PROCEEDINGS

FEMA WORKSHOP, JUNE 26-28, 2001

OKLAHOMA CITY, OK

ISSUES, RESOLUTIONS, AND RESEARCH

NEEDS RELATED TO EMBANKMENT DAM

FAILURE ANALYSIS

US DEPARTMENT OF AGRICULTURE

Acknowledgements

The project proposal and scope of work were developed and submitted by Dr.

Greg Hanson and Darrel Temple of the ARS as a joint effort with Bill Irwin of the

NRCS. The steering committee which helped organize the Workshop on Issues,

Resolutions, and Research Needs Related to Embankment Dam Failure Analysis

included the following members:

Dr. Greg Hanson, USDA-ARS

Bill Irwin, USDA-NRCS

Darrel Temple, USDA-ARS

Wayne Graham, USBR

Charles Pearre, USACE

Ed Fiegle, GA Dept. of Natural Resources

Terry Hampton, Gannett Fleming

Brandee Hancock, and Ruth Treat of the ARS-PSWCRL served as the

administrative staff in organizing the meeting, corresponding with participants,

and making local arrangements. Kevin Cook and Brandee Hancock assisted in

organizing the proceedings. Nate Snorteland of the U.S. Bureau of Reclamation

served as the facilitator and therefore led all group discussions. Nate Snorteland

contributed heavily to the “Dam Failure Analysis and Research Development

Topics,” section of the proceedings.

PROJECT SPONSOR

Federal Emergency Management Agency

National Dam Safety Program

Research Subcommittee, David Achterberg, (USBR), Chair

500 C Street SW

Washington, DC 20047

PROJECT COORDINATOR

USDA-ARS-PSWCRL

1301 N. Western

Stillwater, OK 74075

TABLE OF CONTENTS

 Page #

OVERVIEW.................................................................................. 1-1

OUTLINE OF THE WORKSHOP AGENDA........................................ 2-1

SUMMARY OF WORKSHOP PRESENTATIONS................................. 3-1

DAM FAILURE ANALYSIS AND RESEARCH DEVELOPMENT TOPICS. 4-1

APPENDICES

A AGENDA

B PRESENTATIONS

C PARTICIPANTS

1-1

1

OVERVIEW

________________________________________________________________________

This workshop is part of a series of workshops being sponsored by the Federal

Emergency Management Agency (FEMA) and administered by the ARS/NRCS of the

USDA. The workshop was a 3-day workshop on “Issues, Resolutions, and Research

Needs Related to Embankment Dam Failure Analysis,” held in Oklahoma City, OK,

June 26-28th, 2001. The product of this workshop is the written report documenting the

results of the workshop. The report will be included in FEMA’s National Dam Safety

Program Act Report Series.

The workshop consisted of convening and facilitating a group of experts with respect to

dam safety associated with embankment dam failure analysis. The objectives of this

work were:

1. To document, in the form of a final report, a state of practice concerning

embankment dam failure analysis;

2. To identify short-term (immediate) and long-term research needs of the

federal and non-federal dam safety community; and

3. To recommend a course of action to address these needs.

By research needs we understood the interest of the National Dam Safety Program to

encompass both short-term (i.e. immediate) and long-term research including areas of

development and technology transfer. These may include such areas as the following:

a vision for the future of computer modeling of embankment breaching processes and

flood routing, basic research of embankment overtopping and breach processes, and

tools to conduct forensic studies. There were 14 areas of research identified and

prioritized by workshop participants. The workshop was a successful undertaking that

produced open communication among a wide range of experts in the field and identified

research and development opportunities that could significantly improve the state-ofthe-practice in the field.

2-1

2

OUTLINE OF THE WORKSHOP AGENDA

________________________________________________________________

A group of 35 individuals were assembled for a three-day workshop on Issues,

Resolutions, and Research Needs Related to Dam Failure Analyses. The group

consisted of invited experts, facilitators, and the FEMA Project Officer for the workshop.

The workshop participants were selected to provide broad representation of individuals

in the topic area. Participants included 15 representatives of 7 different U.S. federal

agencies, 5 representatives from 5 different state dam safety agencies, 9

representatives of 8 different consulting companies, 3 university professors, and 1

representative from a hydropower organization. The group included individuals from 15

different U.S. states and 4 other countries (Canada, United Kingdom, Norway, and

Finland).

The first day and a half was devoted to exchange of information through presentations

by the participants and discussions of embankment dam failures.

Presentations included:

1. Classification and case histories, including the human and economic

consequences, of dam failure.

2. Overview of presently used tools for assessing risk, time to failure, dam

failure processes, outflow hydrograph, and flood routing.

3. State assessment criteria, experience, and case examples.

A tour of the ARS Hydraulic Unit research facilities at Lake Carl Blackwell, OK was

conducted in the afternoon of the second day. The tour included research projects

covering:

1. Apparatus and procedure for measuring erodibility of cohesive materials in

concentrated flow environments (i.e. earthen spillways, streambeds,

streambanks, and embankments).

2. Riffle-pool rock chutes model for a specific application of stream stabilization

on Sugar Creek, OK.

3. Performance studies of vegetated and bare earth on steep channels.

4. Embankment breach discharge model study.

5. Large-scale embankment breach failure study.
2-2

The first half of the third day was devoted to presentations and discussions on research

and new technology related to risk assessment, embankment dam failure, and flood

routing. The afternoon of the third day was devoted to discussions prioritizing research

needs.
3-1

3

SUMMARY OF WORKSHOP PRESENTATIONS

________________________________________________________________

The broad scope of the workshop presentations demonstrates the wide range of

perspectives represented and the importance of the subject to the various entities

involved. The material presented covered the spectrum from addressing concerns with

developing solutions for specific immediate problems to identification of knowledge

deficiencies that impede development of generalized tools, and from concerns related to

the breach process itself to those related to the impacts of the resulting floodwave

downstream. However, the presenters did an excellent job of focusing on the goals of

the workshop and, together, these presentations present a relatively clear picture of the

present state of the science in this area. This section provides a very brief overview of

the material presented in the workshop, those presentations that included papers are

referred by number to appendix B of this report.

1.1 Dam Failures

3.1.1 Classification and Case Histories of Dam Failures – Martin McCann,

National Performance of Dams Program

This presentation focused on an overview of the National Performance of Dams

Program (NPDP). The NPDP acts as a public library of dam performance. The NPDP

has several priorities: facilitating reporting of dam performance, providing access to

basic information, data compilation and presentation, and research. Dr McCann gave

an incident summary for the last 10 years related to total number of incidents, type of

dam, type of incident, hazard classification, and height of dam. Dr. McCann also

discussed the challenges in data collection and archiving of dam incidents/failures. The

information is a resource to support dam engineering, dam safety, and public policy.

3.1.2 Human and Economic Consequences of Dam Failure- Wayne Graham,

USBR (B-1)

Mr. Graham’s presentation focused on 13 dam failures in the U.S. Included was every

U.S. dam failure that caused more than 50 fatalities. The presentation included a

discussion of dam characteristics, cause of dam failure, dam failure warning (if any),

evacuation, and human and economic losses. Loss of life from dam failure can vary

widely. In 1889, the 72-foot high earthfill South Fork Dam near Johnstown, PA. failed,

killing about 2,200 people. This can be contrasted to the period, 1985 to 1994, when

hundreds of smaller dams failed in the U.S. and less than 2% of these failures caused

fatalities. Many of the dam failure images in Mr. Graham’s presentation are proprietary

and not in the public domain. As such, dam failure images used in the presentation are

not included in these proceedings.
3-2

1.2 Present Practice for Predicting Dam Failures

1.2.1 Will a Dam Failure Occur?- Risk Assessment USBR Perspective. –

Bruce Muller, USBR (B-2)

Mr. Muller presented that the Bureau of Reclamation is developing a program to: 1)

quantify the risk of storing water, 2) monitor aspects of performance that indicate

potential for some form of failure mode to develop, and 3) take action to reduce the

likelihood of dam failure. The USBR risk management responsibility comes out of the

Dam Safety Act of 1978 which authorizes the Department of Interior to construct,

restore, operate, maintain, new or modified features of their dams for safety purposes.

1.2.2 Will a Dam Failure Occur?- Risk Assessment USACE Perspective. –

David Moser, USACE (B-3)

Mr. Moser discussed why the U.S. Army Corps of Engineers is interested in risk

assessment and what their objectives are. The Corps of Engineers has approximately

570 dams, 64% of their dams are over 30 years old and 28% are over 50 years old.

Approximately 10% of these dams are categorized as hydrologically or seismically

deficient based on present Corps Criteria. The cost to fix these deficiencies is several

billions of dollars. The Corps traditional approach to handling risk assessment has been

meeting standards and criteria (i.e. design based on Probable Maximum Flood).

Because of the current interest around the world, the Corps Major Rehabilitation

Program, and a need for consistency with other agencies the Corps has a renewed

interest in risk analysis for dam safety. Their objective is to develop methodologies,

frameworks, and software tools necessary for the USACE to proactively manage the

overall level of human and economic risk from their inventory of dams.

1.2.3 Methods Based on Case Study Database. – Tony Wahl, USBR (B-4)

Mr. Wahl focused his discussion on embankment dam breach parameter predictions

based on case studies and the uncertainty of these parameters. This discussion was

based on an evaluation of a database of 108 dam failures. The breach parameters

evaluated were breach width, failure time, and peak outflow. The uncertainty of breach

parameter predictions is very large. Four equations were evaluated for breach width,

five equations were evaluated for failure time, and 13 equations were evaluated for

peak outflow. There is room for improvement in determining these breach parameters

and the uncertainty.

1.2.4 Directions for Dam-Breach Modeling/Flood Routing – Danny Fread

(Retired National Weather Service). (B-5)

Dr. Fread concentrated his discussion on models he has been involved with at the

National Weather Service as well as other types of models that are used in dam-breach

prediction and flood routing. The dam-breach modeling involves the development of

the breach as well as the peak outflow that would be used in flood routing downstream.
3-3

He also discussed research needs to improve these models such as; 1) prototype

embankment experiments; 2) Manning’s n and debris effects; and 3) risk or probabilistic

approaches to dam failures.

1.2.5 RESCDAM-Project – Mikko Huokuna, Finnish Environment Institute (B6)

Mr. Huokuna’s presentation focused on Finland’s dams and reservoirs and the

RESCDAM project. Finland’s dams and reservoirs have been constructed mainly for

flood control, hydroelectric power production, water supply, recreation, and fish culture,

as well as storing waste detrimental to health or the environment. At present, there are

55 large dams in Finland and based on Finnish dam safety legislation 36 dams require

a rescue action plan. The RESCDAM project is meant to improve the dam safety

sector. The activities of the RESCDAM project embrace risk analysis, dam-break flood

analysis, and rescue action improvement. Recommendations for further research

based on the dam break hazard analysis of the RESCDAM project include

determination of breach formation, determination of roughness coefficients for the

discharge channel, and the effect of debris and urban areas on floodwave propagation.

1.2.6 Hazard Classification – Alton Davis, Engineering Consultants Inc. (B-7)

Mr. Davis presented and discussed “FEMA Guidelines for Dam Safety: Hazard Potential

Classification System for Dams.” The FEMA guidelines specified three hazard potential

classifications: 1) low hazard potential, 2) significant hazard potential, and 3) high

hazard potential. The definitions of each hazard potential and selection criteria were

provided in the presentation. Factors such as loss of human life, economic losses,

lifeline disruption, and environmental damage affect classification.

1.3 Current Practice

3.3.1-5 State assessment Criteria, Experience and Case Examples –

John Ritchey, Dam Safety Section State of New Jersey (B-8)

Ed Fiegle, Dam Safety Section State of Georgia (B-9)

Matt Lindon, Dam Safety Section State of Utah (B-10)

David Gutierrez, Dam Safety Section State of California

Cecil Bearden, Dam Safety Section State of Oklahoma.

