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Tacking — The binding of Mulch fibers by mixing them with an adhesive chemical compound during land Restoration projects.

Tafoni — Natural cavities in rocks formed by weathering.

Tailings — The waste material remaining after metal is extracted from ore.

Tailrace —
(1) The part of a Millrace below the water wheel through which the spent water flows; the channel which conducts water away from a water wheel.
(2) A channel for floating away mine tailings and refuse.
(3) A race for conveying water away from a point of industrial application (as a waterwheel or turbine) after use.

Tail Water —
(1) In Hydraulics, water, in a river or channel, immediately downstream from a structure.
(2) In Irrigation, water that reaches the lower end of a field; excess surface water draining especially from a field under cultivation. Tail water is not necessarily lost; it can be collected and reused on the same or adjacent fields.

Tailwater Recovery — The process of collecting irrigation water runoff for reuse in the system.

Tailwater Runoff — Refers to unused irrigation water or rain water that is collected at the base or at the end of an irrigation system or field in a ditch or other impoundment. This water may be reused again for irrigation purposes, left to evaporate, percolate into the ground, treated, and/or discharged to surface bodies of water.

Tank — An artificial pool, pond, reservoir, cistern, or large container for holding and storing water for drinking or irrigation.

Tap — A valve and spout used to regulate delivery of a fluid at the end of a pipe.

Tapered Aeration — A modification of the activated sludge process wherein air is introduced at a higher rate at the head of the tank than in subsequent sections.

Tap Water — Water withdrawn directly from a tap or faucet.

Taproot — A main root that grows straight down. Taproots can go very deep if there is a lack of soil moisture near the surface.

Tarn — A small steep-banked mountain lake or pool, generally formed by a glaciation process.

Taxonomy —
(1) The science, laws, or principles of classifying living organisms in specially named categories based on shared characteristics and natural relationships.
(2) The division of biology concerned with the classification and naming of organisms. The classification of organisms is based upon a hierarchial scheme beginning with Kingdom and ending with Species at the base. The higher the classification level (i.e., going from kingdom to species), the fewer features the organisms have in common. For example, the taxonomy of the Lahontan cutthroat trout (LCT), Oncorhynchus clarki henshawi, is the following:
Kingdom . . . . . . Animal
Phylum . . . . . . . . Chordata
Class . . . . . . . . . Osteichthyes
Order . . . . . . . . . Salmoniformes
Family . . . . . . . . Salmonidae
Genus . . . . . . . . . Oncorhynchus
Species . . . . . . . . clarki
Subspecies . . . . . henshawi

TDS (Total Dissolved Solids) — All the solids (usually mineral salts) that are dissolved in water. Used to evaluate water quality.

Technology-Forcing — Describing standards or levels of pollution and effluent control called for in environmental statutes or regulations for which existing technologies are inadequate and therefore require technical advancements to achieve.

Temperate (Deciduous) Forest — Forested areas characterized by moderate temperatures, weather, or climate, and rainfall from 30 to 60 inches per year. These forests are found in eastern North America, eastern Australia, western, central, and eastern Europe, and parts of China and Japan. Typical deciduous trees in the North American deciduous forests are oak, hickory, maple, ash, and beech.

Temperature Inversion — A surface cooling at the earth’s surface which sometimes leads to an increase in temperature with altitude.

Temporary Hardness — Water hardness that can be reduced or removed by heating the water. Heating drives off carbon dioxide, shifting the carbonate buffer system equilibrium so that carbonate ions combine with dissolved calcium or magnesium ions, form solids, and precipitate. This lowers the calcium/magnesium ion water concentration, lowering the hardness. Also referred to as Carbonate Hardness. Also see Ion Exchange.

Temporary Transfer — The transfer of a water right from one purpose to another for a specifically designated period of time.

Temporary Wetland — A type of Wetland in which water is present for only part of the year, usually during the wet or rainy seasons (e.g., spring). Also referred to as Vernal Pools.

Tenaja — Pools in seasonal streams that may support a flora similar to Vernal Pools upon desiccation.

Tensiometer — An instrument used for measuring the suction or negative pressure of soil water.

Tephra — (Geology) Volcanic material; ash-fall.

Teratogenic — Causing birth defects.

Terminal Lake — A lake with no outlet.

Terminal Moraine — Constitutes the material (Glacial Till) left behind by the farthest advance of a Glacier’s toe. Each different period of glaciation leaves behind its own uniquely developed moraines. Also see Moraines, Lateral Moraines, and Recession Moraine.

Terminal Spill — Refers to those releases made at the terminal ends of the project conveyance or reservoir system. These canal or reservoir releases are not reused on the project’s improved irrigated acreage.

Terminal Velocity — The final velocity of falling solid particles in water or in air or of raindrops in air.

Terminal (Settling) Velocity — For a particle falling in a nonturbulent fluid (liquid or gas), the maximum possible velocity reached when the drag, or frictional resistance, on the particle equals the gravitational force on the particle. The measure is used in the design of chambers in which particles are removed from air or from water by gravitational settling. The horizontal flow rate through the chamber must allow time for the particles to reach the bottom of the Settling Chamber.

Terminus — Refers to the location of water’s final destination, as in the terminus of a river system being a Terminal Lake.

