Glossary “Water Management”

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ECHO SOUNDER — A device for measuring the depth of water or the depth of an object below the surface by sending pressure waves down from the surface and recording the time until the echo returns from the bottom.

ECOLOGICAL IMPACT — The effect that a man-made or natural activity has on living organisms and their non-living (abiotic) environment.

ECOLOGICAL INDICATOR — An individual species or a defined assemblage of organisms that serves as a gauge of the condition of the environment. The term is a collective term for response, exposure, habitat, and stressor indicators. For example, the bacterium Escherichia coli indicates the presence of sewage in water, and the mussel, Mytilus edulis lives in polluted waters.

ECOLOGICAL RISK ASSESSMENT — The application of a formal framework, analytical process, or model to estimate the effects of human actions on a natural resource and to interpret the significance of those effects in light of the uncertainties identified in each component of the assessment process. Such analysis includes initial hazard identification, exposure and dose-response assessments, and risk characteristics.

ECOLOGICAL SUCCESSION — An orderly, directional and therefore predictable process of development that involves changes in species structure and community processes over time. It results from a modification of the physical environment by the community and culminates in a stabilized ecosystem in which maximum biomass and symbiotic functions are maintained.

ECOLOGY — The study of the inter-relationships of living things to one another and to the environment.

ECOSPHERE — The mantle of earth and troposphere inhabited by living organisms; the "bio-bubble" that contains life on earth, in surface waters, and in the air. Also see Biosphere.

ECOSYSTEM — A community of animals, plants, and bacteria, and its interrelated physical and chemical environment. 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.

ECOSYSTEM FUNCTIONS — Processes that are necessary for the self-maintenance of an Ecosystem such as primary production, nutrient cycling, decomposition, etc. The term is used primarily as a distinction from values.

ECOSYSTEM MANAGEMENT — (Environmental) An approach to managing the nation's lands and natural resources which recognizes that plant and animal communities are interdependent and interact with their physical environment (i.e., soil, water, and air) to form distinct ecological units called Ecosystems. The fact that these ecosystems span jurisdictional and political boundaries necessitates a more comprehensive and unified approach to managing them. Implementing the initial stage of a government-wide approach to ecosystem management typically requires clarifying the policy goals and undertaking certain practical steps to apply the principles being considered to include:
[1] Delineating the ecosystem;
[2] Understanding the system(s) ecologies;
[3] Making management choices;
[4] Unifying disparate data and information needs and sources; and
[5] Adapting management on the basis of new information.

ECOSYSTEM STRUCTURE — Attributes related to instantaneous physical state of an ecosystem; examples include species population density, species richness or evenness, and standing crop Biomass.

EFFECTIVE PRECIPITATION (or Rainfall) — That portion of precipitation which remains on the foliage or in the soil that is available for Evapotranspiration, and reduces the withdrawal of soil water by a like amount. As described by the U.S. Bureau of Reclamation, that part of the precipitation falling on an irrigated area that is effective in meeting the Crop Consumptive Use requirements.

EFFICIENCY — (Irrigation) A measure of a distribution system's ability to transport and apply water to a desired effect with a minimum of effort, expense, or waste. With respect to irrigation project efficiency, the following terms generally apply:
[1] Canal Efficiency — The volume of water diverted into a canal system versus total water available for farm headgate deliveries;
[2] Irrigation Efficiency — The percentage of water applied that can be accounted for in soil moisture increase; and
[3] Farm Efficiency — The amount of water actually required for growing a crop compared to the amount of irrigation water that is diverted at the farm headgate.

EFFICIENT WATER MANAGEMENT PRACTICES (EWMP) — The agricultural water use equivalent of Best Management Practices (BMP) as applied to urban water use, efficient water management practices cover the spectrum of methods to improve both the efficiency and conservation of agricultural water use by (1) enhancing irrigation management services, measurement, and accounting; (2) improving the physical system of irrigation delivery, distribution, and drainage; and (3) promoting the modification of and adjustments to the institutional system of water use by agricultural interests to include information and educational programs.

EFFLUENT — (1) Something that flows out or forth, especially a stream flowing out of a body of water. (2) (Water Quality) Discharged wastewater such as the treated wastes from municipal sewage plants, brine wastewater from desalting operations, and coolant waters from a nuclear power plant.

EFFLUENT SEEPAGE — Diffuse discharge of ground water to the ground surface.

EFFLUENT STREAMS — Effluent streams are those leaving a lake.

EJECTOR — (1) A device using a jet of water to withdraw a fluid from a space. (2) A device used to disperse a chemical solution into water being treated.

ELECTRIC POWER WATER (Public Utility) — Water withdrawn by public utilities for hydroelectric power generation and condenser cooling.

ELECTRICAL CONDUCTIVITY — A measure of the salt content of water.

ELUVIATION — (1) The removal of soil material in suspension (or in solution) from a layer or layers of a soil. (2) The transportation of dissolved or suspended material within the soil by the movement of water when rainfall exceeds evaporation.

EMBANKMENT — An artificial deposit of material that is raised above the natural surface of the land and used to contain, divert, or store water, support roads or railways, or for other similar purposes.

