Our Flood and River Monitoring Alarms are tailored to meet specific needs, providing custom-made solutions for mission-critical flood and river level monitoring. Our comprehensive range includes various flood warning systems, flood alarms, and flood mitigation solutions. In light of ongoing climate changes, it is imperative to adapt to evolving weather patterns that bring about increased water volumes within shorter timescales.

Flood and River Monitoring Alarms

These systems can be uniquely configured to detect and report the five common stages of flooding; River; Surface Water; Ground Water; Sewer and Burst Water Pipe. These systems can also be constructed to detect and generate advanced warnings concerning conditions that can contribute to flooding including the blinding of rubbish screens, failed sump pumps, full storm tanks, heavy rainfall, soil saturation and sewer blockages. Systems can also be built to help mitigate incidents, for example the control of pumps to optimise sewer flows to flattened out peaks to prevent overload surcharges and sewer spills.

These systems can report;

  • Surface Water Flooding
  • River Flooding
  • River Level
  • Rubbish Screen Blinding
  • Groundwater Levels / Flooding
  • Sewer Flooding/ Sewer Surcharges
  • Burst Pipe Flooding
  • Storm Tank Level
  • Failed Sump Pumps

rdnet1000 sd12 transmitter

River Level Monitoring

hidden automated wireless river staff gauge

We offer a wide range of solutions from simple high “OK” alarms through to high-precision systems that deliver river depth to mm accuracy. The systems can include multiple measurement points and data can be routed in real-time to existing telemetry, BMS, SCADA, cloud or a remote web server.

Covert automated river staff gauge with telemetry shown in the image above.

BDT Based Automated River Level Alarm / Staff Gauge. High “OK” River Level Alarms

bdt switch food portable flood warning system for battery cctv operation

The simplest and most popular flood sensor these BDT (Bulk Dielectric Transducer) which was first introduced in 2010 for sewer level monitoring.

Unlike float switches which can get trapped by debris the BDT has no moving parts and has minimal hysteresis making it easy to visually verify the set-point. The BDT can be installed in drains, stilling tubes and on river banks within hollow staff gauges and normally is supplied with an integrated wireless communication head unit that contains a sealed for life lithium battery pack with up to 10-years service life.

Systems can be constructed that communicate to existing telemetry, BMS, SCADA, the cloud or a remote web server. Further, they can also include sewer and drainage alarms.

Transmitter Build Options;

10mW to 5W Transmit Power. Approvals to EN-300-220, EN-300-113, FCC-Part 90

Typical Gateway Receiver Connected to a Telemetry Outstation

Gateway Receiver with Relay Outputs

Receiver Build Options;

  • Volt-Free Relay Contacts N/O plus N/C
  • Serial ASCII RDNET1000 protocol
  • LAN – CSV, XML or JSON
  • Tetra – SDS Message encapsulated packets
  • PMR Tier 2 – SDS Message encapsulated packets to confirm the system is operational.

High-Precision Hydrostatic Pressure River Level Monitoring System

A range of single and dual redundant telemetry units that can be used to both power and extract the data from 4-20mA, 0-5V or SDI-12 hydrostatic pressure transducers.

bdt wireless level transmitter 600Interface Options;

  • Single or Dual Channel SDI-12
  • 0-2.5V Analogue 10-bit or 16-bit
  • 4-20mA Analogue 10-bit or 16-bit
  • Pressure equalisation breather vent

Sensor Power Options;

  • 6V DC (for Impress SDI-12)
  • 12V DC for 4-20mA loop transducers

Transmitter Build Options;

  • 10mW to 5W Transmit Power
  • Approvals to EN-300-220, EN-300-113, FCC-Part 90

Receiver Build Options;

  • 4-20mA output
  • SDI-12 converted to 4-20mA
  • o-2V, 0-5V, 0-10V
  • Serial ASCII RDNET1000 protocol
  • LAN – CSV, XML or JSON
  • Tetra – SDS Message encapsulated packets
  • PMR Tier 2 – SDS Message encapsulated packets to confirm the system is operational.

What Else Can these Flood Alarms Do?

  • Switch and control pumps
  • Activate flow diversion valves
  • Activate and drive sirens
  • Activate GSM/SMS messages
  • Activate wide area or on-site paging systems
  • Activate existing alarm systems
  • Interface with telephone dial systems
  • Interface with Scanning Telemetry
  • Interface with rain gauges to permit early warnings


Wireless Automatic River Staff Gauges

wireless staff gauge web banner 

Hydrostatic pressure-based river staff gauge housed in a tough fibreglass stilling tube. Battery powered and able to communicate in real-time over either a licenced or licence free radio channel.

