Stormwater Green Infrastructure Research Needs

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Stormwater Green Infrastructure Research Needs
Results from the 319 NMP
Robert G. Traver, Ph.D., PE ProfessorDepartment
of Civil and Environmental EngineeringVillanova
University Director, Villanova Urban Stormwater
Partnership
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Mission Statement

• The mission of the Villanova Urban Stormwater
  Partnership is to advance sustainable stormwater
  management and to foster the development of
  public and private Partnerships through research
  on innovative SWM Best Management Practices,
  Directed Studies, Technology Transfer and
  Education.
• Research and directed studies will emphasize
  sustainable stormwater management planning,
  implementation, and evaluation.
• Technology transfer will provide tools, guidance
  and education for the professional.
• Partnership Goal is to promote cooperation
  amongst the private, public and academic sectors.

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1998 Sustainable Stormwater

• Watershed Goals
• Flooding
• Water Quality
• Surface Water

• Tools
• Detention

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2008 Sustainable Stormwater

• Watershed Goals
• Flooding
• Water Quality
• Surface Water
• Groundwater
• Stream Channel Geomorphology
• Base Flow

• Tools
• Problem Minimization
• LID
• Product Substitution
• Volume Control
• Infiltration
• Evapotranspiration
• Reuse
• Extended Detention
• Water Quality Treatment
• Manufactured

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from detention basins ? stormwater wetlands
? LID and Volume Reductionfrom an extreme
event flooding ? sustainable focus
Regulations have been enacted at the municipal,
state, and federal level to address stormwater,
focusing on flooding, recharge, water quality,
stream geomorphology and temperature effects (MDE
2000, PaDEP 2006, USEPA 2002, PWD 2008).
Stormwater Management has changed dramatically in
the last decade, as it has moved away from a
flood control perspective toward sustainability
of our rivers and watersheds.
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Generic Stormwater Management

• Good Idea
• Specifications General tied to processes?
• Expected Results General Wide Range of error

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Infiltration Trench
Permeable Pavement
Bioretention
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Porous Pavement
Not a lot of data available!
Cost 23 / Square foot (instead of 1)
From CWP Webpage
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Bioretention Guidelines
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Bioretention BMPs Can Be Used On-line or Off-line

• Advantages
• Reduce the need for pipes
• Control runoff at its source
• Good use of space
• Disadvantages
• Controls only small storms
• No definitive data available

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Bioretention
Cost 7.3 V 0.99 V Vol Water Treated Cubic
Feet Cost Construction, Design and
Permitting May be less as these are areas that
would be landscaped anyway!
From CWP Webpage
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•  
•  

Pa Design Manual 2005
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• Sizing criteria
• a. Surface area is dependent upon storage volume
  requirements but should generally not exceed a
  maximum loading ratio of 51 (impervious drainage
  area to infiltration area see Protocol 2.
  Infiltration Systems Guidelines (Appendix C) for
  additional guidance on loading rates.)
• b. Surface Side slopes should be gradual. For
  most areas, maximum 31 side slopes are
  recommended, however where space is limited, 21
  side slopes may be acceptable.
• c. Surface Ponding depth should not exceed 6
  inches in most cases and should empty within 72
  hours.
• d. Ponding area should provide sufficient surface
  area to meet required storage volume without
  exceeding the design ponding depth. The
  subsurface storage/infiltration bed is used to
  supplement surface storage where feasible.
• e. Planting soil depth should generally be at
  least 18 where only herbaceous plant species
  will be utilized. If trees and woody shrubs will
  be used, soil media depth may be increased,
  depending on plant species.
• 2. Planting Soil should be a loam soil capable of
  supporting a healthy vegetative cover. Soils
  should be amended with a composted organic
  material. A typical organic amended soil is
  combined with 20-30 organic material (compost),
  and 70-80 soil base (preferably topsoil).
  Planting soil should be approximately 4 inches
  deeper than the bottom of the largest root ball.
  

