For the purposes of this chapter, certain terms
and words used herein shall be interpreted as follows:
A.Â
Words used in the present tense include the future
tense; the singular number includes the plural, and the plural number
includes the singular; words of masculine gender include feminine
gender; and words of feminine gender include masculine gender.
B.Â
The word "includes" or "including" shall not limit
the term to the specific example, but is intended to extend its meaning
to all other instances of like kind and character.
C.Â
The word "person" includes an individual, firm, association,
organization, partnership, trust, company, corporation, unit of government,
or any other similar entity.
D.Â
The words "shall" and "must" are mandatory; the words
"may" and "should" are permissive.
E.Â
The words "used" or "occupied" include the words "intended,
designed, maintained, or arranged to be used, occupied, or maintained."
As used in this chapter, the following terms
shall have the meanings indicated:
American Association of State Highway and Transportation
Officials.
The removal of the surface of the land through the combined
action of human activity and the natural processes of a rate greater
than would occur because of the natural process alone.
The work of producing crops and raising livestock including
tillage, plowing, disking, harrowing, pasturing, mushroom growing,
nursery, and sod operations and installation of conservation measures.
Construction of new buildings or impervious area is not considered
an agricultural activity.
As applied to land, a change in topography as a result of
the moving of soil and rock from one location or position to another;
also the changing of surface conditions by causing the surface to
be more or less impervious; land disturbance.
The specified characteristics of the land surface (e.g.,
meadow) prior to a proposed disturbance or prior to a rainfall event
(e.g., amount of moisture in the soil); the basis for calculating
increases in runoff attributable to the disturbance or storm which
must be controlled.
A person, landowner or developer, etc., who has filed an application for approval to engage in any regulated activity defined in § 174-7.
A geologic formation, group of formations, or part of a formation
that contains sufficient saturated, permeable material to yield useful
quantities of groundwater to wells and springs.
Engineering or site drawings maintained by the contractor
during construction of the project and upon which are documented the
actual locations of the building components and changes to the original
contract documents. These documents, or a copy of same, are turned
over to the Township Engineer at the completion of the project.
To reduce the magnitude of the flow rate by increasing the
time it takes to release a specified volume of runoff (for example
the one-year, twenty-four-hour storm event). Attenuation is a method
of reducing the peak flow rates for postdevelopment compared to the
peak flow rates in predevelopment.
The channel at the top-of-bank or point from where water
begins to overflow onto a floodplain.
Portion of stream discharge derived from groundwater; the
sustained discharge that does not result from direct runoff or from
water diversions, reservoir releases, piped discharges, or other human
activities.
Well-compacted earthfilled ridge.
Activities, facilities, designs, measures or procedures used
to manage stormwater impacts from regulated activities to meet state
water quality requirements, to promote groundwater recharge, to prevent
or reduce surface runoff and water pollution, and to otherwise meet
the purpose of this chapter. Stormwater BMPs are commonly grouped
into one of three broad categories or measures: "structural," "nonstructural,"
and "operation and maintenance procedures." In this chapter, nonstructural
BMPs or measures refer to operational and/or behavior-related practices
that attempt to minimize the contact of pollutants with stormwater
runoff, whereas structural BMPs or measures are those that consist
of a physical device or practice that is installed to capture, treat
and reduce stormwater runoff. Nonstructural BMPs include, but are
not limited to, a variety of practices, from low-impact planning and
design, reduction of impervious surfaces, protection of existing vegetated
cover, and minimization of earth disturbances. Structural BMPs include,
but are not limited to, a wide variety of practices and devices, from
large-scale retention ponds and constructed wetlands to smaller-scale
underground treatment systems, seepage beds and trenches, infiltration
facilities, vegetated swales and filter strips, low-impact design,
bioretention (rain gardens), wet ponds, permeable paving combined
with underground seepage beds, detention basins, manufactured devices,
and operation and maintenance procedures. Structural stormwater BMPs
are permanent appurtenances to the project site.
A stormwater retention area that utilizes woody and herbaceous
plants and soils to remove pollutants before infiltration occurs.
The area of land immediately adjacent to any stream, measured
perpendicular to and horizontally from the top-of-bank on both sides
of a stream (see "top-of-bank").
A structural system that intercepts, diverts, stores, and
releases stormwater runoff for future use. Capture and reuse systems
can be used for landscaping irrigation during dry weather, nonpotable
water uses, and on-site stormwater disposal.
Chester County Conservation District.
Chester County Health Department.
Code of Federal Regulations.
Cubic feet per second.