EMBANKMENT DAM — A dam structure constructed of fill material, usually earth or rock, placed with sloping sides and usually with a length greater than its height. Types of embankment dams include:
[1] Earthfill or Earth Dam — An embankment dam in which more than 50 percent of the total volume is formed of compacted fine-grained material obtained from a borrow area (i.e., excavation pit);
[2] Fill Dam — Any dam constructed of excavated natural materials or of industrial waste materials;
[3] Homogeneous Earthfill Dam — An embankment dam constructed of similar earth material throughout, except for the possible inclusion of internal drains or drainage blankets; distinguished from a Zoned Earthfill Dam;
[4] Hydraulic Fill Dam — An embankment dam constructed of materials, often dredged, that are conveyed and placed by suspension in flowing water;
[5] Rockfill Dam — An embankment dam in which more than 50 percent of the total volume is comprised of compacted or dumped pervious natural or crushed rock;
[6] Rolled Fill Dam — An embankment dam of earth or rock in which the material is placed in layers and compacted by using rollers or rolling equipment; and
[7] Zoned Embankment Dam — An embankment dam which is composed of zones of selected materials having different degrees of porosity, permeability, and density.

EMERGENCY ACTION PLAN (Dam) — A predetermined plan of action to be taken to reduce the potential for property damage and loss of lives in a downstream area affected by a dam break or excessive spillway discharges.

EMERGENCY SPILLWAY — A dam spillway built to carry runoff in excess of that carried by the principal spillway; a secondary spillway designed to operate only during exceptionally large floods. Also referred to as Auxiliary Spillway.

EMERGENT — Rising above a surrounding medium, especially a fluid. Having part of a plant aerial and the rest submersed; with parts extending out of the water.

EMERGENT PLANT — A plant that grows in shallow water with the root system submerged under the water and the upper vegetation rising above the water surface.

EMERGENT WETLAND — Typically, a wetland classification characterized by erect, rooted, herbaceous, hydrophytes, excluding mosses and lichens, and which is present for most of the growing season.

ENDEMIC — (Ecology) Confined to, or Indigenous in, a certain area or region, as an endemic plant or animal.

ENERGY — The capacity to perform work, or the potential for power and activity; energy may be captured or held in living matter (e.g., food is stored energy). Various forms of energy include kinetic, potential, thermal, nuclear, rotational, and electromagnetic. Hydroelectric power, a form of potential energy, is derived from flowing water, typically by allowing water to be raised to, or maintained at, an elevated height and then release energy as it flows to a lower level.

ENERGY DISSIPATOR — A structure for slowing the fast moving spillway flows of a dam in order to prevent erosion of the stream channel below the dam.

ENERGY GRADIENT — The change in energy per unit length in the direction of flow or motion.

ENTRAINMENT — (Streams) The incidental trapping of fish and other aquatic organisms in the water, for example, used for cooling electrical power plants or in waters being diverted for irrigation or similar purposes.

ENTRANCE HEAD — The Head required to cause flow into a conduit or other structure, including both entrance loss and Velocity Head.

ENTRAPMENT ZONE — An area of an estuary or other watercourse where seaward-flowing fresh water overlays more dense, saline ocean water resulting in a two-layer mixing zone characterized by Flocculation, aggregation, and accumulation of suspended materials from upstream.

ENVIRONMENT — All of the external factors, conditions, and influences which affect the growth, development, and survival of organisms or a community. The components of an environment include climate, physical, chemical, and biological factors, nutrients, and social and cultural conditions. These influences affect the form and survival of individuals and communities.

ENVIRONMENTAL ANALYSIS — (1) An analysis of alternative actions and their predictable short and long-term environmental effects, which may include physical, biological, economic, social and environmental design factors and their interaction. (2) (NEPA) Systematic process for considering environmental factors in resource management actions.

ENVIRONMENTAL ASSESSMENT (EA) — An environmental analysis prepared pursuant to the National Environmental Policy Act (NEPA) that presents the first thorough examination of alternative plans to positively demonstrate that the environmental and social consequences of an applicable project or action were considered. If it is shown that such activities do, in fact, significantly impact the environment or are otherwise deemed controversial, then an Environmental Impact Statement (EIS) will normally be required.

ENVIRONMENTAL AUDIT — (1) An internal investigation of company compliance with environmental regulations. (2) A study of a site prior to a real estate transaction to uncover potential environmental liability associated with the property, such as the prior improper disposal of hazardous wastes into the ground. (3) An independent assessment of the current status of a party's compliance with applicable environmental requirements or of a party's environmental compliance policies, practices, and controls.

ENVIRONMENTAL EVALUATION — That part of the planning process by governmental agencies that inventories and estimates the potential effects on the human environment of alternative solutions to resource problems, determines the need for an Environmental Assessment (EA) or an Environmental Impact Statement (EIS), and aids in the consideration of alternatives and the identification of available resources.

ENVIRONMENTAL INDICATOR — A measurement, statistic or value that provides a proximate gauge or evidence of the effects of environmental management programs or of the state or condition of the environment.

ENVIRONMENTALISM — Advocacy for or work toward protecting the natural environment from destruction or pollution.

ENVIRONMENTAL MANIPULATION — Actions taken directly or indirectly by man to alter the natural characteristics and evolving patterns of an Ecosystem through alterations to plant or animal life, or habitat conditions.

ENVIRONMENTAL WATER — The water for wetlands, the instream flow for a major river (based on the largest fish flow specified in an entire reach of that river) or, for wild and scenic rivers, the amount of water based on unimpaired natural flow.

EPHEMERAL STREAM — A stream that flows only in direct response to precipitation, and thus discontinues its flow during dry seasons. Such flow is usually of short duration. Most of the dry washes of more arid regions may be classified as ephemeral streams.

