Definitions. As used in this chapter, the following
words shall have the meanings indicated:
ALTERATION
As applied to land, a change in topography as a result of
the moving of soil or 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 §
121-2C of this chapter.
BEDROCK
The solid, undisturbed rock in place either at the ground
surface or beneath surficial soil deposits.
BEST MANAGEMENT PRACTICE (BMP)
Activities, facilities, designs, measures, or procedures
used to manage stormwater impacts from regulated activities, to meet
state water quality requirements, to promote groundwater recharge,
and to otherwise meet the purposes of this chapter. Stormwater BMPs
are commonly grouped into one of two broad categories or measures:
"structural" or "nonstructural." In this chapter, "nonstructural BMPs
or measures" refers 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 and
treat stormwater runoff. Structural BMPs include, but are not limited
to, a wide variety of practices and devices, from large-scale retention
ponds and constructed wetlands to small-scale underground treatment
systems, infiltration facilities, filter strips, low-impact design,
bioretention, wet ponds, permeable paving, grassed swales, riparian
or forested buffers, sand filters, detention basins, and manufactured
devices. Structural stormwater BMPs are permanent appurtenances to
the project site.
[Amended 3-15-2023 by Ord. No. 4262]
BORROW PIT
An open pit from which soil is excavated as a single incident
for use at a single construction site.
CISTERN
An underground reservoir or tank for storing stormwater.
CONVEYANCE
A natural or man-made, existing, or proposed stormwater management
facility, feature or channel used for the transportation or transmission
of stormwater from one place to another. For the purposes of this
chapter, "conveyance" shall include pipes, drainage ditches, channels,
and swales (vegetated or other), gutters, stream channels, and like
facilities or features.
[Added 3-15-2023 by Ord. No. 4262]
CULVERT
A structure with appurtenant works which carries a stream
or concentrated flow under or through an embankment or fill.
DAM
An artificial barrier, including the appurtenant works, constructed
for the purpose of impounding or storing water or any other fluid
or semifluid, or any other bank, fill or structure for highway, railroad
or other purposes which does or may impound water or any other fluid
or semifluid.
DEP
The Pennsylvania Department of Environmental Protection.
DESIGNEE (DESIGNATED REPRESENTATIVE)
Any person or consultant designated by the Township to administer,
review or enforce the provisions of this chapter whether by contract
or by memorandum of understanding.
DESIGN STORM
The magnitude and temporal distribution of precipitation
from a storm event measured in probability of occurrence and duration
(a twenty-five-year, twenty-four-hour storm, for example), used in
the design and evaluation of stormwater management systems.
DETENTION BASIN
An impoundment structure designed to manage stormwater runoff
by temporarily storing the runoff and releasing it at a predetermined
rate.
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
Any subdivision or land development. The improvement of one
lot or two or more contiguous lots, tracts or parcels of land for
any purpose or any alteration of land not for agricultural or conservation
purposes, which includes earthmoving, filling or stripping on a tract.
Development includes, but is not limited to, road construction; utility
installation; public, commercial or industrial facility construction;
and mining and quarrying, and also includes water resource management.
DEVELOPMENT SITE
The specific tract of land for which the regulated activity
is proposed.
DRAINAGE EASEMENT
A right granted by a landowner to a grantee, allowing the
use of private land for stormwater management purposes.
DRAINAGE PLAN
The documentation of the proposed storm management system to be used for a given development site, the contents of which are established in §
121-4H(2).
EARTHMOVING
Any act by which soil or bedrock is cut into, quarried, displaced
or relocated.
EROSION
The physical removal of soil and bedrock by the action of
wind, water, ice or other natural forces.
EVAPOTRANSPIRATION
The combined processes of evaporation from the water or soil
surface and transpiration of water by plants.
[Added 3-15-2023 by Ord. No. 4262]
EXISTING GRADE
The vertical elevation of the ground surface prior to earthmoving
or filling.
FILL
Any act by which earth, sand, gravel, rock or any other material
is deposited, placed, pushed, dumped, pulled, transported or moved
to a new location, and shall include the conditions resulting therefrom.
