Section 250-RICR-150-10-8.5 - DefinitionsA. As used in these rules, the following terms shall, where the context permits, be construed as follows: 1. "Approving agency" means an entity that will enforce or require compliance with the minimum standards in this Part.2. "Aquatic bench" means a 10-15 foot wide bench which is located around the inside perimeter of a permanent pool and is normally vegetated with aquatic plants; the goal is to provide pollutant removal and enhance safety in areas using stormwater ponds.3. "Aquifer" means a porous water-bearing formation of permeable rock, sand or gravel capable of yielding economically significant quantities of groundwater.4. "ASTM" means American Society of Testing Materials.5. "Baseflow" means the portion of streamflow that is not due to storm runoff but is the result of groundwater discharge or discharge from lakes or similar permanent impoundments of water.6. "Bioretention" means a water quality practice that utilizes vegetation and soils to treat urban stormwater runoff by collecting it in shallow depressions, before filtering through an engineered bioretention planting soil media.7. "BMP" means best management practice.8. "Buffer" means a special type of preserved area along a watercourse or wetland where development is restricted or prohibited. Buffers protect and physically separate a resource from development. Buffers also provide stormwater control flood storage and habitat values.9. "Catch basin" means a structure containing a sump placed below grade to conduct water from a street or other paved surface to the storm sewer.10. "Catch basin insert" means a structure, such as a tray, basket, or bag that typically contains a pollutant removal medium (filter media) and a method for suspending the structure in the catch basin. They are placed directly inside of existing catch basins where stormwater flows into the catch basin and is treated as it passes through the structure.11. "Channel" means a natural stream that conveys water; a man-made ditch or swale excavated for the flow of water.12. "Channel protection" or "CPv" means a design criterion which requires 24hour detention of the 1-year, post-developed, 24-hour Type III storm event runoff volume for the control of stream channel erosion.13. "Channel stabilization" means erosion prevention and stabilization of velocity distribution in a channel using jetties, drops, revetments, structural linings, vegetation and other measures.14. "Check dams" means small temporary dams constructed across a swale or drainage ditch to reduce the velocity of concentrated stormwater flows.15. "Cistern" means a container that stores large quantities of rooftop stormwater runoff and may be located above or below ground. Also see Rain Barrel.16. "Clay" means a. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter.c. (Engineering) A fine-grained soil (more than 50% passing the No. 200 sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).17. "Combined sewer overflows" or "CSOs" means combined sewers collect both stormwater runoff and sanitary wastewater in a single set of sewer pipes. When combined sewers do not have enough capacity to carry all the runoff and wastewater or the receiving water pollution control plant cannot accept all the combined flow, the combined wastewater overflows from the collection system into the nearest body of water, creating a CSO.18. "Compaction" means any process by which the soil grains are rearranged to decrease void space and bring them in closer contact with one another, thereby increasing the weight of solid material per unit of volume, increasing the shear and bearing strength and reducing permeability.19. "Contour" means a. An imaginary line on the surface of the earth connecting points of the same elevation.b. A line drawn on a map connecting points of the same elevation.20. "CRMC" means Rhode Island Coastal Resources Management Council.21. "Crushed stone" means gravel-sized particles that pass through a 3-inch sieve and are retained on the No. 4 sieve, and are angular in shape as produced by mechanical crushing. Crushed stone must be washed in order to be used in stormwater BMPs to prevent clogging by fines.22. "Curve number" or "CN" means a numerical representation of a given area's hydrologic soil group, plant cover, impervious cover, interception and surface storage derived in accordance with Natural Resources Conservation Service methods. This number is used to convert rainfall volume into runoff volume.23. "Cut" means a portion of land surface or area from which earth has been removed or will be removed by excavation; the depth below original ground surface to excavated surface.24. "Darcy's law" means an equation stating that the rate of fluid flow through a porous medium is proportional to the potential energy gradient within the fluid. The