attenuate: to reduce the force, effect, or value of
biofiltration and bioinfiltration: the terms are often used interchangeably. Bioinfiltration is when the water passes through the media and then infiltrates into the parent soils below. Biofiltration is when the water going through the media is captured with an underdrain, that then transports the treated water to some receiving system. Source: https://stormwater.pca.state.mn.us/index.php/Bioretention_terminology
Best Management Practice (BMP): a practice, or a combination of practices, that prevent or reduce the release of pollutants and other limit adverse impacts to waterbodies
bioretention system: systems sized for specific treatment and flow control objectives, including a designated soil mix, and perhaps underdrains and flow control structures
check dam: a small, sometimes temporary, dam constructed across a swale drainage ditch or waterway to counteract erosion by reducing water flow velocity
closed infiltration trench: a type of infiltration trench that receives stormwater through an inlet pipe that brings water from the surface to the subsurface of the trench
contributing area: the total area, including pervious and impervious surfaces, contributing runoff
detention facility: holds water temporarily. An example is a pond that has water temporarily after a storm event and returns to a dry state. Water in those ponds infiltrates out slowly through the soils or via an outlet
dispersion: the process of spreading the flow of water over a wide area to ensure lower flow depths and lower velocities
dispersion area: area of land designated for stormwater runoff from an impervious area to be spread out over. This area should be pervious and covered with vegetation to ensure that the water flows slowly and infiltrates into the soils
dispersion trench: a facility designed to receive stormwater runoff and disperse it evenly through vegetated areas. Trenches are typically 2 feet wide and 18 inches deep — length is determined by the size of contributing area
flow path: the path that water takes as it flows from one point to another
flow spreader: a device or system that helps to spread water flowing in a narrow-concentrated path, into a wider, slower, and shallower manner. Flow spreaders are typically installed between a pipe inlet and a stormwater runoff treatment component. An example of a flow spreader is a notched board
groundwater table: water in a saturated zone or stratum beneath the surface
impervious surface: a solid (usually artificial) surface that prevents the infiltration of water into the soil (e.g., roads, roofs, pavements, parking lots)
infiltration rate: the rate at which water moves downward (percolates) through the soil surface to lower layers. It is usually expressed as inches/hour or millimeters/hour
level spreader: similar to flow spreaders, level spreaders are designed to alter concentrated runoff to sheet flow runoff. However, they are typically used upstream of vegetated flow paths or dispersion areas
open infiltration trench: an infiltration trench that receives stormwater in the form of sheet flow that enters from the top of the trench
retention facility: holds water permanently. An example is a pond with a permanent pool of water is an example of a retention pond. Common on the east coast
runoff: water originating from rainfall, snowmelt, and other precipitation that flows off the landscape
sorptive properties: properties that affect sorption, or the physical and chemical process by which one substance becomes attached to another
stormwater runoff: stormwater runoff is generated from rain and snowmelt events that flow over land or impervious surfaces, such as paved streets, parking lots, and building rooftops, and does not soak into the ground. The runoff picks up pollutants like trash, chemicals, oils, and dirt/sediment that can harm rivers, streams, lakes, and coastal waters
transition zone: an approximately 2-foot-wide zone that discourages channeling of water between the edge of the impervious surface and the downslope vegetation. This zone is usually composed of crushed rock (extension of subgrade material), drain rock, or something similar that meets the local planning authority requirements
water quality design flow: the flow rate at or below which 91% of the total runoff volume, as estimated by an approved continuous runoff model, will be treated
watershed: the region of the landscape that drains water to a particular location. Similar concept to contributing area, however watersheds are usually recognized at the landscape level