pike branch at wilton road stream stabilization project

PowerPoint Presentation

Pike Branchat Wilton RoadStream Stabilization Project

January 2017

A Fairfax County, VA, publicationDepartment of Public Works and Environmental ServicesWorking for You!

Introductions: Catie Torgersen, project manager (engineer in the stormwater management field for 9 years)

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Stormwater Planning Division

AgendaProgram DriversWatershed Project ObjectivesSocial GoalsProject HistoryExisting ConditionsStreamRetaining WallsProposed Stream Stabilization ConceptNext stepsContact information

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-45 minute to an hour presentation-answer questions throughout-Discuss:General information on Fairfax County Stormwater Management and the watershedHow the project came aboutProjects goals and objectivesHow the site currently functionsProposed improvementsStream stabilization examplesBasic design and construction timeline (early in the design, so subject to change)2

Stormwater Planning DivisionStormwater Program Regulatory DriversNational Pollutant Discharge Elimination System (NPDES)

Virginia Stormwater Management Program (VSMP)Municipal Separate Storm Sewer Permit (MS4)Discharge from approximately 7,000 storm drain outfallsIncludes watershed planning and project implementation

Total Maximum Daily Loads (TMDLs)Chesapeake BayLocal StreamsEstablishes pollutant loading budget for a given impaired water body to meet water quality standards3

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.)3

Cameron Run Watershed33 sq. mi. in Fairfax County

95% of watershed is developed with a majority of development occurring before implementation of modern stormwater facilities

4http://www.fairfaxcounty.gov/dpwes/watersheds/cameronrun.htmStormwater Planning Division

Pike Branch Facts:Imperviousness= 20.8% (Future 25.5%)Dominant land use= medium density residential

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Project ObjectivesStabilize up to 1,300 feet of stream along Pike Branch, from Telegraph Road to Wilton RoadBetter watershed conditions and reduce downstream impacts throughControlling quantity and mitigate flooding where possibleControlling velocity to reduce erosion and protect infrastructureCreate in-stream and riparian habitat for wildlifeImprove water quality through the removal of phosphorus, nitrogen, and total suspended solids

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Social GoalsMaintain open dialogue and share information.Coordinate with all the stakeholders and the community.Design Team:Rinker Design Associates, P.C.ECS Mid-Atlantic, LLCUtilities Design and Construction DivisionStormwater Management Stormwater Planning DivisionMaintenance and Stormwater Management DivisionUrban Forest Management Division

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Stream Stabilization Timeline71981- Pike Branch Channel Improvements project completed1982- Storms cause sections of the new gabion walls to fail1983- Engineering study conducted to determine corrective actions1983-2007 Various minor maintenance repairs to the channel2008- Pike Branch Phase I emergency repair

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/AAssessment 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/AEmergency repair of a failed retaining wall and broken lateral following a large storm (project located downstream of this stream section near Florence Lane)7


Stream Stabilization Timeline82012- 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 wallFebruary 2013- County constructed a road to the stream to provide access for geotechnical borings and future maintenance constructionJuly 2013- Preliminary geotechnical engineering analysis of Pike Branch completedSeptember 2015- To minimize liability and risk during construction, Fairfax County purchased 6015 Telegraph RoadMay 2016- County demolished the houseSeptember 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 RoadNovember 2016- ECS, the geotechnical consultant, completed a retaining wall assessment and a draft geotechnical report of the stream reach.December 2016- RDA finished the stream stabilization concept

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 analysisN/ACounty 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.8

Project Area Limits9Wilton RoadTelegraph RoadPike RoadPike Branch DriveApproximate limits of disturbanceStormwater Planning DivisionOld Telegraph Road

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 bridge9

Stormwater Easements10Stormwater 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)

FloodplainEasement

-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 Floodplain10


Existing Conditions11

Pike Branch at Wilton Road Story Map

See Story Map (click on hyperlink)

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Stormwater Planning DivisionExisting Conditions12

-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.12

Stormwater Planning DivisionStream Stabilization- Typical Structures Used13

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 habitat13


Typical Structures Used Plunge Pool14

-slow down/reduce the energy of water coming out of the Telegraph Road culvert-lined with imbricated stone (interlocking, rectangular)

