Knowledge Base

SAFE WATER — Water that does not contain harmful bacteria, toxic materials, or chemicals, and is considered safe for drinking even if it may have taste, odor, color, and certain mineral problems.

SAFE YIELD — The rate at which water can be withdrawn from supply, source, or an aquifer over a period of years without causing eventual depletion or contamination of the supply.

SALINATION — The process whereby soluble salts accumulate in the soil.

SALINE — (1) Term used to describe waters containing common salt, or sodium chloride. (2) Of or containing any of the salts of the alkali metals or magnesium.

SALINE/POOR QUALITY AQUIFER — An aquifer containing water that is high in total dissolved solids, and is unacceptable for use as drinking water.

SALINITY — The relative concentration of salts, usually sodium chloride, in a given water sample. It is usually expressed in terms of the number of parts per thousand (0/00) or parts per million (ppm) of chlorine (Cl). Although the measurement takes into account all of the dissolved salts, sodium chloride (NaCl) normally constitutes the primary salt being measured. As a reference, the salinity of seawater is approximately 35 0/00.

SALINITY CONTROL — The physical control, management, and use of water and related land resources in such a way as to maintain or reduce salt loading and concentrations of salt in water supplies.

SALINITY INTRUSION — The movement of salt water into a body of fresh water. It can occur in either surface water or ground water bodies.

SALINIZATION — The accumulation of salts in soil to the extent that plant growth is inhibited. This is a common problem when crops are irrigated in arid regions; much of the water evaporates and salts accumulated in the soil.

SALT — A chemical class of ionic compounds formed by the combination of an acid and a base. Most salts are the result of a reaction between a metal and one or more nonmetals.

SALTATION — Particle movement in water or wind where particles skip or bounce along the stream bed or soil surface.

SALT BALANCE — A condition in which specific or total dissolved solids removed from a specified field, stratigraphic zone, political area, or drainage basin equals the comparable dissolved solids added to that location from all outside sources during a specified period of time.

SALT FLAT — A salt-encrusted flat area resulting from evaporation of a former body of water.

SALT LAKE — A landlocked body of water that has become salty through evaporation.

SALT WATER — Water which contains a relatively high percentage of sodium chloride.

SALT-WATER BARRIER — A physical facility or method of operation designed to prevent the intrusion of salt water into a body of fresh water.

SALT-WATER INTRUSION — The invasion of a body of fresh water by a body of salt water, due to its greater density. It can occur either in surface or ground-water bodies. The term is applied to the flooding of freshwater marshes by seawater, the migration of seawater up rivers and navigation channels, and the movement of seawater into freshwater aquifers along coastal regions.

SAND FILTER — (Water Quality) A device used to remove particles from drinking water prior to distribution to customers. The water is allowed to Percolate through a chamber containing sand of various grain sizes, with the finest grain size located on the top. The particles in the water are removed at the surface of the sand and later discarded by reverse flushing.

SANDSTONE AQUIFER — The type of aquifer supplying groundwater to large parts of the United States upper Middle West, Appalachia, and Texas. The water-bearing formation is often contained by shale strata, and the water has high levels of iron and magnesium.

SAND TRAP — (Irrigation) A device, often a simple enlargement in a ditch or conduit, for arresting the heavier particles of sand and silt carried by the water.

SANITARY LANDFILL — (Water Quality) A disposal site employing methods of disposing of solid wastes in a manner that minimizes environmental hazards by spreading, compacting to the smallest practical volume and applying cover material over all exposed wastes at the end of each operating day.

SANITARY SEAL (WATER WELL) — The neat cement seal at the top of a water well intended to prevent well contamination from surface water or shallow ground water flows containing potential contaminants.

SANITARY SEWER — A pipe or network of pipes which transport only municipal, commercial, or industrial wastewater (sewage) and not rain or storm waters from streets.

SANITARY SURVEY — An on-site review of the water sources, facilities, equipment, operation and maintenance of a public water system to evaluate the adequacy of those elements for producing and distributing safe drinking water.

SANITARY WATER — Water discharged from sinks, showers, kitchens, or other nonindustrial operations, but not from commodes.

