STORMWATER, also spelled STORM WATER, is water that originates during
precipitation events and snow/ice melt.
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 ).
* 6 Regulations
* 6.1.1 Federal requirements * 6.1.2 State and local requirements * 6.1.3 Nonpoint source pollution management
* 7 Public education campaigns * 8 History * 9 See also * 10 References * 11 External links
Relationship between impervious surfaces and surface runoff
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. Further information: Urban runoff
STORMWATER RUNOFF AS A SOURCE OF POLLUTION
Urban runoff being discharged to coastal 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
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
A study of
Cook County, Illinois
An example of Urban flooding control project is the Brays Bayou
Greenway Framework. The Brays Bayou Greenway Framework is federally
funded improvement project. Brays Bayou starts from the Bayou's mouth
at Buffalo Bayou and the Ship Channel in the east to the Barker
Reservoir and George Bush Park in the west. In aim to identify a broad
set of potential recreation and open space opportunities along the 35
miles of Brays Bayou, Brays Bayou and its tributaries provide drainage
to a watershed of approximately 88,000 acres south of downtown Houston
, Texas. Project Brays responses to the present flooding problems in
Managing the quantity and quality of stormwater is termed,
* control of flooding and erosion; * control of hazardous materials to prevent release of pollutants into the environment (source control); * planning and construction of stormwater systems so contaminants are removed before they pollute surface waters or groundwater resources; * acquisition and protection of natural waterways or rehabilitation; * building "soft" structures such as ponds, swales , wetlands or green infrastructure solutions to work with existing or "hard" drainage structures, such as pipes and concrete channels; * development of funding approaches to stormwater programs potentially including stormwater user fees and the creation of a stormwater utility; * development of long-term asset management programs to repair and replace aging infrastructure; * revision of current stormwater regulations to address comprehensive stormwater needs; * enhancement and enforcement of existing ordinances to make sure property owners consider the effects of stormwater before, during and after development of their land; * education of a community about how its actions affect water quality , and about what it can do to improve water quality; and * planning carefully to create solutions before problems become too great.
INTEGRATED WATER MANAGEMENT
Rain garden designed to treat stormwater from adjacent parking lot
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
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 our environment and precious water resources.
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.
State And Local Requirements
A silt fence , a type of sediment control , installed on a construction site
EPA has authorized 46 states to issue
NPDES permits. In addition to
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
Nonpoint Source Pollution Management
Further information: Agricultural wastewater treatment and Erosion control
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 .
PUBLIC EDUCATION CAMPAIGNS
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
Other public education campaigns highlight the importance of green
infrastructure in slowing down and treating stormwater runoff. DuPage
Since humans began living in concentrated village or urban settings,
stormwater runoff has been an issue. During the
* ^ Schueler, Thomas R. "The Importance of Imperviousness."
Reprinted in The Practice of Watershed Protection. 2000. Center for
Watershed Protection, Ellicott City, MD.
* ^ Metcalf, Leonard; Eddy, Harrison P. (1916). American Sewerage
Practice: Disposal of Sewage. III. New York: McGraw-Hill. p. 154.
* ^ Alex Maestre and Robert Pitt; Center for Watershed Protection