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River Ice Network Ice Dusting Operations |
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What ice dusting does:
- Mechanically weaken the ice cover.
- Increases the rate of snow melt 10-15 times.
- May reduce ice thickness 1-6 cm (0.4 to 2.4 inches) per day.
- Advance the melt-out of ice by as much as 6-10 days.
Desirable Physical Properties:
- Good Absorptivity and Thermal Conductivity.
- Specific gravity greater than 1.
- Solid Materials
- Optimal particle size range: 0.1 to 0.3 mm.
- Material needs to be dry to prevent clogging.
- Liquid Materials
- Low Viscosity to aid application.
- Freezing Point less than 32F.
- Non-Toxic and insolubile in water
Environmentally Acceptable:
- Non-toxic
- Use indigenous materials such as sand or mulch.
Cost of Application and Materials
The resources deployed for ice dusting should be cost effective. The costs of dusting material, labor, and equipment used should be evaluated.Application:
- Material must be applied in a thin layer to prevent insulating the snow and ice cover from solar radiation.
- Apply about 1 month before historic ice-out date.
- Apply after bulk of season snowfall. If more than 20cm (about 8 inches) of snow falls on top, a re-application of the dusting material may be needed.
- Application rate of 200 to 700 grams/square meter.
- Apply material to create lines of weakened ice. One or more lines laid down parallel to the river banks, preferablly over the thalweg or centerline of the river. It may be desireable, if river conditions permit, to have ground crews mark the area to be dusted with orange highway safety cones or some other marking visible from the air.
Monitoring:
Once an area is dusted, it should be monitored to measure the amount of ice cover being thinned and the effectiveness of the ice dusting operation. In order to answer the question "What good did the dusting do ?", field measurements need to be taken in the dusted area and in a non-dusted control area which is hydraulically and geographically similiar. To facilitate measurements, the control area should be located within a mile or so of the dusted area. Frequency of measurement may depend on local climatic conditions, but should be taken at least once a week after initial dusting.
- In both the dusted and control area,the ablation
rate, the rate at which the ice is eroded, can be
measured by drilling a hole in the ice and placing a wooden
stick/pole device tightly in the hole as shown in figure 1.
The vertical portion of the pole may be graduated for ease of
remote visual measurement. The pole should extend completely
through the ice with the bottom of the top piece resting on
top of the ice cover.
Initially, the total ice thickness h as shown in figure 1 will give a base condition to compare subsequent measurements with.
A meteorlogical Pyrometer may be employed to measure the amount of direct and reflected sunlight. Measurements should be taken at one foot and 2 foot above the top of snow and/or ice cover, one measurement taken looking up, the other looking down. Some digital pyrometers have displays that may not work well in cold temperatures. For such conditions, an analog pyrometer where one can measure the output voltage directly may be needed. The sensor should be mounted on a bar which can be extended out over the ice cover to take unobstructed measurements. Once the measurements are taken the albedo can be calculated by taking a ratio of the reflected versus the direct sunlight.
Subsequent site visits should measure the amount of ice loss at the surface d, and the total ice thickness h as shown in figure 2. While d will give a measure of surface loss, adding d and h and comparing to the initial h will give a value of erosion on the botton side of the ice cover.
In order to determine the amount of penetration into the ice cover, a core sample is useful to measure the depth of penetration and density. In lieu of an ice core sampler, using a soil sampler or cutting a block of ice out with a chain saw may provide the necessary information.
The date of initial ice breakup and ice-out dates in both the control and dusted areas should be recorded.
Aerial fly-overs augmented with photographs or video can be useful in assessing conditions on the river before, during, and after any ice dusting operation.
Prepared with the technical assistance of: US Army Cold Regions Research and Engineering Laboratory