The USGS provides maps, reports, and information to help others meet their needs to manage, develop, and protect America's water, energy, mineral, and land resources. We help find natural resources needed to build tomorrow, and supply scientific understanding needed to help minimize or mitigate the effects of natural hazards and environmental damage caused by human activities. The results of our efforts touch the daily lives of almost every American.
Figure 1. Number of stations operated by the U.S. Geological Survey in 1994, by State or possession.
The stream-gaging program of the USGS does not represent a single "network" of stations, but is an aggregation of networks and individual streamflow stations that had been established for various purposes. Data from the 7,292 active stations, as well as from discontinued stations, are available through the USGS's National Water Data Storage and Retrieval System (WATSTORE) that holds mean daily-discharge data for about 18,500 locations and more than 400,000 station-years of record, or more than 146 million individual mean daily-discharge values. Additional data are added to the data base each year. The stream-discharge data base is an ever-growing resource for water-resources planning and design, hydrologic research, and operation of water-resources projects.
Figure 2. Number of stations and sources of funds, 1994 fiscal year.
The U.S. Geological Survey stream gaging network is vital to the National Weather Service's river forecast and warning program and the goal to reduce flood damages and loss of life. Without data from this network, this nation would experience increased losses from floods of both life and property [Elbert W. Friday, Jr., Assistant Administrator for Weather Services, National Weather Service, written commun., January 19, 1995].
Transfer of streamflow information for unregulated streams may be accomplished in many ways, ranging from the simple to the complex. Simple methods are interpolation between or extrapolation from stations on the same stream on the basis of drainage-area size. More complex methods may involve transferring information from basins with similar hydrologic characteristics, mapping station data to define approximate lines of equal runoff values, or correlating short records with long records. A statistical technique known as multiple-regression analysis has proven to be effective for defining equations that relate streamflow characteristics to the basin and climatic characteristics that affect streamflow. The resulting equations usually are referred to as "regional relations" because they can be applied to ungaged streams within a defined hydrologic area or region (Jennings and others, 1994).
Trend analysis is another application that requires long records. Concern is widespread that increased greenhouse-gas concentrations in the atmosphere are affecting the climate and the hydrology of the Earth. Analysts have used actual streamflow records to determine whether streamflows are beginning to change as a result of human activities or global warming. Natural climatic episodes of wetter or dryer than normal and lasting longer than a decade have been observed. Given the occurrence of such episodes and the inherent variability of streamflow, record lengths of more than 50 years are essential if real trends are to be detected. Slack and Landwehr (1992) reviewed the USGS data base to identify streamflow records that reflected natural conditions and could be useful in trend analysis. They identified 1,659 stations in the United States and its possessions. Over 500 of these stations have record lengths in excess of 50 years.
Hydrologic systems.---One of the more common uses of streamflow data is to account for and monitor the flow through a river basin or to define the general hydrologic conditions in the basin. Data from about 4,200 active stations are used to understand and evaluate the interactions of ground- and surface-water resources and to monitor diversions and return flows. At the State and interstate level, many of the stations serve a key role in the process of allocating and regulating water rights.
I am writing you on behalf of the Missouri River Basin Association, a coalition of eight states and twenty-eight Indian Tribes in the Missouri basin. For years, we have been working closely with the federal agencies that have jurisdiction in the basin to improve management of the basin's water resources. As you know from your years with the USGS, good water management depends upon good data. An important source of good data has been USGS's Coop Program [Excerpt of letter from J. Edward Brown, President, Missouri River Basin Association to Gordon P. Eaton, Director, U.S. Geological Survey, February 14, 1994].
Regional hydrology.---Stations supplying data that are largely unaffected by manmade storage or diversion furnish much of the data needed for future or long-term needs. Data from about 3,800 active stations can be used to develop regional relations for estimating streamflow characteristics at ungaged sites or sites where only small amounts of streamflow data are available.
Project operation.---Data from stations in this classification are used by water managers in making daily operational decisions. For example, data from about 2,900 active stations are used by the COE, the BOR, and others to operate more than 2,000 flood control, navigation, and water-supply reservoirs.
Hydrologic forecasting.---Data from stations so classified provide information for flood and water-supply forecasting. These stations play a key role in efforts by Federal, State, and local agencies to protect the lives and welfare of the public. More than 3,000 of the stations operated by the USGS are used in the NWS's flood-forecasting system.
Water-quality monitoring.---The evaluation of water quality in rivers, lakes, reservoirs, and estuaries depends on having data on the chemistry of the water and the streamflow. Other program components provide data on the chemical quality of surface- and ground-water resources, sediment in streams and lakes, and water use (fig. 3). To compare the relative amounts of contaminants coming from different sources (various tributaries or wastewater treatment plants), one must know the flux of the contaminants computed as the concentration times the rate of streamflow. Data from about 2,700 active stations in this category provide the streamflow data needed to evaluate the quality of the Nation's surface-water resources.
