Oceanography

The water locked in ice, mostly in Antarctica and in Greenland, is about 1.5 percent of the water in the oceans. But the oceans are so vast that 1.5 percent of them is still a great deal of water-about 5 billion, billion gallons. If we could melt the ice and run it into water mains instead of drawing from rivers, there would be enough water, before Antarctica and Greenland were stripped to bare ground, to take care of needs for thousands of years at the present withdrawal rate. The barrier to using melt-water at the present time is economic. Energy is required to melt ice and there would have to be some way of moving the water to places where it would be used, a further addition to the cost.

The idea of using the ice caps is not so far from being economically reasonable as one might suppose. A fascinating suggestion was made by Professor John Isaacs of Scripps Institution of Oceanography-to tow an iceberg from Antarctica, and collect the fresh water as it melted offshore of water-starved southern California. Isaacs estimated that two battleships would be required for towing the ice to San Diego. The project has not yet gone forward, but it is not because the towing costs would be too high, nor because the iceberg would melt en route, nor because the amount of water gained would not be a significant addition to the local supply. Instead the difficulty is the lack of a way to collect the fresh water as the iceberg melts. That particular problem is a difficult one but apparently not impossible to solve, because the melt-water from an iceberg is less dense than salty sea water so the fresh water would tend to float on the sea water surrounding the iceberg and might be collected before the two mingled.

A good sized iceberg may rise one hundred and fifty feet above the sea with seven hundred feet or more beneath the surface. A cubic iceberg eight hundred feet on an edge would melt to about three and a half billion gallons of water, or about 1 percent of the entire daily United States demand. The population of San Diego County is just about 1 percent of United States population. Therefore, if all the water could be collected from an iceberg, San Diego County needs could be served but an iceberg every day would be needed to do the trick! At any rate, it is comforting to know that the great glaciers and icebergs exist, and that an increasingly clever technology may some day solve the cost problem.

A scheme akin to Isaacs’ in imaginativeness, but further from possible achievement, has been proposed in which large ice-balls would be sent by pipeline from Antarctica to Australia, the heat of friction melting them en route so that they would arrive on Australian croplands as ready-to-use irrigation water.

The amount of usable water in lakes is only about 0.3 percent of that contained in glaciers, but lakes are ordinarily much more conveniently located. Their water can be used without supplying, by one means or another, the tremendous amounts of energy required to melt large masses of ice. The lakes of the world contain about as much water as flows down all the rivers in a year. Lakes are delicate systems; if we began to use them faster than they are replenished, the effects would be so complex and far-reaching that it is almost impossible to estimate what all the consequences would be. If we started to draw water out of Lake Erie, for example, at a tremendous rate, the normal outward flow down the Niagara River would be halted but the inflow to the lake would not be increased. If lake level were lowered 100 feet, water could no longer circulate as it now does. Niagara Falls, between Lake Erie and Lake Ontario, would dry up and Lake Ontario would be cut off from its water supply. We find that use of lakes turns out to be much like use of rivers. We can take from lakes part of what goes into them, or even all that goes in, if we return it; but when we begin mining them, using them beyond the level at which they are restored, the results will be drastic and complicated. Temperatures will change, the fish population will be affected, new kinds of plants will grow, many of the present ones will die, local weather will be affected, even recreation on lakes will be changed. It is not impossible, perhaps, to manage lakes while they are being depleted, though it would be extremely difficult and costly. Lakes can be used as reservoirs to tide us over during years of drought, but long term withdrawals from lakes probably cannot exceed the amount of water flowing in and out of them. Thus they are really only a part of the river system, when long-term water supply is assayed.

The major source of readily available water not being exploited is the underground supply. The total amount in the pores of rocks may be as much as 20 percent of the whole oceanic volume, but only a small fraction can be recovered. The mineable underground water is about a third as much as is locked in ice, and half exists within twenty-five hundred feet of the surface, where it can be fairly easily drilled into and pumped out. The other half is not only expensive to find and retrieve but tends to have too great a salt content for most uses. In the United States the easily reached high quality supply would last five thousand years if we switched to a policy of getting all our water from underground storage. Again we see that the fresh water supply, as a total available amount, is not a serious current problem. In the case of groundwater the difficulty, like that of ice but not so severe, is in its geographic distribution. The eastern and central states have abundant supplies, whereas the western states are in serious trouble. In the Los Angeles area the problem is acute; there is dense population, low and irregular rainfall, and limited groundwater storage.

