Developing a Synthetic, Long-Term Flow Record for the Lower Virgin River Using Flow-Duration Curves

Stephanie L. Bache, Jeffrey Johnson, and Craig T. White

ABSTRACT
The Virgin River is a key component of the water resource portfolios of Nevada and Utah. Arizona has also developed water rights in its 26-mile section of the river between Utah and Nevada. The Virgin River has a 6,000-mi2 (square mile) watershed, which originates in Utah and discharges into Lake Mead approximately 60 miles upstream from the Hoover Dam. The flow in the Virgin River is highly variable, both on a daily and annual basis. Streamflow gage records for the Lower Virgin River in Nevada are limited. Establishment of reliable estimates of daily and annual flows in the Lower Virgin River is of interest to those seeking to understand the river ecosystem, evaluate potential resources for development, and assess associated environmental effects.The most extensive flow data set for the lower Virgin River is the U.S. Geological Survey (USGS) Littlefield Gage (1929 to present), which is cooperatively funded by the Southern Nevada Water Authority (SNWA). A shorter data set is also available for the Virgin River at the USGS Halfway Wash Gage, which was operated from 1978 to 1985 (excluding water year 1984). These data do not adequately reflect long-term variations in river flows as observed at the Littlefield Gage. The purpose of this analysis was to develop a synthetic, daily long-term flow record for the Halfway Wash Gage based on historic flows at both the Littlefield and Halfway Wash Gages. The synthesized flow record for the Halfway Wash Gage is based on the use of flow-duration curves, a statistical method of evaluating the variability of river flows. Flow-duration curves were developed for both the Littlefield and Halfway Wash Gages for the 7 concurrent years of streamflow records, and a flow-duration curve was developed for the Littlefield Gage for its 74-year period of record. Based on the relationships between the 7-year and 74-year flow-duration curves for the Littlefield Gage at corresponding probabilities, the 7-year Halfway Wash flow-duration curve was proportionally adjusted to produce a synthetic flow-duration curve for the Virgin River at Halfway Wash corresponding to the 74-year record. Based on this methodology, a synthetic 74-year daily flow record was developed for the Virgin River at Halfway Wash, which correlates extremely well to recorded flow data at the Halfway Wash Gage and at the downstream Overton Gage. An advantage of this methodology is that it provides reasonable estimates of flow on both a daily and annual basis throughout the entire flow range, enabling the flow record to be used for a variety of analyses.

Keywords:
Citation:
DOI:

Where does the water go? Agreement Investigation

Robert D. Baggs, Jr., and D’Layne M. Reynolds

ABSTRACT
A development project – subdivision, shopping center, or irrigation system – requires the installation of a water meter to account for consumption by a developer or the retail customer. Once installed, it should begin measuring water flow and producing cash flow. Agreement Investigation (AI) is a post-development process that examines the timeliness of these flows. As with so many single-focus processes in a highly complex field and administrative system, investigating one problem often leads to opportunities in other functional areas.

Keywords:
Citation:
DOI:

Trace Element and Radionuclide Concentrations in Walker River Bottom Sediment and Weber Reservoir Sediment Core, West- Central Nevada, 2005

