On January 7, 2010, frazil ice forced a manual reactor shutdown (a 'trip') at the Salem Nuclear Power Plant in New Jersey. In January 2000, ice blockage at Point Beach Nuclear Plant on Lake Michigan caused a rapid fall in cooling water intake levels, triggering an emergency reactor shutdown (a 'scram'). And from January to March 2025, Trenton Water Works in New Jersey had to bypass its primary intake and rely on diesel-powered emergency pumps for nearly two months after frazil ice reduced system capacity [1][2].
These are not isolated incidents. Every winter, water intakes across the northern hemisphere face the same threat. Frazil ice (small ice crystals that form in supercooled flowing water and adhere to screen surfaces) can block an intake in minutes, shutting down hydropower turbines, municipal water treatment plants, industrial cooling systems, and snowmaking operations at exactly the moment they are needed most.
This guide explains the science of ice formation at water intakes, documents the five proven anti-icing methods, and introduces the engineering approach ADENCO has developed specifically for Coanda intake screens operating in extreme cold.
Table of Contents
- The Science of Ice at Water Intakes
- Two Types of Ice Clogging on Coanda Screens
- Five Anti-Icing Methods: How Each Works
- Selecting the Right Anti-Icing Strategy
- ADENCO's Approach to Anti-Icing for Coanda Screens
- Designing for Cold Climate: Specification Checklist
- Frequently Asked Questions
- References
The Science of Ice at Water Intakes
Understanding how ice forms at intake screens is essential for selecting the right prevention strategy. There are three distinct ice formation mechanisms, each requiring a different response.
Frazil Ice
Frazil ice is the most dangerous and least understood threat to water intakes. It forms when turbulent water is cooled just below its freezing point (a state called supercooling) typically by only 0.01°C to 0.1°C [3][4].
The formation process is rapid and self-accelerating:
- Supercooling: Turbulent, fast-flowing water (rapids, riffles, tailraces) loses heat to cold air faster than calm water. The whole depth of water drops below 0°C without forming a stable ice cover.
- Nucleation: Ice crystals form when tiny seed particles (airborne ice crystals, dust, or cavitation bubbles) enter the supercooled water. Initial crystals are approximately 0.3 mm in radius [3].
- Secondary nucleation: Existing crystals collide and break apart in the turbulence, and each fragment becomes a new nucleation site. Crystal production accelerates rapidly, and a river can go from clear water to a thick ice slurry within minutes [3].
- Adhesion: At supercooling of just 0.1°C, frazil ice crystals stick to metal surfaces. At 0.2–0.3°C supercooling, they adhere to virtually any surface including plastics [3]. Crystals accumulate on the wedge wires, filling slot openings and blocking water passage.
The key point: frazil ice adheres to any surface that is at or below 0°C. The most reliable prevention is maintaining screen surfaces above freezing: even by a fraction of a degree [1][5].
Platelet Ice (Anchor Ice)
Platelet ice forms when frazil ice crystals deposit on submerged surfaces (wedge wires, support bars, the weir crest) and grow into solid plates. It is the primary cause of blockage at fully submerged intakes [1]. Unlike loose frazil ice, platelet ice is mechanically strong and cannot be dislodged by flow velocity alone.
Atmospheric Icing
Atmospheric icing occurs when ambient air temperatures are well below freezing and water spray or splash freezes on exposed screen surfaces. This is a concern for surface-mounted screens (including Coanda screens) that are exposed to both water and cold air. Atmospheric icing builds from the air side, not the water side, and is most severe during high-wind, low-temperature conditions.
Two Types of Ice Clogging on Coanda Screens
Research conducted at the NTNU frost laboratory in Norway and through on-site monitoring of a Coanda screen intake identified two distinct clogging mechanisms specific to Coanda screen geometry [6][7]:
Type I: Soft Ice Accumulation
Soft, wet ice slush accumulates on the top surface of the screen wedge wires, just downstream of the wet zone where water enters the slots. The ice adheres to the wedge wire surfaces but does not penetrate between the wires. The screen remains partially open underneath the ice cover, and some water continues to pass through.
