Harford Community Stream Restoration 2013

1. Stream Restoration and The Upper Pohick creek
Watershed
Presented by Michael S. Rolband
P.E., P.W.S., P.W.D.
Wetland Studies and Solutions, Inc.
5300 Wellington Branch Drive . Suite 100 . Gainesville . Virginia 20155
www.wetlandstudies.com
Department of
Fairfax Public Works
County, and
Environmental
Virginia Wetland Services

2. Wetland Studies
and Solutions, Inc.
• Natural & Cultural Resource
consulting firm
• 75 Staff
– Archeology, Engineering, Environmental
Science & Ecology, Environmental
Technology, Compliance, GIS, Regulatory,
Surveying, & Wildlife Biology
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3. Why are we here ?
 To discuss restoration of
the “Harford” stream
with the community
 This area listed for
restoration in the Pohick PC9257
Creek Watershed
Management Plan
PC9258
- Project Number: PC9257
- Project Number: PC9258
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4. Why are we here ?
The stream is eroding.
3.5’ headcut Eroded channel, vertical banks
The storm-water pond and emergency spillway need repair.
Significant deposition in stormwater pond Emergency spillway failure
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5. Why are we here ?
• Erosion results in poor water • The Environmental Protection
quality; high levels of: Agency Chesapeake Bay TMDL
– Total Suspended Solids (TSS) Plan Requires Fairfax County
– Total Nitrogen (TN) pollutant reductions
– Total Phosphorous (TP)
Poor water quality Good water quality
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6. Why are we here ?
• What has caused the
erosion?
• What can be done to fix the
erosion and prevent future
issues?
Dahlgreen Pl tributary (PC9258)
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7. The urban watershed problem
Source: The Federal Interagency Stream Restoration Working Group
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8. Why restore ?
Reconnect to the existing floodplain to:
• Slow velocities
• Increase evapotranspiration
• Remove pollutants (TP, TN, and TSS)
• Improve riparian habitat
• Restore groundwater levels
After planting - 1999
Before restoration After restoration
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9. Design Methodology for Urban Streams
- Natural Channel Evolution -
Evolutionary process considers the channel’s incision, bank
stability, & sedimentation load (aggrading or degrading)
Severe Poor Marginal Suboptimal Optimal
Severe Channel Condition Optimal Channel Condition
South Lakes High School Ellanore Lawrence Park
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10. 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.
Flow Rate vs Drainage Area
• Rock structures – using native diabase rock
• Reinforced bed
• Heavy planting densities – native vegetation only
Reston
Snakeden Branch – Reach 3 McLean Place (after 4.5 yrs)
Flow Rate (cfs)
(after 16 months)
Rural
Drainage Area (sq mi)
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11. Stream Reinforcement
Step Pools Cross Vanes
Reinforced Bed Native Vegetation
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12. Restoration approaches
Priority 1 Restoration - Raise stream to reconnect with the floodplain.
Fewer trees removed
Balanced cut and fill volumes
result in less waste
Width of disturbance
Before After
Snakeden Branch Reach 2 – Priority 1 Restoration
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13. Restoration approaches
Priority 2 Restoration – Excavate floodplain at lower elevation.
Many trees removed
Large cut volumes result in waste material
Width of disturbance
Priority 3 Restoration – Confined stream valleys.
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14. Restoration approaches
Priority 4 Restoration – Stabilize in-place
Snakeden Branch Reach 2
(2003, by others) –
Long-term stability not
achieved using this
approach.
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15. Harford stream: Historic Conditions
1937
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16. Harford stream: Historic Conditions
1971 1972
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17. Harford stream: Historic Conditions
1979 1998
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18. Harford stream: Historic Conditions
2012
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19. Harford stream: Existing Conditions
• Drainage Area
121.1 acres
• Imperviousness
37%
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20. Harford stream: Existing Conditions
Culvert and rip rap channel
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21. Harford stream: Existing Conditions
Sediment deposition
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22. Harford stream: Existing Conditions
Riprap and deposition along paved path
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23. Harford stream: Existing Conditions
3.5’ head cut
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24. Harford stream: Existing Conditions
Debris, incised channel
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25. Harford stream: Existing Conditions
Existing bridge
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26. Harford stream: Existing Conditions
Exposed utility lines
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27. Harford stream: Existing Conditions
• Eroded channel approximately 5-ft deep
• Listed for restoration in watershed plan (PC9258)
Outfall from Dahlgreen Place
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28. Harford stream: Existing Conditions
Incised channel
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29. Harford stream: Existing Conditions
Culvert at Guinea Rd.
