For the purpose of this chapter, the following definitions shall apply unless the context clearly indicates or requires a different meaning.
ACCELERATED EROSION. The removal of the surface of the land through the combined action of a human’s activity and the natural processes of a rate greater than would occur because of the natural processes alone.
AGRICULTURAL ACTIVITIES. The work of producing crops and raising livestock including tillage, plowing, disking, harrowing, pasturing, nursery and sod operations, excluding greenhouse structures, 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 other person who has filed an application to the municipality for approval to engage in any regulated activity defined in § 1043.05.
AS-BUILT DRAWINGS. Engineering or site drawings maintained by the contractor as he or she constructs the project and upon which the documents 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 Municipal Engineer at the completion of the project.
BANKFULL. The channel at the top-of-bank or point from where water begins to overflow onto a floodplain.
BASEFLOW. 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.
BIORETENTION. A stormwater retention area that utilizes woody and herbaceous plants and soils to remove pollutants before infiltration occurs.
BMP (BEST MANAGEMENT PRACTICE). Activities, facilities, designs, measures, or procedures used to manage stormwater impacts from regulated activities, to meet state water quality requirements, to promote infiltration 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 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 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.
BUFFER. See RIPARIAN BUFFER.
CHANNEL. An open drainage feature through which stormwater flows. CHANNELS include, but shall not be limited to, natural and human-made drainageways, swales, streams, ditches, canals and pipes flowing partly full.
CHANNEL EROSION. The widening, deepening or headward cutting of channels and waterways caused by stormwater runoff or bankfull flows.
CISTERN. An underground reservoir or tank for storing rainwater.
CONSERVATION DISTRICT. The Delaware County Conservation District.
CONVEYANCE. A facility or structure used for the transportation or transmission of something from one place to another.
CULVERT. A structure with its appurtenant works, which carries water under or through an embankment or fill.
DAM. A human-made barrier, together with its appurtenant works constructed for the purpose of impounding or storing water or another fluid or semi-fluid. 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 semi-fluid.
DEPARTMENT. The Pennsylvania Department of Environmental Protection.
DESIGN PROFESSIONAL (QUALIFIED). A Pennsylvania registered professional engineer, registered landscape architect, registered professional land surveyor trained to develop SWM site plan or any person licensed by the Pennsylvania Department of State or qualified by law to perform the work required by the chapter.
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 Delaware County Planning Department, Delaware County Conservation District and/or agent of the governing body involved with the administration, review or enforcement of any provisions of this chapter by contract or memorandum of understanding.
DETENTION or TO DETAIN. The prevention of, or to prevent, the discharge, directly or indirectly, of a given volume of stormwater runoff into surface waters by temporary storage.
DETENTION BASIN. 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 soon after a rainfall event and become dry until the next rainfall event.
DEVELOPER. A person who seeks to undertake any regulated earth disturbance activities at a project site in the municipality.
DEVELOPMENT, LAND. Any human-induced change to improved or unimproved real estate, whether public or private, including, but not limited to, land development, construction, installation or expansion of a building or other structure, land division, street construction, drilling and site alteration such as embankments, dredging, grubbing, grading, paving, parking or storage facilities, excavation, filling, stockpiling or clearing. As used in this chapter, DEVELOPMENT encompasses both new development and redevelopment.
DEVELOPMENT SITE. The specific tract or parcel of land where any regulated activity set forth in § 1043.05 is planned, conducted or maintained.
DIAMETER AT BREAST HEIGHT (DBH). The outside bark diameter at breast height which is defined as four and one-half (4.5) feet (1.37m) above the forest floor on the uphill side of the tree.
DIFFUSED DRAINAGE DISCHARGE. Drainage discharge that is not confined to a single point location or channel, including sheet flow or shallow concentrated flow.
DISCHARGE.
(1) (verb) To release water from a project, site, aquifer, drainage basin or other point of interest; and
(2) (noun) The rate and volume of flow of water such as in a stream, generally expressed in cubic feet per second. (See
PEAK DISCHARGE.)
DISCHARGE POINT. The point of discharge for a stormwater facility.
DISTURBED AREA. Unstabilized land area where an earth disturbance activity is occurring or has occurred.
DITCH. A human-made waterway constructed for irrigation or stormwater conveyance purposes.
