Urban Vegetated Roofs in the

Southeastern US

26th AWRC Conference Orange Beach, ALSeptember 6th 2012

Jason Kirby, Katie Sheibley, Julie Price, Matt Winslett, Stephen Watts and Robert Peters

University of Alabama at Birmingham

Environmental Dilemma:Stormwater runoff has been identified by the US

EPA as a major source of pollution in urban and suburban streams, detrimentally impacting sensitive aquatic ecosystems in these watersheds.

Impervious cover reduces the hydrologic time of concentration and amplifies the volume of associated stormwater runoff.

Shanghai Skyline (1990 to Present):

Explosive 20yr growthSignificant environmental

pollution

Why The Concern ?Sediments, metals, oils / grease and general trash

adversely impact urban water bodies.

Stormwater infrastructure is at capacity in many of our cities / communities.Municipal expansion of sewers = $BillionsUrban flooding = $Billions

Due to increases in global population and rates of urbanization, the severity of environmental damage is escalating. 2012 US: 0.30 Billion; 83% Urban 2012 China: 1.34 Billion; 47% Urban 2012 India: 1.23 Billion; 31% Urban (Unicef)

UAB Vegetative Roofs:UAB is currently investigating extensive (shallow)

vegetative roofs for their potential benefits to:Decrease urban runoff and improve water qualityBuilding performance (insulation, cost, durability, etc.)

Urban Research Environment:

Birmingham, AL 35294

Birmingham, AL 35294

Urban Research Environment:

UAB Vegetative Roof Research:History2006: Concept investigation2007- present: CB; thermal investigation2008 - present: Hulsey Center; 14,000 ft2

concept application (20,000 sedum plants)2009 - present: Campbell Hall; vegetation selection2011 - present: BEC; runoff quantity2012 - present: BEC runoff quality AWRRI Funded

Research Objectives:To expand our understanding of vegetated roofs in the

Southeastern US and their role in reducing urban runoff: Determine an optimal plant matrix for stormwater retention and

peak flow reduction.

Evaluate the potential impact of different vegetated roofs on effective curve number (CN) values.

Evaluate runoff water quality during rainfall events (<5yr) irrigated and non-irrigated conditions. new installations and established vegetated roofs. with respect to first-flush effects.

UAB BEC Experimental Roofs:Thirty mini-roof structures (4 ft tall x 12 ft long x 4 ft deep

were constructed. The roof of each “building” is fitted with standard materials required for an extensive vegetated roof, including: waterproofing, insulation, drainage layers, filter fabric, and four inches of green roof soil.

UAB BEC Experimental Roofs:Mini-roofs were planted with the following scenarios

(identical soil: 80% fines, 20% castings):Monoculture Sedum album, a succulent plant; Monoculture Bouteloua curtipendula, a bunchgrass;Monoculture Phlox bifida, a forb; A mixture of the 3 species above, planted in a randomized

arrangementsSoil Only and Conventional Roof Controls

UAB BEC Experimental Roofs:Instrumentation:

Soil Moisture / Temperature (Decagon Devices)Capillary Drip Irrigation (KISSS USA)Surface and Subsurface flow (Campbell Scientific)Ambient Weather Conditions (Davis)

Rainfall duration / intensity, temp, wind speed, heat index, solar intensity,

2011 -2012 RESEARCH RESULTS

Plant Selection:

With minimal drip irrigation the selected plants thrived….

Price, J.G., S.A. Watts, A.N. Wright, R.W. Peters, and J.T. Kirby, 2011. “Irrigation Lowers Substrate Temperature and Enhances Survival of Plants on Green Roofs in the Southeastern United States”. HortTechnology, 21: 586-92.

Plant Selection: (Non Irrigated: Summer 2012)

UAB BEC Experimental Roofs:Previous studies indicate that a vegetated roof can

effectively lower the curve number of a conventional roof from 98 to 82-90*.Lowering runoff volume (attenuated on rooftop)Increasing runoff lag (improve Tc)

However, the vegetated roof performance is closely associated with:Design Storm (<10 yrs) Vegetation selection and soil conditions…Physical coverage, roof slope, ambient conditions,

prior storm events,…

UAB BEC Experimental Roofs:

Methodology utilized to evaluate the effective curve number for the various vegetated roof treatment scenarios was consistent with previous efforts [Carter and Rasmussen, 2008; Prowell, 2006; Getter et al., 2007; and Stumme, 2008].

