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.[1] 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.[2][3] 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.

Storm Drain
Urban runoff flowing into a storm drain

Urban flooding

Walking in the Rain New Orleans
Flooded streets in New Orleans
Natural & impervious cover diagrams EPA
Relationship between impervious surfaces and surface runoff

Urban runoff is a major cause of urban flooding, the inundation of land or property in a built-up environment caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers.[4] Triggered by events such as flash flooding, storm surges, overbank flooding, or snow melt, urban flooding is characterized by its repetitive, costly and systemic impacts on communities, regardless of whether or not these communities are located within formally designated floodplains or near any body of water.[5]

There are several ways in which stormwater enters properties: backup through sewer pipes, toilets and sinks into buildings; seepage through building walls and floors; the accumulation of water on property and in public rights-of-way; and the overflow of water from water bodies such as rivers and lakes. Where properties are built with basements, urban flooding is the primary cause of basement flooding.

Flood flows in urban environments have been investigated relatively recently despite many centuries of flood events.[6] Some researchers mentioned the storage effect in urban areas. Several studies looked into the flow patterns and redistribution in streets during storm events and the implication in terms of flood modelling.[7] Some recent research considered the criteria for safe evacuation of individuals in flooded areas.[8] But some recent field measurements during the 2010–2011 Queensland floods showed that any criterion solely based upon the flow velocity, water depth or specific momentum cannot account for the hazards caused by the velocity and water depth fluctuations.[6] These considerations ignore further the risks associated with large debris entrained by the flow motion.[8]


A creek filled with urban runoff after a storm

Water running off these impervious surfaces tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from roadways and parking lots, as well as fertilizers and pesticides from lawns. Roads and parking lots are major sources of polycyclic aromatic hydrocarbons (PAHs), which are created as combustion byproducts of gasoline and other fossil fuels, as well as of the heavy metals nickel, copper, zinc, cadmium, and lead. Roof runoff contributes high levels of synthetic organic compounds and zinc (from galvanized gutters). Fertilizer use on residential lawns, parks and golf courses is a measurable source of nitrates and phosphorus in urban runoff when fertilizer is improperly applied or when turf is over-fertilized.[2][9]

Eroding soils or poorly maintained construction sites can often lead to increased sedimentation in runoff. Sedimentation often settles to the bottom of water bodies and can directly affect water quality. Excessive levels of sediment in water bodies can increase the risk of infection and disease through high levels of nutrients present in the soil. These high levels of nutrients can reduce oxygen and boost algae growth while limiting native vegetation growth. Limited native vegetation and excessive algae has the potential to disrupt the entire aquatic ecosystem due to limited light penetration, lower oxygen levels, and reduced food reserves. Excessive levels of sediment and suspended solids have the potential to damage existing infrastructure as well. Sedimentation can increase runoff by plugging underground injection systems, thereby increasing the amount of runoff on the surface. Increased sedimentation levels can also reduce storage behind reservoirs. This reduction of reservoir capacities can lead to increased expenses for public land agencies while also impacting the quality of water recreational areas.[10]

Runoff can also induce heavy metal poisoning in ocean life. Small amounts of heavy metals are carried by runoff into the oceans. These metals are ingested by ocean life. These heavy metals cannot be disposed so they accumulate within the animals. Over time, these metals build up to a toxic level, and the animal dies. This heavy metal poisoning can also affect humans. If we eat a poisoned animal, we have a chance of getting heavy metal poisoning too.[11][12]

As stormwater is channeled into storm drains and surface waters, the natural sediment load discharged to receiving waters decreases, but the water flow and velocity increases. In fact, the impervious cover in a typical city creates five times the runoff of a typical woodland of the same size.[13]


A 2008 report by the United States National Research Council (textbox below) identified urban runoff as a leading source of water quality problems.

...further declines in water quality remain likely if the land-use changes that typify more diffuse sources of pollution are not addressed... These include land-disturbing agricultural, silvicultural, urban, industrial, and construction activities from which hard-to-monitor pollutants emerge during wet-weather events. Pollution from these landscapes has been almost universally acknowledged as the most pressing challenge to the restoration of waterbodies and aquatic ecosystems nationwide.

  – National Research Council, Urban Stormwater Management in the United States[14]

Weasel Brook in Passaic, New Jersey has been channelized with concrete walls to control localized flooding.