EROSION — The wearing away and removal of materials of the earth's crust by natural means. As usually employed, the term includes weathering, solution, corrosion, and transportation. The agents that accomplish the transportation and cause most of the wear are running water, waves, moving ice, and wind currents. Most writers include under the term all the mechanical and chemical agents of weathering that loosen rock fragments before they are acted on by the transportation agents; a few authorities prefer to include only the destructive effects of the transporting agents. Various types of water erosion include:
[1] Accelerated — Erosion much more rapid than normal, natural, or geologic erosion, primarily as a result of the influence of the activities of man or, in some cases, of other animals or natural catastrophes that expose bare surfaces, for example, forest fires;
[2] Geological — The normal or natural erosion caused by geological processes acting over long geologic periods and resulting in the wearing away of mountains, the building up of floodplains, coastal plains, etc., and also referred to as natural erosion;
[3] Gross — A measure of the potential for soil to be dislodged and moved from its place of origin, not necessarily the amount of soil that actually reaches a stream or lake, but the amount of soil that can be calculated from water and wind equations;
[4] Gully — The erosion process whereby water accumulates in narrow channels and, over short periods of time, removes soil from this narrow area to considerable depths, ranging from 1-2 feet (0.3-0.6 meters) to as much as 75-100 feet (23-31 meters); [5] Natural — The wearing away of the earth's surface by water, ice, or other natural agents under natural environmental conditions of climate, vegetation, etc., undisturbed by man, and also referred to as geological erosion;
[6] Normal — The gradual erosion of land used by man that does not greatly exceed natural erosion;
[7] Overfall — Erosion caused by water flowing over an overfall;
[8] Rill — An erosion process in which numerous small channels only several inches deep are formed; occurs mainly on recently cultivated soils and/or recent cuts and fills;
[9] Sheet — The removal of a thin, fairly uniform layer of soil from the land surface by runoff waters;
[10] Shore — Removal of soil, sand, or rock from the land adjacent to a body of water due to wave action;
[11] Splash — The spattering of small soil particles caused by the impact of raindrops on wet soils. The loosened and spattered particles may or may not be subsequently removed by surface runoff;
[12] Streambank — Scouring of material and the cutting of channel banks by running water;
[13] Streambed — Scouring of material and cutting of channel beds by running water;
[14] Undercutting — Removal of material at the base of a steep slope, overfall, or cliff by falling water, a stream, wind erosion, or wave action; the removal steepens the slope or produces an overhanging cliff.

EROSION, BANK — Destruction of land areas bordering rivers or water bodies by the cutting or wearing action of waves or flowing water.

EROSION, BEACH — The retrogression of the shore line of large lakes and coastal waters caused by wave action, shore currents, or natural causes other than Subsidence.

EROSION CONTROL — Materials, structures, and actions utilized and taken to reduce or prevent erosion.

EROSION, GROSS — The total of all sheet, gully, and channel erosion in a drainage basin, usually expressed in units of mass.

EROSION CONTROL — The application of necessary measures including artificial structures, vegetative manipulation, water control, or physical soil changes to minimize soil erosion.

EROSION FLOOD PLAIN — A flood plain that has been created by the lateral erosion and the gradual retreat of the valley walls.

ESTUARINE — (1) Of, pertaining to, or formed in, an Estuary. (2) One of the classification systems under the Wetlands and Deepwater Habitats classification system.

ESTUARINE WATERS — Deepwater tidal habitats and tidal wetlands that are usually enclosed by land but have access to the ocean and are at least occasionally diluted by freshwater runoff from the land (such as bays, mouths of rivers, salt marshes, lagoons, etc.).

ESTUARINE ZONE — The area near the coastline that consists of estuaries and coastal saltwater wetlands.

ESTUARY — An area where fresh water meets salt water; for example, bays, mouths of rivers, salt marshes, and lagoons. The Coastal Zone Management Act of 1972 defines an estuary as "that part of a river or stream or other body of water having unimpaired connection with the open sea, where the sea-water is measurably diluted with freshwater derived from land drainage." These brackish water ecosystems shelter and feed marine life, birds, and wildlife.

EUTROPHIC (WATER) — Pertaining to a lake or other body of water characterized by large nutrient concentrations such as nitrogen and phosphorous and resulting high productivity. Such waters are often shallow, with algal blooms and periods of oxygen deficiency. Slightly or moderately eutrophic water can be healthful and support a complex web of plant and animal life. However, such waters are generally undesirable for drinking water and other needs. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus).

EUTROPHICATION — The process of enrichment of water bodies by nutrients. Degrees of Eutrophication typically range from Oligotrophic water (maximum transparency, minimum chlorophyll-a, minimum phosphorus) through Mesotrophic, Eutrophic, to Hypereutrophic water (minimum transparency, maximum chlorophyll-a, maximum phosphorus). Eutrophication of a lake normally contributes to its slow evolution into a Bog or Marsh and ultimately to dry land. Eutrophication may be accelerated by human activities and thereby speed up the aging process.

EVAPORATION — The physical process by which a liquid (or a solid) is transformed to the gaseous state. In Hydrology, evaporation is vaporization that takes place at a temperature below the boiling point.

EVAPORATION, LAND — Evaporation from land surfaces, in contrast to evaporation from free water surfaces.

EVAPORATION, NET RESERVOIR — The evaporative water loss from a reservoir after making allowance for precipitation on the reservoir and runoff that would have occurred from that precipitation from the land area covered by the reservoir. Net reservoir evaporation equals the total evaporation minus the precipitation on the reservoir plus the runoff from the land area covered by the reservoir.