0 50 100 15050

60

70

80

90

100UAB CN

UAB

UGA

MSU

Conventional

Events (UAB 2011)

Cur

ve N

umbe

r

UAB BEC Experimental Roofs:

Irrigated Roof Treatments Mean CNStandard Deviation

Grass 75.0 9.8Phlox 81.0 9.4Sedum 77.3 8.1Mixed 77.4 8.9

Soil Only 76.9 8.4Conventional Roof 98.0

Non-irrigated Roof Treatments Mean CN

Standard Deviation

Grass 76.9 10.0Phlox 78.5 9.3Sedum 75.9 8.6Mixed 77.0 8.7

Soil Only 79.5 9.9Conventional Roof 98.0

•Strong CN improvement

•Attenuated Volumes ~75%

•Irrigated Avg. = 77.7•Non-irrigated Avg. = 77.0

UAB BEC Experimental Roofs:Combination Both treatments P-Value Irrigated P-value Non-irrigated P-valueGrass v. Mixed 0.900 0.796 0.986Grass v. Phlox 0.092 0.061 0.656Grass v. Sedum 0.651 0.337 0.727

Grass v. Soil 0.269 0.583 0.458Mixed v. Phlox. 0.104 0.085 0.667Mixed v. Sedum 0.734 0.448 0.704

Mixed v. Soil 0.301 0.703 0.467Phlox v. Sedum 0.170 0.246 0.448

Phlox v. Soil 0.659 0.330 0.789Sedum v. Soil 0.433 0.898 0.289

Combination Both treatments t-score Irrigated t-score Non-irrigated t-scoreGrass v. Roof -14.829 -11.195 -9.661Mixed v. Roof -15.963 -12.483 -9.720Phlox v. Roof -10.005 -6.750 -7.288Sedum v. Roof -16.165 -11.934 -10.683

Soil v. Roof -9.560 -6.622 -7.015

Based on UAB data currently available, all vegetated roofs are statistically identical yet measurably better than conventional roofs.

Water Quality Research: Ongoing 2012Task 1. Retrofit existing UAB Greenroofs for Water Quality Analysis

Water Quality Research: Ongoing 2012Task 2. Soil Substrate Assessment Green roof soil has been analyzed for mineral nutrients,

including Ca, Mg, K, P, Cu, Fe, Mn, Zn, B, Al, Cd, Cr, Pb, Na, Ni, total C and total N using saturated extract at the Auburn Soil Testing Lab

• Fresh Soil (preserved from original planting)

• Aged 2yr Irrigated• Aged 2yr Non-irrigated• All Controls

Water Quality Research: Ongoing 2012Task 3. Water Quality AnalysisFirst Flush / Storm Composite:• Nutrients (Nitrogen, phosphorus)• Heavy Metals (Cu, Zn, Cr, Pb, Cd) • (TS/TSS/TDS)• Alkalinity• Biological Oxygen Demand (BOD)• Chemical Oxygen Demand (COD)

Grab:• pH• Dissolved Oxygen• Conductivity

Water Quality Research: Ongoing 2012

0123456789

pH

Average pH Levels in Mini-Roof Treatments

Irrigated

Non-Irrigated

00.20.40.60.8

11.21.41.6

Nitr

ate

Con

cent

ratio

n (m

g/L)

Average Nitrate Concentrations in Mini-Roof Structures

Irrigated

Non-Irrigated

RainMixe

dGras

s

Sedum

Phlox

Soil O

nly

Conve

nti...

0

0.1

0.2

0.3

0.4

0.5Average Phosphorus Levels

IrrigatedNon-Ir-rigatedControl

Phos

phor

us C

onen

tratio

n (m

g/L)

Conclusions:Vegetated roofs are potentially viable for use as a

stormwater control technology within urban areas of the southeastern United States.

The benefits and advantages of targeted greenroof research are many and need continued academic, industry, and funding support.

Future UAB Research:Vegetated Roofs:

Augment soils with AAC(autoclaved aerated concrete) to enhance moisture availability and solar reflectance.

Evaluate interaction with rain gardens to potentially improve urban stormwater runoff quality.

Capture / evaluate larger design storms and their impact on effective curve numbers.

….

Acknowledgements:Research funding was provided by the U.S. Department

of Interior, through the Alabama Water Resources Research Institute.

Performed in correlation with:“Experimental Investigation of Runoff Mitigation from Vegetated Roofs”. PI~Dr. Jason T. Kirby

“Experimental Investigation of Stormwater Runoff Quality Originating from Urban Vegetated Roofs” PI~Dr. Jason T. Kirby

UAB Facilities Management Department

Irrigation Water Technologies America, Tremco, and ITSaul Plants.

Questions???