Environmental Site Design


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Discussion on the application of ESD to create a sustainable site design and design an effective stormwater management system

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Environmental Site Design

  1. 1. Low Impact Development What is a Sustainable Site?How do you create a Sustainable Site? AIA, Committee on the Environment – Sustainable Sites Program New Haven, Connecticut
  2. 2. Presenter Background Nationally recognized expert in Low Impact Development (Regulations and Applications) Licensed Professional Engineer (CT) Holds IECA certifications as CPESC & CPSWQ Over 27 years in the Land Development Field and 10 years working with Low Impact Development9/8/2010 Copyright Trinkaus Engineering
  3. 3. What are problems with current development philosophy? Developments not respecting the natural land form, forcing the site to “fit” the development program Excessive land clearing, Massive amounts of earthwork, Significant erosion & sedimentation issues, Difficulty stabilizing the site,9/8/2010 Copyright Trinkaus Engineering
  4. 4. What are problems with current development philosophy? Stormwater Issues Large, interconnected impervious areas, Handling of stormwater is an “afterthought” in the design process, Excessive use of structural systems, Analyze for changes in peak rate only, Emphasis on large, infrequent storm events, No consideration of water quality impacts9/8/2010 Copyright Trinkaus Engineering
  5. 5. What constitutes a Sustainable Site? Preservation of Natural Resources Development which respects the Natural Land Form Minimize site clearing & grading Rainfall is a resource to be embraced and reused Stormwater management is an integral part of the site design9/8/2010 Copyright Trinkaus Engineering
  6. 6. What constitutes a Sustainable Site? Focus of stormwater management: Groundwater Recharge (Volumetric Reduction) Water Quality (Remove Pollutants from the stormwater) Source Control (Treat runoff where it is first generated) Implement “Treatment Train” approach to stormwater9/8/2010 Copyright Trinkaus Engineering
  7. 7. How do we create a Sustainable Site? Implement Low Impact Development Design Strategies9/8/2010 Copyright Trinkaus Engineering
  8. 8. What is Low Impact Development?LID is an ecologically friendly approach to site development and storm water management that aims to mitigate development impacts to land, water, and air. The approach emphasizes the integration of site design and planning techniques that conserve natural systems and hydrologic functions on a site.9/8/2010 Copyright Trinkaus Engineering
  9. 9. How does Low Impact Development work?To manage rainfall at the source using uniformly distributed decentralized micro-scale controls. LID’s goal is to mimic a site’s predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source HYDROLOGIC TRANSPARENCY9/8/2010 Copyright Trinkaus Engineering
  10. 10. What is Hydrologic Transparency?The use of LID design strategies and storm water treatment systems for a development scenario which yields hydrologic conditions matching or in extremely close proximity to the hydrologic conditions of the natural site prior to development.9/8/2010 Copyright Trinkaus Engineering
  11. 11. Low Impact Development Five Basic Tools Encourage Conservation Measures Reduce Impervious Areas Slow Runoff by using landscape features Use Multiple measures to reduce and cleanse runoff Pollution Prevention9/8/2010 Copyright Trinkaus Engineering
  12. 12. Regulatory Requirements (sample site) Open Space Subdivision Total Site Area = 104.50 acres 15% site area (roads) = -15.67 acres Utility Easement = -5.12 acres 50% of Wetlands = -10.83 acres 50% of 25% slopes = -6.12 acres NET AREA = 66.76 acres Allowable Density = 66.76/1.9513 = 34.2 lots (85,000 sq.ft. = 1.9513 acres)9/8/2010 Copyright Trinkaus Engineering
  13. 13. A Typical Layout Is this realistic?9/8/2010 Copyright Trinkaus Engineering
