Design for resilient infrastructure

While it may seem that natural disasters are becoming more frequent and more severe, it isn’t necessarily so. However, more people are moving to areas that are exposed to flooding, tidal waves, and other natural disasters. That makes any one event more destructive —there’s more infrastructure in the way, so the potential loss is greater. Resilient infrastructure can mitigate the consequences.

In “Counting the cost of calamities,” The Economist stated, “The world has succeeded in making natural disasters less deadly, through better early-warning systems for tsunamis, better public information about evacuation plans, tougher building codes in quake-prone areas and encouragement for homeowners to adopt simple precautions such as installing tornado-proof rooms in their homes… [A]djusted for the Earth’s growing population, the trend in death rates is clearly downward.”

One thing after another

Hokusai’s famous wave is a tsunami–a wave generated by an earthquake. Natural disasters don’t always come singly. Resilient infrastructure needs to resist more than one disaster at a time. Shutterstock image.

Structural design has traditionally examined one thing at a time. The engineer considers the loads due to earthquake and wind, say, as separate load cases. Whichever load case results in the greatest load determines the design and detailing of each member.

But some kinds of disasters either go together or follow shortly after others. For example, hurricanes entail high winds, heavy rains, and often storm surges as well. If a bridge resists the wind loads only to wash away in the flood that follows, it hasn’t withstood the hurricane.

Similarly, an earthquake in a seabed will cause a tsunami. A hill in southern California may experience a wildfire in the summer and mudslides the next winter, when there is no vegetation to hold the soil in place during the winter rains. Hurricane Sandy on the east coast in 2012 precipitated both floods and fires.

For truly resilient infrastructure, we need to consider how natural disasters actually occur–and prepare for the whole event, not just one part.

Building codes and zoning matter

Although there are measures individuals can take to prepare for natural disasters, government has perhaps the most important role. In Climate Adaptation Engineering, Bastidas-Arteaga and Stewart distinguish among fragility, vulnerability, and exposure. Building codes can specify more robust construction to reduce fragility. That way if an extreme event occurs, it is less likely to cause damage. Vulnerability is often expressed in terms of the loss due to a specific hazard, such as water rising to a specific elevation in a flood.

Zoning laws can prohibit construction in a floodplain, thus reducing exposure. For example, the city of Toronto, Ontario, and the surrounding area are cut by several ravines. Despite the population density in this large metropolitan area, the ravines remain mostly in their natural state. A major hurricane in 1954 caused massive flooding in the ravines, destroying neighborhoods that had encroached on the ravine lands. Since then, there has been an almost complete ban on building in the ravines. Instead, they serve as parkland, providing green spaces in the city.

The Army Corps of Engineers has spent billions of dollars on dams and levees along the Red River, with more to come. The latest plan involves a dam and a series of levees upstream from Fargo, North Dakota, and a 30-mile channel to divert flood waters. A combination of public- and private financing will pay for the construction.

Flooding in Houston–again

Harvey was the third “500-year” rain event to hit Southeast Texas in three years. This week, Tropical Storm Imelda also earned that distinction, as some areas received more than 40 inches of rain, paralyzing the area as highways morphed into parking lots and first responders performed more than 2,000 rescues Thursday alone. And many residents are now asking themselves: Is Houston worth it?–Houston ChronicleSeptember 20, 2019

Floods in Houston are becoming more frequent and severe, with multiple events every year. The current flood-control strategy is essentially to divert water into the streets. Development of farmlands in the surrounding area means that water runs off rapidly rather than seeping into the ground.

In October 2019 the state of Texas received a federal block grant of $4 billion for flood mitigation infrastructure. According to the governor’s office, the funding will support “large-scale, regional projects that increase the state’s resilience to disasters statewide, protect lives and mitigate against future hurricanes and other natural disasters.”

How governments can encourage resilient infrastructure

In “The rising cost of catastrophes,” The Economist recommends three things governments should do to prepare for natural disasters:

  • Prioritize preparedness rather than wait to respond after disaster strikes. That is, local governments must have shelters in place already and keep them well maintained. This is easier if the shelters are part of the normal infrastructure, such as a school auditorium.
  • Protect natural defenses with zoning laws and other restrictions. Too much paving results in rapid runoff because the water can’t drain into the soil. Building in floodplains leaves infrastructure vulnerable to flooding. Where the risks for such actions must be borne by the public as a whole rather than just the private owner of the property, governments have a role to play in regulating land use.
  • Eliminate perverse incentives that encourage construction in floodplains or in landslide-prone areas. Often government subsidizes flood insurance or provides relief after a disaster, encouraging homeowners to rebuild in the same hazardous area. Why keep doing the same thing while expecting the results to be different?