NPDP Dam Dictionary

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Term AKA Definition
Sump pump A pump used for removing collected water from a sump.
Surcharge To fill or load to excess.
Surcharge capacity The reservoir capacity provided for use in passing the inflow design flood through the reservoir. It is the reservoir capacity between the maximum water surface elevation and the highest of the following elevations: top of exclusive flood control capacity, top of joint use capacity, or top of active conservation capacity.
Surface vibration A method of compacting soil using a vibrating plate or vibrating smooth drum roller used on the surface of soil placed.
Surface water An open body of water such as a river, stream or lake.
Surge A rapid increase in the depth of flow.
Swale A low place in a tract of land. A wide, shallow ditch, usually grassed or paved.
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.