Glossary and Acronyms
Glossary 303(d) List – A list maintained by the State as required by Section 303(d) of the Federal Clean Water Act of waterbodies that do not support their designated uses. It is common to refer to this list as the 303(d) list. The Tennessee Department of Environment and Conservation publishes this list: http://www.tn.gov/environment/water/water-quality_publications.shtml Absorption – A process by which one substance is taken up by another substance, in other words, a substance is assimilated by another substance Adsorption – A process by which dissolved compounds separate from liquid to form a physical or chemical bond to solid materials. Anthropogenic – Originating from or caused by human activities; often describes land use disturbance in watersheds. Antidegradation – Legal policies mandated by the Federal Clean Water Act and implemented in Tennessee through the Water Pollution Control Act that protects water quality by limiting deterioration from the current condition (or to not make matters any worse than they were before). In the context of an NPDES permit, usually means conditions and associated progress of previously issued permits must remain. Baseflow – The portion of flow in a stream that is relatively constant.
Basin – A structural facility that holds stormwater. Best Management Practice (BMP) – A method that is recognized as an efficient, effective, and practical means of preventing or reducing the movement of pollutants into the waters of the state. A BMP may be a physical facility or a management practice achieved through action. Biological Integrity – The capability of supporting and maintaining a balanced, integrated, adaptive community of organisms having a species composition, diversity, and functional organization comparable to that of the natural habitat of the region. Bioretention – An SCM of various physical forms where runoff is captured in a designed structure and pollutants are filtered through physical, chemical, and biological processes. Bioretention facilities are sized to retain a target storage volume, designed with specific vegetation and engineered media, and may incorporate an underdrain to route treated water to a receiving drainage system. Bioswale – A landscape feature that is designed to convey, retain, and treat stormwater.
Buffer – A vegetated strip of land along a sensitive area (like a stream) that helps protect that area from the land disturbance on the adjacent land. SEE RIPARIAN BUFFER. Catch Basin – A structure used to collect stormwater (especially from paved surfaces) and direct the flow to a stormwater drainage system. Channelization – 1) Hydrologic modification and straightening of stream plan form (sinuosity) that may cause destabilization of streambanks and stream bed; 2) the formation of steep channel walls that separate the stream from its primary floodplain. Cistern – A tank that stores captured rainwater runoff from impervious surfaces (most often rooftops) for later use. Clean Water Act (CWA) – A 1972 federal act that provides the basic regulatory framework for the protection of water quality through control of discharge of pollutants into surface waters, including the management of stormwater runoff. Public Law 92-500. Coir Fiber – A natural fiber that is often used in erosion control products (like matting, logs, and socks) as
an environmentally friendly alternative to plastic netting.
Combined Sewer Overflow (CSO)/ Sewer Overflow – Overflow from a sewer system that occurs when the system is overwhelmed with excessive water – typically occurring during a storm event. The overflow results in a discharge of a mixture of partially treated wastewater and runoff to surface water. Concentrated Flow – A flow regime where water flows in a channel – the moving water is concentrated, as opposed to being spread out across the landscape, as in sheet flow. Confluence – The point where one waterbody flows into another.
