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4.24 CHAPTER FOUR

0.I0 I

0.05

Time

E- .05 t. C
FIGURE 4.15 Frazil ice formation: water temperature sequence.

Creating a quiet body of water at the intake location promotes surface ice formation.
At the Billings, Montana, waterworks, frazil ice was a severe winter problem in the tur-
bulent Yellowstone River. In this case, the solution was to enlarge an off-river intake
channel into an earthen forebay with a detention time of approximately 1 h. Surface ice
formed on the nearly quiescent forebay. This insulating ice cover prevented the forma-
tion of additional frazil ice and provided the opportunity for river frazil carried into the
forebay to combine with the surface ice and revert to a passive condition.
To prevent or at least minimize ice clogging, the structure can be built of low-heat-
transfer materials with smooth surfaces not conducive to the accumulation of ice crystals.
Metals such as steel are more susceptible to frazil ice formation because they have a high
heat conductivity and act as a sink for the latent heat released when ice begins to form.
This encourages ice buildup. In contrast, ice does not readily crystallize or grow rapidly
on wood or plastic. Screens can be constructed using fiberglass-reinforced plastic with
low thermal conductivity and a smooth surface. Any exposed metal surfaces can be coated
with an inert material such as black epoxy paint to effect better thermal properties and to
increase radiation heat gain. Screens have been developed that resist frazil ice formation.
Heated intake screens have been used successfully at power plant installations and may
have application at waterworks intakes. Frazil ice does not adhere to objects with tern-

TABLE 4.10 Frazil Ice Mitigation
Criterion Remarks
Location Quiet waters away from turbulence
Protected by ice cover
Deep water
Inlet ports Velocity
Large bar rack opening [< 24 in. (0.6 m)]
Low-heat-transfer materials
Smooth surfaces
Coating to improve thermal characteristics
Temperature Heat to prevent ice adherence
Raise local water temperature 0.18 ° F (0.1 ° C)