Definitions. As used in this article, the following terms shall have
the meanings indicated:
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.
ACCESSORY STRUCTURE
A structure detached from a principal building located on
the same lot and customarily incidental and subordinate to the principal
building or use.
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 submitted a drainage plan or filed an application for approval to engage in any regulated activities as defined in §
186-46D of this article.
AS-BUILT DRAWINGS
A set of engineering or site drawings that delineate the
specific permitted stormwater management facility as actually constructed.
BMP (BEST MANAGEMENT PRACTICE)
Stormwater structures, facilities and techniques to maintain
or improve the water quality of surface runoff; Pennsylvania Handbook
of Best Management Practices for Developing Areas, Spring, 1998.
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 that 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 Mifflin County Planning Commission and/or
agent of the municipality involved with the administration, review
or enforcement of any provisions of this article 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 article.
DEVELOPMENT SITE
The specific tract of land for which a regulated activity
is proposed.
DISCHARGE EASEMENT
The grant of a property right to allow runoff in excess of
the previous quantity and/or rate of flow.
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.
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 municipality after the drainage plan
has been approved. Said permit is issued prior to or with the final
Township approval.
DRAINAGE PLAN
The documentation of the stormwater management system, if any, to be used for a given development site, the contents of which are established in §
186-49C.
EARTH DISTURBANCE
Any activity, including, but not limited to, construction,
mining, timber harvesting and grubbing which alters, disturbs, and
exposes the existing land surface.
EASEMENT
A right-of-way granted for limited use of private land for
a public or quasi-public purpose (e.g., utility lines, discharge easement,
drainage easement), and within which the owner of the property shall
not erect any permanent structures.
EPHEMERAL STREAMS (also EPHEMERAL FLOW)
Streams that carry only surface runoff and are dry except
during precipitation events. The groundwater table is generally located
below the bottom of ephemeral streams.
EROSION
The movement of soil particles by the action of water, wind,
ice, or other natural forces.
EROSION AND SEDIMENT POLLUTION CONTROL PLAN
A plan that is designed to minimize accelerated erosion and
sedimentation. Said plan must be submitted to and approved by the
Mifflin County Conservation District before construction can proceed.
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" on "B" soils 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
(1)
A slope, usually of a road, channel or natural ground specified
in percent and shown on plans as specified herein.
(2)
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
A surface that has been compacted or covered with material
to the extent that it is highly resistant to infiltration by water,
including, but not limited to, conventional impervious surfaces such
as paved streets, roofs, compacted stone, and sidewalks. In addition,
the following shall be considered impervious surfaces when used by
motor vehicles: graveled areas, paver blocks, bricks, and cobblestone.
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.
INTERMITTENT STREAMS (also INTERMITTENT FLOW)
Streams that flow only during wet seasons. The groundwater
table generally is at or above the bottom of intermittent streams
during wet seasons, but drops below the stream bottom during dry seasons.
Stream flow in intermittent streams is primarily due to precipitation,
but does have some groundwater contribution during wet seasons.
LAND DEVELOPMENT
As now defined or as may be defined in the Pennsylvania Municipalities
Planning Code (MPC), the term "land development" means any of the following
activities:
(1)
The improvement of one lot or two or more contiguous lots, tracts,
or parcels of land for any purpose involving:
(a)
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
(b)
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.
(3)
Development in accordance with Section 503(1.1) of the Pennsylvania
Municipalities Planning Code.
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 Kishacoquillas Creek hydrologic model.
MANNING EQUATION (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.
MUNICIPALITY
The Township of Derry, Mifflin County, Pennsylvania.
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.
NPDES
National Pollutant Discharge Elimination System; a permit
issued by the Pennsylvania Department of Environmental Protection
regulating the discharge of wastewater or stormwater from a facility.
NPDES permits are issued under the authority of the Clean Water Act
(P.L. 92-500).
NRCS
Natural Resource Conservation Service (previously SCS).
OPEN CHANNEL
A drainage 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.
PERENNIAL STREAMS (also PERENNIAL FLOW)
Streams that flow year round. Perennial streams derive their
flow from both groundwater and runoff and the groundwater table never
drops below the streambed.
PIPE
A culvert, closed conduit, or similar structure (including
appurtenances) that conveys stormwater.
PROBABLE MAXIMUM FLOOD (PMF)
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).
REDEVELOPMENT
Reconstruction of an existing improved, developed property,
as of the date of adoption of this article.
REGULATED ACTIVITIES
Actions or proposed actions that have an impact on stormwater runoff and that are specified in §
186-46D of this article.
RELEASE RATE
The percentage of predevelopment peak rate of runoff from
a site or subarea to which the postdevelopment peak rate of runoff
must be reduced to protect downstream areas.
RESTRICTIVE COVENANT
A restriction on the use of land usually set forth in the
deed. Restrictive covenants (also known as "deed restrictions") usually
run with the land and are binding upon subsequent owners of the property.
RETENTION BASIN
An impoundment in which stormwater is stored and not released.
Stored water may be released from the basin at some time after the
end of the storm (temporary retention), or else it leaves the basin
through infiltration or evaporation.
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.
SEDIMENTATION
The process by which mineral or organic matter is accumulated
or deposited by the movement of water.
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 article.
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.
SEMIPERVIOUS SURFACES
Material that allows rainfall to seep through to the underlying
strata. Examples include gravel, porous asphalt pavement, and paving
blocks not used for motor vehicles. If these materials are used for
vehicular pathways, parking, and material storage, they are generally
considered to be impervious. Use of these materials in development
sites must be supported by published information concerning infiltration
rates if credit is to be taken for the infiltration volume.
SHEET FLOW
Runoff that flows over the ground surface as a thin, even
layer, not concentrated in a channel.
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).
SOIL GROUP, HYDROLOGIC
A classification of soils by the Natural Resource 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.
SPILLWAY
A depression in the embankment of a pond or basin that 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 times 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 Kishacoquillas
Creek Watershed adopted by Mifflin County as required by the Act of
October 4, 1978, P.L. 864, (Act 167), and known as the "Kishacoquillas Creek Watershed Act 167
Stormwater Management Plan."
STORMWATER MANAGEMENT SITE PLAN
The plan prepared by the applicant or his representative
indicating how stormwater runoff will be managed at the particular
site of interest according to this article.
STREAM
A natural or man-made channel that conveys water in a concentrated
manner. See also "ephemeral stream," "intermittent stream" and "perennial
stream."
STREAM BUFFER
A vegetative strip paralleling the banks of a perennial or
intermittent stream. The buffer shall contain appropriate vegetation
through its width with the exception of a minimum five-foot-wide strip
of land maintained in meadow grass or forbs at its outer boundary.
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 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, 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 that 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.
TR-20
The computer-based hydrologic modeling technique adapted
to the Kishacoquillas Creek Watershed for the Act 167 Plan. The model
has been "calibrated" to reflect actual recorded flow values by adjusting
key model input parameters.
TR-55
A method for determining runoff volumes and rates developed
by the NRCS.
WATERCOURSE
A channel or conveyance of surface water having 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 the Commonwealth of Pennsylvania.
WETLAND
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, including
swamps, marshes, bogs, ferns, and similar areas.