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Mis? Perceptions

• PGC Md, Galli 1993
• gt 60 Infiltration (mostly trenches)
• Most not working as designed
• Listed sediment in pre treatment, location,
  construction and maintenance
• (used 72 hour rule to evaluate)
• Suburban Md Lindsey, Roberts et al. 1992
• 188 basins (repeat of earlier study)
• gt ½ failed gt1/3 sediment buildup

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Mis? Perceptions

• Washington State Hilding 1996
• Majority working
• 1/3 had sediment buildup
• NJ Pine Barrens Princeton Hydro, LLC 2005
• 47 basins - 70 failed the 72 hour test
• Two investigated
• Poor maintenance
• Designers missed restrictive soil layer

So, if you design, locate, construct, and
maintain poorly.. It will fail 50 of the
time..
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Villanova Seepage Pit
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Villanova Seepage Pit
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• Stormwater Control Level How do I design a
  stormwater control measure tailored to meet a
  specific goal based upon the climate, landuse,
  soils and geology for a specific site? What
  maintenance measures are needed to sustain its
  performance, and what is the life cycle
  expectation in longevity and cost?
• Site Level How do I simulate for a site the
  overall performance of multiple stormwater
  controls for both the surface and groundwater
  systems.
• Watershed Level How for a watershed do I first
  set a measurable goal, and how do we measure and
  or project the results of implementation. This
  addresses the issue of how does the benefits of
  each control measure translate to the watershed
  scale as measured by the impact on the water
  body.

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Inherent Variability

• Inflow
• Pollutant loadings
• Rainfall patterns
• Climate
• Performance of the BMP
• Hydrologic Processes
• Environmental Chemistry
• Biology
• Temperature
• Back to Back storms
• Construction
• Maintenance / Replacement

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• .all components of the physical processes and
  tools to include landplaning, and that we are
  just beginning to understand the linkages and
  unit processes needed.

Thanks A. Davis
Thanks A. Davis
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BioInfiltration

• Contributing Watershed
• Question How can we predict for the watershed,
  the hydrologic, pollutant, and thermal imputs to
  the Bioinfiltration Traffic Island?
• Need To enable the design to be tailored to
  landuse, climate and storm size to the incoming
  increased flows and pollutants.
•  
• Pretreatment
• Question How can we design to remove TSS, or
  other pollutants that are not treated by the
  control measure?
• Need To enable the design to be sustainable,
  long lasting, and to treat pollutants (chlorides
  for example) that are not be addressed by the
  other components of the control measure.

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BioInfiltration

• Bioinfiltration - Bowl
• Question What is the hydrological and
  sedimentation processes in the surface bowl?
• Need To enable the design to address both volume
  and erosive flow reduction across the seasons.
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• Bioinfiltration - Vegetation
• Question What are the vegetation processes to
  include maximization of evapotranspiration,
  maintenance of flow paths, and nutrient and
  pollutant reduction?
• Need To enable the design to be tailored to
  individual pollutants, to select plants, and set
  maintenance and possible harvesting programs.

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BioInfiltration

• Bioinfiltration Soil Surface Layer
• Made Soil
• Existing Soil
• Question What is the role of the surface layer,
  made soil, and existing soil, to include
  hydraulic, soil, chemical, and biological
  process?
• Need To again enable the design to be tailored
  to individual pollutants, to set a geometry, and
  maintenance cycle. Which limits the infiltration
  or pollutant removal process? Does the gradation
  of the made soil change over time thus requiring
  replacement? Does the pollutant capture of the
  surface layer require regular replacement? What
  pollutant removal is expected in the existing
  soil after the runoff leaves the control measure?

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Thanks A. Davis
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Per Year 28 events gt 0.5 in 12 events gt 1.0 in
6 events gt 1.5 in (1948 2001)
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Brandywine River
Runoff
6.5 15
ET
24.6- (1.25) 55
Base Flow
14 (.25) 30
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INFILTRATION BMPs
BioInfiltration Traffic Island (BTI)

• Shallow (18), open, vegetated depression,
  sandsoil mixture, with initial mulch layer
• Depth measured using an ultrasonic level detector
• Quality, Rainfall, Depth and temperature
  measurements

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INFILTRATION BMPs
BioInfiltration Traffic Island (BTI)

• 1.3 Ac
• 46 Impervious
• 101 DCIA to BMP
• 450 in/yr

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INFILTRATION BMPs
BioInfiltration Traffic Island (BTI)

• Constructed in 2001
• 4 ft excavation, filled with a 11 sand/soil
  mixture
• Planted with vegetation typically found along the
  eastern seaboard

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Rain Gage
Ultrasonic Level Detector
Invert (El 444.25)
Weir El 445.20
Lysimeters
Soil Moisture Meters
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Measurement
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Hydrologic Performance
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Hydrologic Performance
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Hydrologic Performance
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Output from SlopeFinder program
BTI (4.25 years of data)
EMERSON
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William Heasom
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Example 2005 TI

• 77 Events
• 48 Rainfall
• (not all snow included)
• 7 Events Overflowed
• Yearly Summary
• 5.5 - Overflow
• 2.5 Pre (Meadow B)

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October 6-8th BioInfiltration TI
6.02
Bill Heasom
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Bill Heasom
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GW Mounding?
Machusick
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PERFORMANCE INDICATOR
How should the performance of an infiltration
BMP be assessed?

