Stormwater, also spelled storm water, is water that originates during precipitation events and snow/ice melt. Stormwater can soak into the soil (infiltrate), be held on the surface and evaporate, or runoff and end up in nearby streams, rivers, or other water bodies (surface water).
In natural landscapes such as forests, the soil absorbs much of the stormwater and plants help hold stormwater close to where it falls. In developed environments, unmanaged stormwater can create two major issues: one related to the volume and timing of runoff water (flooding) and the other related to potential contaminants that the water is carrying (water pollution).
Stormwater is also an important resource as the world's human population demand exceeds the availability of readily available water. Techniques of stormwater harvesting with point source water management and purification can potentially make urban environments self-sustaining in terms of water.
Because impervious surfaces (parking lots, roads, buildings, compacted soil) do not allow rain to infiltrate into the ground, more runoff is generated than in the undeveloped condition. This additional runoff can erode watercourses (streams and rivers) as well as cause flooding after the stormwater collection system is overwhelmed by the additional flow. Because the water is flushed out of the watershed during the storm event, little infiltrates the soil, replenishes groundwater, or supplies stream baseflow in dry weather.
A first flush is the initial runoff of a rainstorm. During this phase, polluted water entering storm drains in areas with high proportions of impervious surfaces is typically more concentrated compared to the remainder of the storm. Consequently, these high concentrations of urban runoff result in high levels of pollutants discharged from storm sewers to surface waters.:216
Pollutants entering surface waters during precipitation events is termed polluted runoff. Daily human activities result in deposition of pollutants on roads, lawns, roofs, farm fields, etc. When it rains or there is irrigation, water runs off and ultimately makes its way to a river, lake, or the ocean. While there is some attenuation of these pollutants before entering the receiving waters, the quantity of human activity results in large enough quantities of pollutants to impair these receiving waters.
In addition to the pollutants carried in stormwater runoff, urban runoff is being recognized as a cause of pollution in its own right. In natural catchments (watersheds) surface runoff entering waterways is a relatively rare event, occurring only a few times each year and generally after larger storm events. Before development occurred most rainfall soaked into the ground and contributed to groundwater recharge or was recycled into the atmosphere by vegetation through evapotranspiration .
Modern drainage systems which collect runoff from impervious surfaces (e.g., roofs and roads) ensure that water is efficiently conveyed to waterways through pipe networks, meaning that even small storm events result in increased waterway flows.
In addition to delivering higher pollutants from the urban catchment, increased stormwater flow can lead to stream erosion, encourage weed invasion, and alter natural flow regimes. Native species often rely on such flow regimes for spawning, juvenile development, and migration.
In some areas, especially along the U.S. coast, polluted runoff from roads and highways may be the largest source of water pollution. For example, about 75 percent of the toxic chemicals getting to Seattle, Washington's Puget Sound are carried by stormwater that runs off paved roads and driveways, rooftops, yards, and other developed land.
For Class V stormwater injection wells  the U.S. Environmental Protection Agency reports “the contaminants that have been observed above drinking water standards or health advisory limits in storm water drainage well injectate are aluminum, antimony, arsenic, beryllium, cadmium, chloride, chromium, color, copper, cyanide, iron, lead, manganese, mercury, nickel, nitrate, pH, selenium, TDS, turbidity, zinc, benzene, benzo(a)pyrene, bis(2-ethylhexyl) phtlalate, chlordane, dichloromethane, fecal coliforms, methyl-tertbutyl- ether, pentachlorophenol, tetrachloroethylene, and trichloroethylene.” The U.S. Geological Survey (USGS) reports “Many of the contaminants normally associated with runoff from the Nation's highways have the potential for biological effects. ... Highway-runoff contaminants of particular interest throughout the United States include deicers, nutrients, metals, industrial/urban-organic chemicals, sediment, and agricultural chemicals from industrial, commercial, residential, agricultural, and highway sources.” :3 In addition to the problem of chemical contaminants in stormwater, this USGS report also identifies problems of physical habitat disturbance that Best Management Practices (BMPs) do not eliminate, “Some of the most substantial biological changes caused by development are directly or indirectly related to altered hydrology. Despite efforts to use BMPs to attenuate the hydrologic effects of development, increased peak flows and more flashy runoff will cause physical modifications to the channel shape, bed substrate, and banks of receiving waters, with corresponding effects on aquatic habitat and biota. Loss of forest canopy, increases in paved area, and shallow and(or) muddy detention areas also may cause thermal pollution problems, which can exacerbate chemical stressors on aquatic organisms in receiving waters.” :6
Stormwater is a major cause of urban flooding. Urban flooding is the inundation of land or property in a built-up environment caused by stormwater overwhelming the capacity of drainage systems, such as storm sewers. Although triggered by single events such as flash flooding or snow melt, urban flooding is a condition, characterized by its repetitive, costly and systemic impacts on communities. In areas susceptible to urban flooding, backwater valves and other infrastructure may be installed to mitigate losses.
