IDEAL Stormwater BMP Modeling Framework

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IDEAL Stormwater BMP Modeling Framework

• June 13, 2008
• Joe Fersner, PE

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Integrated Design and Evaluation
Assessment of Loadings

• History/Background of IDEAL
• Modeling Approach
• State of the model

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IDEAL

• A first of its kind post-construction water
  quality model for designing stormwater BMPs and
  calculating their trapping efficiencies.
• Uses

• BMP design for small to large developments
  projects
• TMDL compliance
• Antidegradation restrictions
• Watershed master planning
• LID design

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Development History
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A Regulatory Dilemma
1999
2002
2003
2004
2001
2000

• Compliance with Antidegradation TMDLs
• Needed an explicit BMP model
• Model Hydrology Hydrualics and pollutant yield
  from urban areas.
• Estimate BMP performance.
• Base predictions on accepted predictive
  procedures.

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IDEAL Initiated
2001
2004
2005
2002
2003

• Woolpert hired by OCRM
• Scope of Model
• Literature review
• Watershed Framework
• Post Construction BMP Design Aid Manual and IDEAL
  Spreadsheet

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IDEAL Development

• Primary Researchers
• Dr Bill Barfield Oklahoma State University
• Dr. John Hayes Clemson University

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IDEAL OCRM version

• BMP Trapping
• Sedimentology and soil isotherms
• Hydrology
• Single storm and Total annual runoff
• 4 pollutants
• 3 BMPs
• Pond routing
• Single watershed
• Post-construction

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Watershed Modeling Framework
Directly Connected Impervious Sub Basin
Directly Connected Impervious Sub Basin
Pervious Sub Basin
VFS
VFS
Dry or Wet Detention Basin
Outflow From Watershed
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IDEAL OCRM Model Limitations

• Only for use on the SC coast
• Limited outlet configurations
• Numerous spreadsheet constraints
• Untested BMP algorithms
• No resuspension, denitrification, direct loading
  on BMP, or bacteria growth.

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Greenville County
2002
2004
2005
2001
2003

• Woolpert hired by Greenville County
• Isotherms and Rainfall Analysis
• Continue to use spreadsheet

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Greenville County
2003
2004
2005
2001
2002

• Dry pond verification study

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Greenville County
2004
2001
2002
2003
2005

• Visual Basic Graphic
• User Interface
• (VB GUI) developed
• Bioretention research begun
• Multiple watersheds
• Literature review
• Swales
• Engineered Devices

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Greenville County
2003
2005
2004
2001
2002
Sept

• EPA BMP Design Manual
• EPA/600/R-04/121

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Greenville County
2005
2006
2003
2004
2002

• Bioretention cell added and revised
• Greenhouse study
• Greenville Co. study
• Fecal Coliform loading function

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Greenville County
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Greenville County
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Greenville County
2006
2005
2003
2004
2002

• Sand filter and bioswale added
• Conceptual algorithms developed for engineered
  devices
• Conveyance routing algorithms
• Pipe, Channel, Simple translation
• Model presented to EPA Region 4
• VB GUI revised to current layout
• Distributed Jan 2007 to GC engineers

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Greenville County

• Object oriented VB.net Drag n Drop version

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Summary of versions
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Modeling Framework
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Rainfall Statistics

• Design Storms
• Annual Distribution
• of Storms

12 Storms 0.25 to 10.5
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Hydrology

• SCS Runoff Curve Number Method
• Excess Runoff Hydrograph from
• Gamma distribution unit hydrograph
• Unit rainfall for Storm Type (I, Ia, II, III)

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Sediment Yield

• Pervious Areas - MUSLE
• Impervious Areas - EMC Approach
• EMC varies with type of impervious area
• Modeling dependability improves as local data is
  collected
• Model Sediment Size Distribution
• Used to determine sediment trapping in Vegetated
  Filter Strip and in ponds
• Nutrients and bacteria are sorbed on the exchange
  phase of the clay particles, hence need to know
  concentration of clay size particles
• Pervious areas based on CREAMS equations
• Impervious areas based on NURP data

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Nutrient and Bacteria Loading

• Modeling Nutrients
• Yield based on event mean concentrations (EMCs)
  for each chemical
• EMCs vary based on land use
• Modeling Indicator Bacteria
• Yield based on event mean concentrations (EMCs)
  for bacteria
• EMCs highly variable
• National average 15,000 number/100ml
• Death due to natural mortality (1st order), UV
  exposure, and temperature
• Growth rate (1st order) factored

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BMP Trapping

• Predicts trapping of sediments in ponds through
  overflow rate calculations for 5 particle
  classes.
• Predicts nutrient trapping by settling of
  particulate matter and sorbed portion on trapped
  active clay content of the sediment by isotherms.
• Predicts bacteria trapping using isotherms and
  mortality
• Vegetated Filter Strip (VFS) trapping uses the KY
  VFS
• model

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Output

• Graphical and
• Text

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State of the Model
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IDEAL

• Development team in Stillwater, OK
• Project managed from Columbia, SC
• Version available for Greenville County, SC and
  SC coastal areas (July 2008).

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Ongoing Improvements

• Improvements to conveyance routing and BMP
  interconnectivity relationships.
• Enhanced Bioswale research with EPA-ORD, Edison,
  NJ
• CAD interface
• Engineered Devices

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Future Steps

• Expansion of Isotherms to more geographic areas
• Rainfall statistics for additional geographic
  areas
• Engineered device algorithms development
• GIS interface
• Optimization
• Large scale watershed considerations
• Continue to do performance enhancement
• Continue to use best science available and
  support the model

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Contact Info

• Support
• Ideal_support_at_woolpert.com
• General Questions and Sales
• Stormops_at_woolpert.com
• Download the Greenville County version from
• http//www.woolpert.com/asp/events/IDEAL.asp

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Questions?