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 without treatment.
A storm drain, storm sewer, highway drain, surface water drain/sewer, or stormwater drain 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.
Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques for roads, parking lots, and pedestrian walkways. Permeable pavement surfaces may be composed of; pervious concrete, porous asphalt, paving stones, or interlocking pavers. Unlike traditional impervious paving materials such as concrete and asphalt, permeable paving systems allow stormwater to percolate and infiltrate through the pavement and into the aggregate layers and/or soil below. In addition to reducing surface runoff, permeable paving systems can trap suspended solids, thereby filtering pollutants from stormwater.
A dry well or drywell is an underground structure that disposes of unwanted water, most commonly surface runoff and stormwater, in some cases greywater or water used in a groundwater heat pump. It is a gravity-fed, vertical underground system that can capture surface water from impervious surfaces, then store and gradually infiltrate the water into the groundwater aquifer.
The Nationwide Urban Runoff Program (NURP) was 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.
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.
A retention basin, sometimes called a retention pond,wet detention basin, or storm water management pond (SWMP), is an artificial pond with vegetation around the perimeter and a permanent pool of water in its design. It is used to manage stormwater runoff, for protection against flooding, for erosion control, and to serve as an artificial wetland and improve the water quality in adjacent bodies of water.
The United States Environmental Protection Agency (EPA) Storm Water Management Model (SWMM) is a dynamic rainfall–runoff–subsurface runoff simulation model used for single-event to long-term (continuous) simulation of the surface/subsurface hydrology quantity and quality from primarily urban/suburban areas.
Rain gardens, also called bioretention facilities, are one of a variety of practices designed to increase rain runoff reabsorption by the soil. They can also be used to treat polluted stormwater runoff. Rain gardens are designed landscape sites that reduce the flow rate, total quantity, and pollutant load of runoff from impervious urban areas like roofs, driveways, walkways, parking lots, and compacted lawn areas. Rain gardens rely on plants and natural or engineered soil medium to retain stormwater and increase the lag time of infiltration, while remediating and filtering pollutants carried by urban runoff. Rain gardens provide a method to reuse and optimize any rain that falls, reducing or avoiding the need for additional irrigation. A benefit of planting rain gardens is the consequential decrease in ambient air and water temperature, a mitigation that is especially effective in urban areas containing an abundance of impervious surfaces that absorb heat in a phenomenon known as the heat-island effect.
Surface runoff is the unconfined flow of water over the ground surface, in contrast to channel runoff. It occurs when excess rainwater, stormwater, meltwater, or other sources, can no longer sufficiently rapidly infiltrate in the soil. This can occur when the soil is saturated by water to its full capacity, and the rain arrives more quickly than the soil can absorb it. Surface runoff often occurs because impervious areas do not allow water to soak into the ground. Furthermore, runoff can occur either through natural or human-made processes.
Sustainable drainage systems are a collection of water management practices that aim to align modern drainage systems with natural water processes and are part of a larger green infrastructure strategy. SuDS efforts make urban drainage systems more compatible with components of the natural water cycle such as storm surge overflows, soil percolation, and bio-filtration. These efforts hope to mitigate the effect human development has had or may have on the natural water cycle, particularly surface runoff and water pollution trends.
Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in the vadose zone below plant roots and is often expressed as a flux to the water table surface. Groundwater recharge also encompasses water moving away from the water table farther into the saturated zone. Recharge occurs both naturally and through anthropogenic processes, where rainwater and/or reclaimed water is routed to the subsurface.
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 and wetland management, BMPs may refer to a principal control or treatment technique as well.
Bioretention is the process in which contaminants and sedimentation are removed from stormwater runoff. The main objective of the bioretention cell is to attenuate peak runoff as well as to remove stormwater runoff pollutants.
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.
A percolation trench, also called an infiltration trench, is a type of best management practice (BMP) 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 a shallow excavated trench filled with gravel or crushed stone that is designed to infiltrate stormwater though permeable soils into the groundwater aquifer.
Urban runoff is surface runoff of rainwater, landscape irrigation, and car washing created by urbanization. Impervious surfaces are constructed during land development. During rain, storms, and other precipitation events, these surfaces, 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 and flooding since the amount of water that remains on the surface is greater. Most municipal storm sewer systems discharge untreated stormwater 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.
A check dam is a small, sometimes temporary, dam constructed across a swale, drainage ditch, or waterway to counteract erosion by reducing water flow velocity. Check dams themselves are not a type of new technology; rather, they are an ancient technique dating from the second century AD. Check dams are typically, though not always, implemented in a system of several dams situated at regular intervals across the area of interest.
Water-sensitive urban design (WSUD) is a land planning and engineering design approach which integrates the urban water cycle, including stormwater, groundwater, and wastewater management and water supply, into urban design to minimise environmental degradation and improve aesthetic and recreational appeal. WSUD is a term used in the Middle East and Australia and is similar to low-impact development (LID), a term used in the United States; and Sustainable Drainage System (SuDS), a term used in the United Kingdom.
Low-impact development (LID) is a term used in Canada and the United States to describe a land planning and engineering design approach to manage stormwater runoff as part of green infrastructure. LID emphasizes conservation and use of on-site natural features to protect water quality. This approach implements engineered small-scale hydrologic controls to replicate the pre-development hydrologic regime of watersheds through infiltrating, filtering, storing, evaporating, and detaining runoff close to its source. Green infrastructure investments are one approach that often yields multiple benefits and builds city resilience.
