« PreviousContinue »
The unusually low water level of 1988 exposed many of the sandbars on the bottom of the Mississippi River, such as this one opposite the town of Helena, Ark. A few days after this photograph was taken, a backhoe was able to trench the sandbar, providing a rare opportunity for L'SGS hydrologists to study the bed material of the Mississippi. (Photograph by Robert H. Meade.)
Reflections on Water
By Wayne B. Solley
A look at trends developed from USGS water-use estimates over the past 35 years shows that the Nation's total water use more than doubled from 1950 to 1985. Water withdrawals over the last 5 years, however, have declined by 10 percent. The drought that affected much of the Nation during 1988 also had its effects on water use. Spot sampling during the 1988 drought suggested that water use generally was higher than in recent years. Although nationwide estimates for 1988 were not available, there were some local estimates. Public watersupply withdrawals to meet the demands in Washington, D.C., for example, during June and July were 14 percent above the 5-year average. In parts of Nebraska, farmers and ranchers turned to ground water as a source for irrigation 1 month earlier than normal, and ground-water withdrawals were about twice the quantity withdrawn in recent years.
The USGS has compiled and published estimates of water use in the United States at 5-year intervals since 1950. These water-use estimates can be used to analyze trends in water use, to
appraise present use, and to plan for future uses of the Nation's water resources.
The latest 1985 data show that the 10 percent decline in total water withdrawals was observed in both surfacewater and ground-water withdrawals. The largest decreases were in the thermoelectric power, industrial, and irrigation categories of use.
A total of 399 billion gallons per day of both fresh and saline water was withdrawn from lakes, reservoirs, streams, aquifers, and springs during 1985 to meet the needs for offstream uses such as domestic, commercial, industrial, irrigation, livestock, and thermoelectric power plants. Freshwater withdrawals alone averaged 338 billion gallons per day, equivalent to about 1,400 gallons per day for each person in the United States. In addition, water used for hydroelectric power generation, the only instream (nonwithdrawal) use compiled in 1985, was estimated to be 3,050 billion gallons per day, or 7 percent less than during 1980.
The decrease from 1980 to 1985 in total withdrawals is in contrast to an increasing trend that persisted from 1950 to 1980. A slackening in the rate of increase of total withdrawals from 1970 to 1975 and again from 1975 to 1980, however, marked a downward trend that was confirmed by the 1985 data.
The decrease in offstream use was widely spread across the Nation; 37 States reported less water withdrawn during 1985 than during 1980. Several factors might account for the downturn. Streamflow generally was more plentiful in 1985 than in 1980 because of more rainfall, which reduced the dependence on ground water for irrigation in many areas and the need to irrigate in some areas. On the other hand, demands on the ground-water system tend to lower water levels and increase the need for energy to pump water, which in turn can decrease the availability and quality of the water. Each of these factors can raise the cost of water and make water users, especially irrigators, more selective and efficient in their use of ground water.
Increased use of recycled water, coupled with depressed commodity prices, probably decreased the requirements for industrial and irrigation withdrawals.
Finally, the 1985 estimates are based on more reliable information and analysis than previous estimates in this series. In many instances, it seems that previous estimates may have been too high.
Two water-use categories that are exceptions to the downturn are "public supply" and "rural domestic and livestock." During 1985, withdrawals for public supply were about 7 percent and rural use about 39 percent more than during 1980. The 7-percent increase in public-supply withdrawals corresponds to a 7-percent increase in population served, and the large increase in withdrawals for rural use mainly reflects large increases in fish farming, particularly in Arkansas, Idaho, and Mississippi.
Other highlights from the 1985 data include the following:
• The average withdrawal of freshwater in the United States is equivalent to about 1,400 gallons per person per day for all uses; however, the amount varies greatly from State to State, ranging from a high of 22,200 gallons per capita per day in Idaho to a low of 152 gallons per capita per day in Rhode Island. High per-capita values are characteristic of thinly populated States having large acreages of irrigated land.
• Withdrawals for domestic purposes averaged 78 gallons per capita per day for people served by their own water system and 105 gallons per capita per day for people served by a public-supply system.
• Estimates of withdrawals by source indicate that, during 1985, total surfacewater withdrawals were 325,000 million
gallons per day (Mgal/d), or 10 percent less than during 1980, and total groundwater withdrawals were 74,000 Mgal/d, or 12 percent less than during 1980.
• More water was withdrawn in California (nearly 50,000 Mgal/d) than in any other State, more than twice as much as in either Texas or Idaho, the next largest users. Four states—California, Texas, Idaho, and Florida—accounted for 28 percent of the water withdrawn in the Nation.
• More water was withdrawn (187,000 Mgal/d) during 1985 for thermoelectric power plants to generate electricity than for any other category of offstream use; however, this total was 13 percent less than during 1980. About 56,000 Mgal/d was saline water.
• Irrigation ranks second in offstream water withdrawals in the U.S.—137,000 Mgal/d during 1985, 6 percent less than during 1980. Irrigation accounts for about 80 percent of all consumptive water use in the United States.
• More than 90 percent of the irrigation water was withdrawn in the Western United States. In contrast, almost 90 percent of the thermoelectric power withdrawals were in the Eastern United States.
