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Scientific Investigations Report 2009–5014

Scientific Investigations Report 2009–5014

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This report presents the results of a study of the water resources of the upper Humboldt River basin done in 2007–08 by the U.S. Geological Survey in cooperation with Elko County. The report provides Elko County and State water-resource managers information needed to make informed decisions regarding future use and development of the ground-water resources of the basin. The overall objective of the report is to develop an improved understanding of the water resources of the upper Humboldt River basin. This report describes the hydrogeologic framework, and the occurrence and movement of ground water.

The upper Humboldt River basin covers an area of 4,364 mi2 in northeastern Nevada, and consists of eight hydrographic areas—Marys River Area, Starr Valley Area, North Fork Area, Lamoille Valley, South Fork Area, Huntington Valley, Dixie Creek–Tenmile Creek Area, and the Elko Segment. These eight areas are the headwaters of the Humboldt River, and nearly all of the annual flow of the river in years of average flow originates in these areas. The main tributaries of the upper Humboldt River are South Fork Humboldt River, North Fork Humboldt River, Lamoille Creek, Marys River, and Bishop Creek. High flows during the spring and early summer are dominated by snowmelt runoff and low flows of late summer and autumn of each stream generally are sustained by ground-water discharge to the stream channel. The main exception is the lower reach of Marys River, which has no baseflow and goes dry every summer and autumn.

The upper Humboldt River basin consists of several deep structural basins in which basin-fill deposits of Tertiary and Quaternary age and volcanic rocks of Tertiary age have accumulated. The bedrock of each basin and adjacent mountains are composed of carbonate and clastic sedimentary rocks of Paleozoic age and crystalline rocks of Paleozoic, Mesozoic and Cenozoic age. The permeability of bedrock generally is very low except for carbonate rocks, which can be very permeable where circulating ground water has widened fractures through geologic time. The contrast in permeability of carbonate rocks with other bedrock is evident in the Ruby Mountains. Watersheds in the south end of the mountain range are underlain by carbonate rocks and are drained by ephemeral streams. Watersheds in central and northern parts of the mountain range are underlain by crystalline rocks and are drained by perennial streams.

A thick sequence of alternating sedimentary deposits and volcanic rocks accumulated in basins of the study area from Eocene time to the present. The sequence consists of three hydrogeologic units—volcanic rocks, older basin-fill deposits, and younger basin-fill deposits. The composite thickness of the three units exceeds 5,000 ft in a deep narrow structural basin that extends from southern Huntington Valley to the northern Marys River Area parallel with the Ruby Mountains, East Humboldt Range, and Snake Mountains. Lithologic logs for oil exploration wells indicate that the older basin-fill deposits and volcanic rocks are commonly interbedded. In addition, older basin-fill deposits usually are tuffaceous and consist of interbedded fine-grained lake deposits and coarse-grained deposits of alluvial fans and stream flood plains. Younger basin-fill deposits consist mostly of unconsolidated sand and gravel along stream channels and as thin veneers covering older basin-fill deposits in the northern Marys River and North Fork Areas and in southern Huntington Valley. The principal aquifers in the upper Humboldt River basin are in basin-fill deposits. However, little is known regarding the hydraulic properties of these aquifers. Analysis of aquifer tests and well drillers’ logs would be very useful for making estimates of aquifer properties in the study area.

Ground water in the upper Humboldt River basin moves from recharge areas, which are along mountain fronts, and is discharged as seepage to stream channels, evapotranspiration, and pumpage. The main discharge area in the upper Humboldt River basin is the river flood plain, which can be as much as a mile wide. South of the Humboldt River, ground-water flow is from an extensive recharge area along the western base of the Ruby Mountains and East Humboldt Range and to a lesser extent the eastern base of the Diamond Mountains and Pinon Range. Flow generally is northward along the axes of Huntington Valley and the Dixie Creek–Tenmile Creek Area through a group of unnamed hills to the Humboldt River flood plain west of Elko. Ground-water flow in Lamoille Valley and Starr Valley Area is northwestward directly to the river flood plain. Water-level contours indicate that ground water discharges as seepage to stream channels in areas south of the river.

Ground-water flow in the Marys River Area is to the southwest from the Snake Mountains and south from other parts of the basin to the Humboldt River flood plain. Ground water does not discharge as seepage to the channel of the lower reaches of Marys River.

The North Fork Area consists of two ground-water basins that are connected by streamflow. Sparse water-level data for the upper basin indicate that most ground-water flow is eastward from a recharge area along the base of the Independence Mountains. However, water-level data are not sufficient to determine the direction of ground-water flow in other parts of the upper basin. Ground-water flow in the lower part of the North Fork Area is eastward from the Adobe Range and westward from the Peko Hills toward the North Fork Humboldt River and then southward along the basin axis toward the Humboldt River flood plain.

Water-level contours indicate that the Humboldt River gains flow from ground-water seepage over its entire length in the study area. The contours show sharp upstream inflections where they cross the river and its flood plain from a few miles west of Wells to the west boundary of the study area. Ground-water flow in the Elko Segment is to the southeast from the Adobe Range and northwest from the Dixie Creek–Tenmile Creek Area through the unnamed hills between the Elko Hills and the South Fork Humboldt River. This reach of the river gains about 6,600 acre-ft/yr as ground-water seepage to the river channel. The estimated transmissivity of the aquifer in this flow section is 2,000 ft2/d.

Water levels in the upper Humboldt River basin fluctuate in response to the annual snowmelt runoff, to long-term variations in climate, and to human activities. From 1949 to 1958, water levels at a well in the Marys River and Humboldt River flood plains near Deeth ranged from 8 to 11 ft below land surface in late winter to early spring, but rapidly rose to within several feet of land surface by early to late June. Annual water-level changes at a well near Lamoille were similar to those at the well near Deeth. The Lamoille well is about half a mile from the nearest stream, but it is in an area where streamflow diverted from Lamoille Creek is distributed to meadows and fields by a network of irrigation ditches. Water levels at the well ranged from 11 to 15 ft in early to late winter and rose abruptly to near land surface by late spring or early summer. Water-level rises at this well are dependent on the distribution and timing of irrigation and not on the magnitude of the spring snowmelt runoff.

Water-level changes at a stock well at the southwest side of the South Fork Area are believed to be related to variations in annual precipitation. Since 1970, water levels either rose or declined during four time periods ranging from a few to 15 years. These periods correspond closely with periods of above or below average annual precipitation measured at Elko, and indicate that water levels in the well respond rapidly to variations in climate.

Filling of the South Fork Reservoir, which began in 1988, has resulted in water-level rises in the basin-fill deposits that underlie uplands on the east and west sides of the reservoir. Water level rises at another well, which is about 10 miles north of the reservoir, also could be the result of infiltration losses. Water-level rises at two wells west of Elko are the result of agricultural irrigation and infiltration of treated sewage and residential lawn watering, respectively.

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