Ice heaving, ice jacking or ice push are all names for the same, fairly common winter event on Vermont lakeshores. And, mild winters, like this past one in 2016, with low snow coverage combined with frequent freeze/thaw events can cause some of the more severe ice damage along shorelands. Sheets of ice pushing and expanding against the shore cause berms and some can be damaging to shoreland property. Interestingly, most berms serve as a lake’s natural retaining wall and means for treating stormwater.
During winters when there is low snow cover and little insulation for the ice, it contracts during colder temperatures, which leads to cracks on the top and bottom of ice sheets. As temperatures warm up, water fills these cracks. Then, when temperatures drop, the water freezes and since ice forming expands, it grows and can push ice sheets forcefully against the shore. The ice sheet only knows how to grow during freeze/thaw events, and it doesn’t shrink back until a major spring melt. (This phenomenon has to do with ice properties of compression and tension.)
Gerald Paul from Minnesota in his article, Ice Power, says “…for a lake that is one mile across, when the ice’s temperature rises from 14 to 32 degrees… the ice sheet will expand laterally a total of approximately 32 inches, almost three feet! When conditions are right, this latent force will unleash havoc on shoreland and any structure man has unwisely constructed in its path.”
How to Protect Property from Ice Damage
Vegetated shores are not immune from ice push and shoreland berming, but the network of roots will hold the bank in place and prevent erosion. Shoreland plantings can withstand ice push better than man-made structures, such as seawalls. Plants will shield buildings, like porches or decks, from the ice sheet. Berming is a natural process in lakes and one that helps the lake protect itself by building a wall of defense made of rocks, plants and other natural materials. Natural features along the shore will help minimize ice push damage and the effects of berming. This summer may be a good time to think about reinforcing and arming your bank with a few native plants to prevent a major ice sheet from encroaching on your shore in any future low snow, mild winters. Putting green in your bank is always a good idea.
What Can Be Done with a Berm
Once a berm has occurred, which a few shoreland property owners will discover this spring, shorelines will stay in this altered state (some berms may naturally resettle to where they were before the ice push occurred). The Encroachment Permitting Program does not allow shorelines, established by ice berms, to be reclaimed to the earlier condition or state once they are changed by ice push. Ice push shorelines become the new, natural shoreline.
However, through Encroachment Permitting, landowners are allowed to stabilize their shores to prevent erosion and further ice push effects. Options for shoreland stabilization range from hardscape methods (stone) to bioengineering/ softscape methods (vegetation), depending on the slope and location of the ice push along the shore. The intent of the Encroachment Permitting is to protect the lake, which means guiding the shoreland property owner towards shoreland stabilize methods that benefit both lake and property. Sea walls and other hardscape retaining walls are less likely to get permitted because they create a barrier between the shallow water or lake’s nursery grounds and the shoreland, breaking up the lake ecosystem. Stabilization designs that use vegetation offer the strongest approach for bank stability while providing many lake ecosystem benefits. If you discover damage along your shore, it is best to check with the Agency of Natural Resources Lake and Shoreland Permitting Analysts to learn more about the options for shoreland stabilization and repair because any work below the mean water level would require an Encroachment Permit. Work above the mean water level may fall under the new Shoreland Protection Act and require a Shoreland Permit.
A Note About Drawdowns
Drawdowns, or manipulating the dam to lower the level of water in the lake in the fall, is not an acceptable practice for managing winter ice damage nor for managing aquatic plant growth. While some states continue to use drawdowns as a management technique, Vermont does not have a history of promoting or allowing this practice, with the exception for permitted power generating facilities on a few specific lakes (renewed permits no longer allow for drawdowns). Drawdowns cause severe damage to the littoral habitat — the shallow water nursery grounds – and are not management practices that sustain ecologically healthy lakes. Ice push will occur regardless of lake level and lowering the water level causes the ice sheets to erode and damage the littoral habitat. Vegetated shores remain the best defense and management strategy to protect shorelines from ice push damage.