The use of acoustic Doppler current profilers (ADCPs) from a moving boat is now a commonly used method for measuring streamflow. The technology and methods for making ADCP-based discharge measurements are different from the technology and methods used to make traditional discharge measurements with mechanical meters. Although the ADCP is a valuable tool for measuring streamflow, it is only accurate when used with appropriate techniques. This report presents guidance on the use of ADCPs for measuring streamflow; this guidance is based on the experience of U.S. Geological Survey employees and published reports, papers, and memorandums of the U.S. Geological Survey. The guidance is presented in a logical progression, from predeployment planning, to field-data collection, and finally to post-processing of the collected data. Acoustic Doppler technology and the instruments currently (2008) available also are discussed to highlight the advantages and limitations of the technology. More in-depth, technical explanations of how an ADCP measures streamflow and what to do when measuring in moving-bed conditions are presented in the appendixes. ADCP users need to know the proper procedures for measuring discharge from a moving boat and why those procedures are required, so that when the user encounters unusual field conditions, the procedures can be adapted without sacrificing the accuracy of the streamflow-measurement data.

"The use of acoustic Doppler current profilers (ADCPs) from a moving boat is now a commonly used method for measuring streamflow. The technology and methods for making ADCP-based discharge measurements are different from the technology and methods used to make traditional discharge measurements with mechanical meters. Although the ADCP is a valuable tool for measuring streamflow, it is only accurate when used with appropriate techniques. This report presents guidance on the use of ADCPs for measuring streamflow; this guidance is based on the experience of U.S. Geological Survey and Water Survey of Canada employees and published reports and papers. The guidance is presented in a logical progression, from pre-deployment planning, to field data collection, and finally to post-processing of the collected data. Acoustic Doppler technology and instruments are discussed to highlight their advantages and limitations. More in-depth, technical explanations of how an ADCP measures streamflow and what to do when measuring in moving-bed conditions are presented in the appendices. ADCP users need to know the proper procedures for measuring discharge from a moving boat and why those procedures are required, so that when the user encounters unusual field conditions, the procedures can be adapted without sacrificing the accuracy of the streamflow-measurement data"--Abstract, page 1.

The mission of the U.S. Geological Survey (USGS) Water Resources Discipline is to provide the information and understanding needed for wise management of the Nation's water resources. Inherent in this mission is the responsibility of collecting data that accurately describe the physical, chemical, and biological attributes of water systems. These data are used for environmental and resource assessments by the USGS, other government agencies and scientific organizations, and the general public. Reliable and quality-assured data are essential to the credibility and impartiality of the water-resources appraisals carried out by the USGS.

The Acoustic Doppler Current Profiler (ADCP) is a doppler current meter which uses the moving boat method for rapidly measuring river discharge. The doppler current meter measures the current profiles and boat velocity along a transect across a stream. The ADCP measures profiles of the streams velocity relative to the boat and the velocity of the boat relative to the bed of the stream. The calculation of discharge depends on this data and it is not necessary to know either the compass heading or the actual location of the boat. The transect of the stream can be an arbitrary curve as long as it starts near one side of the stream and ends near the opposite bank.

The techniques and standards for making discharge mea- surements at streamflow gaging stations are described in this publication. The vertical axis rotating-element current meter, principally the Price current meter, has been traditionally used for most measurements of discharge; however, advancements in acoustic technology have led to important developments in the use of acoustic Doppler current profilers, acoustic Dop- pler velocimeters, and other emerging technologies for the measurement of discharge. These new instruments, based on acoustic Doppler theory, have the advantage of no moving parts, and in the case of the acoustic Doppler current profiler, quickly and easily provide three-dimensional stream-velocity profile data through much of the vertical water column. For much of the discussion of acoustic Doppler current profiler moving-boat methodology, the reader is referred to U.S. Geo- logical Survey Techniques and Methods 3–A22 (Mueller and Wagner, 2009).

"Acoustic Doppler current profilers (ADCPs) are typically used for measuring river discharge from a floating platform or boat that is continuously moving across the river from one bank to the other. A hydrographer can also use ADCP's to measure river discharge using the mid-section method in which the ADCP is held in place for a specified duration at multiple discrete locations, or verticals, across the stream. Water velocity data is captured throughout the depth of flow and averaged to obtain a mean velocity estimate integrated over the full depth at each vertical. The depth for each vertical is determined with the ADCP, and representative areas and discharges for each vertical are calculated and summed to obtain a total discharge. This document presents guidance and standard operating procedures specific to deploying ADCPs for open water mid-section measurements"--Introduction, page 2.