EVAPORATION OPPORTUNITY (Relative Evaporation) — The ratio of the rate of evaporation from a land or water surface in contact with the atmosphere, to the Evaporativity under existing atmospheric conditions. It is the ratio of actual to potential rate of evaporation, generally expressed as a percentage. The opportunity for a given rate of evaporation to continue is determined by the available moisture supply.

EVAPORATION PONDS — (Water Quality) Shallow ponds in which sewage sludge is placed to dry and then be removed for further treatment and/or disposal. Also, shallow ponds used to extract through evaporation various chemicals in solution or suspension, e.g., salt evaporation ponds. Also see Evaporites.

EVAPORATION RATE — The quantity of water which evaporates from a given surface per unit of time, usually expressed in inches or depth per day, month, or year.

EVAPORATION, TOTAL — The sum of water lost from a given land area during any specific period of time by transpiration from vegetation and the building of plant tissue; by evaporation from water surfaces, moist soil, and snow; and by interception. It has been variously termed Evaporation, Evaporation from Land Areas, Evapotranspiration, Total Loss, Water Loss, and Fly Off.

EVAPORATIVE COOLING — Cooling of a liquid, such as water, by allowing a portion to evaporate. The process is important in the operation of cooling towers used to cool heated effluents from power plants as well as in the cooling of the human body through the evaporation of perspiration. The process is more effective than convection cooling.

EVAPORATIVITY (Potential Rate of Evaporation) — The rate of evaporation under the existing atmospheric conditions from a surface of water that is chemically pure and has the temperature of the atmosphere.

EVAPORITES — Sediments deposited from an aqueous (water) solution as a result of extensive or local evaporation of a solvent, such as salts in the Great Salt Lake in the western United States.

EVAPOTRANSPIRATION (ET) — The combined processes by which water is transferred from the earth surface to the atmosphere; evaporation of liquid or solid water plus transpiration from plants. Evapotranspiration occurs through evaporation of water from the surface, evaporation from the capillary fringe of the groundwater table, and the transpiration of groundwater by plants (Phreatophytes) whose roots tap the capillary fringe of the groundwater table. The sum of evaporation plus transpiration.

EVAPOTRANSPIRATION, ACTUAL — The evapotranspiration that actually occurs under given climatic and soil-moisture conditions.

EVAPOTRANSPIRATION OF APPLIED WATER (ETAW) — The portion of the total Evapotranspiration which is provided by irrigation.

EVAPOTRANSPIRATION, POTENTIAL — (1) The maximum quantity of water capable of being evaporated from the soil and transpired from the vegetation of a specified region in a given time interval under existing climatic conditions, expressed as depth of water. (2) The water loss that will occur if at not time there is a deficiency of water in the soil for use by vegetation.

EVAPOTRANSPIROMETER — An instrument designed to measure Evapotranspiration as related to a particular place, soil type, and vegetation. The device consists of a block of soil with some planted vegetation enclosed in a container. Evapotranspiration is determined by maintaining a Water Budget for the container, that is, accounting for the water applied, water drained off the bottom, and the change in the moisture content of the soil. If there is a provision for drainage of the soil water, the device is referred to as a Lysimeter.

EXCESS RAINFALL — Effective rainfall in excess of infiltration capacity, resulting in runoff.

EXEMPT LAND (USBR) — Irrigation land in a district to which the acreage limitation and pricing provisions of reclamation law do not apply.

EXTREME HIGH WATER OF SPRING TIDES — The highest tide occurring during a lunar month, usually near the new or full moon. This is equivalent to extreme higher high water of mixed semidiurnal tides.

EXTREME LOW WATER OF SPRING TIDES — The lowest tide occurring during a lunar month, usually near the new or full moon. This is equivalent to extreme lower low water of mixed semidiurnal tides.

EXTREME VALUE SERIES — Hydrological series which includes the largest or smallest values, with each value selected from an equal time interval in the record.

F

FACE (of a Dam) — The external surface of a structure, such as the surface of an appurtenance or a dam.

FALL OVERTURN — A physical phenomenon that may take place in a body of water during early autumn. The sequence of events leading to fall overturn include:
[1] The cooling of surface waters;
[2] A density change in surface waters producing convection currents from top to bottom;
[3] The circulation of the total water volume by wind action; and
[4] Eventual vertical temperature equality.
The overturn results in a uniformity of the physical and chemical properties of the entire water body. Also referred to as Fall Turnover.

FALLOW — (1) Allowing cropland, either tilled or untilled, to lie idle during the whole or greater portion of the growing season. (2) Land plowed and tilled and left unplanted.

FALLS — A waterfall or other precipitous descent of water.

FARM DELIVERY REQUIREMENT — The Crop Irrigation Requirement plus farm losses due to evaporation, deep percolation, surface waste, and nonproductive consumption. The losses are measured by the Farm Irrigation Efficiency, which is the percent of farm-delivered water that remains in the root zone and is available for crop growth.

FARM EFFICIENCY — The consumptive Crop Irrigation Requirement (CIR) divided by the farm water delivery.

FARM HEADGATE DELIVERY (DIVERSION) — That amount of water in acre feet (AF) delivered through a farm headgate.

FARM IRRIGATION EFFICIENCY — An expression comparing the amount of water actually required for growing a crop to the amount of irrigation water that is diverted at the farm headgate. Expressed as a percentage on an annual basis.

