Author(s): Stephen F. Blanchard
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Abstract: The U. S. Geological Survey (USGS) operates a network of approximately7,500 streamgages nationwide. Historically, the USGS measured river discharge through physical measurements of the water velocity and cross-sectional area of the river using a mechanical current meter placed directly into the water. For the last 15years, the USGS gradually has been replacing mechanical meters with hydroacoustic meters for discharge measurements. Hydroacoustic meters currently (2009) are used to make about 47 percent of USGS discharge measurements. Point velocity hydroacoustic meters, can be mounted on a wading rod, allowing discharge measurements to be taken while wading in a stream. More complex acoustic meter systems, such as the acoustic Doppler current profiler (ADCP), are used to measure water velocity, water depth, and boat velocity; then discharge is calculated from this information. The ADCP can be mounted on a variety of platforms, such as manned boats, tethered boats connected to an operator by a rope or cable and used from a bridge or cableway, and remotely controlled boats operated from shore. Hydroacoustic instruments allow the USGS to measure streamflow under extreme flow conditions and in difficult measuring locations. Hydroacoustic meters provide a more accurate flow measurement during low-flow conditions than does a mechanical meter. The ADCP has improved the quality of the measurements by providing more detailed information about the river flow. ADCPs are the most efficient method for measuring discharge, taking minutes rather than the hours associated with other methods. Hydroacoustic meters also allow the USGS to downsize the vehicles needed for field work.
Year: 2009