Reservoir Level Monitoring: Continuous Radar Sensing for UK Reservoirs and Lagoons
TL;DR: Reservoir level monitoring is the continuous, remote measurement of the water level in a reservoir, lagoon or storage pond, using a radar sensor instead of a gauge board read by eye. In England a raised reservoir holding 25,000 cubic metres or more above ground level is regulated under the Reservoirs Act 1975, with inspections that can be up to ten years apart. A breach or an overtopping is not that patient. Continuous reservoir level monitoring watches the level between the statutory visits, so a rising trend or a slow drop is flagged the hour it starts.
Last updated: 9 July 2026
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Key takeaways
- In England a reservoir holding 25,000 cubic metres or more above ground level is a large raised reservoir regulated under the Reservoirs Act 1975.
- Statutory oversight is periodic: a supervising engineer’s statement once a year and a full inspection at least once every ten years.
- Reservoir level monitoring fills the gaps between those visits with a live radar reading and automatic threshold alerts.
- Wales already regulates reservoirs from 10,000 cubic metres, and England is reviewing the threshold for smaller raised reservoirs.
- The AQUAIOT Radar measures level to within 2 mm without contact, so there is no float to jam and nothing to silt up.
What is reservoir level monitoring?
Reservoir level monitoring is the continuous measurement of the water level in a reservoir, lagoon, storage pond or attenuation basin, sent back automatically to a dashboard instead of read by hand on a site visit. A non-contact radar sensor above the water reports the level every few minutes, so overtopping, a slow drop or an abnormal rate of rise is caught as it happens rather than at the next inspection.
The point is not to replace the engineer. It is to close the blind spot between visits. Most raised reservoirs and industrial lagoons are still gauged by eye off a marker board on a weekly walk, which means the level is genuinely unknown for the days in between. Continuous reservoir level monitoring turns that unknown into a live, recorded signal.
Which reservoirs and lagoons have to be monitored?
In England, a structure that holds or could hold 25,000 cubic metres of water above the natural level of the surrounding ground is a large raised reservoir under the Reservoirs Act 1975. Above that line the owner must appoint qualified civil engineers, hold a supervising engineer’s statement each year, act on inspections carried out at least once a decade, and keep a tested on-site emergency flood plan.
That threshold is not fixed for good. Wales already regulates raised reservoirs from 10,000 cubic metres, and the Environment Agency and Defra reservoir safety reform programme is developing proposals for the 10,000 to 25,000 cubic metre band. Plenty of assets fall outside the Act entirely and still carry real risk: agricultural irrigation reservoirs, quarry and settlement lagoons, process and cooling ponds, fire-water storage and SuDS attenuation basins. For all of them, reservoir level monitoring is a low-cost way to see the level without waiting for a person to walk the embankment.
Why is periodic inspection not enough on its own?
Periodic inspection is essential, but it samples the asset a handful of times a year while risk builds continuously. An engineer’s annual statement and the decadal inspection tell you the condition on the day of the visit. A blocked spillway, a prolonged storm or a seeping embankment does not wait for the diary. The 2019 failure of a dam spillway in the north of England, which forced the precautionary evacuation of a whole town, is a reminder that the dangerous moment is rarely the moment someone is on site.
This is where reservoir level monitoring earns its place. A gauge board tells you where the water was on the last visit; a live radar feed tells you where it is right now, and where it is heading. Rate-of-rise alerting is the part a manual read can never provide, because it is the change over minutes and hours, not a single number, that signals a developing problem.
How does continuous reservoir level monitoring work?
Continuous reservoir level monitoring works in three layers: a sensor on the water, secure telemetry off the embankment, and a cloud that turns the reading into an alert. Because the sensor is non-contact and battery-powered, the whole chain retrofits onto a remote, off-grid reservoir without civils, trenching or a shutdown.
- Sense. The AQUAIOT Radar is mounted above the water and reads the level to within 2 mm using 60 GHz millimetre-wave radar, every few minutes, with no float and nothing in contact with the water.
- Connect. Encrypted LoRaWAN and LTE Cat-1 telemetry carry the reading back from a remote embankment, so no mains power or cabling is needed on the dam.
- Alert. The AQUAIOT Cloud checks the level and the rate of rise against your thresholds and sends an alert by email, SMS or app within minutes, keeping a full history for the record.
What does a reservoir level monitoring setup include?
A practical setup centres on a non-contact radar level sensor and the cloud behind it. The AQUAIOT Radar penetrates foam, vapour and condensation, is rated IP68 for full immersion, and comes in ATEX variants for hazardous areas such as fuel or wastewater lagoons. Mounted above the surface, it has no float to jam, no probe to foul and nothing to re-calibrate as sludge builds up on the bed.
Around the reservoir, the same platform extends to the assets that feed and drain it. A Clamp-on Ultrasonic Flow Meter can meter the inflow or the draw-off pipe without cutting into it, so you can reconcile what goes in against what the level shows. The reading sits on the same AQUAIOT Cloud used for sewer and drainage monitoring, and it interlinks naturally with wider flood monitoring, river level monitoring and remote tank level monitoring. For a council, an NHS estate, a housing provider or an industrial site, that means one dashboard for every reservoir, lagoon and pond across the estate.
The commercial case is simple. One caught overtopping, or one early warning of a reservoir running down towards its dead-storage line before a dry spell, protects far more than the monitoring costs to run. Reservoir level monitoring turns a periodic, manual unknown into a controlled, reportable number the whole team can see.
Frequently asked questions
What size reservoir needs to be registered in England?
A reservoir that holds or could hold 25,000 cubic metres of water or more above the natural level of the surrounding ground is a large raised reservoir and must be managed under the Reservoirs Act 1975. Wales regulates from 10,000 cubic metres, and England is reviewing the threshold for smaller raised reservoirs.
Does reservoir level monitoring replace a reservoir inspection?
No. Reservoir level monitoring complements the statutory regime rather than replacing it. The supervising and inspecting engineers remain responsible for the structure; continuous monitoring gives them, and the site team, a live level and an alert between the annual statement and the decadal inspection, plus a full recorded history.
Why use radar instead of a float or a pressure sensor?
A radar sensor sits above the water and never touches it, so there is no float to jam, no submerged probe to foul and no drift as silt builds up. The AQUAIOT Radar reads to within 2 mm, sees through foam and vapour, and is rated IP68 with ATEX variants, which makes it well suited to lagoons and reservoirs that are dirty, corrosive or hazardous.
Can lagoons and ponds outside the Reservoirs Act be monitored the same way?
Yes. Irrigation reservoirs, quarry and settlement lagoons, cooling and process ponds, fire-water stores and SuDS attenuation basins can all use the same reservoir level monitoring approach. They may sit below the 25,000 cubic metre threshold, but overtopping, pollution and supply loss are still real risks that a live level and threshold alerts help control.
By Gianbattista Porru, Digital and IoT lead at AQUAIOT. Gianbattista Porru leads digital and IoT delivery at AQUAIOT, working across smart water monitoring, telemetry, and dashboard projects for UK utilities, councils, housing providers, and public-sector estates.