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8. Bioinfiltration and Evapotranspiration Controls
in WinSLAMM v 10
Robert Pitt, John Voorhees, and Caroline Burger
PV & Associates LLC
Using WinSLAMM for Effective Stormwater Management
Penn State Great Valley
March 13, 2012
Stormwater Constituents that may Adversely Affect Infiltration Device Life and
Performance Sediment (suspended solids) will clog device Major cations (K+, Mg+2, Na+, Ca+2, plus various heavy
metals in high abundance, such as Al and Fe) will consume soil CEC (cation exchange capacity) in competition with stormwater pollutants.
An excess of sodium, in relation to calcium and magnesium (such as in snowmelt), can increase the soil’s SAR (sodium adsorption ratio), which decreases the soil’s infiltration rate and hydraulic conductivity.
Ground Water Mounding“Rules of Thumb”
Mounding reduces infiltration rate to saturated permeability of soil, often 2 to 3 orders of magnitude lower than infiltration rate.
Long narrow system (i.e. trenches) don't mound as much as broad, square/round systems
Modeling Notes
Biofilter routing is performed using the Modified Puls Storage – Indication Method.
Time increments are established by the model, start at 6 minutes
Yield reductions due to runoff volume reduction through infiltration and filtering through engineered soil
• Inflow rate – Low•All runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level below ground rises
Control Practice Overview
Control Practice Overview
• Inflow rate – Moderate•All runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level below ground rises
•Water discharges through underdrain
Control Practice Overview
• Inflow rate – High•Some runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level above ground rises
•Water level below ground rises
•Water discharges through underdrain
Control Practice Overview
• Inflow rate – High•Some runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level above ground rises
•Water level below ground rises
•Water discharges through underdrain and above ground
Control Practice Overview
• Inflow rate – Moderate•Some runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level above ground falls
•Water level below ground falls
•Water discharges through underdrain
Control Practice Overview
• Inflow rate – Moderate•All runoff flows through engineered soil
•Native soil restricts below ground discharge
•Water level above ground zeros out
•Water level below ground falls
•Water discharges through underdrain
Control Practice Overview
• Inflow rate – Zero•No runoff•Native soil restricts below ground discharge
•Water level below ground falls
•Water discharges through underdrain, eventually only through native soil
Underdrain Effects on Water Balance
0.75 inch rain with complex inflow hydrograph from 1 acre of pavement. 2.2% of paved area is biofilter surface, with natural loam soil (0.5 in/hr infilt. rate) and 2 ft. of modified fill soil for
water treatment and to protect groundwater.
No Underdrain
Conventional (3” perforated pipe) Underdrain
Restricted Underdrain
78% runoff volume reduction77% part. solids reduction31% peak flow rate reduction
76% runoff volume reduction for complete 1999 LAX rain year
74% part. solids reduction for complete 1999 LAX rain year
33% runoff volume reduction85% part. solids reduction7% peak flow rate reduction
49% runoff volume reduction91% part solids reduction80% peak flow rate reduction
Biofilter Geometry
Biofilter Datum is always zero ft.
Biofilter Data Entry Form
Biofilter Geometry
Outflow Structure
Information
Biofilter Data Entry Form
Biofilter Data Entry Form
Biofilter Data Entry Form
Additional Output
Other Output Options Time step detail Irreducible concentration Particulate reduction Stage outflow Stochastic seepage rates
Biofilter Water Balance
Biofilter Water Balance Performance Summary, by EventBioF Source Area Number
Rain Number
Rain Depth (in)
Time (Julian Date)
Maximum BioF Stage (ft)
Minimum BioF Stage (ft)
Event Inflow Volume (ac-ft)
Event Hydr Outflow (ac-ft)
Event Infil Outflow (ac-ft)
Event Evap Outflow (ac-ft)
Event Cistern Outflow (ac-ft)
Event Orifice Outflow (ac-ft)
Event Total Outflow (ac-ft)
Event Flow Balance (ac-ft)
Volume Reduction Fraction
Solids Reduction Fraction
7 1 0.01 0 0.12 0 0 0 0 0 0 0 0 0 1 07 2 0.05 31 0.57 0 0.007 0 0.001 0 0 0.006 0.007 0 0.183 07 3 0.1 59 0.71 0 0.015 0 0.002 0 0 0.013 0.015 0 0.095 07 4 0.25 90 1.2 0 0.042 0 0.002 0 0 0.041 0.042 0 0.043 07 5 0.5 120 2.03 0 0.084 0 0.002 0 0 0.082 0.084 0 0.024 07 6 0.75 151 2.46 0 0.125 0 0.002 0 0 0.122 0.125 0 0.018 07 7 1 181 2.5 0 0.165 0.007 0.002 0 0 0.156 0.165 0 0.014 07 8 1.5 212 2.52 0 0.249 0.034 0.003 0 0 0.213 0.249 0 0.01 07 9 2 243 2.52 0 0.335 0.066 0.003 0 0 0.266 0.335 0 0.008 07 10 2.5 273 2.53 0 0.416 0.087 0.003 0 0 0.326 0.416 0 0.008 07 11 3 304 2.52 0 0.497 0.097 0.004 0 0 0.396 0.497 0 0.008 07 12 4 334 2.53 0 0.661 0.149 0.004 0 0 0.507 0.661 0 0.007 0
Stochastic seepage rates Evapotranspiration
Kansas City’s CSO Challenge
Combined sewer area: 58 mi2
Fully developed Rainfall: 37 in./yr 36 sewer overflows/yr by rain > 0.6 in; reduce
frequency by 65%. 6.4 billion gal overflow/yr, reduce to 1.4 billion
gal/yr Aging wastewater infrastructure Sewer backups Poor receiving-water quality
20
744 acres Distributed storage
with “green infrastructure” vs. storage tanks
Need 3 Mgal storage Goal: < 6 CSOs/yr
Kansas City Middle Blue River Outfalls
1/26/2009
Kansas City’s Original
Middle Blue River Plan with CSO
Storage Tanks
Adjacent Test and Control Watersheds
Kansas City 1972 to 1999 Rain Series
Water Harvesting Potential of Roof Runoff
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0.000.200.400.600.801.001.201.401.601.802.00
Evapotranspiration per Month (typical turfgrass)
ET
(inc
hes/
wee
k)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0
0.4
0.8
1.2
1.6
2
Monthly Rainfall
Rai
nfal
l (in
ches
/wee
k)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0.000.200.400.600.801.001.201.401.601.802.00
Supplemental Irrigation Needs per Month (typical turfgass)
Irri
gati
on n
eeds
(inc
hes/
wee
k)
Irrigation needs for the landscaped areas surrounding the homes were calculated by
subtracting long-term monthly rainfall from the regional
evapotranspiration demands for turf grass.
