Category: green infrastructure

Green infrastructure provides a viable alternative to seawalls for storm surge risk

Green infrastructure provides a viable alternative to seawalls for storm surge risk

By Will Bugler

Parks, green spaces and plant-covered hills are an effective defence against storm surges and tsunamis according to a Stanford University study. The research concludes that carefully engineered green infrastructure can offer similar levels of protection as large seawalls, while also benefiting for marine and coastal biodiversity, the aesthetic environment, and reducing costs.

The study, published on 4th May in the journal Proceedings of the National Academy of Sciences, quantified how tsunami waves of different heights interact with structures of various sizes and shapes at the coast. The research calls into question the wisdom of conventional approaches to coastal storm management, which are dominated by hard infrastructure development such as construction of large seawalls.

Three examples of tsunami mitigation parks along the ring of fire that are currently being planned and/or constructed in South Java, Indonesia (image courtesy of A.M.); Miyagi Prefecture, Japan and Constitución, Chile. Miyagi prefecture image and Constitución image credit: Morino Project and Felipe Diaz Contardo (photographer).

Seawalls have many disadvantages. They are expensive and inflexible, so they are hard to adapt if, for example, sea levels rise by more than expected. They can also damage marine ecosystems, and damage local economies in sectors such as fishing or tourism.

“If the wall collapses, the consequences are life shattering,” said senior study author Jenny Suckale, an assistant professor of geophysics in the School of Earth, Energy & Environmental Sciences. “Seawalls can not only create a false sense of security that can discourage swift evacuations. They can also end up breaking apart into blocks of rubble that tsunami waves then toss throughout a city.”

“It’s sort of intuitive that the moment you see it as a threat, you build a wall,” Suckale said. But while it’s true that seawalls can address some tsunami risks, the factors that make a place livable can be far more complicated. Most coastal communities want to maximize their well-being, not minimize their risk at the expense of everything else,” she said. “Do you really want to live behind a huge concrete wall because there is a small chance that a big tsunami will hit you? Let’s put more options on the table and have an informed debate.”

Green infrastructure must be carefully designed

When considering alternatives to sea walls, the study found that green infrastructure solutions needed to be carefully designed and well built in order to deliver the desired levels of protection. The study notes that while coastal forests offer protection against storm surges, it takes decades for trees to grow large enough to offer robust protection, and they are not viable in some areas where protection is most needed – such as to protect vulnerable towns and cities.

The study noted that as much attention needs to be paid to the design and engineering of green infrastructure as to conventional infrastructure development. According to the study, vegetation alone, has little effect on an incoming wave’s energy. However, plants play an important role in fighting erosion, thereby helping to maintain the shape, height and spacing of hills and mounds, which do offer significant protection.

Suckale says that to date, green infrastructure has been designed more for aesthetics than for performance. “Our study shows that design matters. There’s a wrong and a right spacing; there’s a wrong and a right shape,”

“You should not use aesthetic criteria to design this. Right now, our designs are not strategic enough,” she said. “This paper is a starting point for understanding how to design these parks to derive maximum risk mitigation benefits from them.”

To test the efficacy of hills and mounds in providing coastal defences, the researchers modelled what happens when a tsunami wave hits a single row of hills. They found that mounds reflect and dampen a tsunami wave’s energy about as well as a seawall. Hills were also found to perform equally well in the case of a very extreme event – a one-in-a-thousand-year tsunami. As a result, the study concluded that there is little extra value in combining hills with seawalls.

Along with improving the design green infrastructure, the study also recommends that more space should be given between urban development and the water’s edge. The researchers note that homes and infrastructure should be set back with a broad buffer zone between them and multiple staggered rows of hills that are larger toward the shore and smaller inland.

Read the study here.


Cover image Sunabe seawall, Okinawa, Japan
Urban floods: We can pay now or later

Urban floods: We can pay now or later

By Michael Drescher, University of Waterloo

Wild weather seems increasingly widespread these days. Cities are especially vulnerable to extreme weather, meaning that many of us will end up paying for the damage it can cause.

