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GLOSSARY of Storm Water Terms

The Photo Book of Storm Water Features shows pictures of many of the terms listed below. 

Acquisition Program (Buyout Program): A voluntary program in which the government negotiates with private property owners to buy eligible land in the floodplain, with the goal of demolishing or relocating the structure and converting the land to open space. Learn more

Aquatic: Living or growing in or on the water 

Bacteria: Single cell organisms found in nearly every environment on Earth. In large amounts, some types of bacteria such as fecal coliform are harmful to the quality of surface water.

Base Flood: one-percent chance flood, also called a 100-year flood. Base flood is the standard for floodplain management regulations, and determining the need for flood insurance.

Base Flood Elevation: The depth of floodwater associated with a 100-year flood or a flood with a one percent chance of occurring in any given year

BMP or Best Management Practice: Methods, measures, or practices designed to prevent or reduce water pollution and detain small amounts of storm water. Storm Water BMPs can include rain gardens, wetlands, infiltration structures, sediment retention ponds, vegetation strips and grassy swales. Learn more

The study and use of engineering techniques to manage resources such as water and soil, or even in health care and medicine

Bioretention: Various types of storm water Best Management Practices that use engineering techniques, soils and specially-chosen plants to remove pollutants from storm water runoff. One example of bioretention is a rain garden.

Buffer: Undeveloped land covered with plants alongside a stream or lake that absorbs some storm water runoff and pollutants carried by the runoff. Learn more 

Built Upon Area:
Portion of developed land that is covered by impervious or semi-impervious surface such as buildings, and pavement or gravel areas such as roads and parking lots

Buyout Program (Acquisition Program): A voluntary program in which the government enters into negotiations for the purchase of eligible, privately-owned property in the floodplain to demolish or relocate the structure and to convert the land to be used as open space 

Channelize: Engineering technique where the path of a stream is straightened. Often, a concrete path is created to hold the channelized stream water. Channelizing is often ineffective because it increases the speed and danger of the water flow and it removes the natural habitat for aquatic life.

Compost Bin: A container to hold organic materials such as grass clippings, leaves, fruit and vegetable waste like peels or skins, coffee grounds and egg shells while that material decomposes. Compost can then be used as mulch or to loosen and enrich poor soil.

Condensation: The process in the water cycle by which a vapor becomes a liquid; the opposite of evaporation

Conservation: The use of water-saving methods to reduce the amount of water needed for homes, lawns, farming, and industry, and thus increasing water supplies for optimum long-term economic and social benefits

Conservation Easement: Voluntary legal agreement between a landowner and organization (government agency or land trust) that permanently limits some of the land's uses, primarily the right to develop the land

Contaminant: Any substance that when added to water (or another substance) makes it impure and unfit for consumption or use

Community Floodplain: section of the floodplain that is likely to flood in the future, based on zoning of undeveloped land in the watershed. Restrictions apply to building and grading in the Community Floodplain. Flood insurance is recommended in the Community Floodplain but not required. Learn more

Community Rating System (CRS): A program managed by the National Flood Insurance Program (NFIP) to provide incentives for those communities that go beyond the minimum floodplain management requirements to develop extra measures to provide protection from flooding. Learn more 

Cross section: a line on a floodplain map indicating that a flood elevation has been calculated for that section of the creek and floodplain

Detention Basin: Temporary holding areas placed in the stormwater drainage system to temporarily store excess runoff that results from heavy rainfall

Development: Any manmade change to improved and unimproved real estate, including, but not limited to, buildings or other structures, mining, dredging, filling, grading, paving, excavating or drilling operations

Discharge: Water that flows from a stream, pipe, groundwater aquifer, or watershed

Drainage Basin: The area of land that drains to a given point on a body of water. Also called a watershed.

Dry Weather Flow: Runoff that enters the storm water drainage system from every day activities as car washing and lawn watering. Dry weather flow usually has a higher concentration of harmful nutrient chemicals and bacteria than does flow that results from rainfall.