Thanks to these Ofcom licenced radio channel we can install these wireless river staff gauges in areas devoid of cellular coverage. Further communication are in real-time and over distances of up to 5 km with data replicated as either a 4-20mA loop and/or posted to a remote web server.

Features include;

  • Battery powered
  • Accuracy typically +/- 0.5 cm
  • Transmission rate 1-minute to 15-minutes
  • Licenced or licence free radio transmission
  • 100 m to 5 km range, 25 km with repeater
  • Receiver with Analogue 4-20mA output or 0-2V
  • Data compatible with RDNET data Concentrator

Automated Flood Warning Signs

flood warning road diagram

Automated Flood Warning Signs we supply of a range of automated flood warning signs that can operate either autonomously under the control of water levels sensors such as these BDT’s or as part of an integrated remotely controlled system.

Thanks to these unique ultra-low power operating strategies it is possible to operate the signs in areas devoid of power, using solar or battery power. For an example of one in operation, please contact us.

For minimal additional cost the wording on the signs can be 100% bespoke and in virtually any language or multiple languages. Signs can include standard discharge tube flashers or state-of-the-art high intensity LEDs.

How these Flood Warning Signs Communicate

These signs can include a variety of control and communication options from licence free radio through to licenced PMR radio operating on a secure radio channel. These systems also often include a fully automated health monitoring system that reports the operational status of the signs 24/7.

Unlike GSM/GPRS and similar technologies, the majority of these systems operate independently of 3rd party networks, and we even offer operation on an exclusive Ofcom licenced radio band where if a major disaster operation is assured unlike cellular where networks collapse under the weight of traffic.

Automated Flood Sensor Systems

These flood warnings systems can be controlled automatically using a variety of sensors including these award-winning ultra-low power BDT level sensors, through to ultrasonic and microwave level gauges.

To keep cost to a minimum, the vast majority of these sensors operate from batteries and communicate wirelessly. Distances between the sensors can be anything from a few tens of meters and up to many km.

Automated Flood Sign System

automated flood warning sign

Illumination Options

  • The signs can be illuminated using traditional discharge flashing beacons or state-of-the-art high luminosity LEDs. Single or Multiple Signs
  • The systems can comprise anything from as a single sign trough to multiple signs and sirens to cover a variety of junction and road layouts. Custom Design Service
  • The in-house UK-based engineering team can offer a completely bespoke solution to accommodate the most demanding customer requirements. Signs can be totally bespoke, with custom wording,
  • languages and dimensions. Signs are normally supplied for mounting on standard 70 mm diameter poles however they can also be supplied with wall mounting kits.
  • Power Supply Options – No Mains required! The majority of these signs can be operated for long periods from batteries or a combination of batteries and solar and/or wind power.

Portable BDT Switch for Flood and CCTV Control

  • The BDT Switch provides a robust, proven and reliable method of controlling Cameras to verify events such as flooding and to observe the risk of bridge collapses etc during storms, etc in remote locations.
  • Before the BDT Switch a camera would have to be deployed and powered 24/7 or duty cycle controlled. Furthermore, during rainfall the data from the camera would have to be observed irrespective of the water level wasting time.
  • Using the BDT switch the Camera can be switched off completely and only powered when the water level rises to a point of interest triggering the BDT Switch. Aside from extending battery life may fold using the BDT switch enables the event start and stop to be marked eliminating the need for manual observation for the majority of the time.

Flood Warning Systems with SMS Alerts

automated 2 stage flood alarm solar

An affordable, low maintenance, battery/solar-powered SMS flood alarm system designed to deliver a single or dual level warning concerning rising river or groundwater levels over the 2G SMS text network.

SMS Flood Alarm with Staff Gauge

Designed for rapid, self-installation, with no complex software or programming, the system can be supplied housed in a variety of housings, including custom fabricated staff gauges, fibreglass stilling tubes, or aluminium streetlamp column bases.
Robust and Fail-safe BDT Sensing

The system utilises Radio Data Networks unique BDT (Bulk Dielectric Transducer) level transducers for detecting when the water is level exceeding the pre-set limit/s. The BDT has significant advantages over ultrasonic, pressure and float switch technology, as it can detect and report issues associated with silt, ice and weed that can lead to the failure of the other technologies. The BDT has a proven track record in the utility sector where they have collectively accumulated over 5 billion hours of service, since they were first introduced in 2010.
Battery or Solar Powered

The system is ultra-low power in operation, consuming in standby just a few microamp. This makes it possible for us to supply a system with up to 10-years’ service life on a single battery pack.

