An Ounce of Prevention

Flood-conscious Construction & Remediation

As climate change brings on a higher risk of flooding, many municipalities, engineers, contractors, and builders have taken a proactive approach when it comes to flood preventative measures.

There is no denying that large-scale flooding is becoming more and more common. A CBC article referred to “record-breaking levels,” of Lake Ontario in 2017 which left a large area of the Toronto Islands underwater. That same year, another massive storm hit the same region, resulting in over sixty-four millimetres of rain in no more than a couple of hours. All that extra water caused roadways to wash out, sewage to back up, basements to flood, and vehicles to find themselves underwater. And they had no sooner cleaned up from that mess when the city got hit by yet another severe rainstorm which caused another round of flooding.

This is just one example of many similar water-related situations in recent years. Climate change has caused stronger storms and massive rainfall, along with rising water levels – a messy combination, to say the least, especially since the weather has become rather unpredictable at times, making it harder to foresee where the next flood will be.

Like many communities, preparing themselves to prevent the next potential crisis is the approach Toronto has taken with a “$1.25-billion flood-protection project” to “create a new river system capable of preventing catastrophic flooding in the surrounding area,” stated to the article.

These types of disasters have forced engineers to creatively come up with viable solutions for both avoiding and fixing these large-scale flooding issues. One technique that communities use is that of the berm, dike, or levee, a “man-made sediment barrier,” built to protect an area against potential flooding. The Alberta WaterPortal at albertawater.com is an organization that aims to educate the public and give them the information that they need to make informed decisions regarding water management. The organization says berms “are placed in flood-prone areas to protect against erosion, runoff and high water.” Typically, “berms are made of compost, sand, mulch, or gravel materials,” and “their density enables them to slow down and retain floodwater.”

However, berms are not always enough. The Dirt, a blog that reports on landscape architecture news, said that in a move to protect against “future superstorms and long-term sea-level rise,” New York City had planned to create a “set of landscaped berms around the southern tip of Manhattan.” The plan was called the ‘Big U,’ but after securing a substantial amount of funds and “four years of intensive community engagement,” the city suddenly changed its direction “in favor of raising the first proposed segment of the Big U – the waterfront park between 25th Street and Montgomery Street on the east side – by 10 feet.” The article said that instead of berms, “the existing 60-acre East River Park will be buried under the landfill, and its new higher edge will become a wall holding back the East River, which is expected to rise with the Atlantic Ocean by 2.5 feet by 2050.”

New York City is not the only municipality looking at ways to prevent future flooding. Even communities located safe distances from the shore find themselves concerned with potential flooding because, as water levels rise and huge amounts of precipitation fall, drainage becomes an issue no matter where you live.

For this reason, many municipalities now conduct and rely on studies to determine flood-prone areas, and decisions concerning new builds are made with that data in mind, discouraging new builds in risky areas. Some municipalities now require that all new builds be done at a certain elevation above the flood-zone in flood-prone areas.

One obvious problem is that stormwater runoff can overwhelm city sewers and is hard on streams and rivers. The most cost-effective way to deal with stormwater is to get to it near its source by building a basin to collect the water. Water can then be released gradually to avoid eroding and flooding the neighbouring area.

It comes down to planning. Level, the “sustainable building authority set up by the Building Research Association of New Zealand (BRANZ),” says that there are several important decisions that need to be made before building in a flood-risk zone, including whether or not it is even possible to do safely and, if so, where the building should be constructed to be safe.

“According to Level, construction companies can make the most of what drainage is already available by building on the highest part of the site and keeping clear of existing natural drainage channels. Additional drainage can be added to low-lying areas to help minimise potential water build-up,” said New Zealand trades recruiter Tradestaff.

A 2016 article at the green blog The Earthbound Report highlights five things to look for when trying to build a flood-proof home: elevation, floodwalls, dry floodproofing, wet floodproofing, and floating homes. Elevation ensures that the building foundation is higher than the predicted floodwater height. Floodwalls are strong, waterproof walls. Dry floodproofing is done by making the walls of the house watertight and can be done in several ways including using sealant or “building in a waterproof membrane,” says the blog. In wet floodproofing, potential water damage is minimized by “fitting a solid floor rather than wood, moving power outlets up the wall, and ensuring that any unmovable furniture is made of a material that can safely take a soaking,” and “if your house can float, it’s guaranteed to always be above water.”

And no matter where you live, all homes should have a back-flow valve installed to avoid sewer backup. In many municipalities, this is now mandatory in new construction.

When it comes to preventing flooding, another important factor that might be overlooked is trees. One tactic that many forest product companies and private timberland owners have used over the last several decades is planting new trees in the hopes of countering erosion as a result of clear-cutting. The website of forestry company J.D. Irving states that it has planted over one billion trees since 1957.

Trees keep soil from breaking apart, and soil can then hold water in a sponge-like fashion. Roots take up water, preventing the water level of rivers and streams from rising as much. And surprisingly, even the leaves on trees help in flood prevention because they lessen the force of the rain hitting the ground. The harder the rain hits the ground, the more erosion it can cause.

Among those other benefits, common knowledge is that trees also clean the air. A study published in the journal Science with the goal of establishing whether or not restoring forested lands is a good strategy for mitigating climate change found that “earth’s ecosystems could support another 900 million hectares of forests, 25 percent more forested area than we have now. And that by planting more than a half-trillion trees, we could capture about 205 gigatons of carbon, reducing atmospheric carbon by about 25 percent, which would be enough to negate about 20 years of human-produced carbon emissions at the current rate, or about half of all carbon emitted by humans since 1960.”

And when it comes to flood prevention, not only do trees make a difference in the country, they also contribute to decreasing flood damage in cities where water cannot soak into paved surfaces.

Some cities have incorporated a mindset of flood-friendly greenery by adding a splash of green in non-conventional ways, such as a ‘green roof’ on government building rooftops. A green roof controls flooding by having rainwater absorbed into its roof plants instead of rolling off the roof, falling to the streets below. And a bonus to this concept is that green roofs last longer as they protect the underlying roof from extreme temperatures and harsh UV rays. In other words, a green roof has double the life expectancy of a traditional roof.

As they say, “An ounce of prevention is worth a pound of cure,” and when it comes to protecting buildings and infrastructure from flood damage, the more planning that goes into it, the less damage there is likely to be.

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May 31, 2020, 10:22 AM EDT