Contour – A path on the land where the elevation remains constant; describes topography or relief. Contributing Drainage Area (CDA) – The land area from which surface water drains to a specific point of reference. Culvert – Pipe or box structure that drains surface water or runoff under a roadway or embankment. Design Element – A term used in reference to a land area input in the Tennessee Runoff Reduction Assessment Tool that has an identified land area and management. Design Storm – The precipitation depth with a specific return period or frequency which may be used to size and select materials for stormwater treatment. Designated Use – The use of a water resource as identified by the state. In Tennessee, these include fish and aquatic life, recreation, drinking water supply, irrigation, industrial water supply, livestock and wildlife watering, and navigation. Detention – Temporary storage of stormwater to decrease peak flow rate into receiving waters. Typically relates to a basin. Discharge – 1) The release of a water containing pollutants into surface waters, 2) or the volume of water that passes a certain point in time. Downspout Disconnection – Disconnecting the rooftop impervious surface from the stormwater conveyance system as to reduce total runoff volume by allowing downspouts to drain onto pervious surface or into another retention practice. Drainage Area – The area that contributes runoff to a point of reference and is enclosed by a ridgeline or divide. See Basin. Dry Detention – An SCM that provides stormwater flow control designed to temporarily store and release stormwater at an acceptable rate (for permanent stormwater management). Ecoregion – A recurring pattern of ecosystems associated with characteristic combinations of soil and landform that characterise that region-Brunckhorst, D. (2000). Bioregional planning: resource management beyond the new millennium. Harwood Academic Publishers: Sydney, Australia. Ecosystem Services – Collectively, the processes that occur in the environment that benefit humans and society. For example, water purification in wetlands, nutrient cycling in streams, and carbon storage in soil. Effluent – Water that has passed through a treatment process and discharged into the environment. Energy Dissipater – A structure used to absorb the energy carried by concentrated flow and reduce velocity. Engineered Media – Engineered mixture of materials (such as sand, soil, clay, granular activated carbon, perilite, zoelite, compost, organic matter, water treatment residuals, etc.) that is designed to infiltrate and filter pollutants from stormwater runoff. Environmental Site Design – Method of using small-scale stormwater management practices, nonstructural techniques, and better site planning to mimic natural hydrologic runoff characteristics and minimize the impact of land development on water resources. Similar terms include low impact development, green infrastructure, and better site design. Erosion – The detachment and transport of soil or rock due to physical movement of water or air or other
chemical or biological means. Erosion Control Matting – A sheet-like material that is placed on the soil surface to reduce erosion. These materials are typically used to protect the soil during the germination and growth of the permanent vegetation and are made of various materials. Eutrophication – The process of being well nourished; an enrichment of nutrients (mostly nitrogen and phosphorus) in surface waterbodies that may result in excessive aquatic plant growth – frequently associated with algal blooms. Eventually may lead to the filling in and loss of the water body. Evapotranspiration – The sum of evaporation of water from the soil and transpiration of water from plants. Exceptional Tennessee Waters – 1) Surface waters of the state that satisfy a set of characteristics, including being within state or national parks, wildlife refuges, wilderness or national areas; 2) State or Federal Scenic Rivers; Federally-designated critical habitat; 3) waters within an area designated as Lands Unsuitable for Mining; 4) waters with naturally reproducing trout; 5) waters with exceptional biological diversity or; 6) waters with outstanding ecological or recreational value as determined by TDEC. Exfiltration – The process in which water moves out of a media, or permeable pavement. Extended Detention – Design for the temporary storage of stormwater in a detention facility that gradually discharges volume, allowing for increased settling of pollutants and protection of receiving channels. See wet pond. Filter Strip – An SCM that uses dense vegetation with uniform grade to slow runoff and facilitate deposition of sediment in runoff before runoff reaches surface water. First Flush – The stormwater that is first to run off a surface and usually carries the largest load of pollutants. Generally considered to be the first inch of rainfall. Floatables – Litter and debris that will float and travel with water.
