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Water-Resources Investigations Report 01-4234

Estimates of Evapotranspiration from the Ruby Lake National Wildlife Refuge Area, Ruby Valley, Northeastern Nevada, May 1999-October 2000


General Description and Setting

Ruby Valley is an elongated, topographically closed basin in northeastern Nevada about 65 mi southeast of Elko, Nev. (fig. 1). The valley occupies a north-south-trending structural basin in the Great Basin region of the Basin and Range physiographic province. The boundary of the Ruby Valley Hydrographic Area (fig. 1), which generally coincides with the drainage-area boundary, encompasses about 1,000 mi 2 in Elko and White Pine Counties.

Entrance to Ruby Valley is provided by two paved and several dirt roads. Under most weather conditions, access is by numerous gravel-surfaced roads. The residential population is distributed among several ranches around the west, north, and northeast sides of the valley. The principal industry is ranching, supported by large acreages of irrigated hay meadows. Near the center of the valley is Franklin Lake (fig. 2), 3,200 acres of which are managed by the Nevada Division of Wildlife. The Ruby Lake NWR headquarters and Gallagher State Fish Hatchery are located along the east flank of the Ruby Mountains adjacent to Ruby Lake, in the southern part of the valley. Shanty Town, a seasonal community, is about 3 mi south of the refuge headquarters.

Physiography

Named for the red garnets found in the area (Harolds Club, 1951), the Ruby Mountains form the entire western border of Ruby Valley. This mountain range is a narrow, asymmetrical fault block that extends nearly 100 mi to the south from its northern extension near Wells, Nev. Along nearly its entire length, the east slope of the Ruby Mountains is steeper than the west slope; in many places, the crest of the range is west of the drainage divide (Sharp, 1940, p. 343). Several peaks in the range have altitudes that exceed 11,000 ft. The Ruby Mountains merge in the north with the East Humboldt Range (fig. 1), which forms the northeast border of the valley. Summit altitudes of the East Humboldt Range are between 8,000 ft and 11,000 ft. The Ruby Mountains and the East Humboldt Range are the most dominant features in the study area and are the principal source areas for inflow water to Ruby Valley. The eastern border of the valley is composed of low hills and alluvial divides in the north and the Maverick Springs Range (fig. 1), which reaches altitudes of nearly 8,000 ft, in the south.

The floor of Ruby Valley lies just above an altitude of 5,900 ft, making it one of the higher valleys in the Great Basin. The valley is divided into two internally drained basins separated by an alluvial ridge at an altitude of about 6,000 ft. The lowest parts of these two basins are occupied by Franklin Lake in the north and Ruby Lake in the south. Wave action of the two lakes, aided by sediment from Harrison Pass Creek (fig. 2), probably built the alluvial ridge that separates the two lakes (Sharp, 1938, p. 318). The altitude of the valley floor increases northward from Franklin Lake to about 6,100 ft and southward from Ruby Lake to about 6,300 ft. Streams issuing from the east side of the Ruby Mountains north of Harrison Pass Creek and from the southwest flank of the East Humboldt Range terminate in Franklin Lake. Franklin Lake is an intermittent lake that was completely dry for 6 of the 26 years from 1960 to 1986 (Csuti, 1987). The Franklin Lake drainage area covers the northern two-thirds of the Ruby Valley Hydrographic Area. Streams south of and including Harrison Pass Creek and those issuing from the Maverick Springs Range terminate in Ruby Lake. Most of these streams are perennial only in the canyons and along the uppermost parts of the alluvial slopes.

Ruby Lake, in the southern third of Ruby Valley, is the site of the Ruby Lake NWR (fig. 2). The refuge covers nearly 38,000 acres of wetland and adjacent areas consisting of meadow, grassland, and shrub upland. The wetland area is divided into numerous marsh management units that are separated by earthen dikes (visible in fig. 2 as linear features crossing open water). During years of average precipitation, the wetland area covers about 14,000 acres in the spring and declines to about 11,000 acres in the fall. After several years of below-average precipitation, the area of the wetland decreases to about 1,000 acres that generally are located in the southern part of the refuge. The predominant water source for the refuge is spring discharge along the western edge of Ruby Lake. Ruby Lake is thought to have never dried up during any historic droughts (Thompson, 1992, p. 2).

Hydrogeology

The existence of Ruby Lake and associated wetlands stems in large part from the unusual hydro-geology of the southern Ruby Mountains (Eakin and Maxey, 1951, p. 82-83; Dudley, 1967). The southern Ruby Mountains (south of Harrison Pass Creek) consist of a nearly complete Paleozoic section (more than 17,000-ft thick) of mostly carbonate rock ranging in age from Cambrian to Mississippian (?) (Sharp, 1942, p. 651). This Paleozoic section is dominated by two cavernous limestone units with high permeability that are separated by carbonate rocks of low-to-moderate permeability (Dudley, 1967, p. 13). Because limestone can be dissolved by ground water that contains carbon dioxide, springs capable of discharging large quantities of ground water have developed along enlarged fissures within the carbonate rocks of the southern Ruby Mountains.

