rain gardens & Permeable Pavements


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Rain Gardens & Pervious Pavement Presentation

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  • The natural hydrologic cycle is nature’s way of recycling water. Before development much of the water evaporates in the atmosphere or is collected and transpired by vegetation. Most of the rest is conveyed to downstream streams through interflow or groundwater flow. A very small amount is left to flow along the surface. Enter the human activities that disturb land (aka land development). One of the Civil Engineer’s primary objectives is to slow down and clean up the increased surface flow of storm water since the natural hydrologic cycle is interrupted. Sustainable development is fairly new to us (or the specific tools)…and are intended to get us closer to the natural hydrologic cycle than with conventional tools alone do. One such sustainable development tool is bioretention.
  • System overview
  • System overview
  • System overview
  • FAST – Using vegetation and soil to slow down and clean up storm water
  • Water Quality Performance: King County Basin Treatment - remove 80% TSS Enhance Treatment - Basic + 50% Zinc Removal DOE Treatment Basin Treatment - remove 80% TSS Enhanced Treatment - additional treatment of metals particularly Zinc and Copper
  • The design is a balancing act between stormwater management via bioretention and space for parking, etc
  • Site Preparation – limit the grading to within 6” of final grade (Cahill, 2003), complete in stages later. Also ensure excessive compaction does not occur prior to installation Soil subgrade – recommended minimum subgrade soil infiltration rate is 0.1 in/hr. Infiltration rates less than 0.1 in/hr require additional mitigation via perforated underdrains, etc. NOTE – 0.1 in/hr is acceptable as a minimum only if additional surface runoff is NOT directed to pervious section (mitigation is necessary otherwise). 0.1 in/hr = Hydrologic Soil Type C (0.05 – 0.15 in/hr typical) Alderwood soil = C type soil Defined as having moderately fine to fine texture Sandy Clay Loam Pavement section – recommended design is per LID technical guidance manual. NOTE: Aggregate Base is also referred to as the “Reservoir Course”
  • Soil subgrade – recommended minimum subgrade soil infiltration rate is 0.1 in/hr. Infiltration rates less than 0.1 in/hr require additional mitigation via perforated underdrains, etc. NOTE – 0.1 in/hr is acceptable as a minimum only if additional surface runoff is NOT directed to pervious section (mitigation is necessary otherwise). 0.1 in/hr = Hydrologic Soil Type C (0.05 – 0.15 in/hr typical) Alderwood soil = C type soil Defined as having moderately fine to fine texture Sandy Clay Loam “ The principal SCS soil group within King county classified as a till soil is the Alderwood series, which is the most common soil type throughout the western part of the county…Most alluvial soils are classified by the SCS in hydrologic soil groups C and D.” – 2009 KCSWDM, Section 3.2, p 3-24 “ The principal SCS soil group classified as an outwash soil is the Everett series.” – 2009 KCSWDM, Section 3.2, p 3-24 SCS Everett = HSG B (TR-55, USDA 1986) NOTE – approximately 70% of the native soils in the puget sound region are HSG A, B or C
  • A good section view of two of the permeable pavement types. Wearing Course (4” – 8”)* Choker Course (optional, ~4”) - single size crushed granules with the purpose of stabilizing the open-graded wearing surface for paving Aggregate Base (6” min) - is also referred to as the “Reservoir Course” – it is designed, through uniformly graded aggregate, to have a void space of 40%. Due to its functionality to store water to allow time for infiltration to occur, this layer must be at least 6” deep and can reach typical depths of 18”, and maximum depths of 36” (hence the additional cost as compared strictly to conventional pavement sections) Separation Layer - filter layer, typically geotextile but can be amended soil (min depth = 18”) – purpose is to keep soil out of the base material. NOTE: geotextile should pass water at a greater rate than the subgrade soils Source = 2005 LID Technical Guidance Manual for Puget Sound
  • A construction detail for providing a catch basin to catch and convey the ‘overflow’ or ‘failure’ event
  • City of Kirkland example, ~2.5 acre site, cottage-style housing, clustered site plan
  • Meandering gravel sidewalk along north side of internal site road (in lieu of standard curb/gutter/sidewalk). Pervious pavement pathway through native vegetation at east end of commons area. Grasscrete parking pads near east detached garage buildings.
