How long do you think our civilization will last? Are we smart enough to last forever? Can we afford it?
Being civilized costs money, and ongoing costs ratchet up with each new structure. Roads, dams, and cities need maintenance and repair. TVA is spending about $6 million to raise the height of four dams. Those dams were designed to withstand what is called a "probable maximum flood," which is what would happen if the worst imaginable storm parked itself directly over the Tennessee River Valley. Hydrological data has gotten more accurate and detailed since the dams were built, and when TVA recalculated its flood risks with this new data, it discovered that several dams that include earthen banks could be overtopped during a maximum flood. This could erode those banks and cause a catastrophic collapse of the reservoir.
A TVA hydrologist said such conditions are so unlikely, they occur about once in a million years. Maximum floods do happen, but they are typically localized. When Hurricane Frances hit Asheville in 2004, a few unfortunate hollows in the surrounding mountains reached maximum flood levels. The result was mudslides, homes destroyed, and lives lost. Downstream the flooding was bad, but it was within the 100-year risk level, and TVA had no problem managing the flow once it reached their dams. For maximum flooding to happen in the main river channel, it has to happen everywhere upstream. Such a storm would bring unimaginable destruction, but TVA intends for its dams to survive.
Engineering for the worst-case scenario is a good strategy for things like dams and bridges and houses, but we have different standards of longevity for each. To keep homes and buildings out of flood danger, we no longer allow building within the 100-year floodplain of any creek or river. Bridges and roads are usually engineered to accommodate 500-year floods. The highest design standard is the probable maximum flood. While it might make sense to spend a few million to prevent billions of dollars worth of future damage, when you start to think about how far off that future might be, you have to wonder.
We speak of having a century's supply of oil in the ground as if it's good news, and the coal industry brags of being able to provide energy for 700 years. Those numbers are tiny compared to TVA's engineering standards, but they are short relative to human history. It was about 700 years ago that Europeans exhausted their supply of pelts and started colonizing new lands.
I often wonder what Americans were thinking 150 years ago when they decided to slaughter billions of passenger pigeons. Surely they did not intend to forever deprive us of a major food source, but their poor foresight caused the bird's extinction. Laws of supply and demand did not save passenger pigeons, and they have proven poor at protecting wild fisheries and game animals. Only when we control production are we good at matching supply with demand. When nature provides, we tend to exploit the resource rather than conserve and sustain it.
Are we looking far enough into the future to properly value natural resources? We know oil, coal, natural gas, and uranium are finite resources. How long should those supplies last?
The next ice age is scheduled to arrive in 30,000 years. TVA's hydrological data will be worthless then, and it may be obsolete in a few decades if carbon pollution continues unabated. Should we really care whether flood computations done 50 years ago were off by a couple feet? TVA's dams will probably need to be replaced due to wear and tear long before a flood overwhelms them.
When I imagine how future generations will view us, I suspect the unfortunate crop who experience a maximum flood will forgive us if a TVA dam is on the list of casualties, but the folks who ring in New Year's Eve 2999 will surely damn us for all the oil and coal we burned.