Easement: An agreement that allows the government or a person to use private property for a specific purpose, such as to install and maintain storm drainage pipes. Learn more 

Ecosystem: The biological community (living plant and animals) and the non-living environment (water, rocks, chemicals, weather systems) functioning as one system

Erosion: The wearing away of the earth's surface by running water, wind, ice, gravity or other natural or man-made agents. Learn more

The conversion of a liquid (water) into a vapor (a gaseous state) usually through the application of heat energy during the hydrologic cycle; the opposite of condensation

Fecal Coliform Bacteria: A type of bacteria found in the intestines of humans and animals. The presence of fecal coliform bacteria in water is an indicator of a potential health risk for individuals exposed to this water. Fecal coliform can enter waterways through sewage treatment plant discharge, sewage pipe overflows, or from pet and wild animal waste.

FEMA (Federal Emergency Management Agency): A federal agency within the Department of Homeland Security with the responsibility of responding to, planning for, recovering from and mitigating against disaster

FEMA Floodplain: section of the floodplain that is likely to flood now, based on current land use. Development restrictions apply in the FEMA Floodplain and flood insurance is required. Learn more

Fertilizer: A substance used to increase growth of a plant or improve the quality of a crop. When used inappropriately, it can contribute to storm water pollution

Filtration: The act of filtering, such as removing pollutants and sediment from storm water runoff

Flash Flood: Sudden flooding cause by an intense storm dropping large amounts of rain within a brief period. A flash flood occurs with little or no warning.

Flood: A large flow of water over normally dry land, especially one that causes loss or damage. The National Flood Insurance Program defines a "flood" as a general and temporary condition of partial or complete inundation of normally dry land areas from:
(1) the overflow of inland or tidal waters; and,
(2) the unusual and rapid accumulation of runoff of surface waters from any source. Learn more

Flood Fringe:  The outer portion of the flood risk area next to the floodway. The flood water in the flood fringe is generally shallower and flows more slowly than in the floodway. Conditions in the flood fringe are generally less hazardous than in the floodway.

Flood Insurance: Federally-backed policies available to homeowners, renters and business owners that, unlike standard homeowner's insurance, cover flood damage and loss. Learn more

Flood Insurance Rate Map (FIRM):  Official map that shows both the special hazard areas and the risk premium zones that apply to the community. This map is used by the Federal Emergency Management Agency to determine flood insurance rates. Mecklenburg County also uses flood maps to regulate land development.  Learn more about the four areas within the regulated floodplain.

Flood Protection Elevation:
one foot above the depth of floodwater in a one-percent chance flood. The elevation of a building's lowest floor must be at or above the flood protection elevation.

Flood Warning:
Flooding is actually occurring or very likely to occur in the warning area

Flood Watch: Flooding is possible in a specific area during a given time period. These watches are generally issued for flooding that is expecting to occur at least six hours after heavy rains have ended.

Flood Zone: An area of land with a specific flood risk.  Everyone lives in a flood zone—it's just a question of whether a person's risk is low, medium or high. Highest-risk areas are shown on a Flood Hazard Boundary Map or a Flood Insurance Rate Map. Learn more

Floodplain: Areas that are flooded periodically by the overflow of rivers, creeks, streams or lakes.  The regulated floodplain has at least a 1% chance of flooding in any given year. Mecklenburg has 334-miles of FEMA-regulated floodplain. Learn more

Floodplain Bench: A level area of land along a creek where floodwater is allowed to temporarily spill outside the main channel. This reduces stream bank erosion and stabilizes the creek bank. 

Floodplain Management: A comprehensive community program of corrective and preventive measures for reducing future flood damage. These measures generally include zoning, building requirements and special-purpose floodplain ordinances. Learn more

The portion of the flood risk area where flood waters are the deepest, fastest and most destructive.

