Most flood-sensor comparisons are written for the person choosing the measurement. This one is written for the person who has to keep it running: what each sensor family costs in watt-hours, what it needs mechanically, and where the power budget actually goes on an unattended station.
The four flood sensor families
Almost every deployed flood sensor falls into one of four families. The differences that matter operationally are mounting geometry, debris tolerance, and what happens to accuracy when conditions get ugly.
| Family | How it measures | Mounting | Best suited to |
|---|---|---|---|
| Radar (non-contact) | Times a microwave pulse to the water surface from above | Bridge soffit, cantilever arm, or mast over the channel | Rivers with debris, ice, or heavy sediment; anywhere you do not want hardware in the water |
| Pressure, submersible | Reads hydrostatic pressure at a fixed depth | In the water, usually in a stilling well or protective pipe | Stable channels, wells, reservoirs; low-cost continuous stage |
| Pressure, bubbler | Measures the pressure needed to push gas out of a submerged tube | Instrument in a dry enclosure, only the tube gets wet | Sediment-heavy water where a submerged transducer would foul |
| Ultrasonic (non-contact) | Times an acoustic pulse to the water surface | Above the channel, similar to radar | Sheltered sites and lower budgets; accuracy drifts with air temperature and is degraded by heavy rain, fog, and wind |
| Contact / float switch | Closes a circuit when water reaches a set point | At the threshold elevation itself | Threshold alarms — low-water crossings, culverts, basements — where "has it reached this line" matters more than "how deep" |
A practical distinction that gets missed: a threshold sensor is not a cheap stage sensor. It reports a state change, not a curve. If a downstream model needs rate of rise, a float switch cannot supply it no matter how many you install.
What each sensor family actually costs in power
This is the part that surprises people sizing their first network. Compared with the radio, the sensors are almost free.
| Load | Draw pattern | Typical daily contribution |
|---|---|---|
| Contact / float switch | Passive; current flows only through the logger input at the moment of state change | Effectively negligible |
| Submersible pressure transducer | Brief excitation during each sample window | Fractions of a watt-hour per day at 15-minute sampling |
| Radar or ultrasonic level sensor | Short active burst per reading, sleeps between | Low single-digit watt-hours per day; radar generally above ultrasonic |
| Bubbler system | Sensor plus a compressor or gas supply that cycles | Highest of the sensing options; the gas-purge mechanism is the reason |
| Datalogger, duty-cycled | Deep sleep between samples, short active burst | Roughly 1.5-3 Wh/day on a low-power logger |
| Telemetry radio, hourly batch | Wakes to push a reading set, then sleeps | A few Wh/day |
| Telemetry radio, always-on cellular | Stays associated with the network continuously | 25-30 Wh/day |
Bubblers deserve a specific warning. The instrument itself is modest, but the compressor that purges the tube runs on a cycle, and that cycle is a real and recurring load. If you are evaluating a bubbler against a radar sensor purely on unit price, put the compressor duty cycle in the comparison before deciding.
Sizing the station around the sensor you picked
The procedure is the same regardless of sensor family. Design for the worst month, because flood season and the worst solar month tend to be the same weeks.
- Budget energy, not power. Sum every load in watt-hours per day, including sleep current, and include the compressor cycle if you chose a bubbler.
- Add 20-30% for system losses — controller conversion, cable drop, and cold-temperature battery derating.
- Divide by worst-month peak-sun-hours. At 3.5 sun-hours, a duty-cycled logger with an hourly uplink sits comfortably on a 5-15 W panel; an always-on gateway needs 10-40 W.
- Choose battery autonomy. One to three days is adequate for routine monitoring. Anything feeding a warning decision should carry 3-5 days or more.
- Duty-cycle deliberately. Slower sampling in the dry season, event-mode bursts during a rise, cached uploads when the link drops. These choices can halve the panel.
The full worked example, including the battery capacity math, is in our water-level monitoring power guide. If your station also drives a siren or strobe, the burst-load allowance is covered on the flood early warning power page.
Mechanical and siting factors that outlive the spec sheet
Sensor selection is usually decided on accuracy figures. Field survival is decided on these instead.
- Debris and ice. Anything in the water is exposed to whatever the channel is carrying. Non-contact families avoid the problem entirely, which is why radar dominates on rivers that carry timber or ice.
