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.
Tahoe-Prosser Exchange Agreement (California-Nevada)  Also referred to as the "Agreement for Water Exchange Operations of Lake Tahoe and Prosser Creek Reservoir," this agreement was finalized in June 1959 and designated certain waters in Prosser Reservoir in the Truckee River Basin as "Tahoe Exchange Water."  By this agreement, when waters were to be released from Lake Tahoe for a minimum instream flow (50 cfs winter; 70 cfs summer) and when such releases from Lake Tahoe were not necessary for Floriston Rates due to normal flows elsewhere in the river, then an equal amount of water (exchange water) could be stored in Prosser Reservoir and used for releases at other times.  Also see Truckee River Agreement (Nevada and California).
Tahoe Regional Planning Agency (TRPA) (Lake Tahoe - California and Nevada)  A bi-state regulatory agency created in July 1968 as part of a provisional California-Nevada Interstate Compact developed by the joint California-Nevada Interstate Compact Commission which was formed in 1995.  The TRPA was the first bi-state regional environmental planning agency in the United States.  The TRPA was intended to oversee land-use planning and environmental issues within the Lake Tahoe Basin and is dedicated to preserving the beauty of the region.  Today, the TRPA leads the cooperative effort within the basin to preserve, restore, and enhance the unique natural and human environment of the region and is a leading partner in a comprehensive program which monitors water quality, air quality, and other threshold standard indicators.  The TRPA's Environmental Thresholds Carrying Capacities (ETCC) programs are designed to address the following thresholds:
 Water Quality
 Air Quality
 Soil Conservation
 Vegetation
 Fisheries
 Wildlife
 Scenic Resources/Community Design
 Recreation
 Noise
The structure of the TRPA consists of a 15-member Governing Board which sets TRPA policy, oversees administration of the agency, approves all amendments to the Lake Tahoe Basin Regional Plan and reviews major project applications.  The Governing Board is advised by a 19-member Advisory Planning Commission made up of area planning and natural resource management professionals, and lay persons.  The Executive Director directs approximately 50 staff members in the following principal functional areas:  (1) Environmental Education; (2) Environmental Improvement Program (EIP) Facilitation; (3) Environmental Compliance Division; (4) Project Review Division; and (5) Long Range Planning Division.  Representation on the TRPA's Governing Board is as follows:
 (1)  Governor of California Appointee (California);
 (2)  Governor of California Appointee (California);
 (3)  California Assembly Speaker Appointee (California);
 (4)  California Senate Rules Committee Appointee (California);
 (5)  El Dorado County Appointee (California);
 (6)  Placer County Appointee (California);
 (7)  City of South Lake Tahoe Appointee (California);
 (8)  Governor of Nevada Appointee (Nevada);
 (9)  Nevada Government Appointee (Nevada);
 (10)  Nevada Department of Conservation & Natural Resources Appointee (Nevada);
 (11)  Washoe County Appointee (Nevada);
 (12)  Douglas County Appointee (Nevada);
 (13)  Carson City Appointee (Nevada);
 (14)  Nevada at-Large Appointee (Nevada);
 (15)  Presidential Appointee (United States)
In late 1995 the TRPA created the Shorezone Partnership Committee of 20 organizations and entities to lessen the problems among those interested in the future development of Lake Tahoe.  Those represented included:  California and Nevada state lands; California and Nevada state parks, California Department of Fish and Game, California Tahoe Conservancy, Lahontan Regional Water Quality Control Board; League to Save Lake Tahoe; Nevada Division of Wildlife; Tahoe Lakefront Owners Association; TRPA; Tahoe Research Group; Tahoe-Sierra Preservation Council; U.S. Army Corps of Engineers; U.S. Forest Service; commercial property owners; Lake Tahoe marinas; Lake Tahoe tour-boat operators; other private property owners; and Lake Tahoe Basin recreation concessionaires.
Taiga  A subarctic, evergreen coniferous forest of northern Eurasia located just south of the Tundra and dominated by firs and spruces.  Also referred to as a Boreal Forest.  Also see Biome.
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.
Tar Balls  Non-volatile hydrocarbon clumps remaining in water after the volatile fractions have evaporated from crude oil that has been discharged or spilled into the marine environment.  When washed ashore, these residues, which range in size from marbles to beach balls, spoil beaches and marine habitat.
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
TCID  See Truckee-Carson Irrigation District (TCID) (Nevada).
TDS (Total Dissolved Solids)  All the solids (usually mineral salts) that are dissolved in water.  Used to evaluate water quality.
