What the Flood of 2013 tells us about the importance of a healthy urban forest

Trees are often associated with nature; the woods, the forest, or perhaps a national park. But trees are also an important part of our urban landscape. Walk down any City street or enjoy some time in a park, and you’ll recognize the numerous contributions of trees to a City’s environment.

Perhaps most obviously, the shade that trees provide helps to develop a more enjoyable outdoor experience. They offer respite from the hot summer sun. In the winter, trees can help block cold arctic winds. This simple contribution of one of our more omnipresent resources is what helps to make a neighborhood, business district, or park usable and bearable.

Trees are well recognized to provide multiple community benefits. Recent research has suggested that trees may be a factor in reducing crime, increasing health and general feelings of well being, improving property value, and increasing enjoyment or use in business districts. In addition to these important contributions to a community’s “sense of place” a tree also has significant infrastructural value. Tree lined streets tend to have calmer traffic, trees can help sequester carbon, and reduce air particulate matter and pollution. and produce oxygen.

It’s fair to say that an “urban forest” is not so much trees in a City, but rather a forest with buildings in it. Regardless of the urbanization of a City, these trees continue to provide natural benefits and habitat. Perhaps of most recent importance is the contribution of trees to minimizing and managing the impact of stormwater.

This year Grand Rapids experienced a wet spring; very wet. So much so, in fact, that the Grand River exceeded it’s previous high water level set in 1985. Torrential downpours and unfettered precipitation overwhelmed our drainage systems and flooded the Grand River.

While this year was exceptionally rainy, extreme rainfall events are not uncommon in the Midwest. Complicating matters, we have covered over many of our natural rainwater filters with pavement for businesses, houses, and parking lots. Therefore, our cities have developed a massive web of stormwater infrastructure buried beneath our streets that is designed to handle stormwater and reduce urban flooding.

Historically, these systems were built to handle both stormwater and sewage simultaneously. However, as Cities have developed increasing impervious surfaces, our treatment plants have been required to handle increasing volumes of water. During heavy or significant rain events, the system can exceed their capacity. Managers are left with a choice: let the wastewater back up the system and into homes and buildings, or discharge untreated or partially treated water directly into the river system? Understandably, the latter is the option most often chosen.

Since the 1990s, cities have been separating their stormwater and sewage systems to prevent this problem. For decades, the City of Grand Rapids has exposed the old system and added a network of infrastructure to handle either stormwater, or wastewater, not both. It’s a huge project, both in terms in work and investment.

Currently, Grand Rapids has only a few CSOs remaining. Discharges of sewage into the Grand River are infrequent. But when the system is forced to handle a large amount of rain water, little can be done to prevent system backages except to discharge partially treated wastewater directly into our river system. This spring, the system handled so much water that as much as 300,000,000 gallons of partially treated sewage was expelled directly into the Grand River.

As we begin to look at our City as an urban environment in which we live, work, and play, traditional infrastructure development can be invasive, cumbersome, and expensive. Instead, Green Infrastructure (or the connected systems of plants or green-space within a City) is sometimes looked at as a more human-friendly approach to solving infrastructural issues.

From an engineer’s standpoint, Trees and other greenery can help to capture storm-water. Tree leaves and branches intercept rain-water and help slow the interception rates into our storm systems. Moreover, trees and other plants use large amount of water to grow. Keeping these areas un-paved can also vastly improve the soil’s ability to naturally intercept large amounts of rain and runoff.

A 2008 study (Annis Water Resources Institute at GVSU) which looked at the contribution of Grand Rapids’ trees in terms of infrastructure value determined that Grand Rapids urban forest canopy can manage as much as 500,000,000 gallons of storm-water during a substantial rainfall event. The cost of increasing the City’s storm-water system capacity by the same amount could be as much as $368,916,122!

Recognizing the value of trees, city officials adopted an urban tree canopy goal of 40% in 2011. Assuming that 34.6% urban tree canopy can intercept 500,000,000 gallons of stormwater, an increase in tree canopy of 21% (to 56.7%) may increase the interception capacity of the urban forest enough to intercept discharge volume of the 2013 event (300,000,000 gallons or a grand total of 800,000,000 gallons).

Unfortunately, many engineers generally prefer quick approaches and sure bets. Rather than attempting to harness the power of green infrastructure, we often find that archaic strategies lead to incredibly intrusive projects that tear up our green space in efforts to install large pipes or new roads. Not only do we lose the infrastructural value of the lost public space, but we’re also forced to endure traffic shifts, loud noises, and destructive invasions of our natural environment.

Rather than losing trees to infrastructural “improvements”, it is important that we recognize the value and protect the benefits of a rich, diverse urban tree canopy. As an asset, trees don’t just benefit us in terms of reductions in infrastructure needs and costs, but also contribute directly to our sense of place, community pride, and neighborhood composition. As our city continues to grow, it’s important that we consider the role trees may provide in developing a livable, economically sustainable, and environmentally conscience urban landscape.