SATURATED — (1) Generally, filled to capacity; having absorbed all that can be taken up; soaked through with moisture. (2) (Hydrologic) A condition often used in reference to soils in which all voids or pore spaces between soil particles are filled with water. (3) (Chemistry) Describes a solution in its most concentrated state in which dissolved material can remain in solution under given conditions of temperature, pressure, etc.

SATURATED ZONE — The zone in the earth's crust, extending from the water table downward, in which all open pore spaces in the soil or rock are filled with water at greater than atmospheric pressure. A termed used synonymously with the Zone of Saturation. Also referred to as Phreatic Zone.

SATURATION — The condition of a liquid when it has taken into solution the maximum possible quantity of a given substance at a given temperature and pressure.

SAUSAGE DAM — A dam composed of loose rock that has been wrapped with wire into cylindrical bundles and laid in a horizontal or vertical position.

SCENIC WATERWAY — Rivers or river segments chosen for scenic and recreation qualities to be preserved in their natural state.

SCHEDULE OF COMPLIANCE — Description of remedial actions to be accomplished by the permit holder (type of facility to be installed or alternative control measures to be established) and a sequence of actions leading to compliance with applicable standards.

SCHEDULED DELIVERY — Operation of a water delivery system to meet predetermined needs, generally based on user water orders.

SEA — (1) One of the larger bodies of salt water, less than an ocean, more or less landlocked and generally forming part of, or connecting with, an ocean or a larger sea. (2) An inland body of water, especially if large or if salty or brackish.

SEAL — A tight and perfect closure as against the passage of water.

SEA LEVEL — The level of the surface of the sea, especially measured at its mean position midway between mean high and low water.

(WELL) SEAL — (Hydraulics) The watertight seal established in the annular space between the outermost water well casing and the drill hole to prevent the inflow and movement of surface water or shallow ground water, or to prevent the outflow or movement of water under artesian pressures. The term also includes a Sanitary Seal.

SEAS (World) — The following constitute a listing of the principal the seas of the world in alphabetical order: Adriatic Sea, Aegean Sea, Amandson Sea, Andaman Sea, Arabian Sea, Arafura Sea, Aral Sea, Baltic Sea, Banda Sea, Barents Sea, Bearing Sea, Beaufort Sea, Bellingshausan Sea, Bismark Sea, Black Sea, Caspian Sea, Caribbean Sea, Celebes Sea, Celtic Sea, Chukchi Sea, Coral Sea, Davis Sea, Dead Sea, D'Urville Sea, East China Sea, East Siberian Sea, Flores Sea, Greenland Sea, Halmahera Sea, Ionic (Ionian) Sea, Irish Sea, Java Sea, Kara Sea, Labrador Sea, Laptev Sea, Ligurian Sea, Mediterranean Sea, Molucca Sea, Norwegian Sea, North Sea, Philippine Sea, Red Sea, Ross Sea, Salton Sea, Savu Sea, Scotia Sea, Sea of Azov, Sea of Cortez, Sea of Crete, Sea of Galilee, Sea of Hebrides, Sea of Japan, Sea of Marmara, Sea of Okhotsk, Sibuyan Sea, South China Sea, Sulu Sea, Tasman Sea, Timor Sea, Tyrrhenian Sea, Weddell Sea, White Sea, Yellow Sea.

SEASHORE — (1) Land by the sea. (2) (Legal) Ground lying between high-water and low-water marks; the Foreshore.

SEASONAL or INTERMITTENT STREAMS — Streams which flow only at certain times of the year when it receives water from springs, rainfall, or from surface sources such as melting snow.

SEASONAL WETLANDS — Wetland areas flooded or taking on the characteristics of a wetland only during specific periods of the year or seasons.

SECONDARY DATA — (Data Analysis) Typically, data acquired from published sources as opposed to data acquired from direct observation or measurement such as a survey. Contrast with Primary Data.

