Flow sensor for a river

Hello. I am developing a project to measure the flow of a river branch in the city. This river branch has dirty water. I'm researching a suitable flow sensor to measure flow.

I've found flow sensors that don't use turbines, as they are based on magnetic effect, I think they would be more suitable, but their price is very high (about $6000).

Do you have any suggestions on which sensor to use?

Thanks

Look at yacht boatspeed sensors - there are some that have no moving parts. Of course, being marine equipment, they will be expensive too, but hopefully not as bad.

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How many sensors will you need? Measuring "flow" in a stream is very hard to do without building a dam and letting the water flow over the dam through a know size rectangular opening. Measuring the depth at that point will let you compute the flow.
Paul

Do you need to measure continuously, or just take samples?

Hi, thanks for the reply. I will use as many sensors as necessary, if not possible with just one. A dam could be a problem because materials can accumulate in the dam (garbage) and disrupt the process.

continuously

dam

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Do want to know the flow volume or just that fact that there is water flowing? BIG difference.
Paul

I'd look into seeing how someone else has solved the problem.


https://va.water.usgs.gov/online_pubs/OFR95-713rev.html#:~:text=How%20Does%20the%20USGS%20Measure%20Streamflow%3F%20In%20order,that%20passes%20a%20given%20location%20along%20a%20stream

How Streamflow is Measured

What, exactly, do you want to measure?
Water volume per second?
Linear water velocity?

The purpose of the measurement is to design a computer flood forecasting system for the city. In the case of my project, only at one point, which will serve as a study base. It would be interesting to maintain a data collection station, even after the project is completed, for study purposes. It is also important that the measurement is continuous, as I have no way of knowing exactly when the flooding will occur.

I need the volume of water to use it in a hydrological forecasting model

Then a flow speed sensor won't be sufficient. Water volume flow = area x velocity, usually measured in sections and totaled.

If you have access to a weir with rectangular opening, this makes the calculation much easier, as you need only measure flow velocity and water height in weir.

Yes, I need the cross section of the stream (area). I plan to use an ultrasonic sensor to measure it

is not more than 5 meters

The flow rate varies across the stream, from negative in vortices or zero at the margins.

And you have already said that putting something into the water will not work because of trash in the water. Perhaps first get rid of the trash.
Paul

It is not possible to get rid of garbage, it is a problem for the city and will not be the purpose of the project. The project could inform the city hall if a stream needs to be cleaned, for example, if the flow changes, but for that I need a robust system that can withstand the poor conditions of the stream.

And the way the USGS measures stream flow will not work for your situation?

This is very different from your first plan. Can you explain the relationship between stream flow and trash in the stream? Just what is the "trash" and how will it affect the flow?
Paul