Carl E. Thodal and Michael S. Lico

ABSTRACT
The Walker River Paiute Tribe is concerned that operations at the Yerington copper mine in Lyon County, Nevada, have contaminated water resources on the Walker River Indian Reservation. Mining in the Walker River Basin, including at the Yerington site, began in the mid-1800s; large-scale open-pit mining began in 1952 and continued intermittently until closure of the mine in 2000 because of bankruptcy. Investigations authorized by the Comprehensive Environmental Response, Compensation, and Liability Act began in the late 1990s in response to reports that elevated concentrations of trace elements and radionuclides have been measured in ground water, tailings leachate, and leachate-contaminated soil samples. The U.S. Geological Survey, in cooperation with the Walker River Paiute Tribe, began an investigation in 2005 to establish a chronology of the sediment quality of Weber Reservoir. Bottom-sediment samples were collected from six river sites and one drain site tributary to Weber Reservoir and two sediment cores were collected from Weber Reservoir for determination of selected major and trace elements, and radionuclides. Construction of Weber Reservoir began in 1933, storage began in 1934, and construction of the dam was completed in 1935. Mean concentrations and activities of constituents measured in bottom-sediment samples from river sites, both upstream and downstream of the mine, and from the drain site downstream of mine tailings, generally were lower than those measured in the reservoir sediment. Advisory concentrations for iron and manganese were exceeded in all the samples and the advisory concentration for arsenic was equaled in one riverbed sample collected downstream of the mine. The concentration of mercury in one reservoir sample collected from pre-reservoir sediment was near the advisory concentration, and all samples, except one river-bottom sample, exceeded a sediment effects threshold concentration that may adversely affect freshwater invertebrates. No other advisory concentration or activity in the sediment samples was exceeded. Cesium-137 data from a sediment core collected from Weber Reservoir show a clearly defined peak in sediment from a depth of 2.2–2.5 feet below the sediment surface and initial detection was in the sample from a depth of 2.8–3.2 feet. Assuming a linear rate of sedimentation and neglecting density compaction, sediment accumulated in Weber Reservoir at a rate of 0.06 feet per year during the 70 years since construction of the reservoir was completed. Each 0.3-foot length of sediment core represents about 5.5 years. Maximum concentrations of aluminum, arsenic, beryllium, cadmium, copper, iron, lead, manganese, thorium, and zinc measured in the core were from the subsample that represents sedimentation during 1957–62. Of the 37 other analytes measured, 17 also had maximum concentrations in this subsample. Maximum concentrations of chromium and nickel were from the subsample deposited during 1979–84 and maximum concentrations of uranium were from two adjacent subsamples deposited before the reservoir was constructed until 1944. Radium-226, radium-228, and gross alpha radioactivity had maximum activities in the subsamples from the interval deposited during 1968–73 and gross beta radioactivity had maximum activities in two adjacent subsamples deposited during 1940–51. Maximum concentrations of mercury and molybdenum were from the subsample deposited during 1935–40. Contaminants from the Yerington copper mine site can be delivered to Weber Reservoir by direct fallout of windborne dust, fluvial transport of dust blown from the site to drainages, stormwater runoff from the site into the river, and contaminated ground water that discharges into Wabuska Drain. Concentrations and activities of constituents of concern in the sediment-core subsamples indicate varying rates of deposition; but, because each subsample represents sediment that accumulated over 5–6 years, episodic stormwater releases from the mine site would be diluted by normal sedimentation. The samples of river-bottom sediment generally had lower concentrations and activities than the reservoir-core samples, but the differences were small because both were derived from sources with a common geology owing to more than a century of mining in the Walker River Basin.

Keywords:
Citation:
DOI:

Technical Note: New method for calculating activity coefficients of surface ions in concentrated electrolytes

Anpalaki J. Ragavan

ABSTRACT
This technical note was intended to introduce a new method for calculating activity coefficients of surface ions in concentrated 1:1 electrolytes that would benefit geo-chemical modeling of environmental and industrial processes, which is currently severely hindered due to the unavailability of an equation to calculate the activity coefficients of ions adsorbed onto solid surfaces and/or located near solid surfaces in solution-solid interfaces also known as surface ions. In an electrolyte solution Coulomb forces between ions affect the thermodynamic and physical properties of the system. Hence law of mass action is strictly valid only when activities are used instead of concentrations. The only currently available Debye-Huckel (Onsager, 1933; Onsager and Fuoss, 1932; Wingrave, 2001) equation and its extended forms for calculating activity coefficients in real electrolyte solutions are limited to low electrolyte concentrations less than 0.01 moles (M) due to the use of linearized Poisson-Boltzmann equation in their derivation (Onsager, 1933; Onsager and Fuoss, 1932; Wingrave, 2001). Debye-Huckel equation also assumes that the dielectric constant of solvent molecules is unaffected by the concentration of solute ions in solution which limits its use to homogeneous solutions of concentrations less than 0.001 moles (Onsager, 1933; Onsager and Fuoss, 1932; Wingrave, 2001). It is frequently necessary to work with high concentrations of inert electrolytes present. A theoretically based activity coefficient equation for surface ions was derived in this paper based on rigorous electrostatic and thermodynamic laws and non-linear Poisson-Boltzmann equation, and used to simulate the activity coefficients of ions located at or near solid surfaces in solution-solid interfaces of 1:1 aqueous electrolyte solutions. The dielectric constant (DC) of the solvent molecules near the solid surface was calculated as a continuous function of the solute ion concentration. The mathematical incompleteness of Debye-Huckel equation was corrected in the derived equation with the use of non-linearized Poisson-Bolzmann equation. The derived equation gave reasonable results for ions of all types and valences at all concentrations of 1:1 electrolytes. The derived equation can also be easily extended to other type (1:2 and 2:2) of electrolytes.

Keywords:
Citation:
DOI: