Glossary

Aquatic Corridor — An area of land and water which is important to the integrity and quality of a stream, river, lake, wetland, or other body of water. An aquatic corridor usually consists of the actual body of water ("corridor" usually connotes a river or stream), the adjacent buffer, and a fringe of adjacent upland areas.

BMPs (Best Management Practices) — Methods that have been determined to be the most effective, practical means of preventing or reducing pollution from non-point sources, such as pollutants carried by urban runoff.

Buffer — An area adjacent to a lake or estuarine shoreline, wetland edge, or streambank, where a) critically important ecological processes and water pollution control functions take place, and b) development may be restricted or prohibited for these reasons.

Cluster or Open Space Development — The use of designs which incorporate open space into a development site; these areas can be used for either passive or active recreational activity or preserved as naturally vegetated land.

Combined Sewer Overflow — Discharge of a mixture of storm water and domestic waste, occurring when the flow capacity of a sewer system is exceeded during rainstorms.

Conservation Easements — A practice used to apply and enforce restrictions to preserve natural resources. Typically, a landowner will grant very specific rights concerning a parcel of land to a qualified recipient (e.g. public agency or non profit land conservancy organization). The easement gives the recipient the right to enforce the restrictions. The recipient does not assume ownership but does assume long-term responsibility for enforcement and stewardship of the easement. For example, a wildlife management agency may obtain easements in forested floodplains from private landowners that help them manage wildlife and fish.

Floodplain — A generally flat, low-lying area adjacent to a stream or river that is subjected to inundation during high flows. The relative elevation of different floodplains determines their frequency of flooding, ranging from rare, severe storm events to flows experienced several times a year. For example, a "100-year floodplain"would include the area of inundation that has a frequency of occurring, on average, once every 100 years.

Green Infrastructure — Green infrastructure refers to natural systems that capture, cleanse and reduce stormwater runoff using plants, soils and microbes. On the regional scale, green infrastructure consists of the interconnected network of open spaces and natural areas (such as forested areas, floodplains and wetlands) that improve water quality while providing recreational opportunities, wildlife habitat, air quality and urban heat island benefits, and other community benefits. At the site scale, green infrastructure consists of site-specific management practices (such as interconnected natural areas) that are designed to maintain natural hydrologic functions by absorbing and infiltrating precipitation where it falls.

Illicit Connections — Illegal and/or improper waste discharges into storm drainage systems and receiving waters.

Impacted Stream or Subwatershed — A very general, watershed imperviousness-based classification category for a subwatershed with 11 to 25% impervious cover. Urbanization is generally expected to lead to some impacts on stream quality, but the type and magnitude of these effects can vary significantly among different watersheds at similar levels of imperviousness.

Impervious Cover — Any surface in the urban landscape that cannot effectively absorb or infiltrate rainfall; for example, sidewalks, rooftops, roads, and parking lots.

Imperviousness — The percentage of impervious cover by area within a development site or watershed, often calculated by identifying impervious surfaces from aerial photographs or maps.

Karst — A type of topography that is formed on limestone, gypsum, and other rocks by dissolution, and is characterized by sinkholes, caves, and underground drainage.

Macroinvertebrates — Aquatic insects and larvae without a backbone, able to be seen by the unaided eye.

National Pollutant Discharge Elimination System (NPDES) — Established by Section 402 of the Clean Water Act, this federally mandated permit system is used for regulating point sources, which include discharges from industrial and municipal facilities and also stormwater discharges from discrete conveyances such as pipes or channels.

Nonpoint Source — Diffuse pollution source; a source without a single point of origin or not introduced into a receiving stream from a specific outlet. The pollutants are generally carried off the land by stormwater. Common nonpoint sources are agriculture, forestry, urban areas, mining, construction, dams, channels, land disposal, saltwater intrusion, and city streets.

Non-stormwater Flows — Runoff which occur from sources other than rainwater; for example, personal car washing, lawn watering overspray, street cleaning, or pressure-washing of restaurant waste disposal facilities.