In the United States about one third of the flow of all streams is used at least once, so that we are beginning to use a significant fraction of the major readily available water supply. At the present rate of growth of use and of population we will come pretty close to using an amount of water equal to total stream flow by the year 2000. But use does not necessarily consume water. In fact we have not even included under use the water that makes electricity at hydroelectric stations, where water turns the turbines and is not changed chemically even though it has performed an important service. Water is consumed only if, as a result of use, it does not return to the stream system, from whence it can be withdrawn again. Eventually, of course, even though it has evaporated or has been taken out of circulation in manufacturing, it will return as rain or snow to land or ocean, and so find its way back some day to the stream supply. It is obvious that some water can be used more than once. It can be withdrawn from streams, used, returned to the stream and used again. The water of the Ohio River is used three times over in its course to the Mississippi, and one of its tributaries is used seven times. If there were no losses by evaporation when water was withdrawn, and if everyone returned the used water in the condition in which he found it, the present supply would be sufficient forever. If it were not for evaporation losses, treatment of used water, perhaps polluted by minor contaminants but not salty, could almost solve our problems. In theory, every house could have a tank and all the water from dishwashing and bathing could go through a purification plant and be returned to the tank. But there would be a net loss; water is drunk, used for gardening, evaporates from the swimming pool, is lost as steam from the teakettle.

The best estimates are that water consumption today is only about one third of water withdrawal. Most of the consumption is attributed to evaporation from irrigation. Little of the evaporation loss is directly from water that is spread on the fields, but is due to evapo-transpiration of growing plants. An acre of com can withdraw three thousand gallons of water from the soil each day and send most of it out into the atmosphere through the leaves as water vapor. Of course what has evaporated is available again at some future time. The general water cycle is one of income, storage, and outgo, much like a checking account.

There are quite reliable figures for the water loss during irrigation; only 40 percent of all the water used is returned to streams. This is in contrast to municipal use, in which 90 percent is returned, or industrial use, in which 90 percent is returned. The problem of how much water is lost is still a tricky one because no one knows how much of the water evaporated from a lettuce field in California ends up in the Mississippi River after it has condensed and fallen as rain in eastern Iowa.

But most predictions of the growth of irrigation indicate that it will soon begin to lower significantly the volume of the stream flow of the whole earth.

The degree of reuse of water is determined to a large extent by the change in composition that takes place when water is withdrawn, used, and returned. Water used for baths or showers is little altered. It has had a little dirt and soap added, but it is otherwise unchanged. If bath water could be isolated from the household waste water and treated it would cost little to restore it to its original condition. In contrast, consider the water that emerges from kitchens that have various types of disposal units that grind garbage into sludge that is flushed into drains. This water is loaded with a variety of ground-up organic materials that must be oxidized away or settled out before the water returns to potable quality.

Industry poses the same variety of problems. Water used as a coolant in steel making returns to its source unchanged, except for added heat. However, water used in some of the chemical treatments of iron and steel becomes rich in chromium, sulfuric acid, or other chemicals. To clean up cooling water costs little; to clean up chemically altered water costs a lot. There is no simple solution to the reuse problem.

To return water to streams in a condition similar to that in which it was taken requires separation and special treatment of the water, according to the specific uses to which it was put. The cleaning treatments cost money, so that the problem is one of economics, rather than merely of supply or methods for cleaning.

In addition to the constant supply of water that comes from rain we must consider the amounts stored at present in lakes, in glacier ice, and underground. All of these natural reservoirs can be “mined.” By mining we mean using a supply for which rate of withdrawal exceeds rate of replacement. We cannot view mining of water reservoirs as a practical approach in the long run. How long could we exist if we did not use the normal daily atmospheric supply, but relied entirely on melting glaciers, or on draining the Great Lakes to supply water to Arizona? If we do not insist on a perpetual water supply and decide to take water only from glaciers, lakes, and underground, how long could man survive before all these reserves were depleted?