But how much we pay — and when — is largely up to us. We could, for example, pay now to prepare ourselves and limit future damage, or we can pay later to repair our properties and restore the environment.

Urban flooding — and other complex, environmental challenges — can be solved when communities work together to share their experiences and knowledge. In Canada, the Faculty of Environment at the University of Waterloo is taking the lead on this as part of the UN Sustainable Development Solutions Network.

Urban floods on the rise

Many factors contribute to the increasing risk of flooding in urban areas. For one, in many regions climate change seems to be causing more intense downpours than what have occurred in the past.

This is a problem because the storm-water systems built just a generation ago were not designed to handle the amounts of rain we are seeing now — and expecting in the future.

The growth of cities also contributes to urban flood risk. The increased construction of hard, sealed surfaces hinders rain from soaking into the soil and causes runoff. If there is too much runoff, the water pools and enters our lakes and rivers, dragging oil, metals, road salt or pesticides with it.

Or it can turn into a flood.

The density of sealed ground continues to grow in urban areas. We just keep on adding more houses, more roads, more parking lots. From 1991 to 2011, the built-up urban area in major Canadian cities increased by more than 20 per cent.

On top of that, houses are being built closer together and they get ever bigger. More than half of the homes built after 2001 are larger than 140 square metres. When you factor in that these new homes come with patios, parking pads, driveways and sidewalks, it’s no wonder we have a problem.

Level of preparedness

Unfortunately, city dwellers, by and large, are not well-prepared for urban floods. A recent study found that most people do not know if they are living in flood-prone areas and, if they do, many do not take measures to protect themselves against flooding.

They may not know that many home insurance policies do not cover water damage from flooding, but only damage from broken pipes or similar issues. Or if the policies do cover flood damage, that the coverage might be limited.

And governments may refuse to bail house owners out, so to speak, if they could have purchased insurance add-ons that do cover flood damage.

Even so, most municipalities do not address the issue of urban floods as effectively as they could — maybe because their budgets are too strained to act or they have other, seemingly more pressing, priorities.

Recently, flooded-out residents in Ontario have filed lawsuits against their municipalities, and a few years ago in Illinois, a major insurance company filed nine class action lawsuits against municipalities over this.

How can homeowners prepare?

It is not a question of whether wild weather will affect your neighbourhood, but when. Somebody will pay for it — and it might be you.

You could pay upfront to protect yourself against damage or afterwards to fix it. There are a number of things that people can do to protect their homes, their neighbourhoods and the environment against the damages caused by urban floods:

  1. Purchase add-on flood protection with your home insurance.
  2. Keep the water from getting in. Covers can prevent water from rushing in through basement window wells, and foundation grading can direct surface water away from your house. You could also install a sump pump or sewer backflow prevention system.
  3. Install on-site water storage to collect and store rainwater for safe release later. Some municipalities sell rain barrels; larger water storage tanks are even better.
  4. Green infrastructure solutions can slow down rainwater runoff and help the ground soak up the water. Rain gardens — specifically designed depressions with plants for increased water infiltration — and green roofs are options. Patios and driveways can be built with permeable pavements.
  5. Talk to your neighbours, your neighbourhood association and your city councillor about urban floods. These strategies work best when many people in a neighbourhood take action together.

Change can be expensive, but municipalities are increasingly providing tax incentives or financial assistance to pay for some of them.

Nothing will provide 100 per cent protection against the potential losses from urban floods, but planning ahead reduces the odds that you will be flooded and may reduce your costs when a flood does occur.

The ConversationThe neat thing is that by acting with foresight and heeding this advice, we can protect ourselves, protect our neighbours and protect the environment, all at the same time.


Michael Drescher, Associate Professor, University of Waterloo. This article was originally published on The Conversation. Read the original article.

Cover photo by Fred/flickr (CC BY-SA): Flood waters rise in the Montreal neighbourhood of Cartierville in May 2017.