Interim Policy and Technical Guidance on Broadband Acoustic Doppler Current Profilers
In Reply Refer To: April 26, 1993
Mail Stop 415
OFFICE OF SURFACE WATER TECHNICAL MEMORANDUM 93.15
SUBJECT: Interim Policy and Technical Guidance on Broadband
Acoustic Doppler Current Profilers
Several Districts or Areas are acquiring broadband acoustic
doppler current profilers (BB-ADCP) in fiscal year 1993.
Technical information and guidance on using the BB-ADCPs are
needed as we begin to collect basic data with them. The Office of
Surface Water (OSW) has initiated work to provide policy and
technical guidance on use of BB-ADCP's for discharge measurements.
This work includes: (1) writing a discharge-measurement
procedures manual; (2) developing and writing a quality-assurance
plan; and (3) documenting and extending discharge-measurement
verifications. Information from these empirical verifications
will be used to set initial policy on acceptable measurement
environment for use of BB-ADCP's in discharge measurements. These
tasks are being done by a team of OSW and District personnel.
The purpose of this memorandum is to inform you that policy and
technical guidance are being developed for the BB-ADCP, to provide
interim policy on using BB-ADCP's for discharge measurements, and
to request information that will contribute to the work outlined
above.
Much of the work needed to provide technical information and
guidance on use of BB-ADCPs in the WRD has already been
accomplished. The vendor is providing training and the California
District has led the WRD in promoting development of the BB-ADCP
for river discharge measurements and in documenting it's usage.
Several Districts have made current-meter measurements to verify
the discharge measured by the BB-ADCP. Please fill out the
attached form if your District has made any such verification
measurements which meet the criteria listed. Send the form and
measurement data to the Office of Surface Water, ATTN: BB-ADCP
Work Group. A continuum has been set up on the QVARSA Prime to
provide a forum for discussing BB-ADCP related topics. The
continuum name is ADCP. You should use this continuum to air and
answer questions, to discuss your experiences and problems with
BB-ADCPs, and to describe ideas and needs for technical support.
System performance and operating characteristics of BB-ADCP's are
changing as hardware and software continue to be developed.
Software, firmware, and documentation revisions are expected to be
issued frequently. Policy and technical guidance will thus be
subject to change and some information may be specific to a
particular system (i.e. signal frequency), or version which may
not be the most current. Some general information, and especially
the QA/QC guidance should be less transitory. The interim policy
provided here is for the 1200 kHz transducers using the transect
software, release 2.62.
POLICY
These policies apply to use of the BB-ADCP for making velocity
profile and discharge measurements from moving boats, and are in
effect until further technical information and more informed
policies are provided.
MEASUREMENT CONDITIONS
The 1200 kHz BB-ADCP can measure discharge for a limited range of
flow conditions. Based on manufacturer recommendations and
preliminary measurement verification information, the following
conditions must be met for general use of the BB-ADCP to measure
velocity profiles or discharge for basic data. Measurements made
at the limits of these conditions generally will not produce
highly accurate results and will require specific error analysis.
AVERAGE AVERAGE MAXIMUM FLOW UNMEASURED DUE
DEPTH VELOCITY TO LIMITED DEPTH OR VELOCITY
6Vbar>0.4 fps 10%
These and other measurement conditions (site characteristics and
instrument operation) must be assessed to correctly set up the
instrument/software, to determine appropriate measurement
techniques, and to check the results for errors. Some measurement
conditions to be assessed are listed on the BB-ADCP Discharge
Measurement Note form. When a measurement condition appears
problematic, measurement documentation should include: (1) a
brief description of the condition, (2) methods used to determine
if the condition (i.e. mobile stream bed) is significant to the
measurement, (3) how the effects of the conditions were accounted
for (i.e. appropriate instrument operating modes, configuration
file settings, tests, and error analyses). Additional
considerations on making discharge measurements are described in
Rantz, 1982. Measurement conditions to be assessed include the
following:
Mobile stream bed
Estimation of flow at channel edges
Pitch and roll of boat platform
Measurement starting and stopping procedures
Side Lobe Interference
Heading (compass) errors
Shallow-depth-caused errors not covered elsewhere
Vessel speed during measurement
Vessel course during measurement
Estimated velocity in unmeasured part of vertical
A minimum of two transects, one in each direction, is required for
a discharge measurement. The measured discharge will be the
average of the transect discharges. If the first two transect
discharges vary by more than 5 percent, under steady flow
conditions, then at least one more set will be obtained. Transect
measurements suspected to contain unusual errors should not be
used to determine the discharge measurement, but should be saved
and summarized on the ADCP Discharge Measurement Note form. The
top width of the unmeasured edge-flow area will be measured as the
distance from the bank to the instrument (not to the stream-gager
or another position on the boat).
TRAINING
The operation of the BB-ADCP uses technology which is highly
complex when compared to use of our standard Price-AA meters.
