building strong

Report
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
US Army Corps of Engineers
BUILDING STRONG®
Presentation Overview
 Background
 Modeling Techniques Used
► Steady
HEC-RAS
► Unsteady HEC-RAS
 Water Surface Elevation Comparison to
Gage Data
USACE, Omaha District
BUILDING STRONG®
L-575 Missouri
River Left Bank
USACE, Omaha District
BUILDING STRONG®
Breach Development
 3 Partial Levee Failure Breaches
4th
► June 5th
► June 9th
► June
 1 Full Levee Failure Breach
► June
13th
• Estimated Width: 300 feet
• Estimated Depth: 11 feet
USACE, Omaha District
BUILDING STRONG®
June 4th 2011
Levee Crest
Landward Toe
Seepage Berm
L-575 1st Sign Potential Levee Failure
USACE, Omaha District
BUILDING STRONG®
Breach
Location
Minimum Levee Elevation
USACE, Omaha District
BUILDING STRONG®
June 5th 2011
L-575 2nd Sign of Levee Failure
USACE, Omaha District
BUILDING STRONG®
June 9th 2011
L-575 3rd Sign of Levee Failure
USACE, Omaha District
BUILDING STRONG®
June 13th 2011
L-575 Full Breach 10:00 AM
L-575 Full Breach 5:00 PM
USACE, Omaha District
BUILDING STRONG®
HEC-RAS Steady Flow Model
 June 5th 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.
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Setup
Add Storage Area to HEC-RAS Model
925
Legend
Vol-Elev
Elevation (ft)
920
915
910
905
900
895
0
50000 100000 150000 200000 250000 300000 350000
Volume (acre- ft)
Elevation-volume curve for
storage area.
The curve was already
available from a previous
study.
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Setup
Add Lateral Weir at the Breach Location
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Setup
Add Lateral Weir at downstream return
USACE, Omaha District
BUILDING STRONG®
L-575 Return Flow 6/16/2011 at 11:00 AM
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Setup
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
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Setup
Review Storage Area Results
Inflow and Outflow
from Storage Area
should be equal.
USACE, Omaha District
BUILDING STRONG®
Steady Flow Model Results
Lower 575 Breach Analysis
Scenario 1 Scenario 2 Scenario 3 Scenario 4 Scenario 5 Scenario 6
Upstream into storage
Breach Width
300
300
300
200
200
200
Breach Depth (To Grade)
~11
~11
~11
~11
~11
~11
Breach Width
0
300
300
0
100
300
Breach Depth
0
1
2
0
1
2
916.17
916.12
916.04
916.06
915.9
915.8
Downstream into channel
Storage Area Elevation NAVD 88
USACE, Omaha District
BUILDING STRONG®
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
USACE, Omaha District
BUILDING STRONG®
HEC-RAS Unsteady Flow Model Setup
 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.
USACE, Omaha District
BUILDING STRONG®
Unsteady Flow Model Setup
Breach Parameters
USACE, Omaha District
BUILDING STRONG®
Unsteady Flow Model Setup
Breach Progression Parameters
USACE, Omaha District
BUILDING STRONG®
Unsteady Flow Model Setup
Breach Parameters for Downstream Notch
USACE, Omaha District
BUILDING STRONG®
Unsteady Flow Model Results
Plan: 575_init Storage Area: Lower575
918
918
Legend
Stage
916
916
914
912
912
Stage (ft)
Elevation NAVD88
914
Elevation 916.7 NAVD88
Time: 4 to 5 Days or 96 to 120 Hrs
910
910
908
908
906
906
904
904
902
902
14
14
15
15
16
16
17
17
6/1/2011
T ime
18
18
19
19
20
20
21
21
Date (June)
USACE, Omaha District
BUILDING STRONG®
Gage Data
 5 gage locations
► USACE
study gage
► 3 Staff Gages set during the flood
► USGS Temporary Gage Set
USACE, Omaha District
BUILDING STRONG®
Gage Locations
Staff Gages
USGS Temp Gage
USACE Study Gage
USACE, Omaha District
BUILDING STRONG®
Time of Breach
USACE, Omaha District
BUILDING STRONG®
Secondary Levee at Hamburg, IA
June 18, 2011
USACE, Omaha District
BUILDING STRONG®
August 29, 2011
USACE, Omaha District
BUILDING STRONG®
Post Flood
November 2011
USACE, Omaha District
BUILDING STRONG®
Questions
USACE, Omaha District
BUILDING STRONG®

similar documents