The runoff also increases temperatures in streams, harming fish and other organisms. (A sudden burst of runoff from a rainstorm can cause a fish-killing shock of hot water.) Also, road salt used to melt snow on sidewalks and roadways can contaminate streams and groundwater aquifers.[15]

One of the most pronounced effects of urban runoff is on watercourses that historically contained little or no water during dry weather periods (often called ephemeral streams). When an area around such a stream is urbanized, the resultant runoff creates an unnatural year-round streamflow that hurts the vegetation, wildlife and stream bed of the waterway. Containing little or no sediment relative to the historic ratio of sediment to water, urban runoff rushes down the stream channel, ruining natural features such as meanders and sandbars, and creates severe erosion—increasing sediment loads at the mouth while severely incising the stream bed upstream. As an example, on many Southern California beaches at the mouth of a waterway, urban runoff carries trash, pollutants, excessive silt, and other wastes, and can pose moderate to severe health hazards.

Because of fertilizer and organic waste that urban runoff often carries, eutrophication often occurs in waterways affected by this type of runoff. After heavy rains, organic matter in the waterway is relatively high compared with natural levels, spurring growth of algae blooms that soon consume most of the oxygen. Once the naturally occurring oxygen in the water is depleted, the algae blooms die, and their decomposition causes further eutrophication. Algae blooms mostly occur in areas with still water, such as stream pools and the pools behind dams, weirs, and some drop structures. Eutrophication usually comes with deadly consequences for fish and other aquatic organisms.

Excessive stream bank erosion may cause flooding and property damage. For many years governments have often responded to urban stream erosion problems by river engineering through construction of hardened embankments and similar control structures using concrete and masonry materials. Use of these hard materials destroys habitat for fish and other animals.[16] Such a project may stabilize the immediate area where flood damage occurred, but often it simply shifts the problem to an upstream or downstream segment of the stream.[17]

Urban flooding has significant economic implications. In the US, industry experts estimate that wet basements can lower property values by 10%-25% and are cited among the top reasons for not purchasing a home.[18] According to the U.S Federal Emergency Management Agency (FEMA), almost 40% of small businesses never reopen their doors following a flooding disaster.[19] In the UK, urban flooding is estimated to cost £270 million a year in England and Wales; 80,000 homes are at risk.[20]

A study of Cook County, Illinois, identified 177,000 property damage insurance claims made across 96% of the county's ZIP codes over a five-year period from 2007-2011. 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.[18]

Despite concerted efforts, many communities lack the funds to fully address these issues, and often seek funds elsewhere. Numerous watersheds within Los Angeles County, California do not meet state water quality standards, despite spending $100 million a year on clean water programs to combat issues such as urban runoff. To combat this problem, officials have introduced a measure that would assess a fee to homeowners and local businesses in attempt to raise $290 million for effective urban runoff management.[21]

Prevention and mitigation

Percolation trench
A percolation trench infiltrates stormwater through permeable soils into the groundwater aquifer.
Oil-grit separator USGS 2002
An oil-grit separator is designed to capture settleable solids, oil and grease, debris and floatables in runoff from roads and parking lots

Effective control of urban runoff involves reducing the velocity and flow of stormwater, as well as reducing pollutant discharges. A variety of stormwater management practices and systems may be used to reduce the effects of urban runoff. Some of these techniques (called best management practices (BMPs) in the US), focus on water quantity control, while others focus on improving water quality, and some perform both functions.[22]

Pollution prevention practices include low impact development (LID) or green infrastructure techniques - known as Sustainable Drainage Systems (SuDS) in the UK, and Water-Sensitive Urban Design (WSUD) in Australia and the Middle East - such as the installation of green roofs and improved chemical handling (e.g. management of motor fuels & oil, fertilizers and pesticides).[13][23] Runoff mitigation systems include infiltration basins, bioretention systems, constructed wetlands, retention basins and similar devices.[24][25]

Providing effective urban runoff solutions often requires proper city programs that take into account the needs and differences of the community. Factors such as a city's mean temperature, precipitation levels, geographical location, and airborne pollutant levels can all affect rates of pollution in urban runoff and present unique challenges for management. Human factors such as urbanization rates, land use trends, and chosen building materials for impervious surfaces often exacerbate these issues.