Characteristics:
- Occurs when ice particles in the approaching water contact the screen surface
- Screen remains partially functional
- Can become free of ice on its own when water temperature rises above 0°C
- Flow reduction is gradual, not sudden
Type II: Solid Ice Formation Between the Wedge Wires
Solid ice forms between the screen wedge wires before any ice particles reach the screen from the water. This occurs when the screen itself cools below 0°C due to extreme air temperatures (observed at air temperatures of −13.8°C to −14.0°C and screen temperatures of −5.9°C to −7.1°C in laboratory tests) [6].
Characteristics:
- Occurs in extreme cold even without frazil ice in the water
- Screen blockage is rapid and complete
- Does not become free of ice while freezing conditions persist
- Requires active intervention or temperature rise to restore flow
The Norwegian research found an encouraging result: the Coanda screen reopened without any operational intervention after all ice blockage events once conditions improved [6]. The screen performed well under all normal winter conditions and was entirely self-cleaning. Complete blockage occurred only during the most extreme supercooling events.
Five Anti-Icing Methods: How Each Works
1. Electric Heating Elements
Principle: Resistance heating elements embedded in or attached to the screen structure maintain the wedge wire surface temperature above 0°C, preventing ice nucleation.
How it works: Low-wattage heating cables or elements are integrated into the screen panel during manufacturing, routed along support bars or embedded in the wedge wire mounting structure. A temperature sensor and controller activate heating when water or air temperature approaches 0°C.
Effectiveness: Very high. Since frazil ice cannot adhere to surfaces above 0°C, even minimal heating (raising surface temperature by 0.5–1.0°C) is fully effective against both Type I and Type II clogging [1][5].
Limitations: Requires an electricity supply at the intake site. Energy consumption is modest (typically 100–500 W/m² of screen area depending on ambient conditions) but requires cabling to an electricity supply.
Best for: Sites with available electrical infrastructure; all screen types including Coanda screens.
2. Warm Water Recirculation
Principle: A portion of downstream water (which is above 0°C after passing through the collection chamber) is recirculated back to the intake, warming the approaching water and the screen surface.
How it works: A small recirculation pump takes water from the collection chamber or downstream pipe and returns it to the weir crest upstream of the screen, or directly onto the screen surface. The recirculated water (even at just 1–2°C) is warm enough to prevent supercooling at the screen face [1][5].
Effectiveness: High for moderate cold conditions. The warming effect depends on the ratio of recirculated flow to incoming cold flow, and on the temperature differential.
Limitations: Requires a pump (electricity), return piping, and sufficient warm water volume. In extreme cold, the recirculated water may itself cool below 0°C before reaching the screen. It also reduces the net flow through the system.
Best for: Hydropower and municipal intakes where downstream water is available at above-freezing temperatures; sites where small pumps are already present.
3. Heated Compressed Air Diffuser
Principle: A pressurized system releases heated air bubbles beneath or in front of the intake screen, creating a mixing zone that pushes frazil crystals away from the screen surface and introduces heat.
How it works: A compressor and air heater supply warm, pressurized air through a coarse-bubble diffuser installed at the base of the screen or weir structure. The rising bubbles create vertical circulation that brings warmer water up from depth (in lakes) or mixes heat into the near-screen zone [8][9].
Effectiveness: Good to high, depending on installation geometry and water body characteristics. Most effective in lake and reservoir intakes where warmer water exists at depth.
Limitations: Requires compressor, heater, and electricity supply. Less effective in shallow, fast-flowing mountain streams where warm water at depth is not available. Continuous air supply is needed during freezing events.
Best for: Lake and reservoir intakes; submerged screens; large municipal and industrial intakes.
4. Insulated Enclosure
Principle: An insulated housing around the screen traps residual heat from the water flow, preventing the screen surface from cooling to air temperature.
How it works: The screen is enclosed in an insulated structure (fiberglass, foam, or composite panels) that shields it from wind and cold air while allowing water to flow through. The water itself, at approximately 0.5–4°C, provides enough heat to keep the screen above freezing: as long as the enclosure prevents heat loss to the air.