A natural or artificial watercourse that conveys, continuously
or periodically, flowing water. Channels include, but shall not be
limited to, natural and human-made drainageways, swales, streams,
ditches, canals, and pipes flowing partly full.
The widening, deepening, or headward cutting of channels
and waterways caused by stormwater runoff or bankfull flows.
An underground reservoir or tank for storing rainwater.
Surface runoff from rainfall events, which converges and
flows primarily through water conveyance features such as swales,
gullies, waterways, channels or storm sewers and which exceeds the
maximum specified flow rates of filters or perimeter controls intended
to control sheet flow.
A series of holistic design practices that maximize protection
of key land and environmental resources, preserve significant concentrations
of open space and greenways, evaluate and maintain site hydrology,
and ensure flexibility in development design to meet community needs
and complementary and aesthetically pleasing development. Conservation
design encompasses the following objectives: conservation/enhancement
of natural resources, wildlife habitat, biodiversity corridors and
greenways (interconnected open space); maintenance of a balanced water
budget by making use of site characteristics and infiltration; incorporation
of unique natural, scenic and historic site features into the configuration
of the development; preservation of the integral characteristics of
the site as viewed from adjoining roads; and reduction in maintenance
required for stormwater management practices. Such objectives can
be met on a site through an integrated development process that respects
natural site conditions and attempts, to the maximum extent possible,
to replicate or improve the natural hydrology of a site.
A conservation district, as defined in § 3(c) of
the Conservation District Law [3 P.S. § 851(c)], which has
the authority under a delegation agreement executed with DEP to administer
and enforce all or a portion of the erosion and sediment control program
in this commonwealth; the Chester County Conservation District.
A facility or structure used for the transportation or transmission
of something from one place to another.
A structure with its appurtenant works which carries water
under or through an embankment or fill.
A human-made barrier, together with its appurtenant works,
constructed for the purpose of impounding or storing water or another
fluid or semifluid. A dam may include a refuse bank, fill, or structure
for highway, railroad, or other purposes which impounds or may impound
water or another fluid or semifluid.
Pennsylvania Department of Environmental Protection.
A Pennsylvania registered professional engineer or registered
professional land surveyor trained to develop stormwater management
plans.
The magnitude and temporal distribution of precipitation
from a storm event measured in probability of occurrence (e.g., a
five-year storm) and duration (e.g., 24 hours), used in the design
and evaluation of stormwater management systems.
The discharge prevention, either directly or indirectly,
of a given volume of stormwater runoff into surface waters by temporary
storage; the volume of runoff that is captured and released into the
waters of the commonwealth at a controlled rate.
An impoundment designed to collect and retard stormwater
runoff by temporarily storing the runoff and releasing it at a predetermined
rate. Detention basins are designed to drain completely shortly after
any given rainfall event and are dry until the next rainfall event.
A person who seeks to undertake any regulated earth disturbance
activities at a project site in the Township.
The construction, reconstruction, conversion, structural
alteration, relocation or enlargement of buildings or other structures,
the placement of mobile homes, mining, dredging, grading, filling,
paving, excavation, drilling operations, or any use or extension of
land. As used in this chapter, development encompasses both new development
and redevelopment.
The specific tract or parcel of land where any regulated activity set forth in § 174-7 is planned, conducted, or maintained.
The outside bark diameter at breast height which is defined
as 4.5 feet (1.37 m) above the forest floor on the uphill side of
the tree.
Drainage discharge that is not confined to a single point
location or channel, including sheet flow or shallow concentrated
flow.
The point of discharge for a stormwater facility.
Unstabilized land area where an earth disturbance activity
is occurring or has occurred.
A human-made waterway constructed for irrigation or stormwater
conveyance purposes.
Channel or ditch, together with a ridge, constructed across
a sloping land surface on the contour or with predetermined grades
to intercept and divert surface runoff before it gains sufficient
volume and velocity to create harmful erosion.
That portion of the property line of the lot, tract, or parcels
of land being developed, located such that overland or pipe flow from
the project site would be directed towards it by gravity.
That land area contributing runoff to a single point and
that is enclosed by a ridgeline.
A stormwater management facility designed to transport stormwater
runoff that includes channels, swales, pipes, conduits, culverts,
and storm sewers.
A right granted by a landowner to a grantee allowing the
use of private land for stormwater management purposes. A right-of-way
granted to use private land to facilitate the flow of water, within
which the owner shall erect no permanent structures but may use the
land in any other way not inconsistent with the grantee's right or
other applicable regulations.
A permit issued by the Township after the drainage plan has
been approved.
