Best Management Practice (BMP). (1)A measure that is implemented to protect water quality and reduce the potential for pollution associated with storm water runoff. (2) Any program, technology, process, siting criteria, operating method, measure, or device that controls, prevents,removes, or reduces pollution.

Clean Water Act (CWA). The Federal Water Pollution Control Act enacted in 1972 by Public Law 92-500 and amended by the Water Quality Act of 1987. The Clean Water Act prohibits the discharge of pollutants to Waters of the United States unless said discharge is in accordance with an NPDES permit. The 1987 amendments include guidelines for regulating municipal, industrial, and construction storm water discharges under the NPDES program.

Coefficient of Runoff. Percentage of gross rainfall which appears as runoff.

Construction Activity. Includes clearing, grading, or excavation and contractor activities that result in soil disturbance.

Construction Site. The area involved in a construction project as a whole.

Contractor. Party responsible for carrying out the contract per plans and specifications.

Debris. Any material including floating woody materials and other trash, suspended sediment, or bed load moved by a flowing stream.

Degradation. General and progressive lowering of the longitudinal profile of a channel by erosion.

Dike. (1) Usually an earthen bank alongside and parallel with a river or open channel to restrict overflow (See Levee). (2) An asphalt concrete berm along the edge of a shoulder.

Disturbed Areas. Areas that have been purposefully cleared, grubbed, excavated, or graded by the contractor; ground surface that has been disrupted by construction activities, including construction access/roads, staging, and storage sites producing significant areas of exposed soil and soil piles

Ditch. Small artificial channel, usually unlined.

Drain. Conduit intercepting and discharging surplus ground or surface water.

Drainage. (1) The process of removing surplus ground or surface water by artificial means. (2) The system by which the waters of an area are removed. (3) The area from which waters are drained; a drainage basin.

Drainage Area(Drainage Basin) (Basin). That portion of the earth's surface upon which falling precipitation flows to a given location.

Drainage Course. Any path along which water flows when acted upon by gravitational forces.

Easement. Right to use the land of others.

Environmental Protection Agency (EPA). Agency that issued the regulations to control pollutants in storm water runoff discharges (The Clean Water Act and NPDES permit requirements).

Erosion. The wearing away of natural (earth) and unnatural (embankment, slope protection, structure, etc.) surfaces by the action of external forces. In the case of drainage terminology, this term generally refers to the wearing away of the earth's surface by flowing water. It can also refer to the wear on a structural surface by flowing water and the material carried therein.

Erosion Control. Vegetation, such as grasses and wildflowers, and other materials, such as straw, fiber, stabilizing emulsion, protective blankets, etc., placed to stabilize areas disturbed by grading operations, reduce loss of soil due to the action of water or wind, and prevent water pollution.Excavation. The process of removing earth, stone, or other materials.

Excavation. The process of removing earth, stone, or other materials.

Existing Vegetation. Any vegetated area that has not already been cleared and grubbed.

Fair Weather Prediction. When there is no precipitation in the forecast between the current
calendar day and the next working day.

Filte.  A porous article or mass (as of fabric or even-graded mineral aggregate) through which water will freely pass but which will block the passage of soil particles.

Flow.  A term used to define the movement of water, silt, sand, etc.; discharge; total quantity carried by a stream.

General Permit.  A general permit for storm water discharges associated with industrial or
construction activity issued by EPA or a delegated state under the NPDES storm water regulations.

Gravel.  Rock larger than sand and smaller than cobble, arbitrarily ranging in diameter from 5 to 50 mm.

Impervious.  A surface that cannot be easily penetrated; for instance, rain does not readily penetrate asphalt or concrete surfaces.

Infiltration.  The passage of water through the soil surface into the ground.

Inlet.  An entrance into a ditch, storm drain, or other water conveyance system.

Isohyet/Isohyetal Line.  A line drawn on a map or chart joining points that receive the same amount of precipitation.

Isohyetal Map.  A map containing isohyetal lines and showing rainfall intensities.

Mulch. A natural or artificial layer of plant residue or other material that covers the land surface and conserves moisture, holds soil in place, aids in establishing vegetation, and reduces temperature fluctuations.

"n" Value. The roughness coefficient in the Manning formula for determination of the discharge coefficient in the Chezy formula, • V = C(RS)1/2 , where C = (1/n )R1/6

National Pollutant Discharge Elimination System (NPDES). EPA.s program to control the discharge of pollutants to waters of the United States. NPDES is a part of the federal CWA, which requires point and non-point source dischargers to obtain permits. These permits are referred to as NPDES permits.

Nonactive Construction Area. Any area not considered to be an active construction area. Typically, active construction areas become nonactive construction areas whenever construction activities are expected to be discontinued for a period of 20 or more days during the winter season.

Non-Point Sources (NPS). Diffuse sources from which contaminants originate to accumulate in surface water or groundwater. These sources can add to a cumulative problem with serious health or environmental consequences.

Notice of Intent (NOI). A formal notice to the EPA or a state agency having delegated NPDES authority that a construction project seeking coverage under a General Permit is about to begin. The NOI provides information on the owner, location, and type of project, and certifies that the permittee will comply with conditions of the construction General Permit. The NOI is not a permit application and no approval is required. Some local permits may require submittal of a Notice of New Construction (NONC) in lieu of filing a NOI with the state or EPA.

Notice of Termination (NOT). A formal notice to the EPA or delegated state agency for General Permit site terminating coverage under the permit.

Off-Site Drainage. Flow of water that originates outside the property.

On-Site Drainage. Flow of water that originates inside the property.