  14. 14. What is Environmental Site Design? Environmental Site Design (ESD) is considered part of Low Impact Development Design Tools It was development in Maryland to complement the 2000 Stormwater Management Design Manual for the State of Maryland The ESD approach is to design a site which protects the natural resources on a site and maintains the hydrologic characteristics of the site.9/8/2010 Copyright Trinkaus Engineering
  15. 15. Environmental Site Design The largest benefit of LID can be achieved by implementing Environmental Site Design Concepts Preservation of critical natural resources Places development on land most suitable for development Helps match pre-development hydrology9/8/2010 Copyright Trinkaus Engineering
  16. 16. ESD Site Assessment – Primary Conservation Areas Inland Wetlands & Watercourses Vernal Pools Steep Slopes (>25%) 100-year Floodway and Floodplain Upland Soil Types with Moderate to High infiltration rates (Class A & B Soils)9/8/2010 Copyright Trinkaus Engineering
  17. 17. ESD Site Assessment – Secondary Conservation Areas Upland areas adjacent to wetlands, watercourses, & vernal pools (variable distance – suggested min. 25- 50’) Habitat for sensitive species Scenic views and areas Vegetation systems, unusual tree species Existing drainage patterns9/8/2010 Copyright Trinkaus Engineering
  18. 18. Why should we protect these resources? Undisturbed woodlands provide great filtering of overland flow, reduces runoff by rainfall interception by canopy, provides evapotranspiration, carbon storage Wetlands provide trapping of TSS, and attenuation of nutrients – provide denitrification of Nitrogen, recharge groundwater9/8/2010 Copyright Trinkaus Engineering
  19. 19. Why should we protect these resources? Restricting construction on Steep Slopes reduces soil disturbance, reduces or eliminates erosion & sedimentation issues, does not create stabilization issues Well Drained soils have the ability to infiltrate large amounts of runoff – dense development on them should be minimized9/8/2010 Copyright Trinkaus Engineering
  20. 20. Why should we protect these resources? Significant trees and unusual portions of the site topography all provide natural (habitat) and aesthetic benefits to the end users and should be preserved9/8/2010 Copyright Trinkaus Engineering
  21. 21. ESD Site Assessment Process Obtain Accurate Topographic information Obtain delineation of inland wetlands & watercourses by soil scientist Determine presence of vernal pools or other sensitive environmental areas (swamps, marshes, ponds, flood prone areas, etc.)9/8/2010 Copyright Trinkaus Engineering
  22. 22. ESD Site Assessment Process Determination of upland soil types in the field by soil scientist Determine the general infiltration rates of the soils (NRCS data) Define steep slopes (>25%)9/8/2010 Copyright Trinkaus Engineering
  23. 23. ESD Site Assessment Process Determine generalized types of vegetation (meadows, brush, deciduous woods, evergreen woods, etc) Determine existing drainage patterns on the site9/8/2010 Copyright Trinkaus Engineering
  24. 24. Site Analysis Process Remove wetland/watercourse/vernal pools from potential development area Remove the upland area immediately adjacent to wetland/watercourse systems to preserve the biological integrity (width of area will vary, suggested 25 - 50’, could be larger depending upon quality of wetland)9/8/2010 Copyright Trinkaus Engineering
  25. 25. Wetlands, Soils & Watershed Boundaries9/8/2010 Copyright Trinkaus Engineering
  26. 26. Site Analysis Process Remove 25% slopes from development area Highlight those soil areas with moderate to fast infiltration rates (Soil Class A and B) Highlight unusual vegetative features on the site(i.e. 200 yr old Oak tree in the middle of a field, Ridge line, unusual scenic vista)9/8/2010 Copyright Trinkaus Engineering
  27. 27. Slopes and Vegetation9/8/2010 Copyright Trinkaus Engineering
  28. 28. Results of Site Analysis Through the protection of the environmentally sensitive features noted previously, you will have determined the optimum area for development NEXT STEP Evaluate hydrologic patterns and think about how storm water will be handled on the site as part of the site design9/8/2010 Copyright Trinkaus Engineering