Terrace —
(1) (Erosion and Irrigation) An embankment or combination of an embankment and channel constructed across a slope to control erosion by diverting and temporarily storing surface runoff instead of permitting it to flow uninterrupted down the slope. Outlets may be soil infiltration only, vegetated waterways, tile outlets, or combinations thereof.
(2) (Geological) An old alluvial plain, ordinarily flat or undulating, bordering a river, lake, or the sea. Stream terraces are frequently called second bottoms, as contrasted to flood plains, and are seldom subject to overflow. Marine terraces were deposited by the sea and are generally wide.
(3) Also, a Berm or discontinuous segments of a berm, in a valley at some height above the Flood Plain, representing a former abandoned flood plain of the stream.

Terracing — A series of levels on a hillside, one above the other; dikes built along the contour of sloping farm land that hold runoff and sediment to reduce erosion. Hillside farming on terraces greatly reduces water erosion of soil.

Terraqueous — Composed of land and water.

Terrestrial — Living or growing on land rather than in water or air.

Terrigenous — Derived from or originating on the land (usually referring to sediments) as opposed to material or sediments produced in the ocean (marine) or as a result of biologic activity (biogenous).

Territorial Waters — (Legal)
(1) The waters under the sovereign jurisdiction of a nation or state including both marginal sea and inland waters.
(2) In international law, waters subject to the jurisdiction of a sovereign nation, as distinguished from High Seas, and consisting of waters within the nation, waters that are boundaries between nations, and coastal waters. Such jurisdiction extends also to the air space above and to the bed beneath those waters. Jurisdiction over boundary waters, such as lakes or rivers, is fixed by treaties; the limit of the jurisdiction of each nation is usually an imaginary line drawn through the center of such waters. In the United States each state exercises jurisdiction over waters wholly within the state, but streams forming part of the system of interstate waterways are subject to federal government control. Also see Interstate Compact.

Tertiary Wastewater Treatment — Selected biological, physical, and chemical separation processes to remove organic and inorganic substances that resist conventional treatment practices; the additional treatment of effluent beyond that of primary and secondary treatment methods to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process:
(1) First, in the Primary Wastewater Treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes;
(2) Second, in the Secondary Wastewater Treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds; and
(3) Third, the Tertiary Wastewater Treatment process consists of flocculation basins, clarifiers, filters, and chlorine basins or ozone or ultraviolet radiation processes. Tertiary techniques may also involve the application of wastewater to land to allow the growth of plants to remove plant nutrients.

Test Hole (Test-Well) — (Hydraulics) A well hole drilled for experimental or exploratory purposes.

Thalweg — Longitudinal line along a stream bottom that follows the deepest part of the channel.
(1) The line connecting the deepest points along a stream.
(2) The lowest thread along the axial part of a valley or stream channel.
(3) A subsurface, ground-water stream percolating beneath and in the general direction of a surface stream course or valley.
(4) The middle, chief, or deepest part of a navigable channel or waterway.

Theoretical Oxygen Demand (ThOD) — The amount of oxygen that theoretically is required to totally oxidize a substance.

Thermal Mass — Materials that absorb heat or coolness and store it for a long period of time. Water and masonry materials can provide thermal mass. Such materials react slowly to temperature variations and are important aspects of any passive heating or cooling system.

Thermal Plant — A power generating plant which uses heat to produce energy. Such plants may burn fossil fuels or use nuclear energy to produce the necessary thermal energy.

Thermal Plume — The hot water discharged from a power generating facility or other industrial plant. When the water at elevated temperature enters a receiving stream or body of water, it is not immediately dispersed and mixed with the cooler waters . The warmer water moves as a single mass (plume) downstream from the discharge point until it cools and gradually mixes with that of the receiving stream. Also see Thermal Pollution.

Thermal Pollution — The influx of heated water, usually from a power plant, wastewater from a factory or sewage treatment plant, or the discharge of other industrial cooling water, into a stream, lake, bay, or ocean, disturbing the temperature of the given body of water. The resulting shift to a warmer aquatic environment can cause a change in species composition and lower the dissolved oxygen content of the water. Also has application to air, through waste heat emitted by industry, home appliances, machines, etc.

Thermal Spring — A spring that brings warm or hot water to the surface. Sometimes called warm spring, or hot spring. Temperature usually 15EF (9.4EC) or more above mean air temperatures.

Thermal Stratification — The vertical temperature stratification of a lake or reservoir which consists of: (a) the upper layer, or Epilimnion, in which the water temperature is virtually uniform; (b) the middle layer, or Thermocline, in which there is a marked drop in temperature per unit of depth; and (c) the lowest stratum, or Hypolimnion, in which the temperature is again nearly uniform.

Thermocline —
(1) The region in a thermally stratified body of water which separates warmer oxygen-rich surface water from cold oxygen-poor deep water and in which temperature decreases rapidly with depth.
(2) A layer in a large body of water, such as a lake, that sharply separates regions differing in temperature, so that the temperature gradient across the layer is abrupt.
(3) The intermediate summer or transition zone in lakes between the overlying Epilimnion and the underlying Hypolimnion, defined as that middle region of a thermally stratified lake or reservoir in which there is a rapid decrease in temperature with water depth. Typically, the temperature decrease reaches 1EC or more for each meter of descent (or equivalent to 0.55EF per foot).

Thermoelectric Power — Electrical power generated using fossil-fuel (coal, oil, or natural gas), geothermal, or nuclear energy.

Thermoelectric Power Water Use — Water used in the process of the generation of Thermoelectric Power. The water may be obtained from a Public Water Supply System or may be self supplied. Also see Self-Supplied Water.

Thermograph — A self-registering thermometer which has a thermometric element consisting either of a bimetallic strip or a metal tube filled with alcohol or mercury, and makes an autographic record on a ruled chart wrapped around a clock-driven cylinder.

