Introduction to Low Impact Development


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Introduction to Low Impact Development

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