Effectiveness: Moderate. Effective for mild frost conditions (air temperature down to approximately −10°C) but insufficient for extreme cold or sustained supercooling events.
Limitations: Does not protect against frazil ice arriving with the water flow. It blocks visual inspection of the screen. It may trap debris against the screen if not designed with adequate bypass.
Best for: Mild cold climate sites; supplementary protection combined with another primary method.
5. Hydrophobic and Anti-Icing Surface Coatings
Principle: Specialized coatings reduce ice adhesion to screen surfaces, making it easier for flow forces to strip ice crystals before they accumulate.
How it works: Superhydrophobic coatings create a surface that water and ice crystals cannot easily bond to. The water contact angle exceeds 150°, meaning water forms droplets that roll off rather than wetting and freezing on the surface. Recent research (2024–2025) has developed photothermal superhydrophobic coatings that combine passive ice repellency with active solar-to-thermal conversion [10].
Effectiveness: Promising but still evolving. Laboratory results show significant delays in ice formation (freezing time extended from 150 to 2,140 seconds in one study) [10]. However, durability in service under continuous flow, abrasion, and biofouling remains a challenge.
Limitations: Coatings degrade over time and require reapplication. Performance in severe supercooling events (where ice adhesion forces are strongest) is not yet proven on an industrial scale. Not sufficient on its own for critical intakes.
Best for: Supplementary protection combined with a primary active method; evolving technology to monitor.
Selecting the Right Anti-Icing Strategy
The optimal strategy depends on site conditions, available infrastructure, and the consequences of intake failure.
| Factor | Electric Heating | Warm Water Recirculation | Air Diffuser | Insulated Enclosure | Surface Coating |
|---|---|---|---|---|---|
| Electricity required | Yes (low) | Yes (pump) | Yes (compressor) | No | No |
| Effective temp. range | All (down to −40°C and below) | Moderate (to −15°C) | Moderate (to −20°C) | Mild (to −10°C) | Supplementary only |
| Frazil protection | Excellent | Good | Good | Poor | Moderate |
| Atmospheric ice protection | Excellent | Moderate | Poor | Good | Moderate |
| Installation complexity | Low–Medium | Medium | Medium–High | Low | Low |
| Operating cost | Low (electricity) | Low (pump energy) | Medium (compressor) | Zero | Recoating cost |
| Best screen type | All types | All types | Submerged screens | Surface-mounted screens | All types |
| Reliability | Very high | High | High | Moderate | Moderate |
For critical intakes (municipal water supply, nuclear cooling, snowmaking during peak season): Use electric heating as the primary method: it is the most reliable and effective across all temperature ranges and ice types.
For moderate cold climates (occasional frost, temperatures rarely below −15°C): Warm water recirculation or insulated enclosure may be sufficient, with lower infrastructure requirements.
For maximum protection: Combine methods: for example, electric heating for the screen surface plus insulated enclosure for atmospheric icing protection. Combining methods provides a backup if one method fails.
ADENCO's Approach to Anti-Icing for Coanda Screens
Standard anti-icing methods were developed for conventional flat screens, submerged cylindrical screens, or trash rack bars. Coanda screens have unique geometry (the curved, tilted wedge wire panel, the acceleration plate, the surface-mounted weir configuration) that requires specially designed anti-icing systems.
ADENCO has developed an anti-icing system designed specifically for Coanda screen geometry. Our approach integrates anti-icing directly into the screen manufacturing process rather than treating it as an accessory added later.
Design Principles
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Integrated, not added on: Anti-icing elements are part of the screen assembly, not external attachments. This ensures uniform heat distribution across the entire wedge wire surface and eliminates thermal cold spots where ice could nucleate.
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Zone-specific heating: The Norwegian research [6] showed that ice clogging occurs in specific zones of the Coanda screen: the transition from acceleration plate to screen panel (Type II) and the downstream edge of the wet zone (Type I). Our system concentrates anti-icing energy where clogging initiates, rather than heating the entire screen uniformly.
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Automatic activation: Temperature sensors at the screen surface trigger anti-icing operation only when conditions approach freezing thresholds. The system is inactive during warm months and uses no energy.