Figure 3. Percentage distribution of funds for U.S. Geological Survey hydrologic data collection, 1994 fiscal year.
Planning and design.---Data from about 1,100 active stations in this category are used to plan and design a specific project, such as a reservoir, levee, water-treatment facility, or hydroelectric powerplant.
The U.S.G.S. basic water data collection program is of vital importance to water resource planning, design, and operation in the United States. Reductions in surface water data collection will have long-term adverse effects on the efficiency and certainty of planning, design, construction, and operation of projects. Civil engineers rely on surface water data for numerous projects, including flood control, pollution control, transportation, and navigation [Excerpt from American Society of Civil Engineers Policy Statement on Surface-Water Data Collection, October 24, 1993].
Legal obligations.---Data from these stations satisfy a legal responsibility of the USGS or of signatories of treaties, compacts, and decrees. The USGS operates about 250 stations in support of 17 interstate compacts, 2 Supreme Court decrees, and 1 international treaty.
The U.S. Supreme Court in a 1954 decree required that the USGS monitor flows in the Delaware River at Montague, New Jersey and the diversions out of the Delaware River Basin through the Delaware and Raritan Canal. The decree settled a water-rights suit in which four States were involved. The USGS operates two stations to monitor the flows as identified in the U.S. Supreme Court decree [William J. Carswell, Jr., Delaware River Master, U.S. Geological Survey, oral commun., January 1995].
Research.---Data from about 700 active stations are collected for particular research or water-investigation studies. As such, the data supply a current need. The length of time that the data will be needed is dictated by the particular project. Some research needs, such as detection of hydrologic trends, can be met only by long-term, high-quality streamflow records.
Detection of hydrologic change requires long-term data sets of greater quality and reliability than are normally needed in the investigations of processes [National Research Council, 1991, p. 223].
The nationwide analysis (Thomas and Wahl, 1993) documented that multiple uses were being made of data collected at stations in the USGS stream-gaging program with about 80 percent of the stations having data uses in two or more of the above categories and about 25 percent having data uses in four or more categories.
Automated telemetry provides the data users with provisional stage and discharge data in a timeframe that meets water-management needs. This technology also permits the USGS field offices to continuously monitor the operation of the hydrologic stations, time visits to stations to coincide with times of maximum need for data (such as during floods) and to service equipment at the stations. Currently, more than half of the 7,292 USGS stations are equipped with automated telemetry.
In addition to the published record, the data collected by the USGS are archived in the nationwide WATSTORE data base. The number of active stations in the WATSTORE data base with associated record lengths is given in figure 4 for each decade from 1900 to 1990. The data in figure 4 also include stations operated by other agencies (primarily State agencies) for which the data are reviewed, archived, and published by USGS. In 1990, data from about 400 stations were provided to the USGS by other agencies.
Figure 4. Number of stations in the U.S. Geological Survey data base, 1900--90.
Beginning with the 1990 water year, Water Data Reports are also available on Compact Disk-Read Only Memory (CD--ROM). The Water Data Reports and the CD--ROM's are distributed to participating agencies and libraries; they also are available for sale by the USGS Earth Science Information Center, Denver, Colorado. Currently (1995), the USGS is developing procedures to allow access to streamflow data by means of Internet. Historical mean daily-discharge data for about 18,500 stations will soon be available through this source.
Maintain a long-term and consistent nationwide data base
Maintain state-of-the-art recorders, sensors, and equipment for data collection
Provide easy access to archived and realtime data
Maintain a skilled staff of hydrologists and hydrologic technicians for collecting and computing the streamflow records
The USGS continues to be committed to the collection and dissemination of high-quality streamflow data as a critical part of its overall mission of providing earth science information for the wise management of the Nation's natural resources. The maintenance of a viable stream-gaging program is an integral part of managing these natural resources.
We believe that the U.S.G.S. basic water quantity data collection activities are: 1) essential, because the value of hydrologic data increases with both the length and continuity of the record; 2) the logical responsibility of the Federal Government because the States cannot possibly assume the support and leadership role of U.S.G.S. for interstate water systems; 3) cost-effective, because coordinated water data collection eliminates overlapping and duplicative efforts [Statements of William J. Carroll, President-elect, American Society of Civil Engineers, before the Subcommittee on Interior and Related Agencies, Committee on Appropriations, U.S. House of Representatives, March 10, 1988].
from U.S. Department of the Interior, U.S. Geological Survey, Fact Sheet FS-066-95