These presentations focused on state assessment criteria, experience and case

examples in relationship to dam failure analysis. This not only included their states but

also information related to states in their region. Current assessment criteria practiced

at the state level for dam failure analyses is variable. Several states conduct in house

assessments, some states require the dam owner to hire a licensed professional, and

some allow the dam owner to conduct the assessments. The analyses are preformed

for the purpose of determining hazard classifications, spillway design floods, flood

zoning, and for establishing inundation areas for use in Emergency Action Plans. The

methods accepted for dam failure analyses vary from state to state. Typical models that
3-4

are used for conducting dam failure analysis and downstream flood routing are HEC-1,

HEC-RAS, DAMBRK, FLDWAV, NWS Simplified DAMBRK, NRCS’s TR-61, WSP2

Hydraulics, and the TR-66 Simplified Dam Breach Routing Procedure. There were

several research needs mentioned in these presentations including; 1) establishment of

a forensic team, 2) refinement of breach parameters, 3) training on present technology,

4) aids for determining Manning’s n values, and 5) refining and understanding actual

failure processes.

3.3.6-9 Federal Assessment Criteria, Experience, and Case ExamplesWayne Graham, USBR (B-12)

Bill Irwin, NRCS (B-13)

James Evans and Michael Davis, FERC (B-14)

These presentations focused on the federal assessment criteria, experience, and case

examples. The USBR, NRCS, and FERC each have a portfolio of dams that they have

ownership of, partnership in, or regulatory responsibility over. These agencies conduct

embankment dam failure analysis and inundation mapping to assign hazard

classification, develop evacuation plans, assess risk, and evaluate rehabilitation needs.

The criteria are agency specific with a recognized need for inter-agency coordination.

There are several recognized uncertainties that require more investigation including; 1)

failure analysis for different types of failure (i.e. overtopping, piping, and seismic), 2)

breach characteristics, 3) Manning’s roughness characteristics, 4) allowable

overtopping, 5) consequences of failure, and 5) quantifying risk.

3.3.10-13 Owners and Consultants Assessment Criteria, Experience, and Case

ExamplesDerek Sakamoto, BC Hydro (B-15)

Ellen Faulkner, Mead & Hunt Inc. (B-16)

Catalino Cecilio, Catalino B. Cecilio Consultants (B-17)

John Rutledge, Freeze and Nichols.

Mr. Sakamoto, representing BC Hydro, presented an overview of the Inundation

Consequences Program for assessing the consequences resulting from a potential dam

breach. The key focus of this program is to provide an improved tool for safety

management planning. This program will provide decision makers with realistic

characterizations of the various situations. It will provide investigators with the ability to

determine effects of parameters such as dam breach scenarios and temporal variations

related to flood wave propagation. This will also provide a powerful communication tool.

Engineering consultants throughout the United States perform dam safety assessments,

which must be responsive to the needs of dam owners and to the requirements of state

and federal regulatory agencies. The purpose of these studies is hazard classification,

emergency action plan, or design flood assessment. Each dam failure study involves

identification of a critical, plausible mode of failure and the selection of specific

parameters, which define the severity of failure. These parameters include ultimate

dimensions of the breach, time required to attain dimensions, and the depth of

overtopping required to initiate failure. The choice of these parameters is influenced by
3-5

what is reasonable to the engineer and also acceptable to the regulatory agency. The

models used for dam safety assessment are based on what the regulatory agencies

consider acceptable.

3.4 Research and New Technology

3.4.1 Risk Assessment Research- David Bowles, Utah State University

Dr. Bowles discussed the ASDSO/FEMA Specialty Workshop on Risk Assessment for

Dams and some requirements for failure modes analyses for use in Risk Assessment.

The workshop scope was to assess state of practice of risk assessment, technology

transfer/training, and risk assessment needs. The outcomes of the workshop followed

four major application areas in current risk assessment practice: failure modes

identification, index prioritization, portfolio risk assessment, and detailed quantitative risk

assessment.

Dr. Bowles also discussed requirements for failure mode analysis for use in risk

assessment which included: understanding how the dam will perform under various

stresses, improving capability of predicting failure, incorporation of uncertainties, and

application over a range of site specific cases.

3.4.2 Research at CSU Related to Design Flood Impacts on Evaluating Dam

Failure Mechanisms - Steve Abt, Colorado State University (B-18)

Dr. Abt’s presentation focused on current dam safety research efforts being conducted

at Colorado State University. The research at CSU has focused on dam embankment

protection including: hydraulic design of stepped spillways (i.e. roller compacted

concrete), hydraulic analysis of articulated concrete blocks, and design criteria for

rounded rock riprap.

3.4.3 Limited Overtopping, Embankment Breach, and Discharge - Darrel

Temple and Greg Hanson, USDA-ARS (B-19)

Mr. Temple and Dr. Hanson discussed research being conducted by the ARS Plant

Science and Water Conservation Laboratory on overtopping of vegetated

embankments. This research includes limited overtopping of grassed embankments,

breach processes, and breach discharge. Long duration flow tests were conducted on

steep vegetated and non-vegetated slopes. The embankment overtopping breach tests

have been conducted on soil materials ranging from non-plastic sandy material to a

plastic clay material. The vegetal cover and soil materials have a major impact on the

timing of breach processes.
3-6

3.4.4 Dam Break Routing - Michael Gee, USACE (B-20)

Dr. Gee gave an overview of HEC models for dam break flood routing. The USACE

Hydrologic Engineering Center provides a program of research, training, and technical

assistance for hydrologic engineering and planning analysis. The future additions to the

suite of HEC models includes dam and levee breaching (i.e. overtopping, and piping).

The HEC-RAS 3.1 release will be available fall of 2001. Dr. Gee presented some

examples of floodwave routing through a river system and the graphic output from HECRAS computations.

3.4.5 Overview of CADAM and Research - Mark Morris, HR Wallingford. (B-21)

Mr. Morris provided an overview of the CADAM Concerted Action Project and the

IMPACT research project. Both of these projects have been funded by the European

Commission. The CADAM project ran between Feb 98 and Jan 2000 with the aim of

reviewing dambreak modeling codes and practice, from basics to application. The

topics covered included analysis and modeling of flood wave propagation, breaching of

embankments, and dambreak sediment effects. The program of study was such that

the performance of modeling codes were evaluated against progressively more complex

conditions.

The IMPACT project focuses research in a number of key areas that were identified

during the CADAM project as contributing to uncertainty in dambreak and extreme flood

predictions. Research areas include embankment breach, flood propagation, and

sediment movement.

3.4.6 Embankment Breach Research - Kjetil Arne Vaskinn, Statkraaft Groner.

(B-22)

Mr. Vaskinn discussed embankment breach research in Norway. The issue of dam

safety has become more and more important in Norway during the last years and much

money has been spent to increase the safety level of dams. Dam break analysis is

performed in Norway to assess the consequences of dambreak and is a motivating

factor for the dam safety work. Norway has started a new research project focusing on

improving the knowledge in this field. The objectives of this project are to improve the

knowledge of rock fill dams exposed to leakage and to gain knowledge on the

development of a breach. There is overlap between the Norway project and that of

IMPACT (discussed by Mr. Morris) so they will be coordinating their research efforts.
4-1

4

DAM FAILURE ANALYSIS RESEARCH AND DEVELOPMENT

TOPICS

________________________________________________________________

Process

Potential research and development ideas were compiled in a brainstorming session

with the workshop participants divided into several small groups. The ideas from all the

groups were then listed on flip charts and posted on the wall. As a group, the

participants grouped and merged the ideas where possible. After all the topics were

listed, the participants were asked to cast votes using three different criteria: Probability

of Success, Value, and Cost. The aggregate score for each topic is based on the

arithmetic sum of votes that topic received in each of the three voting categories.

Each participant was given three sets of 10 colored stickers with which to vote. Each

participant was allowed to cast more than one vote per listed topic as long as the

participant’s total number of votes in each category did not exceed 10. The entire list of

research and development topics and the results of the voting are shown below in Table

1.

TABLE 1 – RESEARCH AND DEVELOPMENT TOPICS AND VOTE TOTALS

NUMBER OF VOTES

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S)

Probability of

Success Value Cost1

1

Update, Revise, and Disseminate the historic data set /

database of dam failures. The data set should include

failure information, flood information, and embankment

properties.

16 16 6

2

Develop forensic guidelines and standards for dam

safety experts to use when reporting dam failures or

dam incidents. Create a forensic team that would be

able to collect and disseminate valuable forensic data.

16 24 14

3

Produce an expert-level video of Danny Fread along

the lines of the previous ICODS videos from Jim

Mitchell, Don Deere, etc.

13 7 9

4

Identify critical parameters for different types of failure

modes. 5 3 6
4-2

NUMBER OF VOTES

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S)

Probability of

Success Value Cost1

5

Perform basic physical research to model different dam

parameters such as soil properties, scaling effects, etc.

with the intent to verify the ability to model actual dam

failure characteristics and extend dam failure

knowledge using scale models.

15 21 4

6

Update the regression equations used to develop the

input data used in dam breach and flood routing

models.

2 7 11

7

Develop better computer-based predictive models.

This would preferably build upon existing technology

rather than developing new software.

14 13 7

8

Develop a process that would be able to integrate dam

breach and flood routing information into an early

warning system.

0 0 0

9

Make available hands-on end-user training for breach

and flood routing modeling that is available to

government agencies and regulators, public entities

(such as dam owners), and private consultants.

11 6 13

10 Validate and test existing dam breach and flood routing

models using available dam failure information. 0 1 1

11

Develop a method to combine deterministic and

probabilistic dam failure analyses including the

probability of occurrence and probable breach location.

5 2 3

12

Using physical research data, develop guidance for the

selection of breach parameters used during breach

modeling.

16 20 16

13 Send U.S. representatives to cooperate with EU dam

failure analysis activities. 10 7 13

14 Lobby the NSF to fund basic dam failure research. 0 2 2

1A higher number in the cost category indicates a lower cost.
4-3

The break down of the individual topics by probability of success is shown if Figure 1.

and Table 2.

1 - Assimilate historic

 data set

2 - Forensic standards

3 - Produce Danny 

 Fread video

4 - Critical failure

 mode parameters

5 - Basic research

6 - Update regression

 equations

7 - Develop improved

 computer models

8 - Integrate models with

 early warning systems

9 - Develop hands-on

 end-user training

10-Validate existing 

 models

11-Combine deterministic/

 probabilistic analysis

12-Breach parameter 

 guidance

13-U.S. reps @

 European activities

14-Lobby NSF

Figure 1. Probability of success 

Number of participant votes

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Research/Development Topics

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

TOPICS

TABLE 2 – RESEARCH TOPICS RANKED BY PROBABILITY OF SUCCESS

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

1

Update, Revise, and Disseminate the historic data set / database.

The data set should include failure information, flood information, and

embankment properties.

16

2

Develop forensic guidelines and standards for dam safety experts to

use when reporting dam failures or dam incidents. Create a forensic

team that would be able to collect and disseminate valuable forensic

data.

16

12 Using physical research data, develop guidance for the selection of

breach parameters used during breach modeling. 16
4-4

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

5

Perform basic physical research to model different dam parameters

such as soil properties, scaling effects, etc. with the intent to verify

the ability to model actual dam failure characteristics and extend dam

failure knowledge using scale models.

15

7

Develop better computer-based predictive models. Preferably build

upon existing technology rather than developing new software. 14

3

Produce an expert-level video of Danny Fread along the lines of the

previous ICODS videos from Jim Mitchell, Don Deere, etc. 13

9

Make available hands-on end-user training for breach and flood

routing modeling that is available to government agencies and

regulators, public entities (such as dam owners), and private

consultants.

11

13 Send U.S. representatives to cooperate with EU dam failure analysis

activities. 10

4 Identify critical parameters for different types of failure modes 5

11

Develop a method to combine deterministic and probabilistic dam

failure analyses including the probability of occurrence and probable

breach location.