The documentation of the stormwater management system, if any, to be used for a given development site, the contents of which are established in § 174-11.
All facilities and natural features used for the movement
of stormwater through and from a drainage area, including, but not
limited to, any and all of the following: conduits, pipes and appurtenant
features, channels, ditches, flumes, culverts, streets, swales, gutters
as well as all watercourses, water bodies and wetlands.
A construction or other human activity which disturbs the
surface of land including, but not limited to, clearing and grubbing,
grading, excavations, embankments, land development, agricultural
plowing or tilling, timber harvesting activities, road maintenance
activities, mineral extraction, building construction, and the moving,
depositing, stockpiling, or storing of soil, rock, or earth materials.
A grant of one or more of the property rights by the property
owner and/or for use by the public, corporation or any other or entity.
A conveyance area that is used to pass peak discharge greater
than the maximum design storm controlled by the stormwater facility.
A structure or activity that changes, expands, or diminishes
the course, current, or cross section of a watercourse, floodway,
or body of water.
A concrete, stone, or other similar structure designed to
reduce the velocity and force of a concentrated flow of water.
Environmental Protection Agency.
The process by which the surface of the land, including water/stream
channels, is worn away by water, wind, or chemical action.
A plan that is designed to minimize accelerated erosion and
sedimentation.
Surface waters of high quality which satisfy Pennsylvania
Code Title 25 Environmental Protection, Chapter 93, Water Quality
Standards, § 93.4b(b) (relating to antidegradation).
The initial condition of a project site prior to the proposed
alteration. If the initial condition of the site is undeveloped land,
the land use shall be considered as "meadow" unless the natural land
cover is proven to generate a lower curve number or Rational "c" value,
such as forested lands. If the existing condition is impervious, the
land use shall be considered "meadow."
Federal Emergency Management Agency.
Uppermost perennial tributary in a watershed that has not
yet confluenced with another perennial stream. The confluence of two
first-order streams forms a second-order stream.
A temporary condition of partial or complete inundation of
land areas from the overflow of streams, rivers, and other waters
of the commonwealth.
A flood that has one chance in 100 or a one-percent chance
of being equaled or exceeded in any given year.
Any land area susceptible to inundation by water from any
natural source or as delineated by the applicable Department of Housing
and Urban Development Federal Insurance Administration Flood Hazard
Boundary Map as being a special flood hazard area.
The channel of a watercourse and those portions of the adjoining
floodplains which are reasonably required to carry and discharge the
one-hundred-year-frequency flood. Unless otherwise specified, the
boundary of the floodway is as indicated on maps and flood insurance
studies provided by the Federal Emergency Management Agency (FEMA).
In an area where no FEMA maps or studies have defined the boundary
of the one-hundred-year-frequency floodway, it is assumed, absent
evidence to the contrary, that the floodway extends from the stream
to 50 feet from the top-of-bank.
The study of landforms associated with river channels and
the processes that form them.
The management of forests and timberlands when practiced
in accordance with accepted silvicultural principles, through developing,
cultivating, harvesting, transporting and selling trees for commercial
purposes, which does not involve any land development.
A vertical distance between the elevation of the design high-water
and the top of a dam, levee, tank, basin, swale, or diversion berm.
The space is required as a safety margin in a pond or basin.
A natural or human-made waterway, usually broad and shallow,
covered with erosion-resistant grasses used to convey surface water.
Alternative roof surfaces that typically consist of waterproofing
and drainage materials and an engineered growth media that is designed
to support plant growth. Green roofs capture and temporarily store
stormwater runoff in the engineered growth media before it is conveyed
to the storm system. A portion of the captured stormwater evaporates
or it is taken up by plants, which helps reduce runoff volumes, peak
runoff rates, and pollutant loads on development sites.
A geotextile material designed to prevent upward or downward
movement of soil or other solids while permitting water movement.
Water beneath the earth's surface that supplies wells and
springs and is often between saturated soil and rock.
The replenishment of existing natural undergroundwater supplies
from rain or overland flow.
The U.S. Army Corps of Engineers Hydrologic Engineering Center
(HEC) - Hydrologic Modeling System (HMS), used to model the Darby-Cobbs,
Crum, and Valley Creek Watersheds during the Act 167 plan development
and the basis for the standards and criteria of this chapter.
Surface waters having quality which exceeds levels necessary
to support propagation of fish, shellfish, and wildlife and recreation
in and on the water by satisfying Pennsylvania Code Title 25, Environmental
Protection, Chapter 93, Water Quality Standards, § 93.4b(a).
A structure which meets the following:
[Added 10-7-2019 by Ord.