FINISHED GRADE
The final vertical elevation of the ground after development.
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
Maps as being a special flood hazard area. Also included are areas
that comprise Group 13 Soils, as listed in Appendix A of the DEP Technical
Manual for Sewage Enforcement Officers (as amended or replaced from
time to time by DEP).
FREEBOARD
The incremental depth in a stormwater management structure
provided as a safety factor of design, above that required to convey
the design runoff event.
GREEN INFRASTRUCTURE
Systems and practices that use or mimic natural processes
to infiltrate, evapotranspirate or reuse stormwater on the side where
it is generated.
[Added 3-15-2023 by Ord. No. 4262]
GROUNDWATER RECHARGE
Any area from which water penetrates and subsequently passes
into the groundwater supply.
IMPERVIOUS SURFACE
A surface that prevents the infiltration of water into the
ground. Impervious surfaces shall include, but are not limited to,
roofs, additional indoor living spaces, patios, garages, storage sheds
and similar structures; and any new streets or sidewalks.
[Amended 2-26-2020 by Ord. No. 4184; 3-15-2023 by Ord. No. 4262]
INFILTRATION STRUCTURE
A structure designed to infiltrate stormwater in whole or
in part (for example, a French drain, infiltration basin, seepage
pit or seepage trench).
LAND DEVELOPMENT
Any of the following activities:
(1)
The improvement of a 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.
(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)
Any lot improvements regulated under the Municipal
Zoning Regulations.
LAND DISTURBANCE
Any activity involving grading, tilling, digging or filling
of ground or disturbing the existing vegetative cover or any other
activity that causes an alteration to the natural condition of the
land.
LOWER MERION DRAINAGE AREA
The area comprised of the Gully Run, Mill Creek, Rock Run
and Arrowmink Creeks and adjacent direct discharge areas.
MAIN STEM
Any stream segment or other conveyance in the Lower Merion
Drainage Area used as a reach in the hydrologic model.
MANAGED RELEASE CONCEPT
A post-construction stormwater management strategy that comprises
the collection, management, and filtration of captured runoff from
the contributing drainage area through a BMP that is preferably vegetated
and includes a release of a portion of the captured runoff through
an underdrain within the BMP.
[Added 3-15-2023 by Ord. No. 4262]
MANNING EQUATION (MANNING FORMULA)
A method for calculating the velocity of flow (e.g., feet
per second) and flow rate (e.g., cubic feet per second) in open channels
based on channel shape, roughness, depth of flow and slope. Open channels
may include closed conduits so long as the flow is not under pressure.
NRCS
The Natural Resource Conservation Service, formerly the Soil
Conservation Service, United States Department of Agriculture.
OPEN CHANNEL
A drainage element in which stormwater is conveyed with an
open surface. Open channels include natural and constructed drainageways,
swales, streams, ditches, canals and pipe flowing partly full.
OPEN-PIT MINING
The continuing or recurring removal of material from below
the ground surface by open excavation.
PEAK DISCHARGE
The maximum rate at which stormwater discharges or leaves
a site. Peak discharge shall be measured in cubic feet per second.
PENN STATE RUNOFF MODEL (PSRM)
The computer based hydrologic modeling technique for the
Lower Merion Draining Area. The model has been calibrated, or adjusted,
to reflect the actual flow values by adjusting certain model input
parameters.
PERSON
Any individual, corporation, partnership, joint venture,
agency, unincorporated association, municipal corporation or agency
within the Commonwealth of Pennsylvania, or any combination thereof.
PIPE
A culvert, closed conduit or similar structure (including
appurtenances) that conveys stormwater.
RATIONAL METHOD
A method of peak runoff calculation using a standardized
runoff coefficient, acreage and rainfall intensity determined by the
return period of the storm event and by the time necessary for the
entire tract to contribute runoff. The formula is Q=CiA, where Q is
the calculated peak flow rate in cubic feet per second, C is the runoff
coefficient, i is the rainfall intensity in inches per hour and A
is the area of the tract in acres.