constant of proportionality is the hydraulic conductivity, which is a property of both the porous medium and the fluid moving through the porous medium. Sizing of filtering BMPs and dry swales is based on this principle.25. "Deep sump catch basins" means storm drain inlets that typically include a grate or curb inlet and at least a four-foot sump to capture trash, debris and some sediment and oil and grease. Also known as an oil and grease catch basin.26. "Deicers" means materials applied to reduce icing on paved surfaces. These consist of salts and other formulated materials that lower the melting point of ice, including sodium chloride, calcium chloride, calcium magnesium acetate, and blended products consisting of various combinations of sodium, calcium, magnesium, and chloride, as well as other constituents.27. "DEM" means Rhode Island Department of Environmental Management.28. "Design points" or "Points of analyses" means common locations at a site where pre-development and post-development conditions can be compared.29. "Design storm" means a precipitation event for which the capacity of a best management practice is sized and designed. Design storms are expressed in terms of Type III, 24-hour events (i.e., 1-year, 10-year, and 100-year storms).30. "Detention" means the temporary storage of storm runoff in a BMP with the goals of controlling peak discharge rates.31. "Detention structure" means a structure constructed for the purpose of temporary storage of surface runoff and gradual release of stored water at controlled rates.32. "Disposal site" means a structure, well, pit, pond, lagoon, impoundment, ditch, landfill or other place or area, excluding ambient air or surface water, where uncontrolled oil or hazardous material has come to be located as a result of any spilling, leaking, pouring, ponding, emitting, emptying, discharging, injecting, escaping, leaching, dumping, discarding or otherwise disposing of such oil or hazardous material. Disposal sites are designated as LUHPPLs.33. "Disturbed area" means an area in which the natural vegetative soil cover has been removed or altered and, therefore, is susceptible to erosion.34. "Diversion" means a channel with a supporting ridge on the lower side constructed across the slope to divert water from areas where it is in excess to sites where it can be used or disposed of safely. Diversions differ from terraces in that they are individually designed.35. "Downstream analysis" means calculation of peak flows, velocities, and hydraulic effects at critical downstream locations to ensure that proposed projects do not increase post-development peak flows and velocities at these locations.36. "Drainage" means the removal of excess surface water or ground water from land by means of surface or subsurface drains.37. "Drainage area" or "watershed" means all land and water area from which runoff may run to a common (design) point.38. "Dry extended detention pond" or "dry pond" or "detention basin" means a stormwater basin designed to capture, temporarily hold, and gradually release a volume of stormwater runoff to attenuate and delay stormwater runoff peaks. Dry extended detention ponds provide water quantity control (peak flow control and stream channel protection) as opposed to water quality control.39. "Dry swale" means an open drainage channel explicitly designed to detain and promote the filtration of stormwater runoff through an underlying fabricated soil media.40. "Dry well" means small excavated pits or trenches filled with aggregate that receive clean stormwater runoff primarily from building rooftops. Dry wells function as infiltration systems to reduce the quantity of runoff from a site. The use of dry wells is applicable for small drainage areas with low sediment or pollutant loadings and where soils are sufficiently permeable to allow reasonable rates of infiltration.41. "Emergency spillway" means an open and/or closed channel designed to safely discharge stormwater flows in excess of the principal spillway capacity.42. "Erosion" meansa. The wearing away of the land surface by running water, wind, ice, or other geological agents, including such processes as gravitational creep.b. Detachment and movement of soil or rock fragments by water, wind, ice or gravity. The following terms are used to describe different types of water erosion: (1) Accelerated erosion - Erosion much more rapid than normal, natural or geologic erosion, primarily as a result of the influence of the activities of man or, in some cases, of other animals or natural catastrophes that expose base surfaces.(2) Gully erosion - The erosion process whereby water accumulates in narrow channels and, over short periods, removes the soil from this narrow area to considerable depths, ranging from 1 or 2 feet to as much as 75 to 100 feet.