Alternatively, the system can be supplied with solar assistance / rechargeable lithium technology which can extend the battery life further or allow for the more frequent reporting of levels.

Automated Self Reporting

sms flood warning system health message

The systems are designed to automatically report typically twice daily, thereby instilling the confidence in flood wardens and the community that the system will work when needed.

SMS Flood Warning System Health Message

Contained within this message is the overall pass / fail of the “System Test”, the status of the Battery High or Low, the state of the solar charger Off or Charging (where applicable), and two engineering values associated with the two BDT Level sensors and an incrementing message number.

With solar-powered systems, normally, during the day (depending upon the position of the sun and weather) the solar charger in on and charging and at night the solar charger is off.

Accelerated Alarm Reporting

When the water level reaches midway up the tip of BDT level sensor, the level change is detected and wakes the unit from sleep and an alarm message is compiled and broadcast.

SMS Flood Warning System Level 1 Message

To ensure that the staff are responsive, the alarm is resent every 5-minutes whilst the flood condition exists.

In the example below for a dual BDT level system with two transducers placed above each other to give a high and high-high level warning.

Virtual Zero Maintenance

With its long battery life, and the use of BDT sensors which have no moving parts, regular maintenance is not required.

We do, however, recommend periodic inspection of the installation conducted to ensure that reeds, weeds will not impede the flow of water into the point of sensing.
Automatic Fault Reporting

The fault message, as below is generated if the unit finds a defect with one of the BDT level sensors or one of the cables is cut or damaged. This is an important function as cables can become damaged by rodents or excessive use of brush cutters when clearing reeds.

Flood and River Level Monitoring

River and Flood Warning Telemetry – Licenced Radio Telemetry or LEO Satellite based without SIM Cards or Cellular Coverage. Proven in service by the EA, Utilities and across the Industrial Sectors.

The flood warning systems can detect and report all five stages of flooding and operate over an exclusive secure radio telemetry band operating under an exclusive Ofcom licence.

  • Surface Water Flooding
  • River Flooding
  • Groundwater Flooding
  • Sewer Flooding/ Sewer Surcharges
  • Burst Pipe Flooding

Resilient Communications

How many times have you suffered from broken calls, had to move to find a better signal, found no signal at all or found the cellular networks totally congested? We would guess many times, and because flood detectors/level sensors to be effective to have to be located up stream in remote areas, also cannot move we have two unique solutions. The first option is these decided Ofcom licenced radio channel and the second is over the LEO Satellite networks.

Either system can be constructed to operate from a single or multiple locations, with flood sensors distributed over areas measuring many square km/miles.
Dual Redundant Sensing, 16-Bit Analogue EA Approved

these Analogue 4-20mA systems have been tried and tested by bodies such as the EA, where two sensors are used in parallel to permit the cross correlation of data to ensure that level sensors/probes are functioning correctly without having to visit the site. Simply the level data should track within a fraction of a percent, however if divergence is observed then a fault can be suspected in one of the sensors.
We offer one of the highest levels of resilience when it comes to communications from these flood sensors. Secure Ofcom Licenced radio and/or military grade LEO Satellite communications

In all cases, we do not require SIM cards of connection to the cellular networks. Not only does this eliminates the reliability and growing risk obsolescence issues associated with the cellular networks but also permits systems to be installed in remote locations without issue. Finally, these communications are totally immune from cyberattack as they do not use the Internet or IP data protocols.

The majority of these flood warning detectors are housed in discrete bollard housings permitting them to be installed in a variety of strategic locations ranging from river banks through to the edge of public highways (cut away section of bollard housed flood alarm shown below). The units can also be supplied in these smart pole mounted boxes with integrated solar panel that can be secured to railings and on poles sunk into the ground alongside riverbanks. The in-sewer / drain flood alarms are mounted under manhole covers and can report back the presence of a storm surcharge which could lead to a breach of flood defences via these solar-powered repeater/booster stations.