Thickener — A Settling Pond or tank where the concentration of solids is increased by allowing settling and the removal of clarified liquid. The solids that are pumped from the bottom of the pond or tank are much thicker than the incoming fluid.

Thiokol — A trademark used for any of various polysulfide polymers in the form of liquids, water dispersions, and rubbers used in seals and sealants.

Third Party (Parties) — The people, communities, and environments not directly engaged in a transfer of water or water rights (i.e., the buyers or sellers) but still affected by the transfer. These affected parties can include areas of origin, Indian tribes, other minority cultures and peoples, communities that depend on irrigated agriculture or water-based recreation, boaters, anglers, and broad segments of the public who care about wetlands, riparian areas, endangered species, instream (minimum) flows, aesthetics, and other environmental values that might be hared
or enhanced by a change in water use.

Third-Party Impacts — Direct and indirect economic, social or environmental effects of a water transfer to a party other than the seller or buyer.

Threatened Species — Any plant or animal species likely to become an “endangered” species within the foreseeable future throughout all of a significant area of its range or natural habitat; identified by the Secretary of the Interior as “threatened”, in accordance with the 1973 Endangered Species Act (ESA).

Three-Mile Limit — The limit of the marginal sea of three miles included in the territorial waters of a state.

Threshold Odor Number (TON) — A value indicative of the maximum dilution which can be made of a sample with its odor remaining detectable. A higher TON indicates a stronger odor.

Threshold Pollutant — A substance that is harmful to a particular organism only above a certain concentration, or threshold level.

Throughfall — In a vegetated area, the precipitation that falls directly to the ground, or the rainwater or snowmelt that drops from twigs or leaves.

Tides — The alternate rising and falling of the surface of oceans, and of seas, gulfs, bays, rivers, and other water bodies caused by the gravitational attraction of the moon and sun occurring unequally on different parts of the earth. The tide ebbs (falls) and flows (rises) twice in each lunar day (24 hours and 51 minutes). It is occasioned by the attraction of the sun and the moon (the tide-raising force of the latter being three times that of the former), acting unequally on the waters in different parts of the earth, thus disturbing their equilibrium. High tide upon one side of the earth (Direct Tide) is accompanied by high tide upon the other side (Opposite Tide). Therefore, when the sun and the moon are in conjunction or opposition, as at the new moon and the full moon, their combined action
produces a tide greater than usual, called Spring Tide. When the moon is at first or third quarter, the sun’s attraction in part counteracts the moon’s, causing a smaller high tide than usual (and a higher low tide), called Neap Tide. The flow or rising of the water is called Flood Tide; the reflux, Ebb Tide.

Tidewater —
(1) Water that inundates land at flood tide.
(2) Water affected by the tides, especially tidal streams.
(3) Low coastal land drained by tidal streams.

Till (Glacial) — Till is the mixture of rocks, boulders, and soil picked up by a moving Glacier and carried along the path of the ice advance. The glacier deposits this till along its path — on the sides of the ice sheet, at the toe of the glacier when it recedes, and across valley floors when the ice sheet melts. These till deposits are akin to the footprint of a glacier and are used to track the movement of glaciers. These till deposits can be good sources of ground water, if they do not contain significant amounts of impermeable clays. Also see Moraines, Lateral Moraines, and Terminal Moraines.

Tillage — Plowing, seedbed preparation, and cultivation practices.

Tilth — (1) The general physical condition of soil as it relates to agriculture use. (2) Land used for agriculture, as opposed to pasture or forest.

Tilting Gate — (Hydraulics) A hinged gate counterbalanced by weights, that automatically opens and closes with a change in head.

Time-Domain Electromagnetics (TDEM) — (Geophysics) A high technology form of Dowsing (Dousing), or groundwater exploration, used to search for underground bodies of water (aquifers). The technique employs a grid pattern of electric wires placed on the surface of the ground. The wires are charged with a rapidly pulsating electric current and then the resultant electronic “echoes” are carefully analyzed. These data are then used to construct a three-dimensional computer model of the water-bearing potential of underground rock formations and sediment layers.

Time of Concentration — The time required for water to flow from the farthest point on the water shed to the gauging station, culvert, or other point of interest.

Time of Travel (TOT) — The time required for a contaminant to move in the Saturated Zone from a specific point to a well.

Time-Weighted Average — Computed by multiplying the number of days in the sampling period by the concentrations of individual constituents for the corresponding period and dividing the sum of the products by the total number of days. A time-weighted average represents the composition of water that would be contained in a vessel or reservoir that had received equal quantities of water from the stream each day for the year.

Titrant — A solution of known strength or concentration; used in Titration.

Titration — (Chemistry) (1) A method, or the process, of determining the strength of a solution, or the concentration of a substance in solution, in terms of the smallest amount of it required to bring about a given effect in reaction with another known solution or substance, as in the neutralization of an acid by a base. (2) A process whereby a solution of known strength (the Titrant) is added to a certain volume of treated sample containing an indicator. A color change shows when the reaction is complete (the end point).

Titrator — An instrument, usually a calibrated cylinder (tube-form), used in Titration to measure the amount of Titrant being added to the sample.

TMDL — Total Maximum Daily Load (TMDL) is the amount of a particular pollutant that a particular stream, lake, estuary or other waterbody can 'handle' without violating state water quality standards.

Toe —
(1) The downstream edge at the base of a dam.
(2) The break in slope at the foot of a stream bank where the bank meets the bed.
(3) The line of a natural or fill slope where it intersects the natural ground.
(4) The lowest edge of a backslope of a cut where it intersects the roadbed or bench.

