Storm Water

Firstly I need to apologize to the people of our region. The last article that I wrote for this paper was about watering trees and within 24 of press time, we had one of the biggest rainfalls in recent memory. As the consistent victim of Murphy’s Law, I take all responsibility for the deluge.

All joking aside, the flooding in the city of Thunder Bay was severe and rare and my thoughts are with all those who experienced losses.

If nothing else, all this rain and flooding provides the best opportunity to illustrate just how crucial trees are in urban environments to assisting in managing storm water runoff. Cities are vast networks of impervious surfaces including roofs, sidewalks, roads and lawns. Although lawns are not truly impervious, as soil get saturated, they offer very little surface area to collect rainwater and heavy deluges often run right off of them.

Large trees of any species offer an immense surface area on which rainwater can be caught and held. When a tree gets wet, the leaves become heavy with water adhering to their surfaces and the bark, from twigs to trunk, also hold surprisingly large quantities of water. As a heavy rain passes, the water stuck to the tree parts begins to evaporate back to the atmosphere and is thus diverted from storm water systems.

In short but intense deluges, trees will act to slow the flow of water from the skies to the sewers reducing the chances of a system overload.

If you don’t believe me that trees are essentially giant sponges, just look at the studies that show that a healthy urban forest canopy can save millions of dollars in storm water management system costs. It’s easy to visualize if you’ve ever stood under a big tree during a downpour.

Street trees and landscape trees suck up their share of water but the amount of moisture that forested parks and green spaces absorb is even more immense.

Granted trees won’t ever eliminate the need for storm sewers, they should be part of the infrastructure included in any storm water management system. Since trees are simply surface area to temporarily trap water, the bigger the trees are the more water they’ll divert from sewers. This is where arborists join the storm water management team.

Trees return the most benefits to us when they are large but it takes progressive thinking to nurture an urban forest to maturity. From just a few years after planting and every 5 to 10 years for the life of a tree, structural training and good maintenance pruning can extend the life of a tree by 50 years or more. Trees are worth an investment in care just as are new facilities, pipes and pumps.