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Compatible with operation without electricity: For remote sites without electrical infrastructure, ADENCO offers passive anti-icing configurations that use thermal mass, flow management, and screen geometry optimization to extend the range of conditions in which the screen can operate without electricity. Active heating is available for sites with an electricity supply where maximum cold-weather reliability is required.
Contact ADENCO for technical details on our anti-icing systems and to discuss your specific cold climate requirements.
Designing for Cold Climate: Specification Checklist
When specifying a water intake screen for a site where freezing conditions are possible, include these parameters in your specification:
| Parameter | What to Provide | Why It Matters |
|---|---|---|
| Minimum air temperature | Record low and typical winter minimum (°C) | Determines whether passive or active anti-icing is needed |
| Minimum water temperature | Lowest measured or expected water temperature (°C) | Water below 0°C indicates supercooling and frazil ice risk |
| Type of water body | Open channel (turbulent) vs. lake/reservoir (calm) | Turbulent rivers have much higher frazil ice risk than calm lakes |
| River gradient and turbulence | Rapids, riffles or waterfalls upstream of the intake | High turbulence = high supercooling = high frazil ice risk |
| Ice cover history | Does the water body form a stable ice cover in winter? | Stable ice cover insulates water from cold air, reducing frazil ice risk |
| Wind exposure | Degree of wind exposure at the intake site | Wind increases both supercooling rate and atmospheric icing |
| Electricity availability | Is electricity available at the intake? What capacity? | Determines which anti-icing methods are feasible |
| Consequence of failure | What happens if the screen blocks? (lost revenue, safety risk, etc.) | Determines the required redundancy and reliability level |
| Operating season | Year-round or seasonal? Which months? | Defines the duration and severity of anti-icing requirements |
Frequently Asked Questions
How do you prevent ice on water intake screens?
The most reliable method is maintaining screen surface temperature above 0°C using electric heating elements, warm water recirculation, or heated air diffuser systems. Since frazil ice cannot adhere to surfaces above freezing, even minimal heating prevents accumulation. For mild cold climates, insulated enclosures or hydrophobic surface coatings can provide supplementary protection. The choice depends on site temperature range, the availability of electricity, and consequences of intake failure.
What is frazil ice and why does it block intakes?
Frazil ice consists of small ice crystals (approximately 0.3–1.0 mm) that form in supercooled turbulent water: water cooled just 0.01–0.1°C below freezing. These crystals adhere to any surface at or below 0°C, accumulating in screen slot openings until flow is blocked. Frazil ice formation is rapid and self-accelerating: secondary nucleation causes crystal production to accelerate rapidly within minutes, and a screen can go from fully open to fully blocked in under an hour during severe supercooling events.
Do Coanda screens work in cold climates?
Yes. Research at the NTNU frost laboratory in Norway demonstrated that Coanda screens perform well under all normal winter conditions and are entirely self-cleaning. Complete ice blockage occurred only during extreme supercooling events, and the screens reopened without operational intervention once conditions improved. For intakes that must operate all winter (such as snowmaking or year-round municipal supply) ADENCO's anti-icing systems prevent blockage even in the most severe conditions.
What temperature causes frazil ice?
Frazil ice forms when water is supercooled below 0°C: typically by only 0.01°C to 0.1°C. This supercooling occurs most readily in turbulent, open-channel flows exposed to air temperatures well below freezing. Calm, deep water bodies are less susceptible because the surface freezes into a stable ice cover that insulates the water below from further cooling. Frazil ice crystals begin adhering to metal surfaces at supercooling of just 0.1°C.
Can a heated screen prevent frazil ice blockage?
Yes. Heating is the most effective and reliable anti-icing method. Frazil ice cannot nucleate or adhere to a surface that is above 0°C. Heating elements with low power consumption (100–500 W/m² depending on conditions) integrated into the screen structure are sufficient to maintain the surface above freezing even in extreme ambient temperatures below −30°C. The energy cost is modest compared to the consequences of intake blockage.
How does ADENCO's anti-icing system differ from standard systems?
