NPDP Dam Dictionary

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Term AKA Definition
Tailrace See afterbay.
Tailwater The water in the natural stream immediately downstream from a dam. The elevation of water varies with discharge from the reservoir.
Tainter gate A term used by the Corps of Engineers to describe radial gates (see gate).
Talus Sloping accumulation of rock debris; also, rock fragments at the base of a cliff from slides or falls. Rock fragments mixed with soil at the foot of a natural slope from which they have been separated.
Tamp To pound or press soil to compact.
Tamper A tool for compacting soil in spots not accessible to rollers.
Tamping A method of compacting soil using the impact of a power or hand tamper on the surface of the soil placed.
Tamping roller One or more steel drums, fitted with projection feet, used to densify soil. See sheepsfoot roller.
Tectonics The science that deals with the structure of the earth's crust.
Terminal structure Portion of spillway downstream from chute, tunnel or conduit, which generally dissipates or stills releases. Concrete portion of an outlet works downstream from a conduit, tunnel, or control structure. The structure dissipates or stills releases. See stilling basin.
Terrestrial Living or growing on land.
Test pit Pit dug for geologic investigation or inspection and testing of earthwork placement.
Thalweg Deepest part of a river channel in a cross section of a river profile. The path of deepest flow.
Thermal sand Sand used to dissipate heat away from buried electrical cables.
Thermal stratification The formation of layers of different temperatures in bodies of water.
Thermocline The middle layer of a lake, separating the upper, warmer portion (epilimnion) from the lower, colder portion (hypolimnion). See metalimnion.
Thick arch dam An arch dam with a base thickness to structural height ratio of 0.3 or greater (previously defined as 0.5 or greater).
Thickness or width of dam The thickness or width of a dam as measured horizontally between the upstream and downstream faces and normal to the axis or centerline crest of the dam.
Thin arch dam An arch dam with a base thickness to structural height ratio of 0.2 or less (previously defined as 0.3 or less).
Threatened A legal classification for a species which is likely to become endangered within the foreseeable future.
Threatened species Any species which has potential of becoming endangered in the near future.
Thrust block Anchor block A massive block of concrete built to withstand a thrust or pull.
Tie lines Transmission line connecting two or more power systems.
Toe The point of intersection between the upstream or downstream face of the dam and natural ground, for example, the upstream or downstream toe of a dam.
Toe drain Open jointed tile or perforated pipe located at the toe of the dam used in conjunction with horizontal drainage blankets to collect seepage from the embankment and foundation and conveys the seepage to a location downstream from the dam.
Toe weight Additional material placed at the toe of an embankment dam to increase its stability.
Top of active conservation capacity The reservoir water surface elevation at the top of the capacity allocated to the storage of water for conservation purposes only. See reservoir.
Top of dam See crest elevation.
Top of dead capacity The lowest elevation in the reservoir from which water can be drawn by gravity.
Top of exclusive flood control capacity The reservoir water surface elevation at the top of the reservoir capacity allocated to exclusive use for regulation of flood inflows to reduce damage downstream. See reservoir.