• Annual runoff capture efficiency
• - Influenced by drainage area characteristics
• Post storm ponded time
• Most regulations include ponded time
• 72 hr failure
• Ponded recession rate
• Can be related to physical properties
• Direct indication of the infiltration process

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PERFORMANCE INDICATOR
Ponded Recession Rate

• Not always constant with depth
• Each BMP has its own characteristic recession
  limb (shape) from storm to storm
• Can be compared over time (longevity)

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SEASONAL VARIATION
Summary of Regressions

• All obs. regressions are significant at the gt95
  level
• Predicted variations (viscosity correction) all
  lie well within the 95 CI of the regressions

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LONGEVITY
PCIB
Low (3-61) ratio of DCIA to BMP area Inflow with
characteristically low TSS concentrations Shallow
bed Maintenance Vacuum Closed bed, no
vegetation, mulch, organic matter, or freeze-thaw.
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LONGEVITY
IT
Extremely high (1301) ratio of DCIA to BMP
area Inflow with characteristically high TSS
concentrations Closed bed, no vegetation, mulch,
organic matter, or freeze-thaw Deep No Maintenance
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LONGEVITY
Points to Ponder Re IT

• PA BMP Manual(51 DCIA to BMP ratio)
• IT (1301) 130 / 5 2626 times the annual
  sediment load
• 80 equivalent years of operation

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LONGEVITY
BTI
Heavily vegetated, Protective mulch layer, High
organic matter content in surficial soil Some
level of TSS pretreatment Shallow bed Freeze-thaw
action Can be maintained Moderate (101) DCIA to
BMP ratio
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Design recommendations Need to understand the
unit processes!

• CHOOSE your BMP based upon..
• How dirty is runoff?
• Look for clean sources!
• Is pretreatment practical?
• What is in it?
• How much rain falls?
• What Level of Maintenance?
• RISK

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Infiltration Risk Idea
Manhole
Storage
1 Runoff goes to Raingarden Pretreatment
Larger Storms 1 goes to UG Storage
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WWW.VILLANOVA.EDU/VUSP
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PERFORMANCE INDICATOR
Incremental Slopes (PCIB and IT)
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PERFORMANCE INDICATOR

• Each BMP has been the subject of continuous
  monitoring in total, approximately ten years
• Needed an impartial, quantitative, and efficient
  method to find and calculate hundreds of slopes
• Visual Basic program created to find and
  calculate the recession rates or slopes
  (SlopeFinder)

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LONGEVITY
BioInfiltration Traffic Island (BTI)
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LONGEVITY
Pervious Concrete Infiltration Basin (PCIB)
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LONGEVITY
Infiltration Trench (IT)
(log scale)
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LONGEVITY

• Only the IT shows visual evidence of a systematic
  change (decrease) in performance
• All three BMPs show significant (two-fold)
  seasonal variation

What is the origin of seasonal variation in
infiltration BMP performance? Why does only one
(IT) show a systematic decrease?
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SEASONAL VARIATION
What is the origin of seasonal variation?
BioInfiltration Traffic Island
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SEASONAL VARIATION
What is the origin of seasonal variation?
Infiltration Trench
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SEASONAL VARIATION

• The viscosity of water varies two-fold over
  average annual temp. ranges

Where K hydraulic conductivity LT-1 k
intrinsic permeability L2 ? fluid density
L-1T-1 g gravitational acc. LT-2 µ
fluid dynamic viscosity ML-1T-1
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INFILTRATION TESTING
Soil texture-based classification
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INFILTRATION
Assumptions

• One dimensional flow
• Homogeneous (area averaged)
• Negligible influence of ponded depth
• Saturated conditions, no influence of soil
  moisture potential

Except Infiltration Trench
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INFILTRATION
Infiltration Trench (IT)

