Erosion and Sediment Pollution Control Program Manual.pdf

Top-of-Slope Berm -----A low berm constructed/maintained at the top of a fill slope for the purpose of
directing runoff from the top of the fill to a suitable conveyance structure, such as a channel or
pipe, discharging to a sediment basin or trap. See Standard Construction Detail #6-4.
Topdressing -----A thin layer of soil applied to a turf.
Topographic Map -----A map providing contours at sufficient intervals to adequately depict the surface
features of a site.
Topography -----A general term that includes the characteristics of the ground surface such as plains,
hills, mountains, degree of relief, steepness of slope, and physiographic features.
Topsoil -----Surface soil usually containing organic matter.
Total Dissolved Solids -----A measure of the amount of material dissolved in water, typically
carbonates, bicarbonates, chlorides, sulfates, phosphates, nitrates, etc.
Total Disturbed Area -----That portion of a project site where earth disturbance activities are planned
to occur. For permitting purposes it is measured to the nearest tenth of an acre.
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.
Total Project Area -----The entire project site, including areas that are or will be subject to earth
disturbance activity as well as those that will not. For permitting purposes, it is measured to the
nearest tenth of an acre.
Total Solids (TS) -----Total dissolved solids plus total suspended solids.
Total Storage Volume -----The available storage in a basin, pond, or trap at the elevation where the
required freeboard is provided.
Total Suspended Solids (TSS) -----A measure of the solids found in water that can be removed by
filtration, typically silt, man-made wastes, etc.
Toxic -----Causing acute or chronic damage to biological tissue following physical contact or
absorption.
TR-55 -----An NRCS publication describing a method of estimating runoff from small urban watersheds.
TR-60 -----An NRCS publication providing specifications for earth dams and reservoirs.
Tracking Slopes (Trackwalking) -----A method of surface roughening in which a tracked vehicle,
typically a dozer with blade raised, runs up and down a fill slope leaving short horizontal
depressions in the surface. See Figure 11.3.
Tractive Force -----The drag on a stream bank caused by passing water which tends to pull soil
particles along with the streamflow.
Transient Flow -----Unsteady flow during a change from a steady-flow state to another steady-flow
state.
Transition Zone -----1. The area between habitats or ecosystems. 2. The area between uplands and
wetlands.
Transmissivity -----The rate at which water moves through a unit width of an aquifer or confining bed
under a unit hydraulic gradient. It is a function of properties of the liquid, the porous media, and
the thickness of the porous media.
Transpiration -----The process by which water vapor escapes from living plants, principally from the
leaves, and enters the atmosphere.
Trap Efficiency -----The ratio of sediment retained within a sediment basin or trap to the sediment
inflow, expressed as a percentage.
Trapezoidal Channel -----A channel whose cross-section has a relatively flat bottom and sloping sides.
Trash Rack ------A structure attached to the top of a principal spillway riser for the purpose of
preventing floating debris from entering the pipe and plugging it. See Standard Construction
Detail # 7-5.
Trench -----A long, narrow excavation for the purpose of burying a pipeline or utility line.
Trench Breakers -----Openings in the side of a trench just upslope of a trench plug to allow water in
the trench to discharge to a waterbar.
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