Dead Run Stream Restoration May 2014


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Dead Run Stream Restoration May 2014

Middle Potomac Watershed Plan Implementation

Public Meeting
McLean Community Center
April 23, 2014

Published in: News & Politics, Technology
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  • Fluvial Geomorphology Principles
    Lanes Balance Equation
    Changes in one variable tip the balance and must be accounted for by a shift in a
    combination of the other variables. Streams adjust their width, depth, slope, and pattern
    through erosional and depositional processes to accommodate changes in discharge
    and sediment load.
    When discharge and sediment load are not significantly changing, stream adjustment
    processes shift toward stability. Streams that transport sediment loads and convey
    flows without significant erosion or deposition are in balance and have achieved
    dynamic equilibrium. Dynamic equilibrium represents a state of natural stability.
    Streams in dynamic equilibrium maintain a consistent dimension, pattern, and profile in
    the current environment, although some change may occur in the short term. Changes in watershed hydrology or sediment supplies (i.e. current environment), may result in changes in the dimension, pattern and/or profile, as the stream adjusts to a new state of
  • Conduct Geomorphic and Watershed (HH assessment).
    Incision (also know as downcutting or headcutting) can occur independently or
    simultaneously with meander migration. The bed is eroded and the base level of the
    stream is lowered. Downcutting increases bank height, which can eventually lead to
    bank failure and channel widening. Widening and downcutting continue until equilibrium
    is regained.
    Aggradation occurs when sediment supply exceeds transport capacity and the stream
    deposits sediment in the channel. Aggradation can be triggered by an increase in
    sediment supply due to upstream channel erosion or land development, or by a
    decrease in discharge, which reduces the transport capacity of the system. Deposition
    continues until a new state of dynamic equilibrium is achieved.
  • Stream Design Approaches – Natural Channel Design – 3 design approaches 1)Analog 2)Empirical 3)Analytical. All 3 are part of the NCD process.

    Analog approaches use a stream in dynamic equilibrium as a template for design. This approach represents one of three approaches to NCD. Empirical design uses equations derived from regional data sets of various channel characteristics of dynamically stable streams. Analytical design makes use of hydraulic equations and sediment transport functions to derive equilibrium conditions. These three approaches must be given equal validity if the end product meets the above definition of stream design.

    1- Analog / Reference Reach
    2-Empirical: e.g. Regional Curves
  • NCD process
    Dimension Plan Profile
  • NCD process
    Hydrologic Analysis
    Hydraulic Analysis
    Bankfull Discharge
  • Design strategies
    Priority 1 establish new channel at historic FP elev.
    Priority 2 Create New Floodplain and Stream Pattern Below the Historical Floodplain Elevation but Above Current Stream Elevation
    Priority 3 Widen FP at existing BF elev.
    Priority 4 Stabilize channel in place
  • Ex Cond Seg 1
  • Ex Cond Seg 1
  • Ex Cond Seg 1
  • Ex Cond Seg 1 – special features
  • Seg 1 Aerial overview
  • Seg 1 XS
  • Seg 1 Upper Rest
  • Seg 1 Mid Rest
  • Seg 1 Lower Rest
  • Ex Cond Seg 2-3
  • Ex Cond Seg 2-3
  • Ex Cond Seg 2-3
  • Ex Cond Seg 2-3
  • Ex Cond Seg 2-3
  • Seg 2 & 3 Upper Aerial
  • Seg 3 Lower Aerial
  • Seg 2 Rest.
  • Alt Alignment
  • Alt Access 3 lower
  • Alt Access 3 lower
  • Goose Creek – small trib
  • Selma Estates constructed riffle
  • Taft Ave.
    Riffle and modified CV aka Jhook
  • Dead Run Stream Restoration May 2014

