What is Stormwater Management?
According to EPA, stormwater management is the effort aimed at reducing and channeling rainwater runoff or melted snow from urban areas, streets, lawns, and homes to improve water quality. It also helps to reverse the negative effects of urban and rural stormwater flooding caused by agriculture and human activities such as infrastructural constructions.
Stormwater is water that comes from rain or melting snow and ice. In a natural situation, the stormwater is supposed to infiltrate to the ground or evaporate. In habitats like forests, for instance, the soil absorbs considerable amounts of stormwater and plants help hold significant amounts, ensuring that very little runs off.
Furthermore, plants, grass, leaves, and stems among other components in the forest slow the runoff, ensuring that the water drains to the rivers or underground slowly. In urban areas, however, plants are few, and the pavements and surfaces are constructed in a way that only allows very little or no water to infiltrate the ground.
The result of this is increased surface runoff and this is where stormwater management becomes handy, especially in reducing rainwater runoff or melted snow from the streets, lawns, and urban areas to improve water quality by preventing harmful bacteria, chemicals, heavy metals, eroded soil, and other bacteria from draining into wetlands, rivers, streams, lakes, or oceans.
Importance of Stormwater Management
1. Maintain the natural hydrologic cycle
Stormwater management plays a critical role in the maintenance of healthy streams, lakes and aquatic life as well as support human uses by maintaining the natural hydrologic cycle. Without proper stormwater management, infiltration can decrease reducing soil replenishment and groundwater recharge. It is worth noting that soil moisture is essential in sustaining vegetation and the reason it has a role to play in maintaining the natural hydrologic cycle.
Besides, the loss of groundwater recharge can reduce the baseflow in streams and flow that exists between storms, which sustains aquatic life. Stormwater management also helps to replenish underground water, ensuring that humans have adequate water for domestic and agricultural purposes.
2. Prevent an increased risk of flooding
Effective stormwater management helps to keep flooding in check. Areas that embrace stormwater management have a low risk of flooding and thus, less likely to experience the negative effects of flooding. Urban areas and other areas with less vegetation are likely to experience flooding upon heavy downpours unless proper management techniques are used.
In these areas, intensity thunderstorms increase the runoff of precipitation, and the presence of drainage systems quickens the runoff to streams. Furthermore, flooding is more likely to cause loss of life and property damage in areas without proper stormwater management techniques.
3. Prevent undesirable stream erosion
By reducing the speed and amount of water running to the streams, stormwater management helps to prevent excessive erosion. If stormwater is not managed, it can cause excessive erosion that may prevent the stream from fulfilling its normal function of conveying water and sediment.
Furthermore, without stormwater management, stormwater can make streams and rivers flood affecting the livelihoods of the surrounding communities. A flooded stream will break its banks, causing the excess water to spill to the surrounding farms destroying crops.
It can also make streams change shape and enlarge, resulting in changes in the distribution of streambed sediments as well as meander patterns. The change in streams can also cause a decline in plant and animal diversity.
4. Protect water quality
Stormwater management plays a critical role in ensuring water quality. Contaminants such as grease, oil, pesticides, metals, plastic and pesticides from gardens and normal daily uses tend to build upon surfaces. If stormwater is not managed, it can carry the contaminants to water sources such as streams, lakes, oceans, and even groundwater.
The pollution is high in urban areas where pavement deterioration, tire and brake pad wear, and emissions and spills from vehicles can easily find their way to water sources. With the use of stormwater management systems, some of these pollutants can be removed before the water gets into the streams.
5. Prevent soil erosion
In agricultural lands, stormwater can affect the productivity of the land by washing away the rich soil cover. It can also transport manure from plants in addition to topsoil, lowering the productivity of farms. If not well managed, stormwater runoff, especially in sloppy areas, can make agricultural land not suitable for agriculture through soil erosion. It can also increase the cost of production as farmers try to create a good environment for agriculture.
Stormwater Management Systems
1. Green roofs
Homeowners are encouraged to adopt green roofs as a method to manage floodwater. Green roofs are roofs with different types of vegetation. The vegetation and materials on the green roof can trap some rainwater, ensuring that the water does not run off the surface. In addition to managing stormwater, green roofs also help in the reduction of energy costs, atmospheric pollution, and heat island by creating an attractive environment. Green roofs are attractive for their water balance, water quality, and peak flow benefits.
2. Rain barrels and cisterns
A cost-effective way to manage stormwater is the use of rain barrels and cisterns to harvest water from rooftops for reuse. In this stormwater harvesting method, you may need to alter your roofing by including water harvesting components like gutters and downspouts that will channel water to rain barrels and cisterns. You can use the harvested water for domestic purposes like toilet flushing or even agriculture.
