The Science of Making Outdoor Ice on Portland Ponds

12/27/2011 - It is a rite of passage for generations of Portland residents whether it’s children learning to skate for the first time, pick up hockey games with friends, family time on the ice or grandparents watching their grandchildren skating and reminiscing about past skating days in Portland.

The process of making ice is a labor of love, because it is not a process that comes easily. This article is designed to help residents and outdoor ice enthusiasts understand the step by step process involved to create an outdoor ice surface in our City.

Step #1: Staff preparation on the rigors of making ice
The training/preparation begins prior to the potential start of the ice making season. Athletic Facilities Staff which are a division of the Recreation Dept, review the process, determine their roles and prepare the necessary equipment as well as the ponds themselves.

Step #2: Wait for ideal ice making conditions
Consistent low temperatures (below 20 degrees) for several days are required to allow frost to develop below the surface of the ground. This will prevent the water from just soaking into the ground when preparing the rink area. Some snow is ok, it helps thicken the ice base and acts like a cold plate when we have warm ups.

Step #3: Time to make the ice
While many believe the area is just flooded (sometimes we just flood to attain the right level), but the process actually involves layering the water in both thin and thick layers (depending on the weather conditions). The staff attaches a 2 inch fire hose from an adjacent hydrant (specifically installed for this) for the water. It takes about 3 to 4 days of layering the water to get a pond established under ideal conditions (under 20 degrees). During the ice building stage, crews work around the clock until the ice is established. There needs to be at least a week between steps 2 and 3 for a rink to be ready during ideal circumstances.

Step #4: Sustaining the ice
Once the ice is established, staff will perform a maintenance program of sweeping the ponds. The ice shavings are used to fill holes and cracks that may have formed in the ice. Water is sprayed often to the repaired areas and to increase overall ice thickness.

There are several influences that can affect the conditions of outdoor ice and these conditions either bring you back to “Step #2” or adversely affect the quality of ice. Once the surface is compromised, you have to start over.

Water Motion
Several of our ponds have either storm water flow or natural spring that can disrupt the ice quality and disrupt the surface. Working around the influxes of water can be challenging at Deering Oaks Pond and Ludlow.

Temperature
The air temperature needs to be well below the 32 degree freezing point. Warmer temperatures prevent staff from making high quality ice. It is also important to not use the ponds until a substantial thickness has been achieved. Proper ice thickness helps to prevent the ice from chipping and breaking. Using the ice before it is ready or when there is a warm up, damages the surface with footprints, tires tracks and iced snow banks from partial shoveling

Snow Accumulation
If snow falls prior to achieving the necessary frost level this will insulate the ground and prevent the ice from forming properly. The skating area needs to be free of snow prior to any water application. It is also not a good idea to attempt to make ice when it is snowing. The water will mix with the snow and form slush. When it freezes the skating surface becomes rough and will easily crack with use.
The ponds are a secondary job for our crews with snow clearing from the Portland Downtown district, school route sidewalks and City plazas (City Hall, Police Dept, Cumming Center etc) are our main focus during storm events. However, once the staff is released from those public safety missions, we hit the ponds!

Equipment
When ice thickness allows, we use trucks, Bobcats and even large tractors. When the ice is thinner we will use small snow blowers, small riding tractor with small blower and of course, shovels.

For more information about the conditions of our outdoor winter sites please visit us at: http://www.portlandmaine.gov/winterfunspots/