(3) Rill erosion - An erosion process in which numerous small channels only several inches deep are formed.(4) Sheet erosion - The spattering of small soil particles caused by the impact of raindrops on wet soils. The loosened and spattered particles may or may not subsequently be removed by surface runoff.43. "Erosive velocities" means velocities of water that are high enough to wear away the land surface. Exposed soil will generally erode faster than stabilized soils. Erosive velocities will vary according to the soil type, slope, structural, or vegetative stabilization used to protect the soil.44. "Exfilter" means a conventional stormwater filter without an underdrain system. The filtered volume ultimately infiltrates into the underlying soils.45. "Extended detention" or "ED" means a stormwater design feature that provides for the gradual release of a volume of water over a 24- to 48-hour interval in order to increase settling of urban pollutants and protect downstream channels from frequent storm events.46. "Filter strip" means a strip of permanent vegetation to treat sheet flow from adjacent impervious areas by causing deposition of transported material, thereby reducing sediment flow.47. "Filtering practices" means practices that capture and store stormwater runoff and pass it through a filtering media such as sand, organic material, or the native soil for pollutant removal. Stormwater filters are primarily water quality control devices designed to remove particulate pollutants and, to a lesser degree, bacteria and nutrients. Filtering systems include sand filters, organic filters, bioretention, and tree filters.48. "Floodplain" means areas adjacent to a stream or river that are subject to flooding or inundation during a storm event that occurs, on average, once every 100 years (or has a likelihood of occurrence of 1/100 in any given year).49. "Flow splitter" means an engineered, hydraulic structure designed to divert a percentage of storm flow to a BMP located out of the primary channel, or to direct stormwater to a parallel pipe system, or to bypass a portion of baseflow around a BMP.50. "Forebay" means a storage space located near a stormwater BMP inlet that serves to trap incoming coarse sediments before they accumulate in the main treatment area.51. "Grade" means a. The slope of a road, channel or natural ground.b. The finished surface of a canal bed, roadbed, top of embankment, or bottom of excavation; any surface prepared for the support of construction, like paving or laying a conduit.c. To finish the surface of a canal bed, roadbed, top of embankment or bottom of excavation.52. "Grass channels" means traditional vegetated open channels, typically trapezoidal, triangular, or parabolic in shape, whose primary function is to provide non-erosive conveyance, typically up to the 10-year frequency design flow. They provide limited pollutant removal through filtration by grass or other vegetation, sedimentation, biological activity in the grass/soil media, as well as limited infiltration if underlying soils are pervious.53. "Gravel" means a. "Pea" gravel is an aggregate consisting of mixed sizes of 1/4-inch to 3/4-inch particles that normally occur in or near old streambeds and have been worn smooth by the action of water. Pea gravel is often used as a filter layer in stormwater BMPs.b. According to the Unified Soil Classification System, gravel is a soil having particle sizes that pass through a 3-inch sieve and are retained on the No. 4 sieve; may be angular in shape as produced by mechanical crushing. Also referred to as "crushed stone." Crushed stone can be used as a media for stormwater best management practices.c. Type of impervious surface when used for road, driveway, or parking surfaces.54. "Gravel WVTS" means a wet vegetated treatment system that maintains a saturated gravel bed and provides treatment by stormwater movement through the gravel bed and plant/soil treatment processes.55. "Green roofs" means multilayered, constructed roof systems consisting of a vegetative layer, media, a geotextile layer, and a synthetic drain layer installed on building rooftops. Rainwater is either intercepted by vegetation and evaporated to the atmosphere or retained in the substrate before being returned to the atmosphere through transpiration and evaporation.56. "Ground cover" means plants that are low growing and provide a thick growth that protects the soil as well as providing some beautification of the area occupied.57. "Groundwater recharge" means the process by which water that seeps into the ground, eventually replenishing groundwater aquifers and surface waters such as lakes, streams, and the oceans. This process helps maintain water flow in streams and wetlands and preserves water table levels that support drinking water supplies.58. "Groundwater recharge volume" or "Rev" means