FARM POND — A water impoundment made by constructing a dam or embankment or by excavating a pit or "dug out".

FARM SURFACE RUNOFF (TAILWATER) — A portion of the Farm Headgate Delivery that flows off the lower portion of the farm or field surface (drain ditch) flow. This is one loss component considered in Farm Irrigation Efficiency.

FARM WASTE AND DEEP PERCOLATION — The amount of irrigation water delivered to the crop area from a canal turnout or ground water pump that is not consumptively used on the crop area. Includes water moving through the root zone to the water table, water intercepted by drainage systems, and surface waste to natural or constructed drainage systems, and non-cropped areas.

FEEDWATER — (Water Quality) Water input into a desalting or water treatment plant.

FERTIGATION — The use of irrigation water as a vehicle for spreading fertilizer on the land.

FERTILIZER — Any organic or inorganic material of natural or synthetic origin that is added to a soil to supply elements essential to plant growth. Various types of fertilizers include acid-forming, blended, bulk-blended, chemical, coated, conditioned, granular, liquid, non-granular, prilled, solution, straight, and suspension.

FETCH — (1) The distance traveled by waves in open water, from their point of origin to the point where they break. (2) The distance the wind blows over water or another homogeneous surface without appreciable change in direction.

FIELD — (1) A broad, level, open expanse of land; a meadow. (2) A cultivated expanse of land, especially one devoted to a particular crop. (3) A portion of land or a geologic formation containing a specified natural resource. (4) A wide, unbroken expanse, as of ice.

FIELD (MOISTURE) CAPACITY — The capacity of soil to hold water. It is measured by the soil scientist as the ratio of the weight of water retained by the soil to the weight of the dry soil.

FIELD DIVERSION — An interception channel near the contour to carry runoff to a waterway. Intervals vary with the precipitation, slope, and cropping.

FIELD-MOISTURE CAPACITY — The quantity of water which can be permanently retained in the soil in opposition to the downward pull of gravity.

FIELD-MOISTURE DEFICIENCY — The quantity of water which would be required to restore the soil moisture to Field-Moisture Capacity.

FIELD PERMEABILITY — Permeability corresponding to the temperature which occurs under field conditions.

FIELD SPRINKLER SYSTEM — A system of closed conduits carrying irrigation water under pressure to orifices designed to distribute the water over a given area.

FILTER — A device used to remove solids from a mixture or to separate materials. A porous material through which a liquid or gas is passed in order to separate the fluid from suspended particular matter. Suspended materials are frequently separated from water using filters.

FILTER BED — A layer of sand or gravel on the bottom of a reservoir or tank, used to filter water or sewage.

FILTER CAKE — (1) The solids or semisolids deposited on a filter as a fluid is moved through it. (2) The remaining solids or semisolids on a filter after the fluid in a material is extracted by a negative pressure.

FILTER FEEDER — An aquatic animal, such as a clam, barnacle, or sponge, that feeds by filtering particulate organic material from water.

FILTER STRIP — A strip or area of vegetation used for removing sediment, organic matter, and other pollutants from runoff and waste water.

FILTER ZONE (of a Dam) — A band or zone of granular material that is incorporated into a dam and is graded (either naturally or by selection) so as to allow seepage to flow across or down the filter without causing the migration of material from zones adjacent to the filter zone.

FILTERABLE — Of particles that are sufficiently small to allow their passage through filters capable of retaining most particles. For example, a filterable virus is one that will pass through a filter that will normally retain bacteria.

FILTRATE — Liquid that has been passed through a filter.

FILTRATION — (1) The process in which suspended matter is removed from a liquid through a medium which is permeable to the liquid but not to the suspended material. (2) (Water Quality) A treatment process, under the control of qualified operators, for removing solid (particulate) matter from water by means of porous media such as sand or a man-made filter; often used to remove particles that contain Pathogens.

FINAL CLARIFIER — (Water Quality) A gravitational settling tank installed as part of some wastewater treatment plants and placed after the biological treatment step. The tank functions to remove suspended solids.

FINISHED WATER — (Water Quality) Water that has completed a purification or treatment process; water that has passed through all the processes in a water treatment plant and is ready to be delivered to consumers. Contrast with Raw Water.

FIRM CAPACITY — For public drinking water supplies, the system delivery capacity with the largest single water well or production unit out of service.

FIRM YIELD — The maximum annual supply of a given water development that is expected to be available on demand, with the understanding that lower yields will occur in accordance with a predetermined schedule or probability.

"FIRST IN TIME, FIRST IN RIGHT" — A phrase indicating that older water rights have priority over more recent rights if there is not enough water to satisfy all rights.

FIXED GROUND WATER — Water held in saturated material within pore spaces so small that it is permanently attached to the walls, or moves so slowly that it is usually not available as a source of water for pumping.

FLATBOAT — A boat with a flat bottom and square ends used for transportation of bulky freight, especially used in shallow waters.

FLAT-WATER — Of or on a level or slow-moving watercourse.

FLOAT — (1) To remain suspended within or on the surface of a fluid without sinking. To cause to remain suspended without sinking or falling. (2) To put into water; launch. (3) To flood (land), as for irrigation.

FLOATER — A Wetland plant that floats on the surface of the water.

FLOC — Generally, a very fine, fluffy mass formed by the aggregation of fine suspended particles, as in a precipitate. In terms of water quality, clumped solids or precipitates formed in sewage by biological or chemical activity.