Toe Drain and Outfall — A drainage conduit from a dam’s structure used to carry seepage water away from the dam and can allow seepage quantities to be measured.

Toe Wall — The downstream wall of a structure.

Toeslope — The lowermost portion of the footslope component of an erosional slope. It is distinguished from the upper footslope by a greater accumulation of pedisediment. Also, the lowermost, most gently sloping portion of any slope.

Tolerant species — Those species that are adaptable to (tolerant of) human alterations to the environment and often increase in number when human alterations occur.

Tonnage — The number of tons of water that a ship displaces when afloat.

Tons per Acre-Foot — The dry mass of dissolved solids in 1 acre-foot of water. It is computed by multiplying the concentration of the constituent, in milligrams per liter (mg/L), by0.00136.

Tons per Day — The rate representing a mass of 1 ton of a constituent in streamflow passing a cross section in 1 day. It is equivalent to 2,000 pounds per day, or 0.9072 metric tons per day.

Total Carbon (TC) — (Water Quality) A measure of the amount of carbon-containing compounds in water. The measure includes both organic and inorganic forms of carbon as well as compounds that are soluble and insoluble. The typical laboratory analysis involves the conversion of all forms of carbon to carbon dioxide and the subsequent measurement of the carbon dioxide produced. The parameter represents an estimate of the strength of wastewater and the potential damage that an effluent can cause in a receiving stream or other body of water as a result of the removal of Dissolved Oxygen from the water. The measurement of total carbon requires less sample, is more rapid, and yields more reproducible results than the measurement of either the Chemical Oxygen Demand (COD) or the Biochemical Oxygen Demand (BOD). Also see Total Organic Carbon (TOC).

Total Coliform — The Escherica coli and similar gram negative bacteria that are normal inhabitants of fecal discharges. The total coliform group is recognized in the drinking water standards of public health criteria.

Total Coliform Bacteria — A particular group of bacteria that are used as indicators of possible sewage pollution. This group includes coliforms that inhabit the intestine of warm-blooded animals and those that inhabit soils. They are characterized as aerobic or facultative anaerobic, gram-negative, nonspore-forming, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 35 degrees centigrade. In the laboratory, these bacteria are defined as all the organisms that produce colonies with a golden-green metallic sheen within 24 hours when incubated at 35 degrees centigrade plus or minus 1 degree centigrade on M-Endo medium (nutrient medium for bacterial growth). Their concentrations are expressed as the number of colonies per 100 mL of sample.

Total Constituent — The total amount of a given constituent in a representative suspended-sediment sample, regardless of the constituent’s physical or chemical form. This term is used only when the analytical procedure assures measurement of at least 95 percent of the constituent present in both the dissolved and suspended phases of the sample. A knowledge of the expected form of the constituent in the sample, as well as the analytical methodology used, is required to judge when the results should be reported as “total”. (Not that the word “total” serves a double meaning here, first indicating that the sample consists of a suspended-sediment mixture and second that the analytical method determined all of the constituent in the sample.)

Total Discharge — The quantity of a given constituent, measured as dry mass or volume, that passes a stream cross section per unit of time. When referring to constituents other than water, this term needs to be qualified, such as “total sediment discharge”, “total chloride discharge”, etc.

Total Dissolved Solids (TDS) — (Water Quality) A measure of the amount of material dissolved in water (mostly inorganic salts). Typically aggregates of carbonates, bicarbonates, chlorides, sulfates, phosphates, nitrates, etc. of calcium, magnesium, manganese, sodium, potassium, and other cations which form salts. The inorganic salts are measured by filtering a water sample to remove any suspended particulate material, evaporating the water, and weighing the solids that remain. An important use of the measure involves the examination of the quality of drinking water. Water that has a high content of inorganic material frequently has taste problems and/or water hardness problems. As an example, water that contains an excessive amount of dissolved salt (sodium chloride) is not suitable for drinking. High TDS solutions have the capability of changing the chemical nature of water.
High TDS concentrations exert varying degrees of osmotic pressures and often become lethal to the biological inhabitants of an aquatic environment. The common and synonymously used term for TDS is “salt”. Usually expressed in milligrams per liter.

Total Head — Energy contained by fluid because of its pressure, velocity, and elevation, usually expressed in feet of fluid (foot-pounds per pound).

Total Inorganic Carbon (TIC) — (Water Quality) The total amount of inorganic salts of carbonates and bicarbonates present in water without regard as to whether the salts are in suspended particulate form or dissolved. Water that contains an excessive amount of these salts is considered to be Hard Water. The dissolved materials interfere with the functioning of soaps and detergents and can form adherent scale in boilers, pipes, and steam equipment.

Total Inorganic Nitrogen (TIN) — A measure of the total Nitrate, Nitrite, and Ammonia concentrations of a body of water, typically measured in milligrams per liter (mg/l) or micrograms per liter (ìg/l). From the point of view of a planktonic algae, nitrate, nitrite, and ammonia are all very suitable sources of nitrogen for growth. Also see Carlson’s Trophic State Index (TSI).

Total Inorganic Phosphate (TIP) — A measure of the concentration of usable phosphorus (soluble Phosphates) contained in a body of water. Soluble phosphates readily contribute to algae growth in water.

Total Kjeldahl Nitrogen (TKN) — The total concentration of nitrogen in a sample present as ammonia or bound in organic compounds.

Total Load — All of a constituent in transport. When referring to sediment, it includes suspended load plus bed load.