SEDIMENT — (1) In the singular the word is usually applied to material in suspension in water or recently deposited from suspension. In the plural the word is applied to all kinds of deposits from the waters of streams, lakes, or seas, and in a more general sense to deposits of wind and ice. Such deposits that have been consolidated are generally called sedimentary rocks. (2) Fragmental or clastic mineral particles derived from soil, alluvial, and rock materials by processes of erosion, and transported by water, wind, ice, and gravity. A special kind of sediment is generated by precipitation of solids from solution (i.e., calcium carbonate, iron oxides). Excluded from the definition are vegetation, wood, bacterial and algal slimes, extraneous light-weight artificially made substances such as trash, plastics, flue ash, dyes, and semisolids.

SEDIMENTATION — (1) Strictly, the act or process of depositing sediment from suspension in water. Broadly, all the processes whereby particles of rock material are accumulated to form sedimentary deposits. Sedimentation, as commonly used, involves not only aqueous but also glacial, aeolian, and organic agents. (2) (Water Quality) Letting solids settle out of wastewater by gravity during treatment.

SEDIMENTATION BASIN (SB) — A surface water runoff storage facility intended to trap suspended solids, suspended and buoyant debris, and adsorbed or absorbed potential pollutants that are carried by surface water runoff. The sedimentation basin may be part of an overall multipurpose detention and retention facility.

SEDIMENTATION TANKS — Wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.

SEDIMENT CONTROL — The control of movement of sediment on the land, in a stream or into a reservoir by means of manmade structures; such as debris dams, wing dams, or channelization; land management techniques, or natural processes.

SEDIMENT (CATCHMENT) DAM — A structure used specifically to trap sediment in water and prevent its transport further downstream.

SEDIMENT-DELIVERY RATIO — The ratio of sediment yield to gross erosion, expressed in percent.

SEDIMENT DISCHARGE, TOTAL — The rate at which dry weight of sediment passes a section of a stream or the quantity of sediment, as measured by dry weight or by volume, that is discharged in a given time.

SEDIMENT POOL — The reservoir space allotted to the accumulation of submerged sediment during the life of the structure.

SEDIMENTS — Soil, sand, and minerals washed from the land into water, usually after rain. They pile up in reservoirs, rivers, and harbors, destroying fish and wildlife habitat, and clouding the water so that sunlight cannot reach aquatic plants. Careless farming, mining, and building activities will expose sediment materials, allowing them to wash off the land after rainfall.

SEDIMENT STORAGE — The accumulation, in a reservoir, of sediment that would normally be carried downstream without the project.

SEDIMENT STORAGE (RESERVOIR) — That portion of total reservoir storage dedicated for sediment deposition and encroachment. Normally a part of Dead Storage.

SEEPAGE — (1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The Interstitial movement of water that may take place through a dam, its foundation, or its Abutments. (3) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field. Seepage is generally expressed as flow volume per unit of time. During the process of priming (a field during initial irrigation), the loss is called Absorption Loss.

SEEPAGE BED — A trench or bed more than 36 inches (0.91 meter) wide containing at least 12 inches (30.5 centimeters) of clean, coarse aggregate and a system of distribution piping through which treated sewage may seep into the surrounding soil.

SEEPAGE LAKES — Lakes whose ecology is determined primarily by ground water rather than surface water.

SEEPAGE LOSSES — A measure of water losses in a conveyance system due to water being seeped into the surrounding soils. Seepage losses from canals and other conveyance systems depend on: (1) the permeability of the surrounding soil; (2) the wetted surface of the canal; and (3) the difference in level of the water in the canal and the adjacent groundwater table. Broadly, the seepage losses range from 15-45 percent of diverted flow for unlined canals and from 5-15 percent for lined canals.

SEEPAGE PIT — A covered pit with lining designed to permit treated sewage to seep into the surrounding soil.

SEEPS — Groundwater/surface water connections caused by river or stream erosion into a near-surface aquifer.

SELF-PRODUCED WATER — A water supply (usually from wells) developed and used by an individual or entity.

SELF-PURIFICATION — The ability of a body of water to rid itself of pollutants. The removal of organic material, plant nutrients, or other pollutants from a lake or stream by the activity of the resident biological community. Biodegradable material added to a body of water will gradually be utilized by the microorganisms in the water, lowering the pollution levels. If excessive amounts of additional pollutants are not added downstream, the water will undergo self-cleansing. This process does not apply to pollution by non-biodegradable organic compounds or metals.

