Runoff Mitigation from Urban

Vegetated Roofs in the Southeastern

US

Jason Kirby, Katie Rigney, Julie Price, Matt Winslett, Ronald Sherrod, Stephen Watts and Robert Peters

University of Alabama at Birmingham

25th AWRC Conference Orange Beach, ALSeptember 9th 2011

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 our urban streams. (NPDES Permits)

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

Due to increases in global population and rates of urbanization, the severity of environmental damage is escalating. 2009 US: 0.30 Billion; 83% Urban 2009 China: 1.33 Billion; 45% Urban 2009 India: 1.15 Billion; 32% Urban

An Urban Research Environment:

Birmingham, AL 35294

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.)

An Urban Research Environment:

Birmingham, AL 35294

UAB Vegetative Roof Research:History

2006: Concept investigation; two MSCE2007-present: Chemistry Building; thermal

investigation2008 -present: Hulsey Center; 14,000 ft2 concept

application (20,000 sedum plants)2009 -present: Campbell Hall; vegetation selection2010 -present: BEC; irrigation and runoff 2011-present: Campbell Green house; soil

amendments

Research Objectives: (Presentation)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.

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 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,

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 conditionsPhysical coverage, roof slope, ambient conditions…

UAB BEC Experimental Roofs:Monitored Storm Events (February – June 2011):

Event Rainfall (in) Design Storm

2/25/2011 0.84 <5 year2/28/2011 0.32 <5 year3/27/2011 0.84 <5 year4/4/2011 1.29 <5 year4/11/2011 0.76 <5 year6/10/11 0.52 <5 year6/17/11 1.65 <5 year6/21/11 1.69 <5 year6/22/11 0.99 <5 year

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 2/11 - 6/11)

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

Preliminary UAB Results:•Strong CN improvement

•Consistent with literature

•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.

UAB BEC Experimental Roofs:We anticipate that differences in the flow reduction

and retention of stormwater of unique vegetated roof scenarios may not be completely evident until after the plants have been in place for at least a full growing season.

By this time, the plants will have had time to more fully envelop the soil surface and develop dense root masses (dependent upon inherent root morphology and sufficient soil moisture).

Conclusions:NRCS curve number data across the various

vegetated roof applications are similar with those observed in published research outside the investigational area.

Vegetated roofs are potentially viable for use as a stormwater control technology within urban areas of the southeastern United States.

Future UAB Research:Vegetated Roofs:

Plant selection (ET, survival, irrigation, age,…)Augment soils with AAC(autoclaved aerated concrete) to

enhance moisture availability and solar reflectance.Water quality of vegetative roof runoff.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

UAB Facilities Management Department

Irrigation Water Technologies America, Tremco, and ITSaul Plants.

Questions???