Storm-waterMitigationusingUrbanForestManagementAshlynCarter,Farhana Khan,andJulieNicholson|E522|Spring2017

INTRODUCTION

Stormwater management is an important component in cityplanning, especially as urbanizationincreases.

The more impervious surfaces reduce the water infiltrationleading to an increase in stormwater runoff, which occurs whenrainwater or melted snow flows over the streets, lawns andother sites creating negative economic and environmentalimpacts within the cities.

We identified the flooding zones in Bloomington and of thoseareas, we examined one specific block in Bloomington - Indianabetween 7th and Kirkwood.

The purpose of the study wasto (1) re-inventory the current treecover (2) assess and evaluate the tree cover and potential areasfor implementing stormwatermanagement tools.

METHODS

Conducted a re-inventory of the street trees on both sides ofIndiana Avenue between 7th and Kirkwood.

Cataloged the existing trees’ diameter at breast height (DBH),species, condition, maintenance requirements, and age.

Cross examined with the existing 2007 and 2012 tree inventoryto identify the tree change over time.

Utilized data with direct observations to construct stormwatermanagement recommendations.

Figure3.Streettrees onNIndianaAvenue

Figure2.FEMA100yearflood mapofDunn Meadow

QUESTIONCan trees be an effective tool in urban stormwater management?

Figure4.Street trees onNIndianaAvenue

7

3

0 0

1

0 0 00 0

2

0

3

0 0 0

I MMATURE SEM I MATURE MATURE SENESCENT

MATURITY DISTRIBUTION (2 0 0 7&2 0 1 2 )

Maple ( Sugar ,Red) Oak ( Pin) Ash( Gr een) Elm ( Am er ican)

80%

12%

8%

PERCENT MATURITY (2 0 0 7 &2 0 1 2 )

im m at ur e sem im at ur e m at ur e

8

1

0 0

4

3

2

0

4

1

0 0

I MMATURE SEM I MATURE MATURE SENESCENT

MATURITY D ISTRIBUTION(2017)

Maple ( Sugar ,Red) Oak ( Pin) Unknown Species ( New Tr ees)

72%

20%

8%

PERCENT MATURITY (2 0 1 7 )

im m at ur e sem im at ur e m at ur e

ANALYSIS

As a trees lifetime increases, the amountof rainfall intercepted increases, where more surface area =more evapotranspiration.

Trees are able to intercept this rainwater through twomain mechanisms:(1) Tree roots grownear the surface since thatis where themajority of the nutrients lie. The roots areable to soakup and store more of the rainwater and prevent it from flushingchemicals into unwantedplaces and preventing soil erosion.(2) The leaves, branches, and bark will also catch the rainfall reducing the overall amount of runoff.

The differencebetween semi-mature andmature: Once atree is considered mature, it is providingthemaximum amountofbenefits available to the community.

Table 1 shows how each tree seen in the most recent inventory (2017) can provide between 3,000-5,000 more rainfall interception once full maturity is reached.

Tree Semi-Mature(gallons/year) Mature(gallons/year)

SugarMaple 5,619(21’) 7,358(40’)

RedMaple 5,720(21’) 7,607(40’)

PinOak 2,569(11’) 7,353(25’)

RECOMMENDATIONS&CONCLUSION

ACKNOWLEDGMENTSDr. Burney Fischer for the access to the 2007 and 2012 Bloomington Street TreeInventory and use of the National Tree Benefit Calculator for tree maturityinformation.

Increase tree cover: Thewider the canopycover the more rainwater the tree willbe able to absorb thus reducing a lot of costs in building sewerage treatmentplants. The city of Seattle did a cost benefit analysis of increasing the canopycover from 18%to 38% and the results suggested thatit would double thestormwater retention capacity by more than $41 million

Creating tree wells and curb extensions: Tree wells do not take up space,in addition to providing ecological service they also provide shade to thevehicles parked under them and reduce th e quantity of hydrocarbonsand suspended particulate matter in the air.

Convert impermeable surfaces: There was a computer modelling done whichshows that for every 1% of impermeable land which is transformed intowoodland , the runoff would be reduced by 0.5%. Tress which are planted aspart of “sustainable urban drainage System schemes” have been proved to beeffective in controlling floodingin urban areas.

RESULTS

Figure11.Photo ofpermeables idewalks from asuccess fuls tudyinOregon

Figure10.Examplealternatives idewalkdes ignthatcouldbeadaptedinDunnMeadow

Figure9.Visualrepresentations for increaseforestcover

OakImmatureis0-10’

Semi-matureis11-24’Matureif25-39’Senescentif40’+

AshImmatureis0-5’,

Semi-matureis6-10’Matureis11-25’Senescent25’+

MapleImmatureis0-20’

Semi-matureis21-39’Matureis40-50’Senescentis50’+

ElmImmatureis0-5’,

Semi-matureis6-19’Matureis20-35’Senescent45’+

Creating artificial rain gardens and tree islands: Many of the tree lawn andareas that have a lot of utility lines can be converted into rain-gardenspatches with native trees and plants. These rain gardens reduce stormwater runoffs. In addition to reducing the quantity of storm water run-offs they add aesthetic value to the property, they are easy to maintainand they also keep the water clean.

Figure12.Conceptualmodel ofanadaptableraingarden

Figure1.FEMA100yearflood mapofDunn Meadow

Table1.Values takenfromtheNationalTreeBenefitCalculator ofgallons interceptedperyearbasedonmaturity level

Figure5.Piechartshowing2007&2012breakdownoftree maturity.

Figure6.Bargraph displayingbreakdownofmaturitybytreespecies for 2007&2012data.

Figure7.Piechartshowing2017breakdownoftreematurity.

Figure8.Bargraph displayingbreakdownofmaturitybytreespecies for 2017data.