  • Picture of bioretention swales between homes
  • Unique siting of detention vault = under commons building = limited site disturbance/development footprint
  • Detention facility cost savings = 42% Actual project savings ~ $35% when considering additional coordination with City of Kirkland staff, materials costs (pervious pavement)
  • rain gardens & Permeable Pavements

    1. 1. Sustainable Design David C. Hilgers, ASLA, LEED-AP Michael Moody, PE, LEED-AP
    2. 2. <ul><ul><li>Presentation Overview: </li></ul></ul><ul><ul><ul><li>Sustainable Design Introduction </li></ul></ul></ul><ul><ul><ul><li>Sustainable Toolbox </li></ul></ul></ul><ul><ul><ul><ul><li>Vegetated Roofs </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Rainwater Harvesting </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Bioretention </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Permeable Pavement </li></ul></ul></ul></ul><ul><ul><ul><li>Sustainable Synergy </li></ul></ul></ul>Sustainable Design
    3. 3. Sustainable Residential Design
    4. 4. Sustainable Design <ul><ul><li>Sustainable Development Toolbox: </li></ul></ul><ul><ul><ul><li>Vegetated Roofs </li></ul></ul></ul><ul><ul><ul><li>Rainwater Harvesting </li></ul></ul></ul><ul><ul><ul><li>Bioretention </li></ul></ul></ul><ul><ul><ul><li>Permeable Pavement </li></ul></ul></ul>
    5. 5. LEED Credits & Stormwater (LEED-NC v-2.2) SS Credit 5.2 Site Development , Maximize Open Space (1 point) (vegetated roof area, permeable pavement area, rain gardens) SS Credit 6 Stormwater Management (2 points) 6.1 Quantity control – reduce discharge rate 6.2 Quality control – remove pollutants SS Credit 7 Heat Island Effect (2 points) 7.1 Non-roof – permeable pavements, open grid 7.2 Roof area – vegetated roof 50% WE Credit 1 Water Efficiency (2 points) 1.1 & 1.2 Rainwater Harvesting systems Sustainable Design
    6. 6. <ul><ul><li>Vegetated Roofs </li></ul></ul><ul><ul><li>Zero Energy Idea House </li></ul></ul><ul><ul><li>Green Roof </li></ul></ul>
    7. 7. Vegetated Roofs <ul><li>Vegetated Roofs Design Considerations </li></ul><ul><li>Structure </li></ul><ul><li>Building type, Roof type, Roof Slope, Weight limitations (15-30 lbs/sf) </li></ul><ul><li>Site Considerations </li></ul><ul><li>Microclimate, Orientation, Exposure, Habitat </li></ul><ul><li>Maintenance Considerations </li></ul><ul><li>Access, intensity, client use </li></ul><ul><li>Design Details </li></ul><ul><li>Edge treatments, mechanical equipment </li></ul><ul><li>coordination, drainage types, OTHERS! </li></ul>
    8. 8. Vegetated Roofs <ul><li>Components </li></ul><ul><li>Waterproof Membrane </li></ul><ul><li>Modified Asphalt (Bitumen) </li></ul><ul><li>Thermoplastic (EPDM or PVC) </li></ul><ul><li>Drainage Layer </li></ul><ul><li>Drain Mat, Channels, Gravel layer </li></ul><ul><li>Growing Media </li></ul><ul><li>Engineered Soil Mix, </li></ul><ul><li>70% aggregate / 30% organic </li></ul><ul><li>Vegetation </li></ul><ul><li>Drought and heat tolerant, low biomass </li></ul>
    9. 9. City of Bellevue Clinkston / Brunner Architects Shirey Contracting Builder
    10. 13. Going Green at the Beach Stanwood, WA
    11. 17. Glendale Country Club Pro Shop
    12. 18. Rainwater Harvesting <ul><ul><li>Rainwater </li></ul></ul><ul><ul><li>Harvesting </li></ul></ul><ul><ul><li>Planning & Design </li></ul></ul><ul><ul><li>Project Review </li></ul></ul>