SEMIARID — A term applied to regions or climates where moisture is normally greater than under arid conditions but still definitely limits the growth of most crops. Dryland farming methods or irrigation generally are required for crop production. The upper limit of average annual precipitation in the cool semiarid regions is as low as 15 inches (38.1 cm). Whereas in tropical regions it is as high as 45 or 50 inches (114.3 or 127.0 cm).

SETTLING BASIN — An enlargement in the channel of a stream to permit the settling of materials carried in suspension.

SETTLING CHAMBER — (Water Quality) An enclosed container into which wastewater contaminated with solid materials is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the container for removal.

SETTLING POND — (Water Quality) An open Lagoon into which wastewater contaminated with solid pollutants is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the lagoon and the liquid is allowed to overflow out of the enclosure.

SEWAGE — The liquid waste from domestic, commercial, and industrial establishments.

SEWAGE SYSTEM — Pipelines or conduits, pumping stations, force mains, and all other structures, devices, and facilities used for collecting or conducting wastes to a point for treatment or disposal.

SEWAGE TREATMENT — The processing of wastewater for the removal or reduction of contained solids or other undesirable constituents.

SHALLOW WELL — A well with a pumping head of 20 feet or less, permitting use of a suction pump.

SIPHON, also Syphon — (1) A pipe or tube fashioned or deployed in an inverted U shape and filled until atmospheric pressure is sufficient to force a liquid from a reservoir in one end of the tube over a barrier higher than the reservoir and out the other end. (2) (Zoology) A tubular organ, especially of aquatic invertebrates such as squids or clams, by which water is taken in or expelled.

SIPHON TUBES — (Irrigation) Small curved pipes, typically 0.5-4.0 inches (1.3-10.2 centimeters) in diameter, that deliver water over the side of a head ditch or lateral to furrows, corrugations, or borders.

SLACK WATER — (1) The period at high or low tide when there is no visible flow of water. (2) An area in a sea or river unaffected by currents; still water.

SLACKWATER CHANNEL — A navigation channel in a canal or river where the water surface elevation is controlled by a dam or dams with locks.

SLIP-OFF SLOPE BANK — The bank of a meandering stream which is not eroded by stream action, and which may be built up gradually.

SLIPWAY — (Nautical) A sloping surface leading down to the water, on which ships are built or repaired and then more readily moved back into the water.

SLOPE — The side of a hill or mountain, the inclined face of a cutting, canal or embankment or an inclination from the horizontal. In the United States, it is measured as the ratio of the number of units of horizontal distance to the number of corresponding units of vertical distance. The term is expressed as a percent when the slope is gentle, in which cast the term Gradient is also used.

SLOPE PROTECTION — The protection of a Slope against wave action or erosion.

SLOPING GAGE — A staff gage used to register the elevation of the water surface in a stream channel, conduit, reservoir or tank, with a scale graduated to represent vertical elevation. A sloping gage is usually installed on a flat sloping bank where it is desirable to increase the accuracy of reading the gage.

SLOW SAND FILTER — Essentially, a concrete basin covered with graded gravel and about 3 feet of sand used to pass raw water through at low velocity, resulting in substantial removal of chemical and biological contaminants. Cleaning is accomplished by removing the surface layers of sand at periodic intervals. These are then washed and stored for reuse.

SLUDGE — (1) (Water Quality) Semisolid material such as the type precipitated by a Sewage Treatment Plant. The terms Biosolids, sludge, and Sewage Sludge can be used interchangeably. (2) Mud, mire, or ooze covering the ground or forming a deposit, as on a riverbed. (3) Finely broken or half-formed ice on a body of water, especially the sea.

SOIL — The meaning of this term varies depending on the field of consideration: (1) Pedology — the earth materials which have been so modified and acted upon by physical, chemical, and biological agents that it will support rooted plants; (2) Engineering Geology — the layer of incoherent rock material that nearly everywhere forms the surface of the land and rests on Bedrock, also called Regolith; (3) Ecology — A dynamic natural body on the surface of the earth in which plants grow, composed of mineral and organic materials and living forms.