Non-supporting Stream or Subwatershed — A very general, watershed imperviousness-based classification category for a stream or subwatershed with more than 25% total impervious cover. Urbanization is generally expected to lead to some impacts on stream quality, but the type and magnitude of these effects can vary significantly among different watersheds at similar levels of imperviousness. These non-supporting streams are usually not candidates for restoration of relatively healthy aquatic ecosystems, but often can benefit from some physical rehabilitation designed to reduce additional degradation (for example, excessive erosion and siltation) that affects downstream areas.

Open Space — A portion of a site which is permanently set aside for public or private use and will not be developed. The space may be used for passive or active recreation, or may be reserved to protect or buffer natural areas.

Package Treatment Plant — A small, onsite waste treatment facility designed to handle the specific needs of a specialized, small, or remotely located waste generator; for example, a treatment plant that services a trailer park.

Point Source — A stationary location or fixed facility from which pollutants are discharged; any single identifiable source of pollution, such as a pipe, ditch, ship, ore pit, or factory smokestack.

Riparian Buffer — A transition zone between water and upland environments to protect the aquatic environment from pollution and sedimentation. It is measured from the top of the bank of the stream, or the wetland boundary.

Rooftop Runoff — Rainwater which falls on rooftops, does not infiltrate into soil, and runs off the land.

Sensitive Stream or Subwatershed — A very general, watershed imperviousness-based classification category for a stream or a subwatershed with less than 10% impervious cover, that is potentially still capable of supporting stable channels and good to excellent biodiversity. Urbanization is generally expected to lead to some impacts on stream quality, but the type and magnitude of these effects can vary significantly among different watersheds at similar levels of imperviousness.

Sinkhole — A landform created by subsidence of soil, sediment, or rock as underlying strata are dissolved by groundwater. A sinkhole may form by collapse into subterranean voids created by dissolution of limestone or dolostone or by subsidence as these strata are dissolved. A sinkhole is a depressional surficial feature and is generally circular in plan view. The boundary of a sinkhole is five feet beyond the point where the depression returns to the surrounding grades.

Stream — A perennial or intermittent watercourse having a defined channel (excluding manmade ditches) which contains flow from surface and groundwater sources during at least 50 percent of an average rainfall year.

Stormwater Best Management Practice — A structural or non structural technique designed to temporarily store or treat stormwater runoff in order to mitigate flooding, reduce pollution, and provide other amenities.

Stormwater "Hotspots" — Land uses or activities that generate highly contaminated runoff. Examples include fueling stations and airport de-icing facilities.

Stormwater Runoff — Rainwater which does not infiltrate into the soil and runs off the land.

Subwatershed — A smaller geographic section of a larger watershed unit with a drainage area between 2 to 15 square miles and whose boundaries include all the land area draining to a point where two second order streams combine to form a third order stream.

Total Maximum Daily Load (TMDL) — A Total Maximum Daily Load (TMDL) is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that amount to the pollutant's sources. A TMDL is the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources. The calculation must include a margin of safety to ensure that the waterbody can be used for the purposes the State has designated. The calculation must also account for seasonal variation in water quality.

Transferable Development Rights (TDRs) — A form of incentive for developers in which the developer purchases the rights to an undeveloped piece of property in exchange for the right to increase the number of dwelling units on another site. Often used to concentrate development density in certain land areas.

Watershed — An area of land that drains water, sediment and dissolved materials to a common receiving body or outlet. The term is not restricted to surface water runoff and includes interactions with subsurface water. Watersheds vary from the largest river basins to just acres or less in size. In urban watershed management, a watershed is seen as all the land which contributes runoff to a particular water body.

Wetland — An area of land that has a predominance of hydric soils and is inundated or saturated with water at a frequency and duration sufficient to support a prevalence of vegetation typically adapted to saturated soil conditions. Usually found in depressions, adjacent to bodies of water, or along flood plains or coastal waters.

Zoning — A set of local government regulations and requirements that govern the use, placement, spacing and size of buildings and lots (as well as other types of land uses) within specific areas designated as zones primarily dedicated to certain land use types or patterns.