Flow Path – The path water takes as it moves across land surfaces. Forebay – A separate segment within a stormwater basin used to trap sediment, chosen to facilitate maintenance and removal of the sediment. Use of a forebay is intended to facilitate sedimentation and thus protect other unit treatment processes. Green Infrastructure (GI) – Using natural hydrologic features and open space to manage water and provide environmental and community benefits. Similar terms include low impact development and environmental site design. Green Roof – A rooftop that is covered with beds or a single bed of soil and vegetation and designed to infiltrate precipitation. An extensive application uses media depths between 4-6 inches deep, while an intensive application is deeper than 6 inches. Also known as a vegetated roof. Groundwater – Water below the ground surface. Heavy Metals – Elements, such as zinc, mercury, lead, and copper. These elements can become dissolved in stormwater and are prone to accumulate in urban areas due to anthropogenic activities (mainly automobile use). Hotspots – A term used to describe land use or activities that pose a relatively higher potential threat to surface or groundwater pollution due to the nature of contaminants that are associated with the operations and land use. Some examples are, but not limited to, gasoline stations, trash collection areas, mulching operations, chemical storage facilities, car washes, nurseries, golf courses, etc. Hydraulic Residence Time (HRT) – The time that a volume of water is held within a defined area. Generally, the longer the HRT, the more effective the treatment of stormwater pollution. Hydric Soils – A soil that is saturated, flooded, or ponded long enough during the growing season to develop anaerobic conditions that favor the growth and regeneration of water-loving vegetation. Hydrocarbons – Organic chemical compounds that are made up of solely carbon and hydrogen. Predominantly used as combustible fuel and, as solid state, asphalt. A pollutant of concern in urban areas due to their contribution to ground level ozone and smog. Hydrograph – A graph that depicts the flowrate past a specific point of reference as a function of time.
Hydrologic Unit Code (HUC) – A standardized watershed classification system created by the USGS. See Section II B for more on Tennessee HUCs. Illicit Discharge – Any discharge to a municipal separate storm sewer that is not entirely composed of stormwater, except discharges authorized under an NPDES permit and discharges resulting from fire fighting activities. Impaired Water – A segment of surface waters that has been identified as failing to support its designated uses. Impervious Surface – 1) A hard surface that either prevents or limits the movement of water into the soil as would naturally occur in a pre-development condition. 2) A hard surface that causes water to runoff in greater quantities than that occurring under natural or pre-development conditions, usually associated with building structures or pavement. Infiltration – The movement of water into the ground surface.
Infiltration Trench – A runoff reduction facility that captures stormwater in a long and narrow pit that is filled with porous material (usually a sand mixture) and holds water until it has time to soak into surrounding native soils; usually used in areas with poor draining soils. Inlet – The location where water flows into a structure or facility. Interflow – The rapid lateral flow of water below the ground surface and above the water table. Karst – Geological formations shaped by the dissolution of soluble rock, usually carbonate rock like limestone or dolomite. Load – 1) A measurement of total mass of a constituent in water. 2) The product of the concentration and the water volume Low Impact Development (LID) – A style of development that incorporates techniques to minimize impacts to natural resources, preserves ecosystem services, and implements best management practices to mimic natural hydrology. Management – A clearly defined state of soil and vegetation that provides the desired degree of infiltration and contaminant removal under the design conditions. This design condition is considered to be 15 years following stabilization, when the site has reached a reasonable level of maturity and is undergoing only gradual changes. The management is the defined desired endpoint, and depends on a series of techniques to get from the current disturbed condition to that endpoint. A management has clearly defined specifications including vegetation type and density, soil hydrologic characteristics, etc. The term Cover is sometimes used to describe a management that has minimal inputs. Managed Vegetated Area (MVA) – An SCM that describes and area that sustains a determinant density and type of vegetated cover such that it intercepts rainfall, covers the soil surface and has an established root matrix. Maximum Extent Practicable (MEP) – Technology-based discharge standard for MS4s to reduce pollutants in stormwater discharges as established by the CWA. MS4 operators shall develop and implement their programs to reduce the discharge of pollutants to the maximum extent practicable, including management practices, control techniques and system, design and engineering methods, and such other provisions appropriate for the control of pollutants. Minimum Control Measure – Stated requirements from the USEPA for permitted groups to be in
compliance and include the implementation of selected BMPs to minimize stormwater and related
pollutants into surface waters.
