by alluvial dams, especially by the coalescence of fans composed of detritus carried down by streams from opposite sides of valleys. In glaciated regions dams were formed in valleys by glacio-fluvial deposition during the Pleistocene; and barriers of various kinds, which impound water have been created in river flood plains by alluvial deposition.

ALLUVIAL GROUNDWATER — Ground water that is hydrologically connected to a surface stream that is present in permeable geologic material, usually small rock and gravel.

ALLUVIAL LAND — Areas of unconsolidated alluvium, generally stratified and varying widely in texture, recently deposited by streams, and subject to frequent flooding.

AMBIENT WATER QUALITY STANDARDS — The allowable amount of materials, as a concentration of pollutants, in water. The standard is set to protect against anticipated adverse effects on human health or welfare, wildlife, or the environment, with a margin of safety in the case of human health.

ANNUAL FLOOD — The highest peak discharge of a stream in a Water Year.

ANNUAL FLOOD SERIES — A list of annual floods for a given period of time.

ANNUAL LOW-FLOW — The lowest flow occurring each year, usually the lowest average flow for periods of perhaps 3, 7, 15, 30, 60, 120, or 180 consecutive days.

ANTECEDENT PRECIPITATION — Precipitation which occurred prior to a particular time over a specific area or Drainage Basin. Usually applied as a measure of moisture in the top layer of the soil which would affect runoff from additional rainfall.

ANTECEDENT PRECIPITATION INDEX (API) — An index of moisture stored in a basin before a storm, calculated as a weighted summation of past daily precipitation amounts.

ANTECEDENT SOIL WATER — Degree of wetness of a soil prior to irrigation or at the beginning of a runoff period, typically expressed as an index.

ANTECEDENT STREAMS — Antecedent streams are those in place before the rising of mountain chains. As the mountains rise, the streams cut through at the same rate and so maintain their positions.

APPLIED WATER DEMAND — The quantity of water delivered to the intake of a city's water system or factory, the farm headgate, or a marsh or other wetland, either directly or by incidental drainage. For in-stream use, it is the portion of the stream flow dedicated to in-stream use or reserved under federal or state Wild and Scenic River Acts. Applied water includes the water that returns to groundwater, a stream, canal, or other supply source that can be reused or recycled and thus is not the same as Net Water Demand.

APPURTENANT STRUCTURES (of a Dam) — Auxiliary features of a dam such as an outlet, spillway, powerhouse, tunnel, etc.

AQUIFER — A geologic formation, a group of formations, or a part of a formation that is water bearing. A geological formation or structure that stores or transmits water, or both, such as to wells and springs. Use of the term is usually restricted to those water-bearing structures capable of yielding water in sufficient quantity to constitute a usable supply.

AQUIFER, BASIN-FILL — An aquifer located in a basin surrounded by mountains and composed of sediments and debris shed from those mountains. Sediments are typically sand and gravel with some clay.

AQUIFER SYSTEM — A body of permeable and relatively impermeable materials that functions regionally as a water-yielding unit. It comprises two or more permeable units separated at least locally by confining units (Aquitards) that impede ground-water movement but do not greatly affect the regional hydraulic continuity of the system. The permeable materials can include both saturated and unsaturated sections.

ARABLE LAND — Land capable of being cultivated and suitable for the production of crops.

ARCH DAM — Curved masonry or concrete dam, convex in shape upstream, that depends on arch action for its stability; the load or water pressure is transferred by the arch to the Abutments.

AREA-CAPACITY CURVE — A graph showing the relation between the surface area of the water in a reservoir and the corresponding volume.

AREA FLOODED — Area of a floodplain that is flooded in a specific stream reach, watershed, or river basin; may be for a single flood event, but is usually expressed as an average, annual value based on the sum of areas from all individual flood events over a long period of time, such as 50 to 100 years, and adjusted to an average value.

AREA (SUB-AREA), HYDROGRAPHIC — Primarily these are sub-drainage systems, typically valleys, within a more comprehensive drainage basin. Hydrographic Areas (Valleys) may be further subdivided into Hydrographic Sub-Areas based on unique hydrologic characteristics (e.g., differences in surface flows) within a given valley or area.

AREA OF A LAKE — The space occupied by the water surface. The area of a lake, generally, is something that cannot be determined with great exactitude; often the figure given is an arbitrary one, and figures from different sources show considerable disagreements. This comes about, because some error is inherent in any of the procedures devised for determining area; because measurements may be made from hydrographic maps which differ in accuracy and detail, and in time at which the map was made. This latter becomes important where lakes fluctuate greatly in levels. Some differences may arise also where different mathematical procedures are followed in making measurements. Also, often arbitrary decisions must be made as to location of shore line, the inclusion or exclusion of islands, and boundaries between a lake and connecting water, all of which consequently affect the computed area. Area is usually expressed square miles and acres; or where the metric system is used in square kilometers and square meters.

