-
Amended
soil: Soil with compost tilled in to restore
natural capacities to treat, store and infiltrate water. Amending soil
reduces runoff, promotes plant health and reduces needs for watering and
application of fertilizers and herbicides. The
Stormwater Management Manual for
Western Washington
(Best Management Practice T5.13) recommends tilling in 10 percent dry weight
of compost into the top 8 inches of topsoil and breaking up at least 4
inches of subsoil below this.
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Best
Management Practice
(BMP):
A practice or combination of
practices that prevent or reduce adverse affects of stormwater runoff and/or
associated pollutants.
-
Bioretention:
A vegetated depression located on the site that is designed to collect,
store and infiltrate runoff. Typically includes a mix of amended soils and
vegetation.
-
Buffer
strip:
A
zone where plantings capable of filtering stormwater are established or
preserved and where construction, paving and chemical applications are
prohibited.
-
Catchbasin:
A
collection structure below ground designed to collect and convey water into
the storm sewer system. It is designed so that sediment falls to the bottom
of the catchbasin and not directly into the pipe.
-
Check
dam:
An
earthen, rock or log structure used in grass swales to reduce water
velocities, promote sediment deposition and enhance infiltration.
-
Culvert:
A
conduit used for the passage of surface water under a road or other
embankment.
-
DEQ:
Department of Environmental Quality
-
Design
storm:
A
rainfall event of specified size and return frequency(i.e., a storm what has
the likelihood of occurring once every 10 or 100 years) that is used to
calculate the runoff volume and peak discharge rate.
-
Detention: Basin
An
area designated to temporarily store storm runoff so a controlled outflow
can slowly empty the area.
-
Detention
system:
Temporary storage of stormwater to control the rate of release, allow for
infiltration and provide treatment.
-
Detention:
The
temporary storage of storm runoff to control peak discharge rates and
provide gravity settling of pollutants.
-
Detention
time:
The
amount of time that a volume of water will remain in a detention basin.
-
Discharge:
The
rate of flow(the volume of water passing a point in a given period of time)
leaving an area usually expressed as cubic feet per second.
-
Drainage
area:
The
total tributary area of a watershed usually expressed in square miles, acres
or square feet.
-
Drainage
facility:
Any
facility used to transport or store stormwater.
-
Drawdown:
The
gradual reduction in water level in a basin due to the combined effect of
infiltration and evaporation.
-
Efficiency: measure of how well a BMP or BMP
system removes pollutants.
-
Erosion:
The
wearing away of the land surface by wind, water, ice and gravity dislodging
soil particles. Evidence of erosion are gullies, rills, sediment, plumes,
etc.
-
Evapotranspiration:
A
process where vegetation absorbs, uses and releases water.
-
Facultative
plants:
Plants capable of adapting to varying environments.
-
Fill:
Added
earth which changes the contour of the land.
-
Filterra®: similar in concept to bioretention in its function
and applications, with the major distinction that Filterra® has
been optimized for high volume/flow treatment and high pollutant removal. It
takes up little space and may be used on highly developed sites such as
landscaped areas, green space, parking lots and streetscapes.
-
Filtration:
A process in which filtering, or treatment, takes place.
-
First
flush:
The
delivery of a highly concentrated pollutant loading during the early stages
of a storm due to the washing effect of runoff on pollutants that have
accumulated on the land.
-
Flood
plain:
For
a given flood event that area of land adjoining a continuous watercourse
that has been covered temporarily by water.
-
Freeboard:
The
space from the top of an embankment to the highest water elevation expected
for the largest design storm to be stored. The space is required as a safety
margin in a pond or basin.
-
Geotextile:
A
woven fabric capable of passing water but able to hold back soil. (Filter
Fabric)
-
Groundwater Level:
The
upper surface or top of the saturated portion of the soil or bedrock layer
that indicates the uppermost extent of groundwater.
-
Green
roof:
roof of a building which is partially
or completely covered with plants. It may be a tended roof garden or a more
self-maintaining ecology
-
Groundwater:
Naturally existing water beneath the earth’s surface between saturated soil
particles and rock that supplies wells and springs.
-
Hydrology:
Scientific study of
the properties, distribution and effects of water on the Earth's surface, in
the soil and underlying rocks, and in the atmosphere.
-
Hydrophilic
plants:
Vegetation adapted to wet conditions.
