Midsection ADCP Measurements for Check Measurements

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Detailed Description

In this video, we will highlight the advantages of using an ADCP with the midsection method as a check measurement. Note: Use of trade names is for descriptive purposes only, and does not imply endorsement by the USGS. For additional videos in this series, visit the following link: https://www2.usgs.gov/humancapital/ecd/hydrotube/hydrotube-ADCP.html


Date Taken:

Length: 00:02:34

Location Taken: Augusta, ME, US


Hi, my name is Nick Stasulis and I am a hydrologic technician with the Maine Office of the New England Water Science Center. In this video, we will highlight the advantages of using an ADCP with the midsection method as a check measurement.

Hopefully, your office QA plan has a well established set of criteria for when check measurements are needed. This likely includes information such as percent difference from the shifted rating, rated uncertainty of the measurement, known changes to the control condition, or other information. Be sure you are clear on this criteria, regardless of what measurement method you are using.

When making a moving boat ADCP measurement we are commonly limited to one cross section and usually only that one ADCP is available. Typically, users simply reconfigure the ADCP and collect an additional moving boat measurement. Even though the unit is reconfigured, the compass calibration repeated and a new moving bed test collected, there is still potential for errors to be repeated in the check measurement as the same moving boat method is being used to compute discharge.

These factors are why use of the midsection method provides great advantages for a check measurement. First, you are simply using a completely different method for computing discharge, which doesn’t rely on bottom tracking. Remember that bottom tracking is how the ADCP measures it’s speed and direction as it moves across the channel, and with midsection, the ADCP is assumed to be stationary, so bottom tracking isn’t necessary. A midsection measurement would also allow you to use the same ADCP and likely the same measuring location as the original measurement if you are limited to only one measuring location. Since bottom tracking isn’t necessary, moving bed is not an issue, and moving bed tests are not required.

Using this method as a check measurement could also be useful in cases where there were issues with the moving boat measurement and completing a transect due to debris, ice, river traffic or other similar issues.

When using the midsection method with the same ADCP as the original measurement, it’s recommended you down-power the ADCP, change the battery if possible, and configure the unit using the manufacturer’s software. Also, try changing the cross section, if possible.

Hopefully you see that despite the small extra cost for enabling the midsection option with an ADCP, there is great potential for improving the validity of your check measurements when using ADCPs.