FLOCCULATE — To aggregate or clump together individual, tiny particles into small clumps or clusters.

FLOCCULATION — (Water Quality) In water and wastewater treatment, the agglomeration or clustering of colloidal and finely divided suspended matter after coagulation by gentle stirring by either mechanical or hydraulic means such that they can be separated from water or sewage.

FLOE — An ice flow. Also a segment that has separated from such an ice mass.

FLOE ICE — Ice usually several feet thick, which has formed on the surface of a body of water and then has broken into pieces and is floating on the water's surface.

FLOOD, or Flood Waters — (1) An overflow of water onto lands that are used or usable by man and not normally covered by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean. (2) As defined, in part, in the Standard Flood Insurance Policy (SFIP): "A general and temporary condition of partial or complete inundation of normally dry land areas from overflow of inland or tidal waters or from the unusual and rapid accumulation or runoff of surface waters from any source."

FLOOD, 100-YEAR — A 100-year flood does not refer to a flood that occurs once every 100 years, but to a flood level with a 1 percent or greater chance of being equaled or exceeded in any given year. Areas between the 100-year and the 500-year flood boundaries are termed Moderate Flood Hazard Areas. The remaining areas are above the 500-year flood level and are termed Minimal Flood Hazard Areas.

FLOOD, ANNUAL — The highest peak discharge in a water year.

FLOOD-BASE DISCHARGE — A value of high flow usually computed during the first 5 years of station operation that, on the average, is exceeded about three times per year.

FLOOD CAPACITY — The flow carried by a stream or floodway at bankfull water level. Also, the storage capacity of the flood pool at a reservoir.

FLOOD CONTROL (STORAGE) — The control of flood waters by the construction of flood storage reservoirs, flood water retaining structures, channel improvements, levees, bypass channels, other engineering works, or vegetative changes.

FLOOD CONTROL POOL — Reservoir volume reserved for flood runoff and then evacuated as soon as possible to keep that volume in readiness for the next flood.

FLOOD CREST — The maximum stage or elevation reached by the waters of a flood at a given location.

FLOOD DAMAGE — The direct and indirect economic loss caused by floods including damage by inundation, erosion, or sediment deposition. Indirect damages may also include emergency costs and business or financial losses. Evaluation may be based on the cost of replacing, repairing, or rehabilitating; or the comparative change in market or sales value; or on the change in income or production caused by flooding.

FLOOD DURATION CURVE — A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.

FLOOD FORECASTING — Flood forecasts are primarily the responsibility of the National Weather Service, National Oceanic and Atmospheric Administration (NOAA), and are used to predict flood stages and times and indicate areas subject to flooding.

FLOOD FREQUENCY — A statistical expression or measure of how often a hydrologic event of a given size or magnitude should, on an average, be equaled or exceeded. For example, a 50-year frequency flood (2 percent change of occurrence) should be equaled or exceeded, on the average, once in 50 years.

FLOOD FREQUENCY CURVE — (1) A graph showing the average interval of time within which a flood of a given magnitude will be equaled or exceeded once. (2) A similar graph but plotted with the Recurrence Intervals of floods plotted instead.

FLOODGATE — (1) A gate used to control the flow of a body of water. Also referred to as a Water Gate. (2) Something that restrains a flood or an outpouring.

FLOODING — Temporary inundation of all or part of the floodplain along a well-defined channel or temporary localized inundation occurring when surface water runoff moves via surface flow, swales, channels, and sewers toward well-defined channels. Flooding is not necessarily synonymous with Flooding Problem.

FLOODING PROBLEM — The disruption to community affairs, damage to property and facilities, and the danger to human life and health that occurs when land use is incompatible with the hydrologic-hydraulic system.

FLOOD, INTERMEDIATE REGIONAL — A flood having a one percent probability, or an average frequency of occurrence on the order of once in 100 years, although the flood may occur in any year. The intermediate regional flood is based on statistical analyses of streamflow records available for the watershed and analyses of rainfall and runoff characteristics in the "general region of the watershed."

FLOOD IRRIGATION — The application of irrigation water where the entire surface of the soil is covered by a sheet of water, called Controlled Flooding when water is impounded or the flow directed by border dikes, ridges, or ditches.

FLOOD, MAXIMUM PROBABLE — The greatest flood that may be expected at a place, taking into account all pertinent factors of location, meteorology, hydrology, and terrain.

FLOOD OF RECORD — The highest observed river stage or discharge at a given site during the period of record keeping. May not necessarily be the highest known stage.

FLOOD PEAK — The maximum instantaneous discharge of a flood at a given location. It usually occurs at or near the time of the flood crest, i.e., the maximum stage or elevation reached by the flood flow.

FLOOD PLAIN, also Floodplain — (1) A strip of relatively smooth land bordering a stream, built of sediment carried by the stream and dropped in the slack water beyond the influence of the swiftest current. It is called a Living Flood Plain if it is overflowed in times of high water but a Fossil Flood Plain if it is beyond the reach of the highest flood. (2) The lowland that borders a stream or river, usually dry but subject to flooding. (3) That land outside of a stream channel described by the perimeter of the Maximum Probable Flood.

FLOOD PLANE — The position occupied by the water surface of a stream during a particular flood. Also, loosely, the elevation of the water surface at various points along the stream during a particular flood.

FLOOD PREVENTION — Methods or structural measures used to prevent floods.

FLOOD PROBABILITY — The statistical probability that a flood of a given size will be equaled or exceeded in a given period of time.

