Ground-water resources of Pavant Valley, Utah

Water Supply Paper 1794




Pavant Valley, in eastern Millard County in west-central Utah, is in the Great Basin section of the Basin and Range province. The area of investigation is 34 miles long from north to south and 9 miles wide from east to west and comprises about 300 square miles. Agriculture, tourist trade, and mining are the principal industries. The population of the valley is about 3,500, of which about half live in Fillmore, the county seat of Millard County. The climate is semiarid and temperatures are moderate. Average normal annual precipitation in the lowlands is estimated to range from 10 to 14 inches. Precipitation is heaviest during the late winter and spring, January through May. The average monthly temperature at Fillmore ranges from 29?F in January to 76?F in July; the average annual temperature is 52?F. Because of the aridity, most crops cannot be grown successfully without irrigation. Irrigation requirements were satisfied for about 60 years after the valley was settled by diverting streams tributary to the valley. Artesian water was discovered near Flowell in 1915. By 1920 flowing artesian wells supplied about 10 percent of the irrigation water used in the valley, not including water from the Central Utah Canal. The Central Utah Canal was constructed in 1916 to convey water to the Pavant Valley from the Sevier River. Especially since 1916, the quantity of surface water available each year for irrigation has changed with the vagaries of nature. The total percentage of irrigation water contributed by ground water, on the other hand, gradually increased to about 15 percent in 1945 and then increased rapidly to 45 percent in 1960; it will probably stabilize at about 50 percent. Sand and gravel deposits of Recent and Pleistocene age are the principal aquifers in Pavant Valley. These deposits are coarser, more extensive, and more permeable near the mountains and become progressively finer .and less .permeable westward away from the mountains. As ground water moves westward from the recharge areas near the mountains, it becomes confined beneath clay beds; thus artesian conditions prevail in the lower parts of the valley. Although as many as 12 saturated beds of sand and gravel are penetrated in drilling wells to depths of 800 feet, they constitute, generally, one aquifer. The beds of coarser material are interconnected laterally, and the confining beds between them are not perfect aquicludes but merely impede the vertical movement of water. Artesian pressure increases with depth; thus, there is a continual upward flow of water from the lowest to the highest aquifer, and water not withdrawn through wells is discharged at the land surface or into basalt flows along the western edge of the valley. Most recharge to the sand and gravel aquifers enters the ground on the alluvial fans as percolation from streams, irrigation ditches, and irrigated fields. Some recharge results from underflow from the canyons and the face of the mountains and also from precipitation on the alluvial fans. Leakage from the Central Utah Canal is a major source of recharge to alluvial aquifers in the northern half of the valley. The Pavant Flow in the western part of the valley and the basalt underlying the area west of the Black Rock Volcano in the southern part are both major unconfined basalt aquifers. The Pavant Flow is recharged by upward leakage of water from the underlying artesian aquifer, by percolation of irrigation water, by water moving laterally in shallow sand and gravel deposits, and by precipitation on outcrops along the western side of the valley. The basalt underlying the area west of the Black Rock Volcano is recharged by precipitation in the mountains, leakage from the artesian aquifer, and percolation of irrigation water. The ,basalt ,aquifers are relatively thin, averaging 30-60 feet in thickness where -they supply water to irrigation wells. The valley is divided into six districts based on geologic and hydrologic diffe

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USGS Numbered Series
Ground-water resources of Pavant Valley, Utah
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Water Supply Paper
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U. S. Govt. Print. Off.,
v, 78 p. :illus. and portfolio (2 fold. illus., 8 fold. maps) ;24 cm.