FLUM (Floodplain Land Use Map): Flood maps developed by Mecklenburg County and used to regulate new development 

Gabion basket: Wire basket filled with rock and placed along the stream banks to reduce erosion

Grandfathering: Allowing an existing structure or property use to remain even though it does not comply with restrictions or regulations that were approved after it was built

Grass Swale: A Low Impact Development/BMP technique that uses a specially-designed drainage ditch planted with thick grass to slow the flow of storm water runoff and filter pollutants such as sediment and excess nutrients

Greenway: A recreational trail for the public in a floodway that is usually surrounded by trees or plants. In Charlotte-Mecklenburg, many greenway trails are built along creeks. 

Habitat: Place where a plant, animal or microscopic organism naturally lives and grows

Hazard Mitigation Program: A program run by the Federal Emergency Management Agency (FEMA) and North Carolina Division of Emergency Management to protect lives and property from natural and human-made hazards such as flooding

Hazardous waste: Any discarded solid, liquid, or gaseous material that can harm humans or animals

Headwaters: The beginning point of a stream or upper reaches of a stream near its source

Hydrologic cycle: Also known as the water cycle. The paths water takes through its various states--vapor, liquid, solid--as it moves throughout the ocean, atmosphere, streams and groundwater.  

Hydrology: A science dealing with the properties, distribution and circulation of water

Illicit Connection: Any connection to the storm water drainage system that is not permitted, or a legal connection that is used for illegal purposed such as to dispose of pollutants such as wastewater from a Laundromat, car wash or similar business

Illicit Discharge: Any disposal into the storm drain system for which a person or business does not have a permit

Impaired waters list: Creeks, streams or other bodies of water that do not meet state water quality standards. Under Section 303(d) of the Clean Water Act, states are required to develop lists of impaired waters. 

Impervious area: Surface that water cannot penetrate such as rooftops, parking lots, driveways and roads. Areas with more impervious surfaces generally contribute more to storm water runoff pollution and the amount (volume) of storm water runoff.

Infiltrate: Water sinks slowly into the soil, reducing the amount that runs off and allowing pollutants to be absorbed naturally

Infiltration Trench: A rock-lined trench designed to hold storm water runoff and allow it to seep into the soil or groundwater, filtering out pollutants and reducing erosion

Invasive Plants: Plants that were brought to this area by humans and are not native to this area.  They spread rapidly and uncontrollably. Some examples include kudzu, Japanese honeysuckle, mimosa and nandina. Learn more

Levee:  A man-made structure, usually an earthen dike, designed to contain, control or divert the flow of water to provide protection from temporary flooding

Level Spreader: A BMP designed to spread storm water across the ground in a level manner, allowing pollutants to be filtered through plants and special types of soils

Low Impact Development (LID): The use of special landscaping techniques to reduce the impact that land development has on water quality. Rather than letting storm water run off or forcing it into a drainage and pipe system, LID captures storm water on site, filters it through vegetation and lets it gradually soak into the ground or into streams. Learn more

Macroinvertebrates: Creatures without backbones that are large enough to be seen without a microscope, such as snails, worms, fly larvae, and crayfish ("crawdads"). Certain organisms can survive only in water that's very clean, so finding those in water samples means the water is probably healthy.

Meanders: Freely-swinging, winding stream channels

Mitigate: To minimize; lessen the severity

Monitor: To observe a system for changes and keep records of the data collected

National Flood Insurance Program (NFIP): A program that provides flood insurance coverage through private insurance companies for personal and business property. Damage claims and the cost of operating the program are funded through insurance premiums, not tax dollars.  Le​a​rn more

National Pollutant Discharge Elimination System (NPDES): A federally-mandated program through the Clean Water Act that regulates pollutants discharged directly into the surface water system. Learn more

Nitrogen: A nutrient essential to both plants and animals. It is a key ingredient in fertilizer. Too much can act as a pollutant, causing algae blooms and fish kills.