FLOOD PROFILE — A graph showing the relationship of water surface elevation to location, the latter generally expressed as distance above mouth for a stream of water flowing in an open channel. It is generally drawn to show surface elevation for the crest of a specific flood, but may be prepared for conditions at a given time or stage.

FLORA — (1) A term used to describe the entire plant species of a specified region or time. (2) The sum total of the kinds of plants in an area at one time. All plant life associated with a given habitat, country, area, or period. Bacteria are considered flora.

FLOW — The rate of water discharged from a source given in volume with respect to time.

FLOWAGE — (1) The act of flowing or overflowing. (2) The state of being flooded; a body of water, such as a lake or reservoir, formed by usually deliberate flooding. (3) An outflow or overflow.

FLOW AUGMENTATION — The addition of water to a stream especially to meet instream flow needs.

FLOW BOUNDARIES — Anything which inhibits ground water flow, such as a ground water divide or an impermeable geologic unit.

FLOW DURATION CURVE — A cumulative frequency curve that shows the percentage of time that specified discharges are equaled or exceeded.

FLOWLINE (STREAMLINE) — (1) The general path that a particle of water follows under laminar flow conditions. (2) The line indicating the direction followed by ground water toward points of discharge. Flow lines are perpendicular to Equipotential Lines.

FLOW METER — A device which allows for measurement of stream flow by measuring velocity in a given cross-sectional area.

(GROUND WATER) FLOW MODEL — (1) A digital computer model that calculates a hydraulic head field for the modeling domain using numerical methods to arrive at an approximate solution to the differential equation of ground-water flow. (2) Any representation, typically using plastic or glass cross-sectional viewing boxes, with representative soil samples, depicting ground-water flows and frequently used for educational purposes.

FLOW, LAMINAR — Flow of water in well-defined flow lines in which the viscous force is predominant; in channels it occurs at a Reynolds Number smaller than 500-2,000 and through porous media at Reynolds Number smaller than 1-10.

FLOW, MODIFIED — That streamflow which would have existed had the works of man in or on the stream channels and in the drainage basin been consistent throughout the period of record. Usually used with an adjective such as "present" or specific year to mean that the flow record was modified to represent the record that would have been obtained had the "present" conditions prevailed throughout the period of record. Modified flow is equal to Virgin Flow minus the amount of Streamflow Depletion occurring at the specified time.

FLOW, NATURAL — The rate of water movement past a specified point on a natural stream from a drainage area which has not been affected by stream diversion, storage, import, export, return flow or change in consumptive use resulting from man's modification of land use. Natural flow rarely occurs in a developed country.

FLOW, NET — A graphical representation of flow lines and Equipotential Lines for two-dimensional, steady-state ground-water flow.

FLOW, OVERLAND — The flow of rainwater or snowmelt over the land surface toward stream channels. Upon entering a stream, it becomes runoff.

FLOW PATH — The subsurface course a water molecule or solute would follow in a given ground-water velocity field.

FLOW RATE — The rate, expressed in gallons or liters-per-hour, at which a fluid escapes from a hole or fissure in a tank. Such measurements are also made of liquid waste, effluent, and surface water movement.

FLOW RESOURCES Versus STOCK RESOURCES — Flow resources are resources that are not permanently expendable under usual circumstances; they are resources which are replaced. They are commonly expressed in annual rates at which they are regenerated. Examples are fresh-water runoff and timber. Stock resources can be permanently expended and whose quantity is usually expressed in absolute amounts rather than in rates. Examples are coal and petroleum deposits.

FLOW, STEADY — A flow in which the magnitude and direction of the specific discharge are constant in time.

FLOW, TURBULENT — A flow in which successive flow particles follow independent path lines, and head loss varies approximately with the square of the velocity. In stream channels it occurs at a Reynolds Number greater than 5,000.

FLOW, UNIFORM — A characteristic of a flow system where specific discharge has the same magnitude and direction at any point.

FLOW VELOCITY — The volume of water flowing through a unit cross-sectional area of an aquifer.

FLOW, VIRGIN — That streamflow which would exist had man not modified conditions on or along the stream or in the drainage basin.

FLOWING WELL — An Artesian Well having sufficient head to discharge water above the land surface; a well where the Piezometric Surface lies above the ground surface..

FLOWMETER — A gauge indicating the velocity of wastewater moving through a treatment plant or of any liquid moving through various industrial processes.

FLUID — Having particles which easily move and change their relative position without a separation of the mass, and which easily yield to pressure; capable of flowing; liquid or gaseous.

FLUVIAL — Of or pertaining to rivers and streams; growing or living in streams ponds; produced the action of a river or stream.

FOREBAY — The water behind a dam. A reservoir or pond situated at the intake of a pumping plant or power plant to stabilize water levels; also a storage basin for regulating water for percolation into ground water basins.

FOREBAY RESERVOIR — A reservoir used to regulate the flow of water to a hydroelectric plant; it may also serve other purposes such as recreation.

FORECAST (FORECASTING) — (Statistics) A forecast is a quantitative estimate (or set of estimates) about the likelihood of future events based on past and current information. This "past and current information" is specifically embodied in the structure of the econometric model used to generate the forecasts. By extrapolating the model out beyond the period over which it was estimated, we can use the information contained in it to make forecasts about future events. It is useful to distinguish between two types of forecasting, ex post and ex ante. In an ex post forecasts all values of dependent and independent variables are known with certainty and therefore provides a means of evaluating a forecasting model. Specifically, in an ex post forecast, a model will be estimated using observations excluding those in the ex post period, and then comparisons of the forecasts will be made to these actual values. An ex ante forecast predicts values of the dependent variable beyond the estimation period using values for the explanatory variables which may or may not be known with certainty.

