1. US Army Corps of Engineers BUILDING STRONG ® Methods for Determining Maximum Flood Elevations Landward of Failed Levees: An Example from the Great Missouri River Flood of 2011 Presenter: Lowell Blankers, PE, CFM Flood Risk and Floodplain Management USACE, Omaha District Co Authors: Laurel Hamilton, EI Roger Kay, PE Tony Krause, PE, CFM May 2012

2. BUILDING STRONG ® USACE, Omaha District Presentation Overview  Background  Modeling Techniques Used ► Steady HEC-RAS ► Unsteady HEC-RAS  Water Surface Elevation Comparison to Gage Data

3. BUILDING STRONG ® USACE, Omaha District L-575 Missouri River Left Bank 21 Miles 4.8 Miles

4. BUILDING STRONG ® USACE, Omaha District Breach Development  3 Partial Levee Failure Breaches ► June 4 th ► June 5 th ► June 9 th  1 Full Levee Failure Breach ► June 13 th Estimated Width: 300 feet Estimated Depth: 11 feet

5. BUILDING STRONG ® USACE, Omaha District June 4 th 2011 L-575 1 st Sign Potential Levee Failure Levee Crest Landward Toe Seepage Berm

6. BUILDING STRONG ® USACE, Omaha District Breach Location Minimum Levee Elevation

7. BUILDING STRONG ® USACE, Omaha District June 5 th 2011 L-575 2 nd Sign of Levee Failure

8. BUILDING STRONG ® USACE, Omaha District June 9 th 2011 L-575 3 rd Sign of Levee Failure

9. BUILDING STRONG ® USACE, Omaha District June 13 th 2011 L-575 Full Breach 10:00 AM L-575 Full Breach 5:00 PM

10. BUILDING STRONG ® USACE, Omaha District HEC-RAS Steady Flow Model  June 5 th 2011 Hydraulic Modeling Begins  Modeling Objectives ► Determine water surface elevations landward of the levee and to determine levee elevations for a secondary levee at Hamburg, IA ► Determine time available to construct temporary levees once a full breach occurs.

11. BUILDING STRONG ® USACE, Omaha District Steady Flow Model Setup Elevation-volume curve for storage area. The curve was already available from a previous study. Add Storage Area to HEC-RAS Model

12. BUILDING STRONG ® USACE, Omaha District Steady Flow Model Setup Add Lateral Weir at the Breach Location

13. BUILDING STRONG ® USACE, Omaha District Steady Flow Model Setup Add Lateral Weir at downstream return

14. BUILDING STRONG ® USACE, Omaha District L-575 Return Flow 6/16/2011 at 11:00 AM

15. BUILDING STRONG ® USACE, Omaha District Estimate the Elevation Landward of the Levee Estimate an elevation in for storage area. Set in the steady flow file Run model and review the storage area inflow and outflow. Adjust the elevation and rerun to balance the inflow and outflow Steady Flow Model Setup

16. BUILDING STRONG ® USACE, Omaha District Inflow and Outflow from Storage Area should be equal. Steady Flow Model Setup Review Storage Area Results

17. BUILDING STRONG ® USACE, Omaha District Steady Flow Model Results Lower 575 Breach AnalysisScenario 1Scenario 2Scenario 3Scenario 4Scenario 5Scenario 6 Upstream into storage Breach Width300 200 Breach Depth (To Grade)~11 Downstream into channel Breach Width0300 0100300 Breach Depth012012 Storage Area Elevation NAVD 88916.17916.12916.04916.06915.9915.8

18. BUILDING STRONG ® USACE, Omaha District Time to Fill Storage Area Elevation-volume curve for storage area was used with weir equation to estimate time to fill the area behind the levee. Manual calculation required since not computed in Steady Flow RAS Model Elevation 916.17 NAVD88 at approximately 68 hours after breach

19. BUILDING STRONG ® USACE, Omaha District  Initial set up similar to the Steady Flow Modeling.  The breach data was not set in the geometry of the lateral weirs.  Levee breach parameters entered into the Levee Breach option under the Unsteady Plan File. HEC-RAS Unsteady Flow Model Setup

20. BUILDING STRONG ® USACE, Omaha District Unsteady Flow Model Setup Breach Parameters

21. BUILDING STRONG ® USACE, Omaha District Unsteady Flow Model Setup Breach Progression Parameters

22. BUILDING STRONG ® USACE, Omaha District Unsteady Flow Model Setup Breach Parameters for Downstream Notch

23. BUILDING STRONG ® USACE, Omaha District Unsteady Flow Model Results 918 916 914 912 910 904 908 906 902 1415161718192021 Elevation NAVD88 Date (June) Elevation 916.7 NAVD88 Time: 4 to 5 Days or 96 to 120 Hrs

24. BUILDING STRONG ® USACE, Omaha District Gage Data  5 gage locations ► USACE study gage ► 3 Staff Gages set during the flood ► USGS Temporary Gage Set

25. BUILDING STRONG ® USACE, Omaha District Gage Locations Staff Gages USGS Temp Gage USACE Study Gage

26. BUILDING STRONG ® USACE, Omaha District Time of Breach

27. BUILDING STRONG ® USACE, Omaha District Secondary Levee at Hamburg, IA June 18, 2011

28. BUILDING STRONG ® USACE, Omaha District August 29, 2011

29. BUILDING STRONG ® USACE, Omaha District Post Flood November 2011

30. BUILDING STRONG ® USACE, Omaha District Questions