The Humboldt River Basin Assessment
Progress Report
October 1996

Executive Summary

The Humboldt River Basin Assessment was designed to evaluate the regional water resources of the Humboldt River Basin. The assessment consists of three phases, each of which would focus on specific parts of the basin and on differing hydrologic issues. Phase one began on October 1, 1995 and is scheduled to be completed by September 30, 1998. Phase one studies will focus on the middle Humboldt River Basin and will consist of:

1. Obtaining hydrologic data and making it available through data bases maintained by the U.S. Geological Survey,
   
2. Defining the hydrogeologic framework,
   
3. Defining ground-water conditions, and
   
4. Refining ground-water budgets and water balances.
   

Introduction

Background

The Humboldt River Basin covers an area of nearly 17,000 square miles in Nevada, and is the only major river basin that is entirely in the State (fig. 1). The headwaters of the Humboldt River are in the high mountains of northeastern Nevada. In most years, the river terminates at the Humboldt Sink in western Nevada. Water from the Humboldt Sink spills out of the basin into the Carson Sink only in years when winter or spring floods require large releases from Rye Patch Reservoir. The average flow of the Humboldt River near Imlay (fig. 1) is about 195,000 acre-feet per year (Bauer and others, 1996, p. 311).

Streamflow of the Humboldt River and its tributaries and ground water are used by diverse, and sometimes competing, interests in the basin. Streamflow historically has been used for agricultural purposes--mainly irrigation of crops and meadows and for watering stock. However, wetlands along the river and its tributaries provide wildlife habitat, and infiltration of streamflow through stream channels is a source of ground-water recharge in the basin. Until about 1980, most ground-water use in the Humboldt River Basin was for irrigation of crops, for municipal and domestic purposes, and for industrial purposes at a few mines scattered throughout the basin. Ground-water use has increased during the last 10-15 years as a result of the development of large gold mines (fig. 1) and the resulting increase in population. Gold mines used about 32,000 acre-feet of ground water for mining and milling purposes in 1995. Several of the mines have extended below local ground-water levels and the mines sites were dewatered at rates ranging from 540 acre-feet to 77,000 acre-feet in 1995. Total ground water pumped for mine dewatering in the Humboldt River Basin in 1995 was about 166,000 acre-feet.

Excess water from mine dewatering is reinjected into aquifers nearby or infiltrates to underlying aquifers from storage reservoirs. However, dewatering rates at three of the mines are such that water also must be discharged into the Humboldt River or one of its tributaries. Pumpage of large volumes of ground water for mining use and dewatering has resulted in:

1. Water-level declines of tens to hundreds of feet in areas of pumping;
   
2. Water-level rises in areas of reinjection or infiltration from reservoirs; and
   
3. Increases in the flow of the Humboldt River and one of its tributaries, Maggie Creek.
   

Agencies of Federal, State, and local government and other groups are interested in the long-term viability of the water resources of the Humboldt River Basin because of their regulatory responsibilities and the many varied water uses in the basin. In response to recent increases in mining use and the effects associated with mine dewatering, the U.S. Geological Survey, in cooperation with the Nevada Department of Conservation and Natural Resources and the U.S. Bureau of Land Management, has undertaken the Humboldt River Basin Assessment to evaluate the regional water resources of the basin. This assessment is based on an agreement made between the Department of Interior, Barrick Goldstrike Mines Inc., and Santa Fe Pacific Gold Corporation. Support for the program is being provided in part by Barrick Goldstrike Mines Inc. and Santa Fe Pacific Gold Corporation.

The objectives of the Humboldt River Basin Assessment are to:

1. Provide a scientific appraisal of the ground-water and surface-water resources of hydrographic areas in the Humboldt River Basin;
   
2. Quantify the contribution of each hydrographic area to the quantity and timing of flows in the mainstem Humboldt River; and
   
3. Assess the effects of all major water uses in the basin, including mine-related activities, on the quantity, quality, and beneficial uses of those water resources.
   

A long-term plan for the Humboldt River Basin assessment was developed by the U.S. Geological Survey, with input from the Nevada Department of Conservation and Natural Resources, Bureau of Land Management, Barrick Goldstrike Mines Inc., and Santa Fe Pacific Gold Corporation. Planning also included a series of public meetings in Elko, Winnemucca, Carson City, and Reno at the University of Nevada. These meetings were held to inform the general public of the Humboldt River Basin Assessment and to use public input to identify water-related issues in the basin. More than 100 people attended the four meetings.

