[Adopted by the City Council of the City of Harrisburg 5-14-2013 by Ord. No. 6-2013. Amendments noted where applicable.]
Stormwater Management Act: see 32 P.S. § 680.1 et seq.
Editor's Note: This ordinance also repealed former Part 9 (Chs. 9-901 through 9-915), Spring Creek and Paxton Creek Watershed Stormwater Management Plan, adopted 11-12-2006 by Ord. No. 17-2006, as amended.
This Part 9 (Part 9-900, including Chapters 9-901 through 9-921) shall be known and may be cited as the "City of Harrisburg Stormwater Management Ordinance."
The governing body of the City of Harrisburg finds that:
Inadequate management of accelerated stormwater runoff resulting from development throughout a watershed increases flood flows and velocities, contributes to erosion and sedimentation, overtaxes the carrying capacity of existing streams and storm sewers, greatly increases the cost of public facilities to convey and manage stormwater, undermines floodplain management and flood reduction efforts in upstream and downstream communities, reduces groundwater recharge, threatens public health and safety, and increases nonpoint source pollution of water resources.
A comprehensive program of stormwater management, including reasonable regulation of development and activities causing accelerated erosion, is fundamental to the public health, safety, welfare, and the protection of the people of the City of Harrisburg and all the people of the commonwealth, their resources, and the environment.
Inadequate planning and management of stormwater runoff resulting from land development and redevelopment throughout a watershed can also harm surface water resources by changing the natural hydrologic patterns; accelerating stream flows (which increase scour and erosion of streambeds and stream banks thereby elevating sedimentation); destroying aquatic habitat; and elevating aquatic pollutant concentrations and loadings such as sediments, nutrients, heavy metals, and pathogens. Groundwater resources are also impacted through loss of recharge.
Stormwater can be an important water resource by providing groundwater recharge for water supplies and base flow of streams, which also protects and maintains water quality.
Public education on the control of pollution from stormwater is an essential component in successfully addressing stormwater issues.
Federal and state regulations require certain municipalities to implement a program of stormwater controls. These municipalities are required to obtain a permit for stormwater discharges from their separate storm sewer systems under the National Pollutant Discharge Elimination System (NPDES).
Nonstormwater discharges to the municipal separate storm sewer system can contribute to pollution of waters of the commonwealth.
The purpose of this Part 9 is to promote health, safety, and welfare within the City of Harriburg, Dauphin County, by minimizing the harms and maximizing the benefits described in § 9-901.2 of this Part 9 through provisions intended to:
Meet legal water quality requirements under state law, including regulations at 25 Pa. Code Chapter 93 to protect, maintain, reclaim, and restore the existing and designated uses of the waters of the commonwealth.
Manage accelerated runoff and erosion and sedimentation problems close to their source by regulating activities that cause these problems.
Preserve the natural drainage systems to the maximum extent practicable.
Maintain groundwater recharge, to prevent degradation of surface and groundwater quality, and to otherwise protect water resources.
Maintain existing flows and quality of streams and watercourses.
Preserve and restore the flood-carrying capacity of streams and prevent scour and erosion of stream banks and streambeds.
Manage stormwater impacts close to the runoff source, with a minimum of structures and a maximum use of natural processes.
Provide procedures, performance standards, and design criteria for stormwater planning and management.
Provide proper operations and maintenance of all temporary and permanent stormwater management facilities and best management practices (BMPs) that are constructed and implemented.
Provide standards to meet the NPDES permit requirements.
Implement an illegal discharge detection and elimination program within the MS4 permitted urbanized areas to address nonstormwater discharges into the City of Harrisburg's separate storm sewer system.
Primary authority. The City of Harrisburg is empowered to regulate land use activities that affect runoff by the authority of the Act of October 4, 1978, P.L. 864 (Act 167), 32 P.S. § 680.1 et seq., as amended (the Stormwater Management Act); and the Third Class City Code, Act 317 of 1931, P.L. 932, 53 P.S. § 35101 et seq., as amended.
Secondary authority. The City of Harrisburg also is empowered to regulate land use activities that affect runoff by the authority of the Act of July 31, 1968, P.L. 805, No. 247 (the Pennsylvania Municipalities Planning Code), as amended.
This Part 9 shall apply to all areas of the City of Harrisburg, any regulated activity within the City of Harrisburg, and all stormwater runoff entering into the City of Harrisburg's municipal separate storm sewer system from lands within the boundaries of the City of Harrisburg.