Several factors must be evaluated and understood in order to
optimize the set-up of the BB-ADCP for a particular measurement,
and to evaluate the quality of that measurement. Districts using
or planning to use BB-ADCPs are encouraged to develop expertise in
the use of this device. Parties making discharge measurements
using the BB-ADCP must include a person who has (1) attended
initial training in the use of the BB-ADCPs; (2) become familiar
with the basic principals of operation of BB-ADCPs; (3) learned
the principal BB-ADCP velocity and discharge measurement error
sources and how to evaluate and minimize them; and (4) knows the
operation and options of the Transect Software. This information
can be gained by experience, RDI manuals, other relevant
literature, and training. Initial training is currently defined
as attendance of a workshop taught by RDI personnel or Mike
Simpson of the California District, USGS. A BB-ADCP course is
being developed to address training needs.
MEASUREMENT DOCUMENTATION
Measurements made with the BB-ADCP should be documented on the
standard 9-275 C or G, (all applicable information) and on the
attached BB-ADCP Discharge Measurement Note form. (This form is
not an official government form and may be revised in a subsequent
memorandum. Your comments on how it may be improved are welcomed
in the ADCP continuum.) Each measurement should be checked. The
BB-ADCP configuration file and the raw data file for each of the
transects making up the measurement should be saved on floppy
diskette. Districts may wish to archive additional files or data.
We hope to have a software modification that will create a log-
form for each measurement that includes site measurement
condition, instrument configuration, and measurement data.
Charles W. Boning
Attachments
WRD DISTRIBUTION: A, B, FO, PO
ATTACHMENT 1
BB-ADCP VERIFICATION MEASUREMENT REQUEST FORM
The Office of Surface Water (OSW) requests discharge measurement
data from BB-ADCPs in conjunction with data from standard
discharge determination procedures, for the purpose of making
verifications of BB-ADCP collected discharge data.
In order for data to be used as a BB-ADCP discharge verification,
the following criteria should be met: The true discharge at the
site of the BB-ADCP measurement must be known to an accuracy of
5 percent or better. The true discharge estimate should be based
on a stage-discharge relation which is very stable for the part of
the rating within which the measurement was made. The stability
of the rating must be well documented by standard current meter
measurements which plot within 5 percent. A concurrent discharge
measurement using standard methods is always desirable but is not
required where documentation of rating stability is very good.
To supply OSW with your data for this verification effort, please
fill out this form and attach the items specified on page 3.
District or Field Office _________________________________________
Date ____________________
Contact Person ______________________ Telephone no. ______________
ADCP Measurements
Date(s) of measurements ____________________
Time period in which measurements were made ______________________
Number of transects used to determine discharge __________________
Was TRANSECT used? Yes _____ No _____
Measurement Conditions
Flow (uniform, rapidly varying, etc.) ____________________________
Cross-section (sand, rock, mud, etc.) ____________________________
Stage (steady, fluctuating, steady rise, etc.) ___________________
Maximum measured cross-sectional depth ___________________________
Minimum measured cross-sectional depth ___________________________
Cross-sectional width ____________________________________________
Estimated mean channel velocity __________________________________
Was the appearance of unusually high suspended
sediment concentrations observed or noted during
the ADCP measurements? ___________________________________________
Was the water unusually clear? ___________________________________
Was substantial movement of the cross-sectional bottom
material observed, noted, or suspected during the
ADCP measurements? _______________________________________________
Remarks (unusual conditions, etc.) _______________________________
__________________________________________________________________
__________________________________________________________________
ADCP Deployment
Boat mounting location (bow, starboard side, etc.) _______________
Was any ferrous material present in the ADCP mount or other boat
equipment? If yes, specify ______________________________________
__________________________________________________________________
Were the transects run near any large structures containing
ferrous materials, such as bridges or high-tension towers? If
yes, specify distance type and approximate distance from transects
__________________________________________________________________
__________________________________________________________________
__________________________________________________________________
Specify method used to determine transect edge distances (EDL,
steel tape, estimate by eye, etc) ________________________________
Non-ADCP Determination of Discharge
Non-ADCP discharge determination for the period of ADCP
measurements made from:
1. ______ gaging station rating curve
2. ______ Price AA or pygmy meter measurement(s)
3. ______ Neil Brown current meter measurements
4. ______ other (specify) _____________________________________
Description of Instrument
Instrument owner _________________________________________________
Instrument I.D. no. (i.e. serial no. or W no.) ___________________
Transducer frequency __________________________ kHz
Beam angle ___________ degrees
Type of transducer head: Concave _____ Convex _____
Attachments
Please attach the relevant items specified in the following
checklist:
1. ______ ADCP CONFIG file (printout or on disk)
2. ______ All ADCP raw data files on disk
3. ______ Copies of the ADCP measurement note forms
4. ______ Copies of the standard discharge measurement note
forms if standard current meter measurements were made
5. ______ A copy of the current rating table
6. ______ Copies of the last five discharge measurements made
at the station to confirm the rating
7. ______ Any miscellaneous field note forms
8. ______ Other documentation which may be helpful
Please return this form plus the attachments to:
U.S. Geological Survey
Indiana District
5957 Lakeside Boulevard
Indianapolis, IN 46278
Attention: Scott Morlock