the post-development design recharge volume (on a storm event basis) required to minimize the loss of annual pre-development groundwater recharge. The Rev is determined as a function of annual pre-development recharge for site-specific soils or surficial materials, average annual rainfall volume, and amount of impervious cover on a site.59. "Gully" means a channel or miniature valley cut by concentrated runoff through which water commonly flows only during and immediately after heavy rains. The distinction between gully and rill is one of depth. A gully is sufficiently deep that it would not be obliterated by normal tillage operations, whereas a rill is of lesser depth and would be smoothed by ordinary farm tillage.60. "Hazard classification" for dams means a rating for a dam that relates to the probable consequences of failure or misoperation of the dam, which is a determination made by the DEM Director based on an assessment of loss of human life, damages to properties or structures located downstream of the reservoir, or loss of use as a drinking water supply. A higher hazard dam does not imply that it is more likely to fail or be misoperated than a lower hazard dam.61. "Head" or "Hydraulics" means a. The height of water above any plane of reference.b. The energy, either kinetic or potential, possessed by each unit weight of a liquid expressed as the vertical height through which a unit weight would have to fall to release the average energy possessed. Used in various terms such as pressure head, velocity head, and head loss.62. "Herbaceous perennial" means a plant whose stems die back to the ground each year.63. "Hydrodynamic separators" means a group of stormwater treatment technologies designed to remove large particle total suspended solids and large oil droplets, consisting primarily of cylindrical-shaped devices that are designed to fit in or adjacent to existing stormwater drainage systems. The most common mechanism used in these devices is vortex-enhanced sedimentation, where stormwater enters as tangential inlet flow into the side of the cylindrical structure. As the stormwater spirals through the chamber, the swirling motion causes the sediments to settle by gravity, removing them from the stormwater.64. "Hydrograph" means a graph showing variation in depth or discharge of a stream of water over a period of time.65. "Hydrologic cycle" means the distribution and movement of water between the earth's atmosphere, land, and water bodies.66. "Hydrologic soil group" or "HSG" means a Natural Resource Conservation Service classification system in which soils are categorized into four runoff potential groups. The groups range from A soils, with high permeability and little runoff production, to D soils, which have low permeability rates and produce much more runoff.67. "Illicit discharges" means unpermitted discharges to waters of the state that do not consist entirely of stormwater or uncontaminated groundwater except certain discharges identified in the RIPDES Phase II Stormwater General Permit.68. "Impaired waters" means those waterbodies not meeting water quality standards. Pursuant to Section 303(d) of the federal Clean Water Act, 33 U.S.C. § 1313 (2018), each state prepares a list of impaired waters (known as the 303(d) list) which is presented in the state's Integrated Water Report as Category 5 waters. Those impaired waters for which a TMDL has been approved by US EPA and is not otherwise impaired, are listed in Category 4A.69. "Impervious cover" or "I" means those surfaces that cannot effectively infiltrate rainfall consisting of surfaces such as building rooftops, pavement, sidewalks, driveways, compacted gravel.70. "Infill" means a development site that meets all of the following: the site is currently predominately pervious (less than 10,000 square feet of existing impervious cover); it is surrounded (on at least 3 sides) by existing development (not including roadways); the site is served by a network of existing infrastructure and does not require the extension of utility lines or new public road construction to serve the property; and the site is 1 acre or less where the existing land use is commercial, industrial, institutional, governmental, recreational, or multifamily residential.71. "Infiltration practices" means stormwater treatment practices designed to capture stormwater runoff and infiltrate it into the ground over a period of days.72. "Infiltration rate" means the rate at which stormwater percolates into the subsoil measured in inches per hour.73. "Land use with higher potential pollutant load" or "LUHPPL" means area where the land use has the potential to generate highly contaminated runoff, with concentrations of pollutants in excess of those typically found in stormwater.74. "Landfill" means a facility or part of a facility established