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Introduction to Low Impact Development
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Introduction to Low Impact Development

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  • 1. Low Impact Development Engineering and Landscape Design Considerations Richard Lucera, PE, CFM
  • 2. Regulations
    • Federal Clean Water Act
    • California Porter Cologne Act
    • Municipal Separate Stormwater Sewer Systems Permit
    • Section 401 Certification
    • Water Conservation in Landscaping Act
  • 3. Fundamental Concepts of L.I.D.
    • Conserve Natural Resources That Control and Filter Stormwater
    • Minimize and Disconnect Impervious Surfaces
    • Direct Runoff to Places Suitable for Filtration or Infiltration
    • Mimic Natural Hydrology Via IMPs (Integrated Management Practices)
    • Pollution Prevention Through Education
  • 4. Integrated Management (Treatment) Practices
    • Bioretention
    • Bioswales
    • Infiltration Ponds & Trenches
    • Permeable Pavement
    • Rainwater Harvesting (Conservation)
  • 5. Treatment Mechanisms
    • Filtration – Physical Straining of Coarse Solid Contaminants Through Surface Vegetation, Adhesion to Soil or Filtration Medium Particles (Quality)
    • Microbial Breakdown of Pathogens and Organics (Quality)
    • Load Reduction Through Evapotranspiration or Infiltration. Effective Results on Widest Range of Stormwater Contaminants (Quantity)
  • 6. Bioretention
  • 7. Bioretention Functionality
    • Provides Storage Prior to Treatment
    • Physical Adhesion of Contaminants within Soils (Suspended Solids)
    • Evapotranspiration (Root uptake and Evaporation. Dissolved Nutrients Removed from Surface Water Balance)
    • Biological Consumption of Organics and Pathogens
    • Can Involve Infiltration or Sub-Drain Connection Dependant on Soils and Other Sub-Surface Conditions
    • Increased “Routing Time”
  • 8. Bioretention: Planting Guidelines
    • 1000 trees/shrubs per acre
    • 3 species each of trees and shrubs
    • Shrub-to-tree ratio of 2:1 - 3:1
    • Plant species tolerant of pollutants and varying wet/dry conditions
    • Non-invasive plant species
    • Trees near the perimeter provide wind protection/shade
    • Provide planting soil 4’ deep
    • 2” – 3” of mulch for erosion protection
  • 9. Bioretention: Maintenance
    • Bi-annual plant health inspection
    • Removal of diseased/dead/invasive plants
    • Routine checks for standing water
    • Debris/sediment removal at inflow point
    • Replace mulch every 2–3 yrs
    • Replace soil every 5–10 yrs, or as needed
    • Unclog under-drain, as needed
    • Erosion control, as needed
  • 10. Bioswale
  • 11. Bioswale Functionality
    • Filtration Through Surface Vegetation or Grass (Suspended Solids)
    • Increase “Routing Time”
  • 12. Bioswale: Maintenance
    • Bi-annual inspection for erosion, debris, sediment, and damaged vegetation
    • Mow grass, as necessary (1–2 times/yr), and repair bare or sparse patches
    • Remove litter/debris
    • Remove sediment deposits greater than 3” deep, or that cover vegetation
    • Regularly inspect for standing water
    • Inspect for channelization over time
  • 13. Infiltration Pond & Trench
  • 14. Infiltration Pond and Trench Functionality
    • Provides Surface or Sub-Surface Storage Prior to Treatment
    • Physical Adhesion of Suspended Solids
    • Biological Consumption of Pathogens and Organics
    • “ Bioinfiltration” Utilizes Evapotranspiration Benefits
    • Mass Load Reduction – Minimal Reconnection to Surface Waters
    • Most Effective Treatment IMP
    • Application Heavily Dependant on Native Soils and Sub-Surface Conditions
  • 15. Infiltration Pond: Maintenance
    • Inspect bi-annually for:
      • erosion
      • Sediment/debris
      • standing water
    • Trim vegetation at beginning and end of wet season
    • Remove sediment and regrade when sediment deposits exceed 10% of basin volume
    • If basin appears clogged (slow drainage), remove sediment deposits and scarify soils
    • Observe drain time after construction and periodically thereafter to ensure functionality of facility
  • 16. Infiltration Trench: Maintenance
    • If drain time exceeds 72 hours, remove rock fill, excavate 2” from all surfaces, and replace clean fill
  • 17. Infiltration Trench
  • 18. Infiltration Pond Infiltration Pond
  • 19. Permeable Pavement Permeable Non-Permeable
  • 20. Permeable Pavement Functionality
    • “ Permeability” Created By Joints and Spaces within Traditional Materials
    • Provides Storage within Material Voids (V BMP )
    • Treatment Consists of Trapping Coarse Solids Within Geofabric and Additional Benefits From Attenuation
    • Some Systems Can Utilize Infiltration For Additional Treatment Benefits
  • 21. Permeable Pavement: Maintenance
    • Vacuum surface 2-3 times/yr
      • End of wet season
      • Middle and/or end of dry season
    • Inspect outlets annually
    • Maintain landscaping and prevent soil from being washed onto pavement
    • Minimize use of salt and/or other treatments for de-icing
  • 22. Rainwater Harvesting
  • 23. Rainwater Harvesting Functionality
    • Primarily a Conservation Mechanism
    • Provides Storage to Alleviate Irrigation or Other “Greywater” Domestic Needs
