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EVALUATION OF NEW MODELS FOR SIMULATING EMBANKMENT DAM BREACH
Tony L. Wahl
Bureau of Reclamation – Denver, CO
ASDSO 2009 2
What is CEATI International?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”
ASDSO 2009 4
Interest GroupsInterest 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
ASDSO 2009 5
Dam Safety Interest Group (DSIG)Dam Safety Interest Group (DSIG)
» Areas of Interest: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
ASDSO 2009 6
Dam-Break Modeling: Recent HistoryDam-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
ASDSO 2009 7
Modeling Breach DevelopmentModeling 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”
ASDSO 2009 8
Physically-Based Breach ModelingPhysically-Based Breach Modeling
» Dr. Danny Fread recognizedneed for modeling erosionprocesses to obtain betterresults in near field
» May 18, 1980 eruption ofMt. St. Helens createdlandslide dam on Toutle River
» Dr. Fread developed NWS-BREACH model to analyze possible breach of this dam
» NWS-BREACH released to public in 1988
ASDSO 2009 9
Modeling Developments in 1990sModeling 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
ASDSO 2009 10
CEATI Dam Erosion and Breach ProjectCEATI 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 1980s1. Regression models for predicting peak outflow
2. Regression models for predicting breach parameters
3. Breach erosion models, such as NWS-BREACH
ASDSO 2009 11
Shortcomings of Available MethodsShortcomings 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
ASDSO 2009 12
Large-Scale Physical TestsLarge-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
ASDSO 2009 13
Project ObjectivesProject 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.
ASDSO 2009 14
ParticipantsParticipants» 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
ASDSO 2009 15
Project OverviewProject 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
ASDSO 2009 16
Tasks in Phase 2Tasks in Phase 2
1. Evaluation of three numerical breach models– SIMBA (ARS)
– HR-BREACH (HR Wallingford)
– FIREBIRD BREACH (Montreal Polytechnic)
2. Evaluation of methods for quantifying erodibility of cohesive embankment materials
leading to…
3. Integration of breach modeling technologies into HEC-RAS dynamic routing model
4. Potential efforts to facilitate integration with commercial flood routing models
ASDSO 2009 17
The Models: Common CharacteristicsThe 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
ASDSO 2009 18
The ModelsThe 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 process1. surface erosion leading to development of a headcut on the
downstream face of the embankment
2. headcut advance through the crest to initiate the breach
3. breach formation as the headcut advances into the reservoir
4. 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.
ASDSO 2009 19
The ModelsThe 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
ASDSO 2009 20
The ModelsThe 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
ASDSO 2009 21
Model EvaluationModel Evaluation
» Evaluate model performance against large-scale laboratory tests and case-study data– 2 ARS outdoor laboratory tests
2.3-m high homogeneous dams, overtopping1 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)
ASDSO 2009 22
ARS TestsARS 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 ofmaterials
» Constant inflow, smallreservoir
Hanson, G.J., Cook, K.R., Hunt, S. 2005. Physical modeling of overtopping erosion and breach formation of cohesive embankments. Transactions of the ASAE, 48(5):1783-1794.
ASDSO 2009 23
Norwegian Tests - Part of IMPACTNorwegian 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 peakinflow
– Flow regulation not attempted forgravel dam test
– Inflow was too little, too latefor zoned test
ASDSO 2009 24
Oros Dam (Brazil, 1960)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
ASDSO 2009 25
ASDSO 2009 26
Oros Dam - SummaryOros 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
ASDSO 2009 27
Banqiao Dam (China, 1975)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
ASDSO 2009 28
Evaluation CriteriaEvaluation Criteria
» Evaluate performance using– 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
ASDSO 2009 29
Current StatusCurrent 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
ASDSO 2009 30
ChallengesChallenges» 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
CEATI Information:Chris Hayes
Director, Business Development1155 Metcalfe St., Suite 1120
Montreal, QC H3B 2V6
(514) 866-5377 | www.ceatech.ca | [email protected]