Definitions of BMP Categories and Types
These definitions will help you decide which BMP category your BMP data fits into. The Chesapeake Bay
Program's Urban Storm Water Workgroup is currently finalizing these definitions.	
BMP
Definition
Cateqorv A: Wet Ponds and Wetlands
Practices that have a combination of a permanent pool, extended
detention or shallow wetland equivalent to the entire water quality
storage volume. Practices that include significant shallow
wetland areas to treat urban storm water but often may also
incorporate small permanent pools and/or extended detention
storage. (MD 2000)
Wet pond
A storm water management pond designed to obtain runoff and
always contains water. (Prince George's LID Report)
Wet extended detention pond
Combines the pollutant removal effectiveness of a permanent
pool of water with the flow reduction capabilities of an extended
storage volume.
(http://www. deq. state. id. us/water/stormwater cataloq/
doc bmp47.asp)
Multiple pond system
A group of ponds that collectively treat the water quality volume.
(New York Stormwater Management Design Manual)
"Pocket" pond
A wetland that has such a small contributing drainage area that
little or no baseflow is available to sustain water elevations during
dry weather. Water elevations are highly influenced, and in some
cases, maintained by a locally high water table. (Technical Note
#77 from Watershed Protection Techniques. 2(2): 374-376)
Shallow wetland
A wetland that provides water quality treatment entirely in a wet
shallow marsh. (New York Stormwater Management Design
Manual)
Extended detention wetland
A wetland system that provides some fraction of the water quality
volume by detaining storm flows above the mash surface. (New
York Stormwater Management Design Manual)
Pond/wetland system
A wetland system that provides a portion of the water quality
volume in the permanent pool of a wet pond that precedes the
marsh for a specified minimum detention time. (New York
Stormwater Management Design Manual)
"Pocket" wetland
A storm water wetland design adapted for the treatment of runoff
from small drainage areas (< 5 acres) and which has little or no
baseflow available to maintain water elevations and relies on
groundwater to maintain a permanent pool. (MD 2000)
Submerge gravel wetland
One or more treatment cells that are filled with crushed rock
designed to support wetland plants. Stormwater flows
subsurface through the root zone of the constructed wetland
where pollutant removal takes place.
(http://www.qeorqiastormwater.com/vol2/3-3-5.pdf)
Constructed wetland
Constructed wetlands are systems that perform a series of
pollutant removal mechanisms including sedimentation, filtration,
absorption, microbial decomposition and vegetative uptake to
remove sediment, nutrients, oil and grease, bacteria and metals.
Wetland systems reduce runoff velocity thereby promoting
settling of solids. Plant uptake accounts for removal of dissolved
constituents. In addition, plant material can serve as an effective
filter medium and denitrification in the wetland can remove
nitrogen. (EPA Handbook: Urban Runoff Pollution Prevention and
Control Planning)
Retention pond (wet)
Surface pond with a permanent pool.
Wetland basin with open water surfaces
Similar to retention ponds except that a significant portion (usually
50% or more) of the permanent pool volume is covered by
emergent wetland vegetation, (www.purdue.edu)
Retention Basin
Capture a volume and retain that volume until it is displaced in
part or in total by the next runoff event. Maintains a significant
permanent pool volume of water between runoff events. (EPA:

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http://www. epa. gov/ost/stormwater/usw c. pdf)
Cateqorv B: Drv Detention,
Hvdrodvnamic Structure
Practices used to moderate flows and remains dry between
storm events.
Dry pond
Designed to moderate influence on peak flows and drains
completely between storm events, (www.dea.state.id.us/
water/stormwater catalog/chapter5 5.asp)
Underground dry detention facility
Designed to dry out between storms and provides storage below
around in tanks and vaults, (www.dea.state.id.us/
water/stormwater catalog/chapter5 5.asp)
Cateqorv C: Drv Extended Detention
A storm water design feature that provides gradual release of
volume of water in order to increase settling of pollutants and
protects downstream channels from frequent storm events.