REACH
Any of the natural or constructed runoff conveyance channels
used for modeling purposes to connect the subareas and transport flows
downstream.
REGULATED ACTIVITY
Action(s) or proposed action(s) which affect the management of stormwater runoff and which are governed by this chapter as specified in §
121-2C.
REGULATED IMPERVIOUS SURFACE
Proposed impervious surface as part of a current proposed
activity and all existing impervious surfaces installed after November
17, 1999, as part of a previous activity.
[Added 3-15-2023 by Ord. No. 4262]
RELEASE RATE
The percentage of the predevelopment peak rate of runoff
for a development site to which the post development peak rate of
runoff must be controlled to protect areas downstream.
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 average once
every 25 years.
RIPARIAN BUFFER
A permanent area of trees and shrubs located adjacent to
streams, lakes, ponds, and wetlands.
[Added 3-15-2023 by Ord. No. 4262]
RUNOFF
That part of precipitation which flows over the land.
SCS
The Soil Conservation Service, United States Department of
Agriculture (now NRCS).
SEDIMENT
Earth and rock in suspension in water or settled out of water
as a deposit on land or beds of bodies of water.
SEDIMENTATION
The process by which mineral or organic matter is accumulated
or deposited by the movement of water.
SEDIMENT BASIN
A barrier, dam or detention basin located and designed to
retain rock, sand, gravel, silt, soil or other material transported
by water.
SITE
Any lot or parcel of land or combination of contiguous lots
or parcels of land under one ownership where earthmoving, filling
or stripping is, was or will be performed.
SOIL
All earth material of whatever origin that overlies bedrock.
SOIL-COVER COMPLEX METHOD
A method of runoff calculation developed by SCS which relates
soil type and land use/cover to a runoff parameter called a Curve
Number (CN).
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 DRAINAGE PROBLEM AREAS
Areas identified by the municipalities within the Lower Merion
Drainage Area which lack adequate stormwater collection or conveyance
facilities resulting in a hazard to persons or property.
STORM SEWER
A system of pipes or other conduits which carries stormwater
but does not convey domestic sewage or industrial wastes.
STORMWATER
Drainage runoff from the surface of the land resulting from
precipitation or snow or ice melt.
STORMWATER CONTROL MEASURE
Physical features used to effectively control, minimize,
and treat stormwater runoff. Also may be referred to as "stormwater
management practice (SMP)." [See "best management practice (BMP)."]
[Added 3-15-2023 by Ord. No. 4262]
STORMWATER MANAGEMENT
The set of actions taken to control water in its hydrological
cycle with the objective of providing surface drainage, flood control,
erosion and sedimentation control and reducing pollutants in stormwater
runoff.
STORMWATER MANAGEMENT FACILITY
Any structure, natural or man-made, that, due to its condition,
design, or construction, conveys, stores, or otherwise affects stormwater
runoff quality, rate, or quantity, including best management practices
and stormwater control measures. Typical stormwater management facilities
include, but are not limited to, detention and retention basins, open
channels, storm sewers, pipes, and infiltration structures.
[Added 3-15-2023 by Ord. No. 4262]
STREAM ENCLOSURE
A bridge, culvert or other structure in excess of 100 feet
in length upstream to downstream which encloses a regulated water
of the commonwealth.
STRIPPING
The removal of vegetation, including trees, and/or topsoil.
Stripping shall not include, or be deemed to include, the normal process
of gardening or property maintenance.
SUBAREA
The smallest unit of the watershed breakdown, used for the
hydrologic modeling, and for which runoff control 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.
SWALE
A low-lying stretch of land which gathers or carries stormwater
runoff.
TYPE II STORM
The Soil Conservation Service design storm for this area,
based on typical rainfall patterns.
WATERCOURSE
Any natural or artificial swale, stream, channel, drain or
culvert in which waters flow continuously or intermittently.
WETLAND
Areas that are inundated or saturated by surface water 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, and similar areas.
[Amended 3-15-2023 by Ord. No. 4262]