No. HR-430]
Is used for the production, processing, keeping, storing, sale
or shelter of an agricultural commodity as defined in Section 2 of
the Act of December 19, 1974 (P.L. 973, No. 319), known as the "Pennsylvania
Farmland and Forest Land Assessment Act of 1974,"[1] or for the storage of agricultural equipment or supplies;
and
Area where land use or activity generates highly contaminated
runoff, with concentrations of pollutants in excess of those typically
found in stormwater, including but not limited to: vehicle salvage
yards and recycling facilities; vehicle fueling stations; vehicle
service and maintenance facilities; vehicle and equipment cleaning
facilities; fleet storage areas (bus, truck, etc.); industrial sites
based on standard industrial codes; marinas (service and maintenance);
outdoor liquid container storage; outdoor loading/unloading facilities;
public works storage areas; facilities that generate or store hazardous
materials; commercial container nurseries; and other land uses and
activities as designated by an appropriate review authority.
A graph representing the discharge of water versus time for
a selected point in the drainage system.
The hydrologic cycle or balance that sustains quality and
quantity of stormwater, baseflow, storage, and groundwater supplies
under natural conditions.
A classification of soils by the Natural Resources Conservation
Service (NRCS), formerly the Soil Conservation Service (SCS), into
four runoff potential groups. The groups range from A soils, which
are very permeable and produce little runoff, to D soils, which are
not very permeable and produce much more runoff. Infiltration rates
of soils vary widely and are affected by subsurface permeability as
well as surface intake rates. Soils are classified into four HSGs,
A, B, C, and D, according to their minimum infiltration rate.
The study of the properties, distribution, circulation and
effects of water on the earth's surface, soil and atmosphere.
A horizontal surface that has been compacted or covered with
a layer of material so that it is highly resistant to infiltration
by water, including but not limited to buildings, structures, and
paved areas such as driveways, sidewalks, parking lots, patios, decks,
swimming pools, tennis courts, etc. For the purposes of determining
compliance with this chapter, stone surfaces routinely used for vehicle
parking and movement shall be considered impervious.
A retention basin, detention basin, or other stormwater management
facility designed to retain stormwater runoff and release it at a
controlled rate.
Development that occurs on smaller parcels that remain undeveloped
but are within or in very close proximity to urban or densely developed
areas. Infill development usually relies on existing infrastructure
and does not require an extension of water, sewer, or other public
utilities.
Movement of surface water into the soil, where it is absorbed
by plant roots, evaporated into the atmosphere, or percolated downward
to recharge groundwater.
A structure designed to direct runoff into the undergroundwater
(e.g., infiltration beds or trenches, dry wells, French drains, seepage
pits, or trenches, bioinfiltration areas (rain gardens), porous pavement
with underground infiltration beds, etc.).
The flow entering the stormwater management facility and/or
BMP.
The upstream end of any structure through which water may
flow.
The depth of accumulated rainfall per unit of time.
A stream that flows only part of the time. Flow generally
occurs for several weeks or months in response to seasonal precipitation
or groundwater discharge.
The lowest surface, the floor or bottom of a culvert, drain,
sewer, channel, basin, BMP, or orifice.
A type of topography or landscape characterized by surface
depressions, sinkholes, rock pinnacles/uneven bedrock surface, underground
drainage, and caves. Karst is formed on carbonate rocks, such as limestone
or dolomite.
Any of the following activities:
The improvement of one lot or two or more contiguous
lots, tracts, or parcels of land for any purpose involving:
A group of two or more residential or nonresidential
buildings, whether proposed initially or cumulatively, or a single
nonresidential building on a lot or lots regardless of the number
of occupants or tenure; or
The division or allocation of land or space,
whether initially or cumulatively, between or among two or more existing
or prospective occupants by means of, or for the purpose of, streets,
common areas, leaseholds, condominiums, building groups, or other
features.
A subdivision of land.
A low earthen berm constructed perpendicular to the direction
of slope and extending across the width of the slope for the purpose
of intercepting surface runoff and spreading it behind the berm to
enhance infiltration and reduce erosion and runoff from the slope.
The purpose of a level spreader is to prevent concentrated erosive
flows from occurring and to spread out stormwater runoff uniformly
over the ground as sheet flow.
A soil horizon or condition in the soil profile or underlying
strata that includes one of the following:
A seasonal high water table, whether perched
or regional, determined by direct observation of the water table or
indicated by soil mottling.
A rock with open joints, fracture or solution
channels, or masses of loose rock fragments, including gravel, with
insufficient fine soil to fill the voids between the fragments.
