Figure 1. Price AA current meter used by 

USGS to measure streamflow. Photograph 

by J.M. Shelton, USGS.

Figure 2. USGS hydrographer making a 

streamflow measurement. Photograph by 

J.M. Hall, USGS.

Acoustic Doppler 

Current Profiler

Until the 1990s, the U.S. Geological 

Survey (USGS) had been making streamflow measurements using the same type 

of equipment for more than 100 years. 

The Price AA current meter (fig. 1) was 

developed by USGS engineers in 1896. 

Until recently, the majority of all streamflow measurements made by the USGS 

were made using this instrument (fig. 2). 

In the mid-1990s, a new technology 

emerged in the field of inland streamflow 

monitoring. The acoustic Doppler current 

profiler (ADCP), originally developed 

for oceanographic work, was adapted for 

inland streamflow measurements (fig. 3). 

This instrument is transforming the 

USGS streamgaging program.

The ADCP 

transmits an acoustic 

pulse through the 

water column. A 

“Doppler shift” is 

measured as the signal 

is reflected off of 

particles in the water, 

such as sediment and

microorganisms. Based 

on the assumption that 

the particles in the 

water are traveling at 

the same velocity as 

the water itself, a water 

velocity is computed.

The ADCP 

calculates its location 

relative to a starting 

point using “bottomtracking” technology. The bottomtracking measurement is made when 

the ADCP transmits an acoustic pulse 

through the water column to “locate” 

the streambed and measure water depth. 

Based on the assumption that the streambed is stationary and using an internal 

compass and pitch and roll sensors, the 

ADCP computes the speed and direction 

of the boat movement. During periods of 

high flow, the rocks and sediment along 

the streambed may be transported by 

the higher velocities. During these 

“moving-bed” 

conditions, a global 

positioning system 

(GPS) can be 

integrated with the 

system for a georeferenced location 

to correct for an 

erroneous bottomtracking computation. With measured 

velocity, depth, and 

speed, the software 

computes a total discharge for a cross 

section in real time (fig. 4).

The ADCP has enabled USGS 

hydrographers to make faster, more 

accurate streamflow measurements in a 

wider range of conditions than previously 

possible. The USGS South Carolina 

Water Science Center incorporates 

the use of ADCPs in its streamgaging 

program from mountain rivers in the 

upstate Blue Ridge to tidal canals in the 

Atlantic Coastal Plain.

Figure 3. Acoustic Doppler current profiler (ADCP), mounted 

on side of inflatable raft, is connected to an onboard computer 

to measure streamflow. Photograph by J.M. Hall, USGS.

Hydroacoustic Applications in South Carolina:

Technological Advancements in the Streamgaging Network

500 375

0.0 2.0 4.0 6.0 8.0

250 125 0

0.00

1.87

3.75

5.62

7.50

9.37

11.25

13.12

15.00

DEPTH, IN FEET

VELOCITY MAGNITUDE, IN FEET PER SECOND

LENGTH, IN FEET

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2008-3001

February 2008 Printed on recycled paper

Figure 4. Acoustic Doppler current profiler software 

displays streamflow in real time.
Figure 5. In situ acoustic Doppler 

equipment mounted to USGS 

streamgaging station. Photograph 

by J.M. Shelton.

Figure 7. Example of index-velocity rating 

at a tidally influenced creek.

Figure 6. Example of the stage-to-streamflow relation at a tidally influenced creek.

Acoustic Doppler current profilers have enabled hydrographers to measure streamflow in extreme conditions. Broad River below Ninetynine Island Reservoir, South Carolina. Photograph by J.M. Shelton, USGS.

For more information contact:

Director (e-mail: dc_sc@usgs.gov)

USGS South Carolina Water Science Center

720 Gracern Road, Suite 129

Columbia, South Carolina 29210

Or visit the following Web site:

http://sc.water.usgs.gov

In situ Index Velocity 

Measurements 

Acoustic Doppler technology 

also has been developed for in situ 

deployments (fig. 5). Many streams do 

not have a direct streamflow-to-gage 

height (water-surface elevation referenced 

to a datum) relation (fig. 6). These sites 

include streams influenced by control 

structures, aquatic plant growth, general 

backwater effects, and tidal effects. 

Historically, computation of streamflow 

at these sites has been difficult. Deploying in situ acoustic Doppler instruments 

allows the USGS to “index” the mean 

channel velocity. At these “indexvelocity” sites, a mean channel velocity 

is computed by dividing the measured 

streamflow by the cross-sectional 

area (from a standardized area rating). 

The computed mean velocity then is 

compared to the velocity reported by 

the in situ velocity meter. Multiple 

measurements can be used to produce 

an index-velocity rating (fig. 7).

The USGS South Carolina Water 

Science Center uses index-velocity 

The use of hydroacoustic instrumentation for real-time streamflow 

measurements, in addition to fixed 

installations for the computation of 

long-term record, has enabled the 

USGS South Carolina Water Science 

Center to collect quality hydrologic data 

for diverse hydrologic settings.

methods at multiple sites. In the 

upstate Piedmont region, backwater

effects from lakes necessitate the use 

of index-velocity methods to compute 

streamflow in the Pacolet River. In 

most of the Coastal Plain, in situ 

velocity meters are required to compute 

streamflow in the tidally affected areas.

U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

By John M. Shelton, Associate Director 

 (803)750-6112, jmshelto@usgs.gov

R2 = 0.4102

–4,000

–2,000

0

2,000

4,000

6,000

8,000

9.5 10 10.5 11 11.5

GAGE HEIGHT, IN FEET

STREAMFLOW, IN CUBIC FEET PER SECOND

0

0.1

0

0.2

0.3

0.4

0.5

0.6

0.7

0.5 1.0 1.5 2.0

INDEX VELOCITY, IN FEET PER SECOND

MEAN VELOCITY, IN FEET PER SECOND

R2 = 0.9972

y = 0.4112x – 0.008