SOIL ABSORPTION FIELD — A sub-surface area containing a trench or bed with clean stones and a system of piping through which treated sewage may seep into the surrounding soil for further treatment and disposal.

SOIL CLASSIFICATION — — The systematic arrangement of soils into groups or categories on the basis of their characteristics. Broad groupings are made on the basis of general characteristics and subdivisions on the basis of more detailed differences in specific properties. Soil Taxonomy is the study of soil classification systems.

SOIL ERODIBILITY — An indicator of a soil's susceptibility to raindrop impact, runoff, and other erosive processes.

SOIL EROSION — The detachment and movement of soil from the land surface by wind or water.

SOIL MANAGEMENT — The basis of all scientific agriculture, which involves six essential practices: (1) proper tillage; (2) maintenance of a proper supply of organic matter in the soil; (3) maintenance of a proper nutrient supply, including water; (4) control of soil pollution; (5) maintenance of the correct soil acidity; and (6) control of erosion.

SOIL MOISTURE (SOIL WATER) — Water diffused in the upper part of the Unsaturated Zone (Zone of Aeration) of the soil, from which water is discharged by the Transpiration of plants, by Evaporation, or Interflow.

SOIL-MOISTURE DEPLETION — The process where soil water is removed by crops through Evapotranspiration.

SOIL-MOISTURE DEFICIENCY (or DEFICIT) — The difference between the water-holding capacity of the soil and the instantaneous soil moisture.

SOIL MOISTURE REGIME — The changes in the moisture content of soil during a year.

SOIL MORPHOLOGY — The physical constitution, particularly the structural properties, of a soil profile as exhibited by the kinds, thickness, and arrangement of the horizons in the profile and by the texture, structure, consistency, and porosity of each horizon.

SOIL PROFILE — A vertical section of the soil from the surface through all its horizons. The three basic horizontal layers that may be observed in a soil profile are the A, B, and C horizons. The A horizon, or topsoil, is the main source of plant nutrients. Soluble materials leach from the A horizon down to the subsoil, or B horizon. This is the zone of clay accumulation. The deepest layer, the C horizon, is composed of partially weathered bedrock.

SOIL STRUCTURE — The physical properties of different soils. Sand has little structure because sand particles do not tend to stick together, whereas clay has a firm structure because clay particles tend to pack tightly together to form a solid material.

SOIL TAXONOMY — — The systematic study and arrangement of soils into classifications based on their characteristics.

SOIL WATER — Water present in the soil pores.

SOLID — A state of matter, neither liquid nor gas. The solid state of water is ice.

SOLID WASTE — (Water Quality) Any garbage, refuse, sludge from a waste treatment plant, water supply treatment plant, or air pollution control facility, and other discarded material, including solid, liquid, semisolid, or contained gaseous materials resulting from industrial, municipal, commercial, mining, and agricultural operations, and from community and institutional activities.

SPECIFIC CAPACITY (of a Well) — In ground water hydrology, the ratio of the discharge or yield of a well, usually measured in gallons per minute per foot, to drawdown after a period of sustained pumping.

SPECIFIC DISCHARGE (SPECIFIC FLUX) — For ground water, the rate of discharge per unit area, measured at right angles to the direction of flow.

SPECIFIC DRAWDOWN — The drawdown in a well per unit discharge.

SPECIFIC ENERGY — The sum of the piezometric head and the velocity head; total energy, with respect to the bottom of a conduit or channel as a datum.

SPECIFIC HUMIDITY — The mass of water vapor per unit mass of moist air.

SPECIFIC STORAGE — The volume of water removed or added within the unit volume of an aquifer per unit change in head.

SPECIFIC YIELD (GROUND WATER) — The ratio of the volume of water that a rock will yield by gravity, after being saturated, to its own volume, expressed as a percentage.

SPILLWAY — The channel or passageway around or over a dam through which excess water is diverted. If the flow is controlled by gates, it is a controlled spillway; if the elevation of the spillway crest is the only control, it is an uncontrolled spillway.

SPRAY — (1) A cloud or mist of fine liquid particles, as of water from breaking waves. (2) A jet of fine liquid particles, or mist, as from an atomizer or spray gun.