Standard anti-icing systems are designed for flat screens or trash rack bars and do not account for Coanda screen geometry. ADENCO's system is integrated during manufacturing, provides zone-specific heating targeted at the points where clogging starts, as identified by Norwegian research, activates automatically based on surface temperature, and is available in both active (heated) and passive configurations depending on the availability of electricity.
What is the cost of anti-icing for a water intake screen?
Anti-icing systems typically add 15–30% to the cost of the screen assembly, depending on the method selected and site conditions. The cost of not having anti-icing (measured in lost hydropower production, emergency diesel pump operation, or snowmaking downtime during peak season) typically exceeds the anti-icing investment within the first winter of operation.
Should I specify anti-icing for my intake screen?
If your intake site experiences water temperatures approaching 0°C or air temperatures below 0°C during the operating season, yes. The question is not whether ice will form, but when. For snowmaking intakes, anti-icing is essential: snowmaking operates exclusively in freezing conditions. For hydropower and municipal intakes in northern latitudes, anti-icing is strongly recommended. The cost of prevention is a fraction of the cost of an unplanned shutdown.
References
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Daly, S.F. et al. (2023). "Prevention of Water Intake Blockage by Ice during Supercooling Events." Journal of Cold Regions Engineering, Vol. 37, No. 1. ASCE. DOI: 10.1061/JCRGEI.CRENG-676
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"Trenton Water Works Adds Temporary Pumps to Avoid Plant Ice Shutdowns." Community News, 2025. Retrieved April 2026, from https://www.communitynews.org/news/local/trenton-water-works-adds-temporary-pumps-to-avoid-plant-ice-shutdowns/
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"Frazil Ice." Wikipedia. Retrieved April 2026, from https://en.wikipedia.org/wiki/Frazil_ice
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"A Mathematical Model for Supercooling Process and Its Application to Frazil Ice Evolution." Nature Scientific Reports (2023). DOI: 10.1038/s41598-023-33097-z
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USBR. "Prevention of Frazil Ice Clogging of Water Intakes." REC-ERC-74-15 (1974). Retrieved April 2026, from https://www.usbr.gov/tsc/techreferences/hydraulics_lab/pubs/REC/REC-ERC-74-15.pdf
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Gebre, S. et al. (2014). "Performance of Coanda-Effect Screens in a Cold Climate." Journal of Cold Regions Engineering, Vol. 28, No. 4. ASCE. DOI: 10.1061/(ASCE)CR.1943-5495.0000073
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Lia, L. et al. (2023). "Reducing Ice Accumulation on Coanda Screen Intakes." NTNU, Norway. Retrieved April 2026, from https://ntnuopen.ntnu.no/ntnu-xmlui/handle/11250/2824885
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Hazen and Sawyer. "Frazil Ice Intake Challenges: Balancing Environmental Impacts with Plant Operation." Retrieved April 2026, from https://www.hazenandsawyer.com/articles/frazil-ice-intake-challenges-balancing-environmental-impacts-with-plant-ope
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"Prevention of Ice Formation to Prevent Frazil with Bubble Tubing." Retrieved April 2026, from https://bubbletubing.com/bubble-tubings-solutions/deicing-bubble-tubing/prevention-of-ice-formation/
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"Scalable Robust Photothermal Superhydrophobic Coatings for Efficient Anti-Icing and De-Icing." Nature Communications (2024). DOI: 10.1038/s41467-024-54058-8
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"Fish Protection, Wedgewire Intake Screens, and Frazil Ice." IAHR Library. Retrieved April 2026, from https://www.iahr.org/library/infor?pid=26762
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Wahl, T.L. (2003). Design Guidance for Coanda-Effect Screens. U.S. Bureau of Reclamation, Research Report R-2003-03. Denver, CO.
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"Advances in Frazil Ice Evolution Mechanisms and Numerical Modelling in Rivers and Channels in Cold Regions." MDPI Water, Vol. 15, No. 14, 2582 (2023). DOI: 10.3390/w15142582
Published by ADENCO: Advanced Engineering Coanda Intake Screens. ADENCO's anti-icing technology is designed specifically for Coanda screen geometry, providing reliable water intake operation in the most extreme cold climate conditions. Contact our engineering team to discuss your cold climate intake requirements.