RiverPro velocity underestimation

[alex_hauet]

Dear all. In many of our RiverPro measurements, we have observed an underestimation of velocity for the cells just below the surface ping, probably due to interference between the surface ping and the BB ping below it. As a result, in Extrap we can observe a layer with a strong underestimation of speed. This problem only affects one cell on the vertical, so TRDI maintains that it won’t significantly bias the total discharge… but there will be a bias for sure!

Have you observed the same issue with your RiverPro ?

Thanks!

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[Baddocke]

Hi Alex – haven’t seen this here but will look further?

Here’s an example attached.

Regards – Evan.

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[alex_hauet]

Thanks Evan. RDI told me that it was probably interference between the surface pig and the BB ping below, and that it probably only happened for a given depth of about 2m. We observed this with 3 different RiverPro…

[dave@genesishydrotech.com]

I checked 10 or so RiverPro measurements and found 1 that showed this behaviour. It was even labeled bin_3.

I am guessing that it may take a specific combination of water temperature and backscatter to cause this issue.

Dave

[Kristoffer Florvaag-Dybvik]

Hi, Alex.

I have not seen this in a discharge measurement, but I have seen a similar feature in a test with a RiverPro anchored in a lake. I really hope I would have noticed it in my own discharge measurements, and I have had a new look at some of them now without seeing the feature. The anchored riverpro shows a HIGHER velocity magnitude (and east and north velocity) in the first bin below the surface bins in WinRiver when I average a lot of ensembles. See attached screenshot. (The reason it was anchored is that we used the data to check if a still lake was actually still when testing fro flow disturbance). If not averaging, we only see low velocity magnitudes in the top bins and higher velocity magnitudes in the rest of the bins, since they are more noisy.

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[Kristoffer Florvaag-Dybvik]

Hi Alex and all.

I have seen something similar on a StreamPro measurement as well. Overestimation of speed in the 5th bin. Depth around 1-1.3 meters, down to 2 meters. ARC boat. Clear water in the outlet of a lake. I don’t know what this is. If it was some double reflection phenomena the erroneous velocity should have followed the shape of the river bed.

I have used this instrument many times and this is the only time I have seen this happen.

Any ideas?

Kristofffer

PS: I know it was too shallow for the ARC boat to be ideal here. DS

 

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[Ole]

Hi Alex

I also checked several RiverPro measurements and none of them showed this behaviour. However, I forwarded yout question to the operations technicians to get a wider spectrum of responses.

Best
Ole

~~~~~~~~~~~
Ole Rössler
Federal Institute of Hydrology
Koblenz, Germany
email: roessler at bafg.de

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