The implementation of citywide maintenance strategies such as street sweeping programs can also be an effective method in improving the quality of urban runoff. Street sweeping vacuums collect particles of dust and suspended solids often found in public parking lots and roads that often end up in runoff.[26]

Yellow Fish
Blue drain and yellow fish symbol used by the UK Environment Agency to raise awareness of the ecological impacts of contaminating surface drainage

Educational programs can also be an effective tool for managing urban runoff. Local businesses and individuals can have an integral role in reducing pollution in urban runoff simply through their practices, but often are unaware of regulations. Creating a productive discussion on urban runoff and the importance of effective disposal of household items can help to encourage environmentally friendly practices at a reduced cost to the city and local economy.[27]

See also


  1. ^ "Runoff (surface water runoff)". USGS Water Science School. Reston, VA: U.S. Geological Survey (USGS). 2016-12-02.
  2. ^ a b Water Environment Federation, Alexandria, VA; and American Society of Civil Engineers, Reston, VA. "Urban Runoff Quality Management." WEF Manual of Practice No. 23; ASCE Manual and Report on Engineering Practice No. 87. 1998. ISBN 1-57278-039-8. Chapter 1.
  3. ^ Schueler, Thomas R. (2000) [initial publ. 1995]. "The Importance of Imperviousness" (pdf). In Schueler; Holland, Heather K. The Practice of Watershed Protection. Ellicott City, MD: Center for Watershed Protection. pp. 1–12. Retrieved 2014-12-24.
  4. ^ "Surface Runoff - The Water Cycle". USGS Water Science School. USGS. 2016-12-15.
  5. ^ Center for Neighborhood Technology, Chicago IL "The Prevalence and Cost of Urban Flooding." May 2013
  6. ^ a b Brown, Richard; Chanson, Hubert; McIntosh, Dave; Madhani, Jay (2011). Turbulent Velocity and Suspended Sediment Concentration Measurements in an Urban Environment of the Brisbane River Flood Plain at Gardens Point on 12–13 January 2011. Hydraulic Model Report No. CH83/11. Brisbane, Australia: The University of Queensland, School of Civil Engineering. pp. 120 pp. ISBN 978-1-74272-027-2.
  7. ^ Werner, MGF; Hunter, NM; Bates, PD (2006). "Identifiability of Distributed Floodplain Roughness Values in Flood Extent Estimation". Journal of Hydrology. 314 (1–4): 139–157. doi:10.1016/j.jhydrol.2005.03.012.
  8. ^ a b Chanson, H., Brown, R., McIntosh, D. (2014). "Human body stability in floodwaters: the 2011 flood in Brisbane CBD". Hydraulic structures and society - Engineering challenges and extremes. Proceedings of the 5th IAHR International Symposium on Hydraulic Structures (ISHS2014), 25–27 June 2014, Brisbane, Australia, H. CHANSON and L. TOOMBES Editors, 9 pages. pp. 1–9. doi:10.14264/uql.2014.48. ISBN 978-1-74272-115-6.CS1 maint: Multiple names: authors list (link)
  9. ^ G. Allen Burton, Jr., Robert Pitt (2001). Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers. New York: CRC/Lewis Publishers. ISBN 978-0-87371-924-7.CS1 maint: Uses authors parameter (link) Chapter 2.
  10. ^ Oregon Environmental Council. Chapter 1: Impacts of urban stormwater runoff. Retrieved from website: http://www.oeconline.org/our-work/rivers/stormwater/stormwater report/impacts
  11. ^ Bortman, Marci (2011). "Marine Pollution". Environmental Encyclopedia. 3: 21–34.
  12. ^ Weiss, Kenneth R. (2009). Endangered Oceans. Farmington Hills, MI: Glenhaven Press. pp. 39–45.
  13. ^ a b Protecting Water Quality from Urban Runoff (Report). EPA. February 2003. EPA 841-F-03-003.
  14. ^ National Research Council (United States) (2009). Urban Stormwater Management in the United States (Report). Washington, D.C.: National Academies Press. p. 24. doi:10.17226/12465. ISBN 978-0-309-12539-0.
  15. ^ United States Geological Survey. Atlanta, GA. "The effects of urbanization on water quality: Urban runoff." Accessed 2009-12-30.
  16. ^ Laws, Edward A.; Roth, Lauren (2004). "Impact of Stream Hardening on Water Quality and Metabolic Characteristics of Waimanalo and Kane'ohe Streams, O'ahu, Hawaiian Islands". Pacific Science. 58 (2): 261–280. doi:10.1353/psc.2004.0019. hdl:10125/2725. ISSN 0030-8870.
  17. ^ "Ch. 3. Channelization and Channel Modification". National Management Measures to Control Nonpoint Source Pollution from Hydromodification (Report). EPA. 2007. EPA 841-B-07-002.
  18. ^ a b "The Prevalence and Cost of Urban Flooding." May 2013, Center for Neighborhood Technology, Chicago IL.
  19. ^ Federal Emergency Management Agency (U.S.). "Protecting Your Businesses," last updated March, 2013, http://www.fema.gov/protecting-yourbusinesses Archived 2013-09-17 at Archive.today
  20. ^ Parliamentary Office of Science and Technology, London, UK. "Urban Flooding." Postnote 289, July 2007
  21. ^ Sewell, Abby (2013-01-03). "County seeks parcel fee to pay for projects to combat urban runoff". Los Angeles Times.
  22. ^ "Ch. 5: Description and Performance of Storm Water Best Management Practices". Preliminary Data Summary of Urban Storm Water Best Management Practices (Report). Washington, D.C.: U.S. Environmental Protection Agency (EPA). August 1999. EPA-821-R-99-012.
  23. ^ Reduce Runoff: Slow It Down, Spread It Out, Soak It In (Video). EPA. 2009.
  24. ^ California Stormwater Quality Association. Menlo Park, CA. "Stormwater Best Management Practice (BMP) Handbooks." 2003.
  25. ^ New Jersey Department of Environmental Protection. Trenton, NJ. "New Jersey Stormwater Best Management Practices Manual." April 2004.
  26. ^ "Parking Lot and Street Cleaning". National Menu of Stormwater Best Management Practices. EPA. 2014-08-06. Archived from the original on 2015-08-28. Retrieved 2014-12-24.
  27. ^ Ballo, Siaka; Liu, Min; Hou, Lijun; Chang, Jing (2009-07-10). "Pollutants in stormwater runoff in Shanghai (China): Implications for management of urban runoff pollution". Progress in Natural Science. 19 (7): 873–880. doi:10.1016/j.pnsc.2008.07.021.
  • McGinn, Anne Platt (2004). Human Activities That Threaten the Worlds Oceans. Farmington Hills, MI: Glennhaven Press. pp. 144–157.