ARTESIAN — A commonly used expression, generally synonymous with Confined and referring to subsurface (ground) bodies of water which, due to underground drainage from higher elevations and confining layers of soil material above and below the water body (referred to as an Artesian Aquifer), result in underground water at pressures greater than atmospheric.

ARTESIAN AQUIFER — A commonly used expression, generally synonymous with (but a generally less favored term than) Confined Aquifer. An artesian aquifer is an aquifer which is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which ground water is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself.

ARTESIAN PRESSURE — The pressure under which Artesian Water in an Artesian Aquifer is subjected, generally significantly greater than atmospheric.

ARTESIAN WATER — Ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called Artesian Pressure, and the formation containing artesian water is an Artesian Aquifer or Confined Aquifer.

ARTESIAN WELL — (1) A well bored down to the point, usually at great depth, at which the water pressure is so great that the water is forced out at the surface. The name is derived from the French region of Artois, where the oldest well in Europe was bored in 1126. (2) A well tapping a Confined or Artesian Aquifer in which the static water level stands above the top of the aquifer. The term is sometimes used to include all wells tapping confined water. Wells with water levels above the unconfined water table are said to have positive artesian head (pressure) and those with water level below the unconfined water table, negative artesian head. If the water level in an artesian well stands above the land surface, the well is a Flowing Artesian Well. If the water level in the well stands above the water table, it indicates that the artesian water can and probably does discharge to the unconfined water body.

ARTESIAN ZONE — A zone where water is confined in an aquifer under pressure so that the water will rise in the well casing or drilled hole above the bottom of the confining layer overlying the aquifer.

ARTIFICIAL RECHARGE — The designed (as per man's activities as opposed to the natural or incidental) replenishment of ground water storage from surface water supplies such as irrigation or induced infiltration from streams or wells. There exist five (5) common techniques to effect artificial recharge of a groundwater basin:
[1] Water Spreading consisting of the basin method, stream-channel method, ditch method, and flooding method, all of which tend to divert surface water supplies to effect underground infiltration;
[2] Recharge Pits designed to take advantage of permeable soil or rock formations;
[3] Recharge Wells which work directly opposite of pumping wells, although they generally have limited scope and are better used for deep, confined aquifers;
[4] Induced Recharge which results from pumping wells near surface supplies, thereby inducing higher discharge towards the well; and
[5] Wastewater Disposal which includes the use of secondary treatment wastewater in combination with spreading techniques, recharge pits, and recharge wells to reintroduce the water into deep aquifers thereby both increasing the available groundwater supply and also further improving the quality of the wastewater.
Also referred to as Induced Recharge. Also see Natural Recharge, Incidental Recharge, Injection, and Perennial Yield.

ASSIGNMENT OF WATER — The transfer of a water right application or permit from one person to another. This can be done in conjunction with the sale of land.

AVAILABLE WATER — The portion of water in a soil that can be absorbed by plant roots, usually considered to be that water held in the soil against a tension of up to approximately 15 atmospheres.

AVAILABLE WATER HOLDING CAPACITY — The capacity of a soil to hold water in a form available to plants. Also, the amount of moisture held in the soil between field capacity, or about one-third atmosphere of tension, and the wilting coefficient, or about 15 atmospheres of tension.

AVERAGE ANNUAL FLOOD DAMAGES — The weighted average of all flood damages that would be expected to occur yearly under specified economic conditions and development. Such damages are computed on the basis of the expectancy in any one year of the amounts of damage that would result from floods throughout the full range of potential magnitude.

AVERAGE ANNUAL RECHARGE — The amount of water entering an aquifer on an average annual basis. In many, if not most, hydrologic conditions, "average" has little significance for planning purposes as there may exist so few "average" years in fact.

AVERAGE ANNUAL RUNOFF (YIELD) — The average of water-year (October 1-September 30) runoff or the supply of water produced by a given stream or water development project for a total period of record; measured in cubic feet per second or acre-feet.

AVERAGE DISCHARGE — In the annual series of the U.S. Geological Survey's (USGS) reports on surface-water supply, the arithmetic average of all complete water years of record whether or not they are consecutive. Average discharge is not published for less than 5 years of record. The term "average" is generally reserved for average of record and "mean" is used for averages of shorter periods, namely daily mean discharge.