Harvesting rainwater for home and agriculture use also comes with additional benefits such as reduction of the water utility bill and better use of natural resources. Furthermore, when the collected water is used to irrigate landscaped areas, the water is infiltrated into the soil or evapotranspired by vegetation.
3. The use or installation of permeable pavements
Another effective way to control stormwater is the use of permeable pavements. This method is ideal for large projects that have large parking or projects in urban areas. Permeable surfaces have porous asphalt that allows water to infiltrate to the ground.
Porous materials like permeable interlocking concrete pavers, porous asphalt, pervious concrete, and grid can be used in parking lots, sidewalks and driveways to enable rainwater to infiltrate into the soil and into the groundwater.
In small drainage areas with low runoff, swales can be used to transport water as an alternative to the concrete open channels and underground storm sewers. Swales manage stormwater by slowing runoff, facilitating infiltration, and filter pollutants as runoff flow through the system. Swales can be dry or vegetated channels depending on individual preferences.
5. Vegetated filter strips
In areas that are gently sloping, especially where the channelized flow is not likely, vegetated filter strips work best. The strips are bands of dense vegetation where water runoff is directed. They slow the water runoff allowing water to infiltrate into the ground.
They are effectively used to manage runoff from roads and highways, small parking lots, roof downspouts and impervious surfaces. The vegetated strips slow the runoff allowing sedimentation, evapotranspiration, infiltration into the underlying native soil and filtration through the soil matrix and root zone.
6. Curb and gutter elimination
Another effective way to manage stormwater is to eliminate tools that encourage water to run off quickly. Tools that collect water like gutters and curbs collect and transport runoff quickly to the drainage as they do not allow infiltration. If they are not used to collect water for use, they should be removed. You can also add curb cuts to direct runoff by channeling water to pervious areas and filtered through LID features. An effective way to replace curbs and gutters is to use swales to convey runoff.
7. Sand and organic filters
Sand and organic filters can be successfully used to manage runoff by removing particulate metals, floatables, and pollutants. In most water treatment systems, sand and organic filters are part of the treatment solutions used for removing pollution from the water before they can be discharged to the receiving water or groundwater or for reuse.
8. Bioretention areas
Bioretention or rain gardens can be used to manage stormwater by directing it to the designated area. Bioretention areas are shallow, landscaped depressions that filter runoff through soil and vegetation. An effective way to create bioretention areas is to use native grasses and wildflowers as part of the system. Water from the roof gutter can be directed to the garden using rain chains.
9. Constructed wetlands
People or governments with large tracts of land can construct wetlands that mimic natural wetlands. The wetlands should be built with an objective of holding saturated water just below the soil surface or on the surface and allowing it to infiltrate slowly into the ground. The constructed wetlands should also have diverse flora and fauna components that thrive on the created environment.
10. Riparian Buffers
Another way that can be used to control and manage stormwater is the creation of riparian buffers. Riparian buffers are special areas where development is prohibited or restricted usually along a shoreline, stream, lake or wetland. The main goal of creating riparian buffers is to separate and protect the marine areas from destruction, encroachment or disturbance. A well designed and maintained buffer zone can sustain the integrity of aquatic ecosystems and habitats by trapping pollutants and particles that can destroy the water system.
11. Infiltration basin
The creation of the infiltration basin is feasible in areas with soils that are highly permeable. The basin offers temporary storage of stormwater runoff. The inflation basins do not have a structural outlet. Instead, the outflow of water from the basin is through the surrounding soil and evaporation. If necessary, the infiltration basin can also be combined with an extended detention basin to enable the basin to hold additional stormwater.
12. Detention Ponds
Detention ponds can be used to store water temporarily and this is the feature that makes it ideal for stormwater management. The ponds can be excavated or constructed in natural depressions that are dry during low flow periods. In the detention ponds, water must be allowed to stay long enough to settle out the solid particles.
13. Retention Ponds
Retention ponds function in the same way as detention ponds but with an added benefit of flood control. Although they are primarily designed to improve the quality of water from stormwater flows, they are not designed to dry out. Instead, they are designed to retain water permanently as part of their volume. Water quality improvement is through settling – gradual infiltration into the underground.
14. Onsite detention
Onside detention is a simple method, which can be used to collect rainwater on a site, store it temporally, and then release it slowly to ensure it does not worsen the downstream flooding. The method can be most effective in urban and residential areas stormwater management.