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 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
Meeting Outline
2
• 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

Fairfax County Department of Public Works and Environmental Services
3
Department of Public Works and
Environmental Services
Land
Development
Services
Capital
Facilities
Solid Waste Stormwater
Stormwater Planning
Division
Maintenance and
Stormwater
Management Division
Wastewater

Fairfax County Stormwater Management Major Program Areas
4
• 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

Stormwater Infrastructure
5
• 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

Program Drivers and Project Types
6
• 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

Countywide Watershed Planning
7
“Healthy Watersheds, Healthy
Communities”
• 30 Designated
Watersheds
• All 15 watershed plans
have been adopted by
Fairfax County

Accotink Creek Watershed Management Plan
8
http://www.fairfaxcounty.gov/dpwes/watersheds/accotinkcreek.htm

9
http://www.fairfaxcounty.gov/dpwes/stormwater/projects/project_list.htm

Wakefield Run Stream Restoration
10

Brookfield Pond Repair and Retrofit
11

Brookfield Pond Repair and Retrofit
12

Mantua Elementary School Stormwater Retrofit (proposed)
13

DPWES Stormwater Planning Division 14
http://www.fairfaxcounty.gov/dpwes/watersheds/accotinkcreek.htm
Stormwater Citizen Complaints

Stormwater Citizen Complaints

Project Limits
16
Reach 2

Supervisory Districts and Existing Easements
17

Supervisory Districts and Existing Easements
18

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
19
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.

Why Restore Streams?
• Eroding bed and banks are threatening private property and
creating sediment pollution
20

Why Restore Streams?
• Erosion results in poor water
quality; high levels of:
– Total Suspended Solids (TSS)
– Total Nitrogen (TN)
– Total Phosphorous (TP)
21
• The Environmental Protection
Agency Chesapeake Bay
TMDL Plan Requires Fairfax
County pollutant reductions
Poor water quality Good water quality

General Approach
• What caused the current
erosion problems?
• What can be done to fix the
erosion and prevent future
issues?
22

The Urban Watershed Problem
23
Source: The Federal Interagency Stream Restoration Working Group

Overall Goals
• Reconnect to the existing floodplain to:
– Slow velocities
– Increase evapotranspiration
– Remove pollutants (TP, TN, and TSS)
– Improve riparian habitat
– Restore groundwater levels
24
Before restoration After restoration

Channel Evolution Model
25

Design Methodology for Urban Streams
• Natural Channel Evolution
– Evolutionary process considers the channel’s incision, bank stability, and
sedimentation load (aggrading or degrading)
26
Severe Poor Marginal Suboptimal Optimal
Severe Channel Condition
South Lakes High School
Optimal Channel Condition
Ellanor Lawrence Park

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
27
Wolftrap Creek (after 2 years)Rabbit Branch (after 7 months)

Stream Reinforcement
28
Reinforced Bed
Step Pools Cross Vanes

Stream Reinforcement
29
Toe Wood
Log J-Hook
Native Vegetation
In-Stream Habitat Log Sill

Restoration Approaches
Priority 1 Restoration – Raise stream to reconnect with floodplain.
30
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.
31
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.
32

Crook Branch: Historic Conditions
33
1937 1954

34
1994 2004

35
2013

Crook Branch: Existing Conditions
• Drainage Area:
– 827.8 acres
• Imperviousness:
– 35%
• Average
Channel Slope:
– 0.0081
36

37

38

39

40

41

42

43

44

45

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.
46

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
47

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
48

Stream Restoration Design Process
49
THEDESIGNPROCESS
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 Meeting
Citizen Meeting

50
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
• Drip line heavily impacted during restoration, minimal chance of survival, AND
• Human safety hazard to trails, houses, bridges, etc.

51
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

Examples – Snakeden Reach 2
52
Pre-Construction Construction
Post-Construction 5 Months After Construction

Examples – Rabbit Branch
53
Post-Construction 8 Months After Construction

Post Construction After plant establishmentPost-Construction
Examples – Big Rocky Run Tributary
54

Planting – Trees & Shrubs
55
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

Planting – Riparian Seed Mix
56
• 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:

Greater Biodiversity
57
• 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

Conclusion
58
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.

Next Steps
59
• 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

Questions?
60

Additional Information
For additional information, please contact
www.fairfaxcounty.gov/dpwes
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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