At-Source Basket
A basket-style filtration system inserted into a pit in order to intercept gross pollutants prior to entry to the stormwater system.

Australian Height Datum (AHD)
Established in 1971 as a national level datum based on the average mean sea level around the Australian coast line. Determined by a national levelling survey and continuous tide gauge readings over a period of 3 years at 30 locations.

Average Recurrence Interval (ARI)
The average elapsed time in years between the occurrence of floods of an equivalent size. e.g. a 1 in 50 year storm should describe flows equivalent to a storm that may occur once in 50 years. Most pipe systems are designed for approximately 1 in 5 or 10 year flows.

Best Management Practices (BMP)
Activities or structural improvements that help reduce the quantity and improve the quality of stormwater run-off. BMPs include treatment requirements, operating procedures, and practices to control site run-off, spillage or leaks, sludge or waste disposal, or drainage from raw material storage.

Bio-Filter
Dense vegetation designed to filter stormwater run-off as it passes through.

Boom
A floating boom is usually installed across open channels or outlet structures and consists of a floating boom and weighted mesh skirt designed to trap floating litter and debris.

Buffer Strip or Zone
Strip of grass or other erosion-resistant vegetation located between a waterway and an area of more intensive land use.

Bypass Flow
The proportion of stormwater flow that exceeds the nominated treatable flow.

Catchment
An area bounded by physical constraints that drains water to a common point.

Catch Pit
An entry way to the storm drain system, usually located in the kerb line. (Refer Gully Pit)

Collection Efficiency (CE)
The percentage of pollutants that are retained in the filter.

Conduit
Any channel or pipe used to transport flowing water.

Conveyance
The process of water moving from one place to another.

Constructed Wetland
A constructed wetland system is seen as a tertiary level of stormwater treatment designed to retain fine sediments and nutrients. It commonly has two components; a relatively deep upstream pond for trapping settleable solids and a wetland consisting of a shallow pond containing extensive macrophyte vegetation designed to remove fine settleable solids and nutrients.

CSO
A combined flow consisting of stormwater and raw sewage. This flow is usually the result of excess sewage flows being deliberately or sometimes accidentally discharged directly into the stormwater system. The combined flows then discharge directly to receiving waters.

Culvert
A short, closed (covered) conduit that passes stormwater run-off under an embankment, usually a roadway. A rectangular or square concrete culvert is referred to as a box culvert.

Cumec
Unit of flow measurement. One cumec is one cubic metre per second of flow. It is equal to 1000 litres per second of flow.

Detention
A stormwater system that delays the downstream progress of stormwater run-off in a controlled manner, typically by using temporary storage areas (Detention Basin) and a metered outlet device.

Discharge
The volume of water (and suspended sediment if surface water) that passes a given location within a given period of time. Symbolised as Q and dimensioned as either litres per second (l/sec) or cumecs (cubic metres per second - m³/sec).

Drain Inlet Insert
A device (tray, bag, or basket) installed in a drain inlet or catch basin to treat stormwater run-off.

Drop Manhole
Manhole with a vertical misalignment between upstream and downstream pipe inverts.

Dry Weather Flow (DWF)
The flow of stormwater during dry weather.

Eductor Truck
Vehicle with high-powered suction capabilities used for the removal of captured pollutants from GPT devices.

End-Of-Line
Describes the position of an installed device as being at the end of a piped stormwater line or open drain.

EPA
Environment Protection Authority.

Erosion
Removal of soil particles by wind and water. Often the eroded debris (silt or sediment) becomes a pollutant via stormwater run-off. Erosion occurs naturally but can be intensified by human activities such as farming, development, road-building, and timber harvesting.

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

FSL
Finished Surface Level.

Floatables
Buoyant materials such as plastic bottles, polystyrene, organic materials etc. often found in stormwater flows.

Flood
A temporary rise in flow or stage of any watercourse or stormwater conveyance system that results in stormwater run-off exceeding its normal flow boundaries and inundating adjacent, normally dry areas.

Flood Control
The specific regulations and practices that reduce or prevent the damage caused by stormwater run-off.

Freeboard
The vertical distance between the normal maximum water surface level within a structure and the level of the surface cover or grate.

Grading
The cutting and/or filling of the land surface to a desired slope or elevation.

Gradient
The vertical slope of the conduit or channel. Usually measured in terms of percent or horizontal to vertical ratio. e.g. 1 in 50 equates one unit vertically to 50 units horizontally. In percentage terms this is equal to a gradient of 2.0% (2 vertically to 100 horizontally).

Gross Pollutants
Stormwater laden debris typically larger than 3mm including litter, cans, bottles, plastic bags, vegetation, silt and sediments.

Gross Pollutant Trap (GPT)
A device used to intercept the gross pollutants being transported in stormwater.

Gully Pit
An entry way to the storm drain system, usually located in the kerb line. (See also Catch Pit).

Headloss
Change in pressure line elevation due to friction or the inclusion of a structure or constriction.

Holding Pond
A pond or reservoir, usually made of earth, built to store polluted run-off for a limited time.

Illegal connection
Any discharge to a municipal separate storm sewer that is not composed entirely of stormwater and is not authorised.

Impermeable Material
A soil or material whose properties prevent movement of water through the material.

