As used in this chapter, the following terms shall have the meanings indicated:
ACCELERATED EROSIONThe removal of the surface of the land through the combined action of human activities and the natural processes, at a rate greater than would occur because of the natural process alone.
ALLUVIAL SOILS (AS)Refers to the low area adjoining and including any water or drainage course or body of water subject to periodic flooding or overflow and delineated as alluvial soils or local alluvium by the Soil Conservation Service, United States Department of Agriculture, in the Soil Survey of Montgomery County, Pennsylvania, 1967. The boundary for this floodplain must be verified using hydrologic and hydraulic engineering studies.
A. Bermudian silt loam (BM).
Bowmansville Silt Loam (Bp).
Boundary Alluvial Land (Bo).
Rowland Silt Loam, Coal Overwash (Ru).
ALTERATIONAs applied to land, a change in topography as a result of the moving of soil and rock from one location or position to another; the changing of surface conditions by causing the surface to be more or less impervious; or, earth disturbance.
APPLICANTA landowner, developer or other person who has filed an application for approval to engage in any regulated earth disturbance activity at a project site in the Township.
BMP (BEST MANAGEMENT PRACTICE)Activities, facilities, designs, measures or landscape/vegetative procedures used to manage stormwater impacts from regulated earth disturbance activities, to meet state water quality requirements, to promote groundwater recharge and to otherwise meet the purposes of this chapter. BMPs include, but are not limited to, infiltration, filter strips, low-impact design, bioretention, wet ponds, permeable paving, grassed swales, forested buffers, sand filters and detention basins.
BMP OPERATIONS AND MAINTENANCE PLANA 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.
CALIPERThe diameter of the main trunk of a tree. Caliper measurement shall be taken at a point on the trunk six inches above natural ground line for trees up to four inches in caliper and at a point 12 inches above the natural ground line for trees over four inches in caliper.
CUTB. The difference between a point on the original ground and a designated point of lower elevation on the final grade.
The material removed in an excavation.
DAMAn 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 STORMThe 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.
DESIGNEEThe agent of Skippack Township involved with the administration, review or enforcement of any provisions of this chapter by contract or memorandum of understanding.
DETENTION BASINAn impoundment structure designed to manage stormwater runoff by temporarily storing the runoff and releasing it at a predetermined rate.
DEPThe Pennsylvania Department of Environmental Protection.
DEVELOPERA person that seeks to undertake any regulated earth disturbance activities at a project site in the Township.
DEVELOPMENTSee "earth disturbance activity." The term includes redevelopment.
DEVELOPMENT SITEThe specific tract of land where any earth disturbance activities in Skippack Township are planned, conducted or maintained.
DISCHARGEThe outflow of water, silt or other mobile substances passing along a conduit, watercourse or channel or released from any type of detention basin or stormwater management facility.
DRAINAGE EASEMENTA right granted by a landowner to a grantee allowing the use of private land for stormwater management purposes.
EARTH DISTURBANCE ACTIVITYA 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 and the moving, depositing, stockpiling or storing of soil, rock or earth materials.
EROSIONThe process by which the surface of the land, including channels, is worn away by water, wind or chemical action.
EXCAVATIONAny act by which earth, sand, gravel, rock or any other similar material is cut into, dug, quarried, uncovered, removed, displaced or relocated and shall include the conditions resulting therefrom.
EXISTING CONDITIONSThe 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.
FILLA. An act by which earth, sand, gravel, rock or any similar material is placed, located, added to or moved upon the ground surface as well as the conditions resulting therefrom.
The material used to make a fill.
FINANCIAL SECURITYAn irrevocable letter of credit with a federal or commonwealth lending institution, a corporate surety bond from a bonding company authorized to do business within the commonwealth or such other guaranty approved by the Solicitor in an amount approved by the Township Engineer.
FINISHED GRADEThe final vertical elevation of the ground after development.
FREEBOARDA vertical distance between the elevation of the design high water and the top of a dam, levee, tank, basin or diversion swale. The space is required as a safety margin in a pond or basin.
GRADEA slope, usually of a road, channel or natural ground specified in percent and shown on plans as specified herein.
A. TO) GRADE To finish the surface of a roadbed, top of embankment or bottom of excavation.
GROUND COVERLow-growing plant materials planted and growing in such a manner so as to conceal the earth surface.
