Stormwater Retention Simulation on
the Gateway Building Green Roof
Syracuse, NY
Elliot Alexander, Douglas Daley, and Krystal White
State University of New York College of Environmental Science and Forestry
ESF Green Roof
• Intensive green roof
• Wider diversity of plant
species, including
shrubs and trees
▫ Alvar Pavement Barrens
▫ Dune
• Deeper substrate >6”
• Park-like and accessible
ESF Gateway Bldg – Dune Profile
Growing Medium Specifications
Property
Metric
(Intensive)
Bulk Density
74.4 lb/CF
(saturated)
Pore Volume
74%
Maximum Water
Holding Capacity
53%
Air-Filled Porosity at
max WHC
20.9%
Permeability
0.02 cm/sec
pH
6.1
Organic Matter
9.3% by mass
Alvar and Dune Plant Community (May
2013)
Research Questions
• Is the green roof a functional community?
▫
▫
▫
▫
▫
▫
Hydrology (water flux)
Energy flux
Plant survival, growth and reproduction
Pollinators
Carbon and nutrient sequestration
Resilience to succession, invasive species
• How does the public react to the green roof?
Performance Monitoring
• Climate
▫ Microclimate effects on
x Plant community
x Hydrology
x Energy transfer
▫ Temperature, RH, radiation
• Hydrology
▫ Water storage (soil moisture, unsaturated flow)
▫ Runoff and drainage
▫ ET
Focus
• Water flux
• Heat flux
• Connected in the realm of design by
▫ Soil characteristics
x Water retention
▫ Nutrient management
x Leaching
x External inputs of NPK
Energy Balance – Radiation at Soil
Surface
Rn = S + λ ⋅ ET + J H
• Energy balance to (R) and
from soil (W/m2)
• Components
1. Sensible heat (soil to
atmosphere)
2. Latent heat of vaporization
and evapotranspiration
3. Soil heat flux (to deeper
soil)
Typical partitioning of the global solar radiation as it reaches the land surface:
(a) contributions to the net radiation;
(b) net radiation partitioned into its components (Jury and Horton, 2004).
Surface Energy Balance
• Net Radiation = 65% of 1350 W/m^2 = 877
W/m^2
• Soil heat flux = 5% of Global radiation = 68
w/m^2
Figure 4.3 Components of the surface energy balance during daytime (left) and nighttime (right)
(Jury and Horton, 2004).
Steady Soil Heat Flux
dT
J H = −λe
dz
• Vertical heat
flux (W/m2)
is described
by Fourier’s
Law
• Temperature
gradient
• Soil thermal
conductivity
Figure 4.4 Effective soil thermal conductivity (a) and diffusivity (b) as a function of water content for
various soil types. Numbers in parentheses refer to porosity (Jury and Horton, 2004).
Heat Flux
• Moist sand
– Moisture content = 0.3
– Figure 4.4, λe =1.0 W/m-K
• ΔT =T2 – T1 =20 – 15 = 5 C = 5 K
• JH = -(1.0)(5) = -5 W/m2
QUIZ
• Net Radiation on the earth surface is
approximately what % of Global Radiation?
Autumn Performance
• First year growth
• Plant canopy approaching senescence
• What effect does the greater soil depth have on
heat transfer (insulation)?
▫ 2-inch typical soil depth (extensive roof) versus 8inch (intensive roof)
• What heat effects do reflecting surfaces (walls)
and shadows (vegetation, roof penetrations)
have?
Soil Temperature Diurnal Variation at 2-inch Depth
40
Temperature (Celsius)
35
30
25
Air Temperature
Middle 2 inch depth
20
West/Fence 2 inch depth
15
10
5
9/5
9/6
9/7
9/8
9/9
Date - Time
9/10
9/11
9/12
Soil Temperature Diurnal Variation at 8-inch Depth
40
Temperature (Celsius)
35
30
25
Air Temperature
Middle 8 inch depth
20
West/Fence 8 inch depth
15
10
5
9/5
9/6
9/7
9/8
9/9
Date - Time
9/10
9/11
9/12
November
Comparison of Fall Soil Temperature in 2 locations
20
300
250
15
Temperature (Celsius)
200
10
150
100
5
Air Temperature
West/Fence 2 inch depth
Building 2 inch depth
50
West/Fence 8 inch depth
Building 8 inch depth
Net Radiation
0
11/9
0
11/11
11/13
11/15
11/17
11/19
11/21
-50
-5
-100
-10
Date - Time
-150
20
Winter Air and Soil Temperature at Two Locations on
10
Gateway Center Green Roof
Precipitation
9
15
8
Temperature (Celsius)
10
7
5
South Fence, 2
Inch Depth
West Fence, 2
Inch Depth
South Fence, 8
Inch Depth
6
0
11/24
Air
Temperature
12/4
12/14
12/24
1/3
1/13
1/23
2/2
2/12
5
-5
4
-10
3
-15
2
-20
1
-25
0
Date - Time
West Fence, 8
Inch Depth
Research Question
How closely does HYDRUS 1-D simulation of
green roof soil match observations of
stormwater retention?
Green Roof Hydrologic Soil Properties
•
HYDRUS Simulation of the Green Roof
Soil
1. Simulation of the 100 year storm event (5
inch/hour) with a 2 hour duration
2. Same storm simulation followed by 1 week of
no precipitation
• Both used a soil thickness of 12 inches
Rainfall Infiltration and
Storage
12 inches
Soil Saturation
Stormwater
Retention
Evapotranspiration
Transition?