Non-point source pollutants: Pollution that cannot be traced to a single point because it comes from many individual places or a widespread area. Learn more

Nutrient: An element or compound, such as nitrogen, phosphorous, and potassium that is necessary for plant growth. If there are too many nutrients in a stream or lake, that can cause an overgrowth of algae and other plants that kill fish and other aquatic life.

Nutrient pollution: Human-caused addition of excess nutrients, such as grass clippings and pet waste that is carried to creeks, lakes and rivers by storm water runoff

100-year flood: More accurately referred to as a "one percent chance flood." There is a one percent chance that a flood this large will happen in that area in any given year.

100-year floodplain: The land adjacent to a river, lake, creek or stream that has a one percent chance within any given year of being inundated by water during a flood. Also called Special Flood Hazard Area (SFHA.)

Open space: Natural areas containing no buildings or other development

Outfall: The place where a sewer, drain or stream empties

Pervious: Surface that allows water to seep into the ground

Phosphorus: A plant nutrient and an essential ingredient in fertilizer. High levels of phosphorus can cause algae blooms and fish kills.

Pocket wetlands: Small wetlands close to a stream that hold flood water that has spilled over the banks

Point Source Pollution: A type of pollution that can be traced to a specific source such as a factory or sewage treatment plant. Most of this type of pollution is highly regulated at the state and federal levels.

Pollutant: Something that makes the water, land or air dirty and unhealthy

Pollutant Loading: The transfer of pollutants from one place to another, such as sediment carried by storm water runoff into a stream

Pollution: The act or process of contaminating the soil, water or atmosphere by the release of harmful substances

Pool: Deeper area of a stream or river that slows the speed of the water flow and provides habitat for certain types of fish and aquatic life

Pre-FIRM: a building that was constructed before the community's first Flood Insurance Rate Map

Precipitation: The part of the hydrologic cycle when water, in a liquid or solid state, falls from the atmosphere to Earth, such as rain or snow

Rain barrel: A large container placed underneath a downspout to capture and hold rain water

Rain garden: A small depression dug into the ground, then landscaped with specially-chosen plants. The rain garden collects and stores excess water, allowing it to slowly seep into the soil. The roots of the plants absorb many pollutants, keeping them from entering our streams and lakes. Also referred to as a Bioretention cell. Rain gardens are a type of Best Management Practice (BMP.)

Restoration: Correcting damage done to a stream or floodplain. This usually includes stabilizing the stream bank, restoring the path of the stream to a more natural design, slowing the flow of the water, providing for floodwater storage and filtration, improving water quality and enhancing the habitat for plants and aquatic life.

Retrofit: To install a new BMP or improve an existing BMP near existing buildings, roads or parking lots

Riffle: A section of river or stream with rapid, turbulent flow; generally shallow. Riffles add oxygen to the water that supports wildlife.

Riparian buffer: Area of grass, shrubs or trees alongside a stream or body of water. The buffer provides shade for the stream and filters pollutants from storm water runoff.

Riprap: Large rocks or broken concrete used to stabilize stream banks or other slopes

Runoff: Rain water that flows across surfaces rather than soaking into the ground. It may pick up and carry a variety of pollutants before eventually entering a creek, river or lake. Storm water runoff in Charlotte-Mecklenburg is not treated before it goes into the creeks or lakes.

Scour: The removal of particles of soil and rock by fast-moving water. Scoured stream banks can become unstable and can cause bridge supports to become unsafe or even collapse.

Sediment: Loose particles of clay, soil and sand that are released from the earth's surface through erosion.  Sediment is a pollutant because it eventually settles to the bottom, smothering aquatic life and interfering with the flow of the stream.

Special Flood Hazard Area (SFHA): land with at least a one percent chance of flooding in a given year

Storm water: Rainwater, snow melt or even water from a garden hose that is not absorbed into the soil. Learn more

Storm water wetlands: An area of land designed with particular types of soils to hold excess storm water runoff and specially-chosen plants to absorb pollutants from the runoff

Stream enhancement: Improving the design and flow of a stream, creating structures in the streambed and banks where aquatic life, wildlife and plants wildlife can live, reshaping and stabilizing the stream bank, and providing for flood water storage.