- Sediment. A submerged transducer in silty water needs a maintenance plan. This is the specific problem bubblers exist to solve.
- Mounting geometry. Non-contact sensors need a clear vertical shot at the water. A bridge soffit is convenient but can put the sensor over the wrong part of the channel; check the sightline at low flow as well as high.
- Weather sensitivity. Ultrasonic readings drift with air temperature and degrade in heavy rain and fog. Those are the exact conditions during a flood, which is worth weighing against the lower unit cost.
- Ingress rating on the boring parts. The sensor is usually the best-sealed component on the pole. Connectors and cable glands are where water actually gets in. Specify IP67 as a baseline and IP68 on any route that can be submerged.
Supplier questions worth asking before you order
These separate a station-grade supplier from a catalog reseller, on both the sensor side and the power side:
- What is the sensor's current draw during a reading, and its sleep current between readings? Both numbers, not just one.
- If it is a bubbler, what is the compressor duty cycle and its energy cost per day?
- What ingress rating applies to the connectors and cable glands, not just the sensor body?
- What wind load is the mounting hardware rated for, and does the mount clear the site's flood elevation?
- For the power platform: can you show IEC 61215 design-qualification reports for the panel, and is the assembly factory ISO 9001 audited with a current certificate?
- Do lithium packs ship with UN38.3 transport-test documentation?
- What QC evidence ships with each batch — flash-test data, photographs, video?
Where LinkSolar fits
We do not make flood sensors, and we will not try to sell you one. We supply the layer underneath: panel, LiFePO₄ battery, charge controller, IP-rated enclosure, and pole hardware, sized around whatever sensor and telemetry you have already chosen, and consolidated into one shipment instead of four.
- Sensor-agnostic. Your measurement hardware, your telemetry, your data platform.
- Custom electrical specification: panel voltages from 3 V to 48 V, custom footprints down to 35 × 22 mm for embedded designs.
- Samples in 7-14 days for custom mini panels; integrated-system lead times confirmed at quote.
- MOQ from 5, so a few stations can be piloted before a network rollout.
- One contact, one proforma invoice, one shipment, with pre-shipment QC evidence from ISO 9001, CE and RoHS certified partner factories.
For component-level hardware you can order now, see our pole mount range and mini solar panels. The environmental monitoring panel selection guide matches panel class to sensor class, and our cold-climate battery notes cover derating for freeze-prone sites.
FAQ
What is a flood sensor?
A flood sensor measures water level, or detects the presence of water, at a fixed point and reports it to a logger or telemetry system so a rise can be caught early. The term covers both continuous stage measurement, which reports a water surface elevation on a schedule, and threshold detection, which reports only that water has reached a defined point.
What are the main types of flood sensors?
Four families cover nearly all deployments: radar and ultrasonic sensors measure from above without touching the water; submersible pressure transducers read hydrostatic pressure at depth; bubbler systems infer depth from the pressure needed to purge gas from a submerged tube; and contact or float switches close a circuit when water reaches a set point. Radar handles debris and ice best; bubblers handle sediment best; float switches are threshold alarms rather than stage sensors.
How much power does a flood sensor use?
Far less than most people assume. A float switch is effectively passive, a submersible pressure transducer draws fractions of a watt-hour per day at 15-minute sampling, and radar or ultrasonic sensors sit in the low single-digit watt-hours per day. Bubblers are the exception because of the compressor cycle. At almost every station the telemetry radio, not the sensor, sets the power budget.
Do flood sensors need their own solar panel?
No. The sensor, logger, and radio normally share one solar panel and one battery bank, sized around the total load. A separate panel per device adds cost and maintenance without adding reliability. What does deserve separation is a fused output per high-current device, so a burst load such as a siren cannot drag down the logger's supply.
Which flood sensor is best for a river with debris?
A non-contact radar sensor, mounted above the channel. Because nothing sits in the water, timber, ice, and sediment cannot foul or destroy the instrument. Ultrasonic sensors mount the same way at lower cost, but their accuracy degrades in heavy rain and fog, which is a real drawback on a station that exists to work during storms.
Sizing a power platform around a flood sensor you have already chosen?
Send the sensor and modem datasheets, your reporting interval, and the site region. We will come back within 1 business day with a sized panel, battery, and enclosure package — RFQ response within 24 hours, custom panel samples in 7-14 days.
