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
Control Practice Overview
• Inflow rate – Low
• All runoff flows
through engineered
soil
• Native soil restricts
below ground
discharge
• Water level below
ground rises
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.
Conventional (3” perforated
pipe) Underdrain
33% runoff volume reduction
85% part. solids reduction
7% peak flow rate reduction
No Underdrain
78% runoff volume reduction
77% part. solids reduction
31% peak flow rate reduction
76% runoff volume reduction for complete
1999 LAX rain year
74% part. solids reduction for complete 1999
LAX rain year
Restricted Underdrain
49% runoff volume reduction
91% part solids reduction
80% 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
Biofilter Water Balance
Biofilter Water Balance Performance Summary, by Event
BioF
Event
Event
Event
Source
Time
Maximum Minimum Inflow
Hydr
Event Infil Evap
Area
Rain
Rain
(Julian
BioF
BioF
Volume Outflow Outflow Outflow
Number Number Depth (in) Date)
Stage (ft) Stage (ft) (ac-ft)
(ac-ft)
(ac-ft)
(ac-ft)
7
1
0.01
0
0.12
0
0
0
0
7
2
0.05
31
0.57
0
0.007
0
0.001
7
3
0.1
59
0.71
0
0.015
0
0.002
7
4
0.25
90
1.2
0
0.042
0
0.002
7
5
0.5
120
2.03
0
0.084
0
0.002
7
6
0.75
151
2.46
0
0.125
0
0.002
7
7
1
181
2.5
0
0.165
0.007
0.002
7
8
1.5
212
2.52
0
0.249
0.034
0.003
7
9
2
243
2.52
0
0.335
0.066
0.003
7
10
2.5
273
2.53
0
0.416
0.087
0.003
7
11
3
304
2.52
0
0.497
0.097
0.004
7
12
4
334
2.53
0
0.661
0.149
0.004
Event
Cistern
Outflow
(ac-ft)
0
0
0
0
0
0
0
0
0
0
0
0
Event
Orifice
Outflow
(ac-ft)
0
0
0
0
0
0
0
0
0
0
0
0
0
0.006
0.013
0.041
0.082
0.122
0.156
0.213
0.266
0.326
0.396
0.507
Event
Total
Outflow
(ac-ft)
0
0.007
0.015
0.042
0.084
0.125
0.165
0.249
0.335
0.416
0.497
0.661
Event
Flow
Balance
(ac-ft)
Volume Solids
Reduction Reduction
Fraction Fraction
0
1
0
0
0.183
0
0
0.095
0
0
0.043
0
0
0.024
0
0
0.018
0
0
0.014
0
0
0.01
0
0
0.008
0
0
0.008
0
0
0.008
0
0
0.007
0
Other Output Options

Time step detail
 Irreducible concentration
 Particulate reduction
 Stage outflow
 Stochastic seepage rates

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
Kansas City Middle Blue River Outfalls

20
744 acres
 Distributed storage
with “green
infrastructure” vs.
storage tanks
 Need 3 Mgal storage
 Goal: < 6 CSOs/yr
Kansas City’s
Original
Middle Blue
River Plan
with CSO
Storage Tanks
1/26/2009
Adjacent Test and Control Watersheds
Kansas City 1972 to 1999 Rain Series
Water Harvesting Potential of Roof
Runoff Supplemental Irrigation Needs
Evapotranspiration per Month
(typical turfgrass)
per Month (typical turfgass)
1.50
1.00
0.50
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Monthly Rainfall
Rainfall (inches/week)
2
1.5
1
0.5
0
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Irrigation needs (inches/week)
ET (inches/week)
2.00
2.00
1.50
1.00
0.50
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
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.
Percent reduction in annual roof runoff
Reductions in Annual Flow Quantity from Directly
Connected Roofs with the use of Rain Gardens
(Kansas City CSO Study Area)
100
90
80
70
60
50
40
30
20
10
0
0.1
1
10
Percent of roof area as rain garden
100
Household water use (gallons/day/house) from
rain barrels or water tanks for outside irrigation
to meet ET requirements:
January
February
March
April
42
172
55
104
July
August
September
October
357
408
140
0
May
June
78
177
November
December
0
0
Percentage reduction in annual
roof runoff
Reductions in Annual Flow Quantity from Directly
Connected Roofs with the use of Rain Barrels and
Water Tanks (Kansas City CSO Study Area)
100
90
80
70
60
50
40
30
20
10
0
0.001
0.01
0.1
Rain barrel/tank storage (ft3 per ft2 of roof area)
1
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.
rain barrel
storage per
house (ft3)
tank height
tank height
# of 35 gallon
size required size required if
rain barrels
if 5 ft D (ft)
10 ft D (ft)
0
0
0
0
4.7
1
0.24
0.060
9.4
19
47
2
4
10
0.45
0.96
2.4
0.12
0.24
0.60
118
470
25
100
6.0
24
1.5
6.0
Examples from plans prepared by
URS for project streets.
Construction will be completed in
spring and summer of 2012.
Annual Runoff Reductions from Paved Areas or Roofs
for Different Sized Rain Gardens for Various Soils
Reduction in Annual Impervious
Area Runoff (%)
100
10
clay (0.02 in/hr)
silt loam (0.3 in/hr)
sandy loam (1 in/hr)
1
0.1
1
10
Rain Garden Size (% of drainage area)
100
Clogging Potential for Different Sized Rain
Gardens Receiving Roof Runoff
Years to Clogging
10000
1000
100
years to 10 kg/m2
years to 25 kg/m2
10
1
0.1
1
10
100
Rain Garden Size (% of roof area)
Clogging not likely a problem with rain gardens from roofs
Clogging Potential for Different Sized Rain
Gardens Receiving Paved Parking Area Runoff
Years to Clogging
1000
100
10
years to 10 kg/m2
years to 25 kg/m2
1
0.1
1
10
100
Rain Garden Size (% of paved parking area)
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
The most
comprehensive fullscale study
comparing
advanced
stormwater
controls available.
Available at:
http://pubs.usgs.gov/
sir/2008/5008/pdf/sir_
2008-5008.pdf
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
1.3
Expected Change
(being monitored)
No Controls
6.7
515% increase
Swales +
Pond/wetland +
Infiltration Basin
1.5
78% decrease,
compared to no
controls
15% increase over
pre-development
Pre-development
Monitored Performance of Controls at
Cross Plains Conservation Design
Development
Construction
Phase
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%
Water Year
WI DNR and USGS data