• The total amount of consumptivefreshwater use —that is, water withdrawn that is evaporated, transpired, incorporated into products and crops, consumed by humans or livestock, or otherwise removed from the immediate water supply—averaged 92,300 Mgal/d during 1985, or 9 percent less than during 1980.
Before 1980, USGS water-use estimates were derived from a variety of sources and ranged widely in accuracy and consistency. In 1977, the Congress of the United States recognized the need for uniform, up-to-date, and reliable information on water use and directed the USGS to establish a National WaterUse Information Program to complement USGS data on the availability and quality of the Nation's water resources. Thus, the National Water-Use Information Program became part of the USGS FederalState Cooperative Program; as of 1988, 49 States and Puerto Rico are participating in the program at various levels of involvement.
The National Water-Use Information Program is designed to be the source for accurate, consistent, timely, and accessible water-use information. The goals of the program are to collect and compile reliable site-specific and aggregated water-use information, to develop and refine computerized water-use information systems at State and national levels, to devise new methods and techniques to improve the collection and the analysis of water-use information, and to disseminate the information in ways that are beneficial to a variety of users. As the National Water-Use Information Program develops, more emphasis will be placed on interpretive studies and the integration of water-use information with other water-resources projects.
The latest national water-use estimates were compiled for 1985 and are published in U.S. Geological Survey Circular 1004, "Estimated Use of Water in the United States in 1985." A new Aggregated Water-Use Data System (AWUDS) was developed and installed on each USGS District computer to store and manage the water-use information compiled for this report. Although the information is published by State and waterresources region, the AWUDS data base contains more than 120 data elements for 3,225 counties and 222 water-resources subregions.
Analysis of field data and evaluations of existing water-use data were more comprehensive and more detailed in the compilation of data for the 1980 and 1985 water-use reports than for previous water-use reports thanks to support from the broader National Water-Use Informa
tion Program. The collection, compilation, and analysis of the 1985 water-use information was a 2-year cooperative effort between the U.S. Geological Survey, other Federal agencies, and numerous State and local organizations. As the State water-use information programs are developed and refined, the timeliness and accuracy of water-use data at the State and the national levels will continue to improve.
Selenium in the San
By Robert J. Gilliom
Agricultural drainage problems in the San Joaquin Valley of central California have attracted national attention since 1983, when selenium in water from subsurface tile-drainage systems in the central part of the western valley was found to have toxic effects on waterfowl. Other constituents of drain water, particularly dissolved solids, boron, chromium, and molybdenum, may cause water-quality problems also, but selenium is the most widespread problem and the most limiting constraint on management alternatives.
This article summarizes the results and implications of USGS studies and related research by others through 1987, the halfway point of a 5-year study, on the sources, distribution, and mobility of selenium in the San Joaquin Valley. The USGS is a participating agency in the San Joaquin Valley Drainage Program, which is cooperatively managed by the U.S. Department of the Interior and the State of California.
Geologic Source and Distribution in Soil
Selenium-related problems are most likely to occur in areas where soils are formed of sediments from the marine
Three specific areas of the
western San Joaquin
Valley.. .have the highest
sedimentary formations of the Coast
Effects of Irrigation on the
The key to evaluating the origin and present-day distribution of high-selenium concentrations in ground water is understanding the redistribution by irrigation water of soluble forms of selenium. Irrigation has had regional-scale effects on ground-water recharge and discharge and on the movement of soluble salts, including selenium. The dominant influences on ground water since the early 1900's have been increased recharge of irrigation water to ground water in the semiconfined zone and historic pumping of ground water from the confined zone.
These agricultural activities have caused the water table to rise over much of the western part of the valley. The rising water table reflects a net recharge rate to the ground-water system in excess of its capacity to transport water to areas of discharge. Importation of surface water has led to increased application of irrigation water and hence increased rates of recharge to the system. Concur
rently, pumpage from the confined zone
Distribution of Selenium in
The present-day areal and depth distribution of selenium in the ground water of the central western valley is the result of a combination of natural processes and changes in the hydrologic system caused by irrigation and groundwater withdrawals. In the natural hydrologic system, soluble forms of selenium are concentrated along with other solutes in saline soils of the lower and middle parts of Coast Range alluvial fans. The first few decades of irrigation of the alluvial-fan soils leached much of the readily mobile selenium from the soil into the ground water. The present-day areal distribution of selenium in shallow ground water follows many of the same general patterns of soil salinity before much of the area was extensively irrigated (figs. 5 and 6). Within about 10 to 20 feet below the water table, selenium concentrations commonly range from 10 to 50 micrograms per liter (u.g/L), but they are 10 to 100 times higher where the water table has been near the land surface and evaporative concentration has occurred. Within the range of 20 to 150 feet below the water table, an interval of variable thickness occurs in which selenium concentrations are commonly 50 to more than 1,000 |xg/L. Water in this interval is derived principally from recharge of earlier irrigation water. Native ground water, with selenium concentrations of less than 10 (J-g/L, is below the high-selenium water.
The large quantity of high-selenium ground water in the central part of the