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Design for Stream Crossing Resiliency

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  1. Designing Improved Stream Crossings - Engineering Standards & Guidance –Presented byDavid C. Nyman, P.E.October 2013

  2. Design for Stream Crossing Resiliency • ….by accounting for natural stream processes

  3. Design for Stream Crossing Resiliency • More frequent, more intense storms: • Streams convey more water…

  4. Design for Stream Crossing Resiliency • More frequent, more intense storms: • Streams convey more water… • …sediment

  5. Design for Stream Crossing Resiliency • More frequent, more intense storms: • Streams convey more water… • …sediment

  6. Design for Stream Crossing Resiliency • More frequent, more intense storms: • Streams convey more water… • …sediment • …and debris

  7. Design for Stream Crossing Resiliency • More frequent, more intense storms: • Streams convey more water… • …sediment • …and debris

  8. Design for Stream Crossing Resiliency… • …streams also convey wildlife

  9. Habitat Connectivity & Flood Resiliency: A “Win-Win” Design Scenario

  10. River and Stream Continuity Partnership Guidance:MA River and Stream Crossing Standards General Standards • Spans (bridges, open-bottom culverts) strongly preferred(but where these are impractical, well designed culverts may be appropriate) • If culvert, then it should be embedded • Span the channel: 1.2 x bankfull width • Natural bottom substrate within structure • Design with streambed characteristics • Openness > 0.82 feet (0.25 meters )

  11. Smart Stream Crossing Design: • Apply the Stream Crossing Standards* • Design for Capacity and Stability • Provide for Resiliency *Applicable for non-tidal streams… For tidal streams: preserve or restore natural tidal exchange.

  12. Smart Stream Crossing Design: • Apply the Stream Crossing Standards Convey the “bankfull discharge” through the crossing in a sustainable, natural channel (for replacement structures: to the extent practicable)

  13. Smart Stream Crossing Design: • Apply the Stream Crossing Standards Convey the “bankfull discharge” through the crossing in a sustainable, natural channel (for replacement structures: to the extent practicable) • Design for Capacity and Stability Convey a range of greater than bankfull flows, while sustaining this natural channel and the structure

  14. Smart Stream Crossing Design: • Apply the Stream Crossing Standards Convey the “bankfull discharge” through the crossing in a sustainable, natural channel (for replacement structures: to the extent practicable) • Design for Capacity and Stability Convey a range of greater than bankfull flows, while sustaining this natural channel and the structure • Provide for Resiliency Withstand extreme events without losing the structure

  15. Smart Stream Crossing Design:1. Apply the Stream Crossing Standards • Cross Section Geometry • Streambed • Vertical Alignment Convey the “bankfull discharge” through the crossing in a sustainable, natural channel

  16. Smart Stream Crossing Design:1. Apply the Stream Crossing Standards • Cross Section Geometry • Streambed • Vertical Alignment

  17. A brief primer on “Bankfull Width”

  18. Design to the River and Stream Crossing Standards

  19. BankfullDischarge Design to the River and Stream Crossing Standards Bankfull discharge = the water discharged when a stream just begins to overflow into the active floodplain. Bankfull stage = the elevation at bankfull discharge Bankfull width = the width at bankfull stage

  20. Bankfull Stage Design to the River and Stream Crossing Standards Bankfull discharge ~ 1.5 Year Frequency Event (varies)

  21. BankfullStage Design to the River and Stream Crossing Standards Topographic breaks in slope Flat depositional surface of the floodplain Depositional features Changes in vegetation Undercuts in bank Changes in bank material particle size Other erosion features on upper bank (e.g., scour around roots) Stain lines or lower extent of lichens or mosses on boulders or structures

  22. Bankfull Stage Design to the River and Stream Crossing Standards Bankfull Width

  23. Design to the River and Stream Crossing Standards Bankfull Width 1.2 x Bankfull Width

  24. Span: bridge or open bottom culvert Bankfull Width 1.2 x Bankfull Width

  25. Bankfull width

  26. Bridge span Bankfull width

  27. Span: bridge or open bottom culvert Open Area Open Area (ft2) = Openness Ratio (ft) Structure Length (ft) Openness Ratio (m) >0.82 ft for General Standards*(*Optimum Standards have greater openness and minimum clearance requirements)

  28. Smart Stream Crossing Design:1. Apply the Stream Crossing Standards • Cross Section Geometry • Streambed • Vertical Alignment

  29. Span: bridge or open bottom culvert Preserve existing stream bed (preferred); or if necessary, Provide for bed material comparable to natural channel and that results in depths and velocities at a variety of flows.

  30. Streambed Culvert with Stream Simulation 1.2 x Bankfull Width Provide for bed material comparable to natural channel and that results in depths and velocities at a variety of flows.

  31. Design for the Streambed Requires analysis of • Streambed material

  32. Design for the Streambed Requires analysis of • Streambed material

  33. Design for the Streambed Requires analysis of • Streambed material • Bedform (how the material is arranged in the natural channel)

  34. Design for the Streambed Requires analysis of • Streambed material • Bedform (how the material is arranged in the natural channel) Requires an understanding of stream morphology

  35. Crossing design for a steep gradient boulder & cobble dominated stream…

  36. …may differ from the design for a flatter-gradient stream with a sand & gravel bed.

  37. Smart Stream Crossing Design:1. Apply the Stream Crossing Standards • Cross Section Geometry • Streambed • Vertical Alignment

  38. Analysis of the “Long Profile” From Gubernick & Bates, Stream Simulation Design for AOP, Culvert Summit 2006

  39. Analysis of the “Long Profile” From Gubernick & Bates, Stream Simulation Design for AOP, Culvert Summit 2006

  40. Analysis of the “Long Profile” New Span From Gubernick & Bates, Stream Simulation Design for AOP, Culvert Summit 2006

  41. Smart Stream Crossing Design:2. Design for Capacity and Stability • Capacity for Design Flows • Stability Considerations Convey a range of greater than bankfull flows, while sustaining this natural channel and the structure

  42. Smart Stream Crossing Design:2. Design for Capacity and Stability • Capacity for Design Flows • Base flows addressed by bankfull channel design • Peak flows based on accepted engineering standards

  43. Smart Stream Crossing Design:2. Design for Capacity and Stability

  44. Engineering Design Standards Statutory Review Requirements • MGL Chapter 85 • No bridge on a public highway having a span in excess of ten feet… shall be constructed or reconstructed by any county or town except in accordance with plans and specifications therefor approved by the department. Said department shall approve or alter to meet its approval all such plans submitted to it and shall determine the maximum load which any such bridge may safely carry… • Requires review by MassDOT District/Bridge • Applies to any span >10 ft (including multiple barrels)

  45. Engineering Design Standards Statutory Review Requirements • Item 49 – USDOT Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s Bridges

  46. Engineering Design Standards Statutory Review Requirements • MGL Chapter 85 • Design to MassDOT/ASHTO bridge standards • 2009 MassDOT LRFD Bridge Manual • AASHTO LRFD Bridge Design Specifications • Submittal Requirements • Hydraulic report • Geotechnical report • Structural design requirements • Scour analysis/scour protection at spans

  47. Smart Stream Crossing Design:2. Design for Capacity and Stability • Design Flows – what about climate change? • Precipitation Data • TP-40 is out of date • New data options… • Stream Gage Data • USGS Regression Equations for Massachusetts are out of date • New data options… • Even with updated data, forecasting using historic data may be problematic • Provide for resiliency…