The flood alarms are 100% battery powered and the internal electronics are fully encapsulated to exceed the IP68 standard to withstand prolonged submersion during the flood. The system operates using these proven BDT sensing technology that has no moving parts eliminating the risk of sticking float switches a common problem that is often caused by insect, leaves and dirt infiltration. BDT technology is also generally outperforms conductivity type systems as it is immune to trigger by wet leaves. Battery life is typically 10-years and unlike GSM/SMS-based systems which are both power hungry and expensive to operate, these power-efficient design and lean radio protocols permits each unit to automatically send a uniquely coded health message every 5 or 15 minutes (version dependant) which the receiver station automatically constantly monitors to confirm the system is operational.
Flood Alarm housed in bollard

Flood Alarm Sensor and Transmitter housed in a Roadside Bollard.

At the receiving end we offer a number of options. The first is these “Utility Gateway Receiver” this unit permits the flood alarm system to be interfaced with existing telemetry outstations, building management systems (BMS), etc. by a series of volt free contacts. Utility Gateways can also simultaneously be configured to deliver analogue levels (0-2V) or 4-20mA or report sewer blockages and CSO spills from other Radio Data Networks devices. Utility gateways can serve anything from between a single Flood Alarm to up to 64 over an area of many square Km. The second option is the Utility Hub, this is a small receiver that is ideal for use in factories and small communities but is restricted to serve a maximum of 5 flood alarms. Either solution units can be used with an external PSTN telephone auto-dialler offering unrivalled performance when compared to SMS/GSM “push and pray” based SMS / Text units.

We offer the choice of two operating distances. The first is 300 m to 1 km (topology dependant) and thanks to these special exclusive Ofcom licensed radio band (subject to a small annual fixed charge) we can also offer systems capable of operation over distances from 500 m to 10 km radius. Range can also be enhanced by using a pole mounted “Booster” system where a short range Flood Alarm is combined with one of these Booster units mounted up high to enhance signal propagation.

The picture to the left shows the complete flood alarm in a stone effect bollard housing. Visible are the ground anchors which are generally set into the ground and concreted in place to secure the unit thus preventing it from being washed away.

Subject to a minimum order quantity the flood alarms can be ordered in a variety of colourful bollards. Please contact Merlin for details.

Wide Area Wireless Flood Alarm Key Features;

  • Solid state flood detection technology without moving parts
  • Long Battery Life up to 10-years (version dependant)
  • Electronics sealed to > IP68
  • Discrete compact bollard housing available in a variety of colours and finishes
  • Unlimited number of flood detection points / locations
  • Operating radius 300 m to 10Km version dependant for Licenced Radio or Unlimited for LEO Satellite
  • Fully compatible with BDT Blocked Sewer and CSO Spill detection system which can detect flood waters attempting to bypass flood defences through the drains and sewers.
  • Unique secure data protocol with 32-bit (4-billion) address and 16-bit error check sum.
  • Utility Gateway provides simple interface to existing telemetry and alarm systems (no software required)
  • Optional Ofcom protected radio spectrum (used for non-satellite systems)
  • Bollard measures 600 mm tall, 280 mm diameter up to 300 mm (max) diameter.
  • Mounting stake galvanised steel
  • Ability to interface directly to wide area paging systems or PSTN voice dialling systems
  • Able to interface with GSM and SMS reporting system (not these preferred option)
  • Coverage area extendable by using repeaters to cover entire cities.
  • CE, R&TTE, RE-D and EN-300-220-1 Compliant Design

Unique; Construct Mixed Flood Alarm, Storm Drain and Sewer Surcharge Alarms on One Platform

SMS Text Flood Warnings

flood warning sms text

Flood Warnings delivered by SMS Text to communities

Many communities and businesses suffer flooding through the sewers and storm-drains backing up into their properties. To cater for this these flood alarm systems can also be equipped with these BDT blocked sewer detectors that can simultaneously report both surface and sewer flooding.

Please speak to the Merlin sales department for further details.

What Else Can these Flood Alarms Do?

  • Switch and control pumps
  • Activate flow diversion valves
  • Activate and drive sirens
  • Activate GSM/SMS messages
  • Activate wide area or on-site paging systems
  • Activate existing alarm systems
  • Interface with telephone dial systems
  • Interface with Scanning Telemetry
  • Interface with rain gauges to permit early warnings

We have a new range of flood defences available here; https://merlin-industrial.com/flood-barriers

0 65m flood barrier 

Vat GB591551821 Company Number 02906480 – 1994
Dun and Bradstreet, Number (581590544)
NATO Code Number (NCAGE KD520)
EORI Number GB591551821000

Email info@merlin-industrial.com

Merlin Industrial Products @ 2024 Errors and Omissions Excepted


Call 01752 690622 / 0800 0418 650 (UK)