Webinar - Principles of Extrapolation and Screening of Velocity Profiles

Principles of Extrapolation and Screening of Velocity Profiles

View the webinar presented by our guest speaker, Daniel Wagenaar - Xylem Senior Hydrologist. Covering Velocity Profile Principles, Extrapolation of Velocity Profiles, Implementation of Screening Distance and more. (If you would like a PDF copy of the presentation, please make a request at info.apac@xyleminc.com)

Key Points Covered:

  • Velocity Profile Principles
  • Extrapolation of Velocity Profiles
  • Implementation of Screening Distance
  • RSL (SonTek):  RiverSurveyor Live Software (SonTek)
  • QRev (USGS):  Software for Computation and Quality Assurance of Acoustic Doppler Current Profiler Moving-Boat Streamflow Measurements

The extrapolation and screening of velocity profile measurements from Acoustic Doppler Current Profiler instruments are essential aspects of the measurement process.  It is important to understand the fundamental principles of velocity profiles within a channel and the reason why the extrapolation process can have substantial impact on the final discharge calculation. 

The presence and magnitude of flow disturbance in the velocity profile under certain flow conditions can be associated with the Acoustic Doppler Current Profiler and or Platform used during the measurement.  The impact of flow disturbance on velocity profile measurements are well defined and can be omitted from the velocity profile using existing techniques.  The development of velocity profile extrapolation and implementation of screening distance varies between real-time data collection and post processing  applications and it is essential that operator has full understanding of the different processes involved.

Questions and Answers from the Webinar:

Q. If you use the USGS option in river surveyor, does it detect if it’s a S5 or M9 and set the blanking distances accordingly?

A. RiverSurveyor Live automatically detects if a RiverSurveyor S5 or M9 is connected and apply the required screening distance for the USGS option.  In the case of the RiverSurveyor S5, the screening distance will be 0.000m

Q. Is it possible to take Bathimetry survey by ADCP?
    For rivers like Mahanadi in India having 3000m  to 6000m wide how it is possible to take discharge remotely without a boat?

A. The current "Unmanned Surface Vehicle" technology can only operate within couple of kilometres.  The range of 3 - 6km is well outside available range.  The risk of losing or damaging and instrument when operating remotely at these distances would be very high.

Q. Did S5 blanking distance review in Mueller have the streamlined flow attachment to the bottom of the board?

A. Based on the information available, Dave Mueller verified the instruments and platforms available at the time of research. 

Q. Does it work only in shallow depths? I would like to know whether the instruments works more than 3000 m?

A. The Acoustic Doppler Current Profilers most commonly used on the market ranges from 3MHz to 600KHz with measurement range of 5 to 100m respectively.  There are lower frequencies 250 KHz available from SonTek that can measure up to 180m.  The measurement range of 3000m is not achievable with current ADCP technology 

Q. You've discussed the extrapolation near the surface, has research been conducted near the river/stream bottom?  i.e. sand vs rocks vs cobbled vs weeds/plants

A. The extrapolation process of the velocity profile accounts for both the top (transducer depth + blanking distance) and bottom (area of side lobe interference) unmeasured zones, depending on the extrapolation method used. There are number of research papers on the impact of roughness on velocity profile, especially sediment related research.

Guest Speaker: Daniel Wagenaar

Daniel WagenaarDaniel started his hydrographic career in South Africa as hydrographer with experience in surface water and ground water monitoring.  He continued with his career progression as Technical Manager of hydrographic operations overseeing all computations including rating development and data processing.  He expanded his 29 years’ experience in hydrographic operations by accepting Manager of Water Monitoring Systems position in Australia, responsible for the design of business process frame works and the development of operational standards, quality assurance systems and training.  His focus at SonTek consist of the development of Acoustic Doppler measuring techniques, enhancement of surface water methodology, quality assurance and data management principles used in collection of Acoustic Doppler data.  The assessment of latest research, International Standards and Organizational requirements forms a key component in the development and enhancement of measuring techniques.  Daniel holds a B.Sc. in Water Engineering from Central University Technology and B.Sc. in Geohydrology from Free State University. 

View the Webinar