Where properties are built with basements, urban flooding is the primary cause of basement and sewer backups. Although the number of casualties from urban flooding is usually limited, the economic, social and environmental consequences can be considerable: in addition to direct damage to property and infrastructure (highways, utilities and services), chronically wet houses are linked to an increase in respiratory problems and other illnesses. Sewer backups are often from the sanitary sewer system, which takes on some storm water as a result of Infiltration/Inflow.
Urban flooding has significant economic implications. In the U.S., industry experts estimate that wet basements can lower property values by 10 to 25 percent and are cited among the top reasons for not purchasing a home. According to the Federal Emergency Management Agency almost 40 percent of small businesses never reopen their doors following a flooding disaster. In the UK, urban flooding is estimated to cost £270 million a year (as of 2007) in England and Wales; 80,000 homes are at risk.
A study of Cook County, Illinois, identified 177,000 property damage insurance claims made across 96 percent of the county’s ZIP codes over a five-year period from 2007 to 2011. This is the equivalent of one in six properties in the County making a claim. Average payouts per claim were $3,733 across all types of claims, with total claims amounting to $660 million over the five years examined.
An example of an urban flooding control project is the Brays Bayou Greenway Framework in Houston, Texas. Brays Bayou and its tributaries drain a watershed of approximately 88,000 acres south of downtown Houston. The federally-funded improvement project created a short-term solution by improving the bayou's drainage capacity, and identified a broad set of potential recreation and open space opportunities along the 35 miles of the bayou and tributaries.
An example of urban stormwater creating a sinkhole collapse is the February 25, 2002 Dishman Lane collapse in Bowling Green, Kentucky where a sinkhole suddenly dropped the road under four traveling vehicles. The nine-month repair of the Dishman Lane collapse cost a million dollars but there remains the potential for future problems.
In undisturbed areas with natural subsurface (karst) drainage, soil and rock fragments choke karst openings thereby being a self-limitation to the growth of openings.:189–190, 196 The undisturbed karst drainage system becomes balanced with the climate so it can drain the water produced by most storms. However, problems occur when the landscape is altered by urban development.:28 In urban areas with natural subsurface (karst) drainage there are no surface streams for the increased stormwater from impervious surfaces such as roofs, parking lots, and streets to runoff into. Instead, the stormwater enters the subsurface drainage system by moving down through the ground. When the subsurface water flow becomes great enough to transport soil and rock fragments, the karst openings grow rapidly.:190 Where karst openings are roofed by supportive (competent) limestone, there frequently is no surface warning that an opening has grown so large it will suddenly collapse catastrophically.:198 Therefore, land use planning for new development needs to avoid karst areas.:37–38 Ultimately taxpayers end up paying the costs for poor land use decisions.
Managing the quantity and quality of stormwater is termed, "Stormwater Management." The term Best Management Practice (BMP) or stormwater control measure (SCM) is often used to refer to both structural or engineered control devices and systems (e.g. retention ponds) to treat or store polluted stormwater, as well as operational or procedural practices (e.g. street sweeping). Stormwater management includes both technical and institutional aspects.
Integrated water management (IWM) of stormwater has the potential to address many of the issues affecting the health of waterways and water supply challenges facing the modern urban city. IWM is often associated with green infrastructure when considered in the design process. Professionals in their respective fields, such as urban planners, architects, landscape architects, interior designers, and engineers, often consider integrated water management as a foundation of the design process.
