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Show SOURCES OF GROUND WATER. 27 U N D E R G R O U N D W A T E R. GENERAL COXDITIOK& SOURCE. The underground water supply in the valleys of Utah Lake and Jordan River, as is well known, is maintained by the snow and rain that fall on their drainage areas. In considering the sources of the supply, the precipitation tributary to Utah Lake and Jordan River can conveniently be divided into that on the mountains and that on the main valley. It has been stated, that the actual precipitation in the mountains probably exceeds the amount shown by the recorded data. Moreover, neither the rainfall nor the snowfall is evenly distributed. The precipitation is greater in the northern than in the southern half of the area under consideration, and in contiguous localities there are differences due to varying topographic conditions. More precipitation is likely to occur in the vicinity of the higher peaks, and in the mountain recesses that are well protected from the sun large quantities of snow linger long after the general mantle has disappeared. Of the total precipitation on the mountains, part is evaporated, part joins the run- off, and part becomes underground water. Evaporation occurs either directly- from snow, from a free surface of water, and from water contained in soils and brought to the surface by capillary action- or indirectly by transpiration through the growth of plants. Of the portion which joins the run- off part runs directly out of the mountains, part flows to small lakes at the head of Big Cottonwood Creek and Provo River, and part is absorbed by the. soil and rocks over which the streams flow and joins the subterranean store. A final portion of the precipitation on the mountains becomes underground water directly by absorption by the surface on which the rainfall occurs. Part of this underground water reaches the surface again by capillary action in the soils and by the life activity of plants and is finally evaporated; another part after remaining underground a shorter or longer time reaches the surface again by springs and seepage, and, joining the run- off little by little, maintains the perennial flow of the streams; another part joins the more permanent supply of underground water. It is impossible, because of the complexity of the subject and the lack of data, to state the amount of water which annually replenishes this more permanent supply of underground water, but the quantity is equivalent to the precipitation minus the run- off and the amount evaporated. From the incomplete facts at hand it appears that the run- off, measured at the mouths of the canyons, although varying greatly, approximates 50 per cent of the precipitation, but the total evaporation is unknown. Although exact figures repre-resenting the amount evaporated can not be obtained, yet experiments on evaporation from snow, soils, and vegetation in the mountain areas would afford valuable data. The amount of precipitation in the valley is better known, and the figures for Salt Lake City and Provo are typical. Here, as in the mountains, part of the precipitation joins the run- off, part is evaporated, and part becomes underground water; but there are practically no measurements of these different quantities. Direct run- off of the precipitation on the valley is comparatively small, owing to the open nature of the country and to the fact that no great accumulations of snow occur, and the seepage run- off probably constitutes the main amount. Evaporation from soils and vegetation dissipates probably the largest part of the rain that falls on the valley, especially during the summer. The increase of the more permanent underground water supply due to the rainfall on the valley is consequently small. A basis for judgment is furnished by comparing the condition of the valley east and west of Jordan River. Precipitation is perhaps slightly less in the western part of the valley, but the difference is not enough to cause the marked contrast. The scarcity of ground water within easy reach of the surface in the western part of the valley, compared with the abundance easily accessible in the eastern part, implies that the rainfall on the valley contributes a proportionally small amount to the store of underground water. Existing conditions are due to the fact that on the west only a few feeble and generally intermittent streams are tributary to the valley, whereas on the east a number of large perennial streams flow from the Wasatch Mountains, supplying water that is distributed |