in accordance with a valid site assignment for the disposal of solid waste into or on land. Landfills are designated as LUHPPLs.75. "Level spreader" means a device for distributing stormwater uniformly over the ground surface as sheet flow to prevent concentrated, erosive flows and promote infiltration.76. "Limit of disturbance" means a line delineating the boundary of the area to be disturbed during a development or redevelopment project. Area outside this boundary shall not be touched.77. "Low impact development" or "LID" means a site planning and design strategy intended to maintain or replicate predevelopment hydrology through the use of site planning, source control, and small-scale practices integrated throughout the site to prevent, infiltrate and manage runoff as close to its source as possible.78. "Maximum extent practicable" means to show that a proposed development has met a standard to the maximum extent practicable, the applicant must demonstrate the following: a. All reasonable efforts have been made to meet the standard in accordance with current local, state, and federal regulations,b. A complete evaluation of all possible management measures has been performed, andc. If full compliance cannot be achieved, the highest practicable level of management is being implemented.79. "Mulch" means a natural or artificial protective layer of suitable materials, usually of organic matter such as wood chips, leaves, straw, or peat, placed around plants that aids in soil stabilization, soil moisture conservation, prevention of freezing, and control of weeds. In addition, mulches serve as soil amendments upon decomposition (for organic mulches).80. "Native plants" means plants that are adapted to the local soil and rainfall conditions and that require minimal watering, fertilizer, and pesticide application.81. "Non-structural controls" means pollution control techniques, such as management actions and behavior modification that do not involve the construction or installation of devices.82. "Off-line" means a stormwater management system designed to manage small storm events by diverting a percentage of stormwater flow away from the storm drainage system. Flow from large storm events will bypass this stormwater management system.83. "Oil separators" or "Particle separators" means a device consisting of 1 or more chambers designed to remove trash and debris and to promote sedimentation of coarse materials and separation of free oil (as opposed to emulsified or dissolved oil) from stormwater runoff. Oil/particle separators are typically designed as off-line systems for pretreatment of runoff from small impervious areas, and therefore provide minimal attenuation of flow. Also called oil/grit separators, water quality inlets, and oil/water separators.84. "On-line" means a stormwater management system designed to manage stormwater in its original drainage channel or pipe network such that all stormwater flow will be directed to and through the stormwater management system.85. "Open channels" or "Swales" or "Grass channels" means systems that are used for the conveyance, retention, infiltration and filtration of stormwater runoff.86. "Outfall" means the point where water flows from a conduit, stream, or drain.87. "Outlet" means the point at which water discharges from stormwater practices such as pipes or channels.88. "Outlet control structure" means a hydraulic structure placed at the outlet of a channel, spillway, pond, etc., for the purpose of dissipating energy, providing a transition to the channel or pipe downstream, while achieving the discharge rates for specified designs.89. "OWTS" means onsite wastewater treatment system.90. "Peak discharge rate" means the maximum instantaneous rate of flow during a storm, usually in reference to a specific design storm event.91. "Peak flow control" means criteria intended to address increases in the frequency and magnitude of a range of potential flood conditions resulting from development and include stream channel protection, conveyance protection, peak runoff attenuation, and emergency outlet sizing.92. "Performance monitoring" means collection of data on the effectiveness of individual stormwater treatment practices.93. "Permanent pool" or "Wet pool" means an area of a stormwater management practice that has a fixed water surface elevation due to a manipulation of the outlet structure.94. "Permeability" means the rate of water movement through the soil column under saturated conditions.95. "Permeable paving materials" means materials that are alternatives to conventional pavement surfaces and are designed to increase infiltration and reduce stormwater runoff and pollutant loads. Alternative materials include porous asphalt, pervious concrete, and various pavers and open-celled grids.96. "Piping" means removal of soil material