The Humboldt River Basin Assessment will consist of three phases that would extend past the year 2000. Each phase will consist of a series of related and interdependent studies. Presently available funding is sufficient to carry the assessment only through phase one, which is discussed in this report. The U.S. Geological Survey, Bureau of Land Management, and Nevada Department of Conservation and Natural Resources are actively seeking additional funding sources, including mining companies and other water users, agencies of local, State, and Federal government, and Congressional appropriations. Without continued funding, the assessment cannot continue past 1998 when phase one will be completed

Phase one of the assessment began in October 1995, and focuses on the middle part of the Humboldt River Basin (fig. 1). Phase one studies consist of:

1. Obtaining hydrologic and climatic data being collected in the basin and making these data available through the U.S. Geological Survey National Water Information System data bases;
   
2. Defining the hydrogeologic framework;
   
3. Defining ground-water conditions; and
   
4. Refining ground-water budgets and developing a water balance.
   

These studies will be completed and the results published by September 1998.

The middle Humboldt River Basin consists of 13 hydrographic areas that cover 6,430 square miles (fig. 1 and table 1). The 13 areas are tributary to the reach of the Humboldt River that extends from just below Pine Creek on the east to just above Golconda on the west. The principal tributaries to this reach of the river are Rock Creek and the Reese River. Within the middle part of the basin are large areas of irrigated agriculture, a large power plant, and 18 of the 24 mines with permitted water rights in the Humboldt River Basin.

Purpose and Scope

The purpose of this report is to describe progress made as of September 1996 in phase one of the Humboldt River Basin Assessment. Each of the four studies listed above began in fiscal year 1996 and have been partly completed. Objectives of each of the studies and accomplishments made in 1996 are discussed below.

Phase 1 Objectives and Progress as of October 1996

Hydrologic and Climatic data

Large amounts of hydrologic and climatic data have been, and presently are being, collected in the Humboldt River Basin. Some of these data are collected by private industry to satisfy State or Federal monitoring requirements and are reported to the Nevada Division of Water Resources, Nevada Division of Environmental Protection, or U.S. Bureau of Land Management. Other data are collected by State and Federal agencies as parts of other studies. These data can be difficult to access because they are stored in different locations and may be available only as paper files. The only data that are widely accessible are those collected by the U.S. Geological Survey and the U.S. Weather Service. There is a need to bring all hydrologic and climatic data for the Humboldt River Basin together in one data base so that the data are easily accessible. Therefore, the objective of this part of phase one is to obtain hydrologic and climatic data that are being collected in the Humboldt River Basin, and to provide access to the data by way of the internet.

During fiscal year 1996, USGS began making inquiries regarding the availability of hydrologic and climatic data for the Humboldt River Basin. Letters were sent to 14 mining companies that account for most of the active mines in the basin, including the seven mines presently being dewatered. As of September 1996, two of the mining companies had responded to the USGS requests for hydrologic data. One of the mining companies had agreed to release their hydrologic data and had indicated that the data could be made available through the internet. The other mining company, however, indicated that they will release their hydrologic data to USGS, but the data are not to be otherwise available. It is anticipated that additional hydrologic data will be obtained from other mining companies in 1997.

A request also was made to Sierra Pacific Power Company for hydrologic data collected at a network of production wells that are the water supply for the Valmy Power Plant in the Clovers Area (figure 1 and table 1). Part of these data (through 1992) have been released to USGS, and all data through 1996 are expected to be released soon.

Climatic data for the Humboldt River Basin are available through the Natural Resource Conservation Service, the Western Region Climate Data Center, and the Nevada State Climatologist. The Natural Resource Conservation Service publishes monthly and annual summaries of data collected at a network of weather stations. These include snowpack data collected at a number of high-altitude sites in the State. BLM operates a network of weather stations in Nevada that is used for predicting fire conditions during the summer. This network of stations is referred to as RAWS (Remote Area Weather Stations) and the data are available through the Western Region Climate Data Center. These climatic data have been stored on the USGS computer system in Carson City, and within the next few months should be available on the internet.