SPRAY IRRIGATION — Any irrigation by means of nozzles along a pipe or from perforated overhead pipes.

SPREADING BASIN — A surface facility, often a large pond, used to increase the percolation of surface water into a Ground Water Basin.

SPRINKLER IRRIGATION — A pressurized irrigation system where water is distributed through pipes to the field and applied through a variety of sprinkler heads or nozzles. Pressure is used to spread water droplets above the crop canopy to simulate rainfall. These systems include portable and traveling guns, solid or permanent fixtures (overhead or pop ups), center pivots, and periodic moving systems. The efficiencies of these sprinkler systems range from 15 to 85 percent; however, the average of 70 percent is commonly used.

STABLE CANAL SYSTEM — A canal system in which flow disturbances are attenuated.

STATIC WATER DEPTH — (Hydraulics) For a water well, the vertical distance from the centerline of the pump discharge down to the surface level of the free pool while no water is being drawn from the pool or water table.

STATIC WATER LEVEL — (1) The elevation or level of the water table in a well when the pump is not operating. (2) The level or elevation to which water would rise in a tube connected to an Artesian Aquifer or basin in a conduit under pressure.

STORAGE — (1) Water artificially impounded in surface or underground reservoirs for future use. (2) Water naturally detained in a drainage basin, such as ground water, channel storage, and depression storage. The term Drainage Basin Storage, or simply Basin Storage, is sometimes used to refer collectively to the amount of water in natural storage in a drainage basin. (3) (Water Quality) The temporary holding of waste pending treatment or disposal, as in containers, tanks, waste piles, and surface impoundments.

STORAGE CAPACITY, ACTIVE (USABLE) — The volume of water normally available for release from a reservoir below the stage of the maximum controllable level; equal to total capacity less inactive and dead capacity.

STORAGE CAPACITY, CONSERVATION — Storage capacity available for all useful purposes such as municipal water supply, power, irrigation, recreation, fish and wildlife, etc., excluding joint and exclusive flood control capacity.

STORAGE CAPACITY, DEAD — The volume of a reservoir below the sill or invert of the lowest outlet.

STORAGE CAPACITY, EXCLUSIVE FLOOD CONTROL — The space in reservoirs reserved for the sole purpose of regulating flood inflows to abate flood damage.

STORAGE CAPACITY, INACTIVE — The portion of capacity below which the reservoir is not normally drawn, and which is provided for sedimentation, recreation, fish and wildlife, aesthetic reasons, or for creation of a minimum controlled operational or power head in compliance with operating agreements or restrictions.

STORAGE CAPACITY, JOINT USE — The volume of a reservoir available to store water jointly for flood control and conservation purposes.

STORAGE CAPACITY, LIVE — The volume of a reservoir exclusive of dead and surcharge capacity.

STORAGE CAPACITY, SEDIMENT — The volume of a reservoir planned for the deposition of sediment.

STORAGE CAPACITY, SURCHARGE — The volume of a reservoir between the maximum water surface elevation for which the dam is designed and the crest of an uncontrolled spillway, or the normal full-pool elevation with the crest gates in the normal closed position.

STORAGE CAPACITY, TOTAL — The total volume of a reservoir exclusive of surcharge.

STORAGE COEFFICIENT — (1) For surface water, the relation of storage capacity in a reservoir to the mean annual flow of a stream above the dam forming the reservoir. (2) For ground water, primarily in a Confined Aquifer, it is a measure of the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. This definition is similar to that of the Specific Yield for a water-table aquifer. However, confined aquifers remain saturated at all times and therefore water release in not met by drainage of the void spaces as is the case of an Unconfined Aquifer, but due to the change in pore pressure.

STORAGE RATIO — The net available storage divided by the mean flow for one year.

STORAGE-REQUIRED FREQUENCY CURVE — A graph showing the frequency with which storage equal to or greater than selected amounts will be required to maintain selected rates of regulated flow.

STORAGE RESERVOIR — A reservoir that has space for retaining water from springtime snowmelt or other hydrologic events. Retained water is released as necessary for multiple uses — power production, fish passage, irrigation, navigation, municipal and industrial, etc.

STORAGE, SPECIFIC (Ground Water) — The amount of water released from or taken into storage per unit volume of a porous medium per unit change in head.

STORAGE, USABLE — The volume of water normally available for release from a reservoir below the stage of the maximum controllable level.

STREAM — A general term for a body of flowing water; natural water course containing water at least part of the year. In Hydrology, the term is generally applied to the water flowing in a natural channel as distinct from a canal. More generally, as in the term Stream Gaging, it is applied to the water flowing in any channel, natural or artificial. Some classifications of streams include, in relation to time:
[1] Ephemeral Streams — Streams which flow only in direct response to precipitation and whose channel is at all times above the water table.
[2] Intermittent or Seasonal Streams — Streams which flow only at certain times of the year when it receives water from springs, rainfall, or from surface sources such as melting snow.
[3] Perennial Streams — Streams which flow continuously.
And, in relation to ground water:
[4] Gaining Streams — Streams or a reach of a stream that receive water from the zone of saturation. Also referred to as an Effluent Stream.
[5] Insulated Streams — Streams or a reach of a stream that neither contribute water to the zone of saturation nor receive water from it. Such streams are separated from the zones of saturation by an impermeable bed.
[6] Losing Streams — Streams or a reach of a stream that contribute water to the zone of saturation. Also referred to as an Influent Stream.
[7] Perched Streams — Perched streams are either losing streams or insulated streams that are separated from the underlying ground water by a zone of aeration.

STREAMBANK EROSION — The wearing away of streambanks by flowing water.

STREAMBANK EROSION CONTROL — Vegetative or mechanical control of erodible stream banks, including measures to prevent stream banks from caving or sloughing, such as jetties, revetments, riprap and plantings necessary for permanent protection.

STREAMBANK EROSION DAMAGE — Value of land areas destroyed, reduced value of land due to threat of future erosion, and the destruction or damage of wildlife habitat, buildings, bridges, utilities, or other structures.

STREAMBANKS — The usual boundaries, not the flood boundaries, of a stream channel. Right and left banks are named facing downstream (in the direction of flow).

STREAMBANK STABILIZATION — Natural geological tendency for a stream to mold its banks to conform with the channel of least resistance to flow. Also the lining of streambanks with riprap, matting, etc., to control erosion.

STREAMBED — The channel through which a natural stream of water runs or used to run, as a dry streambed.

STREAMBED EROSION — The movement of material, causing a lowering or widening of a stream at a given point or along a given reach.

STREAM CAPTURE — The process whereby a stream rapidly eroding headward cuts into the divide separating it from another drainage basin, and provides an outlet for a section of a stream in the adjoining valley. The lower portion of the partially diverted stream is called a Beheaded Stream.

STREAM CHANNEL — The bed where a natural stream of water runs or may run; the long narrow depression shaped by the concentrated flow of a stream and covered continuously or periodically by water.

STREAM CLEARANCE — The removal of natural or man-caused debris from stream channel areas by mechanical means.

STREAMFLOW — The discharge that occurs in a natural channel. Although the term discharge can be applied to the flow of a canal, the word streamflow uniquely describes the discharge in a surface stream course. Streamflow is a more general term than runoff, as streamflow may be applied to discharge whether or not its is affected by diversion or regulation.

STREAMFLOW DEPLETION — The amount of water that annually flows into a valley or onto a particular land area minus the amount that flows out of the valley or away from the particular land area. It is also the amount of water taken from a stream.

STREAMFLOW REGULATION — The artificial manipulation of the flow of a stream.

STREAMFLOW ROUTING — A technique used to compute the effect of channel storage on the shape and movement of a flood wave.

STREAM GAGING — The quantitative determination of stream flow using Gages, Current Meters, Weirs, or other measuring instruments at selected locations.

STREAM-GAGING STATION — A gaging station where a continuous record of the discharge of a stream is obtained.

STREAM GRADIENT — A general slope or rate of change in vertical elevation per unit of horizontal distance of the water surface of a flowing stream.

STREAMLET — A small stream.

STREAMLINE (FLOWLINE) — (1) A line that is parallel to the direction of flow of a fluid at a given instant. (2) The path followed by a particle of water as it moves through a saturated soil mass.

