The Benefits of Green Stormwater Infrastructure
Green stormwater infrastructure takes us back to our roots – literally. The amount of impervious surfaces in cities, i.e. concrete, presents an enormous challenge for stormwater management as none of it is absorbed before it enters our stormwater systems. An estimated 10 trillion gallons of untreated stormwater runoff enters sewer systems every year (NRDC.org). A city block can generate almost 5 times as much runoff as a forested area of equal size. Green stormwater infrastructure uses natural elements such as soil and plants to turn rainfall into a resource instead of a stormwater challenge. Some examples include roof and rain gardens, permeable pavement, infiltration basins, and bioswales.
What is the purpose of green stormwater infrastructure?
A big advantage of green stormwater infrastructure is that it helps to keep stormwater systems from being flooded. This is especially true for Combined Sewer systems, which combines stormwater with wastewater from domestic and/or industrial activities before traveling on to a treatment facility. Flooding can cause contamination of drinking water supplies, which can lead to health issues for the population. Flooding can also damage city infrastructure, requiring costly repairs. Climate change has and will increase the occurrence of extreme rain events, so combating flooding is only increasing in priority. By decreasing stormwater runoff volume, green stormwater infrastructure also decreases erosion in streams connected to stormwater outlets. Erosion in streams can cause an increase in pollutants like Chemical Oxygen Demand, Nitrogen and Phosphorus and can be disastrous to aquatic life and our ecosystems.
Infiltration basins are installed along street curbs. They appear to be a part of the sidewalk however stormwater flows into them and can help improve street drainage, reduce puddles and ponds, decrease stormwater entering the sewer system, beautifies the community and makes waterways cleaner.
Green stormwater infrastructure and infiltration basins also prevent excess runoff from absorbing major pollutants often found on impervious surfaces. There is therefore less treatment and cost necessary for stormwater runoff with green stormwater infrastructure. These pollutants can range from road salt to trash. While most green stormwater infrastructure returns captured rain to replenish groundwater under the soil, which can replenish the water supply by restoring aquifers, some green stormwater infrastructures are able to reuse the captured rainwater for domestic use like toilet water.
An important benefit of green stormwater infrastructure, especially in cities, is improved air quality. Cities are on average 4-5 degrees higher in temperature compared to forests (EPA.gov). City infrastructure, such as buildings and roads, reflect the sun that contributes to this heat. Increasing temperature increases ground-level ozone, an ever-increasing occurrence in cities recently due to climate change. Ground-level Ozone is associated with increased rates of asthma and respiratory illnesses. Green stormwater infrastructure helps both decrease the temperature and ozone in its surrounding area through carbon sequestration.
Even just the presence of green stormwater infrastructure is an opportunity to educate the public about mitigating the adverse environmental impacts of our built environment. It helps build a sense of community by improving aesthetics and is often seamlessly incorporated into city parks or sidewalks with “gray” infrastructure, which is more traditional stormwater infrastructure like storm drains.
An Example of Green Stormwater:
Contech Engineered Solutions has developed an excellent example of incorporating green and gray infrastructure with their Filterras. Filterras are infiltration basins which are installed on inlet curbing where a plant (typically a small tree or shrub depending on your climate) is incorporated into a traditional storm drain design. Traditional storm drains immediately direct stormwater into detention storage systems and eventually discharge – however with a Filterra system, stormwater is filtered of pollutants first by using the plants’ roots and specialized filter media. “Root zone microorganisms” use the filter media as a food source and break down pollutants (like dissolved metals and oil & grease) in the stormwater that the plant then absorbs. Removal efficiency of pollutants ranges from 34%-87% depending on the pollutant (Filterra 3rd party research). There is also a built-in downstream pipe that bypasses the filtration system directly to the detention storage system when or if an extreme precipitation event occurs. Considering this bypass, the Filterra still filters on average 90% of the stormwater runoff.
Maintenance and installation for Filterras is currently one of the most cost effective options out there. Filterra systems have a variety of configurations, so are flexible enough to integrate into most (if not all) site plans. The stormwater treatment is shallow and therefore has a low-impact and smaller design. Filterras meet, and sometimes exceed, state and federal regulations for stormwater pollutant removal efficiencies. It’s already been approved by 10 state and federal agencies and is predicted to be approved by more soon. Maintenance includes pruning the branches, removing any trash or rocks, and replacing the top 3 inch layer of mulch with new mulch every six months. The rest of the Filterra system is self-sustaining and needs no maintenance! As an added bonus, the first year of maintenance is included with the purchase of every system.
If you need to install a stormwater filtration system we hope you consider green stormwater infrastructure. With all the added benefits of these systems it can be a great option for keeping our waterbodies clean.
Stormwater Compliance Solutions maintains all types of stormwater systems within the Tri-State areas on the east coast and in Colorado on the west coast. Contact us if you need maintenance on your system. You can also visit our website for more information on Engineering and Water Runoff Solutions or BMP Maintenance and Inspection Services.