Technology-Based  Describing emission or effluent limitations that are not defined in terms of allowable releases that achieve a desirably low ambient pollutant concentration, but instead are based on the pollutant control efficiency that is achievable using current levels of technology.
Technology-Based Limitations  (EPA) Industry-specific effluent limitations applied to a discharge when it will not cause a violation of water quality standards at low stream flows.  Usually applied to discharges into large rivers.
Technology-Based Standards  (EPA) Effluent limitations applicable to direct and indirect sources which are developed on a category-by-category basis using statutory factors, not including water-quality effects.
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.
Teleconnection  (Meteorology) A term which describes the influence of an aberration in weather patterns in one part of the world to cause strange weather in another area of the globe.  Also see El Ni?o, El Ni?o/Southern Oscillation (ENSO), and Hurricane Forecasting.
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.  Also see Biome.
Temperature  The degree of hotness or coldness.  Also, a measure of the average energy of the molecular motion in a body or substance at a certain point.
Temperature Gradient  The rate of change of temperature with increase in height or decrease in depth.
Temperature Inversion  A surface cooling at the earth's surface which sometimes leads to an increase in temperature with altitude.
Temperature Regulation  The processes through which an organism's temperature is adjusted to certain metabolic requirements or conditions in its environment.  For example, the act of human perspiration promotes surface skin evaporation which cools the body.
Temperature Scale  The temperature scale adopted by a 1960 international conference was based on a fixed temperature point, the Triple Point of water, at which the solid, liquid, and gas are in equilibrium.  The temperature of 273.16 K (Kelvin) was assigned to this point.  The freezing point of water was designated as 273.15 K, equaling exactly 0? on the Celsius Temperature Scale.  The Celsius scale, which is identical to the Centigrade Temperature Scale, is named for the 18th-century Swedish astronomer Anders Celsius, who first proposed the use of a scale in which the interval between the freezing and boiling points of water is divided into 100 degrees.  By international agreement, the term Celsius has officially replaced Centigrade.
Tempest  A violent windstorm, frequently accompanied by rain, snow, or hail.
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.
Tennessee Valley Authority (TVA)  A Depression-era federal government project created in 1933 to control and harness the Tennessee River and its tributaries.  The TVA became perhaps the best known of President Franklin Roosevelt's "New Deal" public works projects.  The TVA currently operates 47 dams, 11 coal-fired and 2 nuclear power plants, and an extensive power transmission system.  The Tennessee Valley Authority Power System encompasses the state of Tennessee and parts of the states of Kentucky, Virginia, North Carolina, Georgia, Alabama, and Mississippi, and borders the Mississippi River on the west.
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.  Also see Operational Spill.
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 obtai
Test Hole (Test-Well)  (Hydraulics) A well hole drilled for experimental or exploratory purposes.
(Local) Test-Well Site Designation (Nevada)  The local test-well site designation used in Nevada is based on the identification of a site by hydrographic area and by the official rectangular subdivision of the public lands referenced to the Mount Diablo (located east of Walnut Creek, California) ba
Test-Well Site Identification (U.S. Geological Survey)  The standard U.S. Geological Survey (USGS) site identification is based on the grid system of latitude and longitude.  The number consists of 15 digits.  The first six digits denote the degrees, minutes, and seconds of latitude; the next seven digits denote degrees, minutes, and seconds of longitude; and the last two digits (assigned sequentially) identify the sites within a 1-second grid.  For example, site 365227114554401 is at 36?52?27? latitude and 114?55?44? longitude, and it is the first site recorded in that 1-second grid.  The assigned number is retained as a permanent identifier even if a more precise latitude and longitude are later determined.  Also see (Local) Test-Well Site Designation (Nevada).
Tetrachloroethylene (Perchloroethylene, PCE)  A solvent often used for degreasing and in dry cleaning which sometimes makes its way into water wells and other ground water supplies.  Studies have shown that high concentrations of the chemical can cause liver and kidney damage, including cancer, in animals.  In humans, however, not enough information is available to say it is a definite carcinogen.  The U.S. Environmental Protection Agency's (EPA) safe drinking water standard for tetrachloroethylene is 0.005 parts per million (ppm).  Also referred to as Perchloroethylene (PCE) and Perclene.
Texture  Refers to relative proportions of clay, silt, and sand in soil.
Thalweg  (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.
