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"Creating Green Stormwater with Bioretension"
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Creating Green Stormwater with
BioretentionAllen P. Davis
Department of Civil and Environmental EngineeringUniversity of Maryland
College Park, MD 20742
July 21, 2010
The Problem:
(Sub)urbia
Rainfall
-Erosive,
-Polluting
-Stream
Degradation
-Chesapeake
Bay Water
Quality
ChallengesIMPERVIOUS AREA
Urban Pollutants
Bioretention (Rain Gardens)
Quality: Filtration, Adsorption, Biodegradation
Hydrology: Pooling, Storage Infiltration, & Evapotranspiration
PONDING STORAGE AREA
PLANTING SOIL
FLOW ENTRANCEPOINT
VEGETATION
UNDERDRAIN
MEDIA
MEDIA: Sand, Soil, Organic Matter
Bioretention
Dennis Ave. Silver Spring, MD
Installed March 2006
Silver Spring
Bioretentionresearch & monitoring
Silver Spring Hydrograph0
0.05
0.1
0.15
0.2
0.25
0.30
1
2
3
4
5
6
7
8
9
10
12:00 16:00 20:00 0:00 4:00 8:00 12:00 16:00 20:00 0:00 4:00
Rai
nfa
ll (c
m)
Flo
w (L
/s)
Time of Day
5/11 to 5/13/08 Hydrograph, 2.86 in.
Inflow
Outflow
Rainfall
Bioretention Performance Metrics
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 0.5 1 1.5 2 2.5 3
Ru
no
ff d
epth
dis
char
ge
(in
)
Rainfall depth in (in)
Pavement
SS Bioretention
Woods - C Soil
Woods - B Soil
Olszewski, Davis, et al. In Progress
Water Quality
College Park Silver Spring
Input InputOutput Output
5101520304050607080859095
2
4
6
10
40
100
200
400
600
98 2
25
60
2
4
6
11
10
199
40
100
200
400
600
25
60
Exceedance Probability
TS
S E
MC
(m
g/L
)
CP in CP out
SS in SS out
No Flow/Below Limit
TSS (College Park & Silver Spring)
Li & Davis, J. Env. Eng. 2009
Bioretention
5101520304050607080859095
6
10
20
40
100
200
400
98 2
120
60
56
10
199
20
40
100
200
400
120
60
5
Exceedance Probability
Zin
c E
MC
(u
g/L
)
CP in CP out
SS in SS out
No Flow/Below Limit
Zinc (CP & SS)
Li & Davis, J. Env. Eng. 2009
Metals Accumulation - PbNavy Yard
Surface
0-10
10-20
20-30
30-40
40-50
50-60
60-70
70-80
80-90
Dep
th (
cm)
Dimensionless TSS or Normalized Captured Pb Deposit
-10
0
10
20
30
40
50
60
70
80
90
0.0 0.2 0.4 0.6 0.8 1.0
Dissolved Pb
Media Pb prediction
TSS
-1000
-500
0
0 100 200 300 400 500 600mg/kg
Li & Davis, Env. Sci. Technol. 2008
Total Phosphorus (CP& SS)
Li & Davis, J. Env. Eng. 2009
5101520304050607080859095
0.06
0.08
0.1
0.2
0.6
0.8
0.4
11
0.06
0.08
0.1
0.2
0.6
0.8
0.05 0.05
0.4
199
Exceedance Probability
Ph
os
ph
oru
s E
MC
(m
g/L
as
P)
CP in
CP out
SS in
SS out
No Flow/Below Limit
Nitrogen
Runoff
Enhanced Nitrate Removal with Internal Storage
Kim et al. Water Environ. Res. 2003
Media
Mulch
Overflow
Underdrain
Anoxic Denitrification Zone NO3 N2
Mass Loads (kg/ha/yr)CP SS
In Out In Out
TSS 1190 37 570 38
Chromium 0.09 0.015 0.02 ~0.007
Copper 0.26 0.073 0.12 0.045
Lead 0.09 0.013 0.03 ~0.005
Zinc 1.0 0.063 0.36 0.017
Chloride 6800 458 320 25
TN 27 7.2 9.6 3.6
Nitrate 12 2.5 3.7 ~0.19
TKN 15 4.1 6.0 3.6
TP 3.6 0.72 0.9 0.38
TOC 44 154 43 78
Li & Davis, J. Env. Eng. 2009
Excellent Management of Hydrology Media Area & Depth
Excellent Particulate & Bacteria Removal Filtration: Depth not Important; Surface
Accumulation Adsorption
Metals, Hydrocarbons Excellent; Surface Accumulation
Phosphorus, Nitrogen, Complex, Depth important
Biological Processes Important Denitrification (Nitrate removal) Biological Predation Vegetation in uptake & degradation
What we know so far…
Technology Maturity First installed in Greenbelt MD in
1992 First UMD Campus in 2003 Major demonstration in UMD in 2004 Now widespread throughout Mid Atlantic
