Knowledge Base

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.

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).

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.

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.

TEST HOLE (TEST-WELL) — (Hydraulics) A well hole drilled for experimental or exploratory purposes.

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

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.

TOE — (1) The downstream edge at the base of a dam. (2) The line of a natural or fill slope where it intersects the natural ground. (3) 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.

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

TOTAL WATER USED — Total water withdrawal which does not include recirculation.

TRANSFER (of Water) — Refers to the movement of water from one reservoir or storage facility to another.

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) 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.

TRANSPIRATION — (1) 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. (2) 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.

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.

TREATMENT PLANT — A structure built to treat wastewater before discharging it into the environment.

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.

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.