Specific Definitions.
ACCELERATED EROSION
The removal of the surface of the land through the combined
action of man's activity and the natural processes of a rate
greater than would occur because of the natural process alone.
AGRICULTURAL ACTIVITIES
The work of producing crops and raising livestock including
tillage, plowing, disking, harrowing, pasturing and installation of
conservation measures. Construction of new buildings or impervious
area is not considered an agricultural activity.
ALTERATION
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.
APPLICANT
A landowner or developer who has filed an application for approval to engage in any regulated activities as defined in §
25A-104 of this chapter.
BMP (BEST MANAGEMENT PRACTICE)
Stormwater structures, facilities and techniques intended
to maintain or improve hydrologic regime or improve the water quality
of surface runoff.
CHANNEL EROSION
The widening, deepening, and headward cutting of small channels
and waterways, due to erosion caused by moderate to large floods.
CISTERN
An underground reservoir or tank for storing rainwater.
CULVERT
A structure with appurtenant works which carries a stream
under or through an embankment or fill.
DAM
An artificial barrier, together with its appurtenant works,
constructed for the purpose of impounding or storing water or another
fluid or semifluid, or a refuse bank, fill or structure for highway,
railroad or other purposes which does or may impound water or another
fluid or semifluid.
DESIGN STORM
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.
DESIGNEE
The agent of the Bucks County Planning Commission and/or
agent of the Borough Council involved with the administration, review
or enforcement of any provisions of this chapter by contract or memorandum
of understanding.
DETENTION BASIN
An impoundment structure designed to manage stormwater runoff
by temporarily storing the runoff and releasing it at a predetermined
rate.
DETENTION DISTRICT
Those subareas in which some type of detention is required
to meet the plan requirements and the goals of Act 167.
DEVELOPER
A person, partnership, association, corporation, or other
entity, or any responsible person therein or agent thereof, that undertakes
any regulated activity of this chapter.
DEVELOPMENT SITE
The specific tract of land for which a regulated activity
is proposed.
DOWNSLOPE PROPERTY LINE
That portion of the property line of the lot, tract, or parcels
of land being developed located such that all overland or pipe flow
from the site would be directed towards it.
DOWNSTREAM HYDRAULIC CAPACITY ANALYSIS
Any downstream capacity hydraulic analysis conducted in accordance
with this chapter shall use the following criteria for determining
adequacy for accepting increased peak flow rates:
A.
Natural or man-made channels or swales must be able to convey
the increased rate of runoff associated with a two-year return period
event within their banks at velocities consistent with protection
of the channels from erosion. Acceptable velocities shall be based
upon criteria included in the DEP "Erosion Acid Sediment Pollution
Control Program Manual."
B.
Natural or man-made channels or swales must be able to convey
the increased twenty-five-year return period rate of runoff without
creating any hazard to persons or property.
C.
Culverts, bridges, storm sewers or any other facilities which
must pass or convey flows from the tributary area must be designed
in accordance with DEP, Chapter 105, regulations (if applicable) and,
at a minimum, pass the increased twenty-five-year return period rate
of runoff.
D.
No new channels or conveyance facilities shall be authorized
by this language.
DRAINAGE CONVEYANCE FACILITY
A stormwater management facility designed to transmit stormwater
runoff and shall include streams, channels, swales, pipes, conduits,
culverts, storm sewers, etc.
DRAINAGE EASEMENT
A right granted by a landowner to a grantee, allowing the
use of private land for stormwater management purposes.
DRAINAGE PERMIT
A permit issued by the Borough Council after the drainage
plan has been approved. Said permit is issued prior to or with the
final Borough approval.
EARTH DISTURBANCE
Any activity including, but not limited to, construction,
mining, timber harvesting and grubbing which alters, disturbs, and
exposes the existing land surface.
EROSION
The movement of soil particles by the action of water, wind,
ice, or other natural forces.
EXISTING CONDITIONS
The initial condition of a project site prior to the proposed
construction. 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 lower curve numbers or Rational "C"
value, such as forested lands.
FLOOD
A general but temporary condition of partial or complete
inundation of normally dry land areas from the overflow of streams,
rivers, and other waters of this commonwealth.
