Crook Branch at Mantua Elementary School Stream Restoration Project

A Fairfax County, VA, publication

Department of Public Works and Environmental Services

Working for You!

January 9, 2017

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

Status and General Schedule

• Data Collection (Completed)• Stream Restoration Design Process (In Progress)

– Pre-Concept Plan Development (Completed)– Concept (35%) Design Plan Development (Currently Developing)– Field Walk - Spring 2017– Preliminary (65%) Design Plan Development– Final Design Plan Development – Fall 2017– Construction Documents

• Construction (± 12 months)– Bidding and Contract Award– Pardon Our Dust Community Meeting– Construction date dependent on future funding

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Meeting Outline

• Site Location and Project Limits• Discuss General Design Approach• Review Historical Data• Existing Conditions• Data Collection Process• Design Goals• Design Philosophy and Channel Sizing• Construction Access and Options• Projected Tree and Trail Impacts• Schedule• Q&A

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Project Limits

Reach 2

Reach 3

Trib

utar

y 2

Tributary 1

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Existing Easements

Conservation Easement

Storm Drainage and Floodplain Easement

Floodplain Easement

Storm Drainage Easement

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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• Richmond, 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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General Design Approach• Review historical data to help understand evolution• Data Collection

• Document existing conditions to identify design constraints and specific goals and objectives

• Stream measurements to utilize in design process• Stream Sizing and Design

• Channel Cross-Section• Alignment• Profile• Stabilization and Flow Direction Structures• Protection of utilities and bridges• Vegetation

• Construction Access• Floodplain Impacts

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Crook Branch: Existing Conditions

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12DPWES Stormwater Planning Division


Crook Branch: Historic Conditions

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EXISTING CONDITIONS PLAN

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DESIGN GOALS

What are the design goals?• General Goals

• Stabilize stream• Reduce excess sediment from being transported downstream• Reduce excess nutrients from entering the waterway• Improve aesthetics• Reduce hazards (steep, eroding banks)• Reconnect stream to floodplain• Improve Riparian Buffers

• Additional Project Specific Goals• Protect valuable infrastructure – utilities and bridge

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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.

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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

Snakeden Branch (after 1 year)Rabbit Branch (after 7 months)



Stream Structures and Bed 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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Crook Branch: Channel Sizing

• Drainage Area: – 827.8 acres

• Imperviousness:– 35% = URBAN

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Design – Proposed Cross Sections

Section 1 Section 2

Section 3

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Design – Proposed Alignment

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Design – Proposed Bridge Realignment

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Design – Proposed Access

Construction Entrance 1

Construction Entrance 2

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Design - Tree ImpactsTree 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• Long-living, healthy, native species that help to stabilize the banks and floodplain• Increased bio-diversity

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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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Design – Tree Impacts

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Design – Floodplain Impacts

Floodplain Easement

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Pre-Construction Construction

Post Construction After plant establishmentPost-Construction



Examples – Big Rocky Run Tributary

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Examples – Rabbit Branch

Pre-Construction Construction

Post-Construction 8 Months After Construction

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Status and General Schedule

• Data Collection (Completed)• Stream Restoration Design Process (In Progress)

– Pre-Concept Plan Development (Completed)– Concept (35%) Design Plan Development (Currently Developing)– Field Walk - Spring 2017– Preliminary (65%) Design Plan Development– Final Design Plan Development – Fall 2017– Construction Documents

• Construction (± 12 months)– Bidding and Contract Award– Pardon Our Dust Community Meeting– Construction date dependent on future funding

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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