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Taming the Alabama River

Taming the Alabama River. 2012 Alabama Water Resources Conference. Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc. Objective & Scope. Develop a more accurate model Utilize new data Address scientific opinion about effective model Produce regulatory products

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Taming the Alabama River

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  1. Taming the Alabama River 2012 Alabama Water Resources Conference Patrick Dobbs & Clay Campbell AMEC Environment & Infrastructure, Inc.

  2. Objective & Scope • Develop a more accurate model • Utilize new data • Address scientific opinion about effective model • Produce regulatory products • Produce non-regulatory (Risk MAP) products

  3. Cottrell Landing LOMR

  4. USGS Profile Estimate

  5. Alabama River Watershed

  6. Upper Alabama Watershed

  7. Historic Flooding

  8. Hydrology Results Comparison

  9. Hydraulics Method and Analysis • Alabama-Coosa River - From the Millers Ferry Lock and Dam to the Jordan Dam • 187 miles • 6 counties • State Capital • 12 river crossings • 12 main bridges • 22 relief bridges • 1 dam – R. F. Henry Lock and Dam • 162 cross-sections • HEC-RAS 4.1.0

  10. Survey • Road/deck elevations were collected • Field verification • Deck thickness • Bridge width • Rail height • Piers • Number of • Width • Sloping abutments

  11. Hydraulics - Boundary Conditions Known WSEL were set at the Millers Ferry Lock and Dam based on a headwater rating curve from the USACE WCM

  12. Hydraulics – Parameters & Floodway • HEC-RAS Guidance • Contraction/Expansion coefficients • Ineffective area • Manning’s ‘n’ coefficient • Aerial imagery • Survey photos • Field visits • Floodway – similar to effective

  13. Calibration • March 1990 flood event • March 15th – 16th • 8 to 13 inches of rain • Most recent large flood event to affect the Upper Alabama Watershed • Affected homes • Near Montgomery ~ 500 • Near Millbrook ~ 200 to 250 • Dallas County ~ 1,700 • Represents floodplain characteristics of recent history • Development • Clearing and grubbing • Dam construction • Channel maintenance

  14. Calibration vs. High Water Mark Elevations • 23 HWMs • Within+/- 0.5’ of 17 HWMs; +/- 1.0’ of 19 HWMs; +/- 2.0’ of all HWMs • Calibrated by adjusting Manning’s ‘n’ values • All values are within the acceptable range presented in HEC-RAS Hydraulic Reference Manual (USACE, 2010)

  15. Calibration vs. High Water Mark Elevations

  16. Results Revised 1% WSELs are on average 2.6 feet below the effective WSELs Greatest difference occurs just south of Montgomery ~5 feet below the effective Calibration to HWMs justify the difference between revised and effective BFEs

  17. 1% Comparison to Effective

  18. Base Floodplain Comparison – Selma, AL

  19. Base Floodplain Comparison – Montgomery, AL

  20. Base Floodplain Comparison – Wetumpka, AL

  21. Stakeholder Involvement/Expectations • Stakeholders • USACE • USGS • Alabama Power Company • Counties/Municipalities bordering the river • Expectation - Lower BFEs due to 2008 USGS publication

  22. Cottrell Landing Effective Revised

  23. Questions • Patrick Dobbs & Clay Campbell • AMEC Environment & Infrastructure, Inc.

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