  29. 29. Developable Area9/8/2010 Copyright Trinkaus Engineering
  30. 30. LID Design Strategies Applied Preserve Large Portions of Site Reduce Connected Impervious Areas Increase Time of Concentration by using landscape features Use Multiple measures to reduce and cleanse runoff at the source Remove Pollutants from Storm Water9/8/2010 Copyright Trinkaus Engineering
  31. 31. LID Techniques Apply Open Space or Cluster Development to preserve large contiguous portions of the site Layout the geometry of the road to follow the existing contours How you will convey stormwater to the discharge point? How will you meet Groundwater Recharge & Water Quality requirements? What treatment systems are available to meet these requirements that will work on the site?9/8/2010 Copyright Trinkaus Engineering
  32. 32. Road & Lot LayoutRoad layout follows ex.contours, lots are locatedwithin “developable area” Large extents of propertyDensity is protected as Open Spaceconcentrated on Class 24 Lots – 64+ acres ofC soils, minimal preserved Open Spacedensity on Class Bsoils9/8/2010 Copyright Trinkaus Engineering
  33. 33. Stormwater Discharge Points Intermittent streamStormwater dischargepoints to maintain pre- 24 Lots – 64+ acres ofdevelopment drainage preserved Open Spacepatterns Intermittent stream9/8/2010 Copyright Trinkaus Engineering
  34. 34. Stormwater ConveyanceConventional curb & gutter Vegetated swales along both sides of road 24 Lots – 64+ acres of preserved Open Space9/8/2010 Copyright Trinkaus Engineering
  35. 35. LID Techniques Minimize direct impacts to wetlands & watercourses Can you disconnect proposed impervious areas on the site? Layout building lots to have construction (House, driveway, well, sewage disposal system) on land most suitable for development Implement “Site Fingerprinting” to minimize land clearing & soil disturbance Minimize soil compaction by limiting the area of grading. Consider specifying measures to address soil compaction, if unavoidable9/8/2010 Copyright Trinkaus Engineering
  36. 36. Site Layout – LID Source ControlsImpervious area disconnection –driveway runoff as overland flowacross 75’ of vegetated surface Site Fingerprinting – defined clearing area as percentage of lot area 24 Lots – 64+ acres of Meadow filter strip with Bioretention systems for preserved Open Space Micro-berm at edge of roof drains development envelope 9/8/2010 Copyright Trinkaus Engineering
  37. 37. Hydrologic IssuesGroundwater Recharge Bioretention for roof drains Infiltration Trenches Impervious Area DisconnectionWater Quality Constructed Wetland Subsurface Gravel Wetlands Vegetated swales & Level Spreader9/8/2010 Copyright Trinkaus Engineering
  38. 38. LID Treatment SystemsConstructed Wetland Systemw/forebay & vegetated outletswale to wetland Linear vegetated level spreader Subsurface flow gravel wetland w/forebay & vegetated outlet swale to 24 Lots – 64+ acres of wetland preserved Open SpaceInfiltration trenches for drivewayrunoff 9/8/2010 Copyright Trinkaus Engineering
  39. 39. LID Treatment Systems9/8/2010 Copyright Trinkaus Engineering
  40. 40. What Does the Project Look Like? Ridge top is part of60% of the site preserved Open Space in centeras Open Space of loop road9/8/2010 Copyright Trinkaus Engineering
  41. 41. What Does the Project Look Like? When you consider the woods which remain on the lots, over 76% of the site remains undisturbed9/8/2010 Copyright Trinkaus Engineering
  42. 42. Actual DesignMeadow filterstrip Rain Garden for roof drainsDefined treeclearing limits(sitefingerprinting) 9/8/2010 Copyright Trinkaus Engineering
  43. 43. Actual DesignStorm Water Controls for lots: Utilize “site fingerprinting” to minimize the extent of clearing on each lot Utilize rain gardens for roof drains on every lot (sized for Water Quality Volume) Utilize a “meadow” filter strip with a 3” ‘micro-berm’ below the lawn area on each lot to filter overland runoff & encourage infiltration9/8/2010 Copyright Trinkaus Engineering
  44. 44. Actual DesignLimitdevelopment tomild & moderateslope areas Preserve steep slopes 9/8/2010 Copyright Trinkaus Engineering
