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 Meeting
Mantua Elementary School Cafeteria
Crook Branch at Mantua Elementary School
Stream Restoration Project
Accotink Creek Watershed Plan Implementation

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
2

Meeting Outline
3
• 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

Project Limits
4
Reach 2
Reach 3

Existing Easements
5
Conservation
Easement
Storm Drainage
and Floodplain
Easement
Floodplain
Easement
Storm Drainage
Easement

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
6
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.

General Design Approach
7
• 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

Crook Branch: Existing Conditions
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Crook Branch: Historic Conditions
12

EXISTING CONDITIONS PLAN
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DESIGN GOALS
17
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

Restoration Approaches
Priority 1 Restoration – Raise stream to reconnect with floodplain.
18
Fewer trees removed
Width of disturbance
Balanced cut and fill volumes
result in less waste
Before After

Priority 2 Restoration – Excavate floodplain at lower elevation.
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Width of disturbance
Large cut volumes result in waste material
Many trees removed
Priority 3 Restoration –
Confined stream valleys.

Priority 4 Restoration – Stabilize in-place.
20

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

Stream Structures and Bed Reinforcement
22
Reinforced Bed
Step Pools Cross Vanes

Stream Reinforcement
23
Toe Wood
Log J-Hook
Native Vegetation
In-Stream Habitat Log Sill

Crook Branch: Channel Sizing
• Drainage Area:
– 827.8 acres
• Imperviousness:
– 35% = URBAN
24

Design – Proposed Cross Sections
25
Section 1 Section 2
Section 3

Design – Proposed Alignment
26

Design – Proposed Bridge Realignment
27

Design – Proposed Access
28
Construction
Entrance 1
Construction
Entrance 2

Design - Tree Impacts
29
Tree 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

Stream Restoration Design Process
30
Short 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

Design – Tree Impacts
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35

Design – Floodplain Impacts
36
Floodplain
Easement

Pre-Construction Construction
Post Construction After plant establishmentPost-Construction
Examples – Big Rocky Run Tributary
37

Examples – Rabbit Branch
38
Pre-Construction Construction
Post-Construction 8 Months After Construction

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
39

Additional Information
For additional information, please contact
www.fairfaxcounty.gov/dpwes
DPWES Stormwater Planning Division 40
Dipmani Kumar, Project Manager
Matt Meyers, Branch Chief
Watershed Projects implementation Branch - North
703-324-5500
Dipmani.Kumar@fairfaxcounty.gov
Matthew.Meyers@fairfaxcounty.gov

Crook Branch at Mantua Elementary School Stream Restoration Project

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Editor's Notes