Definitions. As used in this chapter, the following words shall have the meanings indicated:
ALTERATIONAs 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.
APPLICANTA landowner or developer who has filed an application for approval to engage in any regulated activities as defined in §
121-2C of this chapter.
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]
An open pit from which soil is excavated as a single incident for use at a single construction site.
CISTERNAn underground reservoir or tank for storing stormwater.
CONVEYANCEA 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]
A structure with appurtenant works which carries a stream or concentrated flow under or through an embankment or fill.
DAMAn 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.
DEPThe 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 STORMThe 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 BASINAn impoundment structure designed to manage stormwater runoff by temporarily storing the runoff and releasing it at a predetermined rate.
DEVELOPERA person, partnership, association, corporation or other entity, or any responsible person therein or agent thereof, that undertakes any regulated activity of this chapter.
DEVELOPMENTAny 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 SITEThe specific tract of land for which the regulated activity is proposed.
DRAINAGE EASEMENTA right granted by a landowner to a grantee, allowing the use of private land for stormwater management purposes.
DRAINAGE PLANThe 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).
Any act by which soil or bedrock is cut into, quarried, displaced or relocated.
EROSIONThe physical removal of soil and bedrock by the action of wind, water, ice or other natural forces.
EVAPOTRANSPIRATIONThe combined processes of evaporation from the water or soil surface and transpiration of water by plants.
[Added 3-15-2023 by Ord. No. 4262]
The vertical elevation of the ground surface prior to earthmoving or filling.
FILLAny 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 GRADEThe final vertical elevation of the ground after development.
FLOODPLAINAny 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).
FREEBOARDThe incremental depth in a stormwater management structure provided as a safety factor of design, above that required to convey the design runoff event.
GREEN INFRASTRUCTURESystems 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]
Any area from which water penetrates and subsequently passes into the groundwater supply.
IMPERVIOUS SURFACEA 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]
A structure designed to infiltrate stormwater in whole or in part (for example, a French drain, infiltration basin, seepage pit or seepage trench).
LAND DEVELOPMENTAny 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.
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.
Any lot improvements regulated under the Municipal Zoning Regulations.
LAND DISTURBANCEAny 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 AREAThe area comprised of the Gully Run, Mill Creek, Rock Run and Arrowmink Creeks and adjacent direct discharge areas.
MAIN STEMAny stream segment or other conveyance in the Lower Merion Drainage Area used as a reach in the hydrologic model.
MANAGED RELEASE CONCEPTA 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]
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.
NRCSThe Natural Resource Conservation Service, formerly the Soil Conservation Service, United States Department of Agriculture.
OPEN CHANNELA 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 MININGThe continuing or recurring removal of material from below the ground surface by open excavation.
PEAK DISCHARGEThe 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.
PERSONAny individual, corporation, partnership, joint venture, agency, unincorporated association, municipal corporation or agency within the Commonwealth of Pennsylvania, or any combination thereof.
PIPEA culvert, closed conduit or similar structure (including appurtenances) that conveys stormwater.
RATIONAL METHODA 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.
REACHAny of the natural or constructed runoff conveyance channels used for modeling purposes to connect the subareas and transport flows downstream.
REGULATED ACTIVITYAction(s) or proposed action(s) which affect the management of stormwater runoff and which are governed by this chapter as specified in §
121-2C.
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]
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 BASINAn 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 PERIODThe 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 BUFFERA permanent area of trees and shrubs located adjacent to streams, lakes, ponds, and wetlands.
[Added 3-15-2023 by Ord. No. 4262]
That part of precipitation which flows over the land.
SCSThe Soil Conservation Service, United States Department of Agriculture (now NRCS).
SEDIMENTEarth and rock in suspension in water or settled out of water as a deposit on land or beds of bodies of water.
SEDIMENTATIONThe process by which mineral or organic matter is accumulated or deposited by the movement of water.
SEDIMENT BASINA barrier, dam or detention basin located and designed to retain rock, sand, gravel, silt, soil or other material transported by water.
SITEAny 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.
SOILAll earth material of whatever origin that overlies bedrock.
SOIL-COVER COMPLEX METHODA 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 METHODA 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 AREASAreas 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 SEWERA system of pipes or other conduits which carries stormwater but does not convey domestic sewage or industrial wastes.
STORMWATERDrainage runoff from the surface of the land resulting from precipitation or snow or ice melt.
STORMWATER CONTROL MEASUREPhysical 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]
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 FACILITYAny 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]
A bridge, culvert or other structure in excess of 100 feet in length upstream to downstream which encloses a regulated water of the commonwealth.
STRIPPINGThe 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.
SUBAREAThe 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.
SUBDIVISIONThe 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.
SWALEA low-lying stretch of land which gathers or carries stormwater runoff.
TYPE II STORMThe Soil Conservation Service design storm for this area, based on typical rainfall patterns.
WATERCOURSEAny natural or artificial swale, stream, channel, drain or culvert in which waters flow continuously or intermittently.
WETLANDAreas 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]