  45. 45. Hydrologic Issues Conclusion Pre-development infiltration rates are met Water quality goal of 80% TSS removal will be met, other pollutants also reduced Pre-development Tc is closely approximated by the use of vegetated swales and treatment systems that will increase Tc (gravel wetlands, level spreader) Pre-development peak rates are matched for post-development conditions9/8/2010 Copyright Trinkaus Engineering
  46. 46. Other Sustainable Benefits of ESD A resource for reductions of atmospheric carbon dioxide A resource for the long term storage of carbon9/8/2010 Copyright Trinkaus Engineering
  47. 47. The Carbon Cycle9/8/2010 Copyright Trinkaus Engineering
  48. 48. Mixed Northern Hardwood Forests9/8/2010 Copyright Trinkaus Engineering
  49. 49. Where is Carbon stored? Forest – all above & below ground portions of live trees Soils – mineral horizons to a depth of 1 meter Forest Floor – all dead organic matter above mineral/sod horizons, including litter humus & coarse woody debris Understory Vegetation – all live vegetation which are not tree (shrubs, herbaceous species)9/8/2010 Copyright Trinkaus Engineering
  50. 50. Well Established Forest w/understory layers9/8/2010 Copyright Trinkaus Engineering
  51. 51. Carbon Dioxide Storage in Trees Green WT above gnd: Wg=(0.25)(D)(D)H Green WT (total w/roots): Wgt=120%*Wg Dry WT: Wd=72.5%*Wgt Weight of Carbon Stored: Wc=Wd * 50% Weight of Carbon Dioxide stored: Wco=Wd*3.6663 Weight of Carbon Dioxide stored per year: W = Wco/209/8/2010 Copyright Trinkaus Engineering
  52. 52. Example: 20yr old tree, 10” DBH, 30’ height Green WT above gnd: Wg=(0.25)(10)(10)30 = 750 lb Green WT (total w/roots): Wgt=1.20 * 750 = 900 lb Dry WT: Wd=0.725 * 900 = 625.5 lb Weight of Carbon: Wc=625.5 *0.5 = 312.75 lb Weight of Carbon Dioxide: Wco=312.75*3.6663 = 1146.6 lb Weight of Carbon Dioxide/year: W = 1146.6/20 = 57.3 lbs/yr9/8/2010 Copyright Trinkaus Engineering
  53. 53. Actual Site Conditions In NE U.S. – Mixed Northern Hardwoods have an average density of 100 trees/acre 100 * 57.33 lb = 5,733 lbs of carbon dioxide sequestered per acre/yr. 64 acres * 5,733 = 366,912 lbs per site area Assume trees grow to 100 years, then a total of 29,352,960 lbs (14,676 tons) of carbon dioxide will be sequestered from this site in the trees within the Open Space9/8/2010 Copyright Trinkaus Engineering
  54. 54. Carbon Storage in the Soils Both Organic and Inorganic carbon will be stored in the soils Undisturbed soils will store more carbon than disturbed soils NE soils will store 144,703 lbs/acre of carbon over the typical lifecycle of a mixed hardwood forest9/8/2010 Copyright Trinkaus Engineering
  55. 55. Actual Site Conditions 64 acres * 144,703 lb/ac = 9,260,992 lbs (4,630.5 tons) Between storage in trees and soils, the open space on this parcel will store 19,306 tons of carbon over the lifecycle of the forest (100 years)9/8/2010 Copyright Trinkaus Engineering
  56. 56. Vegetated LID Treatment Systems Bioretention systems, constructed wetlands, and vegetated swales will provide additional sources to sequester carbon Plants have large stem or leaf areas, having high rates of photosynthesis (retaining carbon in the plant material) Plants are fast growing, thus having high need for carbon (high capacity for sequestering)9/8/2010 Copyright Trinkaus Engineering
  57. 57. LID Vegetated Systems9/8/2010 Copyright Trinkaus Engineering
  58. 58. Conclusion Preservation of large extents of undisturbed woodlands and native soils will continue to provide valuable resources for sequestering of carbon in the environment The utilization of vegetated LID treatment systems provide additional sources for the storage of carbon9/8/2010 Copyright Trinkaus Engineering
  59. 59. Contact InformationSteve Trinkaus, PE, CPESC, CPSWQTrinkaus Engineering, LLC114 Hunters Ridge RoadSouthbury, CT 06488203-264-4558, Fax: 203-264-4559Email: strinkaus@earthlink.netWebsite: http://www.trinkausengineering.com9/8/2010 Copyright Trinkaus Engineering
  60. 60. QUESTIONS??9/8/2010 Copyright Trinkaus Engineering