through subsurface flow channels or "pipes" developed by seepage water.97. "Plugs" means pieces of vegetation, usually cut with a round tube, which can be used to propagate the plant by vegetative means.98. "Point source" means any discernible, confined and discrete conveyance, including but not limited to, any pipe, ditch, channel, tunnel, conduit, well, discrete fissure, container, rolling stock, concentrated animal feeding operation, landfill leachate collection system, vessel or other floating craft from which pollutants are or may be discharged.99. "Pondscaping" means plantings around stormwater ponds that emphasize native vegetative species to meet specific design intentions. Species are selected for up to six zones in the basin and its surrounding setback, based on their ability to tolerate inundation and/ or soil saturation.100. "Pretreatment" means techniques employed in stormwater BMPs to provide storage or filtering to help trap coarse materials before they enter the system.101. "Principal spillway" means an open and/or closed channel designed to allow a normal range of stormwater flows to discharge from an impoundment.102. "Qualifying pervious area" or "QPA" means the generally flat, natural or landscaped vegetated areas that are fully stabilized and where discharge from impervious areas may be directed via sheet flow in order to obtain a Stormwater Credit.103. "QA" means quality assurance.104. "QAP" means quality assurance plan.105. "QC" means quality control.106. "Rational equation" means an empirical equation acceptable for estimating peak flow rates for small urbanized drainage areas with short times of concentration, but not for estimating runoff volume. The Rational Equation is Q=CiA; where Q = peak discharge, C = rational Method runoff coefficient, i = rainfall intensity (inches/hour); and A = drainage area (acres).107. "Redevelopment" means any construction, alteration, or improvement that disturbs a total of 10,000 square feet or more of existing impervious area where the existing land use is commercial, industrial, institutional, governmental, recreational, or multifamily residential.108. "Responsible authority" means authority responsible for long-term maintenance of stormwater BMPs.109. "Retention" means the amount of precipitation on a drainage area that does not escape as runoff. It is the difference between total precipitation and total runoff.110. "Right of way" or "ROW" means right of passage, as over another's property. A route that is lawful to use. A strip of land acquired for transport or utility construction.111. "RIPDES" means Rhode Island Pollutant Discharge Elimination System.112. "Riser" means a type of outlet control structure that consists of a vertical pipe that extends from the bottom of a pond BMP and houses the control devices (weirs/orifices) to achieve the discharge rates for specified designs.113. "Runoff" means the water from rain, snowmelt, or irrigation that flows over the land surface and is not absorbed into the ground, instead flowing into surface waters or land depressions.114. "Safety bench" means a flat area above the permanent pool and surrounding a stormwater basin designed to provide a separation from the basin pool and adjacent slopes.115. "Sand" means a. (Agronomy) A soil particle between 0.05 and 2.0 millimeters in diameter.b. A soil textural class.c. (Engineering) According to the Unified Soil Classification System, a soil particle larger than the No. 200 sieve (0.074mm) and passing the No. 4 sieve (approximately 1/4 inch).116. "SARA 312 generator" means a facility that is required by the Emergency Planning and Community Right to Know Act, 42 U.S.C § 116 also known as Title III of the Superfund Amendments and Reauthorization Act of 1989 (SARA Title III), to submit an inventory of the location of hazardous chemicals which are located at the site. SARA 312 generators are designated as LUHPPLs.117. "Seasonal high groundwater table" or "SHGT" means the elevation of the groundwater table during that time of the year at which it is highest as determined by direct observation or by interpretation of hydromorphic features in the soil profile.118. "Sediment" means solid material, both mineral and organic, that is in suspension, is being transported, or has been moved from its site of origin by air, water, gravity, or ice and has come to rest on the earth's surface either above or below sea level.119. "Sediment chamber" or "forebay" means an underground chamber or surface impoundment designed to remove sediment and/or floatables prior to a primary or other secondary stormwater treatment practice.120. "Seepage" means a. Water escaping through or emerging from the ground.b. The process by which water percolates through the soil.121. "SESC" means soil erosion and sediment control.122. "Setbacks" means the minimum distance