Harford Community Stream Restoration 2013


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Harford Community Stream Restoration 2013

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Harford Community Stream Restoration 2013

  1. 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. 2. Wetland Studiesand Solutions, Inc. • Natural & Cultural Resource consulting firm • 75 Staff – Archeology, Engineering, Environmental Science & Ecology, Environmental Technology, Compliance, GIS, Regulatory, Surveying, & Wildlife Biology Wetland 2
  3. 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 Wetland 3
  4. 4. Why are we here ?The stream is eroding.3.5’ headcut Eroded channel, vertical banksThe storm-water pond and emergency spillway need repair.Significant deposition in stormwater pond Emergency spillway failure Wetland 4
  5. 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 Wetland 5
  6. 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) Wetland 6
  7. 7. The urban watershed problem Source: The Federal Interagency Stream Restoration Working Group Wetland 7
  8. 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 - 1999Before restoration After restoration Wetland 8
  9. 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 OptimalSevere Channel Condition Optimal Channel Condition South Lakes High School Ellanore Lawrence Park Wetland 9
  10. 10. Urban Stream - Design Realities1. 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 RestonSnakeden Branch – Reach 3 McLean Place (after 4.5 yrs) Flow Rate (cfs)(after 16 months) Rural Drainage Area (sq mi) Wetland 10
  11. 11. Stream ReinforcementStep Pools Cross VanesReinforced Bed Native Vegetation Wetland 11
  12. 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 disturbanceBefore After Snakeden Branch Reach 2 – Priority 1 Restoration Wetland 12
  13. 13. Restoration approachesPriority 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. Wetland 13
  14. 14. Restoration approaches Priority 4 Restoration – Stabilize in-placeSnakeden Branch Reach 2(2003, by others) –Long-term stability notachieved using thisapproach. Wetland 14
  15. 15. Harford stream: Historic Conditions 1937 Wetland 15
  16. 16. Harford stream: Historic Conditions 1971 1972 Wetland 16
  17. 17. Harford stream: Historic Conditions 1979 1998 Wetland 17
  18. 18. Harford stream: Historic Conditions 2012 Wetland 18
  19. 19. Harford stream: Existing Conditions • Drainage Area 121.1 acres • Imperviousness 37% Wetland 19
  20. 20. Harford stream: Existing Conditions Culvert and rip rap channel Wetland 20
  21. 21. Harford stream: Existing Conditions Sediment deposition Wetland 21
  22. 22. Harford stream: Existing Conditions Riprap and deposition along paved path Wetland 22
  23. 23. Harford stream: Existing Conditions 3.5’ head cut Wetland 23
  24. 24. Harford stream: Existing Conditions Debris, incised channel Wetland 24
  25. 25. Harford stream: Existing Conditions Existing bridge Wetland 25
  26. 26. Harford stream: Existing Conditions Exposed utility lines Wetland 26
  27. 27. Harford stream: Existing Conditions • Eroded channel approximately 5-ft deep • Listed for restoration in watershed plan (PC9258) Outfall from Dahlgreen Place Wetland 27
  28. 28. Harford stream: Existing Conditions Incised channel Wetland 28
  29. 29. Harford stream: Existing Conditions Culvert at Guinea Rd. Wetland 29
  30. 30. Harford stream: Existing Conditions Heavy deposition in sediment forebay Wetland 30
  31. 31. Harford stream: Existing Conditions Emergency spillway showing signs of failure Wetland 31
  32. 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 Wetland 32
  33. 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 Wetland 33
  34. 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 Wetland 34
  35. 35. community Involvement In the Plan Development ProcessObjective – 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 Wetland 35
  36. 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) Wetland 36
  37. 37. Stream restoration design processTree impact considerationsEcological / 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. Wetland 37
  38. 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 varietyIncised 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 withRestored (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. Wetland 38
  39. 39. Examples - Snakeden Reach 2 Pre-Construction Construction Post-Construction 5 Months After Construction Wetland 39
  40. 40. Examples - Snakeden Reach 3 Pre-Construction Post-Construction 15 Months After Construction Wetland 40
  41. 41. Examples – Snakeden reach 13 Pre-Construction Post-Construction Wetland 41
  42. 42. Examples – Big Rocky Run Tributary Pre-Construction ConstructionPost Construction Post-Construction After plant establishment Wetland 42
  43. 43. Examples - Sheffield ConstructionPre-Construction Post-Construction Wetland 43
  44. 44. PLANTING – TREES & SHRUBSSplit 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 Wetland 44
  45. 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! Wetland 45
  46. 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 Wetland 46
  47. 47. technical review• Fairfax County Department of Public Works and Environmental Services• US Army Corps of Engineers• Virginia Department of Environmental Quality Wetland 47
  48. 48. Conclusion1. 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. Wetland 48
  49. 49. Questions?Wetland 49
  50. 50. For more information• 703-324-5500, TTY 711• SWPDMail@fairfaxcounty.gov• www.fairfaxcounty.gov/dpwes/stormwater• A Fairfax County, Virginiapublication, April 2013 Wetland 50