DOWNSLOPE PROPERTY LINE. The 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.
DRAINAGE CONVEYANCE FACILITY. A stormwater management facility designed to transport stormwater runoff that includes channels, swales, pipes, conduits, culverts and storm sewers.
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 stormwater management site plan has been approved.
EARTH DISTURBANCE ACTIVITY. A construction or other human activity which disturbs the surface of the land, including, but not limited to, clearing and grubbing; grading; excavations; embankments; road maintenance; building construction; the moving, depositing, stockpiling or storing of soil, rock or earth materials.
EMERGENCY SPILLWAY. A conveyance area that is used to pass peak discharge greater than the maximum design storm controlled by the stormwater facility.
ENCROACHMENT. A structure or activity that changes, expands or diminishes the course, current or cross-section of a watercourse, floodway or body of water.
EROSION. The process by which the surface of the land, including water/stream channels, is worn away by water, wind or chemical action.
EROSION AND SEDIMENT CONTROL PLAN. A plan that is designed to minimize accelerated erosion and sedimentation. Said plan must be submitted to and approved by the appropriate conservation district before construction can begin.
EXCEPTIONAL VALUE (EV) WATERS. Surface waters of high quality which satisfy 25 Pa. Code Ch. 93, § 93.4b(b) (relating to anti-degradation).
EXISTING CONDITIONS. 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.
FEMA. Federal Emergency Management Agency.
FINANCIAL HARDSHIP. A situation where the greatest possible profit cannot be fully realized from development/redevelopment on a given parcel of land due to added costs or burdens associated with the design, construction and/or maintenance of stormwater structures, facilities, buffers and/or setbacks.
FLOOD. A temporary condition of partial or complete inundation of 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 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.
FLOODWAY. The channel of a watercourse and those portions of the adjoining floodplains which are reasonably required to carry and discharge the 100-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 100-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.
FLUVIAL GEOMORPHOLOGY. The study of landforms associated with river channels and the processes that form them.
FOREST MANAGEMENT/TIMBER OPERATIONS. Planning and associated activities necessary for the management of forest lands. These include timber inventory and preparation of forest management plans, silvicultural treatment, cutting budgets, logging road design and construction, timber harvesting and reforestation.
FREEBOARD. 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.
GRADE.
(1) (noun) A slope, usually of a road, channel, or natural ground, specified in percent and shown on plans as specified herein; and
(2) (verb) To finish the surface of a roadbed, the top of an embankment, or the bottom of an excavation.
GRASSED WATERWAY. A natural or human-made waterway, usually broad and shallow, covered with erosion-resistant grasses used to convey surface water.
GROUNDWATER. Water beneath the earth’s surface that supplies wells and springs and is often between saturated soil and rock.
GROUNDWATER RECHARGE. The replenishment of existing natural underground water supplies from rain or overland flow.
HEC-HMS. The U.S. Army Corps of Engineers, Hydrologic Engineering Center (HEC) - Hydrologic Modeling System (HMS). This model was used to model the Darby-Cobbs and Crum Creek watersheds during the Act 167, being 32 P.S. §§ 680.1 et seq. plan development and was the basis for the standards and criteria of this chapter.
HIGH QUALITY (HQ) WATERS. 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 25 Pa. Code Ch. 93, § 93.4b(a).
HOTSPOTS. Areas where land use or activities generate highly contaminated runoff with concentrations of pollutants in excess of those typically found in stormwater.
HYDROGRAPH. A graph representing the discharge of water versus time for a selected point in the drainage system.
HYDROLOGIC REGIME. The hydrologic cycle or balance that sustains quality and quantity of stormwater, baseflow, storage and groundwater supplies under natural conditions.
HYDROLOGIC SOIL GROUP. 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.
IMPERVIOUS SURFACE. A surface that prevents the infiltration of water into the ground. IMPERVIOUS SURFACES include, but are not limited to, streets, sidewalks, pavements, driveway areas or roofs. Any surface areas designed to be gravel or crushed stone shall be regarded as IMPERVIOUS SURFACES.
IMPOUNDMENT. A retention or detention basin designed to retain stormwater runoff and release it at a controlled rate.
INFILL. 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.
