1. EVALUATION OF NEW MODELS FOR SIMULATING EMBANKMENT DAM BREACH
Tony L. Wahl
Bureau of Reclamation – Denver, CO

2. What is CEATI International?
Since 1891, the Canadian Electrical Association (CEA) has been the forum for electrical business in Canada
In 1974, CEA initiated its R&D Program to serve the research needs of Canadian electric utilities
In 1998, CEA’s R&D Program opened its doors to international participation
In 2001, CEA Technologies Inc. (CEATI) was separated from the Canadian Electrical Association
CEATI International is now the “Centre for Energy Advancement through Technological Innovation”
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4. Interest Groups 14 Interest Groups in the areas of electrical energy…
Generation
Transmission
Distribution
Utilization
Dam Safety Interest Group
About 40 dam owners
Jointly sponsors research & development projects
Participants from Canada, the United States, Europe, Australia, and New Zealand
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5. Dam Safety Interest Group (DSIG)
Areas of Interest:
Risk assessment for dam safety
The use of geophysical methods in the diagnostics and monitoring of embankment dams
Erosion and piping in dams
Reliability of discharge facilities
Ice loadings
Probability (frequency) of extreme floods
Emergency preparedness
Testing of embedded dam anchors
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6. Dam-Break Modeling: Recent History
Lethal Dam Failures in 1970s
Canyon Lake
Kelly Barnes
Laurel Run
Buffalo Creek
Teton
1977 DAMBRK model developed
Could route peak breach outflows to determine inundation depths, flood consequences
Could determine peak breach outflow, given a description of how a breach would develop
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7. Modeling Breach Development
Concrete dam failure modes (sliding, overturning, structural) are usually instantaneous and complete
Embankment dam failures usually involve erosion, which takes time and depends on many factors
Regression equations to relate breach parameters to dam and reservoir characteristics
Many developed in 1980s and refined in 1990s
Adequate for cases in which the area of interest was in the “far-field”
Too crude for the “near-field”
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8. Physically-Based Breach Modeling
Dr. Danny Fread recognized need for modeling erosion processes to obtain better results in near field
May 18, 1980 eruption of Mt. St. Helens created landslide dam on Toutle River
Dr. Fread developed NWS-BREACH model to analyze possible breach of this dam
NWS-BREACH released to public in 1988
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9. Modeling Developments in 1990s
Flood routing capabilities much improved
2D modeling
Integration with GIS to improve consequence analysis
Little change in breach modeling during this time
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10. CEATI Dam Erosion and Breach Project
Since 2001 the DSIG has had an interest in improving the tools used to model embankment dam erosion and breaching
Key Questions
Will a dam breach?
What is the outflow hydrograph?
What is the warning time?
Available methods mostly unchanged since late 1980s
Regression models for predicting peak outflow
Regression models for predicting breach parameters
Breach erosion models, such as NWS-BREACH
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11. Shortcomings of Available Methods
Regression models for peak outflow
No aid in determining whether breach occurs
Little detail about hydrograph shape or warning time
Regression models for predicting breach parameters
Uncertainties are large, especially for time parameters
Breach initiation time
Breach formation time
Breach erosion models (e.g. NWS-BREACH)
Used sediment transport equations, not true erosion models
Poor modeling of erosion of cohesive materials
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12. Large-Scale Physical Tests
Since 2000, many organizations have been performing small-scale and some large-scale embankment breach tests
European IMPACT Project (22 lab tests and sponsorship of Norwegian field tests)
Norwegian tests (23 lab tests, 5 field tests of 6-m-high dams)
Agricultural Research Service (7 overtopping tests and 4 piping tests of 2-m-high dams)
New breach erosion models under development
Physically-based simulation of erosion processes
Better modeling of the erosion of cohesive soils
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13. Project Objectives
Dam breach erosion project was initiated in 2004, with a focus on erosion and breach processes and prediction of breach outflow hydrographs at the dam
We want to develop physically-based models for overtopping erosion and internal erosion leading to dam breach and facilitate the integration of those technologies into existing flood routing tools like HEC-RAS, MIKE11, Telemac, InfoWorks, etc.
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14. Participants Electricité de France
Case studies…erodimeter and piping erosion research
Hydro Québec / Ecolé Polytechnique Montréal
Numerical modeling of dam breach, development of Firebird breach model
Bureau of Reclamation
Laboratory testing…investigate erodimeters
Agricultural Research Service
Large-scale laboratory testing and development of SIMBA/WinDAM models
HR Wallingford
Large-scale testing (IMPACT project), developers of HR-BREACH model
US Army Corps of Engineers
Integration of breach modeling technology into HEC-RAS suite
Elforsk AB
Model evaluation
Other interested parties and sponsors
BC Hydro, Churchill Falls, Elforsk AB, EoN Vasserkraft, Great Lakes Power, Manitoba Hydro, New York Power Authority, Ontario Power Generation, Seattle City Light, Scottish & Southern Energy, National Weather Service
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15. Phase 1: Information Gathering
Project Overview
Phase 1: Information Gathering
Reviewed and assembled case-study and large-scale laboratory test data
Reviewed and identified numerical models under development
Phase 2: Model Development and Implementation
Phase 3: Model Enhancement
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16. Tasks in Phase 2 Evaluation of three numerical breach models
SIMBA (ARS)
HR-BREACH (HR Wallingford)
FIREBIRD BREACH (Montreal Polytechnic)
Evaluation of methods for quantifying erodibility of cohesive embankment materials
leading to…
Integration of breach modeling technologies into HEC-RAS dynamic routing model
Potential efforts to facilitate integration with commercial flood routing models
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17. The Models: Common Characteristics
Models are all physically-based
Models utilize quantitative input parameters describing erodibility of cohesive materials
Models are intended to perform well without specific calibration to a particular case
Models are not computationally intensive
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18. The Models SIMBA – Simplified Breach Analysis (USDA-ARS)
Simulates breach by overtopping of homogeneous earth embankments with negligible protection on the downstream face
Four stage failure process
surface erosion leading to development of a headcut on the downstream face of the embankment
headcut advance through the crest to initiate the breach
breach formation as the headcut advances into the reservoir
breach expansion during reservoir drawdown
Erosion formulas are fixed and most calibration factors have been determined from lab testing. Complete model is not calibrated to any specific data set.
