The National Streamflow Information Program

Abstract

The U.S. Geological Survey (USGS) started its first streamgage in 1889 on the Rio Grande River in New Mexico to help determine if there was adequate water for irrigation purposes to encourage new development and western expansion. The USGS currently (2007) operates about 7,400 streamgages nationwide (fig. 1) as part of the National Streamflow Information Program (NSIP). These streamgages provide streamflow information for a wide variety of uses including flood prediction, water management and allocation, engineering design, research, operation of locks and dams, and recreational safety and enjoyment. These streamgages are operated by the USGS, in partnerships with more than 800 Federal, State, Tribal, and local cooperating agencies. In 2007, about 91 percent of these streamgages electronically record and transmit streamflow information to the World Wide Web in near real-time (http:// waterdata.usgs.gov/nwis). Most of these streamgages transmit the information by satellite, although telephone and radio telemetry also are used in some streamgages. The purpose of this report is to describe how the USGS obtains streamflow information. Streamgaging generally involves (1) obtaining a continuous record of stage—the height of the water surface at a location along a stream or river, (2) obtaining periodic measurements of discharge (the quantity of water passing a location along a stream), (3) defining the natural but often changing relation between the stage and discharge, and (4) using the stagedischarge relation developed in step 3 to convert the continuously measured stage into estimates of streamflow or discharge. Each of these four steps is explained in greater detail below.