Pike Branch at Wilton Road Stream Stabilization Project
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Pike Branch at Wilton Road Stream Stabilization Project
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Pike Branch at Wilton Road Stream Stabilization Project
- 1. A Fairfax County, VA, publication Department of Public Works and Environmental Services Working for You! Pike Branch at Wilton Road Stream Stabilization Project January 2017
- 2. Stormwater Planning Division Agenda Program Drivers Watershed Project Objectives Social Goals Project History Existing Conditions Stream Retaining Walls Proposed Stream Stabilization Concept Next steps Contact information 2
- 3. Stormwater Planning Division Stormwater Program Regulatory Drivers • National Pollutant Discharge Elimination System (NPDES) • Virginia Stormwater Management Program (VSMP) – Municipal Separate Storm Sewer Permit (MS4) – Discharge from approximately 7,000 storm drain outfalls – Includes watershed planning and project implementation • Total Maximum Daily Loads (TMDLs) – Chesapeake Bay – Local Streams – Establishes pollutant loading budget for a given impaired water body to meet water quality standards 3
- 4. Cameron Run Watershed • 33 sq. mi. in Fairfax County • 95% of watershed is developed with a majority of development occurring before implementation of modern stormwater facilities 4 http://www.fairfaxcounty.gov/dpwes/watersheds/cameronrun.htm Stormwater Planning Division
- 5. Stormwater Planning Division Project Objectives Stabilize up to 1,300 feet of stream along Pike Branch, from Telegraph Road to Wilton Road Better watershed conditions and reduce downstream impacts through… Controlling quantity and mitigate flooding where possible Controlling velocity to reduce erosion and protect infrastructure Create in-stream and riparian habitat for wildlife Improve water quality through the removal of phosphorus, nitrogen, and total suspended solids 5
- 6. Stormwater Planning Division Social Goals 1. Maintain open dialogue and share information. 2. Coordinate with all the stakeholders and the community. 3. Design Team: o Rinker Design Associates, P.C. o ECS Mid-Atlantic, LLC o Utilities Design and Construction Division o Stormwater Management o Stormwater Planning Division o Maintenance and Stormwater Management Division o Urban Forest Management Division 6
- 7. Stormwater Planning Division Stream Stabilization Timeline 7 1. 1981- Pike Branch Channel Improvements project completed 2. 1982- Storms cause sections of the new gabion walls to fail 3. 1983- Engineering study conducted to determine corrective actions 4. 1983-2007 Various minor maintenance repairs to the channel 5. 2008- Pike Branch Phase I emergency repair
- 8. Stormwater Planning Division Stream Stabilization Timeline 8 6. 2012- Stream assessment identified 6015 Telegraph Road and 6016 Pike Branch Drive as the most critical areas along this section of Pike Branch requiring stabilization and identified actions to repair wall 7. February 2013- County constructed a road to the stream to provide access for geotechnical borings and future maintenance construction 8. July 2013- Preliminary geotechnical engineering analysis of Pike Branch completed 9. September 2015- To minimize liability and risk during construction, Fairfax County purchased 6015 Telegraph Road 10.May 2016- County demolished the house 11.September 2016- RDA, the design consultant, completed a more detailed stream assessment to determine the stream stabilization potential of Pike Branch, increasing the project area from Telegraph Road to Wilton Road 12.November 2016- ECS, the geotechnical consultant, completed a retaining wall assessment and a draft geotechnical report of the stream reach. 13.December 2016- RDA finished the stream stabilization concept
- 9. Project Area Limits 9 Wilton Road Telegraph Road Pike Road Pike Branch Drive Approximate limits of disturbance Stormwater Planning Division Old Telegraph Road
- 10. Stormwater Easements 10Stormwater Planning Division Storm Sewer and Storm Drainage Easement Floodplain and Storm Drainage Easement Chesapeake Bay Resource Protection Area (RPA) FEMA 100-Year Floodplain (Zone A) Floodplain Easement
- 11. Stormwater Planning Division Existing Conditions 11 Pike Branch at Wilton Road Story Map
- 12. Stormwater Planning Division Existing Conditions 12
- 13. Stormwater Planning Division Stream Stabilization- Typical Structures Used 13
- 14. Stormwater Planning Division Typical Structures Used – Plunge Pool 14