5

6

Update the regression equations used to develop the input data used

in dam breach and flood routing models. 2

8

Develop a process that would be able to integrate dam breach and

flood routing information into an early warning system. 0

10 Validate and test existing dam breach and flood routing models using

available dam failure information. 0

14 Lobby the NSF to fund basic dam failure research. 0
4-5

The break down of the individual topics by value of the item is shown if Figure 2. and

Table 3.

Figure 2. Value of research topic 

Number of participant votes

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Research/Development Topics

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

TOPIC

1 - Assimilate historic

 data set

2 - Forensic standards

3 - Produce Danny 

 Fread video

4 - Critical failure

 mode parameters

5 - Basic research

6 - Update regression

 equations

7 - Develop improved

 computer models

8 - Integrate models with

 early warning systems

9 - Develop hands-on

 end-user training

10 - Validate existing 

 models

11 - Combine deterministic/

 probabilistic analysis

12 - Breach parameter 

 guidance

13 - U.S. reps @

 European activities

14 - Lobby NSF

TABLE 3 – RESEARCH TOPICS RANKED BY VALUE

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

2

Develop forensic guidelines and standards for dam safety experts to

use when reporting dam failures or dam incidents. Create a forensic

team that would be able to collect and disseminate valuable forensic

data.

24

5

Perform basic physical research to model different dam parameters

such as soil properties, scaling effects, etc. with the intent to verify

the ability to model actual dam failure characteristics and extend dam

failure knowledge using scale models.

21
4-6

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

12 Using physical research data, develop guidance for the selection of

breach parameters used during breach modeling. 20

1

Update, Revise, and Disseminate the historic data set / database.

The data set should include failure information, flood information, and

embankment properties.

16

7

Develop better computer-based predictive models. Preferably build

upon existing technology rather than developing new software. 13

3

Produce an expert-level video of Danny Fread along the lines of the

previous ICODS videos from Jim Mitchell, Don Deere, etc. 7

6

Update the regression equations used to develop the input data used

in dam breach and flood routing models. 7

13 Send U.S. representatives to cooperate with EU dam failure analysis

activities. 7

9

Make available hands-on end-user training for breach and flood

routing modeling that is available to government agencies and

regulators, public entities (such as dam owners), and private

consultants.

6

4 Identify critical parameters for different types of failure modes 3

11

Develop a method to combine deterministic and probabilistic dam

failure analyses including the probability of occurrence and probable

breach location.

2

14 Lobby the NSF to fund basic dam failure research. 2

10 Validate and test existing dam breach and flood routing models using

available dam failure information. 1
4-7

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

8

Develop a process that would be able to integrate dam breach and

flood routing information into an early warning system. 0

Figure 3. Cost of research topic (the more votes the lower the cost).

Number of participant votes

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Research/Development Topics

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 Cost 

1 - Assimilate historic

 data set

2 - Forensic standards

3 - Produce Danny 

 Fread video

4 - Critical failure

 mode parameters

5 - Basic research

6 - Update regression

 equations

7 - Develop improved

 computer models

8 - Integrate models with

 early warning systems

9 - Develop hands-on

 end-user training

10-Validate existing 

 models

11-Combine deterministic/

 probabilistic analysis

12-Breach parameter 

 guidance

13-U.S. reps @

 European activities

14-Lobby NSF

Number of participant votes

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

Research/Development Topics

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

TOPICS

TABLE 4 – RESEARCH TOPICS RANKED BY COST

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES
4-8

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

12 Using physical research data, develop guidance for the selection of

breach parameters used during breach modeling. 16

2

Develop forensic guidelines and standards for dam safety experts to

use when reporting dam failures or dam incidents. Create a forensic

team that would be able to collect and disseminate valuable forensic

data.

14

9

Make available hands-on end-user training for breach and flood

routing modeling that is available to government agencies and

regulators, public entities (such as dam owners), and private

consultants.

13

13 Send U.S. representatives to cooperate with EU dam failure analysis

activities. 13

6

Update the regression equations used to develop the input data used

in dam breach and flood routing models. 11

3

Produce an expert-level video of Danny Fread along the lines of the

previous ICODS videos from Jim Mitchell, Don Deere, etc. 9

7

Develop better computer-based predictive models. Preferably build

upon existing technology rather than developing new software. 7

1

Update, Revise, and Disseminate the historic data set / database.

The data set should include failure information, flood information, and

embankment properties.

6

4 Identify critical parameters for different types of failure modes 6

5

Perform basic physical research to model different dam parameters

such as soil properties, scaling effects, etc. with the intent to verify

the ability to model actual dam failure characteristics and extend dam

failure knowledge using scale models.

4

11

Develop a method to combine deterministic and probabilistic dam

failure analyses including the probability of occurrence and probable

breach location.

3
4-9

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) NUMBER OF VOTES

14 Lobby the NSF to fund basic dam failure research. 2

10 Validate and test existing dam breach and flood routing models using

available dam failure information. 1

8

Develop a process that would be able to integrate dam breach and

flood routing information into an early warning system. 0

Prioritization of Research Topics

After the votes were tabulated, each research topic was ranked according to the

aggregate total of votes cast. The rank of each topic in Table 5 and Figure 4 is a

reflection of the combination of value, cost, and probability of success, based on equal

weighting, as determined by the participants. Based on all the input by the participants,

it is the author’s opinion that the following topics were the leading research and

development ideas identified in the workshop.

1. Develop forensic guidelines and standards for dam safety representatives and

experts to use when reporting dam failures or dam incidents. Create a forensic

team that would be able to collect and disseminate valuable forensic data. (Topic

#2)

2. Using physical research data, develop guidance for the selection of breach

parameters used during breach modeling. (Topic #12)

3. Perform basic physical research to model different dam parameters such as soil

properties, scaling effects, etc. with the intent to verify the ability to model actual

dam failure characteristics and extend dam failure knowledge using scale

models. (Topic #5)

4. Update, revise, and disseminate information in the historic data set / database.

The data set should include failure information, flood information, and

embankment properties. (Topic #1)

5. Develop better computer-based predictive models. Preferably these models

would build upon existing technology rather than developing new software.

(Topic #7)
4-10

6. Make available hands-on end-user training for breach and flood routing modeling

which would be available to government agencies and regulators, public entities

(such as dam owners), and private consultants. (Topic #9)

7. Record an expert-level video of Danny Fread along the lines of the previous

ICODS videos from Jim Mitchell, Don Deere, etc. (Topic #3)

8. Send U.S. representatives to cooperate with EU dam failure analysis activities.

(Topic #13)

The participants ranked the previous eight topics the highest overall when the three

different criteria were averaged. The listing of the top 8 here is purely an arbitrary cutoff by the author.

Overall, there were fewer votes cast for cost than for the other two ranking criteria. This

is probably due to the fact that cost is more difficult to estimate than the value or

probability of success. Because of this, the topics above may be in a slightly different

order if cost is not considered as a ranking criterion.

It is interesting to note that only fourteen topics were identified during the workshop.

Previous workshops on different subjects identified a substantial number of topics, and

then their ranking method narrowed their priority list down to a manageable number.

This is not necessarily an indication that there is less to accomplish in the area of dam

failure analysis, it is more an indication that this particular workshop attempted to

combine many tasks into one research topic. It is the author’s opinion that many of the

identified priority items can be broken down into several distinct sub-topics, and doing

so may make it easier to cooperatively address the research needs listed here.

In-order to identify short-term research versus long-term research items the votes cast

for cost were plotted against value for each of the 14 research topics and the plot was

broken into 4 quadrants (Figure 5). The upper left quadrant corresponded to those

items that the participants deemed were of high value and low cost to accomplish. They

were therefore labeled low hanging fruit and could be looked upon as short-term

research items. Items 2 and 12 fell into this quadrant, which were the top two in the

overall score. The upper right were items that based on relative comparison were high

value but also high cost. This quadrant was labeled ‘strategic plan’ indicating that the

items falling in this quadrant would be long-term research items. Items 1, 5, and 7 fell

into this quadrant. These items were also ranked 3 – 5 in the overall scoring. The

lower left quadrant was labeled ‘do later’ and based on relative comparisons contained

research items that were low cost and low value. Items 3, 6, 9 and 13 fell into this

quadrant, 3, 9 and 13 were also ranked 6 – 8 in the overall ranking. The lower right

quadrant was labeled ‘consider’ and based on relative comparisons contained research

items that were low cost and low value. Research items 4, 8, 10, 11, and 14 fell into

this quadrant. This comparison may be found useful in determining the most effective

use of limited resources.
4-11

TOPICS

1 - Assimilate historic

 data set

2 - Forensic standards

3 - Produce Danny 

 Fread video

4 - Critical failure

 mode parameters

5 - Basic research

6 - Update regression

 equations

7 - Develop improved

 computer models

8 - Integrate models with

 early warning systems

9 - Develop hands-on

 end-user training

10 - Validate existing 

 models

11 - Combine deterministic/

 probabilistic analysis

12 - Breach parameter 

 guidance

13 - U.S. reps @

 European activities

14 - Lobby NSF

Figure 4. Research topic ranked by aggregate score

 of probability of success, value, and cost.

Aggregate Score

0 10 20 30 40 50 60 70 80

Research/Development Topics

2 

12 

5 

1 

7 

9 

13 

3 

6 

4 

11 

14 

10 

8 

TABLE 5 – RESEARCH TOPICS RANKED BY AGGREGATE SCORE

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) AGGREGATE

SCORE RANK

2

Develop forensic guidelines and standards for dam safety experts to use when

reporting dam failures or dam incidents. Create a forensic team that would be

able to collect and disseminate valuable forensic data.

54 1

12 Using physical research data, develop guidance for the selection of breach

parameters used during breach modeling. 52 2

5

Perform basic physical research to model different dam parameters such as soil

properties, scaling effects, etc. with the intent to verify the ability to model actual

dam failure characteristics and extend dam failure knowledge using scale

models.

40 3
4-12

TOPIC

NUMBER RESEARCH / DEVELOPMENT TOPIC(S) AGGREGATESCORE RANK

1

Update, Revise, and Disseminate the historic data set / database. The data set

should include failure information, flood information, and embankment

properties.

38 4

7

Develop better computer-based predictive models. Preferably build upon

existing technology rather than developing new software. 34 5

9

Make available hands-on end-user training for breach and flood routing

modeling that is available to government agencies and regulators, public

entities (such as dam owners), and private consultants.

30 6

13 Send U.S. representatives to cooperate with EU dam failure analysis activities. 30 7

3

Record an expert-level video of Danny Frease along the lines of the ICODS

videos from Jim Mitchell, Don Deer, etc. 29 8

6

Update the regression equations used to develop the input data used in dam

breach and flood routing models. 20 9

4 Identify critical parameters for different types of failure modes 14 10

11 Develop a method to combine deterministic and probabilistic dam failure

analyses including the probability of occurrence and probable breach location. 10 11

14 Lobby the NSF to fund basic dam failure research. 4 12

10 Validate and test existing dam breach and flood routing models using available

dam failure information. 2 13

8

Develop a process that would be able to integrate dam breach and flood routing

information into an early warning system. 0 14
4-13

Figure 5. Decision quadrant.