IMPERVIOUS SURFACESThose surfaces which do not absorb rain. All buildings, parking areas, driveways, roads, sidewalks and any areas in concrete, asphalt and packed stone shall be considered impervious surfaces within this definition. In addition, all areas determined by the Township Engineer to be impervious within the meaning of this definition will also be classed as impervious surfaces.
IMPOUNDMENTA retention or detention basin designed to retain stormwater runoff and release it at a controlled rate.
INFILTRATION TESTAn in situ test performed in accordance with the current requirements of the DEP by a qualified soil scientist or geotechnical engineer to determine the permeability or percolation capacity of an area for use in designing any infiltration BMPs.
INLETA 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.
MANAGERThe Manager of Skippack Township, Montgomery County, Pennsylvania, or other person so designated by the Board of Supervisors.
MANNING'S EQUATIONA computation to determine stormwater velocity according to the formula:
| V | = | 1.486 R2/3 S1/2 | |
| | | n | |
Where | | |
| V | = | Velocity in feet per second. |
| R | = | Hydraulic radius, equal to the net effective area (A) divided by the wetted perimeter (W. P.): |
| R | = | A | |
| | | W.P. | |
| The wetted perimeter is the linear feet of the drainage facility cross section which is wetted by the water. |
| S | = | The slope of the energy line (for approximation, use water surface slope in wetted stream and stream bed slope in dry stream). |
| n | = | The roughness coefficient. |
National Pollutant Discharge Elimination System, the federal government's system for issuance of permits under The Clean Water Act, whose administration is delegated to DEP in Pennsylvania.
NRCSNatural Resource Conservation Service (previously SCS).
OPEN CHANNELA drainage element in which stormwater flows with an open surface. Open channels include, but shall not be limited to, natural and man-made drainage ways, swales, streams, ditches and canals.
OUTLETPoints of water disposal from a stream, river, lake, tidewater or artificial drain.
PEAK DISCHARGEThe maximum rate of stormwater runoff from a specific storm event.
PERSONAn individual, partnership, public or private association or corporation or a governmental unit, public utility or any other legal entity whatsoever which is recognized by law as the subject of rights and duties.
PIPEA culvert, closed conduit or similar structure (including appurtenances) that conveys stormwater.
PROJECT SITEThe specific area of land where any regulated earth disturbance activities in the Township are planned, conducted or maintained.
RATIONAL METHODA calculation utilized to determine the maximum expected discharge (peak flow) from areas less than 200 acres, or other area as may be approved by the Township Engineer, according to the formula:
| Q | = | CIA |
Where: |
| Q | = | The maximum expected discharge in cubic feet per second. |
| C | = | The runoff factor expressed as a percent of the total water falling on an area. |
| I | = | The rate of rainfall for the time of concentration of the drainage area in inches per hour for a given storm frequency. |
| A | = | The drainage area expressed in acres. |
A copy of an approved BMP operations and maintenance plan which contains the original required endorsements of the Township and which is intended to be recorded with the Montgomery County Recorder of Deeds.
REDEVELOPMENTEarth disturbance activities on land which has previously been disturbed or developed.
REGULATED EARTH DISTURBANCE ACTIVITYEarth disturbance activity of 5,000 square feet or greater. This includes earth disturbance on any portion of, part or during any state of a larger common plan of development. This only includes road maintenance activities involving 25 acres or more of earth disturbance.
RETENTION BASINA reservoir, formed from soil or other material, which is designed to permanently retain a certain amount of stormwater from a catchment area and which also may be designed to temporarily detain additional stormwater runoff from the catchment area or fresh water from streams.
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 the average once every 25 years.
RISERA 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 MAINTENANCEEarth 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.
RUNOFFAny part of precipitation that flows over the land surface.
RUNOFF COEFFICIENTThat portion of a total volume of water which can be expected to flow off a particular surface.
SEDIMENT BASINA barrier, dam or retention or detention basin located and designed to retain rock, sand, gravel, silt or other material transported by water.
SEDIMENT POLLUTIONThe 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 requirement of this chapter.
SEDIMENTATIONThe process by which mineral or organic matter is accumulated or deposited by the movement of water or gravity.
SEEPAGE PIT/SEEPAGE TRENCHAn area of excavated earth filled with loose stone or similar coarse material into which surface water is directed for infiltration into the ground.
