Flood, levee, and erosion control glossary - T
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Tackifier
Material sprayed onto a soil surface to bind
soil particles and prevent erosion.
Tacking
The process of binding mulch fibers together by
the addition of a sprayed chemical compound.
Tailwater
The water surface elevation downstream from a structure such as below a dam, weir, or drop structure.
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Photo of Tailwater Pond. |
Taxa
A taxonomic unit. A taxonomic group of any rank,
including all the subordinate groups. Any group of organisms, populations, or
taxa considered to be sufficiently distinct from other such groups to be
treated as a separate unit.
Terminal Groin
A groin, often at the end of a littoral cell or at the updrift side of an inlet, intended to prevent sediment passage into the channel beyond.
Terrace
An embankment or combination of an embankment and channel, constructed across
a slope to control erosion by diverting surface water.
Photo courtesy of USACE. |
Photo of Terrace. |
Terrace Zone
Portion of a streambank inland from the bank
zone.
Terracing
Dikes built along the contour of sloping farm
land that hold runoff and sediment to reduce erosion.
TESC
Abbreviation for Temporary Erosion and Sediment Control (Plan).
Texture
Refers to relative proportions of clay, silt, and
sand in soil.
T-Groin
A groin built in the shape of a letter "T" with the trunk section connected to land.
Thatch
A layer of organic material between the crown of
the plant and the true soil surface.
Threatened Species
A species that is likely to become
endangered if not protected.
Threshold Velocity
The maximum orbital velocity at which the sediment on the bed begins to move as waves approach shallow water.
Tidal Channel
A major channel followed by tidal currents, extending from offshore into a tidal marsh or a tidal flat; tidal inlet.
Tidal Marsh
Low, flat marshlands traversed by channels and
tidal hollows, subject to tidal inundation; normally, the only vegetation
present is salt-tolerant bushes and grasses. See Wetlands.
Tidal Mud Flat
The unvegetated shore exposed to air during
low tide.
Tidal Wave
Most often used inappropriately to refer to tsunamis
(seismic sea waves). A true tidal wave (also called a Tidal Bore) is a wall of
water that rushes through a straight or river mouth at each incoming tide.
Tidal waves occur in a few specific geographic places such as the Bay of Fundy
in Nova Scotia, Qiantang River in China, and the Severn River in France.
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.
Tie-back
A variety of techniques used to secure the
bulkhead, sea wall, or revetment in place against the bank.
Tile Drain
Designed to carry excess water from the soil.
Tillage
The practice of producing a rough soil surface to
maintain surface residue, conserve soil moisture, and reduce wind erosion; also
conservation tillage.
Tiller
A plant that produces a new plant at the base of
the parent plant.
Time of Concentration
The time period necessary for
surface runoff to reach the outlet of a subbasin from the hydraulically most
remote point in the tributary drainage area.
Tissue Residues
Chemical contaminants present in fish or
shellfish which concentrate in the tissues (e.g., muscle, liver) of organisms.
TMDL
Abbreviation total maximum daily load.
Toe
The break in slope at the foot of a bank where the
bank meets the bed.
Toe of Slope
A point or line of slope in an excavation or
cut where the lower surface changes to horizontal or meets the existing ground
slope; or a point or line on the upper surface of a slope where it changes to
horizontal or meets the original surface.
Toe Zone
Portion of a streambank between the streambed and
the average normal river stage.
Top Bank
The break in slope between the bank and the
surrounding terrain.
Topdressing
A thin layer of soil applied to a turf.
Topographic
The physical features of a surface area
including relative elevations and the position of natural and man-made
(anthropogenic) features.
Topographic
Map
A map depicting terrain relief showing ground elevation, usually
through either contour lines or spot elevations. The map represents the
horizontal and vertical positions of the features represented. It is a graphic
representation delineating natural and man-made features of an area or region
in a way that shows their relative positions and elevations.
Topography
The physical features of a surface area
including relative elevations and the position of natural and man-made
(anthropogenic) features.
Topsoil
The unconsolidated earthy material that exists in its natural state and is or
can be made favorable to the growth of desirable vegetation. Usually the
A-horizon of soils with developed profiles.
