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Crook Branch at Mantua Elementary School Stream Restoration Project

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

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Crook Branch at Mantua Elementary School Stream Restoration Project

  1. 1. 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
  2. 2. 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
  3. 3. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  4. 4. Crook Branch Stream Restoration DPWES Stormwater Planning Division Project Limits 4 Reach 2 Reach 3
  5. 5. Crook Branch Stream Restoration DPWES Stormwater Planning Division Existing Easements 5 Conservation Easement Storm Drainage and Floodplain Easement Floodplain Easement Storm Drainage Easement
  6. 6. 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 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.
  7. 7. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  8. 8. Crook Branch Stream Restoration DPWES Stormwater Planning Division Crook Branch: Existing Conditions 8
  9. 9. Crook Branch Stream Restoration DPWES Stormwater Planning Division Crook Branch: Existing Conditions 9
  10. 10. Crook Branch Stream Restoration DPWES Stormwater Planning Division Crook Branch: Existing Conditions 10
  11. 11. Crook Branch Stream Restoration DPWES Stormwater Planning Division Crook Branch: Existing Conditions 11
  12. 12. DPWES Stormwater Planning Division Crook Branch Stream Restoration Crook Branch: Historic Conditions 12
  13. 13. Crook Branch Stream Restoration DPWES Stormwater Planning Division EXISTING CONDITIONS PLAN 13
  14. 14. Crook Branch Stream Restoration DPWES Stormwater Planning Division EXISTING CONDITIONS PLAN 14
  15. 15. Crook Branch Stream Restoration DPWES Stormwater Planning Division EXISTING CONDITIONS PLAN 15
  16. 16. Crook Branch Stream Restoration DPWES Stormwater Planning Division EXISTING CONDITIONS PLAN 16
  17. 17. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  18. 18. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  19. 19. Crook Branch Stream Restoration DPWES Stormwater Planning Division Restoration Approaches Priority 2 Restoration – Excavate floodplain at lower elevation. 19 Width of disturbance Large cut volumes result in waste material Many trees removed Priority 3 Restoration – Confined stream valleys.
  20. 20. Crook Branch Stream Restoration DPWES Stormwater Planning Division Restoration Approaches Priority 4 Restoration – Stabilize in-place. 20
  21. 21. 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 21 Snakeden Branch (after 1 year)Rabbit Branch (after 7 months)
  22. 22. DPWES Stormwater Planning Division Crook Branch Stream Restoration Stream Structures and Bed Reinforcement 22 Reinforced Bed Step Pools Cross Vanes
  23. 23. DPWES Stormwater Planning Division Crook Branch Stream Restoration Stream Reinforcement 23 Toe Wood Log J-Hook Native Vegetation In-Stream Habitat Log Sill
  24. 24. Crook Branch Stream Restoration DPWES Stormwater Planning Division Crook Branch: Channel Sizing • Drainage Area: – 827.8 acres • Imperviousness: – 35% = URBAN 24
  25. 25. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Proposed Cross Sections 25 Section 1 Section 2 Section 3
  26. 26. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Proposed Alignment 26
  27. 27. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Proposed Bridge Realignment 27
  28. 28. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Proposed Access 28 Construction Entrance 1 Construction Entrance 2
  29. 29. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  30. 30. Crook Branch Stream Restoration DPWES Stormwater Planning Division 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
  31. 31. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Tree Impacts 31
  32. 32. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Tree Impacts 32
  33. 33. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Tree Impacts 33
  34. 34. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Tree Impacts 34
  35. 35. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Tree Impacts 35
  36. 36. Crook Branch Stream Restoration DPWES Stormwater Planning Division Design – Floodplain Impacts 36 Floodplain Easement
  37. 37. Pre-Construction Construction Post Construction After plant establishmentPost-Construction Crook Branch Stream Restoration DPWES Stormwater Planning Division Examples – Big Rocky Run Tributary 37
  38. 38. Crook Branch Stream Restoration DPWES Stormwater Planning Division Examples – Rabbit Branch 38 Pre-Construction Construction Post-Construction 8 Months After Construction
  39. 39. 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 39
  40. 40. Additional Information For additional information, please contact www.fairfaxcounty.gov/dpwes Crook Branch Stream Restoration 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

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