FOREST HYDROLOGY — The study of hydrologic processes as influenced by forest and associated vegetation.

FOREST INFLUENCES — The effects resulting from the presence of forest or brush upon climate, soil water, runoff, streamflow, floods, erosion, and soil productivity.

FOREST LAND — Land which is at least 10 percent occupied by forest trees of any size or formerly having had such tree cover and not currently developed for non-forest use. Lands developed for non-forest use include areas for crops, improved pasture, residential, or administrative areas, improved roads of any width, and adjoining road clearing and power line clearing of any width.

FORFEITED WATER RIGHT — A water right that is no longer valid because of five or more consecutive years of nonuse.

FORFEITURE — The invalidation of a water right because of five or more consecutive years of nonuse.

FOSSIL WATER — Limited subterranean water deposits laid down in past ages but drawn on by modern man.

FOUNDATION (of a Dam) — The natural material on which the dam structure is placed.

FOUNDER — To sink below the water.

FOUNTAIN — (1) An artificially created jet or stream of water; a structure, often decorative, from which a jet or stream of water issues. (2) A spring, especially the source of a stream. (3) A reservoir or chamber containing a supply of liquid that can be siphoned off as needed.

FREE FLOW — (Hydraulics) Flow through or over a structure not affected by submergence or backwater.

FREE-FLOWING — Flowing without artificial restrictions.

FREE-FLOWING STREAM — A stream or a portion of a stream that is unmodified by the works of man or, if modified, still retains its natural scenic qualities and recreational opportunities.

FREE-FLOWING WEIR — A weir that in use has the tailwater lower than the crest of the weir.

FREE-FLOWING WELL — An Artesian Well in which the potentiometric surface is above the land surface.

FREE GROUND WATER — Water in interconnected pore spaces in the Zone of Saturation down to the first impervious barrier, moving under the control of the water table slope.

FREE LIQUIDS — (Water Quality) Liquids capable of migrating from waste and contaminating ground water. Hazardous waste containing free liquids may not be disposed of in landfills.

FREE MOISTURE — Liquid that will drain freely from solid waste by the action of gravity only.

FREE WATER SURFACE (FWS) CONSTRUCTED WETLAND — A type of constructed wetland, a man-made marsh-like area used to treat wastewater. In this type of wetland, the effluent flows through various aquatic plants, with the water level exposed to the air. While this type of wetland is relatively easy to construct, it is not as effective as the Subsurface Flow (SF) Constructed Wetland with respect to associated odors, potential for insect breeding, and risk of public exposure and contact with the water in the system.

FREEZE — (1) To pass from the liquid to the solid state by loss of heat. (2) To acquire a surface of coat of ice from cold.

FREEZING — The change of a liquid into a solid as temperature decreases. For water, the freezing point is 32F (Fahrenheit) or ⁰C (Celsius).

FREEZING POINT — (1) The temperature at which a liquid of specified composition solidifies under a specified pressure. (2) The temperature at which the liquid and solid phases of a substance of specified composition are in equilibrium at atmospheric pressure.

FRENCH DRAIN — An underground passageway for water through the interstices among stones placed loosely in a trench.

FREQUENCY ANALYSIS — A statistical procedure involved in interpreting the past record of a hydrological event to occurrences of that event in the future (e.g., estimates of frequencies of floods, droughts, storage, rainfall, water quality, etc.).

FREQUENCY CURVE — A graphical representation of the frequency of occurrence of specific events.

FREQUENCY DISTRIBUTION — An arrangement of quantities pertaining to a single event, in order of magnitude and frequency of occurrence.

FRESH — (1) Not saline or salty. (2) Free from impurity or pollution.

FRESH-SALT WATER INTERFACE — The region where fresh water and salt water meet.

FRESHWATER — (1) Of, relating to, living in, or consisting of water that is not salty. (2) Water with salinity less than 0.5 (parts per thousand) dissolved salts. (3) Water that contains less than 1,000 milligrams per liter (mg/l) of dissolved solids; generally, more than 500 mg/l of dissolved solids is undesirable for drinking and many industrial uses. (4) (Nautical) Accustomed to sailing on inland waters only.

FRINGE WATER — Water occurring in the Capillary Fringe.

FRONT — (1) Land bordering a lake or river. (2) (Meteorology) A line of separation or interface between air masses of different temperatures or densities.

FRONTAGE — Land adjacent to something, such as a body of water.

FROST — (1) Thin ice crystals in the shape of scales, needles, feathers or fans which are deposited by Sublimation at temperatures of 32°F (0°C) or lower. (2) A temperature low enough to cause freezing. (3) The process of freezing.

FULLY PERMANENT SPRINKLER SYSTEM — An irrigation system usually composed of buried enclosed conduits carrying water under pressure to fixed orifices to distribute water over a given area.

FURROW — A long, narrow, shallow trench made in the ground by a plow for planting and irrigation.

FURROW DAMS — Small earth ridges or rows used to impound water in furrows.

FURROW IRRIGATION — Spreading water by directing it into small channels across the field.

FURROW STREAM — The size of water flow released into the furrow; the size of the stream is adjusted to prevent erosion, limited in amount to the capacity of the furrow, and as needed for the intake rates of the soil involved.