COST

16 12 8 4 0

VALUE

0

5

10

15

20

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

Assimilate Historic

Data Set

1 

2 Forensic Standards

Produce Danny 

Fread Video

3 

Critical Failure

Mode Parameters

4 

5 Basic Research

Update regression

equations

6 

Develop Improved

Computer models

7 

Integrate models with

early warning systems

8 

Develop hands-on

end-user training

9 

Validate existing 

models

10 

Combine deterministic/

probabilistic analysis

11 

Breach Parameter

guidance

12 

U.S. reps @

European activities

13 

14 Lobby NSF

increasing

increasing

Low Hanging

Fruit

Strategic Plan

Do Later Consider

TOPICS

APPENDICES

A

AGENDA

________________________________________________________________________

AGENDA FOR WORKSHOP ON ISSUES, RESOLUTIONS, AND RESEARCH

 NEEDS RELATED TO DAM FAILURE ANALYSES

TUESDAY, June 26 

Morning

Introduction to Workshop Presenter

Introductions (Darrel Temple) 0730

Purpose (where workshop fits into scheme of workshops.) (Gene Zeizel) 0745

Dam Failures

Classification & Case Histories of Dam Failures (Martin McCann) 0800

Human and Economic Consequences of Dam Failure (Wayne Graham) 0830

Present Practice for Predicting Dam Failures

Overview of Presently Used tools

a. Will a Dam Failure Occur?

i. Risk Assessment – USBR Perspective (Bruce Muller) 0850

ii. Risk Assessment – USACE Perspective (David Moser) 0910

b. Time to Failure, Dam Failure Processes, Prediction of Dam Failure Discharge; Peak

Discharge and Outflow Hydrograph.

i. Methods Based on Case Study Database. (Tony Wahl) 0930

Break 1000

ii. Some Existing Capabilities and Future (Danny Fread) 1015

Directions for Dam-Breach Modeling/

Flood Routing

c. Ultimate Use of Peak Discharge and Outflow Hydrograph.

i. RESCDAM-project (Mikko Huokuna) 1045

ii. Hazard Classification (Al Davis, ICODS) 1115

Lunch Break 1145

Afternoon

Current Practice

State Assessment Criteria, Experience, and Case Example

New Jersey (John Ritchey) 1300

Georgia (Ed Fiegle) 1320

Utah (Matt Lindon) 1340

California (David Gutierrez) 1400

Oklahoma (Cecil Bearden) 1420

Break 1440

Federal Assessment Criteria, Experience, and Case Example

Bureau of Reclamation (Wayne Graham) 1500

NRCS (Bill Irwin) 1520

FERC (James Evans and Michael Davis) 1540
WEDNESDAY, June 27 

Morning

Current Practice (cont.)

Private Experience and Case Example

Owners

BC Hydro (Derek Sakamoto) 0740

Consultants

Mead &Hunt Inc. (Ellen Faulkner) 0810

Catalino B. Cecilio Consult. (Catlino Cecilio) 0830

Freeze & Nichols (John Rutledge) 0850

Break 0910-0930

Group Discussions (Nate Snorteland) 0930

Lunch Break 1200

Afternoon

Tour of ARS Hydraulic Laboratory 1300-1500

THURSDAY, June 28 

Morning

Research And New Technology

Risk Assessment Research (David Bowles) 0800

Overtopping and Breach Research

Research at CSU Related to Design Flood Impacts

on Evaluating Dam Failure Mechanisms (Steve Abt) 0830

Limited Overtopping, Embankment Breach

and Discharge (Temple and Hanson) 0900

Break 1000

Dam Break Routing (Michael Gee) 1020

Overview of CADAM and Research (Mark Morris) 1050

Embankment Breach Research (Kjetil Arne Vaskinn) 1120

Lunch Break 1150

Afternoon

Group Discussions (Nate Snorteland) 1330-1600
B

PRESENTATIONS

________________________________________________________________________

B-1

Human and Economic Consequences of Dam Failure

by

Wayne Graham, June 26, 2001

Dam Volume 

Dam Date and Time of Failure Height (ft) Released (ac-ft) Deat

Williamsburg Dam, MA May 16, 1874 at 7:20 a.m. 43 307 138

(Mill River Dam)

South Fork Dam, PA May 31, 1889 at 3:10 p.m. 72 11,500 2,20

(Johnstown Dam)

Walnut Grove Dam, AZ February 22, 1890 at 2 a.m. 110 60,000 abou

Austin Dam, PA September 30, 1911 at2 p.m. 50 850 78

St. Francis Dam, CA March 12-13, 1928 at midnight 188 38,000 420 

Castlewood Dam, CO August 2-3, 1933 at midnight 70 5,000 2 

Baldwin Hills Dam, CA December 14, 1963 at 3:38 p.m. 66 700 5 

Buffalo Creek, WV February 26, 1972 at 8 a.m. 46 404 125 

(Coal Waste Dam)

Black Hills Flood, SD June 9, 1972 at about 11 p.m. 20 700 ??? 

(Canyon Lake Dam) 

Teton Dam, ID June 5, 1976 at 11:57 a.m. 305 250,000 11 

Kelly Barnes Dam, GA November 6, 1977 at 1:20 a.m. 40 630 39 

Lawn Lake Dam, CO July 15, 1982 at 5:30 a.m. 26 674 3 

Timber Lake Dam, VA June 22, 1995 at 11 p.m. 33 1,449 2 
Dam name: Williamsburg Dam (Mill River Dam)

Location: on east branch Mill River, 3 miles north of Williamsburg, MA

Dam Characteristics:

Dam type: earthfill with masonry core wall

Dam height: 43 feet - at time of failure, water 4 feet below crest

Dam crest length: 600 feet

Reservoir volume: 307 acre-feet

Spillway: 33 feet wide

History of Dam:

Purpose: Increase water supply to mill operators

Dam completed: 1865, just months after civil war.

Dam failed: Saturday May 16, 1874 (9 years old) (20 minutes after initial slide, entire dam

failed)

Failure cause: Seepage carried away fill, embankment sliding, then collapse of masonry core

wall (internal erosion)

Details on Detection of Failure/Deciding to warn: After observing large slide, gatekeeper

(Cheney) rode 3 miles on horseback to Williamsburg. Another person living near dam ran 2

miles in 15 minutes after seeing the top of the dam break away.

Details on dissemination of warnings and technologies used: The gatekeeper (who had not

seen the large reservoir outflow) got to Williamsburg at about the time the dam broke. He

conferred with reservoir officials and changed his horse. Some overheard the conversation and a

milkman (Graves) traveled by horse and warned mills downstream. Many people received either

no warning or only a few minutes of warning.

Details on response to the warning:

Description of flooding resulting from dam failure: 20 to 40 foot high floodwave crumpled

brass, silk, and button mills, crushed boarding houses, farmhouses and barns.

The losses included: 138 dead, 750 people homeless

Location mileage flood arrived dead

Dam 0 7:20?

Williamsburg 3 7:40 57 flood 300 feet wide

Skinnerville 4 4

Haydenville 5 7:45 27

Leeds 7 8:05 50

Florence 10 8:35 0

All 138 fatalities occurred in the first 7 miles downstream from the dam.

Prepared by Wayne Graham
Dam name: South Fork (Johnstown)

Location: On South Fork Little Conemaugh River

Dam Characteristics:

Dam type: earthfill

Dam height: 72 feet

Dam crest length: feet

Reservoir volume: 11,500 acre-feet

Spillway:

History of Dam:

Purpose: Originally for supplying water to canal system; at time of failure was owned by South

Fork Hunting and Fishing Club of Pittsburgh.

Dam completed: 1853

Dam failed: May 31, 1889 about 3:10 pm (about 36 years old)

Failure cause: overtopping during an approximate 25-year storm (Drainage area of about 48 sq.

mi.)

Details on Detection of Failure/Deciding to warn:

People were at dam trying to prevent dam failure. Between 11:30 and noon the resident engineer,

on horseback, reached the town of South Fork (2 miles from dam) with a warning. Word was

telegraphed to Johnstown that dam was in danger.

Details on dissemination of warnings and technologies used:

Warnings were not widely disseminated.

Details on response to the warning:

• Little attention paid to warnings due to false alarms in prior years.

• At time of failure, Johnstown was inundated by up to 10 feet of floodwater.

Description of flooding resulting from dam failure: Floodwater reached Johnstown, mile 14,

about 1 hour after failure. Large number of buildings destroyed.

The losses included: about 2,209 fatalities; 20,000 people at risk.

All, or nearly all, of the fatalities occurred in the first 14 miles downstream from South Fork

Dam.

Prepared by Wayne Graham
Dam name: Walnut Grove Dam

Location: On the Hassayampa River, about 40 miles south of Prescott, AZ

Dam Characteristics:

Dam type: Rockfill

Dam height: 110 feet

Dam crest length: 400 feet

Reservoir volume: 60,000 acre-feet?

Spillway: 6 feet by 26 feet

History of Dam:

Purpose: Irrigation and gold placer mining. Dam completed: October 1887

Dam failed: 2 a.m. February 22, 1890 (2 years old)

Failure cause: Overtopped (inadequate spillway cap and poor construction workmanship). The

dam withstood 3 feet of overtopping for 6 hours before failing.

Details on Detection of Failure/Deciding to warn:

11 hours before dam failure an employee was directed by the superintendent of the water storage

company to ride by horseback and warn people at a construction camp for a lower dam about 15

miles downstream from Walnut Grove Dam.

Details on dissemination of warnings and technologies used:

The rider on horseback never reached the lower camp.

Details on response to the warning:

The majority of the 150 or more inhabitants of the (Fools Gulch) camp were calmly sleeping in

their tents. When the roar of the approaching water became audible, it was almost too late for

escape up the hillsides, yet many reached safety by scrambling up the hillside through cactus and

rocks.

Description of flooding resulting from dam failure:

Floodwaters reached depths of 50 to 90 feet in the canyon downstream from the dam.

The losses included:

70 to 100 fatalities

Prepared by Wayne Graham
Dam name: Austin Dam

Location: On Freeman Run, about 1.5 miles upstream from Austin, Pennsylvania. The dam is

located in western PA., about 130 miles northeast of Pittsburgh.

Dam Characteristics:

Dam type: Concrete gravity

Dam height: Between 43 and 50 feet

Dam crest length: 544 feet

Reservoir volume: Between 550 and 850 acre-feet

Spillway: 50 feet long and 2.5 feet deep

History of Dam:

Dam completed: November 1909

Partial failure: January 1910; part of dam moved 18 inches at base and

34 inches at the top.

Dam failed: 2pm or 2:20 pm, September 30, 1911 (2 years old)

Failure cause: Weakness of the foundation, or of the bond between the

foundation and concrete.

Details on Detection of Failure/Deciding to warn:

Harry Davis, boarding in a house on the mountain slope near the dam phoned the Austin

operators at whose warning the paper mill whistle sounded - about 2 pm. The phone operators

warned others but many ignored the warnings.

Details on dissemination of warnings and technologies used:

The mill whistle had blown twice earlier in the day as false signals had been received from

telephone company employees who had been repairing telephone lines. The two false alarms

were the cause of many people losing their lives as many people assumed the whistle (sounded to

warn of dam failure) was another false alarm. Warnings were issued to people in Costello, about

5 miles downstream from the dam. (A person riding a bicycle traveled from the south side of

Austin to Costello to spread the warning).

Details on response to the warning:

Description of flooding resulting from dam failure:

The water traveled from the dam to the town of Austin, a distance of 1.5 miles, in either 11

minutes or in up to 20 to 30 minutes. This results in a travel time of between 3 and 8 miles per

hour.

The losses included:

At least 78 fatalities, all in the first 2 miles downstream from the dam, i.e. in the Austin area.

(About 3 or 4 percent of Austin’s 2300 population)

Prepared by Wayne Graham
Dam name: Saint Francis Dam

Location: north of Los Angeles, CA

Dam Characteristics:

Dam type: Concrete Gravity

Dam height: 188 feet

Dam crest length: ?? feet

Reservoir volume: 38,000 acre-feet

Spillway:

History of Dam:

Purpose: LA Water Supply

Dam completed:

Dam failed: About midnight March 12, 1928 (2 years old)

Failure cause: Foundation failure at abutment

Details on Detection of Failure/Deciding to warn:

No detection before failure. Ventura County Sheriffs office informed at 1:20 am.

Details on dissemination of warnings and technologies used:

Once people learned of failure, telephone operators called local police, highway patrol and phone

company customers. Warning spread by word of mouth, phone, siren and law enforcement in

motor vehicles.

Details on response to the warning:

Description of flooding resulting from dam failure:

Flooding was severe through a 54 miles reach from dam to ocean. The leading edge of the

flooding moved at 18 mph near dam and 6 mph nearer the ocean.

The losses included: 420 fatalities. About 3,000 people were at risk. Damage total of about

$13.5 million includes death claims.

