A water-bearing geologic unit of saturated permeable rock, sand,
or gravel. The source for groundwater withdrawals.
Base flow refers to the water that enters streams by flowing through
the groundwater system, rather than directly over the surface of
the land. Because water moves much more slowly through the ground
than over the surface of the land, groundwater feeds streams gradually
rather than in big pulses after storms. As a result, during prolonged
periods of little to no rain, it is this base flow that keeps streams
The bioretention system (also referred to as a "biofilter")
is a stormwater management practice to manage and treat stormwater
runoff using conditioned soils and planting materials to filter
runoff stored within a shallow depression. To remove pollutants,
the method combines physical filtering and adsorption to soil materials
with bio-geochemical processes in which plant roots break down and
take up pollutants. The system generally consists of an inflow component,
a pretreatment element, an overflow structure, a shallow ponding
area (less than 9" deep), a surface organic layer of mulch,
a planting soil bed, plant materials, and an underdrain system to
convey treated runoff to a downstream facility. “Rain gardens”
(see definition below) are a type of bioretention system.
Effective Impervious Area
Effective impervious area is land surface that sheds stormwater directly into a water body or a storm drain system without providing the opportunity for it to infiltrate.
Transpiration is the process by which plants take in water through
their roots for use in photosynthesis and then give it off through the leaves as a by-product
of respiration. Evaporation is the direct loss of water from the
earth’s surface to the atmosphere. Evapotranspiration refers
to the transfer of water from the earth to the atmosphere through
both these processes combined.
Grass pavers refer to structural materials used to reinforce and stabilize a soil bed within which turf grass is grown. The reinforcement material is usually a plastic or concrete matrix imbedded in the soil, allowing roots to grow down and plants to grow up, but keeping the soil from becoming compacted.
A low-maintenance vegetated roof system that stores rainwater in
a lightweight engineered soil medium, where the water is taken up
by plants and transpired into the air. As a result, much less water
runs off the roof, as compared to conventional rooftops. Green roofs
have been in use in Europe for more than 30 years; they are easy
to incorporate into new construction and can also be used on many
The headwaters of a stream include the small streams that come together
to form the source and upper reaches of the stream. In some cases,
all parts of a river basin, except the mainstem
and main tributaries, can be considered
Any surface through which rainfall cannot pass or be effectively
absorbed (roads, rooftops, paved parking lots, sidewalks, etc.).
An approach to environmentally friendly land use planning. It includes
a suite of landscaping and site design techniques that attempt to
maintain the natural, predeveloped ability of a site to manage rainfall.
LID techniques capture water on site, filter it through vegetation,
and let it soak into the ground where it can recharge the local
water table rather than being lost as surface runoff. An important
LID principle includes the idea that stormwater is not merely a
waste product to be disposed of, but is a resource.
Low-impact development addresses the problems
created by land development through a variety of strategies:
- LID site planning – an approach that minimizes land disturbance
and preserves open space and natural site grading
- Bioretention areas, swales,
and rain gardens – vegetated areas
designed to retain and infiltrate stormwater
- Permeable paving –
alternatively paved areas that allow stormwater to percolate through
the paving material into the soil
- Green roofs – vegetated roofs
that reduce and filter stormwater runoff
- Alternative roadway and parking layouts – designed to
reduce impervious land cover and break up or disconnect impervious
surfaces from one another, so these surfaces can shed rain and
snowmelt into areas where the water can soak into the ground.
The main channel or course of a river or stream.
Pollution that cannot be identified as coming from a specific, localized
Overland stormwater runoff and some airborne deposits fall into
Open Space Preservation (Cluster) Zoning Bylaw
The Town of Ipswich’s Open Space Preservation (Cluster) Zoning bylaw is an example of an increasingly popular type of municipal ordinance or bylaw designed to provide developers incentives, such as density bonuses, to cluster development, preserve environmentally and culturally valuable open space on site, and cause minimal disturbance to the natural terrain.
or Porous Paving Materials
Permeable alternatives to conventional concrete or asphalt. Permeable
or porous asphalt, concrete, and pavers allow stormwater to soak
directly into the ground, reducing surface runoff and enhancing
Shallow landscaped depression that incorporates specialized plantings
and soil with a high infiltration rate. Rain Gardens are used to
control runoff volume and timing and can remove pollutants through
the physical, chemical, and biological processes that occur in plants,
soil, and mulch. See also Bioretention.
The process of capturing and storing runoff, usually from
rooftops, for nonpotable uses such as lawn and garden watering.
Water that infiltrates into the ground, usually from above, that
replenishes groundwater reserves, provides soil moisture, and affords
evapotranspiration (water uptake
and use by plants).
Development that emphasizes protecting open space and farmland,
revitalizing communities, keeping housing affordable, and providing
more transportation choices.
Open, shallow, vegetated channel that slows runoff, filters it,
and promotes infiltration into the ground. To function properly,
swales must be carefully designed and maintained. The vegetation
in swales, usually thick grass, helps to trap pollutants and reduces
the velocity of stormwater runoff, which allows it to percolate
into the ground.
A stream that joins, and thereby feeds, another (usually larger)
stream or river.
A geographic area of land in which all surface and most ground water
flows downhill to a common point, such as a river, stream, pond,
lake, wetland, or estuary.
The sources for some of these definitions include
(See Links for URLs):
Massachusetts Smart Growth Toolkit
Metropolitan Area Planning Council. Massachusetts Low-Impact Development
Massachusetts Department of Fish and Game, Riverways Program,
River Instream Flow Stewards (RIFLS). Glossary