• Trench Infiltration Model (McKsat)
• Conceptually broken into two parts (bottom and
  sides)
• Accounts for the head of ponded water
• Accounts for the Trench geometry (infiltrating
  area)
• Based on Darcys law
• Monte Carlo method used to select best fit
• Flow-weighted sum of squares

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INFILTRATION
Infiltration Trench (IT)
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INFILTRATION
Infiltration Trench (IT)

• Inputs
• Trench geometrystage storage wetted area
• Bounds for K in/hr estimation
• No. of iterations
• Specific storm hydrograph inf. vs. time

• Outputs
• Best fit Ks in/hr
• Error flow-weighted sum of squares
• Simulated hydrograph

Kbottom 0.026 in/hr
Ktop 0.73 in/hr
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SEASONAL VARIATION

• Linear Regressions
• How does the performance change with temperature?
• What portion of this variation might be caused by
  temperature induced viscosity effects?
• Which BMPs are more or less dependant on
  temperature, and why?

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SEASONAL VARIATION

• Assumptions of Linear Regression Model
• Linear relationship is expected
• Normal distribution of residuals around the
  regression
• Constant standard deviation over range of
  independent variable
• Independent observations (autocorrelation)

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SEASONAL VARIATION
What portion of the variation can be attributed
to temperature-induced viscosity effects?
Method

• Determine the average Temp and corresponding K
  in/hr for each regression.
• Based on the average Temp, calculate the
  resulting fluidity
• Solve for k in2
• Using this k in2 vary Temp (f) and fluid
  properties and solve for K in/hr

Where K LT-1 hydraulic conductivity k L2
intrinsic permeability f L-1T-1 fluidity
f (temp.)
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SEASONAL VARIATION
Pervious Concrete Infiltration Basin (PCIB)
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SEASONAL VARIATION
Pervious Concrete Infiltration Basin (PCIB)
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SEASONAL VARIATION
Summary of Regressions

• All obs. regressions are significant at the gt95
  level
• Predicted variations (viscosity correction) all
  lie well within the 95 CI of the regressions

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LONGEVITY
Do the PCIB or BTI show any signs of a systematic
decrease over time?

• Multiple linear regressions (temperature age)

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LONGEVITY

• The IT data show undeniable evidence of a
  decrease over time.
• To be fair, the IT data includes first 1.5 yr of
  operation (PCIB and BTI do not)

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?So.. Mechanisms?

• CONSTRUCTION!
• DESIGN
• How Dirty is the Runoff?
• Can you pretreat?
• Soil infiltration capacity?
• Clogging of Surface Layer / Geotextile
• pretreatment?
• ability to maintain?
• Depth impact?
• Impact of Rain / Soil protection?

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LONGEVITY
What impacts the longevity of infiltration BMPs?

• There are many processes that tend to decrease
  the rate of infiltration.
• There are also many processes and soil
  characteristics that resist degradation and can
  improve the overall rate of infiltration.
• not including native soil profile, depth to
  groundwater, and construction techniques.

Not so good
Bad
Good
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LONGEVITY
PCIB
Low (3-61) ratio of DCIA to BMP area Inflow with
characteristically low TSS concentrations Shallow
bed Maintenance Vacuum Closed bed, no
vegetation, mulch, organic matter, or freeze-thaw.
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LONGEVITY
IT
Extremely high (1301) ratio of DCIA to BMP
area Inflow with characteristically high TSS
concentrations Closed bed, no vegetation, mulch,
organic matter, or freeze-thaw Deep No Maintenance
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LONGEVITY
Points to Ponder Re IT

• PA BMP Manual(51 DCIA to BMP ratio)
• IT (1301) 130 / 5 2626 times the annual
  sediment load
• 80 equivalent years of operation

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LONGEVITY
BTI
Heavily vegetated, Protective mulch layer, High
organic matter content in surficial soil Some
level of TSS pretreatment Shallow bed Freeze-thaw
action Can be maintained Moderate (101) DCIA to
BMP ratio
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Design recommendations

• CHOOSE your BMP based upon..
• How dirty is runoff?
• Look for clean sources!
• Is pretreatment practical?
• What is in it?
• How much rain falls?
• What Level of Maintenance?
• RISK

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Infiltration Risk Idea
Manhole
Storage
1 Runoff goes to Raingarden Pretreatment
Larger Storms 1 goes to UG Storage
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Per Year 28 events gt 0.5 in 12 events gt 1.0 in
6 events gt 1.5 in (1948 2001)
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WWW.VILLANOVA.EDU/VUSP