FLOODPLAIN
Any land area susceptible to inundation by water from any
natural source or delineated by applicable Department of Housing and
Urban Development, Federal Insurance Administration Flood Hazard Boundary
- mapped as being a special flood hazard area. Also included are areas
that comprise Group 13 Soils, as listed in Appendix A of the Pennsylvania
Department of Environmental Protection (PADEP) "Technical Manual for
Sewage Enforcement Officers" (as amended or replaced from time to
time by PADEP).
FLOODWAY
The channel of the watercourse and those portions of the
adjoining floodplains that 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 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 the
bank of the stream.
FOREST MANAGEMENT TIMBER OPERATIONS
Planning and activities necessary for the management of forest
land. These include timber inventory and preparation of forest management
plans, silvicultural treatment, cutting budgets, logging road design
and construction, timber harvesting, site preparation and reforestation.
FREEBOARD
A vertical distance between the elevation of the design high-water
and the top of a dam, levee, tank, basin, or diversion ridge. The
space is required as a safety margin in a pond or basin.
GRADE
A slope, usually of a road, channel or natural ground specified
in percent and shown on plans as specified herein. (To) Grade - to
finish the surface of a roadbed, top of embankment or bottom of excavation.
GRASSED WATERWAY
A natural or constructed waterway, usually broad and shallow,
covered with erosion-resistant grasses, used to conduct surface water
from cropland.
IMPERVIOUS SURFACE
Impervious surfaces are those surfaces which do not absorb
water. All structures, buildings, parking areas, driveways, roads,
sidewalks, and any areas of concrete, asphalt, or packed stone shall
be considered impervious surface. In addition, all other areas as
determined by the Borough Engineer to be impervious within the meaning
of this definition shall also be considered as impervious surface.
IMPOUNDMENT
A retention or detention basin designed to retain stormwater
runoff and release it at a controlled rate.
INFILTRATION STRUCTURES
A structure designed to direct runoff into the ground (e.g.
french drains, seepage pits, seepage trench).
INLET
A surface connection to a closed drain. A structure at the
diversion end of a conduit. The upstream end of any structure through
which water may flow.
LAND DEVELOPMENT
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A.
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The improvement of one lot or two or more contiguous lots, tracts,
or parcels of land for any purpose involving:
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1.
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A group of two or more buildings; or
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2.
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The division or allocation of land or space 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;
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B.
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Any subdivision of land.
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LAND/EARTH DISTURBANCE
Any activity involving grading, tilling, digging, or filling
of ground or stripping of vegetation or any other activity that causes
an alteration to the natural condition of the land.
MAIN STEM (MAIN CHANNEL)
Any stream segment or other runoff conveyance facility used
as a reach in the Tohickon Creek hydrologic model.
MANNING EQUATION IN (MANNING FORMULA)
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.
NONPOINT SOURCE POLLUTION
Pollution that enters a watery body from diffuse origins
in the watershed and does not result from discernible, confined, or
discrete conveyances.
NRCS
Natural Resource Conservation Service (previously SCS).
OPEN CHANNEL
A stormwater management site element in which stormwater
flows with an open surface. Open channels include, but shall not be
limited to, natural and man-made drainageways, swales, streams, ditches,
canals, and pipes flowing partly full.
OUTFALL
Point where water flows from a conduit, stream, or drain.
OUTLET
Points of water disposal from a stream, river, lake, tidewater
or artificial drain.
PARKING LOT STORAGE
Involves the use of impervious parking areas as temporary
impoundments with controlled release rates during rainstorms.
PEAK DISCHARGE
The maximum rate of stormwater runoff from a specific storm
event.
PENN STATE RUNOFF MODEL (CALIBRATED)
The computer-based hydrologic modeling technique adapted
to the Tohickon Creek watershed for the Act 167 Plan. The model has
been "calibrated" to reflect actual recorded flow values by adjoining
key model input parameters.
PIPE
A culvert, closed conduit, or similar structure (including
appurtenances) that conveys stormwater.
PMF - PROBABLE MAXIMUM FLOOD
The flood that may be expected from the most severe combination
of critical meteorologic and hydrologic conditions that are reasonably
possible in any area. The PMF is derived from the probable maximum
precipitation (PMP) as determined on the basis of data obtained from
the National Oceanographic and Atmospheric Administration (NOAA).
RECHARGE VOLUME
A calculated volume of stormwater runoff from impervious
areas which is required to be infiltrated at a site and may be achieved
through use of structural or nonstructural BMPs.