A rock formation, other stratum, or soil condition
that is so slowly permeable that it effectively limits downward passage
of water.
The total amount (generally measured in pounds or kilograms
per acre per year) of material (sediment, nutrients, oxygen-demanding
material, or other chemicals or compounds) brought into a lake, stream,
or water body by inflowing streams, runoff, direct discharge through
pipes, groundwater, the air (aerial or atmospheric deposition) and
other sources over a specific period of time (often annually).
A designated parcel, tract, or area of land established by
a plat or otherwise as permitted by law and to be used, developed,
or built upon as a unit.
Any stream segment or other runoff conveyance used as a reach
in watershed-specific hydrologic models.
The actions taken to restore or preserve the as-built functional
design of any facility or system.
A method for calculation of velocity of flow (e.g., feet
per second) and flow rate (e.g., cubic feet per second) in open channels
based upon channel shape, roughness, depth of flow, and slope. "Open
channels" may include closed conduits so long as the flow is not under
pressure.
The maximum (largest) design storm that is controlled by
the stormwater facility.
A natural ground cover with less than one viable tree of
six inches or greater per 1,500 square feet, with continuous grass
cover, and typically having greater than 75% uniform grass coverage.
A cover condition for which SCS curve numbers have been assigned or
to which equivalent Rational Method coefficients have been assigned.
Municipal separate storm sewer system.
The system created in 1972 under the Clean Water Act to authorize
discharges to local receiving waters only pursuant to governmental
permits, in an effort to reduce point source and nonpoint source pollutants.
Predevelopment condition. In terms of stormwater management,
the land coverage as identified in the latest edition of TR No. 55,
which existed 18 months prior to the application, shall be used for
determining land cover type, except in the case where land cover was
impervious, in which case the condition of meadow shall apply.
See "hydrologic regime."
Undisturbed surface area or depression where stormwater collects
and a portion of which infiltrates and replenishes the underground
water and groundwater.
Any activity regulated by this chapter that is not considered
a redevelopment as defined in this chapter.
National Oceanic and Atmospheric Administration.
Pollution that enters a water body from diffuse origins in
the watershed and does not result from discernible, confined, or discrete
conveyances.
Water flowing in stormwater collection facilities, such as
pipes or swales, which is not the result of a rainfall event or snowmelt.
Passive site design approaches or regulatory approaches that
positively impact water quality and reduce or minimize the generation
of stormwater runoff without requiring the construction of specific
or discrete stormwater management control structures. Methods of controlling
stormwater runoff quantity and quality, such as innovative site planning,
impervious area, land disturbance, and grading reduction, protection
of natural depression areas, temporary ponding on site, and other
techniques.
National Pollutant Discharge Elimination System.
Natural Resource Conservation Service (previously SCS).
A natural or human-made watercourse or conduit in which water
flows with a free surface; a conveyance channel that is not enclosed.
Also known as swales, grass channels, and biofilters or bioswales.
These systems are used for the conveyance, retention, infiltration
and filtration of stormwater runoff.
"Point source" as described in 40 CFR § 122.2 at
the point where the Township's storm sewer system discharges to surface
waters of the commonwealth.
The flow exiting the stormwater management facility and/or
BMP.
Points of water disposal to a stream, river, lake, tidewater,
or artificial drain.
Pennsylvania Association of Conservation Districts.
Pennsylvania Department of Transportation.
The parcel of land from which a land development or subdivision
originates, determined from the date of adoption of this chapter.
Involves the use of parking areas as temporary impoundments
with controlled release rates during rainstorms.
The maximum rate of stormwater runoff from a specific storm
event.
The computer-based hydrologic model developed at Pennsylvania
State University.
The rate of movement of water under hydrostatic pressure
through interstices of rock or soil. For stormwater analysis, it is
typically measured as a distance per unit time (e.g., inches per hour).
A culvert, closed conduit, or similar structure (including
appurtenances) that conveys stormwater.
The Planning Commission of Tredyffrin Township.
Any discernible, confined, and discrete conveyance including,
but not limited to, any pipe, ditch, channel, tunnel, or conduit from
which stormwater is or may be discharged, as defined in state regulations
at 25 Pennsylvania Code § 92.1.
Period after construction during which disturbed areas are
stabilized, stormwater controls are in place and functioning, and
all proposed improvements in the approved land development plan are
completed.
Prior to commencing construction activities.
Undeveloped/natural condition.
Techniques employed in stormwater BMPs to provide storage or filtering to trap coarse materials and other pollutants before they enter the system, but not necessarily designed to meet the water quality volume requirements of § 174-21.
