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A Sediment Budget for Two Reaches of Alameda Creek (1900s through 2006)

A Sediment Budget for Two Reaches of Alameda Creek (1900s through 2006). Paul Bigelow, Sarah Pearce, Lester McKee, and Alicia Gilbreath. Study Questions. Are the study reaches supplying a major source of sediment to the flood control channel?

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A Sediment Budget for Two Reaches of Alameda Creek (1900s through 2006)

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  1. A Sediment Budget for Two Reaches of Alameda Creek (1900s through 2006) Paul Bigelow, Sarah Pearce, Lester McKee, and Alicia Gilbreath

  2. Study Questions • Are the study reaches supplying a major source of sediment to the flood control channel? • What are the dominant processes, and what are the rates of erosion and amount of storage? • What proportion of total sediment load at Niles is derived from the study reaches? • How has the channel changed through time?

  3. Alameda CreekWatershed

  4. Area BehindDams

  5. Study Area

  6. Brief Watershed History Pre-1900: channel ditching, groundwater wells, small dams 1900: Ditching and draining of Tulare Lake 1911: ADLL incision rate of 6 in/yr

  7. 1925: Calaveras Dam, gravel mining 1950s: Four largest flood events on record 1964: San Antonio Dam 1968: Del Valle Dam 1970s: Flood Control Channel construction 1980s to 2000s: Flood Control Channel dredging Oblique view of Pleasanton and Dublin (looking west) during the 1955 flood

  8. Historical Flow Changes

  9. Arroyo De La Laguna Lower Subreach Upper Subreach

  10. Arroyo De La Laguna

  11. Arroyo De La Laguna

  12. Alameda Creek

  13. Sediment Budget Methods • Incision – bed elevation surveys 1959, 1971, 2007 • Bank Erosion & Bar Storage – field surveys and air photo analysis • Cross Section Surveys – historical and current • Flood Plain Storage – field surveys • Only subset of data collected for Alameda Creek Reach (little incision, 90% of drainage area above dams)

  14. Compare Reaches w/ Watershed +Verona Gage +Welch Gage +Study Reaches +Ungaged Tribs = Niles Gage? • Balance the Budget • Estimate Yield at Gages (rating curves) • Estimate Yield for Ungaged tributaries (reservoir sedimentation rate) • Compare Reaches w/ Niles Gage

  15. Sediment Budget Periods • 1901 – 1959 • 1959 – 1971 • 1971 – 1993 • 1993 – 2006

  16. ResultsLong Profiles Arroyo De La Laguna Bed Elevation ~1901 – 1959 4.5 m ave total incision depth 6 – 10 cm/yr

  17. 1959 to 1971 Bed Elevation 1-2 m incision depth 7 – 15 cm/yr

  18. 1971 to 2007 Bed Elevation 0.5 – 0.8 m incision 2 – 6 cm/yr 0.75 m aggradation

  19. Incision Pattern Over TimeIncision Migrating Upstream

  20. Further Upstream

  21. Bank Erosion & Bar Storage Aerial Photograph Analysis • Assessed entire study reach • Focused on four locations • Four time periods • Quantified bank erosion and bar storage

  22. 1939 Photo

  23. 1950 Photo

  24. 1966 Photo

  25. 1993 Photo

  26. 2005 Photo

  27. Location C 1939-1950 1950-1966 1966-1993 1993-2005 Retreat rate 0.0 m/yr Retreat rate 0.9 m/yr Retreat rate 0.6 m/yr Retreat rate 3.8 m/yr 2005 Photo

  28. Bank erosion (metric tonnes/yr)

  29. Channel Cross Sections

  30. Channel Cross Sections 5-6 m 5-6 m

  31. Flood Plain Storage

  32. Sediment Budget by Process - ADLL

  33. Alameda Creek Reach

  34. Overall Watershed Comparisonfor Recent Period (1994 – 2006) Within 5%

  35. Study Reaches Comparison to Niles Gage

  36. Study Area Sediment Yield Comparison to Regional Values

  37. Sediment Budget Take Home Points • Sediment budget has adjusted over several periods of land use alteration and disturbance from floods • Budget dominated by incision in earlier periods, now adjusting through bank erosion • ADLL sediment yield is high for a short reach (0.25% of total stream network length) • But ADLL comprises a small portion of watershed sediment yield (6% of total yield)

  38. Future Channel Evolution Channel Evolution Models • Process-based classification • Describe channel form as it responds to a disturbance • Shows typical channel adjustments to return a balance of sediment transport capacity

  39. Future Response of ADLL Conceptual Scenarios:

  40. Next Steps - Recommendations • Monitor future channel adjustment in ADLL, and continue to stabilize the reach • Given management changes on Alameda Creek, monitor future channel response for sediment supply increase • Conduct a phased watershed sediment budget • Phase 1: Quantitatively (on public lands) and qualitatively (on private lands) assess feasibly manageable sediment • Phase 2 (if needed): Quantitative evaluation of manageable sediment on private lands • Conduct numerical modeling to understand sediment routing to and deposition within the Flood Control Channel

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