AVERAGE WATER YEAR — A tern denoting the average annual hydrologic conditions based upon an extended or existing period of record. Because precipitation, runoff, and other hydrologic variables vary from year to year, planners typically project future scenarios based on hydrologic conditions that generally include average, wet (high-water), and drought (low-water) years.

AVERAGE YEAR WATER DEMAND — The demand for water under average hydrologic conditions for a defined level of development.

AVERAGE YEAR WATER SUPPLY — The average annual supply of a water development system over a long period. For a dedicated natural flow, it is the long-term average natural flow for wild and scenic rivers or it is Environmental Flows as required for an average year under specific agreements, water rights, court decisions, and congressional directives.

AXIAL FLOW — Fluid flow in the same direction as the axis of symmetry of the duct, vessel, or tank.

AXIS (of a Dam) — The horizontal centerline of a dam in the longitudinal direction.

B

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 — the backing up of water through a conduit or channel in the direction opposite to normal flow. 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 Back Siphonage.

BACKGROUND — Value for a parameter that represents the conditions in a system prior to a given influence in space or time.

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.

BACKWASH — A backward flow or water, also referred to as Backrush. (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 Gauging, 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. 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 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.

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.

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.

BALL VALVE — A valve regulated by the position of a free-floating ball that moves in response to fluid or mechanical pressure.

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.

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.

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.

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 ELEVATION — The height in relation to mean sea level (MSL) expected to be reached by the waters of the base flood at pertinent points in the floodplain of Riverine areas.

BASE FLOODPLAIN — The floodplain that would be inundated by a one percent chance flood (100-Year Flood).

BASE FLOW — 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. Also referred to as Groundwater Flow.

BASE LEVEL — The lowest level to which a land surface can be reduced by the action of running water.

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.

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.

BASIC — Describing a solution, sediment, or other material that has a pH greater than 7.0. see Alkaline

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) 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. (2) A naturally or artificially enclosed harbor for small craft, such as a yacht basin.

BASIN FILL — Unconsolidated material such as sand, gravel, and silt eroded from surrounding mountains and deposited in a valley.

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 YIELDS — The amount of water which will flow from a drainage or catchment area in a given storm.

BATHYMETRIC MAP — A map showing the depth (bottom contours) of water in lakes, streams, or oceans. Can be used to calculate lake volume.

BATHYMETRY — (1) The measurement of the depth of large bodies of water (oceans, seas, ponds and lakes). (2) The measurement of water depth at various places in a body of water. Also the information derived from such measurements.

BED — (1) An underwater or intertidal area in which a particular organism is established in large numbers. (2) The bottom of a body of water, such as a stream. (Geology) A rock mass of large horizontal extent bounded, especially above, by physically different material (as in Bedrock).

BEHEADED STREAM — The lower section of a stream that has lost its upper portion through diversion or Stream Piracy.

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. 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.

(2) 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 obtained by putting water to a beneficial use. The right may be lost if beneficial use is discontinued. A beneficial use of water is a use which is of benefit to the appropriator and to society as well. The term encompasses considerations of social and economic value and efficiency of use. In the past, most reasonably efficient uses of water for economic purposes have been considered beneficial. Usually, challenges have only been raised to wasteful use or use for some non-economic purpose, such as preserving in-stream values. Recent statutes in some states have expressly made the use of water for recreation, fish and wildlife purposes, or preservation of the environment a beneficial use

BENEFIT-COST RATIO — The relationship of the economic benefits of an action to its total costs.

BENTHIC DEPOSITS — Bottom accumulations which may contain bottom-dwelling organisms and/or contaminants in a lake, harbor, or stream bed.

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.

BILLOW — A large wave or swell of water.

BIODIVERSITY — Refers to the variety and variability of life, including the complex relationships among microorganisms, insects, animals, and plants that decompose waste, cycle nutrients, and create the air that we breathe. Diversity can be defined as the number of different items and their relative frequencies. For biological diversity, these items are organized at many levels, ranging from complete Ecosystems to the biochemical structures that are the molecular basis of heredity. Thus, the term encompasses different ecosystems, species, and genes. It is generally accepted that human survival is dependent upon the conservation and preservation of this diversity of life forms. Typically five levels of biodiversity are recognized:
[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.

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 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.