Earth disturbance activities and associated stormwater management controls are also regulated under existing state law and implementing regulations. This Part 9 shall operate in coordination with those parallel requirements; the requirements of this Part 9 shall be no less restrictive in meeting the purposes of this Part 9 than state law.
"Regulated activities" are any earth disturbance activities or any activities that involve the alteration or development of land in a manner that may affect stormwater runoff. Regulated activities include, but are not limited to, the following listed items:
Earth disturbance activities.
Construction of new or additional impervious or semipervious surfaces.
Construction of new buildings or additions to existing buildings.
Diversion or piping of any natural or man-made stream channel.
Installation of stormwater management facilities or appurtenances thereto.
Installation of stormwater BMPs.
Approvals issued and actions taken pursuant to this Part 9 do not relieve the applicant of the responsibility to comply with or to secure required permits or approvals for activities regulated by any other applicable codes, laws, rules, statutes, or ordinances. To the extent that this Part 9 imposes more rigorous or stringent requirements for stormwater management, the specific requirements contained in this Part 9 shall be followed.
Notwithstanding any provision(s) of this Part 9, including exemptions, any landowner or any person engaged in the alteration or development of land which may affect stormwater runoff characteristics shall implement such measures as are reasonably necessary to prevent injury to health, safety, or other property. Such measures also shall include actions as are required to manage the rate, volume, direction, and quality of resulting stormwater runoff in a manner which otherwise adequately protects health, property, and water quality.
The degree of stormwater management sought by the provisions of this Part 9 is considered reasonable for regulatory purposes. This Part 9 shall not create liability on the part of the City of Harrisburg, any appointed or elected official of the City of Harrisburg, the Dauphin County Conservation District or any officer, engineer, or employee thereof for any erosion, sedimentation or flood damages that result from reliance on this Part 9 or any administrative decision lawfully made thereunder.
For the purposes of this Part 9, certain terms and words used herein shall be interpreted as follows:
Words used in the present tense include the future tense; the singular number includes the plural, and the plural number includes the singular; words of masculine gender include feminine gender, and words of feminine gender include masculine gender.
The word "includes" or "including" shall not limit the term to the specific example but is intended to extend its meaning to all other instances of like kind and character.
The word "person" includes an individual, firm, association, organization, partnership, trust, company, corporation, or any other similar entity.
The words "shall" and "must" are mandatory; the words "may" and "should" are permissive.
The words "used or occupied" include the words "intended, designed, maintained, or arranged to be used, occupied or maintained."
As used in this Part 9, the following terms shall have the meanings indicated:
- ACCELERATED EROSION
- The removal of the surface of the land through the combined action of human activity and the natural processes at a rate greater than would occur because of the natural process alone.
- AGRICULTURAL ACTIVITIES
- Activities associated with agriculture such as agricultural cultivation, agricultural operation, and animal heavy use areas. This includes the work of producing crops, tillage, land clearing, plowing, disking, harrowing, planting, harvesting crops, or pasturing and raising of livestock and installation of conservation measures. Construction of new buildings or impervious area is not considered an agricultural activity.
- 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; changing of surface conditions by causing the surface to be more or less impervious; land disturbance.
- A landowner, developer, or other person who has filed an application for approval to engage in any regulated activities at a project site within the City of Harrisburg.
- APPROVING AGENCY
- The City of Harrisburg or its designated agent.
- BEST MANAGEMENT PRACTICES (BMPs)
- 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 Part 9. Stormwater BMPs are commonly grouped into one of two broad categories or measures: "nonstructural" or "structural." Nonstructural BMPs are measures referred to as operational and/or behavior-related practices that attempt to minimize the contact of pollutants with stormwater runoff, whereas structural BMPs are measures 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 wet 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.
- BMP MANUAL
- The Pennsylvania Stormwater Best Management Practices Manual as published by the Department of Environmental Protection, Bureau of Watershed Management, document number 363-0300-002, effective date December 30, 2006, and as revised.
- CHANNEL EROSION
- The widening, deepening, and headward cutting of small channels and waterways due to erosion caused by moderate to large floods.
- An underground reservoir or tank for storing rainwater.
- The City of Harrisburg, Dauphin County, Pennsylvania, or its designee.
- COMBINED SEWER
- A system of pipes and inlets that convey both intercepted runoff and stormwater and also include domestic sewage and industrial waste flows.
