By Eur Ing Brian M Back, Radio Data Networks Founder and Managing Director
When flood risk is discussed, attention naturally turns to fluvial flooding from rivers, pluvial flooding from intense rainfall, or groundwater flooding. Yet there is another form of flooding that affects tens of thousands of properties every year, disrupts businesses, damages infrastructure, and carries an estimated annual economic impact exceeding £1 billion — sewer flooding.
Unlike river floods that dominate television news coverage with dramatic imagery of submerged streets and rescue boats, sewer flooding rarely captures headlines. Incidents are typically isolated, highly localised, and often over almost as quickly as they begin. By the time emergency responders arrive, the water may already have receded, leaving behind the unmistakable evidence: stained walls, damaged flooring, warped timber, shorted electrical systems, contaminated possessions, and perhaps most distressing of all, the lingering odour of sewage.
Despite its low public profile, sewer flooding is a significant and growing challenge for the water and flood management sectors. It is also deeply personal for many affected households and businesses. In my own experience, both my parents’ home and one of my commercial premises have suffered repeated sewer flooding events. In the case of the business premises, more than 500mm of sewage-contaminated water inundated the lower ground floor, destroying stock and equipment. What made these incidents particularly surprising was their location: miles away from any recognised floodplain and positioned close to hilltops rather than valley bottoms.
These events highlight a common misconception. Sewer flooding is not confined to traditionally “at-risk” areas. Blocked or surcharged sewers, inadequate drainage capacity, pump failures, and intense rainfall can create flooding almost anywhere within the network.
The challenge of monitoring for sewer flooding
Monitoring sewer flooding presents a unique set of technical difficulties. Unlike rivers or surface water systems, sewers are enclosed underground environments accessible only through inspection chambers. Installing monitoring equipment can be disruptive and costly, particularly where cables or permanent infrastructure are required.
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The sewer environment itself is exceptionally hostile to electronic systems. Chambers operate at near 100% humidity, contain corrosive gases, and may occasionally present explosive atmospheres. Communications are equally challenging, as radio signals are significantly attenuated by metal covers and underground construction.
Conventional river-monitoring technologies, such as ultrasonic or radar level sensors, can be adapted for sewer use, but battery-powered systems often report too infrequently to provide meaningful early warning during rapidly developing surcharge events.
Recognising this challenge, the team at Radio Data Networks (RDN) developed the BDT sewer monitoring system — a solution that, more than 15 years after its introduction, remains one of the UK’s leading sewer flood monitoring technologies.
Purpose-built monitoring for harsh environments
The BDT is a compact, self-contained battery-powered sensor and telemetry unit designed specifically for deployment within sewer chambers, both inside and outside buildings. The system measures and reports sewer conditions every 2.5 seconds, providing near real-time visibility of rapidly changing conditions.
Designed for hazardous environments, the unit complies with ATEX Zone 2 and UKEx requirements and is powered by an intrinsically safe lithium battery pack. Importantly for operational teams, the devices have demonstrated battery lifespans exceeding ten years in the field. Fully sealed to IP68, the monitors are capable of surviving complete chamber inundation.
For corporate users and facilities managers, BDT alarms and telemetry can be integrated seamlessly into Building Management Systems (BMS) via RDN Utility Gateways, while also providing secure 24/7/365 access through web-based monitoring portals.
Beyond sewer flooding
While originally developed for sewer monitoring, the same technology is now being deployed more widely across flood resilience applications, from alarm systems to controlling the lifting of flood adaptive platforms.
Mounted within tough GRP poles, BDT units are increasingly used to provide rapid warnings of pluvial flooding, blocked culverts, and rising surface water levels. In urban environments where surface water flooding can develop with little warning, the ability to detect and communicate changing conditions within seconds is particularly valuable and is also being used in various sectors to trigger cameras.
The technology also has applications in groundwater monitoring, particularly in basements and below-ground structures where infiltration is managed through sump systems.
Further up within buildings, sewer stacks themselves can become blocked or surcharged, leading to internal flooding events. To address this, RDN has also developed dedicated sewer stack monitoring solutions capable of communicating directly with BMS platforms and the company’s Sentinel web portal.
As climate change places increasing pressure on ageing drainage infrastructure, sewer flooding is likely to become an ever more important component of the UK’s flood resilience agenda. Greater awareness, combined with robust monitoring and early warning technologies, will be essential in helping utilities, businesses, and property owners reduce damage, disruption, and risk.
For further information, contact the team at Radio Data Networks
This article appeared in Issue 12 of Flood Industry magazine, May/Jun 2026. You can view it here.