Also known as low impact development (LID) in the United States, or Water Sensitive Urban Design (WSUD) in Australia, IWM has the potential to improve runoff quality, reduce the risk and impact of flooding and deliver an additional water resource to augment potable supply.
The development of the modern city often results in increased demands for water supply due to population growth, while at the same time altered runoff predicted by climate change has the potential to increase the volume of stormwater that can contribute to drainage and flooding problems. IWM offers several techniques, including stormwater harvest (to reduce the amount of water that can cause flooding), infiltration (to restore the natural recharge of groundwater), biofiltration or bioretention (e.g., rain gardens), to store and treat runoff and release it at a controlled rate to reduce impact on streams and wetland treatments (to store and control runoff rates and provide habitat in urban areas).
There are many ways of achieving LID. The most popular is to incorporate land-based solutions to reduce stormwater runoff through the use of retention ponds, bioswales, infiltration trenches, sustainable pavements (such as permeable paving), and others noted above. LID can also be achieved by utilizing engineered, manufactured products to achieve similar, or potentially better, results as land-based systems (underground storage tanks, stormwater treatment systems, biofilters, etc.). The proper LID solution is one that balances the desired results (controlling runoff and pollution) with the associated costs (loss of usable land for land-based systems versus capital cost of manufactured solution). Green (vegetated) roofs are also another low cost solution.
IWM as a movement can be regarded as being in its infancy and brings together elements of drainage science, ecology and a realization that traditional drainage solutions transfer problems further downstream to the detriment of the environment and water resources.
In the United States, the Environmental Protection Agency (EPA) is charged with regulating stormwater pursuant to the Clean Water Act (CWA). The goal of the CWA is to restore all "Waters of the United States" to their "fishable" and "swimmable" conditions. Point source discharges, which originate mostly from municipal wastewater (sewage) and industrial wastewater discharges, have been regulated since enactment of the CWA in 1972. Pollutant loadings from these sources are tightly controlled through the issuance of National Pollution Discharge Elimination System (NPDES) permits. However, despite these controls, thousands of water bodies in the U.S. remain classified as "impaired," meaning that they contain pollutants at levels higher than is considered safe by EPA for the intended beneficial uses of the water. Much of this impairment is due to polluted runoff, generally in urbanized watersheds (in other US watersheds, agricultural pollution is a major source).:15
To address the nationwide problem of stormwater pollution, Congress broadened the CWA definition of "point source" in 1987 to include industrial stormwater discharges and municipal separate storm sewer systems ("MS4"). These facilities are required to obtain NPDES permits. In 2017, about 855 large municipal systems (serving populations of 100,000 or more), and 6,695 small systems are regulated by the permit system.
EPA has authorized 47 states to issue NPDES permits. In addition to implementing the NPDES requirements, many states and local governments have enacted their own stormwater management laws and ordinances, and some have published stormwater treatment design manuals. Some of these state and local requirements have expanded coverage beyond the federal requirements. For example, the State of Maryland requires erosion and sediment controls on construction sites of 5,000 sq ft (460 m2) or more. It is not uncommon for state agencies to revise their requirements and impose them upon counties and cities; daily fines ranging as high as $25,000 can be imposed for failure to modify their local stormwater permitting for construction sites, for instance.
Agricultural runoff (except for concentrated animal feeding operations, or "CAFO") is classified as nonpoint source pollution under the CWA. It is not included in the CWA definition of "point source" and therefore not subject to NPDES permit requirements. The 1987 CWA amendments established a non-regulatory program at EPA for nonpoint source pollution management consisting of research and demonstration projects. Related programs are conducted by the Natural Resources Conservation Service (NRCS) in the U.S. Department of Agriculture.
Education is a key component of stormwater management. A number of agencies and organizations have launched campaigns to teach the public about stormwater pollution, and how they can contribute to solving it. Thousands of local governments in the U.S. have developed education programs as required by their NPDES stormwater permits.
