Crook Branch at Mantua Elementary School Stream Restoration Project

A Fairfax County, VA, publication

Department of Public Works and Environmental Services

Working for You!

February 1, 2016

Community MeetingMantua Elementary School Cafeteria

Crook Branch at Mantua Elementary School Stream Restoration ProjectAccotink Creek Watershed Plan Implementation

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Crook Branch Stream Restoration

DPWES Stormwater Planning Division

Meeting Outline

• Fairfax County Stormwater Management and Program Drivers• Accotink Creek Watershed Management Plan• Crook Branch Stream Restoration – Project Scope• Stream Restoration Approaches• Crook Branch – Historical and Existing Conditions• Design Approach• Illustrative/Example Projects• Next Steps• Q&A

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Fairfax County Department of Public Works and Environmental Services

Department of Public Works and Environmental Services

Land Development Services

CapitalFacilities

Solid Waste

Stormwater

Stormwater

Planning

Division

Maintenance and

Stormwater

Management Division

Wastewater

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Fairfax County Stormwater Management Major Program Areas

• Inspection and maintenance of conveyance systems (pipes and appertunces)

• Inspection, maintenance, and rehabilitation of stormwater management facilities

• Dam Safety • FEMA/NFIP/CRS programs• Emergency and Flood Response• Watershed planning and monitoring• Design and implementation of capital improvement projects ,

including stream restoration and water quality projects

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Stormwater Infrastructure

• Conveyance System– 1,600 miles pipe and

constructed channel– 43,000 structures– 6,800 outfalls

• Management Facilities– 1,540 County Maintained – 3,720 Privately Maintained

• State Regulated Dams

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Program Drivers and Project Types

• Chesapeake Bay Total Maximum Daily Load (TMDL)• Other (local streams) TMDLs• MS4 permit• Major project types

Stream and outfall restorations Stormwater Pond retrofits Site retrofits using Green Infrastructure

• List of projects is developed from watershed plans, and referral from a variety of sources including the maintenance division and citizen complaints

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Countywide Watershed Planning

“Healthy Watersheds, Healthy Communities”

• 30 Designated Watersheds

• All 15 watershed plans have been adopted by Fairfax County

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Accotink Creek Watershed Management Plan

http://www.fairfaxcounty.gov/dpwes/watersheds/accotinkcreek.htm

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Accotink Creek Watershed Management Plan

http://www.fairfaxcounty.gov/dpwes/stormwater/projects/project_list.htm

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Accotink Creek Watershed Management Plan Wakefield Run Stream Restoration

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Accotink Creek Watershed Management Plan Brookfield Pond Repair and Retrofit

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Accotink Creek Watershed Management Plan Brookfield Pond Repair and Retrofit

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Accotink Creek Watershed Management Plan Mantua Elementary School Stormwater Retrofit (proposed)

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http://www.fairfaxcounty.gov/dpwes/watersheds/accotinkcreek.htm

Stormwater Citizen Complaints

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Stormwater Citizen Complaints

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Project Limits

Reach 2

Reach 3

Reac

h 4

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Supervisory Districts and Existing Easements

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Supervisory Districts and Existing Easements

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Wetland Studies and Solutions, Inc.Natural & Cultural Resources consulting firm

• Founded in 1991• Consulted on 5,000+ project sites

encompassing 200,000+ acres• 100+ staff

Expertise• Geographic Information Systems• Environmental Science• Archeology• Surveying• Regulatory and Permit Compliance• Environmental Engineering• Landscape Design• Ecosystem Restoration

Acquisition by The Davey Tree Expert Company:• Expertise in tree protection, assessment, and analysis• Largest employee-owned service company in U.S.• Founded in 1880

Locations:• Gainesville, VA• Roanoke, VA• Odenton, MD

Virginia’s First LEED® Gold-Certified Office

Crook Branch Restoration Project Team– Brian Chromey, P.E.– Mike Marsala, P.E., C.F.M.– Aaron Estep, E.I.T.– Matt MacFarland, E.I.T.

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Why Restore Streams?• Eroding bed and banks are threatening private property and creating

sediment pollution

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Why Restore Streams?

• Erosion results in poor water quality; high levels of:– Total Suspended Solids (TSS)– Total Nitrogen (TN)– Total Phosphorous (TP)

• The Environmental Protection Agency Chesapeake Bay TMDL Plan Requires Fairfax County pollutant reductions

Poor water quality Good water quality

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General Approach

• What caused the current erosion problems?

