The World in 2050_ Four Forces Shaping Civilization's Northern Future - Laurence C. Smith [55]
Might the southern Ogallala be saved by sound conservation measures, like converting to drip irrigation? “We don’t see it,” snorted Mulligan to my question. It sounds great in theory, but his well data show that in practice, converting center pivots from sprinklers to dripping hoses doesn’t slow the speed of the Ogallala’s depletion. Instead, farmers just run their new drip systems longer so as to pull out the same volume of water, resulting in the same net drawdown. The hard fact is that there just isn’t any way to save an aquifer whose natural recharge is one-half to one inch per year, when it is being drawn down a foot or more per year. Ironically, the single biggest benefit of drip irrigation to farmers isn’t delaying the Ogallala’s death but ensuring it, by allowing access to its last remaining dregs.236 These wells are the final straws into a doomed giant once thought to be invincible.
Oil and Water Truly Don’t Mix
Everyone knows that it takes water to get food. Less obvious is how much energy it takes to get water (for pumping, moving, purifying, and so on). And hardly anyone grasps how much water is needed to get energy. But like hopeless lovers, water and energy are inextricably intertwined. Pressure on water resources, therefore, is intimately linked to pressures on coal, oil, and natural gas resources. Except for wind and certain forms of solar power, even renewable energy sources demand a lot of water.
Power plants—regardless of whether they run on coal, natural gas, uranium, biomass, garbage, or whatever—use water in at least two important ways: to make steam to turn a turbine and thus generate electricity; and to get rid of excess heat. The single greatest demand for water in the energy sector today is for the cooling of power plants. Over half of all water withdrawals in the United States alone, slightly more than for irrigating crops, are used for this purpose. That’s a half-billion acre-feet of water per year (enough to flood the entire country ankle-deep in water) to cool off our power plants. In some parts of Europe the percentage of water withdrawn for energy production is even higher.237
The total amount of water needed depends greatly on the fuel used, on plant design, whether the water is recycled, the type of cooling apparatus, and so on. But in all cases the volume of water needed to operate the power plant is large, even greater than the volume of fuel. This is why plants are sited next to water bodies or perched over large aquifers. It’s not uncommon to find a coal-fired power plant on a riverbank hundreds of miles from the nearest coal mine: It is cheaper to carry the coal to the water, rather than the other way around. The Three Mile Island nuclear power plant, site of the 1979 accident described in the previous chapter, really is on an island, stuck out in the middle of the Susquehanna River.
Power plants bite into water supply by reducing both its quality and its quantity. Water recycled back into a river is hotter than the water withdrawn, sometimes by as much 25°C.238 For plants located on large bodies of water like the ocean, this doesn’t introduce significant environmental harm. Putting hot water into a river or lake, however, degrades aquatic ecosystems for many reasons. Warm water holds less dissolved oxygen, slows the swimming speed of fish, and interferes with their reproduction. Desirable cool-water species like trout and smallmouth bass are replaced by warm-water species like carp.
The second problem is water consumption, meaning irrevocable water loss. Most power plants use “wet” cooling towers—or even open ponds—to deliberately evaporate water into the atmosphere, providing cooling in the same way that evaporating sweat cools your skin. Evaporation losses from