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.