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Show 3 6 UNDERGROUND WATER IN VALLEYS OF UTAH. inch, and generally the greatest pressures are little more than sufficient to raise the water into railroad tanks. Temperature measurements of the water from flowing wells afford some data bearing on the downward increment of heat in the unconsolidated valley deposits, but there are a number of disturbing factors. Adjacent to the mountains the waters are unusually cool:; the presence of hot springs tends to disturb conditions, and the depths from which the waters; flow are often not known. The common rate of downward increase in temperature appears to be slightfy less than 1° F. in 50 feet, but the facts obtained do not warrant a closer statement. It may be of local interest, however, to observe that in general the temperature of the water increases with the depth of the wells at approximately that rate. Few measurements have been made, but it is common experience that the yield of many flowing wells in the area under consideration has decreased. The most comprehensive measurements are those made of the wells owned by Salt Lake City near Liberty Park ( p. 44). Comparing the discharge of 12 of these wells in August, 1890, with the yield of the same wells in September, 1902, it appears that in the interval of twelve years the flow of one had increased, but that thosa of the others had materially decreased. Such decrease, however, may be due largely to clogging of the pipes, for the total yield of the Liberty Park area has been maintained with little decrease by sinking new wells. Decrease in yield is conspicuously apparent in Lehi and Spanish Fork, where flowing wells formerly could be obtained much more generally than now, and is notable elsewhere throughout the valley, especially adjacent to the boundary of the flowing area. Decrease in flow of individual wells is so retimes due to clogging up with sand and clay, and often can be remedied by cleaning or by the use of casing. But the general decrease is to be explained chiefly by the large increase in the number of wells which draw on the general supply. It is also to be remembered that for the past few years the annual precipitation has been considerably below the mean. The artesian wells are used for stock, irrigation, and domestic purposes. The amount used for stock is comparatively small, and, save for watering small gardens, artesian water as yet is not extensively used for irrigation, except locally. Probably over a thousand acres are thus irrigated in Utah Lake Valley, the principal areas being below Lehi and Payson. The artesian supply is much used for domestic purposes, and in general furnishes an admirable quality of water, containing much less dissolved salts and being much purer than shallow ground water. An attempt wTas made to estimate the total number of flowing wells in the area studied, but the result is to be taken only as a rough approximation. There are about 5,000 flowing wells in the valleys of Utah Lake and Jordan River, and possibly somewhat more than half of these occur in the southern valley. Assuming an average of 15 gallons a minute, a total yield of about 150 second- feet is thus indicated. Outside of the area in which flowing wells are obtained underground water is recovered either from shallow dug wells that tap the upper surface of underground water or from driven wells in which the water comes from a relatively deep horizon and is under pressure which causes it to rise toward the surface. To save the expense of " driving," shallow wells are often dug within the area in which flowing wells can be obtained. Occupying the center of the valley and extending approximately to the limit at which flowing wells can be obtained, ground water lies within 10 feet of the surface, and locally, as has been mentioned, swampy conditions exist. As the base of the mountains is approached the depth to ground water increases and is over 50 feet on much of the upland where, over large areas, the distance to water is unknown. Water is recovered from these wells generally by buckets and hand pumps. Comparatively few windmills are in operation. An average wind velocity of not less than 6 miles an hour a is stated to be required to drive a windmill; and since the mean wind velocity at Salt Lake a Wilson, H. M., Pumping for irrigation: Water- Sup. and Irr. Paper No. 1, U. S. Geol. Survey, 1896, p . 27. i |