Impervious Surface
Hard ground cover that prevents or retards the entry of water into the soil and increases runoff, such as asphalt, concrete, rooftops.

In-Line
Describes the position of an installed device as being located on the line of a piped storm water line or open drain.

Infiltration
The portion of rainfall or surface run-off that moves downward into the subsurface rock and soil.

Invert
The lowest point of the cross section in any pipe, conduit or open channel.

Invert Level (IL)
The reduced level at the lowest point of the cross section in any conduit or open channel.

Levee
A fill embankment used to protect areas from rising floodwaters from streams or rivers.

Lintel
The pre-cast component of a gully pit that collects the majority of flow and is constructed along the kerb line.

Litter Basket
(Refer At-Source Basket)

Media Filter
A filter containing sand, compost, sand peat, or perlite and zeolite designed to filter constituents (particulates, oil, bacteria, or dissolved metals) out of stormwater run-off as it passes through the filter.

MUSIC

MUSIC is an acronym for Modelling Software for Urban Stormwater Improvement Conceptualisation. It is a stormwater management planning system developed by the Cooperative Research Centre for Catchment Hydrology and is widely used by engineers and planners in Australia. Click here to read more about it.

Nonpoint-Source Pollutants
Pollutants from many diffuse sources. Nonpoint-source pollution is caused by rainfall or snowmelt moving over and through the ground. As the run-off moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters, and even underground sources of drinking water.

Obvert
The highest level in a conduit.

Obvert Level
The reduced level describing the highest level in a conduit.

Oil and Grease Arrester
A device designed to capture oil and grease being transported in a stormwater flow.

Outlet/Outfall
The point where wastewater or drainage discharges from a sewer or stormwater pipe, ditch, or other conveyance to a receiving body of water.

Point-Source Pollutants
Pollutants from a single, identifiable source such as a factory or refinery; also called single-point-source pollution.

Pollutant Loading
The total quantity of pollutants in stormwater run-off.

Primary Treatment
The screening of stormwater flows to remove gross pollutants including sediment and coarse particles.

Primary Treatment Device
A device designed to offer a primary level of treatment of a stormwater flow.

Retro-Fit
The modification of stormwater management systems through the construction and/or enhancement of wet ponds, wetland plantings, or other BMPs designed to improve water quality.

Return Period
(Refer ARI)

Run-off
Drainage or flood discharge that leaves an area as surface flow or as pipeline flow.

Sanitary Sewer
A system of underground pipes that carries sanitary waste or process wastewater to a treatment plant.

Screenings
Materials removed from wastewater by screening processes. For example, faecal matter, toilet tissue, plastics, and condoms.

Sediment
Soil, sand, and minerals washed from land into water, usually after rain. Sediment can destroy fish-nesting areas, clog animal habitats, and cloud waters so that sunlight does not reach aquatic plants.

Sheet Flow
The portion of precipitation that moves initially as overland flow in very shallow depths before eventually reaching a stream channel.

Site Run-Off
Any drainage or flood discharge that is released from a specified area.

Storm Drain
An opening leading to an underground pipe or open ditch for carrying surface run-off, separate from the sanitary sewer or wastewater system.

Storm Surge
An increase in water level above the normal water level on the open coast due to the action of wind stress and atmospheric pressure on the sea surface.

Stormwater Management
Functions associated with planning, designing, constructing, maintaining, financing, and regulating the facilities (both constructed and natural) that collect, store, control, and/or convey stormwater

Stormwater Quality Improvement Device (SQID)
Refer Gross Pollutant Trap

Surface Run-Off
The portion of rainfall that moves over the ground toward a lower elevation and does not infiltrate the soil.

Surface Water
Water that remains on the surface of the ground, including rivers, lakes, reservoirs, streams, wetlands, seas, and estuaries.

SWMP
Stormwater management plan or program.

Total maximum daily load (TMDL)
The maximum allowable loading of a pollutant that a designated water body can assimilate and still meet numeric and narrative water quality standards. Allocation of named pollutants is on percentage basis.

Trash Racks
A series of metal vertical and/or horizontal metal bars positioned across a drainage channels and designed to intercept litter and debris. Bars are typically spaced 40-100mm depending on the target pollutants.

Treatable Flow Rate (TFR)
The flow at which the treatment device is required to filter in accordance with the specified rate of filtration.

Treatment Train
The selection and sequential ordering of structural treatments in order to achieve optimal pollutant removal.

Urbanised Area
A Bureau of the Census determination of a central place (or places) and the adjacent densely settled surrounding territory that together have a minimum residential population of 50,000 people and a minimum average density of 1,000 people/mi.2

Urban Run-off
Stormwater from urban areas, which tends to contain heavy concentrations of pollutants from urban activities.

Water Quality Objectives (WQOs)
Generally, it defines maximum levels for various contaminants within receiving waters that would result in minimal impacts to the environment or water users.

Watershed
Geographical area that drains to a specified point on a water course, usually a confluence of streams or rivers. Also known as drainage area, catchment, or river basin. (In the UK the term "watershed" refers to what in the US is called the drainage divide, and the term "catchment" refers to what in the US is called a watershed.)

Wet Weather Flows
Water entering storm drains during rainstorms/wet weather events.

Wetland
A naturally occurring area inundated or saturated by surface or groundwater and capable of sustaining vegetation typically adapted for life in such conditions.