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Accotink Tributary at Oakford Drive Stream Restoration

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Accotink Tributary at Oakford Drive Stream Restoration

35 Percent Concept Plan Update

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Accotink Tributary at Oakford Drive Stream Restoration

  1. 1. A Fairfax County, VA, publication Department of Public Works and Environmental Services Working for You! Accotink Tributary @ Oakford Drive Stream Restoration 35 Percent Concept Plan Update July 2015
  2. 2. Stormwater Planning Division Agenda • Program Drivers • Watershed Overview • Existing Conditions • Design Goals and Objectives • Proposed Design • Design Features • Schedule 2
  3. 3. Stormwater Planning Division Stormwater Program Drivers • Municipal Separate Storm Sewer Permit (MS-4) – Easement rights and responsibilities to maintain/upgrade • Chesapeake Bay Total Maximum Daily Loads (TMDL) – Regulates amount of pollutants in waterways • Other Local TMDLs • Maintenance of Existing Facilities • Dam Regulations • Public Safety /Emergency Response – Flooding – Snow Removal 3
  4. 4. Stormwater Planning Division Accotink Watershed • 52 square mile watershed • Second largest in Fairfax County • More than 111 miles of streams • 27 percent + impervious • The Oakford project was identified in the Accotink Watershed Management Plan as project AC9202 4
  5. 5. Stormwater Planning Division Watershed Overview 5
  6. 6. Stormwater Planning Division Existing Conditions • Fallen trees • Actively eroding banks • Incised channels • Over-widened channels 6
  7. 7. Stormwater Planning Division Existing Conditions • Undercutting of trees 7
  8. 8. Stormwater Planning Division Existing Conditions • Exposed tree roots • Undercutting of streambank 8
  9. 9. Stormwater Planning Division Design Goals and Objectives • Goals: – To restore approximately 1,300 linear feet of stream – To reduce sediment and nutrient inputs – To stabilize areas of erosion and scour • Objectives: – Improve water quality by reducing sediment inputs from eroding banks – Reconnect stream channel to adjacent floodplain – Construction of in-stream structures, step- pools, and riffle-pools to improve habitat diversity and stabilize the streambed 9
  10. 10. Proposed Design 10
  11. 11. Proposed Design 11
  12. 12. Stormwater Planning Division Typical Cross Sectional Area • Raising the channel bed to connect to floodplain • Nested channel design for low and high flows • Narrowing the channel 12
  13. 13. Stormwater Planning Division In Stream Structures – Cross Vane • “U” shaped structure of boulders • Reduce velocity • Direct water • Reduce near bank stress • Grade control • Pool formation 13
  14. 14. Stormwater Planning Division In Stream Structures - Root Wads • Large woody debris • Current diffuser • Natural cover for fish and aquatic organisms 14
  15. 15. Stormwater Planning Division Construction Access • Access off S Drive and Carleigh Parkway • Timber matting along the length of the access route • Fencing around the site • Main staging area will be off Carleigh Parkway 15
  16. 16. Stormwater Planning Division Construction Times • Our construction times comply with the Code of Fairfax Noise restrictions (Section 108-4) • No construction activities: – Between 9:00 pm and 7:00 am – Before 9:00 am on Sundays – Before 9:00 am on Federal holidays • No unloading equipment -- Before 6:00 am 16
  17. 17. Stormwater Planning Division Example – During Construction 17
  18. 18. Stormwater Planning Division Example – During Construction 18
  19. 19. Stormwater Planning Division Example – Before 19
  20. 20. Stormwater Planning Division Example – After 20
  21. 21. Stormwater Planning Division Example – After One Year 21
  22. 22. Stormwater Planning Division Landscaping • Urban forester coordination • 56 trees more than 12” DBH (diameter at breast height) to be removed • Each tree to be removed will be evaluated • Native seed mix • Native trees and shrubs will be planted 22
  23. 23. Stormwater Planning Division Example Plant Schedule 23
  24. 24. Stormwater Planning Division What’s Next? • Iterative design process – 35 percent, 95 percent and 100 percent design plan submittals with internal reviews – Site walks to validate design and tree removal • Coordination with utility companies • Permits from U.S. Army Corps of Engineers, Department of Environmental Quality, and VDOT • Estimated final plan authorization date: February 2016 24
  25. 25. Stormwater Planning Division Construction Timeline • The bidding process for construction can take approximately 3 months after final authorization of the final plan set • Funds for construction are determined by project readiness and priority for Fiscal Year 2017, and also Board of Supervisors’ approved budget • Construction duration: 6 to 9 months 25
  26. 26. Additional Information For additional information, please contact www.fairfaxcounty.gov/dpwes Stormwater Planning Division 26 Vivian Bui (703)324-5609 Vivian.Bui@fairfaxcounty.gov

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