Stream restoration: Correcting damage done to a stream, to include reshaping and stabilizing the stream bank, restoring the path of the stream to a more natural design, slowing the flow of the water, providing for flood water storage, improving water quality and enhancing the habitat for plants and aquatic life. Learn more

Stream structures:
Typically large flat stones that are placed in the stream bed to create a ripple effect in the stream during low flows. The ripple effect can increase levels of dissolved oxygen which may make the water purer and more able to support aquatic life. 

Substantial Damage: Damage of any origin to a structure in which the cost of repairing that structure would equal or exceed 50% of the market value of that structure before the damage occurred. In Mecklenburg County, substantial damage also includes two events in a ten year period where flood-related damages equals or exceeds 25% of the market value of the structure before the damage occurred.

Substantial Improvement:  Any repair, reconstruction, or improvement of a structure, where the cost equals or exceeds 50% of the building's market value. In Charlotte-Mecklenburg, "substantial improvement" occurs when one improvement or repair equals 50 percent of the market value OR two improvements of at least 25 percent of the building's value occur within a ten-year period. Substantial improvement does not include either any project for improvement of a building to correct existing state or local code violations or any alteration to a "historic building," provided that the alteration will not preclude the building's continued designation as a "historic building." Learn more

Surface water: An open body of water such as a stream, river, pond, lake or reservoir

SWIM buffer (Surface Water Improvement and Management buffer): An area along streams, lakes and waterways that cannot be cleared of vegetation or developed. The size of the SWIM buffer is defined by local ordinances. The buffers are one aspect of a multi-faceted SWIM program designed to reduce pollutant levels in local streams and lakes. Learn more

Total Maximum Daily Load (TMDL): Total amount of pollutants that a stream can contain without impairing the water or violating clean water laws. Learn more

Total Suspended Solids (TSS): The amount of tiny particles of solid matter contained in a water sample.  The amount of TSS is a way to measure water quality.

Tributary: A smaller stream that flows into a larger river, creek or stream

Wastewater: Water in the sanitary sewer system which comes from sinks, toilets, showers, washing machines, etc. Wastewater is not the same as storm water runoff. Wastewater is treated before being released into the creeks. However, storm water runoff is not treated in Charlotte-Mecklenburg.

Watershed: A region of land drained by a single stream, river or drainage network. Also known as a drainage basin

Water cycle (also known as the hydrologic cycle): The paths water takes through its various states--vapor, liquid, solid--as it moves throughout the ocean, atmosphere, streams and groundwater  

Water pollution: Any human or animal-caused contamination of water that reduces its usefulness to humans and other living things

Water quality: The chemical, physical and biological condition of water, usually in respect to whether it is suited for a particular purpose such as supporting aquatic life

Water quality monitoring: Regular testing of water from lakes and streams to determine how healthy it is. Scientists measure the temperature; amount of oxygen; levels of certain bacteria, metals and toxic chemicals; and turbidity or how clear the water is. Scientists also count the number of fish, insects, plants and small organisms like snails, worms and insect eggs. Learn more

Waterway: A natural or man-made place for water to run through, such as a river, stream, creek or channel

Wetland: A collective term for land areas such as swamps or marshes that are wet because they are close to a body of water or are flooded regularly. Wetlands can be created by nature or by people. Wetlands store flood water and are effective at removing certain pollutants from storm water runoff.

Wet pond: Also called a storm water pond. These are created to store runoff during and after storms, reducing flood risks. The water is slowly released into the stream. Besides reducing flood risks, wet ponds also filter out pollutants by allowing sediment to settle and by plants that absorb excess nutrients from the runoff.

Yard waste: Leaves, grass clippings, yard and garden debris that result from yard care.