Further reading

  • Harry C. Torno; Jiri Marsalek; Michel Desbordes, eds. (1986). Urban Runoff Pollution. Nato ASI Subseries G:. Berlin: Springer-Verlag. ISBN 978-3-540-16090-8.
Back River (Maryland)

Back River is a tidal estuary in Baltimore County, Maryland, located about 2 miles (3 km) east of the city of Baltimore. The estuary extends from the community of Rosedale, southeast for about 8.8 miles (14.2 km) to the Chesapeake Bay. The watershed area is 39,075 acres (15,813 ha) and includes Essex Skypark Airport and the Back River Wastewater Treatment Plant.

First flush

First flush is the initial surface runoff of a rainstorm. During this phase, water pollution 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.

Irvine Ranch Water District

Irvine Ranch Water District (IRWD) is a California Special District formed in 1961 and incorporated under the California water code. IRWD headquarters are located in Irvine, California.

IRWD offers the following services: potable water sales, sewer service and sale of reclaimed (or recycled) water and serves the city of Irvine and portions of Costa Mesa, Lake Forest, Newport Beach, Orange, Tustin and unincorporated areas of Orange County. IRWD has more than 101,000 connections with more than 300,000 customers spanning over 180 square miles (470 km2) of service area in Orange County.

Las Vegas Wash

Las Vegas Wash is a 12-mile-long channel which feeds most of the Las Vegas Valley's excess water into Lake Mead. The wash is sometimes called an urban river, and it exists in its present capacity because of an urban population. The wash also works in a systemic conjunction with the pre-existing wetlands that formed the oasis of the Las Vegas Valley. The wash is fed by urban runoff, shallow ground water, reclaimed water, and stormwater.The wetlands of the Las Vegas Valley act as the kidneys of the environment, cleaning the water that runs through it. The wetlands filter out harmful residues from fertilizers, oils, and other contaminants that can be found on the roadways and in the surrounding desert.