The specific area of land where any regulated activities
in the Township are planned, conducted, or maintained.
Any person licensed by the Pennsylvania Department of State
or otherwise qualified by law to perform work required by this chapter.
The depth of accumulated rainfall per unit time.
Volume per unit of time.
A rainfall-runoff relation used to estimate peak flow.
A method for computing quantities of stormwater runoff. The
rational formula relates runoff to rainfall by the following equation:
|
Q = c * i * a
|
|
Q
|
=
|
Peak runoff in cubic feet per second.
| |
|
c
|
=
|
Runoff coefficient which is actually the ratio
of the peak runoff rate to the average rainfall rate for a period
known as the time of concentration.
| |
|
i
|
=
|
Average rainfall intensity in inches per hour
for a period equal to the time of concentration.
| |
|
a
|
=
|
Drainage area in acres.
|
Any stream segment or other runoff conveyance used in the
watershed-specific hydrologic models.
Any water bodies, watercourse or wetlands into which surface
waters flow.
The replenishment of groundwater through the infiltration
of rainfall, other surface waters, or land application of water or
treated wastewater.
Demolition and subsequent rebuilding of impervious surface.
Original documents revised to suit the as-built conditions
and subsequently provided by the engineer to the applicant. The engineer
reviews the contractor's as-built drawings against his/her own records
for completeness, then either turns these over to the applicant or
transfers the information to a set of reproducibles, in both cases
for the applicant's permanent records.
Any development that proposes or consists of demolition or
removal of existing structures or impervious surfaces at a site and
replacement with new impervious surfaces. Maintenance activities,
such as top-layer grinding and repaving, interior remodeling projects
and tenant improvements are not considered to be redevelopment.
Action or proposed action that involves the alteration or development of the land in a manner that may affect stormwater runoff, have an impact on stormwater runoff quality or quantity and that are specified in § 174-7.
Defined under NPDES Phase II regulations as earth disturbance
activity of one acre or more with a point source discharge to surface
waters or the Township's storm sewer system or five acres or more
regardless of the planned runoff. This includes earth disturbance
on any portion of, part, or during any stage of a larger common plan
of development.
A volume of flow being discharged from a stormwater management
facility or structure per specified unit of time (cubic feet per second,
gallons per minute, etc.) or designated design storm (e.g., ten-year
predevelopment flow storm). The specified release rates contained
within this chapter are the maximum percentages of predevelopment
peak rate of runoff from a site or subarea that can be released after
development.
Replacement of the impervious surface that does not involve
reconstruction of an existing paved (impervious) surface.
Reconstruction of and full replacement of an existing paved
(impervious) surface.
A basin, either natural or human-made, which contains or
will contain the water or other fluid impounded by a dam.
A structure in which stormwater is stored and not released
during the storm event. A retention basin/pond is designed to retain
a permanent pool of water during dry weather and potentially detain
waters from a specific drainage area, or designed for infiltration
purposes and does not have an outlet. The retention basin/pond designed
for infiltration purposes must infiltrate stored water in three days
or less.
The average interval, in years, within which a storm event
of a given magnitude can be expected to recur. For example, the one-hundred-year-return-period
rainfall would be expected to recur on the average of once every 100
years. The probability of a one-hundred-year storm occurring in any
one year is 0.01 (i.e., a one-percent chance).
Land adjoining and immediately upgradient from rivers or
streams that is vegetated with a combination of trees, shrubs, and
herbaceous plants. A riparian buffer functions to maintain the integrity
of stream channels to reduce the impact of upland sources of pollution
by trapping, filtering and converting sediments, nutrients, and other
chemicals, and supply food, cover and thermal protection to fish and
other wildlife.
A vertical pipe extending from the bottom of a detention
facility or pond that is used to control the discharge rate from the
detention facility or pond for a specified design storm.
Earth disturbance activities within the existing road cross
section, such as grading and repairing existing unpaved road surfaces,
cutting road banks, cleaning or clearing drainage ditches, and other
similar activities.
A drainage conduit or pipe that collects water runoff from
a roof and leads it away from the structure.
The temporary ponding and gradual release of stormwater falling
directly onto flat roof surfaces using controlled-flow roof drains
in building designs.
The surface and subsurface network of roots which supports
a tree.
Any part of precipitation that flows over the land surface.
Tredyffrin Township Subdivision and Land Development Ordinance.[2]
Soil Conservation Service, United States Department of Agriculture.
Solid material, both mineral and organic, that is in suspension,
is being transported or has been moved from its site of origin by
water or air.
