INFRASTRUCTURE DAMAGE: POWER LINES & BUILDINGS DURING STORMS
Peter Duinker, Halifax Tree Project
2021-05-18
In Halifax, we know well about the damage trees can do to powerlines and buildings when we get a significant storm with high winds. All the photos found at the end of the article were taken on the Halifax Peninsula immediately after Hurricanes Juan (2003) and Dorian (2019) Here is the issue in a nutshell. First, we want trees - especially big ones - in our streets. The trees provide exceptional ecosystem services in the streetside ecosystem (see our article series on Urban-Tree Values). Second, we have less than adequate soils in the city environment, especially in Halifax, meaning that streetside trees have difficulty finding enough suitable soil into which to send anchor roots. And third, the streetside environment is home to the trees as well as most of the aerial cabling we need for electricity distribution and telecommunications. We have inadvertently boxed ourselves into a messy situation where infrastructure damage from streetside trees is ultimately inevitable. Whenever street trees come down, power lines are broken and houses are damaged.
This situation is almost totally avoidable. Let’s start with the soil environment, already mentioned in the first article about sidewalks and curbs. The better the soil environment, the better trees will anchor in it and the fewer trees will come down in a wind event. Second in this account is the choice of tree species. Some species anchor well even when the soil environment is hostile, and some anchor relatively worse. Additionally, some tree species wear their weight relatively close to the ground compared to other species, so their propensity to fall down in a wind event is lower.
Now let’s focus on the infrastructure. Across North America, it seems that city layout decision-makers figured that both power lines and trees should be established in exactly the same spot - the tree lawn (the sliver of territory between the curb and sidewalk). If you think about it, that’s an instant recipe for disaster! So what is the solution to that? One - plant no trees below powerlines, or plant trees so small at maturity that they won’t reach the powerlines. Either way, we don’t really develop the treescape in the streets that we enjoy today. So what about putting the powerlines elsewhere? There are two options here. One is put them underground. This is common in some cities around the world, but not in Halifax! Sure, it would be expensive if one has to blast through bedrock to accomplish this, but other places accomplish it, so we could here too.
Another option I have seen in other countries is to string the powerlines overtop the houses. If you look at mature residential neighbourhoods in Halifax from above, you will observe that there are two lines of trees - along the streets and along the property boundaries between backyards. There are essentially no trees between the houses, so why not put the powerlines above the roofs? That would be so easy to accomplish, and given that powerlines are now maintained using bucket trucks, there should be no issue with access. I am given to understand that putting powerlines above buildings is not permitted according to infrastructure bylaws.
So we have a situation - trees that are huge at maturity are planted under powerlines and beside houses. They grow up in such a way that they are above the houses and the powerlines run through the crowns. We can manage the situation simply by dealing with the repercussions of the wind events when they occur - some trees come down, the power goes out, a few houses incur damage, things get cleaned up, and life goes on. That approach seems to work because little has been done in most cities to address this issue in any other way.
My recommendations will favour the trees and not the power company nor the home owners, even though I am a power-grid customer and home owner with a huge street tree hanging over my house. In older neighbourhoods, the powerline system should be optimized to reduce the number of lines on poles. Safe cables like Hendrix cabling should be installed wherever trees and powerlines intersect. In new neighbourhoods like suburban subdivisions, powerlines should be buried underground. Young trees should be pruned carefully so as to minimize interactions with power cables as the trees mature. Species selections for new street trees should be sensitive to the aboveground and nearby infrastructure.
We want reliable electrical service and we want a generous tree canopy in the streets. The more we pay attention to clever methods for coexistence of trees and street-side infrastructure, the lower will be the conflicts (and the power outages, and the damage to homes).