Total Maximum Daily Load (TMDL) — (Water Quality) The maximum quantity of a particular water pollutant that can be discharged into a body of water without violating a water quality standard. The amount of pollutant is set by the U.S. Environmental Protection Agency (EPA) when it determines that existing, Technology-Based effluent standards on the water pollution sources in the area will not achieve one or more Ambient Water Quality Standards. The process results in the allocation of the TMDL to the various Point Sources (PS) of pollutants in the area.

Total Organic Carbon (TOC) — (Water Quality) A measure of the amount of organic materials suspended or dissolved in water. The measure is very similar to the assay of the total carbon content; however, samples are acidified prior to analysis to remove the inorganic salts of Carbonates and Bicarbonates. The assay of total organic carbon represents an estimation of the strength of wastewater and the potential damage that an effluent can cause in a receiving body of water as a result of the removal of Dissolved Oxygen from the water. The measurement of total organic carbon requires less sample, is more rapid, and yields more reproducible results than the measurement
of either the Chemical Oxygen Demand (COD) or the Biochemical Oxygen Demand (BOD). As a pollution indicator, this method is more reliable than the assay of Total Carbon (TC) when the wastewater contains high amounts of total inorganic carbon as well.

Total Recoverable Constituent — The amount of a given constituent that is in solution after a representative suspended-sediment sample has been digested by a method (usually using a dilute acid solution) that results in dissolution of only readily soluble substances. Complete dissolution of all particulate matter is not achieved by the digestion treatment, and thus the determination represents something less than the “total” amount (that is, less than 95 percent) of the constituent present in the dissolved and suspended phases of the sample. To achieve comparability of analytical data, equivalent digestion procedures are required of all laboratories performing such analyses because different digestion procedures are likely to produce different analytical results.

Total Sediment Discharge — The total quantity of sediment passing a section in a unit of time.

Total Sediment Load — The sum of the Bed Load and the Suspended Sediment Load (Discharge).

Total Soil Water Potential — The work per unit quantity of pure water that has to be done to change its energy status to that of soil water at the point under consideration. This equals the sum of matric, gravity, pressure, osmotic, and overburden potentials.

Total Solids (TS) — (Water Quality) A measure of the amount of material that is either dissolved or suspended in a water sample, obtained by allowing a known volume to evaporate and then weighing the remaining residue. Total solids equals the sum of the measurements of Total Dissolved Solids (TDS) and Total Suspended Solids (TSS).

Total Storage (Reservoir) — The volume of storage below the maximum designed water surface level, including Dead Storage.

Total Suspended Particles — A method of monitoring particulate matter by the total weight of a sample of water.

Total Suspended Solids (TSS) — (Water Quality) Solids, found in waste water or in a stream, which can be removed by filtration. The origin of suspended matter may be man-made wastes or natural sources such as silt. Compare to Total Dissolved Solids (TDS).

Total Toxicity — Toxicity as determined by exposing aquatic organisms to samples or dilutions of instream water or treated effluent.

Total Trihalomethanes (TTHMs) — (Water Quality) The sum of the concentrations of individual members of a family of halogenated derivatives of methane in drinking water. The concentrations of the following are employed to compute the sum in milligrams per liter (mg/l): chloroform (CHCl3), dichlorobromomethane (CHCl2Br), dibromochloromethane (CHClBr2), and bromoform (CHBr3). See Trihalomethanes (THMs).

Total Water Used — Total water withdrawal which does not include recirculation.

Totalizing Meters — A water measuring (headgate or surface tailwater runoff point) device which registers or accumulates total flow (for example, in acre-feet).

Township — A territorial subdivision, generally considered six miles long, six miles wide, and containing 36 Sections, each section 1 mile square (640 acres). The Township designation is part of a description of the location of land using the survey system (Public Land Survey System — PLSS) of the United States Government and includes the 40–acre subdivision within a quarter, section, township and range. The public land survey system is based on the concept of a township as a square parcel of land six miles on each side. Its location is established as being so many six-mile units east of a north-south line (called the meridian) and so many six-mile units north or south of an eastwest line (called the baseline). The township is described by township and range, e.g., T.4N, R.23E. Each township is further divided into 36 parts called sections one mile square (each section measuring 5,280 feet on each side). A typical section contains 640 acres; however, some sections may contain more or less acreage than 640.

Toxaphene — (Water Quality) A chemical that causes adverse health effects in domestic water supplies and is toxic to fresh water and marine aquatic life.

Toxemia — A pathological condition in a person or animal caused by the presence of a toxic substance in the body.

Toxic —
(1) Describing a material that can cause acute or chronic damage to biological tissue following physical contact or absorption.
(2) Substances that even in small quantities may poison, cause injury, or cause death when eaten or ingested through the mouth, absorbed through the skin or inhaled into the lungs.

Toxicant — Any chemical that has the potential of causing acute or chronic adverse effects in animals, plants, or humans.

Toxicity —
(1) The ability of a chemical substance to cause acute or chronic adverse health effects in animals, plants, or humans when swallowed, inhaled or absorbed.
(2) The occurrence of lethal or sublethal adverse effects on representative, sensitive organism due to exposure to Toxic Materials. Adverse effects caused by conditions of temperature, dissolved oxygen, or nontoxic dissolved substances are excluded from the definition of toxicity.

Toxicity Characteristic Leaching Procedure (TCLP) — A test that measures the mobility of organic and inorganic chemical contaminants in wastes. The test, designed by the U.S. Environmental Protection Agency (EPA), produces an estimate of the potential for Leachate formation by a waste if it is placed in the ground. If the TCLP is applied to a solid waste sample and the extract leached from the waste or the solid waste sample itself contains concentrations of specified materials exceeding allowable levels, the waste is defined as a Hazardous Waste, meeting the toxicity characteristic.

