The Salton-sea Evaporation Pan

The effects of atmospheric thirst are numerous and striking. When it is excessive it may cause plants to wilt even when they are supplied with abundant water from the soil. Thus a well-irrigated orange grove is sometimes much injured by a hot, dry wind. It has various physiological effects upon man and the lower animals. They are, for example, made thirsty by a thirsty atmosphere. In the terrific summer climate of Death Valley, California—one of the hottest and driest on earth—the traveler finds it impossible to drink enough water to slake his thirst. A thirsty air takes tremendous toll of the water stored in irrigation reservoirs, which must be designed to make allowance for this loss.

On the other hand, it is the thirst of the air that enables the California fruit-growers to dry their products out of doors in the long, rainless summers; lumbermen everywhere to season their boards; and housewives to dry the family wash. Artificial conditions may either increase, or diminish the drying power of the air. Many industries depend upon the use of drying machinery, while there are others in which artificially moistened air must be supplied for certain operations. The amount of moisture in the air is measured by instruments, of many different patterns, called "hygrometers." Instruments for measuring the thirst of the air are called "atmometers," or "evaporimeters.''

One of the common forms of evaporation-measure is a large circular metal pan, in which water is exposed to the air. The depth of the water is measured from time to time; allowance is made for any rain that may have fallen between observations (as determined by a rain-gauge); and the depth of water evaporated is thus obtained. Measurements made with this device are especially useful for engineering purposes. In studying the drying effects of the atmosphere upon plants, botanists use instruments of a very different type, in which eyaporation takes place from a porous surface.

One of the most remarkable series of evaporation measurements ever made was the result of a disastrous flood that occurred in the desert region of southern California in the year 1905. The breaking of dams constructed in connection with an irrigation project allowed the water of the Colorado River to flow into a large depression, below sea level, known as the Salton Sink. By the time the break was closed, at the end of 1906, the flood had formed a lake 475 square miles in extent—the Salton Sea. After its principal supply of water was cut off, the lake diminished rapidly in depth and area for many years, on account of the great excess of evaporation over the very scanty rainfalll. The Weather Bureau installed elaborate apparatus here and utilized the Salton Sea as a mammoth evaporation-pan; the measurements showing an average evaporation from its surface of nearly seventy inches a year.

By: davidbunch

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