RELEASE RATE
The percentage of predevelopment peak rate of runoff from
a site or subarea to which the post development peak rate of runoff
must be reduced to protect downstream areas.
RETENTION BASIN
An impoundment in which stormwater is stored and not released
during the storm event. Stored water may be released from the basin
at some time after the end of the storm.
RETURN PERIOD
The average interval, in years, within which a storm event
of a given magnitude can be expected to recur. For example, the twenty-five-year
return period rainfall would be expected to recur on the average once
every 25 years.
RISER
A vertical pipe extending from the bottom of a pond that
is used to control the discharge rate from the pond for a specified
design storm.
ROOFTOP DETENTION
Temporary ponding and gradual release of stormwater falling
directly onto flat roof surfaces by incorporating controlled-flow
roof drains into building designs.
RUNOFF
Any part of precipitation that flows over the land surface.
SEDIMENT BASIN
A barrier, dam, retention or detention basin located and
designed to retain rock, sand, gravel, silt, or other material transported
by water.
SEDIMENT POLLUTION
The placement, discharge or any other introduction of sediment
into the waters of the commonwealth occurring from the failure to
design, construct, implement or maintain control measures and control
facilities in accordance with the requirements of this chapter.
SEDIMENTATION
The process by which mineral or organic matter is accumulated
or deposited by the movement of water.
SEEPAGE PIT/SEEPAGE TRENCH
An area of excavated earth filled with loose stone or similar
coarse material, into which surface water is directed for infiltration
into the ground.
SHEET FLOW
Runoff that flows over the ground surface as a thin, even
layer, not concentrated in a channel.
SOIL GROUP, HYDROLOGIC
A classification of soils by the soil conservation service
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.
SOIL-COVER COMPLEX METHOD
A method of runoff computation developed by the NRCS that
is based on relating soil type and land use/cover to a runoff parameter
called "curve number" (CN).
SPILLWAY
A depression in the embankment of a pond or basin which is
used to pass peak discharge greater than the maximum design storm
controlled by the pond.
STORAGE INDICATION METHOD
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.
STORM FREQUENCY
The number of tunes that a given storm "event" occurs or
is exceeded on the average in a stated period of years. See "return
period."
STORM SEWER
A system of pipes and/or open channels that convey intercepted
runoff and stormwater from other sources, but excludes domestic sewage
and industrial wastes.
STORMWATER
The total amount of precipitation reaching the ground surface.
STORMWATER MANAGEMENT FACILITY
Any structure, natural or man-made, that, due to its condition,
design, or construction, conveys, stores, or otherwise affects stormwater
runoff. Typical stormwater management facilities include, but are
not limited to, detention and retention basins, open channels, storm
sewers, pipes, and infiltration structures.
STORMWATER MANAGEMENT PLAN
The plan for managing stormwater runoff in the Tohickon Creek
Watershed adopted by as required by the Act of October 4, 1978, P.L.
864, (Act 167), and known as the "Tohickon Creek Watershed Action
167 Stormwater Management Plan."
STORMWATER MANAGEMENT SITE PLAN
The plan prepared by the developer or his representative
indicating how stormwater runoff will be managed at the particular
site of interest according to this chapter.
STREAM ENCLOSURE
A bridge, culvert or other structure in excess of 100 feet
in length upstream to downstream which encloses a regulated water
of this commonwealth.
SUBAREA
The smallest drainage unit of a watershed for which stormwater
management criteria have been established in the Stormwater Management
Plan.
SUBDIVISION
The division or re-division 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, 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 dwellings, shall be exempt.
SWALE
A low-lying stretch of land which gathers or carries surface
water runoff.
TIME OF CONCENTRATION (Tc)
The time 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.
WATER QUALITY VOLUME
A calculated volume of stormwater runoff from impervious
areas which is required to be captured and treated at a site and may
be achieved through use of structural or non-structural BMPs. Numerically,
the water quality volume is a product of the volumetric runoff coefficient,
the site area, and a depth of rainfall of one inch.
WATERCOURSE
Any channel or conveyance of surface waters having a defined
bed and banks, whether natural or artificial, with perennial or intermittent
flow.
WATERS OF THE COMMONWEALTH
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 underground
water, or parts thereof, whether natural or artificial, within or
on the boundaries of this commonwealth.
WETLAND
Those areas that are inundated or saturated by surface or
ground water 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, including
swamps, marshes, bogs, ferns, and similar areas.