SEPARATE STORM SEWER SYSTEMA conveyance or system of conveyances (including roads with drainage systems, Township streets, catch basins, curbs, gutters, ditches, man-made channels or storm drains) primarily used for collecting and conveying stormwater runoff.
SHEET FLOWRunoff that flows over the ground surface as a thin, even layer, not concentrated in a channel.
SITEA lot, tract or parcel of land or a series of lots, tracts or parcels of land joined together.
SLOPEThe face of an embankment or cut section; any ground whose surface makes an angle with the plane of the horizon. Slopes are usually expressed in a percentage based upon vertical difference in feet per 100 feet of horizontal distance.
SOIL-COVER COMPLEX METHODA 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, HYDROLOGICA 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.
SOLICITORThe Solicitor of Skippack Township, Montgomery County, Pennsylvania.
SPILLWAYA 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.
STATE WATER QUALITY REQUIREMENTSAs defined under state regulations (protection of designated and existing uses, See 25 Pa. Code Chapters
93 and
96) including:
A. Each stream segment in Pennsylvania has a "designated use," such as "cold water fishery" or "potable water supply" which is listed in Chapter
93. These uses must be protected and maintained under state regulations.
"Existing uses" are those attained as of November, 1975, regardless whether they have been designated in Chapter
93. Regulated earth disturbance activities must be designed to protect and maintain existing uses and maintain the level of water quality necessary to protect those uses in all streams and to protect and maintain water quality in special protection streams.
Water quality involves the chemical, biological and physical characteristics of surface water bodies. After regulated earth disturbance activities are complete, these characteristics can be impacted by addition of pollutants such as sediment, and changes in habitat through increased flow volumes and/or rates, as a result of changes in land surface area from those activities. Therefore, permanent discharges to surface waters must be managed to protect the streambank, streambed and structural integrity of the waterway to prevent these impacts.
STORM FREQUENCYThe number of times that a given storm event occurs or is exceeded on the average in a stated period of years. See "return period."
STEEP SLOPESSteep slopes, which shall be defined as areas having a slope of 20% percent or greater as identified on a field-generated topographic plan prepared by a registered civil engineer or registered surveyor, using two-foot-interval contours and having an elevation difference of at least eight feet.
STORM SEWERA system of pipes and/or open channels that convey intercepted runoff and stormwater from other sources, but excludes domestic sewage and industrial wastes.
STORMWATERThe surface runoff generated by precipitation reaching the ground surface.
STORMWATER MANAGEMENT FACILITYAny 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.
STRIPPINGThe removal of vegetation, including trees and topsoil. The normal process of gardening or property maintenance shall be excluded from this definition
SUBAREAThe smallest drainage unit of a watershed for which stormwater management criteria have been established in the stormwater management plan.
SURFACE WATERS OF THE COMMONWEALTHAny 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 water, or parts thereof, whether natural or artificial, within or on the boundaries of this commonwealth.
SWALEA 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.
TIME TO PEAK (TP)A factor used in conjunction with the application of the rational method which specifies a lag factor between the time of concentration (Tc) and the peak runoff for a given watershed. For purposes of this chapter, Tp shall equal three for the standard rational method, five for the modified rational method and seven for the DeKalb rational method.
TOWNSHIPSkippack Township, Montgomery County, Pennsylvania.
TOWNSHIP ARBORISTA registered landscape architect designated by the Board of Supervisors to perform the duties of arborist as herein specified.
TOWNSHIP ENGINEERA registered engineer designated by the Board of Supervisors to perform the duties of engineer as herein specified.
TREE DRIPLINEA boundary line marking the outer edges of the branches of a tree.
TREE PROTECTION ZONEAn area 15 feet radially from the trunk of the tree to be retained or the distance from the trunk to the tree dripline, whichever is greater, in which no construction activity shall occur. Where there is a group of trees or woodlands, the tree protection zone shall be the aggregate of the protection zones for the individual trees.
WATERCOURSEA channel or conveyance of surface water, such as a stream or creek, having defined bed and banks, whether natural or artificial, with perennial or intermittent flow.
WATERSHEDRegion or area drained by a river, watercourse or other body of water, whether natural or artificial.
WETLANDThose 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, fens and similar areas.