One example of a local educational program is that of the West Michigan Environmental Action Council (WMEAC), which has coined the term Hydrofilth to describe stormwater pollution, as part of its "15 to the River" campaign. (During a rain storm, it may take only 15 minutes for contaminated runoff in Grand Rapids, Michigan to reach the Grand River.) Its outreach activities include a rain barrel distribution program and materials for homeowners on installing rain gardens.
Other public education campaigns highlight the importance of green infrastructure in slowing down and treating stormwater runoff. DuPage County Stormwater Management launched the "Love Blue. Live Green." outreach campaign on social media sites to educate the public on green infrastructure and other best management practices for stormwater runoff. Articles, websites, pictures, videos and other media are disseminated to the public through this campaign.
Since humans began living in concentrated village or urban settings, stormwater runoff has been an issue. During the Bronze Age, housing took a more concentrated form, and impervious surfaces emerged as a factor in the design of early human settlements. Some of the early incorporation of stormwater engineering is evidenced in Ancient Greece.
Best management practices (BMPs) is a term used in the United States and Canada to describe a type of water pollution control. Historically the term has referred to auxiliary pollution controls in the fields of industrial wastewater control and municipal sewage control, while in stormwater management (both urban and rural) and wetland management, BMPs may refer to a principal control or treatment technique as well.Bioretention
Bioretention is the process in which contaminants and sedimentation are removed from stormwater runoff. Stormwater is collected into the treatment area which consists of a grass buffer strip, sand bed, ponding area, organic layer or mulch layer, planting soil, and plants. Runoff passes first over or through a sand bed, which slows the runoff's velocity, distributes it evenly along the length of the ponding area, which consists of a surface organic layer and/or groundcover and the underlying planting soil. The ponding area is graded, its center depressed. Water is ponded to a depth of 15 cm (5.9 in) and gradually infiltrates the bioretention area or is evapotranspired. The bioretention area is graded to divert excess runoff away from itself. Stored water in the bioretention area planting soil exfiltrates over a period of days into the underlying soils.Bioswale
Bioswales are landscape elements designed to concentrate or remove debris and pollution out of surface runoff water. They consist of a swaled drainage course with gently sloped sides (less than 6%) and filled with vegetation, compost and/or riprap. The water's flow path, along with the wide and shallow ditch, is designed to maximize the time water spends in the swale, which aids the collection and removal of pollutants, silt and debris. Bioswales are also beneficial in groundwater recharge and are effective stormwater mitigation tools. Depending upon the topography of the land, a bioswale may have a meandering or almost straight channel alignment. A bioswale's make-up can be influenced by many different variables, including climate, rainfall patterns, size of the site, budget, and available vegetation that can be planted.
It is important to maintain bioswales to ensure best possible efficiency and effectiveness in removal of pollutants in the stormwater runoff. Planning for these things is an important step, which can include the introduction of filters or large rocks to prevent clogging. Annual maintenance through soil testing, visual inspection, and mechanical testing is also crucial to the health of a bioswale.
A common application is around parking lots, where substantial automotive pollution is settled on the paving and then flushed by the first instance of rain, known as the first flush. The bioswales, or other type of biofilter, can be created around the edges of parking lots to capture and treat the stormwater runoff before releasing it to the watershed or storm sewer.Detention basin
A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of rivers, streams, lakes or bays to protect against flooding and, in some cases, downstream erosion by storing water for a limited period of time. These basins are also called "dry ponds", "holding ponds" or "dry detention basins" if no permanent pool of water exists. Detention ponds that are designed to permanently retain some volume of water at all times are called retention basins. In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality, unless it includes a permanent pool feature.Halifax Water
The Halifax Regional Water Commission (HRWC) is the municipal water, wastewater and stormwater utility serving the residents of the Halifax Regional Municipality (HRM), pursuant to the Public Utilities Act. An autonomous, self-financed utility, Halifax Water is a fully metered water utility providing water, fire protection, wastewater and stormwater services as regulated by the Nova Scotia Utility and Review Board.Infiltration basin
An infiltration basin (also known as a recharge basin or in some areas, a sump or percolation pond), is a type of device that is used to manage stormwater runoff, prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. It is essentially a shallow artificial pond that is designed to infiltrate stormwater through permeable soils into the groundwater aquifer. Infiltration basins do not release water except by infiltration, evaporation or emergency overflow during flood conditions.It is distinguished from a detention basin, sometimes called a dry pond, which is designed to discharge to a downstream water body (although it may incidentally infiltrate some of its volume to groundwater); and from a retention basin, which is designed to include a permanent pool of water.Iron Cove Creek
Iron Cove Creek (also known as Dobroyd Stormwater Channel), a southern tributary of the Parramatta River, is an urban stream west of Sydney Harbour, located in the inner-western Sydney suburbs of Croydon, Ashfield, Haberfield and Five Dock in New South Wales, Australia.
