Erosion and Sediment Pollution Control Program Manual.pdf

Trench Plug -----A flow obstruction, typically constructed from earth-fill sacks, placed in a trench to
prevent flow along the pipe either prior to or after backfilling the trench. See Standard
Construction Detail #13-4.
Trespass -----Any voluntary transgression of law or rule, such as to enter wrongfully upon another’s
land or to infringe upon another’s rights to use water.
Triaxial Test -----A common method of testing soil strength.
Tributary Drainage Area -----The area above a BMP from which runoff would be expected to flow to
the BMP.
TRM -----Turf reinforcement matting.
Trunk Line -----The main conduit for transporting stormwater. The trunk line is typically deeper than
laterals to allow for gravity flow.
TSF -----Trout stock fishery, a stream classification used by PFBC.
TSS -----Total Suspended Solids.
Turbidity -----A measure of the reduced clarity of water caused by suspended particles, such as silt,
clay, organic material, etc.
Turbidity barrier -----A device to prevent sediment transport in a body 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. See Figures 3.14 to 3.17.
Turbulent flow -----The type of flow in which individual water particles move in unpredictable paths.
Turf -----Surface soil supporting a dense growth of grass and associated root mat.
Turf Reinforcement Matting -----A type of erosion control blanket which is intended to increase the
maximum allowable shear stress for a vegetative liner.
Turnout -----A drainage ditch which drains water away from roads.
2b Stone -----The old PennDOT designation for AASHTO #57 stone.
2-year Storm -----1. A storm event of such intensity that it occurs, on average, once every 2 years; 2. A
rainfall event having a fifty-percent chance of being equaled or exceeded in any given year.
Type M Inlet -----A rectangular box-shaped storm water inlet commonly used by PennDOT and other
designers.
Type II Rainfall Distribution -----A standardized distribution of a 24-hour rainfall event, developed by
NRCS, and applicable to most of Pennsylvania per TR-55.
Typical Detail -----A construction detail that applies to more than one application of a BMP on a project
site.
U
Ubiquitous Hydrophytes -----Plant species that grow either in wetland or on upland areas.
Unconsolidated -----Not cemented together or lithified. For example, sand is unconsolidated.
Underdrain -----See sub drain.
Underclay -----A non-bedded clay occurring below a coal seam; also called a plastic clay or soft clay.
Undermining -----The process of scour by hydraulic action that progressively removes earth support
from an engineered structure, such as a culvert or sewer.
Understory -----Plants growing beneath the canopy of other plants, usually grasses, forbs, and low
shrubs.
Unified Soil Classification System -----A classification system based upon soil particle size,
gradation, plasticity index, and liquid limit.
Uniform Flow -----A state of steady flow when the mean velocity and cross-sectional area are
essentially constant in all sections of a reach.
Unit Density -----A density of one gram per cubic centimeter or one gram per milliliter; the density of
water at 4 O C or 39.2 O F.
Unit Hydrograph -----The hydrograph of surface runoff on a given basin due to an effective rain falling
for a unit of time.
Unit Weight of Water -----The weight per unit volume of water (62.4 lb/ft 3 ).
363-2134-008 / March 31, 2012 / Page 555