The movement of ground water toward Ruby Lake from the west is controlled by the permeability and stratigraphic positions of these carbonate rocks. Movement of ground water is significantly enhanced by their eastward dip. Sharp (1942, p. 685) suggests that the large and uniform discharge from Cave Spring, and presumably the discharge from other springs issuing from carbonate rocks along the east side of the southern Ruby Mountains (fig. 2), is primarily interbasin flow originating in areas west of the topographic divide. The highly permeable, eastward-dipping carbonate rocks may transmit large quantities of ground water from infiltrated streamflow originating on the west slope of the Ruby Mountains (Rush and Everett, 1966, p. 13). This infiltrated streamflow appears as springs that discharge from the alluvium along the west margin of and possibly beneath Ruby Lake, thereby providing a substantial portion of inflow to the Ruby Lake NWR.

The floor of Ruby Valley has been downdropped relative to the adjacent mountains, forming a structural basin that is filled with interbedded deposits of gravel, sand, silt, and clay derived primarily from adjacent mountains. These deposits form the basin-fill aquifer, which is bounded and underlain by consolidated rock. According to water-level data collected in September 2000, ground water in the basin-fill aquifer beneath the southern part of Ruby Valley moves toward Ruby Lake from recharge source areas in adjacent mountains (fig. 2). Water-level data also suggest that ground water moves northward from Ruby Lake toward Franklin Lake under a gradient of about 5 ft/mi.

Climate

Ruby Valley is in a middle-latitude desert and steppe climate that is dominated by tropical air masses in the summer and continental polar air masses in the winter (Houghton and others, 1975, p. 13, 69-70). In the Ruby Mountains and East Humboldt Range, average annual precipitation, based on Snowpack Telemetry (SNOTEL) data (1961-90) from five stations (fig. 1) at altitudes ranging from 7,700 to 8,500 ft, is about 32 in. (Greenlee, 1992). Precipitation data collected at the headquarters of Ruby Lake NWR (altitude = 6,012 ft) and a weather station at Arthur in the northern part of Ruby Valley (altitude = 6,300 ft) suggest that average annual precipitation on the valley floor during a 30-year reference period (1961-90) ranged from about 13 to 15 in. During the period of data collection for this study (May 1999-November 2000), total precipitation at the Ruby Lake NWR was about 53 percent of the 30-year average (fig. 3). Average annual precipitation for the 3 years preceding this study (1997-99) was about 12 percent greater than the 30-year average.

Temperature data collected at the refuge headquarters for 1961-90 indicate that daily maximum temperatures in the summer typically exceed 85F and reach 100F on only 1 or 2 days during late July or early August. The average daily minimum summer temperature is about 40F. Daily maximum temperatures during the winter range between 30F and 50F and daily minimum temperatures typically range from about 0 to 30F but have been recorded as low as -15F in January. Evaporation measurements collected from 1978 through 2000 at the refuge headquarters indicate that pan evaporation from April through October is about 48 in.

Plant Communities

Habitats in Ruby Lake NWR include perennial wetlands and adjacent drier areas that support a wide variety of plant communities. The diversity of plants in these communities reflects, in large part, the hydrogeologic setting of the southern part of Ruby Valley. For purposes of this study, the most aerially extensive habitats found on the refuge are grouped by general plant communities and by the source of water consumed by ET.

Wetlands in the refuge consist of areas of open water that contain submerged aquatic vegetation as well as areas of dense bulrush marsh and scattered stands of cattails. Dispersed within the wetlands are small islands covered with grasses and bare soil. Seasonally flooded playas occupy large areas along the north and east sides of the refuge. During prolonged dry periods the playas become sparsely colonized by grasses.

Changes in the type of plant community occur with increasing distance from the wetland as soils become drier and depths to ground water increase. In general, wetland is bordered by meadow in places where the water table rises periodically and causes flooding, or is very near the land surface. Along the west margin of the wetlands a transition occurs from meadow and grassland to desert-shrub upland as land-surface altitudes increase toward the Ruby Mountains. The numerous springs along the western and southern parts of the refuge create areas of lush meadow and riparian habitat. In contrast, the meadows on the eastern side of the refuge are much less extensive and are bordered by large areas of sparse grasses, mixed phreatophytic shrubs, and associated areas of bare soil. These habitats eventually merge with desert-shrub upland along the western flanks of the Maverick Springs Range (fig. 2).


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