Big risk of living in known natural disaster areas

May 20, 2011

In the wake of disastrous Mississippi River flooding, you might wonder why presumably reasonable people continue inhabiting a known flood plain. Other devastation unleashed by nature this year suggests that much of the planet seems fated to be violently shaken, engulfed by wildfires, lashed repeatedly by tornadoes or inundated by seasonal downpours. Is land suitable for agriculture, industry or building homes so scarce that we must populate geologically and climatically vulnerable landscapes?

In fact, scarcity of land that is intrinsically safe and appropriate for development is usually not the reason people settle in places at risk. Other motivations explain our persistent defiance of Mother Nature.

Hope fueled by optimism tops the list. Despite predictions based on nature’s documented history, scientific research and calculated probabilities, people tend to think that natural disasters, while possible, will somehow not occur or affect them. This is a form of denial, a common psychological response in the face of potential adversity.

Although generally aware of nature’s threats, many have faith that technology will effectively resist and even control natural forces. Indeed, designing and constructing buildings requires confronting nature to successfully withstand gravity, wind, earthquakes and moisture. Likewise, dams, levees and diversion channels are built to manage the flow of water and control flooding. Yet, our best technical efforts can never completely avert catastrophic outcomes.

Aesthetic benefits — scenic views, beautiful natural surroundings, proximity to desirable recreational amenities, desire for privacy — induce people to inhabit risky sites. This is why expensive homes get built on steep, potentially unstable slopes or escarpments subject to erosion and mudslides; next to shorelines and beachfronts susceptible to destructive hurricane-force winds and storm surges or in arid climates on parcels covered with dense, oil-rich vegetation that can easily catch fire and rapidly burn.

People also willingly discount nature’s threats to property because of expected economic benefits. Such property might be relatively inexpensive but usable. It might encompass exploitable natural resources and have access to nearby commercial markets. Why else would one develop and cultivate land downstream from a designated spillway in Louisiana, land slated to be purposely inundated in the event of a 100-year Mississippi River flood?

Strong sentiment and a profound sense of rootedness might be the most powerful motivations for people’s willingness to place themselves in harm’s way. Affection for a familiar place and emotional ties to the land, to its culture and traditions, can trump concerns about nature’s possible threats.

Ever since learning to read, I recall seeing yearly springtime news reports about the Mississippi River overflowing its banks and wreaking havoc on levees, farmland, homes and towns. The same tragic reports and photos appeared year after year. And, evidently afflicted every year by the Mississippi’s inevitable rise, flood victims with insurance file claims to cover rebuilding, often in the very same flood plain. Regrettably, these properties, settled decades ago, remain chronically at risk. Neither property owners nor governments can afford the expense of relocation.

Fortunately, in recent decades, adoption of rational land-use policies have curtailed building in some high-risk, environmentally fragile locations. Federal, state and local regulations generally prohibit development within designated flood plains and wetlands. There are constraints on use of property abutting streams, rivers and coastal shorelines; on sensitive wildlife areas; and on sites with contaminated or unstable soils. Many municipalities limit removal of mature trees, clear-cutting of forested areas and construction on steep ground. Sensitivity to preservation and sustainability concerns is higher than ever.

Building codes also have evolved to mitigate threats imposed by nature. Today, structures must be engineered to withstand probable forces generated by earthquakes and hurricane-force winds. But being designed for “probable” forces does not mean a structure will resist all forces. An improbable yet possible seismic jolt or cyclonic blast can generate stresses far exceeding a building’s maximum structural capacity, tearing it apart. And making a building strong enough to resist any and all forces would be prohibitively expensive.

Unforeseen structural stresses were generated last month when hundreds of tornadoes swept across dozens of southeastern states, decimating buildings never designed to withstand tornadic wind velocities. The March earthquake in Japan created a tsunami far exceeding the size of the “probable” tsunami for which the coast’s seawalls were built. With seawalls breached, thousands of structures along the coast received a double whammy, damaged first by earthquake forces and then destroyed by powerful torrents of water.

Sometimes faulty judgment or execution, rather than extraordinary natural forces or sub-optimal construction, can lead to devastation. Such was the case last month when management at Washington Harbour in Georgetown did not have flood walls elevated when the Potomac River flowed over its banks.

We live on this planet facing lots of risks ranging from probable to highly improbable — wet basements, ants in kitchens, roofs leaking, inattentive motorists, falling meteors. Try as we might, we can never live risk-free. All we can do is assess risks and take prudent steps to avoid or minimize them. And, clearly, one such step is not to inhabit flood plains.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.

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