• What can be done to fix the erosion and prevent future issues?

23DPWES Stormwater Planning Division


The Urban Watershed Problem

Source: The Federal Interagency Stream Restoration Working Group

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Overall Goals

• Reconnect to the existing floodplain to:– Slow velocities– Increase evapotranspiration– Remove pollutants (TP, TN, and TSS)– Improve riparian habitat– Restore groundwater levels

Before restoration After restoration



Channel Evolution Model

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Design Methodology for Urban Streams

• Natural Channel Evolution– Evolutionary process considers the channel’s incision, bank stability, and

sedimentation load (aggrading or degrading)

Severe Poor Marginal Suboptimal Optimal

Severe Channel Condition

South Lakes High School

Optimal Channel Condition

Ellanor Lawrence Park

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Urban Stream – Design Realities

1. Significantly more flow than rural streams.2. Significantly more “bankfull” events than in rural watersheds.3. Given site constraints, reinforcement is necessary.

– Rock structures – using native diabase rock– Reinforced bed– Heavy planting densities – native vegetation only

Wolftrap Creek (after 2 years)Rabbit Branch (after 7 months)



Stream Reinforcement

Reinforced Bed

Step Pools Cross Vanes



Stream Reinforcement

Toe Wood

Log J-Hook

Native Vegetation

In-Stream Habitat Log Sill

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Restoration Approaches

Priority 1 Restoration – Raise stream to reconnect with floodplain.

Fewer trees removed

Width of disturbance

Balanced cut and fill volumes result in less waste

Before After

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Priority 2 Restoration – Excavate floodplain at lower elevation.

Width of disturbance

Large cut volumes result in waste material

Many trees removed

Priority 3 Restoration – Confined stream valleys.

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Priority 4 Restoration – Stabilize in-place.



Crook Branch: Historic Conditions

1937 1954




1994 2004




2013

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Crook Branch: Existing Conditions

• Drainage Area: – 827.8 acres

• Imperviousness:– 35%

• Average Channel Slope:– 0.0081

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Plan Development Process

• Project Introduction Meeting (Today)• Data Collection (Partially Completed)• Stream Restoration Design Process*

– Pre-Concept Plan Development (± 3 months)– 35% Design Plan Development (± 5 months)– 65% Design Plan Development (± 3 months)– Final Design Plan Development (± 8 months)– Pre-Construction Review (± 2 months)

• Construction (± 9 months)

*Community meeting to follow County review of pre-concept design. Additional meetings scheduled as we progress toward final design.

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Data Collection

• Obtain topography• Survey, locate, and tag trees (>12” dbh)• Survey channel profile and cross-

sections• Existing streambed sediment sampling• Obtain County GIS utility information• Obtain County floodplain information• Perform wetland delineations and

obtain Jurisdictional Determinations (JD’s) from U.S. Army Corps of Engineers

• Obtain geotechnical soil borings

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Community Involvement In Plan Development

Objective – Partnership between Fairfax County staff and the residents of Mantua and Ridgelea Hills

• Establish community representative(s) to coordinate with County staff as the project progresses

• Community involvement at all levels of the plan development process (Concept, Preliminary, Final Design, and Construction)– Plan review, discussion, and feedback

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Stream Restoration Design ProcessTH

E D

ES

IGN

PR

OC

ES

S

Determine Bankfull Width and Bankfull Area to convey

current flows.

Apply Bankfull Width to reference ranges of

sinuosity and meander radii.

Layout initial design alignment (minimize impact to infrastructure and trees)

Revise restoration design and access

(based on citizen input)Final Design

Citizen MeetingCitizen Meeting

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Stream Restoration Design ProcessTree impact considerations

Ecological / Habitat Value• Size / Diameter• Higher - Climax species: Oaks, Hickory, Holly (mast

producers, long-lived).• Lower – Early successional species: Maples, Poplar

(fast-growing, short-lived).

Existing Condition• Undercut by stream, high proportion of exposed

roots, short life expectancy• Dead, dying, diseased, or damaged trees that pose a human safety hazard• Impacting or pending impact to infrastructure (utilities, roads, trails, etc.)