Hydrogeologic Framework

For most hydrologic studies, an important first step is that of defining the hydrogeologic framework of the study area to provide the foundation upon which subsequent parts of the study can be based. The hydrogeologic framework of an area such as the middle Humboldt River Basin is generally thought of as the information needed to: (1) Define and correlate water-yielding rocks and deposits, (2) Relate those rocks and deposits to rock-stratigraphic units, and (3) Identify those parts of the framework that store and transmit ground water and those parts that impede the movement of ground water. Of particular importance in the middle Humboldt River Basin are the hydraulic properties, thickness, and extent of basin-fill deposits because they constitute some of the principal aquifers in the basin. The U.S. Geological Survey presently (Sept. 1996) is expanding geophysical surveys in the middle Humboldt River Basin. Interpretations of the gravity data collected in these surveys will be used to develop estimates of the thickness of basin-fill deposits in each hydrographic area in the middle Humboldt River Basin. Once these surveys and interpretations are completed the information will be presented as part of a hydrogeologic map of the middle Humboldt River Basin. At present (Oct. 1996), GIS (Geographic Information System) coverages of basemaps and hydrogeologic units have been completed.

Ground-Water Conditions

Definition of ground-water conditions in the middle Humboldt River Basin will form the basis for development of a ground-water model in a later phase of the assessment. The purpose of this study is to describe ground-water conditions in the middle Humboldt River Basin in spring 1982 and spring 1996. The emphasis will be on shallow ground-water conditions.

In the spring of 1982, the U.S. Geological Survey measured water levels at wells throughout the Humboldt River Basin. Measurements were made at 162 wells in the 13 hydrographic areas in the middle part of the basin. In addition, the Nevada Division of Water Resources measured water levels at 65 wells in two of those hydrographic areas. These water levels predate most of the mining activities, including major dewatering, presently underway in the basin, and will be used to develop a map of pre-mining ground-water conditions. However, the water levels will not represent pre-development conditions in the basin because large areas of agriculture were being irrigated by ground water in 1982

In the spring of 1996, the U.S. Geological Survey measured water levels at 211 wells in the middle Humboldt River Basin. In addition, water levels were measured at 115 wells by the Nevada Division of Water Resources, at 21 wells by Sierra Pacific Power Company east of the Valmy Power Plant, and at 184 wells by mining companies at three mines, for a total of 531 wells. These water levels will be used to develop a map of ground-water conditions as of spring 1996. Changes in ground-water conditions will be discussed by comparison of conditions in spring 1982 with conditions in spring 1996 and with hydrographs for selected wells with long periods of water-level record. As of October 1996, preliminary maps of water-level contours have been completed for spring 1982 and spring 1996. The map for 1996 has been converted to a GIS coverage so that it can be combined with other GIS basemap materials.

Water Balance

Water balances and ground-water budgets were developed for only a few selected hydrographic areas in the middle Humboldt River Basin as part of a series of reconnaissance-level studies made by USGS in the 1960's. These budgets were based on sparse hydrologic and climatic data and need to be refined. The purpose of this part of phase one is to refine and update ground-water budgets for each hydrographic area and a water balance for the middle Humboldt River Basin.

The approach will be to: (1) Use presently available precipitation and climatic data to define totals for, and distribution of, annual precipitation in each hydrographic area; (2) Use statistical summaries of USGS streamflow data to define runoff characteristics of each area; (3) Use satellite imagery and other remote-sensing techniques to map areas of ground-water discharge by evapotranspiration; and (4) Use information developed for the hydrogeologic framework to estimate amounts of subsurface ground-water flow between hydrographic areas.

As of October 1996, daily and monthly precipitation data for 63 weather stations in and near the middle Humboldt River Basin had been acquired and reduced to water-year totals. These data will be the basis for refining hydrographic-area water budgets. Hydrographic-area boundaries and distributions of mountain blocks, alluvial fans, and basin lowlands are being developed as GIS coverages, and along with the improved understanding of precipitation distribution, will provide a means of refining estimates of ground-water recharge in each hydrographic area.

Distributions of phreatophytes in several hydrographic areas in eastern Nevada recently have been mapped using satellite imagery. This method of mapping phreatophytes is now being used in the middle Humboldt River Basin. This mapping will provide the basis for refining estimates of ground-water discharge by evapotranspiration.

Streamflow data for the middle Humboldt River Basin presently are being evaluated to identify sources of surface-water inflow, including streamflow gains resulting from ground-water discharge to stream channels. The data also are being used to identify surface-water outflows, including streamflow losses that result from irrigation diversions and infiltration to underlying aquifers. Analysis of these data will provide the basis for developing an overall water balance for the middle Humboldt River Basin.

Reference Cited

Bauer, D.J., Foster B.J., Joyner, J.D., and Swanson, R.A., 1996, Water Resources Data, Nevada, Water Year 1995: U.S. Geological Survey Water-Data Report NV-95-1, 734 p.

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Modified: November 05, 1999 07:33 AM