stormwater stormwater stormwater, also written storm water, is water that originates from precipitation (storm), including heavy rain and meltwater from hail and snow. stormwater can soak into the soil (infiltrate) and become groundwater, be stored on depressed land surface in ponds and puddles, evaporate back into the atmosphere, or contribute to surface runoff. most runoff is conveyed directly as surface water to nearby streams, rivers or other large water bodies (wetlands, lakes and oceans) without treatment. urban runoff entering a storm drain public infrastructuregrand coulee dam assets and facilities airports bridges broadband canals coastal management critical infrastructure dams electricity energy hazardous waste hospitals irrigation schemes levees lighthouses parks pipeline transport ports mass transit public housing state schools public spaces rail roads sewage treatment sewerage sluices solid waste telecommunication utilities water supply weirs concepts asset management appropriation lindahl tax build–operate–transfer design–bid–build design–build earmark fixed cost engineering contracts externality government debt life-cycle assessment maintenance monopoly property tax public–private partnership public capital public finance public good public sector renovation replacement (upgrade) spillover supply chain taxation issues and ideas air traffic control brownfield carbon footprint containerization congestion pricing ecotax ethanol fuel fuel tax groundwater high-speed rail hybrid vehicles land-use planning mobile data terminal pork barrel rapid bus transit recycling renewables reverse osmosis smart grid smart growth stormwater urban sprawl traffic congestion transit-oriented development fuel efficiency waste-to-energy weatherization wireless technology fields of study architecture chemical engineering civil electrical mechanical engineering public economics public policy urban planning examples akashi kaikyō bridge trans-alaska pipeline autobahn brazilian energy independence brooklyn bridge channel tunnel chicago wastewater china's high-speed rail curtiba rapid bus transit danish wind-power british offshore wind-power nuclear power in france solar power in germany hoover dam hong kong int'l airport intercity express interstate highways jamnagar refinery kansai int'l airport panama canal port of shanghai san francisco bay bridge three gorges dam shinkansen spanish high-speed rail french tgv rail spanish autovias and autopistas transcontinental railroad power transmission in the usa category engineering portal in natural landscapes, such as forests, soil absorbs much of the stormwater. plants also reduce stormwater by improving infiltration, intercepting precipitation as it falls, and by taking up water through their roots. in developed environments, such as cities, unmanaged stormwater can create two major issues: one related to the volume and timing of runoff (flooding) and the other related to potential contaminants the water is carrying (water pollution). in addition to the pollutants carried in stormwater runoff, urban runoff is being recognized as a cause of pollution in its own right stormwater is also an important resource as human population and demand for water grow, particularly in arid and drought-prone climates. stormwater harvesting techniques and purification could potentially make some urban environments self-sustaining in terms of water. impacts of stormwater stormwater pollution further information: urban runoff relationship between impervious surfaces and surface runoff stormwater carrying street bound pollutants to a storm drain for coastal discharge. with less vegetation and more impervious surfaces (parking lots, roads, buildings, compacted soil), developed areas allow less rain to infiltrate into the ground, and more runoff is generated than in undeveloped conditions. additionally, passages such as ditches and storm sewers quickly transport runoff away from commercial and residential areas into nearby water bodies. this greatly increases the volume of water in waterways and the discharge of those waterways, leading to erosion and flooding. 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 daily human activities result in deposition of pollutants on roads, lawns, roofs, farm fields, and other land surfaces. such pollutants include trash, sediment, nutrients, bacteria, pesticides, metals, and petroleum byproducts. 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 receiving waters, polluted runoff results in large enough quantities of pollutants to impair receiving waters. 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 storms. 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 moved to waterways through pipe networks, meaning that even small storms 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. stormwater runoff from roadways has been observed to contain many metals including zinc (zn), cadmium (cd), copper (cu), nickel (ni), lead (pb), chromium (cr), manganese (mn), iron (fe), vanadium (v), cobalt (co), and aluminum (al) (sansalone and buchberger, 1997; westerlund and viklander, 2006) and other constituents. 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. industrial stormwater is runoff from precipitation that lands on industrial sites (e.g. manufacturing facilities, mines, airports). this runoff is often polluted by materials that are handled or stored on the sites, and the facilities are subject to regulations to control the discharges. urban flooding retention basin for management of stormwater 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. volunteers clearing gutters in ilorin, nigeria during a volunteer sanitation day. even when there is adequate infrastructure for sanitation, plastic pollution can interfere with storm water runoff creating space for mosquitos to breed in water, and causing flooding. some sewage systems in the global south are frequently overwhelmed by the waste, such as in bangkok, thailand. stormwater creation of sinkhole collapses 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. stormwater management stormwater filtration system for urban runoff rain barrels can reduce runoff from building's downspouts and replace the use of potable water for activities such as gardening. 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. technical aspects 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 like retention basins, buried vaults with various kinds of media filters, and vortex separators to remove coarse solids before they pollute surface waters or groundwater resources; acquisition and protection of natural waterways or rehabilitation; building nature-based solutions such as ponds, swales, constructed wetlands or green infrastructure solutions to work with existing or "hard" drainage structures, such as pipes and concrete channels (constructed wetlands built for stormwater treatment can also serve as habitat for plants, amphibians and fish) institutional and policy aspects 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. 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 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