    • May Incorporate Filtration or Biofiltration Mechanism for Treatment
    • Delivery System Can Operate by Gravity or By Pump System
  • 24. Technical Considerations for Rainwater Harvesting Systems
    • The Goal is Sustainability
    • Many Agencies Require Backflow Prevention Devices if Cross Connection to Public System or Domestic Plumbing is Proposed
    • Tanks Should Be UV Resistant
  • 25. Typical Southern California Rainfall
  • 26. Design Considerations
    • Sizing
    • Location
    • Quality and Quantity of Treatment
    • Technical Limitations
    • Cost
    • Planting and Aesthetics
    • Maintenance
  • 27. Sizing Criteria
    • Volume Based V BMP
      • Bioretention, Bioinfiltration, Media Filtration, Infiltration Trenches and Ponds
    • Flow Based Q BMP
      • Vegetated Swales, Low Flow Diversion
    • Other
      • Rainwater Harvesting
  • 28. Volume Based BMP
    • Urban Runoff Quality Management Approach (Required Storage Volume)
      • C=0.858i 3 -0.78i 2 +0.774i+0.04
      • P 0 =(a x C) x P 6
    • “ C” = Runoff Coefficient
    • “ i” = Watershed Impervious Ratio
    • “ P o ” = Required Storage Depth (inches)
    • “ a” = 1.963 (Regression Constant for 48 Hour Draw Down)
    • “ P 6 ” = Mean Annual Runoff Producing Rainfall Depths (inches)
  • 29. Rainfall in Southern California
    • Location
      • Santa Maria
      • Los Angeles
      • Laguna Beach
      • Riverside
      • Victorville
      • San Diego
      • Oxnard
    • P 6 (inches)
      • 0.65
      • 0.60
      • 0.58
      • 0.50
      • 0.47
      • 0.57
      • 0.65
  • 30. Surface Area Requirements for Storage Zone
    • Work in Connection with Volume Requirements to Determine BMP “Footprint”
    • Required to Minimize Potential for Clogging (2-3’ Max. For Infiltration Ponds, Media Filters and 6” Max. for Bioretention Ponds)
  • 31. Flow Based BMP
    • Q=CiA
      • “ C”=Rational Method Runoff Coefficient (Consult Local Drainage Criteria)
      • “ i” = Runoff Intensity 0.2 Inches/Hour
      • “ A” = Drainage Area in Acres
    • Typical “C” Values
      • 0.35 Vegetated Open Space (Good Condition)
      • 0.55 Single Family Residential
      • 0.70 Commercial
      • 0.85 Industrial or Barren “Hard Pack”
      • 0.95 Paved/Impervious
    • Vegetated Swales Require Minimum Length 300-500 Feet to Provide Adequate “Routing” Time (5-10 Minute)
  • 32. Detailed Standard “C” Values
  • 33. Sizing for Rainwater Harvesting
    • Irrigation Supply/Demand Based
    • City of Austin Method
      • Based Upon Assumption of 1” Demand per Week (St. Augustine Turf Lawn)
      • Tank Size per Lesser of the Following:
        • SF collection area x 5 = Tank Size (Gallons)
        • SF landscaped area x 4 =Tank Size (Gallons)
      • Typical Single Family Residence Requires Approximately 5,000 Gallons
  • 34. Rainwater Harvesting
  • 35. Location
    • The “Spirit of IMPs” – More Frequent and Smaller Measures as Opposed to Larger “End of Pipe”
    • Conveyance is Key
    • Larger Drainage Areas Should Flow to IMPs That Are “Off-Line” (5 Acres or More)
    • Smaller Drainage Areas Can Flow to “On-Line” IMPs, Provided Adequate Overflow is Maintained
  • 36. Quantity and Quality of Treatment
  • 37. Quantity and Quality of Treatment
  • 38. Technical Limitations - Infiltration
    • Highly Dependant on Soil Permeability and Other Sub-Surface Conditions. Consult a Professional Geotechnical Engineer!
      • Requires Site Specific Testing – Single or Double Ring Infiltrometer
      • Considers Variations with Location, Depth, Time, and Season
      • Considers Proximity to Groundwater, Rock, and Karst Formations
      • Considers Potential for “Mounding” and Lateral Migration
      • Conflicts with Compaction Requirements for Engineered Fill
      • Maintain Separation from Buildings, Slopes, Pavement Areas, and Utility Trenches
    • Pre-Treatment to Collect Debris and Sediment is Required
  • 39. Technical Considerations and Limitations for Filtration and Biofiltration
    • Usually Will Require Impermeable Liner and Sub-Drain System
    • Filter Material Thickness Will Vary
      • Sand 6”
      • Other Import Soils and Select Media 2-3’
    • Filtration Will Not Assist with Treatment of Dissolved Nutrients
    • Improperly Maintained Planting Can Result in Leaching of Organic and Other Contaminants Through Sub-Drain
    • Trenches Will Require Cut-Off Structures or Sub-Surface Berms to Prevent “Short Circuiting”
    • Pre-Treatment to Collect Sediment and Debris is Highly Desirable
  • 40. Technical Considerations and Constraints for Permeable Paving
    • Considerations
      • Works Well in Systems That Allow for Small Replacement Sections
      • Low Traffic Areas
      • Restrict to Flat Slopes (2% or Less)
    • Constraints
      • Feasibility of Infiltration Can Be Limited
      • Requires Coordination with Geotech to Achieve the Proper Balance of Stiffness, Permeability, and Storage
  • 41. Relative Hard Cost of IMPs $ $ $ Bioinfiltration $$$ Hardscape $ $ $ Sub-Drain and Liner System $ $ $ $ Bioretention $ Permeable Pavement $ $ $ Filtration $ $ $ Infiltration Trench $ $ Infiltration Planting Select Import Overflow Diversion IMP
  • 42. Lost Opportunity – Land Use Cost Infiltration Trench Permeable Pavement Bioretention Media Filter Infiltration Pond