Level measurement for storm overflow
Ultrasonic measurement is strongly discouraged in storm overflows and, as a rule, in outdoor environments. The technology is based on the speed of sound, which varies according to the surrounding conditions—ambient temperature, atmospheric pressure, presence of gases, dust, etc. –which have a significant impact on the accuracy of the measurement.
Piezoelectric (or rather hydrostatic) measurement is accurate and easy to install. On the other hand, it requires some maintenance—in particular recalibrating to 0 over time. In addition, you have to make sure the membrane doesn’t become fouled.
Nowadays, the most convenient solution is radar: non-contact measurement (no risk of fouling), not affect by climatic conditions and the ambient environment, no maintenance, no drift over time—moreover, it is now cheaper than ultrasonic.
Radar sensors are indeed more robust when the surrounding environment produces significant variations in the above-mentioned parameters. Nevertheless, it consumes more energy than an ultrasonic sensor, so you should take that into consideration if you are looking for an energy standalone system.
I would recommend a bubbler level measurement. Our devices are very energy efficient with an accuracy of 0.1% of the full-scale output. We have equipped storm overflows with no maintenance problems and excellent reliability over time. Installation is also very straightforward.
From what you describe, it sounds like radar level measurement would be the most appropriate, and contrary to what was said above, battery consumption for a standalone unit is not necessarily higher than with ultrasonic. Different suppliers offer a range of sensors (e.g., Endress+Hauser, Vega, etc.)
There are all kinds of ultrasonic devices for CSOs. The worry I would have with piezo is the contact with the effluent (fouling) and hydrostatic equilibrium.
Radar is indeed a good option to consider. algae