Municipal Separate Storm Sewer System (MS4) – A stormwater drainage network (including road drainage systems, municipal streets, catch basins, curbs, gutters, ditches, man-made channels, SCMs, or storm drains) that are owned or operated by a local government or designated entity (such as a State, city, town, borough, county, parish, district, association, or other public body). See Section II C for the MS4s in Tennessee. National Pollutant Discharge Elimination System (NPDES) – A provision of the CWA that prohibits the discharge of pollutants into waters of the United States unless a permit is issued by the USEPA, state, or tribal government. Native Vegetation – Vegetation that is naturally found in an area and adapted to the climate, which makes them good candidates for many bioengineered BMPs. Nonpoint Source (NPS) – Diffuse pollution source without a single point of origin. Commonly references NPS are agriculture, forestry, mining operations, dams, channels, and urbanized areas. Nutrients – Compounds that are needed for growth of any biological organism and often carried in harmful quantities by runoff from over-fertilized areas; high nutrient concentrations lead to eutrophication in surface waters. Major nutrients include nitrogen, phosphorus, and potassium. Outlet – The point of release of water usually through a control, such as a concrete structure. Overflow Spillway – A control structure that safely delivers storm flows that exceeds the capacity of a structural practice to receiving stormwater conveyance system or waters of the state. Pathogen – An organism that causes disease. Percolation (Perc) Test – A test that quantifies the rate of infiltration through soils, which is associated with soil hydraulic conductivity. Perennial Vegetation – Plants live for longer than 2 years and re-establish from the same rootstock. Permeability – The ease at which water flows through soil or rock. Permeable Pavement – Alternative pavement surfaces that allow rainwater or stormwater runoff to filter through voids in pavement surface into an underlying stone reservoir, where it is temporarily stored and/or infiltrated. Permeable Pavers – Interlocking block system typically used in driveways, parking lots, and sidewalks, designed to infiltrate precipitation into a porous subgrade and into native soils or underdrain. Pervious Concrete – Permeable concrete that is mixed of course aggregates (minimal sand) and installed in a special way as to leave pathways for water to infiltrate into a porous subgrade. Physiographic Region – A geographic region with similar geomorphology, rock, and soil structure, also known as provinces. Tennessee has a very diverse physiography with 10 distinct regions: the Unaka Mountains, which is part of the Blue Ridge); the Great Valley of East Tennessee, which is part of the Appalachian Ridge and Valley; the Cumberland Plateau; the Sequatchie Valley; the Western and Eastern Highland Rim; which circles the Central Basin; the Western Valley; the Plateau Slope of W. Tennessee; and the Mississippi Flood Plain. The latter two are part of the Gulf Coastal Plain. Point Source – A confined, discernible conveyance that discharges into surface waters. This term refers to but is not limited to a 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. This term does not include return flows from irrigated agriculture or agricultural runoff. Pollutant – A contaminant in a concentration or amount that adversely alters the physical, chemical, or biological properties of the natural environment. Pollutant Removal – A requirement of permanent stormwater management systems; the desired outcome of treatment stormwater control measures. Generally, total suspended solids is used as a surrogate for overall pollutant removal. Porosity – The ratio of void space to total volume of a soil or other media. Pre-development Conditions – The condition that existed just prior to the disturbance at hand; often a target for design of stormwater control facilities.