Dry extended detention pond (peak quantity
control only)
Dry extended detention ponds (a.k.a. dry ponds, extended
detention basins, detention ponds, extended detention ponds) are
basins whose outlets are designed to detain the stormwater
runoff from a water quality "storm" for some minimum duration
(e.g., 24 hours) which allow sediment particles and associated
pollutants to settle out. Unlike wet ponds, dry extended detention
ponds do not have a permanent pool. However, dry extended
detention ponds are often designed with small pools at the inlet
and outlet of the pond, and can also be used to provide flood
control by including additional detention storage above the
extended detention level, (www.stormwatercenter.net)
Extended detention basin
An impoundment that temporarily stores runoff for a specified
period and discharges it through a hydraulic outlet structure to a
downstream conveyance system. An extended detention basin is
usually dry during non-rainfall periods. (VA DCR website)
Enhanced extended detention basin
An enhanced extended detention basin has a higher efficiency
than an extended detention basin because it incorporates a
shallow marsh in the bottom. The shallow marsh provides
additional pollutant removal and helps to reduce the resuspension
of settled pollutants by trapping them. (VA DCR website)
Group D: Infiltration Practices
Practices that capture and temporarily store the water quality
volume before allowing it to infiltrate into the soil. (MD 2000)
Infiltration Trench
An excavated trench that has been back filled with stone to form a
subsurface basin. Storm water runoff is diverted into a trench
and stored until it can be infiltrated into the soil. (Prince George's,
LID Report)
Infiltration Basin
Relatively large, open depressions produced by either natural site
topography or excavation. When runoff enters an infiltration basin,
the water percolates through the bottom or the sides and the
sediment is trapped in the basin. The soil where an infiltration
basin is built must be permeable enough to provide adequate
infiltration. Some pollutants other than sediment are also removed
in infiltration basins, (epa.gov/owow/nps/education/runoff.html)
Porous Pavement
Pavement that allows storm water to infiltrate into underlying soils
promoting pollutant treatment and recharge. (EPA LID Fact
Sheet)
Cateqorv E: Filterinq Practices
Practices that capture and temporarily store the water quality
volume and pass it through a filter bed.
Filtering and Open Channel Practices
Practices that capture and temporarily store the water quality
volume and pass it through a filter bed of sand, organic matter,
soil or other media are considered to be filtering practices.
Filtered runoff may be collected and returned to the conveyance
system. Vegetated open channels that are explicitly designed to
capture and treat the full water quality volume within dry or wet
cells formed by checkdams or other means. (MD 2000)
Surface sand filter
Both the filter bed and the sediment chamber are above ground.
The surface sand filter is designed as an off-line practice, where
only the water quality volume is directed to the filter.
(www.stormwatercenter.net)

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Underground sand filter
A modification of the surface sand filter, where all of the filter
components are underground. An off-line system that receives
onlv the smaller water quality events, (www.stormwatercenter.net)
Perimeter sand filter
Includes the basic design elements of a sediment chamber and a
filter bed. In this design, however, flow enters the system through
grates, usually at the edge of a parking lot. The perimeter sand
filter is the only filtering option that is on-line, with all flows
entering the system, but larger events bypassing treatment by
entering an overflow chamber, (www.stormwatercenter.net)
Organic media filter
Essentially the same as surface filters, with the sand media
replaced with or supplemented with another medium. The
assumption is that these systems will have enhanced pollutant
removal for many compounds due to the increased cation
exchange capacity achieved by increasing the organic matter,
(www. stormwatercenter.net)
Pocket sand filter
Diverts runoff from the water quality volume into the filter by pipe
where pretreatment is by means of concrete flow spreader, a
grass filter strip and a plunge pool. The filter bed is comprised of
a shallow basin containing the sand filter medium. The filter
surface is a layer of soil and a grass cover. In order to avoid
clogging the filter has a pea gravel "window" which directs runoff
into the sand and a cleanout and observation well.
(httpV/www.wcc.rffcs.usda.aov/watershed/UrbanBMPs/pdf/water/auali
ty/pocketsandfilter.pdf)
Bioretention areas (a.k.a. Rain Gardens)
Primarily for water quality control. These are planting areas
installed in shallow basins in which the storm water runoff is
treated by filtering through the bed components, biological and
biochemical reactions within the soil matrix and around the root
zones of the plants and infiltration into the underlying soil strata
(VA web site).
Swale
In general a swale (grass channel, dry swale, wet swale, water
quality swale) refers to a series of vegetated open channel
management practices designed specifically to treat and
attenuate stormwater runoff for a specified water quality volume.
It is treated through filtering by the vegetation in the channel,
filtering through a subsoil matrix, and/or infiltration into the
underlying soils. (EPA Fact Sheet)
Dry Swale
A type of grassed swale. Controls quality AND volume (Prince
George's LID). An open drainage channel explicitly designed to
detain and promote the filtration of storm water runoff through an
underlying fabricated soil media. (MD 2000)
Infiltration Swale
Planted areas designed specifically to accept runoff from
impervious areas (i.e. parking lots) providing temporary storage
and onsite infiltration.
(http://www.metrocouncil.0rg/environment/Watershed/bmp/CH3 RPPI
mpParking.pdf)
Wet Swale
(a.k.a. Water Quality Swale)
A type of grassed swale. Uses residence time and natural
growth to reduce peak discharge and provide water quality
treatment before discharge to a downstream location (Prince
George's LID). An open drainage channel or depression,
explicitly designed to retain water or intercept groundwater for
water quality treatment. (MD 2000)
Dry Wells
Dry well - small excavated pit, backfilled with aggregate, usually
pea gravel or stone. Function as infiltration systems used to
control runoff from building rooftops (Prince George's LID).
Cateqorv F: Roadwav Systems (sheet
flow to median)
Using a BMP to reduce the total area of impervious cover, thereby
reducing the pollutant and sediment load in a given area.
Sheet flow discharge to stream buffers
Sheet flow is water flowing in a thin layer of the ground surface.
Filter strips are a strip of permanent vegetation above ponds,
diversions and other structures to retard the flow of runoff,
causing deposition of transported material, thereby reducing
sedimentation. (MD 2000)

