Sustainable Ways to Manage Stormwater

An article published online by editor and writer Melissa Denchak highlighted some shocking stormwater statistics coming out of America. Denchak stated that ‘an estimated 10 trillion gallons of untreated stormwater runoff, containing everything from raw sewage to trash to toxins, enters U.S waterways from city sewer systems every year, polluting the environment and drinking supplies… [with] runoff causes significant flooding as well.’ (Denchak 2022). 

Denchak described the ‘U.S Environmental Protection Agency (EPA) estimates that upgrading the stormwater and other public water systems will require at least $150 billion in investment over the next two decades. 

This problem is not unique to the U.S, it is a problem all over the globe. The question is, how do we address the issues caused by stormwater runoff?

In this article, Citygreen will argue that green infrastructure offers a cost-effective solution to handling flooding and stormwater pollution. 

To start, let’s break down the basics. 

Why is Green Infrastructure Important for Managing Stormwater? 

Green infrastructure encompasses a variety of water management practices, such as planted verges, bioretention pits, swales and other measures that capture, filter, and reduce stormwater. Essentially, green infrastructure replicates natural hydrological processes using soil and plants to slow down, recycle and clean stormwater runoff.

Green WSUD stormwater mangement

What is Stormwater Runoff?

Stormwater runoff is the product of a rain event causing water to flow into sewers and waterways. With the expansion of our bustling cities and the widening sprawl of our urban areas, there are more impermeable surfaces than ever, changing the intensity of stormwater runoff. According to Denchak, ‘the average city block can generate more than five times as much runoff as a forested area of equal size’ (Denchak 2022). 

circular economy of water

What is an Example of a Successful Green Infrastructure Project? 

Denchak proposed that New York’s Staten Island Bluebelt was the ‘first and largest green infrastructure project in the U.S.’ A rapid increase in population size saw the Island struggling to deal with sanitary waste and stormwater runoff. The Bluebelt project ‘helped solve these issues by preserving streams, wetland areas, and other drainage corridors (Bluebelts) that use natural mechanisms to capture, store, and filter stormwater’ (Denchak 2022). Nowadays, the Bluebelt comprises more than 14,000 acres and can temporarily hold and filter as much as 350,000 gallons of rainfall. 

WSUD water drain feeding water into the tree soil vault

How does Citygreen Implement and Manage Stormwater Projects?

Over the past three decades, Citygreen has made significant investments in stormwater infrastructure projects. We learnt early on that mimicking natural systems to manage rainfall, is the most cost-effectively way to deal with stormwater runoff.

An example of a green infrastructure design that Citygreen has developed is the Strataflow™ system.  Instead of a traditional bioretention basin, Citygreen’s Strataflow™ uses an underground structural soil vault system, which delivers a high standard of stormwater treatment with a completely natural look. To any passer-by, what you see is a healthy, flourishing tree surrounded by a grassy verge, but beneath the ground is an advanced WSUD. 

This design starts with the Strataflow Kerb Inlet; this device sits in the road kerb alignment, retaining the inherent structure of the concrete kerb. The inlet has a grate (acting as a screen) to stop larger-sized pollutants from entering the system, which inhibits healthy tree growth. 

The inlet lets water from the road carriageway flow through the front grate of the drain at a capacity of up to 18 litres/ 5 gallons per second. This allows the inlet to minimise pollutants entering waterways and reduce flood risks by controlling the stormwater flow entering our city’s underground drains. 

strataflow kerb inlet sitting in the kern

When the water flows through the street, it enters through the inlet and flows underground. From there, the stormwater reaches the advanced structural soil cell system, where the stormwater is stored, filtered and distributed effectively for the benefit of urban trees and proper stormwater management.

The inlet ensures the water drains down at the correct optimal depth beneath the pavement height. From there, the stormwater reaches the structural soil cell system and the tree’s root system, where the stormwater is stored, filtered and distributed effectively to benefit urban trees and proper stormwater management.

animation of how strataflow works to benefits stormwater usage

Essentially, Strataflow™ utilises readily available stormwater rather than potable water to irrigate street trees, which improves the vitality of trees and reduces the impact of stormwater on the local environment, all while maintaining a high natural presentation. 

Stormwater Management Case Study

Pemberton is a small mountain town located 20 minutes North of world-renowned ski resort Whistler in Beautiful British Columbia, Canada.

In 2019 the town of Pemberton was awarded a government grant to upgrade ageing infrastructure and give their tourist town a facelift. Pemberton had some issues with flooding which they were keen to fix and at the same time wanted to create an inviting and enjoyable experience for the visitors and residents of the town.

One of the solutions was the Stratavault system, this system was placed underneath all sidewalks for two reasons. The first was to collect the mass of snow run off and rainfall that would typically flood the town, slow this water down and clean it with the soil held in the Stratavault system then push excess water into a nearby pond where it could be used for irrigation purposes throughout the town. The second was to hold enough soil so the trees that were planted in urban environments could have access to nutrient-rich soil for many years to come.

Book a Citygreen Consultant

Looking for a cost-effective and sustainable stormwater solution? Contact our friendly Citygreen Team today.

How to Determine Urban Canopy Cover

By: Richard J. Magill, Magill & Associates, Inc.

a family enjoying a stroll in an urban park U3FEF23 Urban Canopy Cover Citygreen

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First Urban Tree Canopy Cover Benchmark in Australia

The 202020 Vision and University of Technology Sydney has released the first ever benchmark report on urban tree canopy cover in Australia.