Photos from USGS library and Ventura County Museum of History and Art.

Photos:

Site mileage flood arrived dead

big pile (power plant) 1.5 5 minutes > 11 out of 50

Cal Edison const. camp 17 lhr 20mm 89 of 150

Santa Paula 38.5 3 hours yes

Prepared by Wayne Graham
Dam name: Castlewood Dam

Location: near Franktown, Colorado (about 35 miles upstream from Denver.

Dam Characteristics:

Dam type: rockfill

Dam height: 70 feet

Dam crest length: 600 feet

Reservoir volume: 3430 acre-feet at spillway crest; 5000 acre-feet at elevation of failure.

Spillway: Central overflow, 100 feet long, 4 feet deep.

History of Dam:

Purpose: irrigation

Dam completed: 1890

Dam failed: about midnight August 3, 1933

Failure cause: overtopping

Details on Detection of Failure/Deciding to warn:

The dam begins failing due to overtopping about• midnight. Caretaker lives nearby but phone not

working. Drives 12 miles to use phone. At 2:30 a.m. caretaker uses phone to initiate warning

process.

Details on dissemination of warnings and technologies used:

Residents in upstream areas probably received no official warning. Flooding occurred in Denver

between about 5:30 a.m. and 8:00 a.m. Warnings by police and firemen preceded the arrival of

floodwaters.

Details on response to the warning:

Many people evacuated. A newspaper reported, “A stampede of 5,000, man clad in nightclothes,

fled from the lowlands.” People also drove to the banks of Cherry Creek to view the flood.

Description of flooding resulting from dam failure:

In the Denver area, flooding caused significant damage. The flood depth and velocity, however,

were not great enough to destroy (move or collapse) buildings.

The losses included:

2 fatalities occurred. A woman was thrown into Cherry Creek while viewing the flood on

horseback and a man stepped into a deep hole while wading toward high ground. $1.7 million in.

damage.

Prepared by Wayne Graham
Dam name: Baldwin Hills Dam

Location: Los Angeles, California. The dam was located about midway between downtown

L.A., and LAX (L.A. International Airport).

Dam Characteristics:

Dam type: earthfill

Dam height: 65.5 feet. Water depth of 59 feet when break occurred.

Dam crest length: not determined

Reservoir volume: about 700 acre-feet at time of failure.

Spillway: of f stream storage at top of hill. No spillway?

History of Dam:

Purpose: water supply

Dam completed: 1950

Dam failed: Saturday, December 14, 1963 at 3:38 p.m.

Failure cause: displacement in the foundation

Details on Detection of Failure/Deciding to warn:

11:15 a.m.: crack discovered in dam

12:20 p.m.: reservoir draining begins

1:30 p.m.: LA Dept of Water and Power notifies police

1:45 p.m.: decision made to evacuate

2:20 p.m.: evacuation begins

3:38 p.m.: dam fails

Details or dissemination of warnings and technologies used:

Warnings disseminated by police in patrol cars, motorcycle and helicopter. This event was

covered by radio and television.

Details on response to the warning:

Many people evacuated but “some people were not taking the warnings seriously.

Description of flooding resulting from dam failure:

Flooding extended about 2 miles from dam. Affected area was about 1 square mile which

contained about 16,500 people. The fatalities occurred about I mile downstream from the dam.

The losses included:

5 fatalities; they all resided in condo complex that was flooded but not destroyed. 41 homes

destroyed; 986 houses and 100 apt. buildings damaged, 3000 automobiles damaged. Damage

reported to be $11.3 million.

Prepared by Wayne Graham
Dam name: Buffalo Creek Coal Waste Dam

Location: near Saunders, West Virginia

Dam Characteristics:

Dam type: coal waste

Dam height: 46 feet

Dam crest length: feet

Reservoir volume: 404 acre-feet

Spillway: small pipe

History of Dam:

Purpose: improve water quality, dispose of coal waste

Dam completed: continually changing

Dam failed: February 26, 1972 about 8 a.m. (0 years old)

Failure cause: Slumping of dam face during 2-year rain.

Details on Detection of Failure/Deciding to warn: Owner reps were on site monitoring

conditions prior to dam failure. “At least two dam owner officials urged the Logan County

Sheriff’s force to refrain from a massive alert and exodus.”

Details on dissemination of warnings and technologies used:

Company officials issued no warnings. The senior dam safety official on the site dismissed two

deputy sheriffs (at about 6:30 a.m.) who had been called to the scene to aid evacuation.

Details on response to the warning: Resident’s reaction to the meager warnings that were

issued were dampened due to at least 4 previous false alarms.

Description of flooding resulting from dam failure:

Wave traveled downstream through the 15-mile long valley at 5mph. Over 1,000 homes either

destroyed or damaged.

The losses included: 125 deaths; 4,000 people homeless

All of the fatalities occurred in the first 15 miles downstream from the dam.

Damage total of $50 million.

Prepared by Wayne Graham
Dam name: Black Hills Flash Flood (Canyon Lake Dam)

Location: Rapid City, South Dakota

Dam Characteristics:

Dam type: earthfill

Dam height: 20+? feet

Dam crest length: 500 feet

Reservoir volume: about 700 acre-feet of water released

Spillway: Capacity of 3,200 cfs

History of Dam:

Purpose: Recreational lake in city park

Dam completed: 1933

Dam failed: June 9, 1972 Reports varied between 10:45 and 11:30 (39-years old when failed)

Failure cause: Overtopping

Details on Detection of Failure/Deciding to warn:

There were no dam failure warnings and virtually no flood warnings in Rapid City. The 10pm

TV news wrap-up indicated that the magnitude and seriousness of the flood was not realized at

that time. At 10:30 pm, in simultaneous TV and radio broadcast, people in low-lying areas were

urged to evacuate.

Details on dissemination of warnings and technologies used:

The initial warnings did not carry a sense of urgency because of the complete lack of knowledge

concerning the incredible amount of rain that was falling.

Details on response to the warning:

Description of flooding resulting from darn failure:

Water started flowing over Canyon Lake Dam at 10 am or earlier. The dam failed at 10:45 pm

(or as late as 11:30 pm)

Peak inflow was about 43,000 cfs

Peak outflow was about 50,000 cfs

Flood in Rapid City covered an area up to 0.5 miles wide.

The losses included:

236 fatalities with 17,000 at risk. Of the fatalities: 35 occurred in first 3 miles above dam; 165

below dam; 36 elsewhere Incremental fatalities resulting from dam failure: ???

3,000 injured. Flooding, including that from dam failure, destroyed or caused major damage to

over 4,000 permanent residences and mobile homes. Damage total (failure plus non failure):

$160 million.

Prepared by Wayne Graham
Dam name: Teton Dam

Location: near Wilford, Idaho

Dam Characteristics:

Dam type: earthf ill

Dam height: 305 feet (275 depth at failure)

Dam crest length: feet

Reservoir volume: 250,000 acre-feet released

Spillway: water never reached spillway

History of Dam:

Purpose: irrigation

Dam completed: under final construction/first filling

Dam failed: Saturday June 5, 1976 at 11:57 a.m.; first filling

Failure cause: Piping of dam core in foundation key trench.

Details on Detection of Failure/Deciding to warn:

12:30 am and 7am: dam unattended.

7am to 8am: Survey crew discovers turbid leakage

9:30 am: PCE considers alerting residents but decides emergency situation is not imminent and

is concerned about causing panic.

10 am: larger leak, flowing turbid water

10:30 to 10:45: PCE notifies sheriff’s offices and advises them to alert citizens.

Details on dissemination of warnings and technologies used:

police, radio, television, telephone, neighbor word of mouth. (Included live commercial radio

broadcasts from reporters in aircraft and at Teton Dam)

Details on response to the warning:

Why were there 800 injured?

Description of flooding resulting from dam failure:

Over 3,700 houses destroyed or damaged. 150 to 200 sq. mi. flooded

The losses included:

11 fatalities (6 from drowning, 3 heart failure, 1 accidental gun shot and 1 suicide) with about

25,000 people at risk. 800 injuries. Damage total of $400 million from USGS Open File Report

77-765.

Photos:

Sugar City 12 mi. 1pm 15 ft depth (0 dead)

Rexburg 15 mi. 1:40pm 6 to 8 ft. (2 deaths)

Prepared by Wayne Graham
Dam name: Kelly Barnes Dam

Location: on Toccoa Creek, near Toccoa Falls, Georgia.

Dam Characteristics:

Dam type: earthfill

Dam height: about 40 feet

Dam crest length: 400 feet

Reservoir volume: 630 acre-feet at time of failure

Spillway:

History of Dam:

Purpose: Originally for hydropower. Hydropower abandoned in 1957 and then used for

recreation.

Dam completed: 1899. Enlarged/modified in 1937 and after 1945. Dam failed: Sunday,

November 6, 1977 at 1:20 a.m.

Failure cause: Saturation due to heavy rain caused downstream slope failure.

Details on Detection of Failure/Deciding to warn:

Two volunteer firemen examined the dam around 10:30 p.m. and radiod that dam was solid and

that there was no need for concern or alarm.

Details on dissemination of warnings and technologies used:

With concern over rising water, not dam failure, 1 or 2 families were warned by volunteer

firemen just minutes before dam failure.

Details on response to the warning:

Most people were not warned. It would have been horrible conditions for evacuation - dark,

rainy and cold.

Description of flooding resulting from dam failure:

Flood reached depths of 8 to 10 feet in populated floodplain.

The losses included:

39 fatalities, all within 2 miles of the dam. 9 houses, 18 house trailers, 2 college buildings

demolished. 4 houses and 5 college buildings damaged. Damage total of $2.8 million.

Prepared by Wayne Graham
Dam name: Lawn Lake Dam

Location: In Rocky Mountain National Park, Colorado

Dam Characteristics:

Dam type: Earthfill

Dam height: 26 feet

Dam crest length: about 500 feet

Reservoir volume: 674 acre-feet released

History of Dam:

Purpose: irrigation

Dam completed: 1903

Dam failed: Thursday, July 15, 1982 at about 5:30 a.m.

Failure cause: Piping

Details on Detection of Failure/Deciding to warn:

The dam failure was observed by anyone able to take action until the leading edge of the flood

had traveled about 4.5 miles downstream from Lawn ‘Lake Dam. A trash collector heard loud

noises and observed mud and debris on road. He used an emergency telephone which the

National Park Service had at various locations within the park. The NPS and local government

officials then began to warn and evacuate people located near the watercourse.

Details on dissemination of warnings and technologies used:

NPS Rangers and local police and sheriff used automobiles and went through area to warn. Local

radio station was also broadcasting information on the flood and its movement.

Details on response to the warning:

Most people were taking the warnings seriously as the “Big Thompson” flood of 1976 which

occurred nearby and killed about 140 was still in their memory. Three people died; 1 received no

warning and the other 2 a weak warning not mentioning dam failure.

Description of flooding resulting from dam failure:

Flood covered an area about 13 miles long with first 7 miles in Rocky Mtn. N.P. Flood plain was

generally narrow. Some buildings destroyed. Main street of Estes Park flooded.

The losses included:

3 fatalities. Damages totaled $31 million.

Prepared by Wayne Graham
Dam name: Timber Lake Dam

Location: near Lynchburg, Virginia

Dam Characteristics:

Dam type: earthfill

Dam height: 33 feet

Dam crest length: about 500 feet

Reservoir volume: 1449 acre-feet

Spillway: ungated

History of Dam:

Purpose: Real estate development

Dam completed: 1926

Dam failed: About 11 p.m., Thursday, June 22, 1995

Failure cause: Overtopping

Details on Detection of Failure/Deciding to warn:

Heavy rains in the 4.36 square mile drainage basin above dam prompted the maintenance

director for the homeowners association to reach dam. Due to flooded roads he did not get to the

dam before it failed.

Details on dissemination of warnings and technologies used:

There were no dam failure warnings issued for area downstream from the dam.