Rain Barrel – A small storage container used to capture rooftop runoff from downspouts and store for later use. Rain Garden – A shallow depression (usually 6” deep when complete) in the landscape created to capture rooftop and/or driveway runoff and infiltrate it into the ground. Rain gardens usually contain perennial vegetation, amended soils, and mulch. Rainwater Harvesting – A system of collecting rainwater in tanks and releasing it for later use as a water supply. If managed appropriately, runoff can be reduced. Receiving Waters – A river, stream, lake, or other waterway into which wastewater, treated water, or other material is discharged. Redevelopment – Alteration of developed land that disturbs one acre or more, or less than one acre if part of a larger common development plan, and increases the site or building impervious footprint. Restoration – The management of physical, chemical, or biological characteristics of a site with the goal of returning natural or pre-development functions to sites that formerly supported a healthy aquatic ecosystem. Retention – The process of collecting and holding a designed volume of stormwater runoff that does not leave the SCM as surface flow. Return Frequency – An estimate of the probability of the occurrence of a storm event or stream flow of a certain intensity or magnitude. By definition, the inverse of frequency is the return period, or expected time between similarly sized events. Rip Rap – A layer of protective rock placed in erosion-prone areas or sloughing slopes only to be used when vegetative controls are not adequate. Riparian Buffer/Zone – Area of land that runs between a waterway and land disturbance and provides ecological services for water quality and wildlife habitat. Critical functions of a riparian buffer include providing shade a source of organic matter, stabilizing banks, attenuating stormwater runoff, filtering eroded sediments, and facilitating the uptake and treatment of nutrients. Runoff – The rainfall that is shed by the landscape to a receiving waterbody; when rainfall exceeds the infiltration capacity of the land. Runoff Reduction – A requirement of permanent stormwater management systems; An approach to permanent stormwater management that uses avoidance and minimizing design approaches as well as infiltration-based control measures to reduce the amount of impervious surface runoff. Saturated – A moisture condition when the soil void space is fully occupied with water Sediment – Eroded rock and soil material that has been moved and subsequently deposited. Material generated by weathering or erosion that has been transported by wind, water, or gravity. In watersheds, sediment is transported in streams. Sheet Flow – The thin layer of water that accumulates on the soil surface and moves down gradient as a sheet of water. Siltation – 1) The accumulation or deposition of sediment. 2) Pollution of surface water by fine particulate matter with particle sizes in the silt and clay range; usually associated with loss of biological integrity. Soil Amelioration – A technique of physical manipulation and/or adding soil amendments to restore the lost capacity of a soil to grow plants or hold water. Also called soil restoration. Soil Amendment – A soil additive, usually organic matter, used to increase quality and structure of degraded soils. Soil Texture – The ratio of sand, silt, and clay that creates the mineral soil matrix. Sorption – The combination of the adsorption and absorption processes Storage Volume – Volume of stormwater that a structural control facility is designed to hold. Related to
storage capacity. Stormwater Control Measure (SCM) – Measures meant to directly affect the flow of stormwater and/or contaminants, and that have defined specifications and standards. These measures have one or both of two parts: 1) a defined surface management to encourage infiltration and contaminant removal; and/or 2) a clear Protocol defining engineering design, installation, and maintenance. A measure such as a “good forest” has just a Management, a Measure such as a manufactured stormwater treatment device has just an engineering Protocol, and a “bioretention cell” has both. Stormwater Drainage/Conveyance System – Constructed and/or natural features that function together as a system to collect, convey, channel, hold, inhibit, retain, detain, infiltrate, or divert, stormwater. Stormwater Facility – A constructed component of a stormwater drainage system, designed or constructed to perform a particular function. Some examples are pipes, swales, ditches, culverts, street gutters, detention basins, retention basins, constructed wetlands, infiltration devices, catch basins, oil/water separators, sediment basins, and permeable pavements. Stormwater Management – Any action taken to minimize and mitigate the negative impacts of hydrologic modification and pollutant additions (associated with stormwater infrastructure. This includes physical devices and techniques, but also more general strategies like minimizing fertilizer and pesticide use, reducing illicit discharges to drains, etc. Note that Management will often take place between storm events through preventative approaches, though the purpose is to minimize contaminant availability and hydrologic impact during those events. Stormwater Management Plan (SWMP) – A written plan that describes a comprehensive program to manage the quality of stormwater discharged from the MS4. Stormwater Pollution Prevention Plan (SWPPP) – A written plan that includes site maps, identification of construction/contractor activities that could cause pollutants in stormwater, a monitoring and documentation system to evaluate performance and maintenance, and a description of measures or BMPs to control these pollutants as required by state regulations. Stormwater Retrofit – Updated design of a storm drainage system from a conventional system to a new system that incorporates innovative approaches to minimize impacts to water quality. Because of intensive impervious cover and utility constraints, a compromise of LID goals is usually made. Stormwater Treatment Facility – A type of structure that is designed to reduce pollutants and impacts of stormwater. Stormwater Treatment Wetland – A constructed wetland comprised of multiple cells that receive and treat stormwater runoff. Stormwater Utility – A municipal governing body that operates a stormwater system which provides for the collection, treatment, storage and disposal of stormwater provides benefits and services to all property within the incorporated city limits and, in doing so, shall administer and enforce all policy and ordinance pertaining to stormwater runoff and have the authority to assess user fees. Surface Water – Water collected on the landscape in a stream, river, lake, or ocean (Note: there are no estuaries in Tennessee). Suspended Solids – Sediment that is entrained in the water column and transported downstream in suspension and forms deposits. Swale – A shallow drainage conveyance with relatively gentle side slopes and longitudinal grade and generally conveys flows of less than one foot of water depth. Technique – Method or operation that progresses or sustains progress from one state of management to another higher-functioning management. These can fall in either of two general categories: 1) Methods of getting from “here” to “there”; from the presumed worst-case condition immediately
following development to the desired management endpoint. The Techniques used in a specific
site design will vary greatly depending on these starting conditions. For example, if an area of “good
forest” is left undisturbed, no Technique at all is necessary to achieve a “good forest” management.
