The forecast for wind or snowstorms can give rise to anxiety for many farmers. How do you best prepare for these events? The tips below can assist you in reducing the chance of sustaining damage to your investment. As the elders say, “An ounce of prevention is worth a pound of cure.”
Snow and ice are best dealt with by shape, bracing, spacing, removal, and preparation. In anticipation of a forecasted windy winter event, loose items should be secured or stowed. Additionally, all hardware and rope or strapping should be inspected to ensure tightness and serviceability.
Shape. The best shape for shedding snow is a gothic peak. This is in comparison to a quonset or rounded peak. The steeper angle increases the chances of snow naturally sliding off, and makes it easier to remove the snow that does accumulate. This does not mean that the quonset peak cannot withstand snow loads. It just means that the snow is easier to remove.
Bracing. Appropriate bracing for snow and ice includes wind or end wall bracing at each corner and a solid ridge purlin (see Fig. 2a and 2b). It is recommended that only one overhead purlin be used, as two purlins create a holding pocket for snow. This increases the weight and likelihood of tunnel collapse or plastic damage. Wind bracing and purlin prevents racking of the tunnel from end to end.
Additionally, if a serious snowstorm is forecasted, one might consider shoring up the tunnel with notched 2x4’s that have 8inch x 8inch feet. For gothic peaks, this bracing should be wedged under the end of truss supports or under the ridge purlin. For quonset peaks, the bracing should be wedged under the purlin or in the center of the bow. It is recommended to place these every other bow or every fourth bow.
Spacing. The NRCS high tunnel initiative CODE 325 recommends that a minimum of ten feet or a recommended twenty feet around the tunnel be clear of obstructions. This is to allow space for snow removal equipment and room for the snow which is removed from the sides of the tunnel. The uneven pressures created by snow buildup on the sides unevenly because of neighboring obstructions or uneven removal from each side is a common reason for tunnel collapse.
The spacing between neighboring obstructions or tunnels is not the only span to be concerned with. Decreasing the space between each bow (also known as rib or arch) is one way to increase the high tunnel strength. Generally, in areas with snow events, the bows should be spaced four feet apart.
Removal. The weakest part of the tunnel from end to end is in the middle. This is because there are no end wall braces or anchoring. High tunnels are most stable when there is an even amount of snow build up on each side. Before removing the snow from the top of the tunnel, you should remove it from the sides by shoveling or using a snowblower.
Snow and ice can be removed from inside the tunnel by bumping the bows or pushing up the plastic. This can be accomplished with a soft bristle broom or a long handle with a tennis ball on the end. Start at the bottom and work your way up. If you start at the top, the snow will have nowhere to go. Doing this from inside the tunnel is preferred as you can alternate from one side to the other easily.
Sometimes snow cannot be removed from the inside. To remove snow from the outside, tie knots in a rope every couple of feet. Toss the rope over the tunnel and with another person, drag the rope back and forth using the same principles mentioned above.
Preparation. You will find it prudent to keep a few items on hand. The lumber for bracing to shore up, soft bristle brooms or long handle with a tennis ball, back up poly for covering or patching, and greenhouse repair tape. Also, servicing snow blowing equipment in advance is wise.
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Natural Resources Conservation Service. (2018, October). High tunnel general specifications. Retrieved October 24, 2019, from https://efotg.sc.egov.usda.gov/references/public/AK/AK_325_High_Tunnel_General_Specifications_Oct2018.pdf.
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