Flooding, levels and surface water

How does rain gauge telemetry work?

By the AQUAIOT engineering team. Published 11 August 2026.

• The gauge counts, it does not measure directly. Rainfall is inferred from a tally of fixed volume tips.
• Intensity comes from the timestamps. Tips per interval is what turns depth into millimetres per hour.
• Low power by design. A pulse counter draws almost nothing, so battery life is measured in years.
• Local beats regional. Convective summer rain varies enormously over short distances.

What is actually happening inside the gauge

The mechanism is deliberately simple, which is why it has lasted. Rain lands on a collector of known aperture and is funnelled to a small see-saw carrying two chambers. When the chamber under the funnel has collected a fixed volume, it becomes heavy enough to tip, dumping its contents and swinging the second chamber into place.

Each tip passes a magnet across a reed switch, producing one clean pulse. The telemetry unit does not need to interpret an analogue signal at all, it just counts closures and records when each happened. Multiply the count by the calibrated volume per tip, commonly 0.2 mm, and you have accumulated depth.

This is why the arrangement suits remote deployment so well. Counting occasional switch closures costs almost no power, so a gauge can run for years on a battery, and the data volume is tiny enough to suit low bandwidth links.

How intensity is derived, and why it matters more than total

Total rainfall is the number people quote, but intensity is usually the number that determines whether a drainage system copes.

Because every tip carries a timestamp, intensity falls out of the same data without any extra sensing. Tips in a rolling interval, converted to millimetres per hour, gives a live intensity figure. Twenty millimetres falling steadily over a day is unremarkable. The same twenty millimetres in twenty minutes will overwhelm gullies, fill an attenuation basin and surcharge a combined sewer.

Read against level data elsewhere on the site, intensity becomes diagnostic. If a given intensity used to produce a certain level response and now produces a higher one, something has changed in the drainage: silt in a basin, a partially blocked outlet, or a new connection upstream.

Why a gauge on the site beats a regional figure

Frontal rain in winter is reasonably uniform, and a regional figure represents a site acceptably well. Convective summer rainfall is not uniform at all. An intense cell can deliver a great deal of rain to one part of a town and almost nothing a couple of kilometres away.

For anyone trying to explain why a drainage asset behaved as it did, that gap is the whole problem. Correlating a surcharge or a flood against a regional total that never actually fell on the site produces a misleading conclusion, and it is a weak position to hold if the event has to be explained to a regulator or an insurer.

A gauge on the site produces a defensible local record. It also enables control logic that responds to conditions rather than the calendar, which is the basis of rainfall responsive systems that draw down storage ahead of forecast rain.

The limits worth knowing

Tipping bucket gauges under-read in very intense rain, because water continues to arrive during the fraction of a second the bucket is tipping. Good gauges correct for this, but the effect is real at extremes.

They are also vulnerable to blockage by leaves, silt and insects, and to wind effects around the collector. Siting away from turbulence and obstructions, and inspecting the funnel, are the maintenance items that actually matter. A gauge reporting zero is ambiguous unless you can distinguish no rain from a blocked funnel, which is an argument for checking that the unit is still reporting its regular heartbeat rather than assuming silence means dry.