    1. 1. Middle Potomac Watershed Plan Implementation Dead Run Stream Restoration Project Public Meeting McLean Community Center April 23, 2014 Stormwater Planning Division Department of Public Works and Environmental Services
    2. 2. Meeting Outline • Fairfax County Stormwater Management • Countywide Watershed Plan Implementation • Project Introduction and Objectives • Existing Conditions • Proposed Improvements - Options • Example Projects • Questions?
    3. 3. Fairfax County Department of Public Works and Environmental Services (DPWES)Department of Public Works and Environmental Services Land Development Services Capital Facilities Solid Waste Stormwater Stormwater Planning Division Maintenance and Stormwater Management Division Wastewater
    4. 4. Stormwater Infrastructure • Conveyance System – 1,600 miles of pipe and paved channel – 43,000 structures – 6,800 outfalls • Management Facilities – 1,540 county maintained – 3,720 privately maintained • State Regulated Dams A typical outfall A dam in Fairfax County
    5. 5. Service Drivers In response to The Clean Water Act of 1972  National Pollutant Discharge Elimination System (NPDES)  Virginia Stormwater Management Program (VSMP) Regulations  Municipal Separate Storm Sewer Permit (MS4)  Total Maximum Daily Loads (TMDLs)  Chesapeake Bay  Local Streams
    6. 6. Countywide Watershed Planning “Healthy Watersheds, Healthy Communities” • 30 Designated Watersheds • All 15 watershed plans have been adopted by Fairfax County
    7. 7. Middle Potomac Watershed Plan • Watershed Characterization – Water Quality Monitoring – Land Use Change – Pollutant Loading • Structural Project – 25 Year Plan • Non-Structural Practices – Policy and Regulations
    8. 8. Dead Run Watershed Plan • Dead Run has a drainage area just over 3 square miles • 24 priority projects identified in the watershed management plan • Pond retrofits • LID Stormwater Enhancements • Stream Restoration • Neighborhood Stormwater Improvements /projects/project_list.htm
    9. 9. Approximately one third of the roof is covered with vegetation. The benefits of a “living roof” include: • Reduces the amount of stormwater runoff • Absorbs air pollution and carbon dioxide • Reduces the energy needed to cool the building in summer Partnership:LIDStormwaterEnhancements Dolley MadisonLibrary Vegetated Roof- Delosperma and Allium plants in bloom
    10. 10. Partnership: LID Stormwater Enhancements Dolley Madison Library Sustainable Site Design
    11. 11. Dead Run – Before and After Drainage Area (acres) Phosphorous Removal (lbs/yr) Nitrogen Removal (lbs/yr) Sediment Removal (tons/yr) 415 15 283 3 Stream Restoration
    12. 12. Dead Run – Stream Restoration
    13. 13. Stream Monitoring Program Study Objectives 1. Generate long-term monitoring data. 2. Evaluate relations between observed conditions/trends and BMP implementation. 3. Transfer the understanding gained to other less-intensively monitored watersheds.
    14. 14. Dead Run Stream Restoration
    15. 15. Dead Run Stream Restoration Segment 1 – Dominican Retreat • 2,000 Linear Feet • Extends to Old Dominion Drive • Residential lots along Merrimac Drive and Van Ness Court
    16. 16. Dead Run Stream Restoration Segment 2 – McLean Central Park • 800 Linear Feet • Completely in Park • Starts below previously restored section near library
    17. 17. Dead Run Stream Restoration Segment 3 – McLean Central Park • 1,500 Linear Feet • Extends to Churchill Road • Residential lots along Elizabeth Drive and Carol Rayes Street
    18. 18. Next Steps • Conceptual Design • Land Acquisition/Coordination • Preliminary Design • Public Meeting • Final Design • Project Construction • Funding FY2016 and FY2017 • Community Coordination: Pardon Our Dust • Maintenance and Operation
    19. 19. Natural Channel Design Background and Design Approach
    20. 20. Stream Design Approaches Natural Channel Design 3 design approaches 1)Analog 2)Empirical 3)Analytical
    21. 21. Segment 1 Dominican Retreat
    22. 22. Segment 2 & 3 Mclean Central Park Dead Run Stream Valley Park
    23. 23. Alternative Access
    24. 24. Alternative Access
    25. 25. Instream Structures
    26. 26. Looking upstream at boulder rock toe and constructed riffle Looking upstream at boulder rock toe – 2 and 3 courses
    27. 27. Modified Cross Vane
    28. 28. Modified Cross Vane
    29. 29. Cross Vane Cross Vane Cross Vane
    30. 30. Step Pool
    31. 31. Infill mix comprised of cobbles, gravels, sand, silt, topsoil Larger material, usually cobble Constructed Riffle (aka Reinforced Streambed)
    32. 32. Riffle
    33. 33. Access
    34. 34. During May 2010 Before Feb. 2010 After Sept. 2010
    35. 35. John Palmer Dipmani Kumar Matt Meyers Stormwater Planning Division Department of Public Works and Environmental Services Fairfax County 12000 Government Center Parkway, Suite 449 Fairfax, Virginia 22035 Questions ? Contact Information A Fairfax County Publication, April 2014 To request this information in an alternate format call 703-324-5500, TTY 711 stormwater Thank You!