Iron Cove Creek traverses mostly through residential areas and parkland, making a 2 kilometres (1.2 mi) journey from where it surfaces in Croydon to where it empties into Iron Cove, which is a bay of the Parramatta River, at Five Dock. It also forms much of the border between Croydon and Ashfield upstream from Parramatta Road. Once a natural watercourse abound with native vegetation and wildlife, Iron Cove Creek was transformed in the late 19th century into a stormwater channel that drains a fairly large catchment area in Sydney's inner-western suburbs.Noonday Creek
Noonday Creek is a 20.2-mile-long (32.5 km) stream in Cobb and Cherokee counties in the U.S. state of Georgia. The stream begins near Kennesaw Mountain and ends at Lake Allatoona.
Noonday is a translation of the native Cherokee language name, referring to the solar noon.Permeable paving
Permeable paving is a method of paving vehicle and pedestrian pathways that allows for infiltration of fluids. In pavement design the base is the top portion of the roadway that pedestrians or vehicles come into contact with. The media used for the base of permeable paving may be porous, to allow for fluids to flow through it, or nonporous media that are spaced so that fluid may flow in between the gaps. In addition to reducing surface runoff, permeable paving can trap suspended solids therefore filtering pollutants from stormwater. Examples include roads, paths, and parking lots that are subject to light vehicular traffic, such as cycle-paths, service or emergency access lanes, road and airport shoulders, and residential sidewalks and driveways.
Although some porous paving materials appear nearly indistinguishable from nonporous materials, their environmental effects are qualitatively different. Whether it is pervious concrete, porous asphalt, paving stones or concrete or plastic-based pavers, all these permeable paving systems allow stormwater to percolate and infiltrate the surface areas, bypassing the traditionally impervious materials to the soil below. The goal is to control stormwater at the source, reduce runoff and improve water quality by filtering pollutants in the substrata layers.Rain garden
One of the wide variety of soil-absorption/filter systems, a rain garden, also called a stormwater garden, is a designed depression storage or a planted hole that allows rainwater runoff from impervious urban areas, like roofs, driveways, walkways, parking lots, and compacted lawn areas, the opportunity to be absorbed. The primary purpose of a rain garden is to improve water quality in nearby bodies of water and to ensure that rainwater becomes available for plants as groundwater rather than being sent through stormwater drains straight out to sea. In fact, it can actually reduce rain runoff by allowing stormwater to soak into the ground (as opposed to flowing into storm drains and surface waters which causes erosion, water pollution, flooding, and diminished groundwater) and cut down on the amount of pollution reaching creeks and streams by up to 30%.The plants—a selection of wetland edge vegetation, such as wildflowers, sedges, rushes, ferns, shrubs and small trees—take up excess water flowing into the rain garden. Water filters through soil layers before entering the groundwater system. Deep plant roots also create additional channels for stormwater to filter into the ground. Root systems enhance infiltration, maintain or even augment soil permeability, provide moisture redistribution, and sustain diverse microbial populations involved in biofiltration. Microbial populations feed off plant root secretions and break down carbon (such as in mulch or desiccated plant roots) to aggregate soil particles which increases infiltration rates. Also, through the process of transpiration, rain garden plants return water vapor to the atmosphere.A more wide-ranging definition covers all the possible elements that can be used to capture, channel, divert, and make the most of the natural rain and snow that falls on a property. Thus, the whole garden can become a rain garden, and each component of the whole can become a small-scale rain garden in itself.Retention basin
A retention basin, sometimes called a wet pond, wet detention basin or stormwater management pond, is an artificial lake with vegetation around the perimeter, and includes a permanent pool of water in its design. It is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay.
