Trolley Operated Automatic Discharge System (TOADS)—An Automated System for Horizontal Profiling of Water Velocity and River Discharge Measurements

Fact Sheet 2021-3008
By:  and 



Hydroacoustics have revolutionized how the U.S. Geological Survey (USGS) measures streamflow by increasing the efficiency and quality of the measurement. However, the ability to determine the full range of streamflow at a streamflow-gaging station remains limited because in-person flow measurements still must be made by qualified personnel. As a result, streamflow during flood events typically is measured infrequently in comparison to the duration of the event, usually after the peak flow has occurred. To overcome these difficulties, the USGS has developed the Trolley Operated Automatic Discharge System (TOADS), an automated system for measuring streamflow without the need for onsite personnel. Investment by USGS in TOADS and other innovative technologies and methods provides substantial improvements to flood assessment and watershed management, making the USGS the continued world leader in surface-water hydrology.

Streamflow measurements made with TOADS are analogous to a moving-boat measurement, which measures the flow at a point in a river by moving from bank to bank and measuring water velocities at various depths below the boat. The TOADS uses hydroacoustic technology to profile water velocity across a river while moving vertically through the water column to measure flow at multiple depths. Use of TOADS to measure streamflow can save substantial time and money, provide improved flow ratings by taking numerous targeted automated measurements over a range of conditions, and provide a safe alternative to standard boat measurements when river conditions are hazardous. The TOADS can be programmed to measure flow based on a variety of triggers (including river stage, amount of flow, time of day) and can take repeated measurements at user-specified intervals during floods, droughts, and other events of interest.

Suggested Citation

Johnson, K.K., and Bosch, C.J., 2021, Trolley Operated Automatic Discharge System (TOADS)—An automated system for horizontal profiling of water velocity and river discharge measurements: U.S. Geological Survey Fact Sheet 2021–3008, 2 p.,

ISSN: 2327-6932 (online)

Publication type Report
Publication Subtype USGS Numbered Series
Title Trolley Operated Automatic Discharge System (TOADS)—An automated system for horizontal profiling of water velocity and river discharge measurements
Series title Fact Sheet
Series number 2021-3008
DOI 10.3133/fs20213008
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Central Midwest Water Science Center
Description 2 p.
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details