Proposed Condition• Drip line heavily impacted during restoration, minimal chance of survival, AND• Human safety hazard to trails, houses, bridges, etc.

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Stream Restoration Design ProcessShort term impact for long term benefit• Cleared trees “recycled” as in-stream habitat, grade control, wood-chip

trails, habitat “brush” piles, firewood• Restoration raises the water table, (raises stream bed) which increases

stream access to floodplain and nutrient delivery to roots.• Healthier ecosystem will develop with the density and species variety

of replacement plantings– Mosquito population control via predator habitat– Dense streambank planting will provide shade, reduce water

temperatures, increase oxygenation, increase fish survivability– Dragonfly larva molting access via heavily planted streambank with

shallower slope • Canopy loss will close as remaining trees adjust and react to increased

sunlight, growing to fill in openings

Fewer trees cut = lower restoration cost• Tree-climbing removal method vs. traditional forestry timbering

(minimize impacts to neighboring trees) is expensive.

Lower water table

Higher water table

Incised stream

Restored (raised) stream

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Examples – Snakeden Reach 2

Pre-Construction Construction

Post-Construction 5 Months After Construction

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Examples – Rabbit Branch


Post-Construction 8 Months After Construction

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Post Construction After plant establishmentPost-Construction



Examples – Big Rocky Run Tributary

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Planting – Trees & Shrubs Split into 2 planting zones:

- Riparian- 1 gallon containers (planted at 640 plants/acre)- both trees & shrubs

- Streamside- live stakes/tubelings (planted 1ft o.c.)- shrubs (planted 3 ft o.c.)

Tree Species: Pin Oak, Willow Oak, White Oak, Swamp White Oak, Northern Red Oak, Sweet Gum, Black Gum, River Birch, Sycamore, Red Maple, Box Elder, and Black Willow.

Shrub Species: Silky Dogwood, Southern Arrowwood, American Holly, Service-Berry, Black-Haw, Eastern Redbud, Elderberry, Flowering Dogwood, and Brookside Alder, Hazelnut, Northern Spicebush, Black-Haw, Winterberry.

Eastern Redbud

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Planting – Riparian Seed Mix

• Typical Tree Species• Musclewood• Black Gum• American Sycamore• Red Maple• Eastern Redbud• Flowering Dogwood

• Typical Forbs • Oxeye Sunflower• Joe-Pye Weed• Grass Leaved Goldenrod• PLUS 24 additional species!

• Typical Shrub Species• Witch Hazel• Winterberry• Southern Arrow Wood• Northern Spicebush• Canadian Serviceberry• Black Chokeberry• Black-Haw

• Typical Grass Species• Squarrose Sedge• Riverbank Wild Rye• Foxtail Millet• PLUS 8 additional species!

• Applied at a rate of 125 lbs/acre• Custom mix• Consists of native species found in a healthy, diverse NOVA ecosystem:

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Greater Biodiversity

• Mature forest continues to provide habitat for raptors, woodpeckers, bats and deer

• Recently planted areas provide habitat for small mammals, song birds, fox and deer

• All species benefit from the “edge effect”

• Restored stream allows detrital input to be processed, thus increasing stream health and function

Orchard Oriole

Red-shouldered Hawk

Cottontail Rabbit

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Conclusion

1. The “Crook Branch” tributary of the Accotink Creek Watershed is severely degraded due to urbanization – a situation made worse by inadequate stormwater management.

2. Fully restored streams will provide long-term stability, improved aesthetics, & greater open space usability.

3. Short-term construction disturbance will provide long-term societal and ecological benefits to a heavily used, urban stream valley network.

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Next Steps

• Complete pre-concept design• Continue to work to acquire easements on Reach 1 • Community Meeting to present pre-concept design• Solicit community representation• Authorize design contract with WSSI

– Final Concept Plan– Final Design and Construction Documents

• Hold additional community meetings/stream walks as design progresses

• Complete design and preparation of construction documents• Project bidding and construction

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Questions?

Additional Information

For additional information, please contact

www.fairfaxcounty.gov/dpwes

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Dipmani Kumar, Project ManagerMatt Meyers, Branch Chief

Watershed Projects implementation Branch - North703-324-5500

[email protected]@fairfaxcounty.gov

mailto:[email protected]

mailto:[email protected]

Crook Branch at Mantua Elementary School Stream Restoration Project

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