The process by which mineral or organic matter is accumulated
or deposited by the movement of water. The process occurs when sediment
particles that have been suspended within flowing waters are deposited
on the stream bottom or floodplain.
A barrier, dam, or detention basin located and designed in
such a way as to retain rock, sand, gravel, silt, or other material
transported by water during construction.
The placement, discharge, or any other introduction of sediment
into the waters of the commonwealth.
An area of the earth excavated, having an uncompacted bottom,
completely wrapped with geotextile material and filled with loose
clean stone or similar coarse material into which surface water is
directed for infiltration into the undergroundwater.
A conveyance or system of conveyances (including roads with
drainage systems, municipal streets, catch basins, curbs, gutters,
ditches, human-made channels, or storm drains) primarily used for
collecting and conveying stormwater runoff.
Stormwater runoff flowing in shallow, defined ruts prior
to entering a defined channel or waterway.
A flow process associated with broad, shallow water movement
on sloping ground surfaces that is not channelized or concentrated.
A method of runoff computation developed by NRCS that is
based on relating soil type and land use/cover to a runoff parameter
called "curve number (CN)."
The zone through which contaminants, if present, are likely
to migrate and reach a drinking water well or surface water intake.
A watershed that has been designated by DEP as exceptional
value (EV) or high quality (HQ) waters.
A conveyance that is used to pass and control the discharge
of a design storm that is controlled by the stormwater facility. The
emergency spillway is the conveyance that is used to pass the peak
discharge of the maximum design storm that is controlled by the stormwater
facility.
A place where water flows naturally from a rock or soil upon
the land or into a body of surface water.
As defined under state regulations, protection of designated
and existing uses (see 25 Pennsylvania Code Chapters 93 and 96), including:
Each stream segment in Pennsylvania has a "designated
use," such as "cold-water fishery" or "potable water supply," which
is listed in Chapter 93. These uses must be protected and maintained
under state regulations.
"Existing uses" are those attained as of November
1975, regardless of whether they have been designated in Chapter 93.
Regulated earth disturbance activities must be designed to protect
and maintain existing uses and maintain the level of water quality
necessary to protect those uses in all streams and to protect and
maintain water quality in special protection streams.
Water quality involves the chemical, biological,
and physical characteristics of surface water bodies. After regulated
earth disturbance activities are complete, these characteristics can
be impacted by the addition of pollutants such as sediment and changes
in habitat through increased flow volumes and/or rates as a result
of changes in land surface area from those activities. Therefore,
permanent discharges to surface waters must be managed to protect
the stream bank, streambed, and structural integrity of the waterway
to prevent these impacts.
A reservoir routing procedure based on solution of the continuity
equation (inflow minus outflow equals the change in storage), with
outflow defined as a function of storage volume and depth.
The storm of a specific duration, intensity, and frequency.
The number of times that a given storm event occurs or is
exceeded on the average in a stated period of years (see "return period").
A system of pipes and/or open channels that conveys intercepted
runoff and stormwater from other sources but excludes domestic sewage
and industrial wastes.
Procedures involved in the control of water that runs off
the surface of the land from rain and melting snow.
Those subareas of a watershed in which some type of detention
is required to meet the plan requirements and the goals of Act 167.
Any structure, natural or human-made, that, due to its condition,
design, or construction, conveys, stores, or otherwise affects stormwater
runoff quality, rate, or quantity. Typical stormwater management facilities
include, but are not limited to, infiltration seepage beds and trenches,
bioretention areas (rain gardens), detention and retention basins,
green roof systems, capture and reuse systems, open channels, storm
sewers, pipes, and water quality devices.
A watershed plan for managing those land use activities that
will influence stormwater runoff quality and quantity and that would
impact the watersheds of Tredyffrin Township. The stormwater management
plan includes the approved detailed analysis, design, and drawings
of the stormwater management system required for activities regulated
by this chapter.
The surface runoff generated by precipitation reaching the
ground surface during and immediately after a rainfall event.
A natural watercourse with perennial or intermittent flow.
The land area adjacent to each side of a stream essential
to maintaining water quality (see "buffer").
A bridge, culvert, or other structure in excess of 100 feet
in length upstream to downstream which encloses a regulated water
of the commonwealth.
The smallest drainage unit of a watershed for which stormwater
management criteria have been established in the stormwater management
plan.