Toxic Materials — Any liquid, gaseous, or solid substance or substances in a concentration which, when applied to, discharged to, or deposited in water or another medium may exert a poisonous effect detrimental to people or to the propagation, cultivation, or conservation of animals, or other aquatic life.

Toxicology — The study of chemical agents that cause diminished health and death in organisms, including humans. The study involves the chemistry, recognition, identification, measurement, distribution, and metabolism of hazardous substances to which organisms are exposed. The science also includes the prediction of potential adverse effects of chemicals on organisms, including humans.

Toxic Salt Reduction — Decreasing harmful concentrations of toxic salts in soils, usually by leaching and with or without the addition of soil amendments.

Toxin — Any of a variety of unstable, poisonous compounds produced by some microorganisms and causing certain diseases or physical reactions.

Trace — The amount of rainfall or other form of precipitation which occurs when the quantity is so small that it cannot be measured in the rain gage.

Trace Elements — Elements essential to plant or animal life but required only in small amounts, such as the trace amounts of manganese, zinc, iron, molybdenum, cobalt, and copper.

Trace Metals — A general term for metals found in small quantities (less than 1 milligram per liter — mg/l) in water, usually due to their insolubility.

Tractive Force — The drag on a stream bank caused by passing water, which tends to pull soil particles along with the stream flow.

Tragedy of the Commons — The concept that no one takes responsibility for things that everybody owns.

Transbasin — Generally, the transfer of water from one river basin to another river basin.

Transfer —
(1) Refers to the movement of water from one reservoir or storage facility to another.
(2) A movement of water or water rights that involves a change in point of diversion, a change in type of use, or a change in location of use.

Transfer (Water Right) —
(1) The process of transferring a water right from one person to another.
(2) A passing or conveyance of title to a water right; a permanent assignment as opposed to a temporary lease or disposal of water. Most states require that some formal notice or filing be made with an appropriate state agency so that the transaction is officially recorded and the new owner is recorded as the owner of the water right.

Transfer Rate — The use-rate for a water right that is transferred from an owner to a buyer.

Transfer or Change in Use (Water Right) — Generally, this term refers to a change in the place of use or purpose of use of water authorized by a particular water right. If done in the proper manner, the change can be made without loss of priority.

Transient Flow — Unsteady flow during a change from a steady-flow state to another steady-flow state.

Transient Water System — A non-community water system that does not serve 25 of the same nonresidents per day for more than six months per year.

Transition Zone — The intervening area between distinct environments.

Transitional Storage Reserve — The quantity of water in storage in a particular groundwater aquifer that is extracted during the transition period between natural equilibrium conditions and new equilibrium conditions with groundwater pumped at perennial yield levels.

Translatory Wave — (Hydraulics) (1) A gravity wave that propagates in an open channel and results in appreciable displacement of the water in a direction parallel to the flow. (2) A wave, such as a flood wave, whose water particles constantly progress in the direction of the wave movement; a characteristic of unsteady flow. A gravity wave that propagates in an open channel and results in displacement of water particles in a direction parallel to the flow.

Transmissibility (Ground Water) — The capacity of a rock to transmit water under pressure. The coefficient of transmissibility is the rate of flow of water, at the prevailing water temperature, in gallons per day, through a vertical strip of the aquifer one foot wide, extending the full saturated height of the aquifer under a hydraulic gradient of 100 percent. A Hydraulic Gradient of 100 percent means a one foot drop in head in one foot of flow distance.

Transmission Lines — Pipelines that transport raw water from its source to a water treatment plant, then to the distribution grid system.

Transmissivity, also Coefficient of Transmissivity (ô) — The ability of an aquifer to transmit water. The rate at which water of the prevailing kinematic viscosity is transmitted through a unit width of the aquifer under a unit Hydraulic Gradient. It is equal to an integration of the hydraulic conductivities across the saturated part of the aquifer perpendicular to the flow paths. Also, the rate at which water is transmitted through a unit width of an aquifer under a unit hydraulic gradient. Transmissivity values are given in gallons per minute through a vertical section of an aquifer 1 foot wide and extending the full saturated height of an aquifer under a hydraulic gradient of one in the English Engineering System; in the Standard International System, transmissivity is given in cubic
meters per day through a vertical section of an aquifer 1 meter wide and extending the full saturated height of an aquifer under hydraulic gradient of one. It is a function of properties of the liquid, the porous media, and the thickness of the porous media. Also see Coefficient of Transmissivity.

Transparency — The portion of light that passes through water without distortion or absorption. A measure of the Turbidity of water or other liquids.

Transpiration —
(1) The movement of water from the soil or ground water reservoir via the stomata in plant cells to
the atmosphere.
(2) The quantity of water absorbed, transpired, and used directly in the building of plant tissue during a specified time period. It does not include soil evaporation.
(3) The process by which water vapor escapes from a living plant, principally through the leaves, and enters the atmosphere. As considered practically, transpiration also includes Guttation. Transpiration, combined with Evaporation from the soil, is referred to as Evapotranspiration.

Transpiration Ratio — The number of pounds of water required for transpiration per pound of dry plant tissue produced.

Transport — Conveyance of solutes and particles in flow systems.

Transport Capacity — The ability of a stream to transport a Suspended Load, expressed in terms of the total weight of the suspended particles.

Trap — A device for sealing a passage against the escape of gases, especially a U-shaped or S-shaped bend in a drainpipe that prevents the return flow of sewer gas by means of a water barrier.

Trap Efficiency (of Reservoirs) — The ratio of sediment retained within the reservoir to the sediment inflow of the reservoir expressed as a percentage.