It is distinguished from a detention basin, sometimes called a "dry pond", which temporarily stores water after a storm, but eventually empties out at a controlled rate to a downstream water body. It also differs from an infiltration basin which is designed to direct stormwater to groundwater through permeable soils.
Wet ponds are frequently used for water quality improvement, groundwater recharge, flood protection, aesthetic improvement or any combination of these. Sometimes they act as a replacement for the natural absorption of a forest or other natural process that was lost when an area is developed. As such, these structures are designed to blend into neighborhoods and viewed as an amenity.In urban areas, impervious surfaces (roofs, roads) reduce the time spent by rainfall before entering into the stormwater drainage system. If left unchecked, this will cause widespread flooding downstream. The function of a stormwater pond is to contain this surge and release it slowly. This slow release mitigates the size and intensity of storm-induced flooding on downstream receiving waters. Stormwater ponds also collect suspended sediments, which are often found in high concentrations in stormwater water due to upstream construction and sand applications to roadways.SMART Tunnel
The Stormwater Management And Road Tunnel (SMART Tunnel), , is a storm drainage and road structure in Kuala Lumpur, Malaysia, and a major national project in the country. The 9.7 km (6.0 mi) tunnel is the longest stormwater drainage tunnel in South East Asia and second longest in Asia.
The main objective of this tunnel is to solve the problem of flash floods in Kuala Lumpur and also to reduce traffic jams along Jalan Sungai Besi and Loke Yew flyover at Pudu during rush hour. There are two components of this tunnel, the stormwater tunnel and motorway tunnel. It is the longest multi-purpose tunnel in the world.
In 2011, the SMART tunnel received the UN Habitat Scroll of Honour Award for its innovative and unique management of storm water and peak hour traffic.
It begins at Kampung Berembang lake near Klang River at Ampang and ends at Taman Desa lake near Kerayong River at Salak South. The project is led by the government, including Malaysian Highway Authority (Lembaga Lebuhraya Malaysia, LLM) and the Department of Irrigation and Drainage Malaysia (Jabatan Pengairan dan Saliran, JPS) and also a company joint venture pact between Gamuda Berhad and Malaysian Mining Corporation Berhad (MMC).Sanitary sewer
A sanitary sewer or foul sewer is an underground pipe or tunnel system for transporting sewage from houses and commercial buildings (but not stormwater) to treatment facilities or disposal. Sanitary sewers are part of an overall system called a sewage system or sewerage.
Sewage may be treated to control water pollution before discharge to surface waters. Sanitary sewers serving industrial areas also carry industrial wastewater.
Separate sanitary sewer systems are designed to transport sewage alone. In municipalities served by sanitary sewers, separate storm drains may convey surface runoff directly to surface waters. Sanitary sewers are distinguished from combined sewers, which combine sewage with stormwater runoff in one pipe. Sanitary sewer systems are beneficial because they avoid combined sewer overflows.Sediment basin
A sediment basin is a temporary pond built on a construction site to capture eroded or disturbed soil that is washed off during rain storms, and protect the water quality of a nearby stream, river, lake, or bay. The sediment-laden soil settles in the pond before the runoff is discharged. Sediment basins are typically used on construction sites of 5 acres (20,000 m2) or more, where there is sufficient room. They are often used in conjunction with erosion controls and other sediment control practices. On smaller construction sites, where a basin is not practical, sediment traps may be used.Essential sediment abundance is prevalent in the construction industry which gives insight to future endeavors.
On some construction projects, the sediment basin is cleaned out after the soil disturbance (earth-moving) phase of the project, and modified to function as a permanent stormwater management system for the completed site, either as a detention basin or a retention basin.Storm drain
A storm drain, storm sewer (U.S. and Canada), surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from impervious surfaces such as paved streets, car parks, parking lots, footpaths, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems.
Drains receive water from street gutters on most motorways, freeways and other busy roads, as well as towns in areas with heavy rainfall that leads to flooding, and coastal towns with regular storms. Even gutters from houses and buildings can connect to the storm drain. Many storm drainage systems are gravity sewers that drain untreated storm water into rivers or streams—so it is unacceptable to pour hazardous substances into the drains.