- 15. Stormwater Planning Division Typical Structures Used – Cross Vanes 15
- 16. Stormwater Planning Division Typical Structures Used – Stone Toe Protection 16
- 17. Stormwater Planning Division Typical Structures Used – Wing Deflector 17 http://library.water-resources.us/docs/MMDL/ECO/MM_Description.cfm?ID=38 http://www.corduroybrook.org/wing-deflectors.php
- 18. Stormwater Planning Division Video of Typical Structures Used 18
- 19. Stormwater Planning Division Stream Stabilization-Retaining Walls 19 Wall # Wall Type Condition Recommendation 1 & 2 Metal Sheeting Fair Refurbish 3 Gabion Basket Good None 4 & 5 Concrete Poor Further Analysis* 6 & 9 Riprap Poor Refurbish 7 Bridge Abutment Poor Remove 8 Riprap & Gabion Basket Poor Replace *Further geotechnical analysis required prior to recommendation
- 20. Stormwater Planning Division Stream Stabilization-Retaining Walls 20 Wall # Wall Type Condition Recommendation 10 Gabion Basket Fair Replace 11 Concrete Block Poor Remove 12 Gabion Basket Fair Remove 13 & 15 Riprap Fair Refurbish 14 Wood H-Pile Fair *Further Analysis 16 Wood H-Pile Fair *Further Analysis *Further geotechnical analysis required prior to recommendation 13
- 21. Stormwater Planning Division Retaining Wall Refurbishment- Sheet Pile 21 • Remove surface rust and paint with a marine application coating • Fasten supplemental steel sections to the front of the wall if needed
- 22. Stormwater Planning Division Retaining Wall Refurbishment- H-Pile with Wood Lagging 22 • Replace deteriorated wood sections • Remove surface rust at steel sections and paint with a marine application coating • Re-secure and reinstall loose or missing bolts
- 23. Stormwater Planning Division Retaining Wall Replacement H-Pile with Wood Lagging 23
- 24. Stormwater Planning Division Retaining Wall Replacement H-Pile with Concrete Lagging 24 http://www.vertical-earth.com/services/view/30
- 25. Stormwater Planning Division Construction Example 25
- 26. Stormwater Planning Division Construction Example 26
- 27. Stormwater Planning Division Construction-Access 27 Existing Maintenance Access Road from Pike Road 6015 Telegraph Road Lot
- 28. Stormwater Planning Division 28 Other Pike Branch projects
- 29. Stormwater Planning Division 29 Next Steps – Schedule • Complete Preliminary Design - April 2017 • Complete 95% Design - June 2017 • Community Meeting - June 2017 • Complete Final Design - August 2017 • Construction - TBD
- 30. Online Resources 30 Stormwater Planning Division Website http://www.fairfaxcounty.gov/dpwes/stormwater/ Fairfax County Watershed Planning http://www.fairfaxcounty.gov/nvswcd/newsletter/planning.htm Cameron Run Watershed Plan http://www.fairfaxcounty.gov/dpwes/watersheds/cameronrun.htm EPA Water Quality Laws & Regulations http://www.epa.gov/water/laws.html Stormwater Planning Division To receive project updates, email Catherine.Torgersen@fairfaxcounty.gov or call 703-324-5500, TTY 711.
- 31. Stormwater Planning Division Contact Information Contact Information Design Catherine Torgersen– Project Manager 703-324-5864 Catherine.Torgersen@fairfaxcounty.gov Fairfax County Stormwater Planning Division 703-324-5500 TTY 711 12000 Government Center Parkway Suite 449 Fairfax, Virginia 22035 www.fairfaxcounty.gov/dpwes/stormwater To request this information in an alternate format call 703-324-5500, TTY 711 31
Editor's Notes
- Introductions: Catie Torgersen, project manager (engineer in the stormwater management field for 9 years)
- -45 minute to an hour presentation -answer questions throughout -Discuss: General information on Fairfax County Stormwater Management and the watershed How the project came about Projects goals and objectives How the site currently functions Proposed improvements Stream stabilization examples Basic design and construction timeline (early in the design, so subject to change)
- The County is subject to state and federal stormwater regulations: -NPDES is the national permitting program under the EPA that regulates point source discharges -VSMP regulations recently updated (more stringent and mandates the use of stormwater BMPs for both new and redevelopment projects) -The MS4 program requires the county to prevent the discharge of non-point source pollutants into waterways -MS4 permit has requirements for infrastructure maintenance, watershed improvements (both quantity and quality), and educational and outreach -In addition, must meet the state and federal requirements to clean up the Chesapeake Bay (nutrients impairment), as well as reduce impairments in other local waters (PCB, E. coli, etc.)
