Parking Forest Stormwater Introduction


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The Parking Forest is an assembly of materials to incorporate trees and stormwater management into parking lots without losing parking spaces. This presentation, which is an overview of stormwater and water quality, was presented by Brian Wegener of the Tualatin Riverkeepers and is posted with his permission.

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  • In the urban part of the Tualatin basin we have a separate storm sewer system (unlike muck of Portland). Runoff from streets and parking lots in most cases goes directly to the nearest creek.
  • Sediments containing legacy pollutants are re-suspended in the rapid rise of an urban creek.
  • Trees intercept rain and send it back into the air. Tree roots can help water infiltrate. Fallen leaves can build an organic layer that acts like a sponge.
  • New regulatory requirements from DEQ are pushing changes in stormwater management, with a new emphasis on hydrology as well as chemistry.
  • Here is another way to build a parking lot (or parking forest) that uses trees to intercept rain before it becomes runoff. This site is at WalMart in Hilton Head South Carolina.
  • Compacted soil makes it hard for roots to penetrate.
  • Sacramento had some challenges in implementing tree canopy goals for parking lots through ordinance. Note that some of the parking lots did achieve their 50% canopy goal.
  • We get the largest portion of our rain when the deciduous trees have dropped their leaves.
  • At Sunset Swim Center we planted deciduous trees, Because of the porous concrete parking lot rainfall interception is less critical.
  • At our smaller demonstration project at PCC Sylvania, where there is no pervious pavement we planted native Douglas fir to maximize rainfall interception.
  • Parking Forest Stormwater Introduction

    1. 1. The Trouble with Urban Stormwater Runoff
    2. 2. Street-to-Stream
    3. 3. The Trouble with Urban Stormwater Runoff Pollution Mouth of Willowbrook Creek in Tigard
    4. 4. Stormwater Pollutants •Suspended solids/sediments •Nutrients (nitrogen & phosphorus) •Metals (copper, zinc, lead, cadmium) •Petroleum products - PAH •Bacteria •Pesticides & herbicides •Temperature
    5. 5. The Trouble with Urban Stormwater Runoff Flooding Hall Blvd in Tigard February 1996
    6. 6. The Trouble with Urban Stormwater Runoff Flashy Streams Fanno Creek at Main Street
    7. 7. Developed Conditions
    8. 8. Urban runoff carries pollutants, causes erosion and stirs up contaminated and oxygen depleting sediments.
    9. 9. The Trouble with Urban Stormwater Runoff Stream Bank Erosion Fanno Creek Park - Tigard
    10. 10. Landscapes Forested vs. Developed Haines Falls on the Tualatin River Main Street Tigard
    11. 11. Developed Conditions Courtesy May, U of W
    12. 12. Natural Conditions Courtesy May, U of W
    13. 13. How Trees Manage Stormwater Source: Center for Watershed Protection
    14. 14. Impervious Cover in Developed Areas
    15. 15. Extrapolated Effective Impervious Area Within the Tualatin Basin Urban Growth Boundary Source: Clean Water Services Healthy Streams Plan
    16. 16. New MS4 Permit Requirements 1) Incorporate sitespecific management practices to mimic natural surface or predevelopment hydrologic functions as much as practicable. The site-specific management practices should optimize on-site retention based on the site conditions;
    17. 17. New MS4 Permit Requirements 2) Reduce site specific postdevelopment stormwater runoff volume, duration and rates of discharges to the municipal separate storm sewer system (MS4) to minimize hydrological and water quality impacts from impervious surfaces;
    18. 18. New MS4 Permit Requirements 3) Prioritize and include implementation of LowImpact Development (LID), Green Infrastructure (GI) or equivalent planning, design and construction approaches;
    19. 19. Can we use trees in parking lots for stormwater runoff reduction?
    20. 20. Washington Square Courtesy May, U of W
    21. 21. Challenges of Putting Trees in Parking Lots Photo Source:
    22. 22. Challenges of Putting Trees in Parking Lots A complete canopy
    23. 23. Challenges of Putting Trees in Parking Lots Sacramento Adopted in 1983, Sacramento’s parking lot ordinance requires 50 percent shading within 15 years of development. Fifteen years after development average parking lot shade was 22%, not 50% as stipulated by ordinance.
    24. 24.
    25. 25. Which trees are best for stormwater management? Deciduous? Coniferous? Broadleaf Evergreen?
    26. 26. Average Monthly Precipitation Downtown Portland 8 7 6 Inches 5 4 3 2 1 0 Jan Feb Mar Apr May Jun Jul Month Aug Sep Oct Nov Dec
    27. 27. Rain Throughfall of European Beech in Italy Source: ALDO PAVARI, Director, Forest Experiment Station, Florence, Italy
    28. 28. Rainfall interception by Santa Monica’s municipal urban forest Xiao & McPherson – UC Davis Tree Species Season Range of % Rain Interception Camphor Summer Winter 28.4%-68.4% 19.3%-58.3% Summer Winter 42.5%-70.5% 5.4%-5.5% (Broadleaf Evergreen) Sweetgum (Deciduous)
    29. 29. Sunset Swim Center Parking Lot Deciduous Trees & Pervious Concrete
    30. 30. PCC Sylvania Parking Forest Douglas Fir No Pervious Pavement
    31. 31. Brian Wegener 503.218.2580 "This Project has been funded wholly or in part by the United States Environmental Protection Agency under a federal grant issued under Section 319(h) of the Clean Water Act. The contents of this document do not necessarily reflect the views and policies of the Environmental Protection Agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use."
    32. 32.
    33. 33. Sunset Swim Center Parking Lot Construction Expenses Item Porous Concrete Cost $200,000 Drain Rock $62,000 Excavation $35,000 Mobilization $30,000 Curbs/Sidewalk $26,000 Landscaping $23,500 Soil/Structural Soil/Installation $18,000 Demolition/Removal $11,000 Striping/Wheel Stops/Signs $10,000 French Drain / Drain Pipe $3,000 12 Trees for Linear Well $1,600 Other Stuff $8,500 TOTAL CONSTRUCTION $427,600