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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


More than half of Nevada’s original wetlands have been lost to agricultural and urban development (Dahl, 1990). Wetlands currently account for less than 1 percent of the area of the State (Lico, 1996, p. 267). The only major wetlands in northeastern Nevada are in the Ruby Lake National Wildlife Refuge (Ruby Lake NWR) and nearby Franklin Lake area in the southern half of Ruby Valley (fig. 1). Because of its relative isolation from other wetland areas along the Pacific Flyway, Ruby Valley provides habitat to large numbers of breeding and migratory waterfowl, marsh-dependent birds, and other wildlife. Long-term preservation of wetland in the refuge is tied to the availability of sufficient water to maintain optimal habitat conditions. Not well known, however, is the quantity of water that is needed.

Concerns about the continued viability of the Ruby Lake NWR have prompted the U.S. Fish & Wildlife Service (USFWS) to apply for ground-water rights from the State of Nevada. Although the refuge has existed since 1938, water rights that would ensure its preservation have never been formally acquired. Estimates of evapotranspiration (ET) are needed by USFWS and the State as part of a larger effort to determine a water budget for Ruby Valley, which will be used in future management of the valley’s water resources.

In the arid West, water loss by ET typically represents the largest component of natural outflow in a water budget. Evapotranspiration is the combined loss or transfer of water to the atmosphere through transpiration by plants and direct evaporation from surface-water bodies and soil moisture and from shallow ground water in areas of bare soil (Wilson and Moore, 1998).

Evapotranspiration from the Ruby Lake NWR is thought to be the largest source of natural outflow from Ruby Valley (Eakin and Maxey, 1951, p. 82; Nichols, 2000, p. C44). Although preliminary estimates were made of ground-water ET in Ruby Valley (Nichols, 2000), detailed estimates of ET from habitats in the refuge have not been made. Refining the estimate of annual ET from the refuge would aid in determining the amount of inflow required to maintain wetland habitat and would help in quantifying the total outflow from Ruby Valley.

The water resources of Ruby Valley were last investigated in the late 1940’s (Eakin and Maxey, 1951). The availability of additional hydrologic data and new technologies, particularly in regional water-budget analysis, presents an opportunity to evaluate in more detail the valley’s water resources. In 1999, the U.S. Geological Survey (USGS), in cooperation with the Nevada Division of Water Resources and the USFWS, began a 6-year water-resources investigation to develop an annual water budget for Ruby Valley. The study was planned in terms of two phases of research, each slated to last 3 years. Phase 1 was designed to quantify annual ET from the Ruby Lake NWR, particularly from wetland habitat. The investigation outlined in Phase 2 will develop a water budget for the entire Ruby Valley Hydrographic Area1 (fig. 1) and will incorporate estimates of ET determined in Phase 1.

Purpose and Scope

This report describes the results of the first phase of study in estimating an annual water budget for Ruby Valley. The report presents ET rates computed from micrometeorological data measured in major habitats of the Ruby Lake NWR. Typical habitats include wetland (consisting of open water and bulrush marsh), meadow, grassland, areas of phreatophytic shrubs, playa, and desert-shrub upland. Estimates are presented of annual ET based on seasonal ET rates and habitat distribution for the 2000 water year. This report also briefly describes the methods and instrumentation used to estimate ET from major habitats.

Beginning in May 1999, micrometeorological data were collected during the next 18 months at four sites that represented habitat in open water, bulrush marsh, mixed phreatophytes, and desert-shrub upland, respectively. Daily ET rates at these sites were estimated using the Bowen-ratio method. Data also were collected from mid-May to mid-September 2000 at five short-term sites that included a meadow habitat and four areas containing a mixture of phreatophytic shrubs, using a different data-collection interval at each site. Daily ET rates at these five sites were estimated using the eddy-correlation method. The eddy-correlation equipment was moved at 2- to 12-week intervals to optimize data collection during the summer season. See the section "Methods of Estimating Evapotranspiration" for descriptions of the Bowen-ratio and eddy-correlation methods.

Previous Investigations

One of the earliest water-resources investigations in Ruby Valley was done by the USGS in the late 1940’s (Eakin and Maxey, 1951). The study briefly describes the hydrography of Ruby Valley and presents reconnaissance-level estimates of ground-water recharge and discharge. The hydrogeology of the Ruby Mountains, which border the west side of Ruby Valley, was described by Dudley (1967). Dudley used geomorphic features to infer the hydrology of the Ruby Mountains and their influence on ground-water flow to adjacent valleys. Prudic and others (1995) included Ruby Valley in an evaluation of regional ground-water flow in the carbonate-rock province of the Great Basin. Nichols (2000) included Ruby Valley as part of a regional ground-water study of 16 contiguous valleys in eastern Nevada. Nichols presents annual estimates of ground-water recharge from precipitation and ground-water discharge by ET in Ruby Valley.


The authors would like to thank and express their appreciation to the many private landowners and residents who granted access to their property and provided descriptions of Ruby Valley history. The authors also acknowledge the agencies that assisted in this study, in particular the Elko County and White Pine County Assessors Offices, Gallagher State Fish Hatchery, Bureau of Land Management, U.S. Fish & Wildlife Service, and U.S. Forest Service.

1 Formal hydrographic areas in Nevada were delineated systematically in the late 1960’s by the U.S. Geological Survey and Nevada Division of Water Resources for scientific and administrative purposes (Cardinalli and others, 1968; Rush, 1968). The official hydrographic-area names, numbers, and geographic boundaries continue to be used in Geological Survey scientific reports and Division of Water Resources administrative activities.

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