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Where has all the water gone?

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POSTED: April 5, 2007 5:15 a.m.
It is impossible to use up water. When it is used, it doesn’t disappear. There is as much water on this planet today as there was thousands of years ago. When it rains, the water evaporates or it runs to streams or underground reservoirs. It’s hard to make it do anything else, except temporarily. Likewise, when water from a stream is used, it returns to a stream or evaporates.
The water from your tap goes back to a stream, even if you drink it. If you water your lawn, wash your car or empty your sink, the water goes back to a stream. Some of the water metro Atlanta uses goes to its sewage treatment plants, where it is held temporarily and released more or less clean.
That “more or less” is a reasonable concern for downstream neighbors: How clean is clean enough? But they ought not complain about Atlanta “using up” their water.
Atlanta’s basic problem, apart from downstream neighbors’ concerns, is that it may attract enough people and industry that there won’t be enough water for everybody to use in the short period before it is returned to the streams. There are many facets of the argument but the question of whether Atlanta is using up water can be asked in two ways: Is it logical, and does the evidence support it?
First the logic: What is happening, or can happen, to the water? If there are only two choices, evaporation or drainage back to a stream, Atlanta would have to evaporate a lot of water to keep downstream neighbors from getting their share.
Perhaps Atlantans do evaporate a lot of water. Sprinklers used to water lawns and golf courses allow some water to evaporate, but by far the greatest evaporation comes from plants, trees, shrubs and lawns. Land covered with vegetation can evaporate one- to two-tenths of an inch of water on a sunny, summer day or, about an inch per week.
On the other hand, land covered with buildings and pavement — streets, highways and parking lots — evaporate no water except just after a rain. Even bare ground evaporates a small amount compared with vegetation. According to Atlanta’s Clean Water Initiative, natural ground cover evaporates 40 percent of total rainfall; urban development, just 5 percent. A large-scale analysis of the Chattahoochee basin above West Point shows that a 20 percent increase in forested area from 1919 to 1967 resulted in increased evaporation of about five inches per year. That is five inches less of rainfall equivalent to the flow in the Chattahoochee.
So it may be said — heaven forbid —that the increased paving of Atlanta saves rainwater for downstream neighbors. And it reaches them quicker, being streamlined through gutters and sewers back to streams.
Now consider the direct evidence: Flow of major streams supports the logic. Atlanta’s main source of water is, of course, the Chattahoochee. The headwaters of three other rivers — the South, Yellow and Flint — are in the Atlanta area. The Etowah, which flows westward into the Coosa, supplies some of the northern suburbs.
The U.S. Geological Survey has measured these rivers’ flow for a long time, at some places back to about 1900. If Atlanta is using up the water, the stream flow should have been greatly reduced.
It has not. In fact, the flow of the Chattahoochee at West Point hasn’t decreased appreciably since 1900, indicating that whatever it is that changes the flow of the river — mostly weather and the building of Lake Lanier — cannot be attributed to Atlanta’s growth.
A sticking point in Georgia’s negotiations with Florida and Alabama appears to be how much water can be released from Lake Lanier. Unfortunately, Lake Lanier is the 90-pound weakling when it comes to supplying Florida’s Apalachicola Bay with fresh water. Yearly flow of water past the Buford Dam site has not changed since 1943, except for annual ups and downs. In all that time it was just 9 percent of that flowing into the Apalachicola River below the Georgia line. Nor are the low flows in the Chattahoochee nearly as low or as numerous as they were before Lake Lanier was built in 1957.
Above and below Atlanta, the Chattahoochee flows much as it did in 1900, when there were about 90,000 people, compared to today’s estimated 3 million.
So: Are downstream neighbors worried about Georgia using it up; polluting it ... or is it just the potential for future strangulation? It isn’t clear to most Georgians what this complicated “water war” is all about. But it is abundantly clear, from a few basic facts, that Atlanta is hardly about to dry up the Chattahoochee River.
 

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