crook branch at mantua elementary school stream restoration project
TRANSCRIPT
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Project Limits
Reach 2
Reach 3
Trib
utar
y 2
Tributary 1
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Existing Easements
Conservation Easement
Storm Drainage and Floodplain Easement
Floodplain Easement
Storm Drainage Easement
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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 Stream Restoration
DPWES Stormwater Planning Division
Crook Branch: Existing Conditions
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Crook Branch: Existing Conditions
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Crook Branch: Existing Conditions
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Crook Branch: Existing Conditions
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Crook Branch Stream Restoration
Crook Branch: Historic Conditions
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
EXISTING CONDITIONS PLAN
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
EXISTING CONDITIONS PLAN
Crook Branch Stream Restoration
DPWES Stormwater Planning Division
EXISTING CONDITIONS PLAN
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
EXISTING CONDITIONS PLAN
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Restoration Approaches
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Restoration Approaches
Priority 4 Restoration – Stabilize in-place.
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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)
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Crook Branch Stream Restoration
Stream Structures and Bed Reinforcement
Reinforced Bed
Step Pools Cross Vanes
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Crook Branch Stream Restoration
Stream Reinforcement
Toe Wood
Log J-Hook
Native Vegetation
In-Stream Habitat Log Sill
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Crook Branch: Channel Sizing
• Drainage Area: – 827.8 acres
• Imperviousness:– 35% = URBAN
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Proposed Cross Sections
Section 1 Section 2
Section 3
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Proposed Alignment
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Proposed Bridge Realignment
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Proposed Access
Construction Entrance 1
Construction Entrance 2
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
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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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Tree Impacts
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Tree Impacts
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Tree Impacts
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Tree Impacts
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Tree Impacts
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Design – Floodplain Impacts
Floodplain Easement
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Pre-Construction Construction
Post Construction After plant establishmentPost-Construction
Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Examples – Big Rocky Run Tributary
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Examples – Rabbit Branch
Pre-Construction Construction
Post-Construction 8 Months After Construction
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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
Additional Information
For additional information, please contact
www.fairfaxcounty.gov/dpwes
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Crook Branch Stream Restoration
DPWES Stormwater Planning Division
Dipmani Kumar, Project ManagerMatt Meyers, Branch Chief
Watershed Projects implementation Branch - North703-324-5500
[email protected]@fairfaxcounty.gov