requirements for location of a structural BMP in relation to roads, wells, septic fields, and other structures. Also, the area immediately surrounding a best management practice that provides a separation barrier to adjacent development and acts as filter to remove pollutants and provide infiltration of stormwater prior to reaching the BMP.123. "Shallow WVTS" means a wet vegetated treatment system that consists of aquatic vegetation within a permanent pool ranging in depth from 6" to 18" during normal conditions that is equivalent to the entire WQv and provides treatment via settling and plant/soil treatment processes.124. "Sheet flow" means water, usually storm runoff, flowing in a thin layer over the ground surface.125. "Side slopes" means the slope of the sides of a channel, dam or embankment. It is customary to name the horizontal distance first, as 1.5 to 1, or frequently, 1 1/2: 1, meaning a horizontal distance of 1.5 feet to 1 foot vertical.126. "Silt" means a. (Agronomy) A soil separate consisting of particles between 0.05 and 0.002 millimeter in equivalent diameter.b. A soil textural class.c. (Engineering) According to the Unified Soil Classification System a fine-grained soil (more than 50% passing the No. 200 sieve) that has a low plasticity index in relation to the liquid limit.127. "Site" means 1 or more lots, tracts, or parcels of land to be developed or redeveloped for a complex of uses, units or structures, including but not limited to commercial, residential, institutional, governmental, recreational, open space, and/or mixed uses. When calculating site size, jurisdictional wetland areas defined by DEM or CRMC regulations and undeveloped lands protected by conservation easements should be subtracted from the total site area.128. "Site planning and design strategies" means techniques of planning, engineering, and landscape design that maintain predevelopment hydrologic functions and pollutant removal mechanisms to the extent practical.129. "Soil test" means a chemical analysis of soil to determine needs for fertilizers or amendments for species of plant being grown.130. "Source control" means practices to limit the generation of stormwater pollutants at their source.131. "Stabilization" means providing adequate measures, vegetative and/or structural, that will prevent erosion from occurring.132. "Stormwater" means water consisting of precipitation runoff or snowmelt.133. "Stormwater basin" means a land depression or impoundment created for the detention or retention of stormwater runoff.134. "Stormwater filter" means a stormwater treatment method that utilizes an artificial media to filter out pollutants entrained in urban runoff.135. "Stormwater management plan" means a plan describing the proposed methods and measures to prevent or minimize water quality and quantity impacts associated with a development project both during and after construction. It identifies selected LID source controls and treatment practices to address those potential impacts, the engineering design of the treatment practices, and maintenance requirements for proper performance of the selected practices.136. "Stormwater pollution prevention plan" or "SWPPP" means a plan that identifies potential sources of pollution and outlines specific management activities designed to minimize the introduction of pollutants into stormwater.137. "Stormwater retrofits" means modifications to existing development to incorporate source controls and structural stormwater treatment practices to remedy problems associated with and improve water quality mitigation functions of older, poorly designed, or poorly maintained stormwater management systems.138. "Stormwater treatment train" means stormwater treatment practices, as well as site planning techniques and source controls, combined in series to enhance pollutant removal or achieve multiple stormwater objectives.139. "Stream buffers" means zones of variable width that are located along both sides of a stream and are designed to provide a protective natural area along a stream corridor.140. "Stream order" means the relative size of a stream based on Strahler's (1957) method. Streams with no tributaries are first-order streams, represented as the start of a solid line on a 1:24,000 USGS Quadrangle Sheet. A second-order stream is formed at the confluence of two first-order streams. However, if a first-order stream joins a second-order stream, it remains a second-order stream; it is not until a second-order stream combines with another second-order stream that it becomes a third-order stream, and so on. Peak flow controls (CPv and Qp) are waived for discharges to fourth-order and larger streams.141. "Street sweeper" means equipment that removes particulate debris from roadways and parking lots. Includes mechanical broom sweepers, vacuum sweepers, regenerative