- CONSERVATION DISTRICT
- The Dauphin County Conservation District (DCCD). The Dauphin County Conservation District has the authority under a delegation agreement executed with the Department of Environmental Protection to administer and enforce all or a portion of the regulations promulgated under 25 Pa. Code Chapter 102.
- A structure with appurtenant works that carries a stream and/or stormwater runoff under or through an embankment or fill.
- 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.
- The agent of the City of Harrisburg involved with the administration, review or enforcement of any provisions of this Part 9 by contract or memorandum of understanding.
- DESIGN STORM
- The magnitude and temporal distribution of precipitation from a storm event measured in probability of occurrence (e.g., a twenty-five-year storm) and duration (e.g., 24 hours), used in the design and evaluation of stormwater management systems. Also see "return period."
- DETENTION BASIN
- An impoundment structure designed to manage stormwater runoff by temporarily storing the runoff and releasing it at a predetermined rate.
- DETENTION VOLUME
- The volume of runoff that is captured and released during or after a storm event into waters of the commonwealth at a controlled rate.
- A person, partnership, association, corporation, or other entity, or any responsible person therein or agent thereof, that undertakes any regulated activity of this Part 9.
- DEVELOPMENT SITE (SITE)
- The specific tract of land for which a regulated activity is proposed. Also see "project site."
- DISTURBED AREA
- An unstabilized land area where an earth disturbance activity is occurring or has occurred.
- 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, drainage, or conveyance purposes.
- Any natural or artificial watercourse, trench, ditch, pipe, swale, channel, or similar depression into which surface water flows.
- 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, land development, agricultural plowing or tilling, timber harvesting activities, road maintenance activities, mineral extraction, and the moving, depositing, stockpiling, or storing of soil, rock or earth materials.
- The movement of soil particles by the action of water, wind, ice or other natural forces.
- EROSION AND SEDIMENT POLLUTION CONTROL PLAN
- A plan which is designed to minimize accelerated erosion and sedimentation.
- EXCEPTIONAL VALUE WATERS
- Surface waters of high quality, which satisfies Pennsylvania Code Title 25, Environmental Protection, Chapter 93, Water Quality Standards, § 93.4b(b) (relating to antidegradation).
- EXISTING CONDITION
- 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" unless the natural land cover is proven to generate lower curve numbers or Rational "C" value, such as forested lands.
- The Federal Emergency Management Agency.
- 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 the commonwealth.
- FLOOD FRINGE
- The remaining portions of the one-hundred-year floodplain outside of the floodway boundary.
- 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 Map as being a special flood hazard area. Included are lands adjoining a river or stream that have been or may be inundated by a one-hundred-year flood. 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).
- 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 forestland. 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.
- 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.
- A slope, usually of a road, channel or natural ground, specified in percent and shown on plans as specified herein.
- GROUNDWATER RECHARGE
- Replenishment of existing natural underground water supplies.
- HEC-HMS MODEL CALIBRATED
- The Hydrologic Engineering Center-Hydrologic Modeling System, a computer-based hydrologic model technique adapted to the Spring Creek and Paxton Creek Watershed for the Act 167 Plan. The model has been calibrated by adjusting key model input parameters.
- HIGH-QUALITY WATERS
- Surface water having quality which exceeds levels necessary to support propagation of fish, shellfish, and wildlife and recreation in and on the water by satisfying Pennsylvania Code Title 25, Environmental Protection, Chapter 93, Water Quality Standards, § 93.4b(a).
- HYDROLOGIC SOIL GROUP (HSG)
- Infiltration rates of soils vary widely and are affected by subsurface permeability as well as surface intake rates. Soils are classified into four HSGs (A, B, C, and D) according to their minimum infiltration rate, which is obtained for bare soil after prolonged wetting. The Natural Resources Conservation Service (NRCS) of the United States Department of Agriculture defines the four groups and provides a list of most of the soils in the United States and their group classification. The soils in the area of interest may be identified from a soil survey report, which can be obtained from the local NRCS office or the Dauphin County Conservation District office.
- IMPERVIOUS SURFACE (IMPERVIOUS AREA)
- A surface that prevents the infiltration of water into the ground. Impervious surfaces (or areas) shall include but are not limited to roofs, additional indoor living spaces, patios, garages, storage sheds and similar structures, and any new streets and sidewalks. Decks, parking areas, and driveway areas are not counted as impervious areas if they do not prevent infiltration. Any surface area proposed to initially be gravel or crushed stone shall be assumed to be impervious, unless designed as an infiltration BMP.
