Stream Gaging

Adapted from: U.S. Geological Survey. 1999 "An Overview of the Stream-Gaging Program" [http://water.usgs.gov/wid/html/SG.html] 10/9/99. Also, Mason, Robert R., Jr., and Weiger, Benjamin A.. 1999. "Stream Gaging and Flood Forecasting" [http://water.usgs.gov/public/wid/FS_209-95/mason-weiger.html]

Schematic of a stilling well and shelter at a stream-gaging station.

The growth and development of the United States has been dependent on the availability of water resources. As the population grew during the late 1800s, people moved west into more arid regions of the country where the flow of rivers and streams was much less dependable than in the humid East. The necessity of reliable water supplies led to the need for streamflow data with which to design storage and distribution facilities.

In 1889, the first stream-gaging station operated in the United States by the U.S. Geological Survey (USGS) was established on the Rio Grande near Embudo, New Mexico. The establishment of this early station was an outgrowth of efforts to train individuals to measure the flow of rivers and streams and to define standard stream-gaging procedures. As the need for streamflow data increased, the stream-gaging program operated by the USGS has grown to include, in 1994, 7,292 continuous-record stream-gaging stations in the United States, Puerto Rico, and the Trust Territory of the Pacific Islands. More than 90 percent of these stations are operated with at least partial support from other Federal, State, and local agencies.

The two most fundamental items of hydrologic information about a river are stage, which is water depth above some arbitrary datum, commonly measured in feet, and flow or discharge, which is the total volume of water that flows past a point on the river for some period of time, usually measured in cubic feet per second or gallons per minute. These are the two key factors that are measured by a stream-gaging station.

The general objective of the USGS stream-gaging program is to provide information on streamflow characteristics at any point on any stream. Streamflow data are needed for immediate decision making and future planning and project design. Data, such as that needed to issue and update flood forecasts, are referred to as "data for current needs." Other data, such as that needed for the design of a future bridge or reservoir, are referred to as "data for future or long-term needs." Some data, of course, fit into both classifications; a station that supplies data for flood forecasting and also provides data to define long-term trends clearly fits both classifications.

There is widespread concern 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.

Gilbert, B.K. 1995. Water data program. Fact Sheet FS-065-95. U.S. Geological Survey, Washington, D.C., 4 pp.

Slack, J.R., and Landwehr, J. M. 1992. Hydro-Climatic Data Network (HCDN)---A U.S. Geological Survey streamflow data set for the United States for the study of climate fluctuations, 1874-1988. Open-File Report 92--129. U.S. Geological Survey, Washington, D.C., 193 pp.

Stallings, Eugene. 1991. Institutional and management aspects, flood forecasting and drought prediction by the National Weather Service. Pp. 117-122 In: Paulson, R.W., Chase, E.B., Roberts, R., and Moody, D.W., editors. National water summary 1988-89-Hydrologic events and floods and droughts. Water Supply Paper 2375. U.S. Geological Survey, Washington, D.C.

U.S. Geological Survey. 1995. Federal-State cooperative water-resources program. Fact Sheet FS-052-95. U.S. Geological Survey, Washington, D.C.,  4 pp.

van der Leeden, Frits, Troise, F.L., Todd, D.K. 1990. The water encyclopedia. Second edition. Lewis Publishers, Inc., Chelsea, MI, 808 pp.

Wahl, K.L., Thomas, W.O., Jr., and Hirsch, R.M. 1995. The stream-gaging program of the U.S. Geological Survey. Circular 1123. U.S. Geological Survey, Washington, D.C., 22 pp.

Wahl, K.L. 1995. An overview of the stream-gaging program. Fact Sheet FS-066-95. U.S. Geological Survey, Washington, D.C., 4 pp.