Details on response to the warning:

No dam failure warnings were issued. However, local volunteer firefighters were at a 4 lane

divided highway about 1 mile downstream from Timber Lake Dam to search 3 cars that had

stalled prior to the dam failure. The sudden surge of about 4 feet (at this location) caused by the

dam failure caused the death of one firefighter.

Description of flooding resulting from dam failure:

Aside from flooded roads, very little damage occurred.

The losses included: 2 fatalities. The firefighter died in the search and rescue that started before

dam failure and a woman died as she was driving on a road that crossed the dam failure

floodplain. Aside from dam reconstruction, little economic damage.

Prepared by Wayne Graham
B-2

1

Will a Dam Failure Occur?

Assessing Failure in a

Risk-based Context

Bruce C. Muller, Jr.

U.S. Bureau of Reclamation

Dam Safety Office

Could we predict it today?

Teton Dam - June 5, 1976
2

If we can’t predict dam 

failures, what can we do?

• Recognize the risks associated with storing 

water

• Monitor those aspects of performance that 

would be indicative of a developing failure

• Take action to reduce risk where warranted

Reclamation’s Risk 

Management Responsibility

Reclamation Safety of Dams Act of 1978:

To authorize the Secretary of the Interior 

to construct, restore, operate, and maintain 

new or modified features and existing 

Federal Reclamation dams for safety of 

dams purposes.
3

Reclamation’s Risk 

Management Responsibility

“In order to preserve the structural safety 

of Bureau of Reclamation dams and 

related facilities the Secretary of the 

Interior is authorized to perform such 

modifications as he determines to be 

reasonably required.”

Reclamation Safety of Dams Act of 1978 Sec. 2.

Reclamation’s View of Risk

• Risk = p[load] x p[adverse response] x consequence

• Loads: static, hydrologic, seismic, 

operations

• Adverse Response: loss of storage, uncontrolled 

release, failure

• Consequence: life loss, economic damage, 

environmental damage
4

Risk Management Tools

• Public Protection Guidelines

• Risk reduction actions

• Issue evaluation

– Technical analysis

– Risk analysis

• Performance monitoring

• Facility reviews 

Public Protection Guidelines

Life Loss

Expected Annual Life Loss

.001

.01

Justification for reducing 

risk decreases

Justification to reduce long 

term risk

Justification to reduce risk 

short term risk
5

Roles of Dam Failure Analyses

• Identifying the extent of an adverse 

response to a loading condition

• Defining the outflow hydrograph

• Estimating the consequences of the outflow 

hydrograph

Important Issues

• Validation of technical models

• Addressing uncertainty

• Scalability

• Cost effectiveness

• Balancing unknowns
6

Challenges

• Focus research needs on areas that help 

decision makers reach decisions

• Strive for balance in development of tools 

(breach formation, routing, consequence 

assessment)

• Ensure that tools can be cost effectively 

applied to a wide variety of structures
B-3

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INITIATING

EVENT

SYSTEM RESPONSE OUTCOME EXPOSURE CONSEQUENCES

IDENTIFICATION • STATIC LOADING

• FLOOD

•EARTHQUAKE

•U/S DAM FAILURE

•LANDSLIDE

• OVERTOPPING

• SLOPE FAILIURE

• CRACKING

• PIPIING

• STRUCT/FND FAILURE

• BREACH

• PARTIAL BREACH

•NO BREACH

• TIME OF DAY

• SEASON

• WARNING TIME

• LOSS OF LIFE

• ECONOMIC

• ENVIRONMENTAL

• SOCIAL

ESTIMATION LOADING 

PROB (E)

RESPONSE 

PROB (R|E)

OUTCOME 

PROB 

(O|R,E)

EXPOSURE 

PROB (L|O,R,E)

EXPECTED 

LOSSES

MEASURES

U/S WATERSHED 

CHANGES

U/S DAM 

IMPROVEMENTS

STRUCTURAL 

MODIFICATIONS

SAFETY 

INSPECTIONS

INSTRUMENTATION

OPERATING 

RESTRICTIONS

FORMULATE 

MEASURES

STRUCTURAL 

MODIFICATIONS

WARNING 

SYSTEMS

FLOOD PROOFING

EMERGENCY 

PREPAREDNESS

RELOCATIONS

LAND USE 

ZONING

FRAMEWORK FOR RISK ASSESSMENT

Compare residual risk 

to risk guidelines

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B-4

 1 

The Uncertainty of Embankment Dam Breach Parameter Predictions 

Based on Dam Failure Case Studies 

by Tony L. Wahl1

Introduction

Risk assessment studies considering the failure of embankment dams often make use of breach 

parameter prediction methods that have been developed from analysis of historic dam failures. 

Similarly, predictions of peak breach outflow can also be made using relations developed from 

case study data. This paper presents an analysis of the uncertainty of many of these breach 

parameter and peak flow prediction methods, making use of a previously compiled database 

(Wahl 1998) of 108 dam failures. Subsets of this database were used to develop many of the 

relations examined. 

The paper begins with a brief discussion of breach parameters and prediction methods. The 

uncertainty analysis of the various methods is next presented, and finally, a case study is offered 

to illustrate the application of several breach parameter prediction methods and the uncertainty 

analysis to a risk assessment recently performed by the Bureau of Reclamation for Jamestown 

Dam, on the James River in east-central North Dakota. 

Breach Parameters

Dam break flood routing models (e.g., DAMBRK, FLDWAV) simulate the outflow from a 

reservoir and through the downstream valley resulting from a developing breach in a dam. These 

models focus their computational effort on the routing of the breach outflow hydrograph. The 

development of the breach is not simulated in any physical sense, but rather is idealized as a 

parametric process, defined by the shape of the breach, its final size, and the time required for its 

development (often called the failure time). Breaches in embankment dams are usually assumed 

to be trapezoidal, so the shape and size of the breach are defined by a base width and side slope 

angle, or more simply by an average breach width. 

The failure time is a critical parameter affecting the outflow hydrograph and the consequences of 

dam failure, especially when populations at risk are located close to a dam so that available 

warning and evacuation time dramatically affects predictions of loss of life. For the purpose of 

routing a dam-break flood wave, breach development begins when a breach has reached the 

point at which the volume of the reservoir is compromised and failure becomes imminent. 

During the breach development phase, outflow from the dam increases rapidly. The breach 

development time ends when the breach reaches its final size; in some cases this may also 

correspond to the time of peak outflow through the breach, but for relatively small reservoirs the 

peak outflow may occur before the breach is fully developed. This breach development time as 

described above is the parameter predicted by most failure time prediction equations. 

 

1

 Hydraulic Engineer, U.S. Bureau of Reclamation, Water Resources Research Laboratory, Denver, CO. e-mail: 

twahl@do.usbr.gov phone: 303-445-2155. 
 2 

The breach development time does not include the potentially long preceding period described as 

the breach initiation phase (Wahl 1998), which can also be important when considering available 

warning and evacuation time. This is the first phase of an overtopping failure, during which flow 

overtops a dam and may erode the downstream face, but does not create a breach through the 

dam that compromises the reservoir volume; if the overtopping flow were quickly stopped 

during the breach initiation phase, the reservoir would not fail. In an overtopping failure, the 

length of the breach initiation phase is important, because breach initiation can potentially be 

observed and may thus trigger warning and evacuation. Unfortunately, there are few tools 

available for predicting the length of the breach initiation phase. 

During a seepage-erosion (piping) failure the delineation between breach initiation and breach 

development phases is less apparent. In some cases, seepage-erosion failures can take a great 

deal of time to develop. In contrast to the overtopping case, the loading that causes a seepageerosion failure cannot normally be removed quickly, and the process does not take place in full 

view, except that the outflow from a developing pipe can be observed and measured. One useful 

way to view seepage-erosion failures is to consider three possible conditions: 

(1) normal seepage outflow, with clear water and low flow rates; 

(2) initiation of a seepage-erosion failure with cloudy seepage water that indicates a developing 

pipe, but flow rates are still low and not rapidly increasing. Corrective actions might still be 

possible that would heal the developing pipe and prevent failure. 

(3) active development phase of a seepage-erosion failure in which erosion is dramatic and flow 

rates are rapidly increasing. Failure can no longer be prevented. 

Only the length of the last phase is important when determining the breach hydrograph from a 

dam, but both the breach initiation and breach development phases may be important when 

considering warning and evacuation time. Again, as with the overtopping failure, there are few 

tools available for estimating the length of the breach initiation phase. 

Predicting Breach Parameters

To carry out a dam break routing simulation, breach parameters must be estimated and provided 

as inputs to the dam-break and flood-routing simulation model. Several methods are available 

for estimating breach parameters; a summary of the available methods was provided by Wahl 

(1998). The simplest methods (Johnson and Illes 1976; Singh and Snorrason 1984; Reclamation 

1988) predict the average breach width as a linear function of either the height of the dam or the 

depth of water stored behind the dam at the time of failure. Slightly more sophisticated methods 

predict more specific breach parameters, such as breach base width, side slope angles, and failure 

time, as functions of one or more dam and reservoir parameters, such as storage volume, depth of 

water at failure, depth of breach, etc. All of these methods are based on regression analyses of 

data collected from actual dam failures. The database of dam failures used to develop these 

relations is relatively lacking in data from failures of large dams, with about 75 percent of the 

cases having a height less than 15 meters, or 50 ft (Wahl 1998). 

Physically-based simulation models are available to aid in the prediction of breach parameters. 

Although none are widely used, the most notable is the National Weather Service BREACH 
 3 

model (Fread 1988). These models simulate the hydraulic and erosion processes associated with 

flow over an overtopping dam or through a developing piping channel. Through such a 

simulation, an estimate of the breach parameters may be developed for use in a dam-break flood 

routing model, or the outflow hydrograph at the dam can be predicted directly. The primary 

weakness of the NWS-BREACH model and other similar models is the fact that they do not 

adequately model the headcut-type erosion processes that dominate the breaching of cohesivesoil embankments (e.g., Hahn et al. 2000). Recent work by the Agricultural Research Service 

(e.g., Temple and Moore 1994) on headcut erosion in earth spillways has shown that headcut 

erosion is best modeled with methods based on energy dissipation. 

Predicting Peak Outflow

In addition to prediction of breach parameters, many investigators have proposed simplified 

methods for predicting peak outflow from a breached dam. These methods are valuable for 

reconnaissance-level work and for checking the reasonability of dam-break outflow hydrographs 

developed from estimated breach parameters. This paper considers the relations by: 

• Kirkpatrick (1977) 

• SCS (1981) 

• Hagen (1982) 

• Reclamation (1982) 

• Singh and Snorrason (1984) 

• MacDonald and Langridge-Monopolis (1984) 

• Costa (1985) 

• Evans (1986) 

• Froehlich (1995a) 

• Walder and O’Connor (1997) 

All of these methods except Walder and O’Connor are straightforward regression relations that 

predict peak outflow as a function of various dam and/or reservoir parameters, with the relations 

developed from analyses of case study data from real dam failures. In contrast, Walder and 

O’Connor’s method is based upon an analysis of numerical simulations of idealized cases 

spanning a range of dam and reservoir configurations and erosion scenarios. An important 

parameter in their method is an assumed vertical erosion rate of the breach; for reconnaissancelevel estimating purposes they suggest that a range of reasonable values is 10 to 100 m/hr, based 

on analysis of case study data. The method makes a distinction between so-called largereservoir/fast-erosion and small-reservoir/slow-erosion cases. In large-reservoir cases the peak 

outflow occurs when the breach reaches its maximum depth, before there has been any 

significant drawdown of the reservoir. The peak outflow in this case in insensitive to the erosion 

rate. In the small-reservoir case there is significant drawdown of the reservoir as the breach 

develops, and thus the peak outflow occurs before the breach erodes to its maximum depth. Peak 

outflows for small-reservoir cases are dependent on the vertical erosion rate and can be 

dramatically smaller than for large-reservoir cases. The determination of whether a specific 

situation is a large-reservoir or small-reservoir case is based on a dimensionless parameter 

incorporating the embankment erosion rate, reservoir size, and change in reservoir level during 

the failure. Thus, so-called large-reservoir/fast-erosion cases can occur even with what might be 
 4 

considered “small” reservoirs and vice versa. This refinement is not present in any of the other 

peak flow prediction methods. 