Near its terminus at Las Vegas Bay, the wash passes under the man made Lake Las Vegas through two 7-foot pipes.

Nationwide Urban Runoff Program

The Nationwide Urban Runoff Program (NURP) is a research project conducted by the United States Environmental Protection Agency (EPA) between 1979 and 1983. It was the first comprehensive study of urban stormwater pollution across the United States.

Nonpoint source pollution

Nonpoint source (NPS) pollution is a term used to describe pollution resulting from many diffuse sources, in direct contrast to point source pollution which results from a single source. Nonpoint source pollution generally results from land runoff, precipitation, atmospheric deposition, drainage, seepage, or hydrological modification (rainfall and snowmelt) where tracing pollution back to a single source is difficult.Non-point source water pollution affects a water body from sources such as polluted runoff from agricultural areas draining into a river, or wind-borne debris blowing out to sea. Non-point source air pollution affects air quality from sources such as smokestacks or car tailpipes. Although these pollutants have originated from a point source, the long-range transport ability and multiple sources of the pollutant make it a non-point source of pollution. Non-point source pollution can be contrasted with point source pollution, where discharges occur to a body of water or into the atmosphere at a single location.

NPS may derive from many different sources with no specific solution may change to rectify the problem, making it difficult to regulate. Non point source water pollution is difficult to control because it comes from the everyday activities of many different people, such as lawn fertilization, applying pesticides, road construction or building construction.It is the leading cause of water pollution in the United States today, with polluted runoff from agriculture and hydromodification the primary sources. Other significant sources of runoff include habitat modification and silviculture (forestry).Contaminated stormwater washed off parking lots, roads and highways, and lawns (often containing fertilizers and pesticides) is called urban runoff. This runoff is often classified as a type of NPS pollution. Some people may also consider it a point source because many times it is channeled into municipal storm drain systems and discharged through pipes to nearby surface waters. However, not all urban runoff flows through storm drain systems before entering water bodies. Some may flow directly into water bodies, especially in developing and suburban areas. Also, unlike other types of point sources, such as industrial discharges, sewage treatment plants and other operations, pollution in urban runoff cannot be attributed to one activity or even group of activities. Therefore, because it is not caused by an easily identified and regulated activity, urban runoff pollution sources are also often treated as true non-point sources as municipalities work to abate them.

Paxton Creek

Paxton Creek is a 13.9-mile-long (22.4 km) tributary of the Susquehanna River in Dauphin County, Pennsylvania in the United States.

The Paxton Creek watershed covers an area of 27.4 square miles (71 km2) and joins the Susquehanna River at South Harrisburg, Harrisburg.The name Paxton, or Paxtang, is derived the Susquehannock term "Peshtank", meaning "where the waters stand" or "the place of springs". It is born from two branches on the southern slopes of Blue Mountain to form the main stem in Lower Paxton Township. It then forms Wildwood Lake in Susquehanna Township, then becoming a concrete channel downstream at Harrisburg to mitigate urban runoff and flooding.

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.

Road verge

A road verge is a strip of grass or plants, and sometimes also trees, located between a roadway (carriageway) and a sidewalk (pavement). Verges are known by dozens of other names, often quite regional; see Terminology, below.

The land is often public property, with maintenance usually being a municipal responsibility. Some municipal authorities, however, require that abutting property owners maintain their respective verge areas, as well as the adjunct footpaths or sidewalks.Benefits include visual aesthetics, increased safety and comfort of sidewalk users, protection from spray from passing vehicles, and a space for benches, bus shelters, street lights, and other public amenities. Verges are also often part of sustainability for water conservation or the management of urban runoff and water pollution and can provide useful wildlife habitat. Snow that has been ploughed off the street in colder climates often is stored in the area of the verge by default.

In the British Isles, verges are the last location of habitats for a range of flora.

The main disadvantage of a road verge is that the right-of-way must be wider, increasing the cost of the road. In some localities, a wider verge offers opportunity for later road widening, should the traffic usage of a road demand this. For this reason, footpaths are usually sited a significant distance from the curb.

