Definitions of some commonly used terms in stormwater management and low impact development. For a complete list of terms, see the Connecticut Stormwater Quality Manual on the CT DEP website.
Alternative Site Design |
Innovative site design practices have been developed as alternatives to traditional development to control stormwater pollution and protect the ecological integrity of developing watersheds. Research has demonstrated that alternative site design can reduce impervious cover, runoff volume, pollutant loadings, and development costs when compared to traditional development. |
Aquifer |
A porous water-bearing formation of permeable rock, sand or gravel capable of yielding economically significant quantities of groundwater. |
Baseflow |
The portion of streamflow that is not due to storm runoff but is the result of groundwater discharge or discharge from lakes or similar permanent impoundments of water. |
Bioretention |
A practice to manage and treat stormwater runoff by using a specially designed planting soil bed and planting materials to filter runoff stored in a shallow depression. The areas consist of a mix of elements each designed to perform different functions in the removal of pollutants and attenuation of stormwater runoff. |
Grass Drainage Channels |
Traditional vegetated open channels, typically trapezoidal, triangular, or parabolic in shape, whose primary function is to provide non-erosive conveyance, typically up to the 10-year frequency design flow. They provide limited pollutant removal through filtration by grass or other vegetation, sedimentation, biological activity in the grass/soil media, as well as limited infiltration if underlying soils are pervious. |
Groundwater Recharge |
The process by which water that seeps into the ground, eventually replenishing groundwater aquifers and surface waters such as lakes, streams, and the oceans. This process helps maintain water flow in streams and wetlands and preserves water table levels that support drinking water supplies. |
| Hydrologic Cycle |
The distribution and movement of water between the earth’s atmosphere, land, and water bodies. |
Impaired Waters [303(d)List] |
Those water bodies not meeting water quality standards. This list of impaired waters within each state is referred to as the “303(d) List” and is prepared pursuant to Section 303(d) of the Federal Clean Water Act. |
Impervious Surfaces |
Surfaces that cannot infiltrate rainfall, including rooftops, pavement, sidewalks, and driveways. |
Low Impact Development (LID) |
Low impact development is a site design strategy intended to maintain or replicate predevelopment hydrology through the use of small-scale controls integrated throughout the site to manage runoff as close to its source as possible. |
Native Plants |
Plants that are adapted to the local soil and rainfall conditions and that require minimal watering, fertilizer, and pesticide application. |
Nonpoint Source Pollution |
Pollution caused by diffuse sources that are not regulated as point sources and are normally associated with precipitation and runoff from the land or percolation. |
Open Space Development |
A compact form of development that concentrates density in one portion of the site in exchange for reduced density elsewhere. Also known as cluster or conservation development. |
Permeable Paving Materials |
Materials that are alternatives to conventional pavement surfaces and that are designed to increase infiltration and reduce stormwater runoff and pollutant loads. Alternative materials include modular concrete paving blocks, modular concrete or plastic lattice, cast-in-place concrete grids, and soil enhancement technologies. Stone, gravel, and other low-tech materials can also be used as alternatives for low traffic applications such as driveways, haul roads, and access roads. |
Porous Pavement |
Porous pavement is similar to conventional asphalt or concrete but is formulated to have more void space for greater water passage through the material. |
Primary Stormwater Treatment Practice |
Stormwater treatment practices that are capable of providing high levels of water quality treatment as stand-alone devices; can be grouped into five major categories stormwater ponds, stormwater wetlands, infiltration practices, filtering practices, and water quality swales. |
Rain Barrels |
Barrels designed to retain small volumes of runoff for reuse for gardening and landscaping. They are applicable to residential, commercial, and industrial sites and can be incorporated into a site’s landscaping plan. The size of the rain barrel is a function of rooftop surface area and the design storm to be stored. |
Rain Garden |
Functional landscape elements that combine plantings in depressions that allow water to pool for only a few days after a rainfall then be slowly absorbed by the soil and plantings. |
Secondary Stormwater Treatment Practices |
Stormwater treatment practices that may not be suitable as stand alone treatment because they either are not capable of meeting the water quality treatment performance criteria or have not yet received the thorough evaluation needed to demonstrate the capabilities for meeting the performance criteria. |
Site Planning and Design |
Techniques of engineering and landscape design that maintaining predevelopment hydrologic functions and pollutant removal mechanisms to the extent practical. |
Site Stormwater Management Plan |
Plan describing the potential water quality and quantity impacts associated with a development project both during and after construction. It also identifies selected source controls and treatment practices to address those potential impacts, the engineering design of the treatment practices, and maintenance requirements for proper performance of the selected practices. |
Stormwater |
Water consisting of precipitation runoff or snowmelt. |
Stormwater Treatment Train |
Stormwater treatment practices, as well as site planning techniques and source controls, combined in series to enhance pollutant removal or achieve multiple stormwater objectives. |
Swales, Water Quality |
Vegetated open channels designed to treat and attenuate the water quality volume and convey excess stormwater runoff. Dry swales are primarily designed to receive drainage from small impervious areas and rural roads. Wet swales are primarily used for highway runoff, small parking lots, rooftops, and pervious areas. |
Total Maximum Daily Load (TMDL) |
A calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that amount to the pollutant’s sources, including a margin of safety. |
Vegetated Buffer |
An area or strip of land in permanent undisturbed vegetation adjacent to a water body or other resource that is designed to protect resources from adjacent development during construction and after development by filtering pollutants in runoff, protecting water quality and temperature, providing wildlife habitat, screening structures and enhancing aesthetics, and providing access for recreation. |
Vegetated Roof Covers (Green Roofs) |
Multilayered, constructed roof systems consisting of a vegetative layer, media, a geotextile layer, and a synthetic drain layer installed on building rooftops. Rainwater is either intercepted by vegetation and evaporated to the atmosphere or retained in the substrate before being returned to the atmosphere through transpiration and evaporation. Also referred to as green roofs. |
Water Quality Volume (WQV) |
The volume of runoff generated by one inch of rainfall on a site. |
