Stormwater Calculations - Mathematics and Statistics for the Environment - page 758

Aquifer —A porous, water bearing geologic formation generally restricted to materials capa-
ble of yielding an appreciable supply of water.
Atmospheric deposition —The process by which atmospheric pollutants reach the land
surface either as dry deposition or as dissolved or particulate matter contained in
precipitation.
Average land cover condition —The percentage of impervious cover considered to gen-
erate an equivalent amount of phosphorus as the total combined land uses within the
watershed.
Bankfull flow —Condition where flow fills a stream channel to the top of bank and at a point
where the water begins to overflow onto a floodplain.
Base low —Discharge of water independent of surface runoff conditions, usually a function
of groundwater levels.
Basin —A facility designed to impound stormwater runoff.
Best management practice (BMP) —Structural or nonstructural practice that is designed
to minimize the impacts of changes in land use on surface and groundwater systems.
Structural BMP refers to basins or facilities engineered for the purpose of reducing the pol-
lutant load in stormwater runoff, such as Bioretention, constructed stormwater wetlands,
etc. Nonstructural BMP refers to land use or development practices which are determined
to be effective in minimizing the impact on receiving stream systems, such as preservation
of open space and stream buffers, disconnection of impervious surfaces, etc.
Biochemical oxygen demand (BOD) —An indirect measure of the concentration of biologi-
cally degradable material present in organic wastes. It usually reflects the amount of oxy-
gen consumed in 5 days by biological processes breaking down organic waste.
Biological processes —A pollutant removal pathway in which microbes break down organic
pollutants and transform nutrients.
Bioretention basin —Water quality BMP engineered to filter the water quality volume through
an engineered planting bed, consisting of a vegetated surface layer (vegetation, mulch,
ground cover), planting soil, and sand bed (optional), and into the in-situ material. Also
called rain gardens.
Bioretention ilter —A bioretention basin with the addition of a sand layer and collector pipe
system beneath the planting bed.
Catch basin —An inlet chamber usually built at the curb line of a street or low area, for collec-
tion of surface runoff and admission into a sewer or subdrain. These structures commonly
have a sediment sump at its base, below the sewer or subdrain discharge elevation designed
to retain solids below the point of overflow.
Channel stabilization —The introduction of natural or manmade materials placed within a
channel so as to prevent or minimize the erosion of the channel bed and/or banks.
Check dam —Small dam constructed in a channel for the purpose of decreasing the flow
velocity, minimizing channel scour, and promoting deposition of sediment. Check dams
are a component of grassed swale BMPs.
Chemical oxygen demand (COD) —A measure of the oxygen required to oxidize all com-
pounds, both organic and inorganic, in water.
Chute —A high-velocity, open channel for conveying water to a lower level without erosion.
COE —United States Army Corps of Engineers
Compaction —The process by which soil grains are rearranged so as to decrease void space
and bring them in closer contact with one another, thereby reducing the permeability and
increasing the soils unit weight, and shear and bearing strength.
Constructed stormwater wetlands —Areas intentionally designed and created to emulate the
water quality improvement function of wetlands for the primary purpose of removing pol-
lutants from stormwater.
Contour —A line representing a specific elevation on the land surface or a map.