Storm drains often cannot manage the quantity of rain that falls in heavy rains or storms. Inundated drains can cause basement and street flooding. In many areas require detention tanks inside a property that temporarily hold runoff in heavy rains and restrict outlet flow to the public sewer. This reduces the risk of overwhelming the public sewer. Some storm drains mix stormwater (rainwater) with sewage, either intentionally in the case of combined sewers, or unintentionally.Stormwater detention vault
A stormwater detention vault is an underground structure designed to manage excess stormwater runoff on a developed site, often in an urban setting. This type of best management practice may be selected when there is insufficient space on the site to infiltrate the runoff or build a surface facility such as a detention basin or retention basin.Detention vaults manage stormwater quantity flowing to nearby surface waters. They help prevent flooding and can reduce erosion in rivers and streams. They do not provide treatment to improve water quality, though some are attached to a media filter bank to remove pollutants.Surface runoff
Surface runoff (also known as overland flow) is the flow of water that occurs when excess storm water, melt water, or other sources flows over the Earth's surface. This might occur because soil is saturated to full capacity, because rain arrives more quickly than soil can absorb it, or because impervious areas (roofs and pavement) send their runoff to surrounding soil that cannot absorb all of it. Surface runoff is a major component of the water cycle. It is the primary agent in soil erosion by water.Runoff that occurs on the ground surface before reaching a channel is also called a non point source. If a nonpoint source contains man-made contaminants, or natural forms of pollution (such as rotting leaves) the runoff is called nonpoint source pollution. A land area which produces runoff that drains to a common point is called a drainage basin. When runoff flows along the ground, it can pick up soil contaminants including petroleum, pesticides, or fertilizers that become discharge or nonpoint source pollution.In addition to causing water erosion and pollution, surface runoff in urban areas is a primary cause of urban flooding which can result in property damage, damp and mold in basements, and street flooding.Urban runoff
Urban runoff is surface runoff of rainwater created by urbanization. This runoff is a major source of flooding and water pollution in urban communities worldwide.
Impervious surfaces (roads, parking lots and sidewalks) are constructed during land development. During rain storms and other precipitation events, these surfaces (built from materials such as asphalt and concrete), along with rooftops, carry polluted stormwater to storm drains, instead of allowing the water to percolate through soil. This causes lowering of the water table (because groundwater recharge is lessened) and flooding since the amount of water that remains on the surface is greater. Most municipal storm sewer systems discharge stormwater, untreated, to streams, rivers and bays. This excess water can also make its way into people's properties through basement backups and seepage through building wall and floors.Wastewater
Wastewater (or waste water) is any water that has been affected by human use. Wastewater is "used water from any combination of domestic, industrial, commercial or agricultural activities, surface runoff or stormwater, and any sewer inflow or sewer infiltration". Therefore, wastewater is a byproduct of domestic, industrial, commercial or agricultural activities. The characteristics of wastewater vary depending on the source. Types of wastewater include: domestic wastewater from households, municipal wastewater from communities (also called sewage) and industrial wastewater from industrial activities. Wastewater can contain physical, chemical and biological pollutants.
Households may produce wastewater from flush toilets, sinks, dishwashers, washing machines, bath tubs, and showers. Households that use dry toilets produce less wastewater than those that use flush toilets.
Wastewater may be conveyed in a sanitary sewer which conveys only sewage. Alternatively, it can be transported in a combined sewer which includes stormwater runoff and industrial wastewater. After treatment at a wastewater treatment plant, the treated wastewater (also called effluent) is discharged to a receiving water body. The terms "wastewater reuse" or "water reclamation" apply if the treated waste is used for another purpose. Wastewater that is discharged to the environment without suitable treatment causes water pollution.
In developing countries and in rural areas with low population densities, wastewater is often treated by various on-site sanitation systems and not conveyed in sewers. These systems include septic tanks connected to drain fields, on-site sewage systems (OSS), vermifilter systems and many more.
Stormwater management structures
|Treatment / Containment|