air sweepers, and dry vacuum sweepers.142. "Structural BMPs" means devices that are constructed to manage stormwater runoff.143. "Subgrade" means the soil prepared and compacted to support a structure or a pavement system.144. "Subwatershed" means the area draining to the point of confluence between two first-order tributaries.145. "Technical Release No. 55" or "TR-55" means a watershed hydrology model developed by the US Soil Conservation Service (now US Natural Resources Conservation Service) used to calculate runoff volumes and provide a simplified routing for storm events through ponds.146. "Time of concentration" means time required for water to flow from the most remote point of a drainage area, in a hydraulic sense, to the point of analysis.147. "Toe of slope" means where the slope stops or levels out. Bottom of the slope.148. "Token spillways" or "emergency spillways" means spillways that are placed above the water elevation of the largest managed storm and are required if not already provided as part of the conveyance of the 100-year storm event.149. "Topsoil" means fertile or desirable soil material used to top dress road banks, subsoils, parent material, etc.150. "Total maximum daily load" or "TMDL" means a calculation of the maximum amount of a pollutant that a water body can receive and still meet water quality standards, and an allocation of that amount to the pollutant's sources, including a margin of safety.151. "Total nitrogen" or "TN" means the sum of total Kjeldahl nitrogen, nitrate, and nitrite. Nitrogen is typically the growth-limiting nutrient in estuarine and marine systems.152. "Total phosphorus" or "TP" means sum of orthophosphate, metaphosphate (or polyphosphate) and organically bound phosphate. Phosphorus is typically the growth-limiting nutrient in freshwater systems.153. "Total suspended solids" or "TSS" means the total amount of soils particulate matter that is suspended in the water column.154. "Trash rack" means a grill, grate, or other device at the intake of a channel, pipe, drain or spillway for the purpose of preventing oversized debris from entering the structure and clogging the outlet weir/orifice.155. "Tree filter" means a small bioretention practice that may be contained in a concrete vault with an underdrain connecting to the storm drain system, or may have an open base for infiltration into the underlying soils.156. "Underground detention facilities" means vaults, pipes, tanks, and other subsurface structures designed to temporarily store stormwater runoff for water quantity control and to drain completely between runoff events. They are intended to control peak flows, limit downstream flooding, and provide some channel protection.157. "Underground infiltration systems" means structures designed to capture, temporarily store, and infiltrate the water quality volume over several days, including premanufactured pipes, vaults, and modular structures. Used as alternatives to infiltration trenches and basins for space-limited sites and stormwater retrofit applications.158. "Urban stormwater runoff" means stormwater runoff from developed areas.159. "Velocity head" means the head due to the velocity of a moving fluid, equal to the square of the mean velocity divided by twice the acceleration due to gravity (32.16 feet per second per second).160. "Water balance" means an equation describing the input, output, and storage of water in a watershed or other hydrologic system.161. "Water quality flow" or "WQf" means the peak flow rate associated with the water quality design storm or WQv.162. "Water quality swales" means vegetated open channels designed to treat and attenuate the water quality volume and convey excess stormwater runoff. Dry swales are primarily designed to receive drainage from small impervious areas and rural roads. Wet swales are primarily used for highway runoff, small parking lots, rooftops, and pervious areas.163. "Water quality volume" or "WQv" means the storage needed to capture and treat 90% of the average annual stormwater runoff volume. In Rhode Island, this equates to 1-inch of runoff from impervious surfaces.164. "Watershed inches" means a measurement used to compare stormwater volume requirements between sites of varying sizes. Required volumes in acre-feet can be converted to watershed inches by dividing by the total site area in acres and multiplying by 12 inches/feet.165. "Wet swale" means an open drainage channel or depression, explicitly designed to retain water or intercept groundwater for water quality treatment.166. "Wet vegetated treatment system" or "WVTS" means shallow, constructed pools that capture stormwater and allow for the growth of characteristic emergent vegetation. See also definition of shallow WVTS and gravel WVTS.250 R.I. Code R. 250-RICR-150-10-8.5
Amended effective 11/13/2018