0.1 1 10 1000
10
20
30
40
50
60
70
80
90
100
Percent of roof area as rain gardenPer
cen
t re
du
ctio
n in
an
nu
al r
oof
run
off
Reductions in Annual Flow Quantity from Directly Connected Roofs with the use of Rain Gardens
(Kansas City CSO Study Area)
January 42 July 357February 172 August 408March 55 September 140April 104 October 0May 78 November 0June 177 December 0
Household water use (gallons/day/house) from rain barrels or water tanks for outside irrigation
to meet ET requirements:
0.001 0.01 0.1 10
10
20
30
40
50
60
70
80
90
100
Rain barrel/tank storage (ft3 per ft2 of roof area)
Per
cen
tage
red
uct
ion
in
ann
ual
roo
f ru
nof
f
Reductions in Annual Flow Quantity from Directly Connected Roofs with the use of Rain Barrels and
Water Tanks (Kansas City CSO Study Area)
rain barrel storage per house (ft3)
# of 35 gallon rain barrels
tank height size required if 5 ft D (ft)
tank height size required if 10 ft D (ft)
0 0 0 04.7 1 0.24 0.060
9.4 2 0.45 0.1219 4 0.96 0.2447 10 2.4 0.60
118 25 6.0 1.5470 100 24 6.0
0.12 ft of storage is needed for use of 75% of the total annual runoff from these roofs for irrigation. With 945 ft2 roofs, the total storage is therefore
113 ft3, which would require 25 typical rain barrels, way too many! However, a relatively small water tank (5 ft D and 6 ft H) can also be used.
Examples from plans prepared by URS for project streets.
Construction will be completed in spring and summer of 2012.
0.1 1 10 1001
10
100
clay (0.02 in/hr)
silt loam (0.3 in/hr)
sandy loam (1 in/hr)
Rain Garden Size (% of drainage area)
Red
uct
ion
in A
nn
ual
Im
per
viou
s A
rea
Ru
nof
f (%
)Annual Runoff Reductions from Paved Areas or Roofs
for Different Sized Rain Gardens for Various Soils
0.1 1 10 10010
100
1000
10000
years to 10 kg/m2Linear (years to 10 kg/m2)
Rain Garden Size (% of roof area)
Yea
rs t
o C
logg
ing
Clogging Potential for Different Sized Rain Gardens Receiving Roof Runoff
Clogging not likely a problem with rain gardens from roofs
0.1 1 10 1001
10
100
1000
years to 10 kg/m2Linear (years to 10 kg/m2)years to 25 kg/m2
Rain Garden Size (% of paved parking area)
Yea
rs t
o C
logg
ing
Clogging Potential for Different Sized Rain Gardens Receiving Paved Parking Area Runoff
Rain gardens should be at least 10% of the paved drainage area, or receive significant pre-treatment (such as with long grass filters or swales, or media filters) to prevent premature
clogging.
Available at: http://pubs.usgs.gov/sir/2008/5008/pdf/sir_
2008-5008.pdf
The most comprehensive full-
scale study comparing advanced
stormwater controls available.
Parallel study areas, comparing test with control site
Reductions in Runoff Volume for Cedar Hills (calculated using WinSLAMM
and verified by site monitoring)Type of Control Runoff
Volume, inches
Expected Change (being monitored)
Pre-development 1.3
No Controls 6.7 515% increase
Swales + Pond/wetland + Infiltration Basin
1.5 78% decrease, compared to no
controls15% increase over pre-development
Water Year
ConstructionPhase
Rainfall(inches)
Volume Leaving
Basin (inches)
Percent of Volume
Retained (%)
1999 Pre-construction 33.3 0.46 99%
2000 Active construction 33.9 4.27 87%
2001 Active construction 38.3 3.68 90%
2002
Active construction (site is
approximately 75% built-out)
29.4 0.96 97%
Monitored Performance of Controls at Cross Plains Conservation Design
Development
WI DNR and USGS data