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How Does Stormwater Runoff from Urban Forests Affect Groundwater Recharge?

Updated on November 23, 2012

Urban Forests and Stormwater Management Plans


How does what we plant on the land influence the movement of water? As water conservation becomes an increasingly significant planetary concern, cities, landowners and farmers are becoming aware of how our choices in ground covers affect groundwater hydrology, or the movement of water on, under, and into the land. To gather information that will help cities around the world manage their urban forests and refine their water use and stormwater management plans, researchers are asking questions like these:

What kind of trees contribute more to ground flooding in heavy storms?

What kinds of trees hold water in their branches and leaves to allow more rain to evaporate off rather than funnel down the trunk to the ground?

In Kamloops' McArthur Island Park, many of the trees are wrapped with corrugated plastic troughs of pipe, secured with what looks like bathroom tile grout, leading the rainwater into a holding tote at the base of the tree.

In the bright, warm evenings in this small city at the edge of the Thomson River, people walk over to look at the installation, curious. I spoke with researcher Kyle Bondarchuk one evening as he went about his work measuring the rain water that had accumulated in the totes at the base of the trees during that day's storm.


Kyle Bondarchuk, one of the research assistants, is at work taping the bricks so they don't absorb water in the totes and skew the data.
Kyle Bondarchuk, one of the research assistants, is at work taping the bricks so they don't absorb water in the totes and skew the data. | Source
In the Kamloops study, citizens are eyes and ears for the research, and are involved as volunteers to help measure and record.  The research is a collaboration between Thompson Rivers University, the City of Kamloops, and other partners.
In the Kamloops study, citizens are eyes and ears for the research, and are involved as volunteers to help measure and record. The research is a collaboration between Thompson Rivers University, the City of Kamloops, and other partners. | Source
Weeping Willows find water with their penetrating roots. Natural ground cover allows soil penetration of rainwater.
Weeping Willows find water with their penetrating roots. Natural ground cover allows soil penetration of rainwater. | Source
McArthur Park, Kamloops, Canada.
McArthur Park, Kamloops, Canada. | Source
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Stormwater Runoff in Urban Watersheds Contributes to Flooding


The project is researching how different species of trees funnel rainwater differently. In Kamloops, a semi-arid climate, recharging groundwater is an important factor in reducing water usage and diminishing the city’s ecological footprint. Sometimes in periods of heavy rain, low-lying city areas flood, and spring flooding is usual along the riverbanks and floodplains, as meltwater from the Rocky Mountains makes its way downstream. During the rest of the season, the climate is arid, making water conservation a key factor in the city's stormwater management plan.


The research is a collaboration between Thompson Rivers University, the City of Kamloops, and a number of other private, public, and non-profit sector partners. Under the supervision of Dr Darryl Carlyle-Moses of the Department of Geography, it currently provides the research focus for M.Sc. student Julie Schooling.


How the Urban Forest Impacts Groundwater Recharge

Natural ground cover, like trees and grass, allows more stormwater to penetrate the ground.  Paved surfaces and buildings reduce ground water recharge and increase stormwater runoff. This may contribute to flooding, and to aquifer depletion.
Natural ground cover, like trees and grass, allows more stormwater to penetrate the ground. Paved surfaces and buildings reduce ground water recharge and increase stormwater runoff. This may contribute to flooding, and to aquifer depletion. | Source
To measure stemflow of rainwater shed from the urban forest canopy, tubing is wrapped and caulked around the tree trunk.  Runoff water flows into the tote, and is measured after each precipitation event.
To measure stemflow of rainwater shed from the urban forest canopy, tubing is wrapped and caulked around the tree trunk. Runoff water flows into the tote, and is measured after each precipitation event. | Source

Are Homeowners Involved in Developing your City's Urban Forest?

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Storm Water Management and Groundwater Hydrology


This research has important implications for land use everywhere, for it focuses on the attributes, rather than the species of the trees. The canopy size and shape, branch angles, trunk size and texture, leaf size and shape, and attachment angle of leaf petioles to branch, are some of the elements that influence how much water the tree funnels down to the ground during a precipitation event.


An example shows how this works. Two trees in the study are an American Beech, which funnels a lot of water, and a Horsechestnut, which funnels less.


The Beech has a small angle of branching, whereas the chestnut branches are almost perpendicular to the trunk. As the next series of photographs shows, the leaves of the Beech angle up like tiny saucers because the petioles are stiff and hold the leaves at an angle above the branches, catching the rainwater and directing it in toward the centre of the tree and concentrating it down the trunk. On the other hand, the Chestnut leaves and petioles are soft and drooping, inclining to drip the water off the ends of the branches, dispersing the water or allowing it to evaporate.


American Beech

The American Beech branches angle steeply close to the trunk.
The American Beech branches angle steeply close to the trunk. | Source
The American Beech leaves are stiff, arranged on short, stiff petioles that hold the leaves up like saucers to catch the rain.
The American Beech leaves are stiff, arranged on short, stiff petioles that hold the leaves up like saucers to catch the rain. | Source
The American Beech bark is smooth and slippery, allowing rainwater to slide down easily.
The American Beech bark is smooth and slippery, allowing rainwater to slide down easily. | Source

Horsechestnut

The Horsechestnut branch angles spread the branches almost perpendicular to the trunk, encouraging stormwater to flow away from the tree trunk, not towards it.
The Horsechestnut branch angles spread the branches almost perpendicular to the trunk, encouraging stormwater to flow away from the tree trunk, not towards it. | Source
The Horsechestnut leaves are large and drooping, allowing water to drip off the ends.
The Horsechestnut leaves are large and drooping, allowing water to drip off the ends. | Source
The Horsechestnut bark is slightly rough, creating resistance and holding places for water running down the trunk.
The Horsechestnut bark is slightly rough, creating resistance and holding places for water running down the trunk. | Source

The results of this study may yield important information for city and agricultural land use planning to diminish flooding, recharge ground water, and reduce erosion, and save overburdening stormwater management systems.

In some cities, like Mexico City and Los Angeles that draw their water from aquifers below the city, emergencies loom as ground water depletes. On natural ground cover sites, local species of trees with the characteristics of American Beech might be planted to funnel water into the earth and help recharge the ground water. In cities that frequently have heavy precipitation and flooding, species with characteristics that disperse the rain water, holding it in their canopy until it evaporates, may help reduce flooding. Further research in this study will indicate how choices of tree species in urban forests may affect inputs to the terrestrial water cycle with implications for surface runoff and groundwater hydrology.

The research continues in Kamloops for two years, allowing study of the precipitation of all four seasons.

Where there are paved surfaces or buildings, there is stormwater runoff.
Where there are paved surfaces or buildings, there is stormwater runoff. | Source
Data is being gathered from 40 trees of 22 species in a Kamloops city park.
Data is being gathered from 40 trees of 22 species in a Kamloops city park. | Source
Some trees have steep branch angles.  Totes to collect water runoff blow over in Kamloops' high winds unless they are weighted with bricks.
Some trees have steep branch angles. Totes to collect water runoff blow over in Kamloops' high winds unless they are weighted with bricks. | Source

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    • Janis Goad profile imageAUTHOR

      Janis Goad 

      6 years ago

      Isn't it amazing how the choice of trees can make such a difference? Do you mean flashflooding "here" in your region of Italy?

    • GoodLady profile image

      Penelope Hart 

      6 years ago from Rome, Italy

      Fascinating.

      Perhaps the study will provide the data to encourage planting elder type trees! I know that flash flooding here has become a serious problem; having trees that will help re charge groundwater deposits.

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