The Role of Technology in Designing Green Infrastructure
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When we think of green infrastructure, we might not automatically think of technology. In fact, tech might be the farthest thing from some people’s minds when they see green roofs full of flowering plants, bees, butterflies, and chirping of crickets. But technology is having an increasing effect on green infrastructure, and I think we should leverage tech even more.
Where do we find tech in green infrastructure?
Understanding the energy benefits of green infrastructure is vital for GI to lower the carbon footprint of cities, and to help cool cities in summer. Leveraging technology to understand and design these systems can dramatically improve performance.
Monitoring green infrastructure (GI) is important in determining its efficacy. But monitoring isn’t easy, nor is it very common (most GI is not monitored). Monitoring usually involves placing multiple different types of sensors in and around green infrastructure. Traditionally sensors are connected by cables to a datalogger, and then data is retrieved, usually via internet. Sounds easy, right? Not so fast, sensors aren’t 100% reliable, neither is the internet, and excessive cable distances can exacerbate reliability issues.
Then once we see the data, what does it mean? That might be a difficult question depending upon sensor selection and placement. Let’s say if we want to monitor a green roof for retention; we’ll need to monitor rainfall (water in), soil moisture (water held), and runoff (water out). Monitoring rainfall is easy, usually via a rain gauge such as this one, but monitoring soil moisture can be really difficult, as most soil moisture sensors perform sub-optimally in coarse, highly porous green roof media. The most difficult part, though, is monitoring runoff, as flow meters are very unreliable in unpressurized drainage pipes, various apparatuses designed to insert into drains might clog or might not provide accurate data during high and low flows, and most buildings don’t allow for infrastructure such as tanks to monitor a single drainage area. So if we only monitor rainfall and soil moisture, which is common as those are the easier items, then our picture of performance is likely very incomplete, and inconclusive. Good monitoring is hard!
Fortunately sensor technology is developing quickly. Dr. Darko Joksimovic at Ryerson University is doing some great work using LoRa sensors. These sensors are true IoT (internet of things) devices, as they transmit signals over a low-power local area network. Most larger cities in North America have good LoRa coverage now (similar to cellular coverage), which makes this technology possible to leverage for monitoring GI. Low power usage solves a major problem with older technologies, and wireless signals solve the pesky issue of cable distances. Further, the price of these technologies is dropping, which will hopefully solve another monitoring problem: we need much more high-quality monitoring to better understand GI performance.
Monitoring and smart controls aren’t just technology deployed in the field, these technologies are critical to research laboratories such as Green Roof Diagnostics’ rain simulator. Photo: Green Roof Diagnostics
But why monitor at all? How does monitoring do us any good? Monitoring is critical to understanding actual performance. Cities around the globe are investing in and incentivizing green infrastructure, but often those investments assume that a green roof will retain a certain volume of rainfall, a volume that was likely determined based on a limited-scope and small-scale study. One jurisdiction (which I shall not name) over-estimates retention volume by a factor of two (retention values as “alternative facts”).
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These aren’t games where we win by plugging in the right number to get a permit; these are serious issues dealing with the health of our waterways! More effective monitoring of green infrastructure would start to close some of these factual divides. Further, engineers may be reluctant to trust GI due to lack of track record; monitoring establishes that track record. Worried we’ll monitor and be disappointed? From a research perspective, identifying what doesn’t work is often more valuable than identifying what does work, as those realizations are the fuel that propels the industry toward more reliable solutions.
Monitoring costs can vary widely, from inexpensive DIY systems to turnkey systems, which might range from $5,000 to $15,000. For most installations, that would add about $0.50 to $1 per square foot. Though the majority of monitoring benefits go to the industry as a whole, effective monitoring can easily be a worthwhile investment for building owners who want to improve plant performance, reduce irrigation costs, and confirm energy savings. These benefits can easily pay for monitoring within a few years.
Cross-section of the Polderdak smart control technology. Photo: Metropolder
Smart Controls pick up where monitoring leaves off. Irrigation systems were some of the first applications of smart controls in the landscape; by being “smart”. These use algorithms that determine what to do based on data, such as soil moisture, current weather, and forecasts. Metropolder is doing some groundbreaking work with smart controls in their Polderdak blue-green roof system. As blue-green roofs hold water in storage below the green roof, this allows smart gates or valves to allow just the right amount of water to drain, at just the right time to balance the needs of plants with runoff volume concerns in the neighborhood and city. Metropolder is actively involved in the RESILIO project in Amsterdam, which pilots using smart controls over an entire neighborhood. Talk about high-tech green roofs!
Engineering is another area where tech is sometimes involved in GI design… but not nearly often enough. If we think about some of the core aspect of information technology – large data sets, fast processing speed, ease of manipulating and understanding vast amounts of data – those are exactly the sorts of things we didn’t have many decades ago when most stormwater standards were written.
Hydrograph comparing two different green roof models against observed performance. One model (SWMM Bioretention LID in this case) is substantially more similar to actual performance than the other. i.e. in this case, one model more accurately describes the physical processes within the green roof. This knowledge is critical for designing effective GI, and is only possible via heavily leveraging technology for monitoring and engineering. Photo: Dr. Scott Jeffers
In more recent decades, computer modeling of stormwater design has become more common. But I’m confident in saying that only a fraction of a percent of green roofs were modeled during design. Why so few? Modeling is also hard! Programs such as the US EPA SWMM (Stormwater Management Model) are extremely powerful, but come with a steep learning curve. And with over 30 variables to populate for even modeling just a green roof, ensuring the values are correct requires a skilled hydrologist.
Green Roof Diagnostics is trying to solve some of these problems and make modeling more mainstream via web-based tools such as the retention modeler at purple-roof.com. Dr. Scott Jeffers is a SWMM specialist who is working on integrating SWMM equations into the retention modeler, which should improve accuracy and allow for modeling a wider range of scenarios. I think if more designers and engineers used modeling tools such as these, that green roof profile selection would improve such that profiles are more specific to their climate.
Most of us are probably generally familiar with climate modeling. Green roof stormwater and energy performance are best understood – and designed – via something closer to climate modeling than sizing a bucket. Instead, most stormwater design is closer to sizing a bucket. Though runoff coefficients and curve numbers may be applicable in other situations, green roofs are too complex and too dynamic to be represented by a single number. Following the train of thought three paragraphs up: these oversimplifications pre-date the benefits of current information technology.
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Let’s Embrace Technology in GI
We owe it to the next generation to get green infrastructure right! Technology is a big part of that.
A friend recently asked me what challenges inspire me to work in green infrastructure. I believe the two greatest challenges to humankind are 1) living in greater harmony with the environment, and 2) living in harmony with each other. I believe that green infrastructure is a critical ingredient of #1, and some other articles in this issue of LAM show that GI can contribute significantly to #2 as well.
But what does that have to do with technology? Living in greater harmony with the environment requires that we do our best to understand the environment and design solutions that provide the most benefit while creating little or no harm. Technologies such as monitoring, smart controls, and modeling can contribute immensely to both that understanding and design.
I’m so happy that I work on the marriage of GI and tech on a daily basis. Technology and green infrastructure get along great, and I hope this article inspires several of you to leverage technology in your green infrastructure work.
Brad Garner is a landscape architect, software engineer, and green infrastructure researcher. He leads Green Roof Diagnostics, where his specific focus is on monitoring, performance evaluation, and building hydrologic modeling tools for green roofs.
