Green Roof Opportunities Bruce Gregoire M.S. University of - - PowerPoint PPT Presentation

Green Roof Opportunities

Bruce Gregoire M.S. University of Connecticut Department of Natural Resources and the Environment

Outline

 Background  Green roofs  Objectives  Methods  Results  Conclusions  Future research needs

Background

 Urbanized areas

• High percentage of impervious surfaces
• increased stormwater runoff
• nonpoint source pollution
• 10% increase in effective impervious

area decreases water quality

(Booth and Jackson, 1997; Lombardo et al., 2000; Makepeace et al., 1995; Novotny and Olem, 1994; USEPA, 2009)

Background

 Roof surfaces

• 12% to 21% of imperviousness in urban

areas

• Accounts for ~ 50% of total stormwater

runoff

• Contributes to NPS pollution

(Bannermann et al., 1993; Boulanger and Nikolaidis, 2003; Forster, 1996)

Bishop Center

N

Eagleville Brook Watershed

Eagleville Brook Daylight point Area: ~80 ha ~ 47% impervious area ~18% roof tops

Green roof

Background

 Green roofs offer potential for reducing

stormwater runoff

 Recommended by EPA as a BMP to

control nonpoint source pollution in urban areas.

Green Roofs

 Intensive green roofs  Extensive green roofs

• Modular green roof systems

Chicago City Hall

Stuttgart-Weilimdorf, Germany

ZinCo Int, 2007

Meta-analysis of extensive green roof precipitation retention

Figure 1. Meta-analysis of green roof precipitation retention. The solid vertical line represents an average retention of 56%.

Green Roof Research

 Nutrients

• type of organic matter and fertilizer may

act as source of nutrients in green roof runoff

 Metals

• growing media and vegetation may

influence retention of pollutants

Green Roof Research

 No modular green roof studies  No green roof water quantity/quality

studies in northeastern U.S.

Objectives

• 1. Evaluate the effect of a modular green

roof system in the northeastern United States on stormwater runoff.

• 2. Evaluate the effect of the green roof on

runoff water quality for nutrients, and total and dissolved metals.

Methods

 Paired watershed study design

• Calibration period
• January 25, 2009 to September 1,

2009

• Paired water quantity data collected
• precipitation, treatment and control

watershed runoff

(Clausen and Spooner, 1993)

Control watershed Treatment watershed (Green roof) Drain

Methods

 Green roof growing media

• 75% lightweight expanded shale
• 15% composted biosolids
• 10% perlite

 Modules planted on Earth Day 2009

Methods

 Green roof vegetation

• 10 Sedum species, 12 plugs in each

module:

• S. album (Murale), S. foresterianum subsp.

elegans (Silver Stone), S. kamtschaticum, S. kamtschaticum var. floriferum (Weihenstephaner Gold), S. reflexum, S. selskianum, S. sexangulare, S. spurium (Dragons Blood), S. spurium (Fuldaglut), and S. spurium (John Creech)

Methods

 Treatment period

• September 2, 2009 to September 14,

2010

• 248 m² green roof installed
• Paired water quantity monitoring

continued

• Evapotranspiration measured with

weighing lysimeter

Gant Plaza Green Roof

 334 modules  81%

coverage

 2.6% organic

matter in growing media

 Slow release

fertilizer

Schematic cross-section of green roof in Storrs, CT (Modified from Weston Solutions, Inc.).

Growth media Concrete pavers Weed block Roof structure Module Drainage holes Root barrier/ Filter fabric

Methods

 Treatment period

• Paired water quality samples collected
• Precipitation, green roof and control

runoff

• Water quality analysis
• TN, TKN, NO3+NO2-N, NH3-N, TP,

and PO4-P

• Total and dissolved Cu, Pb, Zn, Cd,

Cr, and Hg

Statistics

 Shapiro-Wilk Test for Normality  Water quantity

• ANOVA
• regression significance during

calibration and treatment period

• ANCOVA
• used to determine changes in slopes and

intercepts of treatment and control watershed regressions between the calibration and treatment periods

Statistics

 Water quality

• No paired water quality data during

calibration period

• Oneway ANOVA and Tukey means

comparison for water quality data

• Trimmed mean if 15% - 50% non-

detects (USEPA, 2000)

Results

 Water Quantity

Calibration Period Average weekly runoff coefficient

Watershed Period Control Treatment Calibration 0.70 0.71

Ratio of runoff to precipitation

Treatment Period

 Average weekly runoff coefficient

Watershed Period Control Treatment Calibration 0.70 0.71 Treatment 0.70 0.56

Ratio of runoff to precipitation

Results

 34% reduction in runoff compared to that

predicted by the calibration regression

% change = Observed – Predicted x 100 Predicted

Calibration Period (n=29) Characteristic Control Treatment Calibration Equation Adjusted runoff (cm wk-1) 0.55 0.67 T=1.23C0.78 C = Control T = Treatment Treatment Period (n=18) ANCOVA Control Treatment Predicted Treatment Observed % Change F p 1.44 1.63 1.07

• 34

63.81 <0.001

Green Roof Water Balance

Input 1 cm % Precipitation 104.9 100 Output1 cm % Runoff 59.2 56.4 Evapotranspiration 45.4 43.3 Residual

• 0.3
• 0.3

1September 2009 to June 2010

Precipitation Retention Compared to Other Studies

 81% coverage compared to 100%

• 100% green roof coverage should increase

precipitation retention from 44% to 54%

 Plaza roof watershed displayed

characteristics of a natural watershed

Meta-analysis of green roof precipitation retention

Figure 1. Meta-analysis of green roof precipitation retention. The solid vertical line represents an average retention of 56%.

Results

 Water quality

Total Nitrogen

TN (mg L-1)

0.1 1

Control Green roof Precipitation

b a a

n = 19

Ammonia nitrogen

NH3-N (mg L-1)

0.0001 0.001 0.01 0.1 1

Control Green roof Precipitation

a a b

n = 19

Total Phosphorus

TP (mg L-1)

0.0001 0.001 0.01 0.1 1

Control Green roof Precipitation

c b a

n = 19

Orthophosphate

PO4-P (mg L-1)

0.0001 0.001 0.01 0.1 1

Control Green roof Precipitation

c b a

n = 19

Dissolved Zinc

Zn (µg L-1) Dissolved

1 10 100

Control Green roof Precipitation

c a b

n = 14

Mass Input/Export - Nitrogen

NH3-N NO3+NO2-N

Mass Input/Export - Phosphorus

PO4-P

Mass Import/Export – Total Metals

Conclusions

 Water quantity

• Green roof precipitation retention 44%
• Average runoff coefficient decreased

from 0.71 to 0.56

Conclusions

 Water quality

• Sink for NH3-N, Zn, and Pb
• Source of TP, PO4-P, and total Cu
• Reduced mass export of TN, TKN,

NO3+NO2-N, Hg, and dissolved Cu

• primarily through a reduction in

stormwater runoff

Conclusions

 Overall the green roof was effective in

reducing stormwater runoff and overall pollutant loading for most water quality contaminants

Future Research Needs

 Study effects of growing media using

expanded shale and composted biosolids in pollutant retention.

 Metal pollutant uptake and stabilization

in the growing media by various Sedum species is unknown

 No standard exists for the composition of

the green roof media and vegetation to reduce NPS pollution

Acknowledgements

This project was funded in part by the CT DEP through a US EPA nonpoint source grant § 319 Clean Water Act

• Jack Clausen
• John Alexopuolos
• CT Dept of Environmental Protection
• UConn Student Chapter of SWCS
• Center for Environmental Sciences and

Engineering

Questions

References

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