Developing Uncertainty Estimates

In a typical risk assessment study, a variety of loading and failure scenarios are analyzed. This 

allows the study to incorporate variability in antecedent conditions and the probabilities 

associated with different loading conditions and failure scenarios. The uncertainty of key 

parameters (e.g., material properties) is sometimes considered by creating scenarios in which 

analyses are carried out with different parameter values and a probability of occurrence assigned 

to each value of the parameter. Although the uncertainty of breach parameter predictions is often 

very large, there have previously been no quantitative assessments of this uncertainty, and thus 

breach parameter uncertainty has not been incorporated into most risk assessment studies. In 

some studies, variations in thresholds of failure (e.g., overtopping depth to initiate breach) have 

been incorporated, usually through a voting process in which study team members and technical 

experts use engineering judgment to assign probabilities to different failure thresholds. 

It is worthwhile to consider breach parameter prediction uncertainty in the risk assessment 

process because the uncertainty of breach parameter predictions is likely to be significantly 

greater than all other factors, and could thus dramatically influence the outcome. For example 

Wahl (1998) used many of the available relations to predict breach parameters for 108 

documented case studies and plot the predictions against the observed values. Prediction errors 

of ±75% were not uncommon for breach width, and prediction errors for failure time often 

exceeded 1 order of magnitude. Most relations used to predict failure time are conservatively 

designed to underpredict the reported time more often than they overpredict, but overprediction 

errors of more than one-half order of magnitude did occur several times. 

The first question that must be addressed in an uncertainty analysis of breach parameter 

predictions is how to express the results. The case study datasets used to develop most breach 

parameter prediction equations include data from a wide range of dam sizes, and thus, 

regressions in log-log space have been commonly used. Figure 1 shows the observed and 

predicted breach widths as computed by Wahl (1998) in both arithmetically-scaled and log-log 

plots. In the arithmetic plots, it would be difficult to draw in upper and lower bound lines to 

define an uncertainty band. In the log-log plots data are scattered approximately evenly above 

and below the lines of perfect prediction, suggesting that uncertainties would best be expressed 

as a number of log cycles on either side of the predicted value. This is the approach taken in the 

analysis that follows. 

The other notable feature of the plots in Figure 1 is the presence of a few significant outliers. 

The source of these outliers is believed to be the variable quality of the case study observations, 

the potential for misapplication of some of the prediction equations due to lack of detailed 

knowledge of each case study, and inherent variability in the data due to the variety of factors 

that influence dam breach mechanics. Thus, before determining uncertainties, an outlierexclusion algorithm was applied (Rousseeuw 1998). The algorithm has the advantage that it is, 

itself, insensitive to the effects of outliers. 
 5 

The uncertainty analysis was performed using the database presented in Wahl (1998), with data 

on 108 case studies of actual embankment dam failures, collected from numerous sources in the 

literature. The majority of the available breach parameter and peak flow prediction equations 

were applied to this database of dam failures, and the predicted values were compared to the 

observed values. Computation of breach parameters or peak flows was straightforward in most 

cases. A notable exception was the peak flow prediction method of Walder and O’Connor 

(1997), which requires that the reservoir be classified as a large- or small-reservoir case. In 

addition, in the case of the small-reservoir situation, an average vertical erosion rate of the 

breach must be estimated. The Walder and O’Connor method was applied only to those dams 

that could be clearly identified as large-reservoir (in which case peak outflow is insensitive to the 

vertical erosion rate) or small-reservoir with an associated estimate of the vertical erosion rate 

obtained from observed breach heights and failure times. Two other facts should be noted: 

• No prediction equation could be applied to all 108 dam failure cases, due to lack of required 

input data for the specific equation or the lack of an observed value of the parameter of 

interest. Most of the breach width equations could be tested against about 70 to 80 cases, the 

failure time equations were tested against 30 to 40 cases, and the peak flow prediction 

equations were generally tested against about 30 to 40 cases. 

Froehlich (1995)

Observed Breach Width (meters)

1 10 100 1000

1

10

100

1000

Von Thun & Gillette (1990)

Observed Breach Width (meters)

1 10 100 1000

Predicted Breach Width (meters)

1

10

100

1000 Line of Agreement

Reclamation (1988)

Observed Breach Width (meters)

1 10 100 1000

1

10

100

1000

Froehlich (1995)

Observed Breach Width (meters)

0 50 100 150 200 250 300

0

50

100

150

200

250

300

Von Thun & Gillette (1990)

Observed Breach Width (meters)

0 50 100 150 200 250 300

Predicted Breach Width (meters)

0

50

100

150

200

250

300 Line of Agreement

Reclamation (1988)

Observed Breach Width (meters)

0 50 100 150 200 250 300

0

50

100

150

200

250

300

Figure 1. — Predicted and observed breach widths (Wahl 1998), 

plotted arithmetically (top) and on log-log scales (bottom). 
 6 

• The testing made use of the same data used to originally develop the equations, but each 

equation was also tested against additional cases. This should provide a fair indication of the 

ability of each equation to predict breach parameters for future dam failures. 

A step-by-step description of the uncertainty analysis method follows: 

(1) Plot predicted vs. observed values on log-log scales. 

(2) Compute individual prediction errors in terms of the number of log cycles separating the 

predicted and observed value, ) e log(xˆ) log(x) log(xˆ / x i = − = , where ei is the prediction 

error, xˆ is the predicted value and x is the observed value. 

(3) Apply the outlier-exclusion algorithm to the series of prediction errors computed in step (2). 

The algorithm is described by Rousseeuw (1998). 

(a) Determine T, the median of the ei values. T is the estimator of location. 

(b) Compute the absolute values of the deviations from the median, and determine the 

median of these absolute deviations (MAD). 

(c) Compute an estimator of scale, S=1.483*(MAD). The 1.483 factor makes S comparable 

to the standard deviation, which is the usual scale parameter of a normal distribution. 

(d) Use S and T to compute a Z-score for each observation, Zi=(ei-T)/S, where the ei's are the 

observed prediction errors, expressed as a number of log cycles. 

(e) Reject any observations for which |Zi|>2.5 

This method rejects at the 98.7% probability level if the samples are from a perfect normal 

distribution. 

(4) Compute the mean, e , and the standard deviation, Se, of the remaining prediction errors. If 

the mean value is negative, it indicates that the prediction equation underestimated the observed 

values, and if positive the equation overestimated the observed values. Significant over or 

underestimation should be expected, since many of the breach parameter prediction equations are 

intended to be conservative or provide envelope estimates, e.g., maximum reasonable breach 

width, fastest possible failure time, etc. 

(5) Using the values of e and Se, one can express a confidence band around the predicted value 

of a parameter as {ˆ 10 , ˆ 10 } 2 2 e e e S e Sx x − − − + ⋅ ⋅ , where xˆ is the predicted value. The use of ±2Se gives 

approximately a 95 percent confidence band. 

Table 1 summarizes the results. The first column identifies the particular method being 

analyzed, the next two columns show the number of case studies used to test the method, and the 

next two columns give the prediction error and the width of the uncertainty band. The rightmost 

column shows the range of the prediction interval around a hypothetical predicted value of 1.0. 

The values in this column can be used as multipliers to obtain the prediction interval for a 

specific case. 
 7 

Table 1. – Uncertainty estimates of breach parameter and peak flow prediction equations. All equations use 

metric units (meters, m3

, m3/s). Failure times are computed in hours. 

Number of Case Studies 

Equation 

Before 

outlier 

exclusion 

After 

outlier 

exclusion 

Mean 

Prediction 

Error, e

(log cycles) 

Width of 

Uncertainty 

Band, ±2Se

(log cycles) 

Prediction interval 

around a hypothetical 

predicted value of 1.0 

BREACH WIDTH EQUATIONS 

USBR (1988)

3( ) B = hw

80 70 -0.09 ±0.43 0.45 — 3.3 

MacDonald and Langridge-Monopolis (1984)

0.769 0.0261( ) Ver Vw hw = ⋅ earthfill 

0.852 0.00348( ) Ver Vw hw = ⋅

non-earthfill (e.g., rockfill)

60 58 -0.01 ±0.82 0.15 — 6.8 

Von Thun and Gillette (1990)

B = 5hw + Cb 2.

where Cb is a function of reservoir size 

78 70 +0.09 ±0.35 0.37 — 1.8 

Froehlich (1995b)

0.32 0.19 B = 0.1803Ko

Vw hb

where Ko = 1.4 for overtopping, 1.0 for 

piping 

77 75 +0.01 ±0.39 0.40 — 2.4 

FAILURE TIME EQUATIONS 

MacDonald and Langridge-Monopolis (1984)

0.364 0.0179( ) f Ver t = 37 35 -0.21 ±0.83 0.24 — 11. 

Von Thun and Gillette (1990)

0.015( ) f w t = h highly erodible 

= 0.020( ) + 0.25 f w t h erosion resistant

36 34 -0.64 ±0.95 0.49 — 40. 

Von Thun and Gillette (1990)

/(4 ) f w t = B h highly erodible 

= /(4 + 61) f w t B h erosion resistant

36 35 -0.38 ±0.84 0.35 — 17. 

Froehlich (1995b)

0.53 0.9 0.00254( ) −

f = Vw hb t 34 33 -0.22 ±0.64 0.38 — 7.3 

USBR (1988)

t 0.011(B) f = 40 39 -0.40 ±1.02 0.24 — 27. 

PEAK FLOW EQUATIONS 

Kirkpatrick (1977)

2.5 = 1.268( + 0.3) Qp hw

38 34 -0.14 ±0.69 0.28 — 6.8 

SCS (1981)

1.85 16.6( ) Qp = hw

38 32 +0.13 ±0.50 0.23 — 2.4 

Hagen (1982)

0.5 0.54( ) Qp S hd = ⋅ 31 30 +0.43 ±0.75 0.07 — 2.1 

Reclamation (1982)

1.85 19.1( ) Qp = hw envelope equation 38 32 +0.19 ±0.50 0.20 — 2.1 
 8 

Number of Case Studies 

Equation 

Before 

outlier 

exclusion 

After 

outlier 

exclusion 

Mean 

Prediction 

Error, e

(log cycles) 

Width of 

Uncertainty 

Band, ±2Se

(log cycles) 

Prediction interval 

around a hypothetical 

predicted value of 1.0 

PEAK FLOW EQUATIONS (continued)

Singh and Snorrason (1984)

1.89 13.4( ) Qp = hd

0.47 Q 1.776(S) p =

38 

35 

28 

34 

+0.19 

+0.17 

±0.46 

±0.90 

0.23 — 1.9 

0.08 — 5.4 

MacDonald and Langridge-Monopolis (1984)

0.412 1.154( ) Qp Vw hw = ⋅ 37 36 +0.13 ±0.70 0.15 — 3.7 

0.411 3.85( ) Qp Vw hw = ⋅ envelope equation 37 36 +0.64 ±0.70 0.05 — 1.1 

Costa (1985)

0.57 Q 1.122(S) p = envelope equation 35 35 +0.69 ±1.02 0.02 — 2.1 

0.42 0.981( ) Qp S hd = ⋅ 31 30 +0.05 ±0.72 0.17 — 4.7 

0.44 2.634( ) Qp S hd = ⋅ envelope equation 31 30 +0.64 ±0.72 0.04 — 1.22 

Evans (1986)

0.53 0.72( ) Qp = Vw

39 39 +0.29 ±0.93 0.06 — 4.4 

Froehlich (1995a)

0.607( ) 0.295 1.24 Qp = Vw hw

32 31 -0.04 ±0.32 0.53 — 2.3 

Walder and O’Connor (1997)

Qp estimated using method based on relative 

erodibility of dam and size of reservoir 

22 21 +0.13 ±0.68 0.16 — 3.6 

Notes: Where multiple equations are shown for application to different types of dams (e.g., highly erodible vs. 

erosion resistant), a single prediction uncertainty was analyzed, with the system of equations viewed as a single 

algorithm. The only exception is the pair of peak flow prediction equations offered by Singh and Snorrason (1984), 

which are alternative and independent methods for predicting peak outflow. 