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Cateqorv G: Impervious Surface
Reduction
Using a BMP to reduce the total area impervious area and
therefore encouraging stormwater infiltration.
Natural area conservation
Maintaining areas such as forests, grasslands and meadows that
encourage stormwater infiltration.
Disconnection of rooftop runoff
Disconnecting the rooftop drainage pipe and allowing it to infiltrate
into the pervious surface thereby reducing the impervious area.
Disconnection of non-rooftop impervious
area
Directing sheet flow from impervious surfaces, i.e. driveways and
sidewalks, to pervious surfaces instead of stormwater drains.
Rain Barrels
Rain barrels retain a predetermined volume of rooftop runoff
(Prince George's LID).
Green Roofs
A multi-layer construction material consisting of a vegetative layer
that effectively reduces urban storm water runoff by reducing the
percentage of impervious surfaces in urban areas. (EPA LID
Fact Sheet)
Cateqorv H; Street Sweeping, Catch
A variety of BMPs that provide stormwater treatment for trash,
litter, coarse sediment, oil and other debris before proceeding
through the stormwater system.
Basin Inserts
On-line storage in the storm drain network
A management system designed to control storm water in the
storm drain network. (MD 2000)
Catch basin inserts
Small, passive, gravity-powered devices that are fitted below the
grate of a drain inlet. Intercept and contain significant amounts of
litter, vegetation, petroleum hydrocarbons and coarse sediments.
(www.kristar.com)
Oil/grit separators
Oil/grit separators - systems designed to remove trash, debris
and some amount of sediment, oil and grease from storm water
runoff based on the principles of sedimentation for the grit and
phase separation for the oil.
(www.metrocouncil.orq/environment/watershed/bmp/CH3 STDet
OilGrit.pdf)
Hydrodynamic Structures
A variety of products for storm water inlets known as swirl
separators, or hydrodynamic structures are modifications of the
traditional oil-grit separator and include an internal component
that creates a swirling motion as storm water flows through a
cylindrical chamber. These designs allow sediment to settle out
as storm water moves in this swirling path. Additional
compartments or chambers are sometimes present to trap oil
and other floatables.
(www.epa.qov/npdes/stormwater/menuofbmps)
Water quality inlets
Also known as oil and grit separators, provide removal of floatable
wastes and suspended solids through the use of a series of
settling chambers and separation baffles. (EPA Handbook: Urban
Runoff Pollution Prevention and Control Planning)
Street sweeping
Seeks to remove the buildup of pollutants that have been
deposited along the street or curb, using a vacuum assisted
sweeper truck.
Deep sump catch basins
Storm drain systems designed to catch debris and coarse
sediment. (www.lapa-west.org/NPSPollution3.pdf)
Cateqorv 1: Stream Restoration
A BMP used to restore the natural ecosystem by restoring the
stream hydrology and natural landscape.
Stream Restoration
Return of an ecosystem to a close approximation of its condition
prior to disturbance. The establishment of predisturbance
aquatic functions and related physical, chemical and biological
characteristics. A holistic process. (NRC, 1999, Restoration of
Aquatic ecosystems www.epa.qov/owow/)

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