Evaluation of new models for simulating embankment dam breach
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EVALUATION OF NEW MODELS FOR SIMULATING EMBANKMENT DAM BREACH. Tony L. Wahl Bureau of Reclamation – Denver, CO. What is CEATI International?. Since 1891, the Canadian Electrical Association (CEA) has been the forum for electrical business in Canada

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Tony L. Wahl

Bureau of Reclamation – Denver, CO

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What is CEATI International? BREACH

  • 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

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Interest Groups BREACH

  • 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

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Dam Safety Interest Group (DSIG) BREACH

  • 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 extremefloods

    • Emergency preparedness

    • Testing of embedded dam anchors

ASDSO 2009

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Dam-Break Modeling: Recent History BREACH

  • 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

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Modeling Breach Development BREACH

  • 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

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Physically-Based Breach Modeling BREACH

  • 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

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Modeling Developments in 1990s BREACH

  • Flood routing capabilities much improved

    • 2D modeling

    • Integration with GIS to improve consequence analysis

  • Little change in breach modeling during this time

ASDSO 2009

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CEATI Dam Erosion and Breach Project BREACH

  • 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

ASDSO 2009

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Shortcomings of Available Methods BREACH

  • 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

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Large-Scale Physical Tests BREACH

  • 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

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Project Objectives BREACH

  • 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

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Participants BREACH

  • 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

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Project Overview BREACH

  • 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

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Tasks in Phase 2 BREACH

  • 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

ASDSO 2009

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The Models: Common Characteristics BREACH

  • 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

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The Models BREACH

  • 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.

ASDSO 2009

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The Models BREACH

  • 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

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The Models BREACH

  • 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

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Model Evaluation BREACH

  • 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)

ASDSO 2009

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  • 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 magnitudedifference 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

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Norwegian Tests - Part of IMPACT BREACH

  • 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 arrivedshortly 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

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Oros Dam (Brazil, 1960) BREACH

  • 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

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Oros Dam - Summary BREACH

  • 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

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Banqiao Dam (China, 1975) BREACH

  • 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

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Evaluation Criteria BREACH

  • 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

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Current Status BREACH

  • 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

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Challenges BREACH

  • 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

ASDSO 2009

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CEATI Information: BREACHChris HayesDirector, Business Development1155 Metcalfe St., Suite 1120Montreal, QC H3B 2V6 (514) 866-5377 | www.ceatech.ca | info@ceatech.ca