STREAM SEGMENT — (Water Planning) Surface waters of an approved planning area exhibiting common biological, chemical, hydrological, natural, and physical characteristics and processes. Segments will normally exhibit common reactions to external stresses, for example, discharge or pollutants.

STREAM TERRACE — A surface representing remnants of a stream's channel or flood plain when the stream was flowing at a higher level. Subsequent downward cutting by the stream leaves remnants of the old channel or flood plain standing as a terrace above the present level of the stream.

STREAM, UNDERGROUND — A subsurface stream which has all the characteristics of a water-course on the surface — a definite channel with bed and banks, a definite stream of water, and a definite source(s) of supply.

SUB BASIN — (1) A portion of a subregion or basin drained by a single stream or group of minor streams. (2) The smallest unit into which the land surface is subdivided for hydrologic study purposes.

SUBIRRIGATION (Subirrigate) — (1) Irrigation below the surface (as by a periodic rise of the water table or by a system of underground porous pipes). (2) Irrigation of crops from water table(s) that are in turn supplied by seepage from above-lying canals, laterals, reservoirs, or irrigated fields.

SUBIRRIGATED LAND — Land with a high water table condition, either natural or artificially controlled, that normally supplies a crop irrigation requirement.

SUBSURFACE IRRIGATION SYSTEM — Irrigation by means of underground porous tile or its equivalent.

SUBSURFACE WATER — All water which occurs below the ground surface.

SUBSOIL — Soil material underlying the surface soil.

SUBSURFACE — Of, relating to, or situated in an area beneath a surface, especially the surface of the earth or of a body of water.

SUBSURFACE 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. (2) The water drained away from irrigated farmland. Also referred to as Agricultural Drainage.

SUBSURFACE DRAINS — Subsurface drains are buried, perforated pipelines designed to collect and convey subsurface water from an irrigated area.

SUBSURFACE FLOW — Water which infiltrates the soil surface and moves laterally through the upper soil layers until it enters a channel.

SUBSURFACE SEEPAGE — Subsurface seepage is movement of water through soils from above-lying bodies of water.

SUBSURFACE WATER — Water below the surface of the ground, including soil moisture, intermediate zone water, capillary fringe water, and ground water.

SURFACE IRRIGATION — A water application whereby water is applied to the soil either by controlled flooding or through some kind of furrow.

SURFACE RUNOFF — That part of the runoff which travels over the soil surface to the nearest stream channel. It is also defined as that part of the runoff of a drainage basin that has not passed beneath the surface since precipitation. Also applies to snowmelt or irrigation water in excess of what can infiltrate the soil surface and be stored in small surface depressions. In terms of surface water quality, may constitute a major transporter of Non-Point Source (NPS) Pollution. The term is misused when applied in the sense of Direct Runoff.

SURFACE SUPPLY (of Water) — Water supply from streams, lakes, and reservoirs.

SURFACE WATER — All waters whose surface is naturally exposed to the atmosphere, for example, rivers, lakes, reservoirs, ponds, streams, impoundments, seas, estuaries, etc., and all springs, wells, or other collectors directly influenced by surface water.

SURFACE WATER DISPOSAL — Refers to the release of reclaimed water or treated effluent directly into a surface body of water (including marshes and wetlands). This does not include water discharged into ponds for holding or Percolation purposes.

SURFACE WATER WITHDRAWALS — Includes all waters taken from streams, rivers, ponds, lakes, reservoirs, springs and all effluent and other waste water.

SUSTAINABLE DEVELOPMENT — Describes those efforts to guide economic growth, especially in less-developed countries, in an environmentally sound manner, with an emphasis on natural resource conservation.

SUSTAINABLE MANAGEMENT — A method of exploiting a resource that can be carried on indefinitely. For example, the removal of water from an aquifer in excess of recharge is, in the long term, not a sustainable management method.

SUSTAINED YIELD — Achievement and maintenance, in perpetuity, of a high-level annual or regular periodic output or harvest of the various renewable land and water resources.

SYSTEM DESIGN CAPACITY — (Water Quality) Plant design capacity plus any blending water added to the desalting plant product.