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Scour & HydraulicsOnline self-study

Stream Stability and Scour Countermeasures

1 PDH · about 60 minutes · Course no. BR-H03 · Instructor: Michael Craig, PE

About the instructor

Michael Craig, PE is Senior Vice President and Southeast Director at Strinteg Corporation, leading bridge inspection and structural engineering across eight states and Puerto Rico. In 27+ years he has inspected over 4,000 structures and completed 3,000+ load ratings and 160+ load tests. He has managed repair and preservation design for complex bridges, including cable-stayed bridges. He holds PE licenses in twelve states, DC and Puerto Rico, SPRAT Level 1, and FAA Part 107 credentials.

Scour calculations at a pier or abutment assume the channel stays where it is. Real streams move sideways, cut down, build up and change form, and those changes can undo a scour evaluation in a few floods. This course covers how to recognize and analyze stream instability at a bridge, and how to select, size, detail and inspect countermeasures against instability and scour. It draws on HEC-20, Stream Stability at Highway Structures, 4th Edition (FHWA-HIF-12-004, 2012), Chapters 1, 2, 4, 5 and 6, and HEC-23, Bridge Scour and Stream Instability Countermeasures, 3rd Edition, Volume 1 (FHWA-NHI-09-111, 2009), Chapters 2 through 5. Section and equation numbers are given so you can check each point. Scenario numbers that do not come from these documents are labeled illustrative.

⬇ Download study guide (PDF)

Learning objectives

  • Recognize channel instability
  • Classify countermeasures
  • Design riprap concepts
  • Inspect countermeasures

Outline

  1. Why stream stability matters at bridges
  2. Geomorphic and hydraulic factors
  3. Sediment continuity: why beds go up or down
  4. Channel form: straight, meandering, braided
  5. The Lane relation for meandering versus braided sand-bed streams
  6. HEC-20's three levels of analysis
  7. Field reconnaissance and rapid assessment
  8. Lateral stability and meander migration
  9. Vertical stability: degradation and aggradation
  10. The HEC-23 countermeasure matrix and four groups
  11. Group 3 and Group 4: biotechnical and monitoring
  12. Selecting countermeasures by problem type
  13. Countermeasures for contraction and local scour
  14. Design approach, service life and cost
  15. Riprap as a system: revetment and pier riprap sizing
  16. Edges, filters and gradation
  17. How riprap fails
  18. Case study: Schoharie Creek, 1987
  19. Inspecting countermeasures
  20. Putting it together: an illustrative workflow
  21. Open the course (26 screens, 2 knowledge checks)
  22. Final quiz — 10 questions, 70% to pass

References

  1. FHWA, HEC-20 Stream Stability at Highway Structures, 4th Edition, FHWA-HIF-12-004, 2012
  2. FHWA, HEC-23 Bridge Scour and Stream Instability Countermeasures, 3rd Edition, FHWA-NHI-09-111 and -112, 2009