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The Difference That Urban Trees Make

The Difference That Urban Trees Make:

Urban developers around the world are joining in the effort to create green cities for future generations.

In an article by Ben Kaplan from We Create Here in Iowa, he mentioned the many benefits of urban trees based on a list created by Dan Burden. Burden is the co-founder of the Walkable and Livable Communities Institute – an organisation focused on creating pedestrian friendly spaces.

The story stated several benefits of urban trees. One is creating a safer environment. This is because street trees “make people drive more carefully” thereby keeping pedestrians safe and reducing stress associated with driving.

“Surprisingly, people perceive driving through areas with street trees as taking less time than driving in areas without street trees,” Kaplan noted.

Second, trees absorb greenhouse gas emissions, lowering the carbon emissions and other particulates in the air. Apart from that, “roads covered by a canopy of mature trees last 40 to 60 percent longer than roads without tree cover.”

The shade also lowers the heat island effect as canopied roads stay cooler on hot days. “Street trees also soak up a lot of water, helping to prevent street flooding and runoff.”

As we mentioned in the blog, street trees actually have more financial benefits to the city than the cost to maintain them. According to Kaplan’s article, it costs $1.2 million a year to maintain all of the 35,000 street trees in their area. But they generate $5 million of positive economic benefits each year.

“The average value per tree is $34 and in total generates $1.3 million a year. Street trees in Cedar Rapids also divert enough stormwater to save the city $1.8 million a year, reduce energy costs by $1.3 milion a year and provide $450,000 worth of air quality improvement and carbon reduction annually.”

“If you want to experience the difference street trees can make as a pedestrian, take a happy hour stroll from the Starlite Room to Belle’s Basix or 101 Gastropub, once on the tree-plentiful north side of 1st Avenue, and walk back on the unshaded south side of the street,” Kaplan said.

Several organisations are aware of the many benefits trees provide. More recently, according to 9&10 News in Michigan, the Greening of Detroit’s Green Corps program is hiring 80 high school students to help take care of the 12,000 trees and green spaces in the city. Since it started, the program has hired more than 1,500 young people to help care for the city’s environment.

These young people will also “work to improve parks and support conservation projects while learning about agriculture and farming at The Greening’s farm gardens”.

Previously, residents of Detroit also united to create a greener city. It is these efforts from communities and organisations that will continue to push others to do their part in creating a greener future.

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Toronto Urban Forest Worth $7B

The trees in the City of Toronto’s urban forest are worth an estimated $7 billion, roughly $700 per tree, according to a recent study by TD Economics.

The report said the city’s urban forest provides residents with over $80 million worth of environmental benefits and cost savings each year. For the average single family household, that’s $125 annual savings.

As Citygreen® previously posted, urban forests do so much more than just beautify the area. Green space provides health, social and psychological benefits to its residents.

Using the City of Toronto’s urban forest as an example, TD Economics demonstrated how “an investment in urban forests is an investment in the overall economic and environmental well-being of urban society”. In the most populous city in Canada, there are 10 million trees of at least 116 different species.

“From a bird’s-eye view, these trees appear as a lush green canopy that covers nearly 30 percent (190 km2) of the City of Toronto. The density of Toronto’s urban forest is on average 16,000 trees per square kilometre or about four trees per person in the city. The majority of Toronto’s urban forest is located in its ravines and river valleys, such as the Don Valley, Highland Creek and Rouge River watersheds, which have been largely undisturbed by the city’s expansion.”

In recent years, there’s been an increase in recognition of the environmental and economic benefits of urban forests. Because of this, Toronto’s urban forest is “viewed as an investment in the economic and environmental wellbeing of the city”.

The report said that each year, Toronto’s urban forest intercepts around 25 million cubic metres of wet-weather flow. Urban forests intercept falling precipitation in their canopy thereby increasing the amount of water absorbed into the ground and reducing soil erosion. “The annual cost savings this provides through reducing burdens on processing infrastructure and mitigating damage is valued at over $50 million.”

As for air pollution, Toronto’s urban forest removes around one-quarter of the annual emissions produced by industry within the city. That’s about 19,000 metric tons of air pollution removed from the atmosphere each year. “The amount of particulate matter removed by Toronto’s urban forest each year is equivalent to the amount released by over one million automobiles or 100,000 single family homes.”

The report estimated that the amount of air pollution abated by the city’s urban forest generates an annual savings of $19 million – just under $2 per tree.

Trees can also reduce the energy consumption of buildings by providing shade, evaporative cooling and blocking winter winds. The annual net cooling effect of a young healthy tree is equivalent to 10 room-sized air conditioners operating 20 hours a day. Each year, Toronto’s urban forest generates $6.5 million in energy savings for businesses and households.

“Reduced energy consumption also avoids 17,000 tonnes of greenhouse gas emissions from emissions intensive energy sources each year, providing an annual savings of $400,000 to $600,000.”

The forests also sequesters over 46,000 tonnes of carbon, equivalent to the annual carbon emissions from 31,000 automobiles or 16,000 single family homes. Properties in Toronto near green spaces have also increased in value.

“Rental rates of commercial office properties are about seven percent higher on sites having a high quality landscape that includes trees.”

“Maintaining our urban forests makes sense, as every dollar spent on maintenance returns $1.35 – $3.20 worth of benefits to residents of the City of Toronto. The cost savings produced by our urban forests make it clear that keeping the green on our streets, keeps the green in our wallets.”

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