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30. Harford stream: Existing Conditions
Heavy deposition in sediment forebay
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31. Harford stream: Existing Conditions
Emergency spillway showing signs of failure
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32. What does fairfax county need from your
association ?
• Guidance from the community regarding:
• The desire for additional project meetings or stream walks
• Details of the Community Association approval process
• An easement to allow the County and its contractors to:
• Survey and develop restoration plans
• Restore the stream
• Maintain the stream
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33. Plan Development Process
• Pre-design Meeting (Tonight)
• Data Collection
• Stream Restoration Design
Process
• Concept Plan Development
• Preliminary Design
• Final Design
• Pre-construction Review
• Construction
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34. Data collection
• Obtain topography
• Survey locate & tag trees (> 8” dbh)
• Survey channel profile and cross-sections
• Sediment sampling
• Perform wetland delineations and obtain
Jurisdictional Determinations (JD’s) from U.S. Army
Corps of Engineers
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35. community Involvement In the Plan
Development Process
Objective – Partnership between Fairfax County staff and the
Lake Braddock Community
• 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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36. Stream restoration design process
Determine Bankfull Width
and Bankfull Area to convey
current flows.
THE DESIGN PROCESS
Apply Bankfull Width to
reference ranges of sinuosity
and meander radii.
Layout initial design
alignment (minimize impact
to infrastructure and trees)
Citizen Meeting
Citizen Meeting
Revise restoration design
and access Final Design
(based on citizen input)
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37. Stream restoration design process
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.
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38. Stream restoration design process
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
Incised stream of replacement plantings
– Mosquito population control via predator habitat
– Dense streambank planting will provide shade, reduce water
Lower water table temperatures, increase oxygenation, increase fish survivability
– Dragonfly larva molting access via heavily planted streambank with
Restored (raised) stream
shallower slope
• Canopy loss will close as remaining trees adjust and react to increased
sunlight, growing to fill in openings
Higher water table
Fewer trees cut = lower restoration cost
• Tree-climbing removal method vs. traditional forestry timbering
(minimize impacts to neighboring trees) is expensive.
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39. Examples - Snakeden Reach 2
Pre-Construction Construction
Post-Construction 5 Months After Construction
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40. Examples - Snakeden Reach 3
Pre-Construction
Post-Construction 15 Months After Construction
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41. Examples – Snakeden reach 13
Pre-Construction
Post-Construction
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42. Examples – Big Rocky Run Tributary
Pre-Construction Construction
Post Construction Post-Construction After plant establishment
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43. Examples - Sheffield
Construction
Pre-Construction Post-Construction
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44. 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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45. PLANTING - Riparian Seed Mix
• Applied at a rate of 125 lbs/acre
• Custom mix
• Consists of native species found in a healthy, diverse NOVA ecosystem:
• Tree Species • Shrub Species
• Musclewood • Witch Hazel
• Black Gum • Winterberry
• American Sycamore • Southern Arrow Wood
• Red Maple • Northern Spicebush
• Eastern Redbud • Canadian Serviceberry
• Flowering Dogwood • Black Chokeberry
• Black-Haw
• Forbs • Grass Species
• Oxeye Sunflower • Squarrose Sedge
• Joe-Pye Weed • Riverbank Wild Rye
• Grass Leaved Goldenrod • Foxtail Millet
• PLUS 24 additional species! • PLUS 8 additional species!
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46. 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
Red-shouldered Hawk
• All species benefit from the “edge
effect”
• Restored stream allows detrital
input to be processed, thus Cottontail Rabbit
increasing stream health and
function
Orchard Oriole
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47. technical review
• Fairfax County Department of Public Works and Environmental Services
• US Army Corps of Engineers
• Virginia Department of Environmental Quality
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48. Conclusion
1. The “Harford” tributary of the Pohick
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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49. Questions?
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50. For more information
• 703-324-5500, TTY 711
• SWPDMail@fairfaxcounty.gov
• www.fairfaxcounty.gov/dpwes/stormwater
• A Fairfax County, Virginia
publication, April 2013
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