Trash Rack —
(1) A barrier placed at the upstream end of a culvert to trap debris but allow water to flow through.
(2) A screen located at an intake fixture of a dam spillway or other such conduit to prevent the ingress of debris.

Travertine — A form of calcium carbonate (CaCO3), such as aragonite or calcite, that is precipitated out of hot mineral springs as it cools upon reaching the ground surface. Travertine becomes colored by minerals in the water and by biological action and is sometimes quarried for use as decorative stone.

Treated (Wastewater) Effluent — Water that has received primary, secondary, or advanced treatment to reduce its pollution or health hazards and is subsequently released from a wastewater facility after treatment.

Treatment — Any method, technique, or process designed to remove solids and/or pollutants from wastestreams and effluents. Also see Pretreatment, Primary Wastewater Treatment, Secondary Wastewater Treatment, and Tertiary Wastewater Treatment.

Treatment Facility — Any place(s) where a community water system or Nontransient-Noncommunity Water System alters the physical or chemical characteristics of the drinking water. Chlorination may be considered as a function of a Distribution System.

Treatment Plant — A structure built to treat wastewater before discharging it into the environment.

Treatment Tank — A water-tight tank designed to retain sewage long enough for satisfactory bacterial decomposition of the solids to take place. Septic Tanks and Aerobic Sewage Treatment Tanks are examples.

Trellis Pattern — A roughly rectilinear arrangement of stream courses in a pattern reminiscent of a garden trellis, developed in a region where rocks of differing resistance to erosion have been folded, beveled, and uplifted.

Trend —
(1) A statistical term referring to the direction or rate of increase or decrease in magnitude of the individual members of a time series of data when random fluctuations of individual members are disregarded.
(2) A unidirectional increasing or decreasing change in the average value of a variable.

Trespass — Any voluntary transgression of law or rule, as to enter wrongfully upon another’s land or to infringe upon another’s rights to use water.

Tributary —
(1) A stream which joins another stream or body of water.
(2) A stream or other body of water, surface or underground, which contributes its water, even though intermittently and in small quantities, to another and larger stream or body of water.

Trickle — To flow or fall in drops or in a thin stream.

Trickle Channel — A longitudinal channel constructed along the center and lowest part of a channel or through a detention or retention facility and intended to carry low flows. Also referred to as a Cunette.

Trickle (Drip) Soil Absorption System — A shallow slow rate pressure-dosed system used for land application of treated wastewater, particularly under soil conditions unsuitable for normal septic tanks and gravity-fed soil absorption systems. In agriculture, drip soil irrigation systems irrigate crops by means of a network of shallow underground pipes fed by a pump. Such a system conserves water used in crop irrigation by applying it at a controlled rate in the root zone, minimizing evaporation and percolation losses. In the drip soil absorption system, the filtered effluent is delivered via supply lines to a subsurface drip field consisting of parallel rows of polyethylene tubing, known as dripper lines. Emitters are installed along these tubes to uniformly distribute and control the flow of effluent. The key to the effective operation of drip soil absorption systems is the slow and controlled rate at which it applies effluent over a large surface area, allowing relatively shallow placement of the dripper lines and long-term use without risk of saturating soils. This allows such systems to be effectively used for subsurface irrigation of trees, shrubs, and gardens in arid regions. Also see Septic Tank Soil Absorption System (ST–SAS).

Trickle Tube — A small diameter pipe to take water by gravity from a farm pond to a drinking receptacle without allowing livestock access to the pond.

Trickling Filter — (Water Quality) A means of secondary sewage treatment used to remove soluble or colloidal organic compounds. The filter consists of a bed of small rocks or other suitable material provides a surface for the growth of microorganisms. As the clarified wastewater (from which the particulate material has been removed) passes through the trickling filter, organic material is metabolized by aerobic processes by the attached organisms.

Trihalomethanes (THMs) —
(1) Any of several synthetic organic compounds formed when chlorine combines with organic materials in water during the disinfection process. The most common THM is chloroform.
(2) A group of low-molecular-weight, halogenated hydrocarbons, derivatives of methane, CH4, in which three halogen atoms (chlorine, bromine, or iodine) are substituted for three of the hydrogen atoms. The subsequent substances typically include the compounds of chloroform (CHCl3), dichlorobromomethane (CHCl2Br), dibromochloromethane (CHClBr2), and bromoform (CHBr3). The sum of these four compounds is referred to as Total Triholomethanes (TTHMs). The group includes suspect human Carcinogens. Small amounts of THMs have been detected in raw water collected from surface sources used as a public water supply, and concentrations have been shown to be increased during the chlorination phase of the water purification process. The most marked increase during
chlorination of drinking water has been recorded in water containing suspended particles and/or humic substances.

Triple Point — The condition of temperature and pressure under which the gaseous, liquid, and solid phases of a substance can exist in equilibrium. For water, at a standard pressure of one (1) atmosphere, this represents a temperature of 273.16 Kelvin (K), 0.01°C (Celsius), and 32.02°F Fahrenheit. Also see Temperature Scale, Celsius [Temperature Scale], Centigrade [Temperature Scale], and Fahrenheit [Temperature Scale].

Trompe — An apparatus in which water falling through a perforated pipe entrains air into and down the pipe to produce an air blast for a furnace or forge.

(Mean) Trophic State Index (TSI) — A measure of Eutrophication of a body of water using a combination of measures of water transparency or turbidity (using Secchi Disk depth recordings), Chlorophyll–a concentrations, and total phosphorus levels. TSI measures range from a scale 20–80 (referred to as Carlson’s Trophic State Index). 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).

