A Fairfax County, VA, publication
Department of Public Works and Environmental Services
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Accotink Tributary @ Oakford Drive Stream Restoration
35 Percent Concept Plan Update
July 2015
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Agenda
• Program Drivers• Watershed Overview• Existing Conditions • Design Goals and
Objectives• Proposed Design• Design Features• Schedule
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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
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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
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Existing Conditions
• Fallen trees
• Actively eroding banks
• Incised channels
• Over-widened channels
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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
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Typical Cross Sectional Area
• Raising the channel bed to connect to floodplain
• Nested channel design for low and high flows
• Narrowing the channel
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In Stream Structures – Cross Vane
• “U” shaped structure of boulders
• Reduce velocity• Direct water • Reduce near bank
stress• Grade control• Pool formation
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In Stream Structures - Root Wads
• Large woody debris
• Current diffuser
• Natural cover for fish and aquatic organisms
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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
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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
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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
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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
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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
Additional Information
For additional information, please contact
www.fairfaxcounty.gov/dpwes
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Vivian Bui
(703)324-5609