Humans want to live peacefully in desirable locations, many of which are popular for their beautiful landscapes and other environmental features. But nature has a mind of its own.
Heavily technical construction projects require complex analysis and intensive planning before they begin. Despite major advancements in technology and civil engineering practices, “nature has a way of getting around it,” said Lily Baldwin, P.E., M.ASCE, president-elect of ASCE’s Environmental and Water Resources Institute.
That’s where nature-based solutions come in. The term refers to civil engineering strategies that use natural elements to protect communities and their infrastructure from environmental risks.
“Nature has a way of doing what it does, so rather than trying to work against it, why don't we consider how nature works when we're coming up with a solution?” said Baldwin.
Where nature-based solutions shine, said Baldwin, is in resiliency and sustainability. Highly customizable, nature-based solutions offer ways to keep projects aligned with their surrounding environments and allow them to rebound quickly after extreme weather events. Nature-based solutions leverage ecosystem services that once properly established require almost no input for a healthy and stable natural system.
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A creek maintenance project from her early career days exemplifies what can go wrong when civil engineers overlook the forces of nature. During the project, her team tried to address the eroding embankment under a bridge using traditional strategies of extending the hardscape, all of which “transferred the water from where it was originally eroding to the next spot along the riverbank.”
A similar issue occurred with a creek close to her home.
“Over a three-year period, I watched the flood control district rebuild the embankment several times after atmospheric rain events,” Baldwin said. “They would rebuild the slope and even reinforced it with netting and seeding. But the existing, straightened channel allowed the water to generate too much energy, and the embankment just kept eroding away.”
In the end, widening the channel allowed it to meander and spread out, dissipating the energy and creating “a much more aesthetic place to walk straight along this creek.”
“So it met the human requirement and the social requirement by reliably draining rain from the adjacent neighborhoods,” she added.
Offering flexibility
Choosing a nature-based solution is “all about location, location, location,” Vamsi Sridharan, Ph.D., M.ASCE, water resources manager at Tetra Tech, emphasized during an ASCE Engineers Week event.
The process begins with an assessment of the unique characteristics of locations where nature-based solutions are being considered.
“If you have different types of shorelines, there's different types of approaches with different footprints that are possible,” he said.
Some possible solutions are dune restorations, artificial oyster reefs, marsh restoration, and living shorelines – shoreline systems “engineered to mimic nature.” Relevant environmental factors include tides, winds, and the steepness of the land.
Solutions that may work in one type of environment could be completely unfit for another.
“There are certain solutions that will not work in very sloping lands. There are certain solutions that will, so if you have extremely aggressive slopes then you might consider solutions like riprap or some sort of step design with a geofabric that can protect your existing slope,” he continued. “But if you have more shallow slopes, you might consider solutions like a protective berm, marsh planting, rain gardens, and other natural solutions.”
Other important factors include erosion rates, currents and tides, and – for urban areas – whether there is adequate land for a nature-based solution.
“So that prioritization is essentially going to be based on what client needs are and what the risk profile of the region is, what the physical and nonphysical infrastructure they're trying to protect is, what the human resources that you're trying to protect are, and taking all of those factors into consideration,” Sridharan said during a follow-up talk.
Changing attitudes toward the concept
Nature-based solutions are gaining traction, but they haven’t always been a go-to choice for civil engineers.
“I don't think nature-based solutions are very new. But it's been a long road to change our mindset,” said Baldwin. “Though civil engineers have known about them for a while now, trying to figure out how to incorporate them into our more traditional projects can still be a challenge.”
Environmental shifts caused by climate change have brought attention to nature-based solutions as an option. The rising frequency and intensity of natural disasters have made it clear that humans must adapt their infrastructure to withstand these conditions.
“The challenge of our changing climate is we're going to be hit with things that are outside our traditional design,” said Baldwin. “We’re going to have a lot of hot days and cold days all within the same community. We're going to end up with a lot of water, and then none. Part of the challenge is building our communities to manage these extremes.”
She sees nature-based solutions as “a more resilient answer” to these challenges.
Coastal areas are particularly affected by climate events such as hurricanes and flooding, and an increased frequency of major storms has raised the stakes for these communities. Other changes, such as sea-level rise and land subsidence, present additional issues.
“If you are living in a coastal community, you have to accept the fact that there are going to be increasingly frequent coastal disasters and compound disasters where things merge – not necessarily having high-precipitation storm events happening on their own,” Sridharan said.
“You don't have storm surges happening as their own thing, high tide happening as its own thing. Invariably, you have a compound disaster that brings all of these things together and results in a perfect storm or a worse case,” he elaborated.
The effects of these storms don’t just hit coastal communities but can impact large swaths of society.
The amount of damage done, Sridharan said, “is very much a function of what sort of policy, programmatic, and structural risk-mitigation protections these communities can give themselves.”
Different environments call for unique solutions
With so many factors involved in infrastructure projects, choosing a solution is not always black and white.
Solutions are a spectrum, said Sridharan. A civil engineer might find that a purely nature-based solution is the answer to a problem, or a hard structure could be what is needed. In some cases, a combination works best.