INFILTRATION. Movement of surface water into the soil, where it is absorbed by plant roots, evaporated into the atmosphere or percolated downward to recharge groundwater.
INFILTRATION STRUCTURES. A structure designed to direct runoff into the underground water (e.g., French drains, seepage pits or seepage trenches).
INFLOW. The flow entering the stormwater management facility and/or BMP.
INLET. The upstream end of any structure through which water may flow.
INTERMITTENT STREAM. 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.
INVERT. The lowest surface, the floor or bottom of a culvert, drain, sewer, channel, basin, BMP or orifice.
LAND DEVELOPMENT. 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.
(2) A subdivision of land; and
(3) Development in accordance with § 503(1.1) of the Pennsylvania Municipalities Planning Code, being 53 P.S. §§ 10101 et seq.
LIMITING ZONE. A soil horizon or condition in the soil profile or underlying strata that includes one of the following:
(1) A seasonal high water table, whether perched or regional, determined by direct observation of the water table or indicated by soil mottling;
(2) 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; and
(3) A rock formation, other stratum or soil condition that is so slowly permeable that it effectively limits downward passage of water.
LOT. 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.
MAIN STEM (MAIN CHANNEL). Any stream segment or other runoff conveyance used as a reach in watershed-specific hydrologic models.
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.
MAXIMUM DESIGN STORM. The maximum (largest) design storm that is controlled by the stormwater facility.
MUNICIPAL ENGINEER. A professional engineer licensed as such in the commonwealth, duly appointed as the Engineer for a municipality, planning agency or joint planning commission.
MUNICIPALITY. Aston Township, Delaware County, Pennsylvania.
NATURAL CONDITION. Pre-development condition.
NATURAL HYDROLOGIC REGIME. See HYDROLOGIC REGIME.
NATURAL RECHARGE AREA. Undisturbed surface area or depression where stormwater collects and a portion of which infiltrates and replenishes the underground and groundwater.
NONPOINT SOURCE POLLUTION. Pollution that enters a waterbody from diffuse origins in the watershed and does not result from discernible, confined or discrete conveyances.
NONSTORMWATER DISCHARGES. Water flowing in stormwater collection facilities, such as pipes or swales, which is not the result of a rainfall event or snowmelt.
NONSTRUCTURAL BEST MANAGEMENT PRACTICE (BMPs). Methods of controlling stormwater runoff quantity and quality, such as innovative site planning, impervious area and grading reduction, protection of natural depression areas, temporary ponding on site and other techniques.
NPDES. National Pollutant Discharge Elimination System, the federal government’s system for issuance of permits under the Clean Water Act, being 33 U.S.C. §§ 1251 et seq., which is delegated to PennDEP in Pennsylvania.
NRCS. Natural Resource Conservation Service (previously SCS).
OPEN CHANNEL. A conveyance channel that is not enclosed.
OUTFALL. “Point source” as described in 40 C.F.R. § 122.2 at the point where the municipality’s storm sewer system discharges to surface waters of the commonwealth.
OUTFLOW. The flow exiting the stormwater management facility and/or BMP.
OUTLET. Points of water disposal to a stream, river, lake, tidewater or artificial drain.
PARENT TRACT. The parcel of land from which a land development or subdivision originates, determined from the date of municipal adoption of this chapter.
PARKING LOT STORAGE. Involves the use of parking areas as temporary impoundments with controlled release rates during rainstorms.
PEAK DISCHARGE. The maximum rate of stormwater runoff from a specific storm event.
PENNSYLVANIA STORMWATER BEST MANAGEMENT PRACTICES MANUAL (DOCUMENT NUMBER 363-0300-002) (DECEMBER 2006). The Best Management Practices Manual published by the Pennsylvania Department of Environmental Protection. The manual is to supplement federal and state regulations and the Department of Environmental Protection’s comprehensive stormwater management policy that emphasizes effective site planning as the preferred method of managing runoff while also providing numerous examples of BMPs that can be employed in the state to further avoid and minimize flooding and water resource problems.
PERENNIAL STREAM. A stream that flows year round. PERENNIAL STREAMS derive their flow from both groundwater and runoff, and the groundwater table never drops below the stream bed.
PERVIOUS AREA. Any area not defined as impervious.
