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Stormwater Strategies
Community Responses to Runoff Pollution

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Aquifer - A subsurface formation of rock, glacial material, or other deposits that contains water and is capable of storing and yielding water to a well or spring.

Base flow - The portion of stream flow that is not runoff and results from seepage of water from the ground into a channel slowly over time. The primary source of running water in a stream during dry weather.

Best Management Practice (BMP), nonstructural - Strategies implemented to control stormwater runoff that focus on pollution prevention such as alternative site design, zoning and ordinances, education, and good housekeeping measures.

Best Management Practice (BMP), structural - Engineered devices implemented to control, treat, or prevent stormwater runoff pollution.

Better site design - A collection of site planning, design, and development strategies that help reduce adverse impacts to the natural environment by recreating, to a certain extent, the original hydrology and plant community of the predevelopment site.

Biochemical Oxygen Demand (BOD)  - The amount of oxygen used by microorganisms in the breakdown or decay of organic matter in a waterbody.

Bioengineering  - Restoration and stabilization techniques that use plants, often native species, to mimic natural functions and benefits.

Biofiltration  - The use of vegetation (usually grasses or wetland plants) to filter and treat stormwater runoff as it is conveyed through an open channel or swale.

Biological diversity  - The concept of multiple species of organisms living together in balance with their environment and each other.

Biological monitoring and biological indicators -  Surveys of aquatic biota in a waterbody where the organisms (plants, macro-invertebrates, and fish) serve as indicators of the quality and characteristics of that waterbody.

Bioretention - The use of vegetation in retention areas designed to allow infiltration of runoff into the ground. The plants provide additional pollutant removal and filtering functions while infiltration allows the temperature of the runoff to be cooled.

Brownfields -  Abandoned or underutilized properties where development is complicated by real or perceived contamination.

Buffer zone  - A designated transitional area around a stream, lake, or wetland left in a natural, usually vegetated state so as to protect the waterbody from runoff pollution. Development is often restricted or prohibited in a buffer zone.

Catchbasin  - An inlet to a storm or combined sewer equipped with a sediment sump, and sometimes a hood, on its outlet pipe to the sewer. Catchbasins can collect some of the sediment and debris washed off the streets, and help to provide a water seal against the venting of sewer gases. Catchbasins should be cleaned out regularly to function properly.

Catchment  - See Watershed

Channel erosion  - The widening, deepening (called channel scour), and upstream cutting of a stream channel caused by moderate and extreme flow events. Channel erosion is one way that a stream reacts to changes in flow patterns.

Chemical water quality  - The quality of a waterbody determined using chemical rather than physical or biological parameters and methods.

Combined sewer overflow (CSO) -  During rainfall events, the volume of stormwater entering a combined sewer system often is far greater than the capacity of the interceptor (large collector pipe) and sewage treatment plant and, as a result, the untreated sewage and stormwater mixture empties directly into receiving waters through designated overflow points.

Combined sewer system -  A sewer system that conveys stormwater runoff along with sanitary sewage and industrial waste.

Consent order -  A legal injunction mandating a party to perform an action.

Conservation Design  - Site design that incorporates conservation measures such as on-site tree preservation, concentrating homes on a limited percentage of the site, preserving natural areas and open space, and reducing the amount of impervious cover.

Constructed stormwater wetland -  A water quality BMP, design to have similar characteristics and functions to a natural wetland, with the specific purpose of treating stormwater runoff through uptake, retention, and settling.

Detention -  The storage and slow release of stormwater following a precipitation event by means of an excavated pond, enclosed depression, or tank. Detention is used for both pollutant removal, stormwater storage, and peak flow reduction. Both wet and dry detention methods can be applied.

Estuary  - A semi-enclosed coastal waterbody such as a bay, mouth of a river, salt marsh, or lagoon, where freshwater and saltwater mix. These waters support a rich and diverse ecology.

Eutrophication  - Nutrient enrichment (nitrogen, phosphorus, and carbon) from sewage effluent, runoff, or atmospheric deposition to surface waters. This process can increase the growth potential for algae and aquatic plants. Excessive eutrophication can leave waterbodies devoid of most life, impede navigation, and result in aesthetic nuisances.

Evapotranspiration  - The loss of water to the atmosphere through the combined processes of evaporation and transpiration, the process by which plants release water they have absorbed into the atmosphere.

Event Mean Concentration (EMC) -  A method for characterizing pollutant concentrations in a receiving water from a runoff event often chosen for its practicality. The value is determined by compositing (in proportion to flow rate) a set of samples, taken at various points in time during a runoff event, into a single sample for analysis.

Filter Strip  - Grassed strips situated along roads or parking areas that remove pollutants from runoff as it passes through, allowing some infiltration, and reductions of velocity.

Flashy stream  - A stream or river that is characterized by dramatic fluctuations in flow, in which sharply higher flows in wet weather can be followed by very low flows in dry weather.

Floatables -  Materials found in runoff that are buoyant, such as polystyrene, plastic, some organic material, or cigarette butts.

Floodplain -  Can be either a natural feature or statistically derived area adjacent to a stream or river where water from the stream or river overflows its banks at some frequency during extreme storm events.

Geographic Information System (GIS)  - A database of digital information and data on land-use, land cover, ecology, and other geographic attributes that can be overlaid, statistically analyzed, mathematically manipulated, and graphically displayed using maps, charts, and graphs.

Groundwater  - Water that flows below the ground surface through saturated soil, glacial deposits, or rock.

Hydrologic flow criteria  - Data used to assess the hydrologic characteristics of a waterbody to determine how closely it mimics expected conditions or patterns, in order to develop and calibrate models, predict flow events, or protect channel and biological integrity.