Thank-You-Ma'am  (Derived from its causing a nodding of the head) A bump or depression in a road; especially a ridge or hollow made across a road on a hillside to cause water to run off and thereby minimize erosion.  Also known as a Water Break.
Thatch  Dead stems that build up beneath certain ground covers and lawn grasses, sometimes becoming so thick and compressed as to impede infiltration by water.
Thaw  (1) To change from a frozen solid to a liquid by gradual warming.  Synonymous with Melt.  (2) To become warm enough for snow and ice to melt.  (3) A period of warm weather during which ice and snow melt.
Theoretical Oxygen Demand (ThOD)  The amount of oxygen that theoretically is required to totally oxidize a substance.
Thermal  Having to do with heat, as a hot spring (Thermal Spring).
Thermal Gradient  A temperature difference between two areas.
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 15?F (9.4?C) 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 1?C or more for each meter of descent (or equivalent to 0.55?F 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).  (See Appendix D-1, Nevada's Endangered and Threatened Species.)
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.
Thunder  The crashing or booming sound produced by rapidly expanding air along the path of the electrical discharge of lightning.
Thunderbird  (Mythology) A spirit of thunder, lightning, and rain in the form of a huge bird in the mythology of certain Native American peoples.
Thundercloud  A large dark cloud charged with electricity and producing thunder and lightning; A Cumulonimbus cloud.  See Cloud.
Thunderhead  A round mass of Cumulus Clouds appearing before a Thunderstorm.
Thundershower  A shower accompanied by thunder and lightning.
Thundersquall  A squall accompanied by thunder and lightning.
Thunderstorm  A storm accompanied by thunder and lightning.
Tidal Marsh  Low, flat marshlands traversed by interlaced channels and tidal sloughs and subject to tidal inundation.  Typically, the only vegetation present is salt-tolerant bushes and grasses (Halophytes).
Tidal Energy  The mechanical energy associated with the rising and falling of water level during the movement of the tides.  Also see Tidal Power.
Tidal Flat  (1) An extensive flat tract of land alternatively covered and uncovered by the tide, and comprising mostly unconsolidated mud and sand.  (2) Saltwater wetlands that are characterized by mud and/or sand.  Tidal flats often occur at the seaward edges of salt marshes.  They're covered with seawater during high tide and become exposed during low tide.  Algae are the dominant plants in tidal flats.  Also referred to as Tide Flat.
Tidal Marsh  A low elevation marshy coastal area formed of mud and the root mat of Halophytic plants, regularly inundated during high tide.
Tidal Power  A form of power obtained from the filling and emptying of a Bay or an Estuary that can be closed by a dam.  The enclosed basin is allowed to fill and empty only during brief periods at high and low tides in order to develop as much power as possible.
Tidal Volume  The volume of water entering and leaving a bay or salt marsh as the water level fluctuates because of the tides.
Tidal Wave  (1) An unusual rise or incursion of water along the seashore, as from a storm or a combination of wind and spring tide.  (2) A Tsunami; a huge sea wave caused by a great disturbance under an ocean, as a strong earthquake or volcanic eruption.  (3) An overwhelming manifestation; a flood.
Tide Cycle  The duration of a given tidal sequence, as for example, a lunar month or a tidal day.
Tide Gate  A swinging gate on the outside of a drainage conduit from a diked field that excludes water at high tide and permits drainage at low tide.
Tideland  (1) Land overflowed during flood tide.  (2) Land underlying the ocean and lying beyond the low-water limit of the tide but being within the territorial waters of a nation.  Often used in the plural.
Tideland (or Tidal) Flooding  The periodic flooding of Tidelands during extremely high tides coupled with strong winds and/or high river stages flowing out over a high tide.
Tidemark  A line or an artificial indicator marking the high-water or low-water limit of the tides.
Tide Pool  Habitat in the rocky intertidal zone that retains some water at low tide.
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
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.
Tile Drainage  Land drainage by means of a series of tile lines laid at a specific depth and grade.
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 gaging 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-Series Analysis  (Statistics) Techniques that attempt to predict the future by using historical data rather than by building cause-and-effect models.  Typically, such techniques are most appropriate when the historical data is relatively well behaved and when forecasts, primarily, are sought and not precise cause-and-effect relationships.  Contrast with Cross-Sectional Analysis.
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.
Title  The right of property, also the legal evidence of one's right of property.
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.
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.
Toilet  A room, shelter, or similar device used for defecation or urination equipped with a bowl-shaped fixture for this purpose fitted with a device for flushing with water.
