Scientific Investigations Report 2005-5286

U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2005-5286

Discharge and Physical-Property Measurements from Virgin River Narrows, AZ, to Lake Mead, NV, February 12, 2003

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Introduction

The Virgin River originates in Zion National Park, Utah, flows in a southwesterly direction across parts of southwestern Utah, northwestern Arizona, and southern Nevada before discharging into Lake Mead (fig. 1). The river sustains riparian habitat with diverse wildlife, including the endangered Virgin River chub and woundfin minnow.

Rapid population growth in southern Nevada has increased demand for additional water supplies. Numerous applications for water rights are before the Nevada State Engineer to develop ground-water resources near the Virgin River. Resource managers have concerns about the effects of future ground-water withdrawals on riparian ecosystems and nearby spring-discharge areas adjacent to the river. Data currently are being collected to help evaluate effects of potential ground-water withdrawals on local and regional water availability, water rights, sensitive wildlife habitats, and other beneficial uses. As part of these efforts, this investigation was initiated to measure discharge, water temperature, and specific conductance along the Virgin River at selected locations between the Virgin River Narrows, Arizona, and Lake Mead, Nevada. Changes in streamflow along the lower Virgin River during periods of minimal surface inflow or evapotranspiration (ET) primarily are the result of exchanges with ground water. Detailed measurements of streamflow, water temperature, and specific conductance help quantify these exchanges.

Purpose and Scope

The purpose of this report is to present synoptic-discharge, water-temperature, and specific-conductance data collected on February 12, 2003, at 19 selected sites along the lower Virgin River. The results of these measurements will help to identify reaches where gains or losses in discharge may be occurring. Synoptic measurements are those done concurrently over a broad area at a set time to give a “snap shot” of hydrologic conditions. These data were collected to help assess changes in stream discharge at points along a reach of the lower Virgin River during a period of minimal ET loss, surface-water inflow, and agricultural diversion. To help in the evaluation, synoptic-discharge data were measured at one tributary inflow and four diversions in the study area.

Description of Study Area

Dixon and Katzer (2002) document a study describing the hydrology and geology of the Virgin River. The current study was limited to the lower 50 mi of the Virgin River beginning at the U.S. Geological Survey (USGS) surface-water gage at Virgin River above the Narrows near Littlefield, Arizona (site 09413700; herein referred to as 'Narrows gage'), and extending to Lake Mead (fig. 1). For purposes of this report, all references to the lower Virgin River indicate the study area.

Figure

Figure 1. Location of study area and synoptic-measurement sites. See table 1 for site information.

The lower Virgin River Basin is drained by a moderately steep meandering river that is bounded on the northwest and west by the East Mormon Mountains and Mormon Mesa, respectively, and on the east and south by the Virgin Mountains (fig. 1). Beaver Dam Wash flows into the lower Virgin River about 0.5 mi above Virgin River at Littlefield, Arizona (site 09415000; herein referred to as 'Littlefield gage'), and is the largest perennial tributary with an annual daily mean discharge of about 2.7 ft3/s (USGS site 09414975). Discharge data are available at URL: <http://waterdata.usgs.gov/nv/nwis/>. Numerous small springs and seeps discharge directly into the river upstream of Littlefield, Arizona, but most are not measurable because of poor measuring conditions or restricted access. Three large ephemeral channels (Big Bend Wash, Toquop Wash, and Halfway Wash) drain into the Virgin River from the northwest and contribute surface discharge only during periods of intense precipitation.

The lower Virgin River channel typically consists of fine to coarse sands with rock riffles, consisting of cobbles and boulders, scattered throughout the reach. Dense vegetation is along the banks of the river and mainly consists of saltcedar (Tamarix ramosissima), cattail (Typha latifolia), and reeds (Phragmites communis).

The major populated areas within the lower Virgin Valley include the municipalities of Littlefield, Mesquite, Bunkerville, and Riverside (fig. 1). Water diverted from the river for these communities has changed from supporting agriculture to supporting residential and recreational developments primarily in Mesquite.

Acknowledgments

The authors acknowledge the following agencies for their participation in this study: National Park Service; Virgin Valley Water District; Southern Nevada Water Authority; Nevada Division of Water Resources; Vidler Water Company, Inc.; CH2M HILL; and Interflow Hydrology, Inc. Special thanks goes to Michael Johnson of the Virgin Valley Water District who helped access the measuring sites and for logistical support during the course of the study.

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