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Defensive Design for Resilient Landscapes

Colorado is the third most wildfire-prone state, according to data compiled by the Insurance Information Institute, with 366,200 homes at high or extreme risk from wildfires last year. In 2017, nearly 111,670 acres were burned in wildfires. The Waldo Canyon Fire in 2012 was among the costliest wildfires nationwide since 1991, III found, with an estimated insured loss of $450 million.

The floods and mudslides that follow wildfires are just as devastating. The 2013 floods that swept through over a dozen Colorado counties destroyed 1,800 homes and caused $4 billion in damage—and cost 10 people their lives.

Although these natural disasters are unpredictable, there are ways landscape professionals can help reduce the impact these events have on their clients’ homes.

Natural resiliency

Resilient design is the principle that working with nature instead of against it can make homes and communities stronger and better able to withstand crises of the “acts of God” variety.

The American Society of Landscape Architects has a guide on resilient design that suggests ways that landscape architects can design spaces that can bounce back following a disaster.

Resilient design combines high-tech mitigation efforts like installing remote sensors to track humidity, wind and vegetation density, with low-tech strategies like designing defensible spaces around structures, ASLA recommends.

One of the challenges to resilient design is that every property is different, so landscapers who want to integrate these principles into their projects need to start from a blank slate with each project.

“Designing for resilience is really site specific,” Bill Melvin, owner of Ecoscape Environmental Design in Boulder, said. “Each property has its own challenges, whether it is going to be the potential for flooding, for fire, for earth movement.”

As such, landscape designers need to take a “multilayered approach toward working with the challenges of each site.”

Landscapers on the Western Slope are working in a more challenging region than other parts of the state. “The mountains, for better or worse, are more prone to the fires and the floods, and more damage naturally due to their geographical location and their terrain. Everything becomes compounded when you have slopes such as we do in the Foothills,” Melvin added.

Melvin said water diversion and fire mitigation practices are always common topics of discussion with his clients depending on the property they live on.

“So much of it entails analysis of the landscape; having a trained eye to be able to read the current needs, but also potential future needs for the property, for the plants, for the soil, for the typography,” he said.

Fires are natural part of ecosystem

The Colorado State Forest Service notes that wildfires are a natural part of the ecosystem and contribute to healthy forests. The agency estimates there are an average 3,189 wildfires in Colorado every year, 97% of which are contained before they spread to 100 acres.

Unfortunately, as more area is developed for residential and commercial use, more people are living and working in the wildland-urban interface (WUI), where man-made structures meet forested land and flammable vegetation. CSFS estimates that more than 2 million people live in the WUI and could be put at risk during a fire.

Fire suppression tactics taken by the Forest Service 100 years ago had a detrimental side effect on Colorado forests by preventing them from thinning naturally, according to Melvin. Ironically, those fire suppression tactics mean unthinned forests are at risk of more devastating fires as there’s more fuel for a wildfire.

Furthermore, some species of plants rely on the effects of natural wildfires to survive. The lodgepole pine, for example, propagates when its cones are exposed to extreme heat and the cones release seeds.

“Fire is a natural part of our ecological regimen for maintaining our forest,” Melvin said. “We have this perfect storm, along with the drought of the century. When you combine that with the onset of a 20-year mountain pine beetle cycle, the 2000s was a really challenging time for our forest ecosystems.”

Fighting floods

Melvin saw first-hand the impact that the 2013 floods had on homeowners, noting that several of his customers “came through it pretty well.”

“Grading and drainage has to be the first priority of any landscaping site, making sure you’re redirecting the water, one, away from the structure; and two, ideally, where it can be utilized, whether that’s a small retention pond or rain garden or swale that is skirting the perimeter of the house.”

Swales can help divert or capture water and even create microclimates for plants that need more water than they would get naturally in Colorado landscapes, Melvin said.

Berms, retaining walls and check dams can help divert earth movement and floodwater away from a property. Sometimes clients will contact Ecoscape asking for these types of installations, and sometimes the team recommends putting in some type of mitigation after visiting the site.

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“We’ve had clients come to us and say, ‘We really want a free-standing wall to deflect future floodwaters,’ and clients whose properties … we’ve analyzed and determined that they’re adjacent to a flood plain and have recommended doing some extensive earthworks,” Melvin said.

If you doubt the impact these strategies can have on a client’s home, consider this experience Melvin had with one of his customers.

“After the Four Mile Fire, we did have a client who brought us in to do a large-scale project over about four acres of land that was a steep ravine,” Melvin said. “We used the burned trees, felled them on the slope and created a series of about 15 check dams along with logs we laid on contour bunds. That was in preparation for soil movement.

“In the end, we had some huge deluges, and we estimated that those check dams caught over 10,000 yards of earth. It ended up saving his house because the soil came within about one inch of broaching his sandbags and taking out his home.”

Melvin said the project cost between $10,000 and $15,000, but was worth so much more to his customer. “In the end, it saved him not only that much damage in his house, but also the interruptions of life: having to move out [and] restore his house that he had been in for about 45 years or so.”

This article originally appeared in our sister publication, Colorado Patio & Landscape


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