- INFILTRATION STRUCTURES
- A structure designed to direct runoff into the ground (e.g., french drains, seepage pits, seepage trench, etc.).
- 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.
- A type of topography or landscape characterized by depressions, sinkholes, limestone towers and steep-sided hills, underground drainage, and caves. Karst is formed on carbonate rocks, such as limestone or dolomite and sometimes gypsum.
- (1) The improvement of one lot or two or more contiguous lots, tracts or parcels of land for any purpose involving:
- (2) Any subdivision of land;
- (3) Development in accordance with Section 503(1.1) of the Pennsylvania Municipalities Planning Code.
- LIMIT OF DISTURBANCE
- A line provided on the SWM site plan that indicates the total area to be disturbed during a proposed earth disturbance activity.
- MAIN STEM (MAIN CHANNEL)
- Any stream segment or other runoff conveyance facility used as a reach in the Dauphin County Act 167 watershed hydrologic model(s).
- 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.
- MUNICIPAL SEPARATE STORM SEWER
- A conveyance or system of conveyances (including roads with drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, or storm drains), which is all of the following:
- (1) Owned or operated by a state, city, town, borough, township, county, district, association or other public body (created under state law) having jurisdiction over disposal of sewage, industrial wastes, stormwater or other wastes;
- (2) Designed or used for collecting or conveying stormwater;
- (3) Not a combined sewer; and
- (4) Not part of a publicly owned treatment works as defined at 40 CFR § 122.2.
- MUNICIPAL SEPARATE STORM SEWER SYSTEM (MS4)
- All separate storm sewers that are defined as "large" or "medium" or "small" municipal separate storm sewer systems pursuant to 40 CFR § 122.26(b)(18), or designated as regulated under 40 CFR § 122.26(a)(1)(v).
- NATIONAL POLLUTANT DISCHARGE ELIMINATION SYSTEM (NPDES)
- The federal government's system for issuance of permits under the Clean Water Act, which is delegated to PADEP in Pennsylvania.
- NOAA ATLAS 14
- Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2, United States Department of Commerce, National Oceanic and Atmospheric Administration, National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland (2004). NOAA's Atlas 14 can be accessed at Internet address: http://hdsc.nws.noaa.gov/hdsc/pfds/.
- NONPOINT SOURCE POLLUTION
- Pollution that enters a water body from diffuse origins in the watershed and does not result from discernible, confined, or discrete conveyances.
- The Natural Resource Conservation Service [previously the Soil Conservation Service(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 not under pressure.
- The point of water disposal from a stream, river, lake, tidewater, or artificial drain.
- The Pennsylvania Department of Environmental Protection.
- 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.
- An 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.
- PERVIOUS AREA
- Any area not defined as impervious.
- A culvert, closed conduit, or similar structure (including appurtenances) that conveys stormwater.
- PLANNING COMMISSION
- The Harrisburg Planning Commission.
- POINT SOURCE
- Any discernible, confined, or 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 § 92.1.
- PROBABLE MAXIMUM FLOOD (PMF)
- The flood that may be expected from the most severe combination of critical meteorological 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).
- PROJECT SITE
- The specific area of land where any regulated activities in the City of Harrisburg are planned, conducted, or maintained.
- QUALIFIED PROFESSIONAL
- Any person licensed by the Pennsylvania Department of State or otherwise qualified by law to perform the work required by this Part 9.
- RATIONAL FORMULA
- A rainfall-runoff relation used to estimate peak flow only.
- Earth disturbance activities on land which has previously been disturbed or developed.
- REGULATED ACTIVITY
- Any earth disturbance activity or any activity that involves the alteration or development of land in a manner that may affect stormwater runoff.
- REGULATED EARTH DISTURBANCE ACTIVITY
- Activity involving earth disturbance subject to regulation under 25 Pa. Code Chapter 92, Chapter 102, or the Clean Streams Law.
- RELEASE RATE
- The percentage of predevelopment peak rate of runoff from a site or subwatershed area to which the post-development peak rate of runoff must be reduced to protect downstream areas.
- RELEASE RATE DISTRICT
- Those subwatershed areas in which post-development flows must be reduced to a certain percentage of predevelopment flows as required to meet the plan requirements and the goals of Act 167.
- RETENTION VOLUME/REMOVED RUNOFF
- The volume of runoff that is captured and not released directly into the surface waters of this commonwealth during or after a storm event.