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Typical Structures Used Cross Vanes15

Grade control structures that mimic natural channelsKeeps the water velocity in check by dissipating energy as it falls over the stepFunnels water towards the center of the stream, protecting the stream banks

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Typical Structures Used Stone Toe Protection 16

-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)

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Typical Structures Used Wing Deflector17

http://library.water-resources.us/docs/MMDL/ECO/MM_Description.cfm?ID=38

http://www.corduroybrook.org/wing-deflectors.php

-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.17


Video of Typical Structures Used18

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Stream Stabilization-Retaining Walls19

Wall #Wall TypeConditionRecommendation1 & 2Metal SheetingFairRefurbish3Gabion BasketGoodNone4 & 5ConcretePoorFurther Analysis*6 & 9RiprapPoorRefurbish7Bridge AbutmentPoorRemove8Riprap & Gabion Basket PoorReplace

*Further geotechnical analysis required prior to recommendation

General- trim vegetation (roots can grow into and cause additional damage to the walls), periodically clean out drain outlets1 & 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 conditions4 & 5 Concrete Wall- within VDOT right-of-way, requires coordination and further discussions on the assessment6 & 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)

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Stream Stabilization-Retaining Walls20

Wall #Wall TypeConditionRecommendation10Gabion BasketFairReplace11Concrete BlockPoorRemove12Gabion BasketFairRemove13 & 15RiprapFairRefurbish14Wood H-PileFair*Further Analysis16Wood H-PileFair*Further Analysis

*Further geotechnical analysis required prior to recommendation

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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 bank13 & 15 Riprap- supplement with additional riprap14 & 16 Wood H-Pile Walls- refine model for factor of safety calculations prior to making wall recommendations 20


Retaining Wall Refurbishment- Sheet Pile 21Remove surface rust and paint with a marine application coatingFasten supplemental steel sections to the front of the wall if needed

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Retaining Wall Refurbishment- H-Pile with Wood Lagging22Replace deteriorated wood sectionsRemove surface rust at steel sections and paint with a marine application coatingRe-secure and reinstall loose or missing bolts

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Retaining Wall Replacement H-Pile with Wood Lagging23

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Retaining Wall Replacement H-Pile with Concrete Lagging24

http://www.vertical-earth.com/services/view/30

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Construction Example25

This project will not follow our typical stream restoration construction, which usually takes place in a stream valley park. 25


Construction Example26

These photos are from the Phase I emergency repair. 26


Construction-Access27

Existing Maintenance Access Road from Pike Road6015 Telegraph Road Lot

Two access points:The existing maintenance access road off of Pike RoadThe vacant lot at 6015 Telegraph RoadStream accessStaging for retaining wall workWe will develop the construction staging and sequencing as the design progresses27

Stormwater Planning Division28

Other Pike Branch projects

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Stormwater Planning Division29

Next Steps ScheduleComplete Preliminary Design - April 2017Complete 95% Design - June 2017Community Meeting - June 2017Complete Final Design - August 2017Construction - TBD

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Online Resources30Stormwater Planning Division Websitehttp://www.fairfaxcounty.gov/dpwes/stormwater/

Fairfax County Watershed Planninghttp://www.fairfaxcounty.gov/nvswcd/newsletter/planning.htm

Cameron Run Watershed Planhttp://www.fairfaxcounty.gov/dpwes/watersheds/cameronrun.htm

EPA Water Quality Laws & Regulationshttp://www.epa.gov/water/laws.html

Stormwater Planning DivisionTo receive project updates, email [email protected] or call 703-324-5500, TTY 711.

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Stormwater Planning DivisionContact InformationContact Information

DesignCatherine Torgersen Project [email protected] County Stormwater Planning Division703-324-5500 TTY 71112000 Government Center ParkwaySuite 449Fairfax, Virginia 22035www.fairfaxcounty.gov/dpwes/stormwater To request this information in an alternate format call 703-324-5500, TTY 71131

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pike branch at wilton road stream stabilization project

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