San Juan Creek

San Juan Creek, also called the San Juan River, is a 29-mile (47 km) long stream in Orange County, California draining a watershed of 133.9 square miles (347 km2). Its mainstem begins in the southern Santa Ana Mountains in the Cleveland National Forest. It winds west and south through San Juan Canyon, and is joined by Arroyo Trabuco as it passes through San Juan Capistrano. It flows into the Pacific Ocean at Doheny State Beach. San Juan Canyon provides a major part of the route for California State Route 74 (the Ortega Highway).

Before Spanish colonization in the 1770s, the San Juan Creek watershed was inhabited by the Acjachemen or Juañeno Native Americans. The Juañeno were named by Spanish missionaries who built Mission San Juan Capistrano on the banks of a stream they named San Juan Creek. The watershed was used mainly for agriculture and ranching until the 1950s when residential suburban development began on a large scale. Since then, the human population has continued to encroach on floodplains of local streams. Flooding in the 20th and 21st centuries has caused considerable property damage in the San Juan watershed.

The San Juan watershed is home to sixteen major native plant communities and hundreds of animal species. However, the watershed is projected to be 48 percent urbanized by 2050. In addition, urban runoff has changed flow patterns in San Juan Creek and introduced pollutants to the river system. Although the main stem of San Juan Creek does not have any major water diversions or dams, some of its tributaries, including Trabuco and Oso Creeks, have been channelized or otherwise heavily modified by urbanization.

Sarasota Bay

Sarasota Bay is a lagoon located off the southwest (Sarasota) and central-west (Manatee) coast of Florida in the United States. Though no significant single stream of freshwater enters the bay, with a drainage basin limited to 150 square miles in Manatee and Sarasota Counties, it is generally treated as an estuary, with three "passes" or inlets, giving access from the Gulf of Mexico. Its source of freshwater has been increased from natural historical levels by urban runoff.

The bay and its surrounding area appeared on the earliest maps of the area, being named Zarazote on one dating from the early 18th century. Hunting in the area had supported native populations for more than ten thousand years as Florida attracted some of the earliest human settlements in the hemisphere. Following the retreat of the glaciers, ocean levels rose creating the current coastline and the natural bounty of Sarasota Bay provided food for inhabitants for over five thousand years before Europeans began exploration of the area in 1513 and later, establishing settlements along its shores.

Sarasota Bay, the largest and deepest coastal bay between Tampa Bay and Charlotte Harbor, is one of twenty-eight estuaries in the country that have been named by the U.S. Congress as an estuary of national significance. The bay lies between barrier islands called keys, that separate the body of water from the Gulf of Mexico and the Florida mainland. Longboat Key, Lido Key, Siesta Key, and Casey Key are the major keys that delineate the main bay and its smaller portions.

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, 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.

Sulphur Creek (California)

Sulphur Creek is a 4.5-mile (7.2 km) tributary of Aliso Creek in Orange County in the U.S. state of California. The creek drains about 6 square miles (16 km2) of residential communities and parks in the southern San Joaquin Hills.

The Sulphur Creek watershed was once part of the territory of the semi-nomadic Acjachemen Native Americans, who were conquered by Spanish conquistadors in the 17th and 18th centuries and called the Juaneño after nearby Mission San Juan Capistrano. During the 19th century, the watershed became part of a rancho and was mostly agricultural and range land until the 1960s, when suburban residential development began in the watershed. Sulphur Creek Dam was built in 1966, forming Laguna Niguel Lake.

Today, the Sulphur Creek drainage basin includes parts of Laguna Niguel, Laguna Hills, and San Juan Capistrano. The creek also flows through parts of Laguna Niguel Regional Park and Aliso and Wood Canyons Regional Park. Urban runoff has changed the once seasonal creek into a permanent stream. Most of the creek has been channelized to control flooding and prevent erosion, although some sections still include riparian habitat.

Thermal pollution

Thermal pollution is the degradation of water quality by any process that changes ambient water temperature. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. When water used as a coolant is returned to the natural environment at a higher temperature, the sudden change in temperature decreases oxygen supply and affects ecosystem composition. Fish and other organisms adapted to particular temperature range can be killed by an abrupt change in water temperature (either a rapid increase or decrease) known as "Thermal shock."