PIPE. A culvert, closed conduit or similar structure (including appurtenances) that conveys stormwater.
PLANNING COMMISSION. The Planning Commission of Aston Township.
POINT SOURCE. 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 Pa. Code § 92a.1.
POST-CONSTRUCTION. 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.
PRE-CONSTRUCTION. Prior to commencing construction activities.
PRE-DEVELOPMENT CONDITION. Undeveloped/natural condition.
PRETREATMENT. 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 § 1043.17.
PROJECT SITE. The specific area of land where any regulated activities in the municipality are planned, conducted or maintained.
QUALIFIED PROFESSIONAL. See DESIGN PROFESSIONAL (QUALIFIED).
RATIONAL FORMULA. A rainfall-runoff relation used to estimate peak flow.
REACH. Any stream segment or other runoff conveyance used in the watershed-specific hydrologic models.
RECHARGE. The replenishment of groundwater through the infiltration of rainfall, other surface waters or land application of water or treated wastewater.
RECONSTRUCTION. Demolition and subsequent rebuilding of impervious surface.
RECORD DRAWINGS. Original documents revised to suit the as-built conditions and subsequently provided by the Engineer to the client. The Engineer reviews the contractor’s as-builts against his or her own records for completeness, then either turns these over to the client or transfers the information to a set of reproducibles, in both cases for the client’s permanent records.
REDEVELOPMENT. Any development that requires 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 re-paving are not considered to be REDEVELOPMENT. Interior remodeling projects and tenant improvements are also not considered to be REDEVELOPMENT.
REGULATED ACTIVITIES. Any earth disturbances activities or any activities that involve the alteration or development of land in a manner that may affect stormwater runoff, including redevelopment.
REGULATED EARTH DISTURBANCE ACTIVITY. Activity involving earth disturbance subject to regulation under 25 Pa. Code § 92a.1, 25 Pa. Code Ch. 102 or the Clean Streams Law, being 25 Pa. Code § 92a.1.
RELEASE RATE. The percentage of existing conditions peak rate of runoff from a site or subarea to which the proposed conditions peak rate of runoff must be reduced to protect downstream areas.
REPAVING. Resurfacing of the impervious surface that does not involve reconstruction of an existing paved (impervious) surface.
REPLACEMENT PAVING. Reconstruction of and full replacement of an existing paved (impervious) surface.
RETENTION or TO RETAIN. The prevention of direct discharge of stormwater runoff into receiving waters or water bodies by temporary or permanent containment in a pond or depression; examples include systems which discharge by percolation to groundwater, and/or evaporation processes and which generally have residence times of less than three days.
RETENTION BASIN. A structure in which stormwater is stored and not released during the storm event. RETENTION BASINS are designed for infiltration purposes and do not have an outlet.
RETURN PERIOD. The average interval, in years, within which a storm event of a given magnitude can be expected to recur. For example, the 25-year return period rainfall would be expected to recur on the average of once every 25 years.
RIPARIAN. Pertaining to anything connected with or immediately adjacent to the banks of a stream or other body of water.
RIPARIAN BUFFER. An area of land adjacent to a body of water and managed to maintain the integrity of stream channels and shorelines to:
(1) Reduce the impact of upland sources of pollution by trapping, filtering and converting sediments, nutrients and other chemicals; and
(2) Supply food, cover and thermal protection to fish and other wildlife.
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.
ROAD MAINTENANCE. 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.
ROOF DRAINS. A drainage conduit or pipe that collects water runoff from a roof and leads it away from the structure.
ROOFTOP DETENTION. The temporary ponding and gradual release of stormwater falling directly onto flat roof surfaces using controlled-flow roof drains in building designs.
RUNOFF. Any part of precipitation that flows over the land surface.
SALDO. Subdivision and land development ordinance.
SEDIMENT. Soil or other materials transported by surface water as a product of erosion.
SEDIMENT BASIN. A barrier, dam or retention 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.
SEDIMENT POLLUTION. The placement, discharge or any other introduction of sediment into the waters of the commonwealth.
SEDIMENTATION. The process by which mineral or organic matter is accumulated or deposited by the movement of water or air.
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 underground water.
SEPARATE STORM SEWER SYSTEM. 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.
