Stormwater management controls the amount of stormwater runoff that comes from impervious surfaces such as streets, driveways, and rooftops in urban areas. In rural areas, stormwater management is more focused on reducing surface runoff from farmland, woodlands, and pastures.
Stormwater is water that comes from rain and snowmelt, plus anything that it picks up on the way, which can include pollutants and debris.
Thus, stormwater management is important to reduce the amount of runoff by slowing the water flow and allowing it to be absorbed. Stormwater management is also critical in preventing pollution and supporting good water quality.
What Is Stormwater Management?
The main objective of stormwater management is to maintain healthy waterways to sustain aquatic life and provide safe water for human uses by reducing the effect of urban development. Stormwater management also aims to prevent floods and unwanted stream erosion, protect water quality, and support the natural hydrological cycle.
When stormwater is absorbed in the soil, pollutants can be filtered out and simultaneously replenishes groundwater aquifers or the water that spills out into surrounding streams and rivers.
However, during heavy rainfall, the stormwater travels into storm sewers and road ditches where debris, chemicals, bacteria, and other pollutants are present. Stormwater can also cause flooding, erosion, turbid waters, damage to infrastructure, and sanitary sewer systems to overflow, which negatively affects the water quality.
But, stormwater design and “green infrastructure” capture and reuse are used to restore water sources. The main purpose is to remove pollutants and slow down the stormwater.
Advantages To Stormwater Management
Proper drainage systems of stormwater and surface water runoff.
It allows water treatment early on.
Avoids infrastructure damage.
It can be used to recharge groundwater sources and reuse rainfall and surface water for irrigation or for household uses.
In urban areas, it creates green and recreational areas.
Disadvantages To Stormwater Management
It requires expert planning, application, operation, and maintenance.
Stormwater management usually requires a lot of labor.
Some stormwater management can cause infiltration systems to become clogged from high sedimentation rates.
Types Of Storage Stormwater Management
Stormwater storage is often used under parking lots, roads, and paved areas within commercial, industrial and residential areas to collect and reduce the flow of stormwater runoff.
Detention ponds are a type of stormwater basin to settle suspended solids typically found in stormwater.
During low flow periods they are dry, but during heavy rainfall, they provide temporary storage for stormwater runoff. The basins allow pollution removal by holding the water long enough to separate the suspended solids.
Retention ponds, also referred to as retention basins, are designed to improve the water quality from stormwater runoff, but they are also used to prevent flooding.
During dry periods, retention ponds do not dry out like detention ponds, therefore, they permanently retain water. Water quality is improved by allowing any suspended sediments to settle, this usually takes between two to four weeks.
On-Site Stormwater Detention
On-site detention collects stormwater or surface water runoff, temporarily stores it, and releases it slowly to prevent flooding the surrounding area.
This method is mainly used in urban and residential areas, so they can be fitted to existing infrastructure such as homes and office buildings.
Rainwater harvesting is a preferred method in urban areas because it conserves potable water and reduces stormwater runoff, but it is also common in rural areas. The harvested rainwater is used to irrigate landscapes. The water is then either removed via vegetation or absorbed by the soil.
Rain that falls into the catchment surfaces can be used for irrigation or in toilet systems with minimal pre-treatment.
Green roofs or rooftop gardens involve a thin layer of plants that grow on a flat or sloped roof. Not only do they store rainwater, but green roofs also improve energy efficiency, reduce urban heat, and they look aesthetically pleasing.
Constructed wetlands are engineered to manage floods, improve water quality, and restore natural habitats for birds and other wetland life. They can also be combined with groundwater recharge systems or soil aquifers.
Types Of Infiltration Stormwater Management
Stormwater infiltration captures and temporarily stores stormwater before it is absorbed into the underlying soil.
Grass filter strips
Infiltration trenches are shallow-dug holes filled with crushed stone to create a reservoir system for stormwater runoff. They can be found next to parking lots or beside streets. The water gradually reaches the bottom of the trench, being filtered on the way down, and eventually reaching the water table.
To avoid sediment penetration, the trench walls are lined with geotextile, and to establish bio-filtration, vegetation is added. While it is a great method for stormwater management, there is some risk of clogging from water that has a high sedimentation concentration.
Grass Filter Strips
Grass filter strips are a permanent area used to reduce sediment, nutrients, pesticides, and other contaminants from stormwater runoff entering a water body.
They also improve the water quality by filtering out sediments and pollutants.
Grass (or vegetated) swales are open grassed channels to slow down the flow of stormwater runoff, allowing the soil to partially absorb the water in the process.
Sedimentation is also slowed down in the swales by check dams and vegetation, which also filters the stormwater runoff, thus improving the water quality by removing contaminants.
A pervious pavement (permeable paving) is a pavement surface that is permeable, with a reservoir made of stone underneath. Many also plant vegetation under or between the stone paving. The reservoir temporarily stores stormwater runoff before it is infiltrated into the soil, improving the water quality.
An infiltration basin or infiltration pond contains highly permeable soil that can temporarily store stormwater runoff. They do not usually have an outlet to discharge runoff like detention basins, instead, the water is infiltrated through the soil, and around 80% of suspended solids are removed.
For the best stormwater quality management, infiltration basins are often coupled with an extended detention basin.
Stormwater Management Monitoring
Part of stormwater management is monitoring the water quality. Each type of stormwater monitoring method is required to collect samples from outfalls. The main parameters in stormwater monitoring include the following:
These measurements are taken with a probe or sensor from the facility’s outfalls system. Probes and sensors are easy to use, and they offer highly accurate continuous measurements.
During rainy seasons, most stormwater management facilities continuously measure the above water parameters, usually followed by testing in a laboratory.
Summing Up Stormwater Management
Stormwater management is necessary for both rural and urban areas to prevent water pollution, store and reuse rainwater, prevent damage to infrastructure from flooding, conserve aquatic environments, and protect human health. If you have any questions regarding stormwater management, or which probe/sensor would best suit your water quality needs, do not hesitate to contact our world-class team at Atlas Scientific.
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