Urban runoff—stormwater discharged to surface waters from roads and parking lots—can also be a source of elevated water temperatures.

Urban stream

An urban stream is a formerly natural waterway that flows through a heavily populated area. Urban streams are often polluted by urban runoff and combined sewer outflows. Water scarcity makes flow management in the rehabilitation of urban streams problematic.Governments may alter the flow or course of an urban stream to prevent localized flooding by river engineering: lining stream beds with concrete or other hardscape materials, diverting the stream into culverts and storm sewers, or other means. Some urban streams, such as the subterranean rivers of London, run completely underground. These modifications have often reduced habitat for fish and other species, caused downstream flooding due to alterations of flood plains, and worsened water quality.

Some communities have begun stream restoration projects in an attempt to correct the problems caused by alteration, using techniques such as daylighting and fixing stream bank erosion caused by heavy stormwater runoff. Streamflow augmentation to restore habitat and aesthetics is also an option, and recycled water can be used for this purpose.

Water pollution

Water pollution is the contamination of water bodies, usually as a result of human activities. Water bodies include for example lakes, rivers, oceans, aquifers and groundwater. Water pollution results when contaminants are introduced into the natural environment. For example, releasing inadequately treated wastewater into natural water bodies can lead to degradation of aquatic ecosystems. In turn, this can lead to public health problems for people living downstream. They may use the same polluted river water for drinking or bathing or irrigation. Water pollution is the leading worldwide cause of death and disease, e.g. due to water-borne diseases.Water pollution can be grouped into surface water pollution. Marine pollution and nutrient pollution are subsets of water pollution. Sources of water pollution are either point sources and non-point sources. Point sources have one identifiable cause of the pollution, such as a storm drain, wastewater treatment plant or stream. Non-point sources are more diffuse, such as agricultural runoff. Pollution is the result of the cumulative effect over time. All plants and organisms living in or being exposed to polluted water bodies can be impacted. The effects can damage individual species and impact the natural biological communities they are part of.

The causes of water pollution include a wide range of chemicals and pathogens as well as physical parameters. Contaminants may include organic and inorganic substances. Elevated temperatures can also lead to polluted water. A common cause of thermal pollution is the use of water as a coolant by power plants and industrial manufacturers. Elevated water temperatures decrease oxygen levels, which can kill fish and alter food chain composition, reduce species biodiversity, and foster invasion by new thermophilic species.Water pollution is measured by analysing water samples. Physical, chemical and biological tests can be done. Control of water pollution requires appropriate infrastructure and management plans. The infrastructure may include wastewater treatment plants. Sewage treatment plants and industrial wastewater treatment plants are usually required to protect water bodies from untreated wastewater. Agricultural wastewater treatment for farms, and erosion control from construction sites can also help prevent water pollution. Nature-based solutions are another approach to prevent water pollution. Effective control of urban runoff includes reducing speed and quantity of flow. In the United States, best management practices for water pollution include approaches to reduce the quantity of water and improve water quality.

Water pollution in the United States

Since the 1960s, water quality in surface water bodies in the United States has generally improved, due to the implementation of the 1972 Clean Water Act. However, many water bodies are still being polluted from one or more categories of sources, which may include agriculture, industry, or urban runoff.

Wood Canyon Creek

Wood Canyon Creek is a 2.8 mi (4.5 km) perennial stream in Aliso and Wood Canyons Wilderness Park, Orange County, California. A tributary of Aliso Creek, it drains a deep undeveloped valley to the west of Aliso Viejo.

The Wood Canyon was populated by the Acjachemen tribe hundreds of years ago; many archaeological sites along the creek provide evidence of their habitation. Spanish explorers and colonists arrived in the mid-18th century, establishing missions and a rancho that extended around the Aliso Creek watershed. Wood Canyon was used first as a cattle grazing area; after California became part of the United States, it was used to graze sheep. From the 1960s onward, the creek's flow has been heavily affected by urban runoff from suburban residential development.

The Wood Canyon watershed drains a portion of the San Joaquin Hills, a short coastal mountain range that uplifted beginning in the mid-Pleistocene (1.22 MYA).

Quality indicators
Treatment options
Disposal options
Air pollution
Water pollution
Soil contamination
Radioactive contamination
Other types of pollution
Inter-government treaties
Major organizations

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