RP-30 non-contact current meter opens up new possibilities

A current meter is an instrument used to measure the velocity (speed) of water flow in rivers, streams, and open channels. It's a crucial tool in hydrology and environmental monitoring, often used to estimate discharge (the volume of water flowing per unit of time). There are different types of current meters available from cup or propeller-types to Electromagnetic once and Acoustic doppler once. All have their advantages and disadvantages and maybe more important their reasons and applications why and where they get used according to their advantages or disadvantages. What all of these have in common is they need to be recalibrated and checked on a regular basis since all of them have moving parts and with that a certain were and tear. The one which get forgotten most often due to lack of knowledge are the non-contact radar once, like the SOMMER RP-30. As the name says non-contact, here we have one of the big advantages there is no wear and tear and therefor also the recalibration part or exchanging parts is not important because there is no wear and tear due to no moving parts.

What all of these meters have in common is their modus operandi: they are typically used while wading through the water, or suspended from bridges or boats. In some rare cases, stationary mounts or floats are used. However, the most common method is wading, and this presents one of the biggest safety concerns for operators. If you must enter the water to take measurements, you are already in a potentially dangerous situation and must adhere to certain safety protocols. While this is a challenge, it can be managed, especially in low to moderate flow conditions. However, once you encounter mid to high flow conditions, it becomes essential to remove personnel from the water. In such cases, you still have the option to suspend the meter from bridges or boats, but this requires having the necessary infrastructure available at the site.

This is where non-contact, radar-based current meters come into play. While these instruments can be used in low-flow conditions, their full potential is realized at medium to high flow levels—situations where other technologies become impractical. For example, when the water is too deep to wade through, too fast to safely enter, or when large amounts of flotsam are present, a different measurement method is required.

Similarly, if you typically use an ADCP boat but the conditions become too rough or there is excessive debris, switching to a non-contact method becomes necessary. These are the situations where non-contact technology truly shines.

The SOMMER RP-30 is the ideal instrument for handling these types of challenging situations. It operates similarly to a traditional current meter, using a section-by-section methodology to measure the surface velocity of the river in various segments. As a result, you obtain a detailed velocity distribution across the entire cross-section.

In the accompanying software, the cross-section of the river is defined and divided into individual segments—essentially the same approach used with traditional current meters. Based on this data, the hydrological model can then calculate the discharge for each specific cross-section and its corresponding velocity distribution.

As mentioned above, the radar current meter is capable of taking measurements even in low-flow conditions, where you can wade into the water and use it much like a conventional current meter. However, the true advantage of the RP-30 emerges under high-flow conditions—where wading is no longer possible. In such cases, when it is unsafe or impractical to enter the water, the RP-30 can be easily and safely deployed from a bridge or cableway. This makes it an invaluable tool in conditions where other instruments are no longer viable for taking measurements.

Especially during flood conditions, non-contact radar current meters prove to be extremely valuable for obtaining data when no other methods are feasible. For example, during the floods in Austria in September 2024, as well as the floods in Spain in 2024 and 2025, these instruments provided reliable data where no other equipment could operate effectively.

Moreover, the RP-30 is designed to be simple and user-friendly, minimizing both physical and psychological barriers. Even users who do not operate the device regularly find it accessible and easy to use. This usability makes the instrument an ideal complement to ADCP boats. While there is some overlap between the two technologies, they primarily fill different roles, effectively covering the limitations of one another and enhancing overall measurement capability.