Trophogenic Region — The area of a body of water where organic production from mineral substances takes place on the basis of light energy and photosynthetic activity.

Trough —
(1) A long, narrow, generally shallow receptacle for holding water or feed for animals; any of various
similar containers for domestic or industrial use.
(2) A gutter under the eaves of a roof.
(3) A long, narrow depression, as between waves or ridges.
(4) A long but shallow depression in the bed of the sea.
(5) (Meteorology) An elongated region of relatively low atmospheric pressure, often associated with a front.

Tsunami — A huge sea wave caused by a great disturbance under an ocean, as a strong earthquake or volcanic eruption.

Tube Settler — A device using bundles of tubes to let solids in water settle to the bottom for removal by conventional sludge collection means; sometimes used in sedimentation basins and clarifiers to improve particle removal.

Tuberculation (Tubercules) — Development or formation of small mounds of corrosion products on the inside of iron pipe. The tubercules so formed roughen the inside of the pipe, increasing its resistance to water flow. See Microbiological Tuberculation.

Tufa — (Geology) The calcareous and siliceous rock deposits of springs, lakes, or ground water. Typically consist of calcium carbonate (CaCO3) deposits created by precipitation from supersaturated waters entering a cold lake from thermal springs. Some forms of shoreline tufa were created by an algal process in which carbon dioxide was extracted by the algae to produce insoluble calcium carbonate; this was then precipitated as aragonite (as opposed to calcite). Several primary forms of tufa have been identified:
[1] Lithoid — deposited in superimposed layers, compact and stony;
[2] Thinolite — made up of elongated skeletal crystals;
[3] Dendritic — the most abundant variety, of branching structure;
[4] Cellular — found as coatings; and
[5] Coralline — occurring in heads and coatings.
Also see Travertine.

Tuffs — (Geology) A volcanic rock composed of ash particles.

Tundra — A type of Ecosystem or Biome dominated by lichens, mosses, grasses, and woody plants. Tundra may be found both at high latitudes (arctic tundra) and high altitudes (alpine tundra). Arctic tundra is underlain by permafrost and is usually saturated, also classifying it also as a Wetlands.

Turbellarian — The tiny eddies created in water by the cilia any of a class (Turbellaria) of mostly aquatic and freeliving flatworms (as a planarian).

Turbid —
(1) Having the lees or sediment disturbed; roiled; cloudy.
(2) Not clear or translucent; clouded, muddy; dull; impure; polluted. Also see Turbidity.

Turbidimeter — A device used to measure the degree of turbidity, or the density of suspended solids in a sample.

Turbidity —
(1) A measure of the reduced transparency of water due to suspended material which carries water quality implications. The term “turbid” is applied to waters containing suspended matter that interferes with the passage of light through the water or in which visual depth is restricted. The turbidity may be caused by a wide variety of suspended materials, such as clay, silt, finely divided organic and inorganic matter, soluble colored organic compounds, plankton and other microscopic organisms and similar substances. Turbidity in water has public health implications due to the possibilities of pathogenic bacteria encased in the particles and thus escaping disinfection processes. Turbidity interferes with water treatment (filtration), and affects aquatic life. Excessive amounts of turbidity also make water aesthetically objectionable. The degree of the turbidity of water is measured by a
Turbidimeter.
(2) The collective optical properties of a water sample that cause light to be scattered and absorbed rather than transmitted in straight lines; the higher the intensity of scattered light, the higher the turbidity. Turbidity is expressed in nephelometric turbidity units (NTU) or Formazin turbidity units (FTU) depending on the method and equipment used.

Turbidity Current — A current in which a limited volume of turbid or muddy water moves relative to surrounding water because of its greater density.

Turbine — A propeller or wheel device driven by the pressure of liquid or gas.

Turbulence — A state of fluid flow in which instantaneous velocities exhibit irregular and apparently random fluctuations.

Turbulent Flow —
(1) (Physics) The motion of a fluid having local velocities and pressures that fluctuate randomly.
(2) The mechanism by which a fluid such as water moves near a rough surface. Fluid not in contact with the irregular boundary outruns that which is slowed by friction or deflected by the uneven surface. Fluid particles move in a series of eddies or whirls. Most stream flow is turbulent, and turbulent flow is important in both erosion and transportation. Contrast with Laminar Flow.

Turning Basin — A widened area in a navigation channel or harbor area which is constructed to enable ships to maneuver in a safe and efficient manner.

Turnout — A structure that diverts water from an irrigation canal to a distribution system or farm delivery point. Turnouts are used at the head of Laterals.

Turnover, Fall — 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 Overturn. Also see Spring Overturn.

Turnover, Spring — A physical phenomenon that may take place in a lake or similar body of water during the early spring, most frequently in lakes located in temperate zones where the winter temperatures are low enough to result in freezing of the lake surface. The sequence of events leading to spring overturn include:
(1) the melting of ice cover;
(2) the warming of surface waters;
(3) density changes in surface waters producing convection currents from top to bottom;
(4) circulation of the total water volume by wind action; and
(5) vertical temperature equality. The overturn results in a uniformity of the physical and chemical properties of the entire water mass. Also referred to as Spring Overturn.

Typhoid Fever — An acute, highly infectious disease caused by a bacillus (Salmonella typhi) transmitted chiefly by contaminated food or water and characterized by high fever, headache, coughing, intestinal hemorrhaging, and rose-colored spots on the skin. Also referred to as Enteric Fever.

Typhoon — A tropical Cyclone occurring in the region of the Philippines or China Sea.