The division or redivision of a lot, tract, or parcel of
land by any means into two or more lots, tracts, parcels, or other
divisions of land including changes in existing lot lines for the
purpose, whether immediate or future, of lease, partition by the court
for distribution to heirs or devisees, transfer of ownership, or building
or lot development; provided, however, that the subdivision by lease
of land for agricultural purposes into parcels of more than 10 acres
not involving any new street or easement of access or any residential
dwelling shall be exempted.
Any and all rivers, streams, creeks, rivulets, ditches, watercourses,
storm sewers, lakes, dammed water, wetlands, ponds, springs, and all
other bodies or channels of conveyance of surface waters, or parts
thereof, whether natural or artificial, within or on the boundaries
of the commonwealth.
A low-lying stretch of land that gathers or carries surface
water runoff.
Stormwater management model developed by EPA for analyzing
stormwater quantity and quality associated with runoff from urban
areas. Both single event and continuous simulation can be performed
on catchments having storm sewers, or combined sewers and natural
drainage, for prediction of flows, stages and pollution concentrations.
See "forestry."
The time required for surface runoff to travel from the hydraulically
most distant point of the watershed to a point of interest within
the watershed. This time is the combined total of overland flow time
and flow time in pipes or channels, if any.
Highest point of elevation in a stream channel cross section
at which a rising water level just begins to flow out of the channel
and over the floodplain.
Tredyffrin Township, Chester County, Pennsylvania.
A professional engineer licensed as such in the Commonwealth
of Pennsylvania, duly appointed as the Engineer for the Township.
Seasonal depressional wetlands that are covered by shallow
water for variable periods from winter to spring but may be completely
dry for most of the summer and fall.
A channel or conveyance of surface water having a defined
bed and banks, whether natural or artificial, with perennial or intermittent
flow.
Any and all rivers, streams, creeks, rivulets, ditches, watercourses,
storm sewers, lakes, dammed water, wetlands, ponds, springs, and all
other bodies or channels of conveyance of surface and undergroundwater,
or parts thereof, whether natural or artificial, within or on the
boundaries of Tredyffrin Township.
Region or area drained by a river, watercourse, or other
body of water, whether natural or artificial. The area upstream and
tributary to a point along a stream, lake, drainage facility or any
point of interest that contributes runoff to that point.
Any and all rivers, streams, creeks, rivulets, ditches, watercourses,
storm sewers, lakes, dammed water, wetlands, ponds, springs, and all
other bodies or channels of conveyance of surface and undergroundwater,
or parts thereof, whether natural or artificial, within or on the
boundaries of the commonwealth.
The uppermost level of saturation of pore space or fractures
by subsurface water in an aquifer. Seasonal high water table refers
to a water table that rises and falls with the seasons due either
to natural or human-made causes.
A structure built over a well or the source of water for
a well.
The surface and subsurface area surrounding a water supply
well, well field, or spring supplying a public water system through
which contaminants are reasonably likely to move toward and reach
the water source.
Pond for urban runoff management that is designed to detain
urban runoff and always contains water.
Those areas that are inundated or saturated by surface or
groundwater at a frequency and duration sufficient to support, and
that under normal circumstances do support, a prevalence of vegetation
typically adapted for life in saturated soil conditions. Wetlands
generally include swamps, marshes, bogs, fens, and similar areas.
For the purposes of regulation under this chapter, wetlands shall
be construed to be all areas meeting the definition of "wetlands,"
as then currently specified by the United States Army Corps of Engineers
and/or the Pennsylvania Department of Environmental Protection. In
any situation in which these sources do not coincide, the more inclusive
area shall be considered to be wetlands under this chapter.
Areas characterized by dense and extensive tree cover growing
closely together so that the driplines touch or overlap and in which
there is more than one viable tree of a diameter of six inches or
greater per 1,500 square feet of lot area; a cover condition for which
SCS curve numbers have been assigned or to which equivalent Rational
Method runoff coefficients have been assigned. This definition also
includes groves of flowering or subcanopy trees, such as dogwood trees
and young forests where the immature branches may not yet be interlocking.
[To determine if an area has more than one viable tree of six inches
or greater caliper per 1,500 square feet, the total area of the land
in question (in square feet) shall be divided by 1,500. If the result
is equal to or less than the number of viable trees of a diameter
of six inches or greater and meets the other stated characteristics,
the area in question is considered a woodland.]
A natural ground cover with more than one viable tree of
six inches or greater caliber per 1,500 square feet, protected from
grazing, with leaf and organic litter and brush adequately covering
the soil. A cover condition for which SCS curve numbers have been
assigned or to which equivalent Rational Method coefficients have
been assigned.
The Tredyffrin Township Zoning Ordinance of 1939, as amended.[3]