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19. The Models HR BREACH (HR Wallingford)
Overtopping or piping-induced breach of cohesive, non cohesive and simple composite (i.e. zoned) structures.
Simulated processes:
Initial erosion of embankment surface protection (grass or rock cover)
Headcut erosion through embankment
Potential failure of breach side slopes by shear or bending
Potential for sliding or overturning of core section
Limited selection of erosion formulas
Not calibrated to any specific data set
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20. The Models FIREBIRD BREACH (Montreal Polytechnic)
Overtopping-induced breach of homogeneous earthfill or rockfill dams
One dimensional unsteady flow, St. Venant equations coupled with sediment continuity
Able to handle transcritical flows
Side slopes are evaluated for ability to resist sliding along a simple inclined face
Choice of erosion formulas
Can be more computationally intensive
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21. Model Evaluation
Evaluate model performance against large-scale laboratory tests and case-study data
2 ARS outdoor laboratory tests 2.3-m high homogeneous dams, overtopping 1 breach, 1 non-breach
3 overtopping breach tests performed in Norway during the IMPACT project (5- to 6-m high dams)
homogeneous clay
homogeneous gravel
zoned embankment
2 real dam failures
Oros (Brazil)
Banqiao (China)
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22. ARS Tests Two overtopped embankments, 2.3 m high
SM Silty Sand, complete breach in 51 minutes
CL Lean Clay, headcut damage, but no breach after 20 hours
2.5 orders of magnitude difference in erodibility of materials
Constant inflow, small reservoir
Hanson, G.J., Cook, K.R., Hunt, S Physical modeling of overtopping erosion and breach formation of cohesive embankments. Transactions of the ASAE, 48(5):
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23. Norwegian Tests - Part of IMPACT
Three overtopped embankments, 5 to 6 m high
Homogeneous clay, placed very wet
Homogeneous gravel, surface frozen
Zoned rockfill with moraine core
Inflow regulated at upstream reservoir
Clay dam: Peak inflow arrived shortly after initial breach… reservoir level went back up… peak outflow driven by peak inflow
Flow regulation not attempted for gravel dam test
Inflow was too little, too late for zoned test
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24. Oros Dam (Brazil, 1960)
35-m high dam, failed by overtopping during construction
Core material probably a Sandy Lean Clay, with PI=10
Well-compacted, except maybe last lifts
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25. ASDSO 2009

26. Oros Dam - Summary
Thick, erosion-resistant embankment, large reservoir
Slow erosion
12 hrs to initiate breach
6.5 to 12 hrs to form breach and drain reservoir
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27. Banqiao Dam (China, 1975)
Hand-built dam with homogeneous earth shells and clay core wall of “arenaceous shale”
Assumed to be poorly compacted and highly erodible
1 hr breach initiation
2 to 2.5 hrs to fully form breach
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28. Evaluation Criteria Evaluate performance using Objective criteria
initial inputs (best available information and judgment)
optimized inputs
Objective criteria
Time to initiate breach (erode through crest)
Time to form breach (reach full width)
Final breach width
Breach widening rate
Peak outflow
Subjective criteria
Do models exhibit appropriate sensitivity?
Ease of determining input data and selecting parameters
Ease of operation
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29. Current Status Team met at last year’s USSD meeting in Portland
Members have been working this summer to perform the evaluation runs
Group will meet again later this week to compare results and try to reach consensus on:
Which models and model components are working well?
What technologies are presently ready to be integrated into state-of-the-art models?
Where is more work needed?
SIMBA and HR-BREACH models are being integrated into USDA WinDAM and Wallingford Software InfoWorks products
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30. Challenges TIME: Too many models, cases, scenarios
Each case study presents unique evaluation challenges
Real failures have questions about dam materials and erodibility, and about observed breach and outflow characteristics
Lab tests have “real-world” logistical complications and limitations related to reservoir size
Failure to accurately model breach initiation phase can require judgment to evaluate how well the model reproduced later stages of the breach process
Evaluation process has already been extremely valuable
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32. CEATI Information: Chris Hayes Director, Business Development 1155 Metcalfe St., Suite 1120 Montreal, QC H3B 2V6 (514) | |