SHALLOW CONCENTRATED FLOW. Stormwater runoff flowing in shallow, defined ruts prior to entering a defined channel or waterway.
SHEET FLOW. A flow process associated with broad, shallow water movement on sloping ground surfaces that is not channelized or concentrated.
SOIL COVER COMPLEX METHOD. 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).
SOURCE WATER PROTECTION AREAS (SWPA). The zone through which contaminants, if present, are likely to migrate and reach a drinking water well or surface water intake.
SPECIAL PROTECTION SUBWATERSHEDS. Watersheds that have been designated by PennDEP as EV or HQ waters.
SPILLWAY. A conveyance that is used to pass the peak discharge of the maximum design storm that is controlled by the stormwater facility.
STATE WATER QUALITY REQUIREMENTS. The regulatory requirements to protect, maintain, reclaim and restore water quality under Pa. Code Title 25 and the Clean Streams Law.
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 conveys intercepted runoff and stormwater from other sources but excludes domestic sewage and industrial wastes.
STORMWATER. Drainage runoff from the surface of the land resulting from precipitation, snow or ice melt.
STORMWATER MANAGEMENT DISTRICT. Those subareas of a watershed in which some type of detention is required to meet the plan requirements and the goals of Act 167.
STORMWATER MANAGEMENT FACILITY. 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, detention and retention basins, open channels, storm sewers, pipes and infiltration structures.
STORMWATER MANAGEMENT PLAN. The watershed plan for managing stormwater runoff for a watershed, adopted by Delaware and Chester Counties as required by the Act of October 4, 1978, P.L. 864 (Act 167), as amended, and known as the Stormwater Management Act. See also WATERSHED STORMWATER MANAGEMENT PLAN.
STORMWATER MANAGEMENT (SWM) SITE PLAN. The plan prepared by the applicant or his or her representative indicating how stormwater runoff will be managed at the particular site of interest according to this chapter, and including all necessary design drawings, calculations, supporting text and documentation to demonstrate that chapter requirements have been met, hereafter referred to as SWM SITE PLAN.
STREAM. A natural watercourse.
STREAM BUFFER. The land area adjacent to each side of a stream essential to maintaining water quality (see also RIPARIAN BUFFER).
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.
SUBAREA (SUBWATERSHED). 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, 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 ten acres not involving any new street or easement of access or any residential dwelling shall be exempted.
SURFACE 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 waters, or parts thereof, whether natural or artificial, within or on the boundaries of the commonwealth.
SWALE. A low-lying stretch of land that gathers or carries surface water runoff.
SWM SITE PLAN. See STORMWATER MANAGEMENT SITE PLAN.
TIMBER OPERATIONS. See FOREST MANAGEMENT.
TIME-OF-CONCENTRATION (Tc). 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.
TOP-OF-BANK. 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.
TR-20. A computer-based hydrologic modeling technique; 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 NRCS.
USDA. United States Department of Agriculture.
UNDEVELOPED CONDITION. Natural condition. (See also PRE-DEVELOPMENT CONDITION.)
VERNAL POND. 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.
WATERCOURSE. A channel or conveyance of surface water 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, impoundments, 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.
WATERSHED. Region or area drained by a river, watercourse or other body of water, whether natural or artificial.
WATERSHED STORMWATER MANAGEMENT PLAN. A watershed plan for managing stormwater runoff for a watershed, adopted by Delaware and Chester Counties as required by the Act of October 4, 1978, P.L. 864 (Act 167), as amended, and known as the Stormwater Management Act (e.g., Chester Creek, Ridley Creek, Crum Creek, Darby-Cobbs Creeks). See also STORMWATER MANAGEMENT PLAN.
WELLHEAD.
(1) A structure built over a well; and
(2) The source of water for a well.
WELLHEAD PROTECTION AREA. 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.
WET BASIN. Pond for urban runoff management that is designed to detain urban runoff and always contains water.
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. WETLANDS generally include swamps, marshes, bogs, fens and similar areas.
WOODS. A natural groundcover with more than one viable tree of a DBH of six inches or greater per 1,500 square feet which existed within three years of application; a cover condition for which SCS curve numbers have been assigned or to which equivalent Rational Method runoff coefficients have been assigned.
(Ord. 928, passed 6-18-2014)