    13. 19. Rainwater Harvesting Clyde Hill Residence Baylis Architects March-Macdonald Contractor System Overview 10,000 gallon tank Buried below ground Non-potable use (irrigation only) Collects from roof and patio area
    14. 20. How much water can we store? Historical weather data Roof area and type Supply Estimate How much water do we need? Historical ET data Landscape area and type Irrigation Demand
    15. 21. Estimate available supply over time Using actual tank size storage Shows deficit or overflow amounts Storage Modeling
    16. 23. Rainwater Harvesting Clyde Hill Residence
    17. 28. Rainwater Harvesting System Overview 3,000 gallon tank vertical above ground Non-potable use (irrigation only) Dual use system – also used for detention requirements Zero Energy House
    18. 30. <ul><li>Stormwater Detention </li></ul><ul><li>Required - 50% of the 2yr storm (24hr event) </li></ul><ul><li>848 gallons of </li></ul><ul><li>available storage </li></ul><ul><li>Work with civil </li></ul>
    19. 32. What is Bioretention? Bioretention is an integrated stormwater practice that uses chemical, biological, and physical properties of plants, microbes, and soils to remove, or retain, pollutants from stormwater. Bioretention
    20. 33. Types of Bioretention Bioretention Cells (Rain Gardens): Shallow Depression with a designed soil mix and a variety of plant material. Not a conveyance system. Bioretention
    21. 34. Types of Bioretention Bioretention Swales: Incorporate the same features as bioretention cells but are designed as part of the conveyance system. Bioretention
    22. 35. Design: Bioretention Components <ul><ul><li>1 – Water Depth </li></ul></ul><ul><ul><li>2 – Amended Soil Depth </li></ul></ul><ul><ul><li>3 – Controlled Overflow </li></ul></ul><ul><ul><li>4 – Planting Types </li></ul></ul>Bioretention
    23. 38. Bioretention Bioretention Site Study How does this work in a real scenario? Using current regulations (DOE 2005 Manual) Residential development at a density of 8 units per acre Assumed 68% of site is impervious
    24. 39. 127 lots
    25. 40. Bioretention Rain Garden Information To treat 91% of runoff = 875 LF To treat 100% of runoff = 3,800 LF Total Linear Feet Proposed = 2,421 LF
    26. 45. Permeable Pavements Permeable Pavement Soil Subgrade Pavement Section Components Factor of Safety
    27. 46. Permeable Pavements Clay loam, silty clay loam, sandy clay, silty clay, or clay < 0.05 D Sandy clay loam 0.05 – 0.15 C (Alderwood, till) Silt loam or loam 0.15 – 0.30 B (Everett, outwash) Sand, loamy sand, or sandy loam > 0.30 A Classification Infiltration Rate (in/hr) Hydrologic Soil Group
    28. 47. <ul><ul><ul><li>Pavement Section Components </li></ul></ul></ul>Native Soil Native Soil Permeable Pavements
    29. 48. Factor of Safety: Unpaved Stone Edge or Catch Basin Overflow Permeable Pavements
    30. 49. Sustainable Synergy Danielson Grove Demonstrating Sustainable Synergy
    31. 50. Tree Retention Native Vegetation Bioretention Swales Permeable Pavement Smaller Detention Vault Sustainable Synergy
    32. 51. Sustainable Synergy
    33. 52. Sustainable Synergy
    34. 53. Sustainable Synergy
    35. 54. $84,000 Conventional 51% 49% 0% 14,000 LID 31% 69% 0% 8,100 8,700 $48,500 Total Detention Area = 2.4 (acres) Percent Coverage Per Lot Required Detention Volume (cubic feet) Detention Volume Provided (cubic feet) Cost for Detention ($) Impervious Grass Pasture Cost Savings = $35,500 (42%) Sustainable Synergy Danielson Grove Cost Comparison
    36. 56. QUESTIONS ??