-
Impervious
surfaces:
Hard surfaces, such as rooftops, roads and parking areas, that prevent or
slow infiltration of water. Lawns with underlying soils compacted by heavy
machinery are considered impervious.
-
Infiltration
capacity:
The
maximum rate at which the soil can absorb falling rain or melting snow.
Usually expressed in inches/hour or centimeters/second.
-
Infiltration:
Downward movement of water from land surfaces into the soil
-
Infiltration
rate:
The
absorption of water into the ground expressed in terms of inches/hour.
-
Integrated management practices (IMP):
Small-scale structural stormwater practices that are distributed throughout
a site to mimic/influence predevelopment site hydrology.
-
Invert:
The
interior surface of the bottom of any pipe.
-
LEED
(Leadership in Energy and Environmental Design):
A voluntary, consensus-based national
standard for developing high-performance, sustainable buildings.
-
Manhole:
A
structure that allows access into a stormwater drainage system.
-
Mulch:
A
natural or artificial layer of plant residue which aids in seedling
germination by reducing the temperature fluctuations, holding moisture and
holding soil in place.
-
Natural
wetland:
Land characterized by the natural presence of water sufficient to support
wetland vegetation.
-
Non-point
source pollution:
Pollution that is not identifiable to any particular source
-
Off-site
detention:
Detention provided at a regional detention facility as opposed to storage
on-site.
-
One
hundred
year flood:
A
flood that has one percent (1%) chance occurring in any given year.
-
On-site
detention:
Stormwater detained on a site verses a regional location.
-
Peak
discharge:
The
maximum instantaneous rate of flow during a storm usually in reference to a
specific design storm event.
-
Permeable:
Ability to absorb water.
-
Rational
formula:
A
simple technique for estimating peak discharge rates for very small
developments based on the rainfall intensity, watershed time of
concentration and runoff coefficient.
-
Retention
basin:
A
stormwater management basin that captures storm water runoff and does not
discharge directly to a surface water body. The water is "discharged" by
infiltration or evaporation.
-
Retention:
The
holding of runoff in a basin without release except by means of evaporation,
infiltration or emergency bypass.
-
Rip-rap:
A
combination of large stone, cobbles and boulders used to line channels,
stabilize banks, reduce runoff velocities or filter out sediment.
-
Roof
garden:
A garden on a flat roof of a
building
-
Runoff
coefficient:
The
ratio of the amount of water that is NOT absorbed by the surface to the
total amount of water that falls during a rainstorm.
-
Runoff:
The
excess portion of precipitation that does not infiltrate into the ground but
"runs off" and reaches a stream, water body or storm sewer.
-
Sediment:
Soil material that is transported from its site of origin by water. May be
in the form of bed load (along the bed), suspended or dissolved.
-
Sheet
flow:
Runoff which flows over the ground surface as a thin even layer, not
concentrated in a channel or pipe.
-
Smart
growth:
Collection of land use planning techniques that features compact, mixed-use,
transit-oriented development with the objective of creating more attractive,
livable, economically strong communities while protecting natural resources.
-
Spillway:
A
depression in the embankment of a pond or basin used to pass peak discharges
in excess of the design storm.
-
Storm
drain:
An
open or enclosed stormwater conveyance system that is connected to a
stormwater/sewer system and requires periodic maintenance.
-
Stormwater:
any water that results from a storm
—generally rainfall. Stormwater either enters the ground (absorption) and
recharges groundwater, evaporates into the atmosphere, or flows over land to
streams, lakes, rivers, and other water features.
-
Stream:
a
river, creek, or surface waterway that has definite banks, a bed, and
visible evidence of continued flow or continued occurrence of water
-
Swale:
an area with dense vegetation that retains and filters the first flush of
runoff from impervious surfaces. It is constructed downstream of a runoff
source. After the soil-plant mixture below the channel becomes saturated,
the swale acts as a conveyance structure to a bio-retention cell, wetland,
or infiltration area. There is a range of designs for these systems. Some
swales are designed to filter pollutants and promote infiltration and others
are designed with a geo-textile layer that stores the runoff for slow
release into depressed open areas or an infiltration zone.
-
Time of concentration:
The
time it takes for surface runoff to travel from the hydraulically farthest
portion of the watershed to the design point.
-
Turbidity:
Sediment, organic matter or other particles that reduce the clarity of
water. Excessive turbidity in streams and other surface waters can directly
impair the growth of aquatic vegetation, and indirectly lead to degraded
fish and wildlife habitat and decreased oxygen in waters.