On the other hand, if the post-construction condition is a bare highly-disturbed mixture of surface
and subsoil and is heavily compacted by traffic, the required techniques to achieve a “good forest”
management in 15 years may well include the following: soil ripping; soil amendments; temporary
vegetative cover; slope erosion control to allow establishment of the temporary vegetation; schemes and other maintenance requirements. Tennessee Runoff Reduction Assessment Tool (TNRRAT) – A computer program that allows designers and plan reviewers to assess whether a project plan meets runoff reduction and pollutant removal requirements based on modeled performance-based outcomes. Treatment Train – A series of structural BMPs that maximizes stormwater treatment by maximizing the number of unit treatment processes achieved in facilities. Turbidity – A measurement of the clarity of water, which is indicative of the light transmissivity and relates to suspended solids in the water column. Ultra Urban – Urban land use that has a high percent impervious. Vegetated Swale – A swale lined with vegetation (see swale) that may or may not have storage capacity. Water Quality Buffer – A setback from the top of a waterbody bank of undisturbed vegetation, including trees, shrubs, and herbaceous vegetation; enhanced or restored vegetation; or the re-establishment of native vegetation bordering streams, ponds, wetlands, springs, reservoirs or lakes, which exists or is established to protect those waterbodies. Water Quality Swale – A swale lined with vegetation with storage capacity in engineered media. Water Quality Volume – Volume of runoff to be captured and treated for pollutants in order to meet water quality regulations/limits in receiving waters. Check local municipal program for specific requirements. Also called Treatment Volume (TV). Water Table – The depth at which soil is saturated with water. Waters of the State – As defined by the Tennessee Water Quality Control Act as any and all water, public or private, on or beneath the surface of the ground, which are contained within, flow through, or border upon Tennessee or any portion thereof except those bodies of water confined to and retained within the limits of private property in single ownership which do not combine to effect a junction with natural surface or underground waters. Watershed – Land area that drains surface water and groundwater to a point of reference. See Section II B for information on Tennessee Watersheds. Wet Weather Conveyance – Man-made or natural watercourses: 1) that flow only in direct response to precipitation runoff in their immediate locality; 2) whose channels are at all times above the groundwater table (excluding piped systems), that are not suitable for drinking water supplies, and 3) in which hydrological and biological analyses indicate that, under normal weather conditions, due to naturally occurring ephemeral or low flow, there is not sufficient water to support fish, or multiple populations of obligate lotic aquatic organisms whose life cycle includes an aquatic phase of at least two months. Wet Pond – An SCM that treats stormwater in a permanent pool of water to remove common pollutants from urban stormwater runoff through sedimentation, biological uptake, and microbial conversion. Wetland – Those 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. Wetlands generally include swamps, marshes, bogs, pocosins, fens, and similar areas.
BMP – Best Management Practice
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