Hydrology  - The science addressing the properties, distribution, and circulation of water across the landscape, through the ground, and in the atmosphere.

Impervious surface  - A surface that cannot be penetrated by water such as pavement, rock, or a rooftop and thereby prevents infiltration and generates runoff.

Imperviousness -  The percentage of impervious cover within a defined area.

Infill development  - Development of vacant lots or enhancement of existing urban properties.

Infiltration  - The process or rate at which water percolates from the land surface into the ground. Infiltration is also a general category of BMP designed to collect runoff and allow it to flow through the ground for treatment.

Integrated Pest Management (IPM)  - The practice of using biological and physical measures to control pests while minimizing or eliminating the use of synthetic chemical pesticides.

Measurable goal - An observable, preferably numerical, achievable target or objective selected by a municipality, or other project manager, or the community that guides and measures the success of the selection, design, and operation or maintenance of a stormwater management measure.

National Pollutant Discharge Elimination System (NPDES) -  A provision of the Clean Water Act that prohibits discharge of pollutants into waters of the United States unless a special permit is issued by the EPA, a state, or (where delegated) a tribal government or and Indian reservation.

Natural buffer -  A variable width area maintained with natural vegetation between a pollutant source and a waterbody that provides natural filtration and other forms of protection.

Outfall  - The point of discharge from a river, pipe, drain, etc. to a receiving body of water.

Overburden  - Material overlying a deposit of useful geologic materials or bedrock.

Peak discharge - The greatest volume of stream flow occurring during a storm event.

Performance standard -  An established amount or limit of a specified pollutant that can be discharged from a land-use activity or BMP.

Polluted runoff  - Rainwater or snowmelt that picks up pollutants and sediments as it runs off roads, highways, parking lots, lawns, agricultural lands, logging areas, mining sites, septic systems, and other land-use activities that can generate pollutants.

Porous pavement and pavers  - Alternatives to conventional asphalt that utilize a variety of porous media, often supported by a structural matrix, concrete grid, or modular pavement, which allow water to percolate though to a sub-base for gradual infiltration.

Retrofit  - The creation or modification of a stormwater management practice, usually in a developed area, that improves or combines treatment with existing stormwater infrastructure.

Runoff  - Water from rainfall, snowmelt, or otherwise discharged that flows across the ground surface instead of infiltrating the ground.

Sanitary sewer system  - Underground pipes that carry only domestic or industrial wastewater to a sewage treatment plant or receiving water.

Sedimentation  - A solid-liquid separation process utilizing gravitational settling to remove soil or rock particles from the water column.

Siltation  - A solid-liquid separation process utilizing gravitational settling to remove fine-grained soil or rock particles from the water column.

Smart Growth  - Development that uses a variety of strategies to enhance existing communities and protect community character in a way that is compatible with the natural environment and attracts economic development. It encourages more town-oriented, transit-focused, and pedestrian-friendly new development while restoring vitality to existing developed areas.

SSO (separate sewer overflow) - Wastewater entering sanitary sewers may be so great, because of blockage, a lack of capacity, inflow and infiltration, or other reasons, that the collection system or sewage treatment plant cannot handle the increased flow. As a result, untreated sewage empties directly into receiving waters, often from manholes or up through sewer connections.

Storm sewer system  - A system of pipes and channels that carry stormwater runoff from the surfaces of building, paved surfaces, and the land to discharge areas.

Stormwater  - Water derived from a storm event or conveyed through a storm sewer system.

Stormwater treatment trainTM -  A series of BMPs or natural features, each designated to treat a different constituent, component, or aspect of runoff, implemented together to maximize pollutant removal effectiveness.

Stormwater utility - A utility established to generate a dedicated source of funding for stormwater pollution prevention activities where users pay a fee based on land-use and contribution of runoff to the stormwater system.

Surface water  - Water that flows across the land surface, in channels, or is contained in depressions on the land surface (e.g. runoff, ponds, lakes, rivers, and streams).

Swale -  A natural or human-made open depression or wide, shallow ditch that intermittently contains or conveys runoff. Can be used as a BMP to detain and filter runoff.

Urban (metropolitan) runoff  - Runoff derived from urban or suburban land-uses that is distinguished from agricultural or industrial runoff sources.

Water (hydrologic) cycle  - The flow and distribution of water from the sky, to the Earth's surface, through various routes on or in the Earth, and back to the atmosphere. The main components are precipitation, infiltration, surface runoff, evapotranspiration, channel and depression storage, and groundwater.

Watershed  - The land area, or catchment, that contributes water to a specific waterbody. All the rain or snow that falls within this area flows to the waterbodies as surface runoff, in tributary streams, or as groundwater.

Wet detention ponds -  A BMP consisting of a permanent pool of water designed to treat runoff by detaining water long enough for settling, filtering, and biological uptake. Wet ponds are also often designed to have an aesthetic or recreational value.

XeriscapingTM -   An alternative landscaping technique that focuses on water conservation through plant selection and site design.

X-year storm event  - The storm event that has a probability of recurring on average once every X-years based on records from previous years.


BMP - Best Management Practice

BOD - Biochemical Oxygen Demand

CFR - Code of Federal Regulations

CSO - Combined Sewer Overflow

EMC - Event Mean Concentration

EPA - United States Environmental Protection Agency

ESC - Erosion and Sediment Control

FEMA - Federal Emergency Management Agency

GIS - Geographic Information System

IPM - Integrated Pest Management

LID - Low Impact Development

MS4 - Municipal Separate Storm Sewer System

NAFSMA - National Association of Flood and Stormwater Management Agencies

NLC - National League of Cities

NPDES - National Pollutant Discharge Elimination System

NRDC - Natural Resources Defense Council

SSO - Separate Sewer Overflow

TND - Traditional Neighborhood Design

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