Fun Below the Waves


Measurement engineers get to poke about in everyone else’s branch of science, and so wind up knowing a little about a lot.

Understanding the physics of what happens below the waves in a reservoir, lake or river pool is the business of physical limnologists.

MEA got to peek into that world after an intensive four-year design effort to create, manufacture and  calibrate our MEA thermistor strings.

These are long three-wire submersible cables studded with highly-matched temperature sensors that can see small changes of 0.001°C, with a matching better than 0.006°C. They can be read by most data loggers using the SDI-12 protocol.

From a layman’s perspective, the most interesting things below the waves happen in summer when the warm upper layer separates from the cold lower layer, creating two very different water bodies within a single one.

Weird stuff happens.

 Water-on-water waves occur along this ‘thermocline’, or sharp temperature gradient. Imagine the thermocline acts as a rubbery glass sheet submerged a metre or two below the surface.

Cold water caused by sudden storms over the catchment can rush down the feeder streams and tunnel under this thermocline to upset water treatment plants downstream.

In autumn, cooling surface waters become heavier than warmer lighter bottom waters and can crash through, over-turning the reservoir and mixing these different water bodies.


The colourful history of MEA’s stratification measurements can be found at Life Beneath the Waves

A buoy supporting an MEA Thermistor String
A Thermistor String suspended from a bouy in a reservoir.


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