BLANKET (of a Dam) — A portion of the physical structure of a dam designed to affect the dams hydrologic characteristics, particularly its seepage and strength characteristics. Types of dam blankets include:
[1] Drainage Blanket — A drainage layer placed directly over the dam's foundation material;
[2] Grout Blanket — The injection of grout to consolidate a layer of the foundation, resulting in greater impermeability and/or strength; and
[3] Upstream Blanket — An impervious layer placed on the reservoir floor upstream of a dam; in the case of an Embankment Dam, the blanket may be connected to the impermeable element in the dam itself.

BLENDING — The mixing or combination of one water source with another, typically a finished source of water with raw water to reuse water while still satisfying water quality standards, for example, mixing of product water from a desalting plant with conventional water to obtain a desired dissolved solids content, or mixing brine effluents with sewage treatment plant effluents in order to reduce evaporation pond size.

BLINDS — Water samples containing a chemical of known concentration given a fictitious company name and slipped into the sample flow of the lab to test the impartiality of the lab staff.

BLOWDOWN — The water drawn from boiler systems and cold water basins of cooling towers to prevent the buildup of solids.

BORDER IRRIGATION — A surface method of irrigation by flooding between two confining border levees or dikes. Typically, these borders vary from 100 to 200 feet wide by 1,000 to 3,960 feet long.

BOTTOM — (1) The deepest or lowest part, as the bottom of a well. (2) The solid surface under a body of water. (3) Often Bottoms: Low-lying alluvial land adjacent to a river, also referred to as bottomland. (4) (Nautical) The part of a ship's hull below the water line.

BOTTOMLAND, also Bottom Land (Soils) — A general term describing generally rich, loamy or fine-textured and poorly drained soils, overlying a shallow water table or possibly adjacent to a stream, lake or other body of water, that exhibits relatively good water holding capacity and slow to moderate infiltration of irrigation water; often associated with a river's floodplain.

BOTTOM LAND HARDWOODS — Forested freshwater Wetlands adjacent to rivers in the southeastern United States, especially valuable for wildlife breeding, nesting, and habitat.

BOUNDARY CONDITIONS — Flow conditions imposed at the ends of a pipeline or canal reach by various physical structures, which must be described mathematically to solve the general equation of flow for hydraulic transient computer models.

BOUNDARY LAYER — The layer of reduced velocity in fluids, such as air and water, that is immediately adjacent to the surface of a solid past which the fluid is flowing.

BOUND WATER — Water molecules that are held tightly to soil or other solids. This water is not easily removed by normal drying and is not available for other purposes such as plant growth.

BRACKISH WATER — Generally, water containing dissolved minerals in amounts that exceed normally acceptable standards for municipal, domestic, and irrigation uses. Considerably less saline than sea water. Also, Marine and Estuarine waters with Mixohaline salinity (0.5 to 30 due to ocean salts). Water containing between 1,000-4,000 parts per million (PPM) Total Dissolved Solids (TDS). The term brackish water is frequently interchangeable with Saline Water. The term should not be applied to inland waters.

BRAIDED STREAM — A complex tangle of converging and diverging stream channels (Anabranches) separated by sand bars or islands. Characteristic of flood plains where the amount of debris is large in relation to the discharge.

BRANCH — (1) A tributary of a river or other body of water. (2) A divergent section of a river, especially near the mouth.

BRIDGE — An over the lake, stream or river structure built so that people can get from one side to the other.

BRIM — The upper surface of a body of water.

BRINE — (1) Water saturated with or containing large amounts of a salt, especially of sodium chloride. According to U.S. Geologic Survey (USGS) classification, water classified as brine contains more than 35,000 ppm (parts per million) total dissolved solids (TDS) of salt; (2a) The water of a sea or an ocean; (2b) A large body of salt water. (3) The wastewater resulting from desalting. It is higher in dissolved solid content than feedwater or product water.

BRINE DISPOSAL — Removing water that contains high concentrations of salt.

BROOK — A natural stream of water, smaller than a river or creek; especially a small stream or rivulet which breaks directly out of the ground, as from a spring or seep; also, a stream or torrent of similar size, produced by copious rainfall, melting snow and ice, etc.; a primary stream not formed by tributaries, though often fed below its source, as by rills or runlets; one of the smallest branches or ultimate ramifications of a drainage system.

BURIED DRAIN — A covered drain usually made of clay, concrete, or plastic pipe installed beneath the ground surface at a planned grade and depth for conveyance of excess groundwater.

BUTTRESS DAM — A dam consisting of a watertight upstream face supported at intervals on the downstream side by a series of buttresses.

BYPASS SYSTEM — A structure in a dam that provides a route for fish to move through or around the dam without going through the turbines.