- Pike Branch Facts: Imperviousness= 20.8% (Future 25.5%) Dominant land use= medium density residential
- Useful to understand the history of this stream section. Pike Branch Channel Improvements project undertaken to resolve periodic flooding of adjacent residences and to prevent further erosion. The construction included lining section of the channel with a one-foot thick gabion mat, erecting several gabion walls and building H-pile and wood lagging retaining walls along the stream. N/A Assessment recommends reinforcing gabion walls with piling, laying gabion mats in front of most walls that experienced toe erosion, and minor repair of specific pile wall sections. N/A Emergency repair of a failed retaining wall and broken lateral following a large storm (project located downstream of this stream section near Florence Lane)
- While the property never flooded, the house is located very close to the streambank, adjacent to a very large sycamore tree growing at the stream edge. The streambank is eroded away at the bottom of the grouted rip-rap and the erosion is compromising wall stability. To stabilize the streambank, the sycamore tree must be removed and the wall replaced. Put the maintenance access road in to get geotech borings for analysis N/A County staff worked with the homeowner, who was willing to sell their property. The restoration of the property will be part of the stream stabilization plan. Brings us to the present.
- Point out: -Culvert under Telegraph Road -Board of Supervisors property -6015 Telegraph Road BOS purchased property (house demolished) -Private properties with stormwater easements -culvert under Wilton Road -private bridge
- -GEM description of easements -Storm Sewer and Storm Drainage Easement -Floodplain and Storm Drainage Easement -Floodplain Easement -Chesapeake bay Resource Protection Area (RPA) -FEMA 100-Year Floodplain
- See Story Map (click on hyperlink)
- -A natural channel follows this evolution model. As flows increase, the channel begins to downcut. The stream is no longer able to access the existing floodplain. The downcutting erodes the banks, causing the channel to widen. Eventually, the channel starts to stabilize and create a new floodplain. A stable channel will contain the baseflow and the 1 to 2-year storm (a storm that has that has a 50% likelihood to occur in a given year). Storms greater than the 2-year storm access the new floodplain. -Pike Branch banks are armored with retaining walls. The walls prevent the banks from widening, so the channel continues to incise. The incision undermines the existing armoring. Over the years, Fairfax County has tried numerous techniques to stop the downcutting- concrete weirs to hold the stream grade/elevation in place, grouted riprap, gabion baskets on the stream floor, rebar reinforcement along the gabion walls. -These were all spot maintenance fixes. As Fairfax County Stormwater Management continued to grow and evolve, we decided to take a more comprehensive approach to the stream stabilization.
- Pike Branch- careful to call it a stabilization -no longer a natural channel- straightened and armored with structures on each side -impossible to return to a natural channel with wide benches and floodplains -Stabilize the existing stream, improve safety, and protect property while bettering water quality and habitat
- -slow down/reduce the energy of water coming out of the Telegraph Road culvert -lined with imbricated stone (interlocking, rectangular)
- Grade control structures that mimic natural channels Keeps the water velocity in check by dissipating energy as it falls over the step Funnels water towards the center of the stream, protecting the stream banks
- -Protects the bottom banks of the stream from erosion (water hits the stone rather than the soft soils) -Photo also shows a reinforced bed mix material (specifically sized to withstand flows in Pike Branch)
- -Structures that protrude from the streambank into the main flow to reduce the stream width. They deflect the flow to the opposite bank to re-establish a natural meander pattern.
- General- trim vegetation (roots can grow into and cause additional damage to the walls), periodically clean out drain outlets 1 & 2 Metal Sheeting Wall- remove surface rust and paint with a marine application coating to protect the surface. Supplemental steel sections fastened to the front if needed. 3 Gabion Baskets (above metal sheeting)- good conditions 4 & 5 Concrete Wall- within VDOT right-of-way, requires coordination and further discussions on the assessment 6 & 9 Riprap- supplement with additional riprap (possibly use bridge abutment debris) 8 Riprap & Gabion Basket Wall- replace with H-pile and lagging (wood or concrete)
- 10 Gabion Basket Wall- replace with H-pile and lagging (wood or concrete) 11 & 12- Concrete Block and Gabion Basket Walls- to be removed and streambank sloped to mimic natural bank 13 & 15 Riprap- supplement with additional riprap 14 & 16 Wood H-Pile Walls- refine model for factor of safety calculations prior to making wall recommendations
- This project will not follow our typical stream restoration construction, which usually takes place in a stream valley park.
- These photos are from the Phase I emergency repair.
- Two access points: The existing maintenance access road off of Pike Road The vacant lot at 6015 Telegraph Road Stream access Staging for retaining wall work We will develop the construction staging and sequencing as the design progresses