A new approach to reduce flooding and sewer overflows: trees

Preston Cole
Superintendent of Environmental Services and MMSD Commissioner
City of Milwaukee, Wisconsin

The Milwaukee area faces some tough challenges when we get significant amounts of rain. Flooding has damaged homes, and rainwater has filled our sewer system to its capacity and beyond. The Milwaukee Metropolitan Sewerage District (MMSD) has made big investments in major construction projects to reduce flooding and increase the quantity of water that it treats.

But there is another way local government is addressing the problems: planting trees.

Trees, of course, offer cooling shade in the summer and provide habitat for birds while they create an attractive natural setting in city neighborhoods. Less obvious is the dramatic benefits trees have on stormwater runoff reduction.

One tree can keep hundreds of gallons of stormwater from rushing into the sewers over a year. Multiply that benefit by the approximately 200,000 trees along Milwaukee’s streets and boulevards and you can quickly see that trees are a very significant factor in reducing flooding and increasing sewer system capacity.

How does a tree keep stormwater from rushing into the sewer system? In fact, there are several ways. The leaves and branches that make up the tree canopy slow the flow of rainwater and promote evaporation. The trees and their root systems absorb some of the rainwater. And trees promote healthier soil conditions, which increase the capacity of the ground to soak up more rain.

In recent years, urban planners have increased their appreciation of the role of trees in managing stormwater. Nowadays, when roadways are planned or redeveloped, trees are included in the design for their direct environmental benefits. That’s a change from years ago when trees were included solely for their aesthetic contributions.

What do trees mean to the taxpayers of this region? Well, if the stormwater benefits of trees were eliminated, MMSD would be forced to make huge investments in new facilities and MMSD would face significant additional costs for treating the stormwater. Fewer trees would bring higher bills for area residents.

Fortunately, our community is on track to increase the number of trees in our area. And people who live in Milwaukee can lend a hand. Trees planted on private property, perhaps right in your front yard, have the same benefits that we see from trees along the street. This spring would be a good time to consider planting a new tree for shade, cooling, beauty and, yes, even stormwater runoff reduction.

You can get more information on planting trees and their benefits by contacting the City of Milwaukee Forestry Division at (414) 286-3595.