Toilet Water  A scented liquid with a high alcohol content used in bathing or applied as a skin freshener.
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.
Top of Bank  The break in slope between the bank and the surrounding terrain.
Top of Dam  The elevation of the uppermost surface of a dam excluding any parapet wall, railings, etc.
Topographic Apex  The head or highest point on an active alluvial fan.
Topographic Maps  Maps with lines showing equal elevation or a region's relief; also showing natural and man-made surface features, including hills, valleys, rivers, and lakes; and man-made features such as canals, bridges, roads, cities, etc.
Topography  The general configuration of the land surface including relief and position of natural and man-made features.
Topside  (Nautical) The surface of a ship's hull above the water line.
Tornado  (1) A rotating column of air usually accompanied by a funnel-shaped downward extension of a Cumulonimbus Cloud and having a Vortex several hundred yards in diameter whirling destructively at speeds of up to 500 miles per hour (800 kilometers per hour).  (2) A violent thunderstorm in western Africa or nearby Atlantic waters.  (3) A whirlwind or hurricane.  Also referred to as a twister.  Scientists rank a tornado's intensity and estimate its wind speed based on observed damage, using a scale developed by the late University of chicago researcher Tetsuya Theodore Fujita.  The rankings are as follows:
 (1)  FO: Gale Tornado - Wind speed:  40-72 miles per hour.  Damage: Some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages signs.
 (2)  F1: Moderate Tornado - Wind speed: 73-112 miles per hour.  Damage: Peels roof coverings; mobile homes pushed off foundations or overturned; moving autos pushed off the roads; attached garages may be destroyed.
 (3)  F2: Significant Tornado - Wind speed: 113-157 miles per hour.  Damage: Considerable damage.  Roofs torn off frame houses; mobile homes demolished; boxcars pushed over; large trees snapped or uprooted; light objects become missiles.
 (4)  F3: Severe Tornado - Wind speed: 158-206 miles per hour.  Damage: Roofs and some walls torn off well-constructed houses; trains overturned; most trees in forests uprooted.
 (5)  F4: Devastating Tornado - Wind speed: 207-260 miles per hour.  Damage: Well-constructed houses leveled; structures with weak foundations blown off some distance; cars thrown; large missiles generated.
 (6)  F5: Incredible Tornado - Wind speed: 261-318 miles per hour.  Damage: Strong frame houses lifted off foundations and carried considerable distances; automobile-size missiles fly thorugh the air for more than 100 meters; trees debarked; steel-reinforced concrete structures badly damaged.
 (7)  F6 - Although he called it "inconceivable", Fujita left open the possibility a tornado could cause a small area of damage even worse than F5 intensity.  But he said evidence of an F6 tornado, with wind speeds up to 379 miles per hour, would probably be masked by damage from surrounding F4 and F5 winds.
On average, only one F5 tornado hits the United States each year.  F5 twisters struck in 1999 in Norman, Oklahoma, in 1998 in Waynesboro, Tennessee and Pleasant Grove, Alabama; in 1997 in Jarrell, Texas; in 1996 in Oakfield, Wisconsin; in 1992 in Chandlier, Minnesota; and in 1990 in Plainfield, Illinois, Goessel, Kansas, and Hesston, Kansas.  In one of the worst U.S. tornadoes on record, seven F5s struck the Midwest on April 3, 1974, including at Xenia, Ohio.
Torrent  (1) A turbulent, swift-flowing stream.  (2) A heavy downpour; a deluge.
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 o
Total Hardness  The total dissolved salts in water, expressed as total parts of dissolved slats in a million parts of water.  Also see Hard Water.
Total Head  Energy contained by fluid because of its pressure, velocity, and elevation, usually expressed in feet of fluid (foot-pounds per pound).
Total in Bottom Material  The total amount of a given constituent in a representative sample of bottom material.  This term is used only when the analytical procedure assures measurement of at least 95 percent of the constituent determined.  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 in bottom materia".
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 (?g/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.  Also see Carlson's Trophic State Index (TSI).
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
Township Line  In the generally recognized U.S. Public Land Survey, every 24 miles a station is indicated measuring both east and west from a predetermined principal meridian.  Similar measurements are also taken north and south from a predetermined base line.  In this manner a succession of quadrilaterals are formed, each roughly 24 miles square.  Each of these is subdivided into 16 smaller quadrilaterals roughly six miles square.  In this system of grid lines, north-south lines become Range Lines and east-west lines become Township Lines.
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.
Tract  An expanse of land or water.
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.