accotink tributary at oakford drive stream restoration

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

2Stormwater Planning Division

Agenda

• Program Drivers• Watershed Overview• Existing Conditions • Design Goals and

Objectives• Proposed Design• Design Features• Schedule


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


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


Watershed Overview


Existing Conditions

• Fallen trees

• Actively eroding banks

• Incised channels

• Over-widened channels


Existing Conditions

• Undercutting of trees


Existing Conditions

• Exposed tree roots

• Undercutting of streambank


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

10

Proposed Design

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Proposed Design


Typical Cross Sectional Area

• Raising the channel bed to connect to floodplain

• Nested channel design for low and high flows

• Narrowing the channel


In Stream Structures – Cross Vane

• “U” shaped structure of boulders

• Reduce velocity• Direct water • Reduce near bank

stress• Grade control• Pool formation


In Stream Structures - Root Wads

• Large woody debris

• Current diffuser

• Natural cover for fish and aquatic organisms


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


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


Example – During Construction


Example – Before


Example – After


Example – After One Year


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


Example Plant Schedule


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


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


Vivian Bui

(703)324-5609

[email protected]

accotink tributary at oakford drive stream restoration

News & Politics

stream channel

proposed design

construction activities

objectives goals

linear feet of stream

channel bed

fairfax county

square mile watershed