Total Dissolved Solids
The total amount in milligrams of
solid material dissolved in one liter of water (mg/L).
Total Maximum Daily Load (TMDL)
The maximum allowable
loading of a pollutant that a designated water body can assimilate and still
meet numeric and narrative water quality standards. TMDLs were established by
the 1972 Clean Water Act. Section 303(d) of the US Water Quality Act requires
states to identify water bodies that do not meet federal water quality
standards. In 1996 the states developed (with EPA approval) a list of water
bodies that failed to meet section 303(d) standards. These are the focus of
TMDLs. Allocation of named pollutants is on percentage basis.
Total Nitrogen
The sum of all nitrogen forms.
Total Phosphorus
The sum of all phosphorus forms.
Total Suspended Solids (TSS)
A measure of the
suspended solids in wastewater, effluent, or water bodies, determined by tests
for total suspended nonfilterable solids. See Suspended Solids.
Toxic Substances/Material
Chemical compounds that are
poisonous, carcinogenic, or otherwise directly harmful to plants and animals.
Trace Metals
Metals such as silver, copper, lead, cadmium,
zinc, and mercury that normally occur in water and sediments at concentrations
less than one part per million (ppm). See Metals, Heavy Metals.
Tractive Force
The drag on a streambank caused by passing
water which tends to pull soil particles along with the streamflow.
Transient Non-Community Water Systems
Public water system
which serves 15 or more service connections but does not serve 15 service
connections used by the same persons for more than 6 months per year; or serves
an average of at least 25 persons per day for at least 60 days per year, but
doesn't serve the same 25 persons for more than 6 months per year. Examples of
TNC water systems include campgrounds, rest stops, parks, or restaurants.
Different individuals use the water from one day to the next, and they do not
live at this facility.
Transmissivity
A measure of the ability of an aquifer to
transmit water.
Transpiration
The process by which plants return moisture
to the air. Plants take up water through their roots and then lose some of the
water through pores in their leaves. As hot air passes over the surface of the
leaves, the moisture absorbs the heat and evaporates into the air.
Tributary (Tributaries)
A body of water flowing into a larger
body of water. For example, the Potomac River is a tributary of Chesapeake Bay.
TRM
Abbreviation for turf reinforcement mat.
Trophic Level
A grouping of organisms that use the next
lower grouping of organisms as a food source. Used to describe where on the
food web organisms feed. For example herbivores feed on plants, and carnivores
feed on herbivores.
Tropical Cyclone
Storms of various intensities that form
over warm tropical and subtropical waters; classified according to intensity
and degree of organization and including tropical disturbances, tropical
depressions, tropical storms, and hurricanes.
Tropical Storm
A warm-core tropical cyclone in which the
maximum sustained surface wind (1 minute mean) ranges from 34 to 63 knots
(39-72.5 mph).
Trough of Wave
The lowest part of a wave form between successive crests. Also that part of a wave below stillwater level.
Tsunami
Long-period, low-height sea waves of seismic origin; generated principally by
undersea earthquakes of magnitudes greater than 6.5 on the Richter scale.
Turbidimeter
A device that measures the cloudiness of
suspended solids in a liquid; a measure of the quantity of suspended solids.
Turbidity
The cloudy appearance of water caused by the
presence of suspended and colloidal matter. Because turbidity reduces the
amount of light penetrating the water column, high turbidity levels may be
harmful to aquatic life (e.g., SAV). Technically, turbidity is an optical
property of the water based on the amount of light reflected by suspended
particles.
Turbidity Barrier
A device to prevent sediment migration
in a body of water, consisting of filter fabric that allows the passage of
water but retaining sediment particles. The fabric is attached to a flotation
device at the top and usually anchored or weighted at the bottom; also
turbidity curtain.
TVA
The Tennessee Valley Authority (TVA) is a federally
owned corporation in the United States that was created in 1933 to provide
navigation, flood control, electricity generation, fertilizer manufacturing,
and economic development in the Tennessee Valley.
Typhoon
Pacific Ocean hurricanes that develop in the
regions off Mexico and Central America. Typhoons typically make landfall in
Asia.
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