- RETURN PERIOD
- The average interval, in years, within which a storm event of a given magnitude can be expected to recur. For example, the probability of a twenty-five-year storm occurring on any one given year is 0.04 (i.e., a 4% chance).
- RIPARIAN BUFFER
- A vegetated area, bordering perennial and intermittent streams and wetlands, that serves as a protective filter to help protect streams and wetlands from the impacts of adjacent land uses.
- 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 right-of-way, such as grading and repairing existing unpaved road surfaces, cutting road banks, cleaning or clearing drainage ditches, and other similar activities. Road maintenance activities that do not disturb the subbase of a paved road, such as milling and pavement overlays, are not considered earth disturbance activities.
- ROOFTOP DETENTION
- Temporary ponding and gradual release of stormwater falling directly onto flat roof surfaces by incorporating controlled-flow roof drains into building designs.
- Any part of precipitation that flows over the land surface.
- RUNOFF CAPTURE VOLUME
- The volume of runoff that is captured (retained) and not released into surface waters of the commonwealth during or after a storm event.
- Soils or other materials transported by surface water as a product of erosion.
- 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 stormwater runoff.
- SEDIMENT POLLUTION
- The placement, discharge, or any other introduction of sediment into the waters of the commonwealth occurring from the failure to properly design, construct, implement or maintain control measures and control facilities in accordance with the requirements of this Part 9.
- 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.
- 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).
- A depression in the embankment of a pond or basin, or other overflow structure, that is used to pass peak discharge greater than the maximum design storm controlled by the pond or basin.
- STATE WATER QUALITY REQUIREMENTS
- The regulatory requirements to protect, maintain, reclaim, and restore water quality under Title 25 of the Pennsylvania Code and the Clean Streams Law, including, but not limited to:
- (1) Each stream segment in Pennsylvania has a designated use, such as "cold water fishery" or "potable water supply," which are listed in Chapter 93. These uses must be protected and maintained, under state regulations.
- (2) "Existing uses" are those attained as of November 1975, regardless whether they have been designated in Chapter 93. 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.
- (3) Water quality involves the chemical, biological, and physical characteristics of surface water bodies. After 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 stream bank, streambed, and structural integrity of the waterway, to prevent these impacts.
- (4) Protection and maintenance of water quality in special protection streams pursuant to 25 Pa. Code Chapter 93.
- 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 also "return period."
- Drainage runoff from the surface of the land resulting from precipitation, snow, or ice melt.
- STORMWATER HOTSPOT
- A land use or activity that generates higher concentrations of hydrocarbons, trace metals, or toxicants than are found in typical stormwater runoff.
- STORMWATER MANAGEMENT FACILITIES
- 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, wet ponds, open channels, storm sewers, pipes and infiltration structures.
- STORMWATER MANAGEMENT PLAN
- The Dauphin County Stormwater Management Plan for managing stormwater runoff in Dauphin County as required by the Act of October 4, 1978, P.L. 864 (Act 167), and known as the "Stormwater Management Act."
- STORMWATER MANAGEMENT SITE PLAN (SWM SITE PLAN)
- The plan, prepared by the applicant or his representative, indicating how stormwater runoff will be managed at the project site in accordance with this Part 9.
- STREAM ENCLOSURE
- A bridge, culvert, or other structure in excess of 100 feet in length upstream to downstream which encloses a regulated waters of the commonwealth.
- 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 (Pennsylvania Municipalities Planning Code, Act of July 31, 1968, P.L. 805, No. 247).
- SUBWATERSHED AREA
- The smallest drainage unit of a watershed for which stormwater management criteria have been established in the stormwater management plan.
- A low-lying stretch of land that gathers or carries surface water runoff.
- TIMBER OPERATIONS
- See "forest management."
- 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.
- TO GRADE
- To finish the surface of a roadbed, top of embankment or bottom of excavation.
- The United States Department of Agriculture.
- A 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.
- The region or area drained by a river, watercourse, or other body of water, whether natural or artificial.
- WATERS OF THE COMMONWEALTH
- Rivers, streams, creeks, rivulets, impoundments, ditches, watercourses, storm sewers, lakes, dammed water, wetlands, ponds, springs and 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.
- Those 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. (The term includes but is not limited to wetland areas listed in the State Water Plan, the United States Forest Service Wetlands Inventory of Pennsylvania, the Pennsylvania Coastal Zone Management Plan and a wetland area designated by a river basin commission. This definition is used by the United States Environmental Protection Agency and the United States Army Corps of Engineers.)