Permit.  An authorization, license, or equivalent control document issued by EPA or an approved state agency to implement the requirements of an environment

Point of Concentration.  That point at which the water flowing from a given drainage area concentrates.

Precipitation. Discharge of atmospheric moisture as rain, snow or hail, measured in depth of fall or in terms of intensity of fall in unit time.

Probability. The chance of occurrence or recurrence of a specified event within a unit of time, commonly expressed in 3 ways. Thus a 10-year flood has a chance of 0.1 per year and is also called a 10%-chance flood.

Probability of Exceedance. The statistical probability, expressed as a percentage, of a hydrologic event occurring or being exceeded in any given year. The probability (p) of a storm or flood is the reciprocal of the average recurrence interval (N).

Quality Assurance/Quality Control. A system of procedures, checks, audits, and corrective actions to ensure that all research design and performance, environmental monitoring and sampling, and other technical and reporting activities are of the highest achievable quality.

Rainfall. Point Precipitation: That which registers at a single gauge. Area Precipitation: Adjusted point rainfall for area size.

Rill Erosion. The formation of numerous, closely spaced streamlets due to uneven detachment of surface soils by runoff on slopes.

Risk Analysis. An economic comparison of design alternatives using expected total costs (construction costs plus risk costs) to determine the alternative with the least expected cost to the public.

Runoff. (1) The surface waters that exceed the soil.s infiltration rate and depression storage. (2) The portion of precipitation that appears as flow in streams. Drainage or flood discharge which leaves an area as surface flow or a pipeline flow, having reached a channel or pipeline by either surface or subsurface routes.

Sand. Granular soil coarser than silt and finer than gravel, ranging in diameter from 0.05 to 5 mm.

Sediment. Fragmentary material that originates from weathering of rocks and is transported by, suspended in, or deposited by water.

Sedimentation. Gravitational deposit of transported material in flowing or standing water.

Sheet Erosion. Erosion of thin layers of soil by sheets of flowing water.

Sheet Flow. Any flow spread out and not confined; i.e., flow across a flat open field.

Silt. (1) Water-Borne Sediment. Detritus carried in suspension or deposited by flowing water, ranging in diameter from 0.005 to 0.05 mm. The term is generally confined to fine earth, sand, or mud, but is sometimes both suspended and bedload. (2) Deposits of Water-Borne Material. As in a reservoir, on a delta, or on floodplains

Slope. (1) Gradient of a stream. (2) Inclination of the face of an embankment, expressed as the ratio of horizontal to vertical projection; or (3) The face of an inclined embankment or cut slope. In hydraulics it is expressed as percent or in decimal form.

Source Control BMP. An effort to prevent or limit the exposure of significant materials to storm water at the source.

Storm Drain. That portion of a drainage system expressly for collecting and conveying former surface water in an enclosed conduit. Often referred to as a 'storm sewer', storm drains include inlet structures, conduit, junctions, manholes, outfalls and other appurtenances.

Storm Water. Storm water runoff, snow melt runoff, and surface runoff and drainage.

Storm Water Management. The recognition of adverse drainage resulting from altered runoff and the solutions resulting from the cooperative efforts of public agencies and the private sector to mitigate, abate, or reverse those adverse results.

Storm Water Pollution Prevention Plan (SWPPP). A plan required by storm water regulations or permits that includes site map(s), an identification of construction/contractor activities that could cause pollutants in the storm water, and a description of measures or practices to control these pollutants.

Surface Waters. Surface waters are those which have been precipitated on the land from the sky or forced to the surface in springs, and which have then spread over the surface of the ground without being collected into a definite body or channel. They appear as puddles, sheet or overland flow, and rills, and continue to be surface waters until they disappear from the surface by infiltration or evaporation, or until by overland or vagrant flow they reach well-defined watercourses or standing bodies of water like lakes or seas.

Temporary Construction Site BMPs. BMPs that are required only temporarily to address a short-term storm water contamination threat. For example, silt fences are located near the base of newly graded slopes that have a substantial area of exposed soil. Then, during rainfall, the silt fences filter and collect sediment from runoff flowing o

Thalweg. The line following the lowest part of a valley, whether under water or not. Usually the line following the deepest part of the bed or channel of a river.

Total Suspended Solids (TSS). The weight of particles that are suspended in water. Suspended solids in water reduce light penetration in the water column, can clog the gills of fish and invertebrates, and are often associated with toxic contaminants because organics and metals tend to bind to particles.

Turbidity. A measure of the amount of material suspended in the water. Increasing the turbidity of the water decreases the amount of light that penetrates the water column. High levels of turbidity are harmful to aquatic life.

Waters of the United States. (a) All waters, which are currently used, were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide; (b) All interstate waters, including interstate wetlands; (c) All other waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, wetlands, sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds, the use, degradation, or destruction of which would affect or could affect interstate or foreign commerce including any such waters: (1) which are or could be used by interstate or foreign travelers for recreational or other purposes; (2) from which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or (3) which are used or could be used for industrial purposes by industries in interstate commerce; (d) All impoundments of waters identified in paragraphs (a) through (d) of this definition; (f) The territorial sea; and (g) Wetlands adjacent to waters (other than waters that are themselves wetlands) identified in paragraphs (a) through (f) of this definition. Waste treatment systems, including treatment ponds or lagoons designed to meet the requirements of CWA (other than cooling ponds as defined in 40 CFR 423.11 (m) which also meet the criteria of this definition) are not waters of the United States. This exclusion applies only to manmade bodies of water which neither were originally created in waters of the United States (such as disposal area in wetlands) nor resulted from the impoundment of waters of the United States.