Definitions of Symbols for Equations Shown in Column 1.

B = average breach width, meters 

Cb = offset factor in the Von Thun and Gillette breach width equation, varies from 6.1 m to 54.9 m as a function 

of reservoir storage 

hb = height of breach, m 

hd = height of dam, m 

hw = depth of water above breach invert at time of failure, meters 

Ko = overtopping multiplier for Froehlich breach width equation, 1.4 for overtopping, 1.0 for piping 

Qp = peak breach outflow, m3

/s 

S = reservoir storage, m3

f t = failure time, hours 

Ver = volume of embankment material eroded, m3

Vw = volume of water stored above breach invert at time of failure, m3
 9 

Summary of Uncertainty Analysis Results

The four methods for predicting breach width all had absolute mean prediction errors less than 

one-tenth of an order of magnitude, indicating that on average their predictions are on-target. 

The uncertainty bands were similar (±0.3 to ±0.4 log cycles) for all of the equations except the 

MacDonald and Langridge-Monopolis equation, which had an uncertainty of ±0.82 log cycles. 

The five methods for predicting failure time all underpredict the failure time on average, by 

amounts ranging from about one-fifth to two-thirds of an order of magnitude. This is consistent 

with the previous observation that these equations are designed to conservatively predict fast 

breaches, which will cause large peak outflows. The uncertainty bands on all of the failure time 

equations are very large, ranging from about ±0.6 to ±1 order of magnitude, with the Froehlich 

(1995b) equation having the smallest uncertainty. 

Most of the peak flow prediction equations tend to overpredict observed peak flows, with most 

of the “envelope” equations overpredicting by about two-thirds to three-quarters of an order of 

magnitude. The uncertainty bands on the peak flow prediction equations are about ±0.5 to ±1 

order of magnitude, except the Froehlich (1995a) relation which has an uncertainty of ±0.32 

orders of magnitude. In fact, the Froehlich equation has both the best prediction error and 

uncertainty of all the peak flow prediction equations. 

Application to Jamestown Dam

To illustrate the application of the uncertainty analysis results, a case study is presented. In 

January 2001 the Bureau of Reclamation conducted a risk assessment study for Jamestown Dam 

(Figure 2), a feature of the Pick-Sloan Missouri Basin Program, located on the James River 

immediately upstream from Jamestown, North Dakota. For this risk assessment, two potential 

static failure modes were considered: 

• Seepage erosion and piping of foundation materials 

• Seepage erosion and piping of embankment materials 

No distinction between these two failure modes was made in the breach parameter analysis, since 

most methods used to predict breach parameters lack the refinement needed to consider the 

differences in breach morphology for these two failure modes. 

Figure 2. — Jamestown Dam and reservoir. 
 10 

The potential for failure and the downstream consequences from failure increase significantly at 

higher reservoir levels, although the likelihood of occurrence of high reservoir levels is low. The 

reservoir rarely exceeds its top-of-joint-use elevation, and has never exceeded elevation 

1445.9 ft. Four potential reservoir water surface elevations at failure were considered in the 

study: 

• Top of joint use, elev. 1432.67 ft, reservoir capacity of about 37,000 ac-ft 

• Elev. 1440.0 ft, reservoir capacity of about 85,000 ac-ft 

• Top of flood space, elev. 1454 ft, reservoir capacity of about 221,000 ac-ft 

• Maximum design water surface, elev. 1464.3 ft, storage of about 380,000 ac-ft 

Breach parameters were predicted using most of the methods discussed earlier in this paper, and 

also by modeling with the National Weather Service BREACH model (NWS-BREACH). 

Dam Description 

Jamestown Dam is located on the James River about 1.5 miles upstream from the city of 

Jamestown, North Dakota. It was constructed by the Bureau of Reclamation from 1952 to 1954. 

The facilities are operated by Reclamation to provide flood control, municipal water supply, fish 

and wildlife benefits and recreation. 

The dam is a zoned-earthfill structure with a structural height of 111 ft and a height of 81 ft 

above the original streambed. The crest length is 1,418 ft at elevation 1471 ft and the crest width 

is 30 ft. The design includes a central compacted zone 1 impervious material, and upstream and 

downstream zone 2 of sand and gravel, shown in Figure 3. The upstream slope is protected with 

riprap and bedding above elevation 1430 ft. A toe drain consisting of sewer pipe laid with open 

joints is located in the downstream zone 2 along most of the embankment. 

Figure 3. — Cross-section through Jamestown Dam. 

The abutments are composed of Pierre Shale capped with glacial till. The main portion of the 

dam is founded on a thick section of alluvial deposits. The spillway and outlet works are 

founded on Pierre Shale. Beneath the dam a cutoff trench was excavated to the shale on both 

abutments, however, between the abutments, foundation excavation extended to a maximum 

depth of 25 ft, and did not provide a positive cutoff of the thick alluvium. The alluvium beneath 

the dam is more than 120 ft thick in the channel area. 

There is a toe drain within the downstream embankment near the foundation level, and a fairly 

wide embankment section to help control seepage beneath the dam, since a positive cutoff was 

not constructed. The original design recognized that additional work might be required to 
 11 

control seepage and uplift pressures, depending on performance of the dam during first filling. 

In general, performance of the dam has been adequate, but, reservoir water surface elevations 

have never exceeded 1445.9 ft, well below the spillway crest. Based on observations of 

increasing pressures in the foundation during high reservoir elevations and significant boil 

activity downstream from the dam, eight relief wells were installed along the downstream toe in 

1995 and 1996. To increase the seepage protection, a filter blanket was constructed in low areas 

downstream from the dam in 1998. 

Results — Breach Parameter Estimates 

Breach parameter predictions were computed for the four reservoir conditions listed previously: 

top of joint use; elev. 1440.0; top of flood space; and maximum design water surface elevation. 

Predictions were made for average breach width, volume of eroded material, and failure time. 

Side slope angles were not predicted because equations for predicting breach side slope angles 

are rare in the literature; Froehlich (1987) offered an equation, but in his later paper (1995b) he 

suggested simply assuming side slopes of 0.9:1 (horizontal:vertical) for piping failures. Von 

Thun and Gillette (1990) suggested using side slopes of 1:1, except for cases of dams with very 

thick zones of cohesive materials where side slopes of 0.5:1 or 0.33:1 might be more appropriate. 

After computing breach parameters using the several available equations, the results were 

reviewed and engineering judgment applied to develop a single predicted value and an 

uncertainty band to be provided to the risk assessment study team. These recommended values 

are shown at the bottom of each column in the tables that follow. 

Breach Width 

Predictions of average breach width are summarized in Table 2. The table also lists the 

predictions of the volume of eroded embankment material made using the MacDonald and 

Langridge-Monopolis equation, and the corresponding estimate of average breach width. 

Table 2. — Predictions of average breach width for Jamestown Dam. 

Top of joint use 

(elev. 1432.67 ft) Elev. 1440.0 ft 

Top of flood space 

(elev. 1454.0 ft) 

Maximum design water surface 

(elev. 1464.3 ft) BREACH WIDTHS 

B, feet

Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval 

Reclamation, 1988 128 58 — 422 150 68 — 495 192 86 — 634 223 100 — 736 

Von Thun and Gillette, 

1990 287 106 — 516 305 113 — 549 340 126 — 612 366 135 — 659 

Froehlich, 1995b 307 123 — 737 401 160 — 962 544 218 — 1307 648 259 — 1554^ 

MacDonald and 

Langridge-Monopolis, 

1984 

 (Volume of erosion, yd3) 

191,000 29,000 — 1,296,000 408,000 61,000 — 2,775,000 1,029,000 154,000 — 6,995,000 1,751,000 263,000 — 11,904,000 

(Equivalent breach width, ft) 281 42 — 1,908^ 601 90 — 4,090^ 1,515^ 227 — 10,300^ 2,578^ 387 — 17,528^ 

Recommended values 290 110 — 600 400 150 — 1000 540 200 — 1300 650 250 — 1418 

* Recommend breach side slopes for all scenarios are 0.9 horizontal to 1.0 vertical. 

^ Exceeds actual embankment length. 

The uncertainty analysis described earlier showed that the Reclamation equation tends to 

underestimate the observed breach width, so it is not surprising that it yielded the smallest 

values. The Von Thun and Gillette equation and the Froehlich equation produced comparable 

results for the top-of-joint-use scenario, in which reservoir storage is relatively small. For the 

two scenarios with greater reservoir storage, the Froehlich equation predicts significantly larger 
 12 

breach widths. This is not surprising, since the Froehlich equation relates breach width to an 

exponential function of both the reservoir storage and reservoir depth. The Von Thun and 

Gillette equation accounts for reservoir storage only through the Cb offset parameter, but Cb is a 

constant for all reservoirs larger than 10,000 ac-ft, as was the case for all four of these scenarios. 

Using the MacDonald and Langridge-Monopolis equation, the estimate of eroded embankment 

volume and associated breach width for the top-of-joint-use scenario is also comparable to the 

other equations. However, for the two large-volume scenarios, the predictions are much larger 

than any of the other equations, and in fact are unreasonable because they exceed the dimensions 

of the dam (1,418 ft long; volume of 763,000 yd3

). 

The prediction intervals developed through the uncertainty analysis are sobering, as the ranges 

vary from small notches through the dam to complete washout of the embankment. Even for the 

top-of-joint-use case, the upper bound for the Froehlich and Von Thun/Gillette equations is 

equivalent to about half the length of the embankment. 

Failure Time 

Failure time predictions are summarized in Table 3. All of the equations indicate increasing 

failure times as the reservoir storage increases, except the second Von Thun and Gillette relation, 

which predicts a slight decrease in failure time for the large-storage scenarios. For both Von 

Thun and Gillette relations, the dam was assumed to be in the erosion resistant category. 

Table 3. — Failure time predictions for Jamestown Dam. 

FAILURE TIMES 

tf, hours 

Top of joint use 

(elev. 1432.67 ft) Elev. 1440.0 ft 

Top of flood space 

(elev. 1454.0 ft) 

Maximum design water surface 

(elev. 1464.3 ft) 

 Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval 

MacDonald and 

Langridge-Monopolis, 

1984 

1.36 0.33 — 14.9 1.79 0.43 — 19.7 2.45* 0.59 — 26.9 2.45* 0.59 — 26.9 

Von Thun and Gillette, 

1990 

 tf = f(hw) 

...erosion resistant

0.51 0.25 — 20.4 0.55 0.27 — 22.2 0.64 0.31 — 25.6 0.70 0.34 — 28.1 

Von Thun and Gillette, 

1990 

 tf = f(B, hw) 

...erosion resistant

1.68 0.59 — 28.6 1.53 0.53 — 25.9 1.33 0.47 — 22.6 1.23 0.43 — 20.9 

Froehlich, 1995b 1.63 0.62 — 11.9 2.53 0.96 — 18.4 4.19 1.59 — 30.6 5.59 2.12 — 40.8 

Reclamation, 1988 0.43 0.10 — 11.6 0.50 0.12 — 13.6 0.64 0.15 — 17.4 0.75 0.18 — 20.2 

Recommended values 1.5 0.25 — 12 1.75 0.25 — 14 3.0 0.3 — 17 4.0 0.33 — 20 

* The MacDonald and Langridge-Monopolis equation is based on the prediction of eroded volume, shown previously in Table 2. 

Because the predicted volumes exceeded the total embankment volume in the two large-storage scenarios, the total embankment 

volume was used in the failure time equation. Thus, the results are identical to the top-of-joint-use case. 

The predicted failure times exhibit wide variation, and the recommended values shown at the 

bottom of the table are based on much judgment. The uncertainty analysis showed that all of the 

failure time equations tend to conservatively underestimate actual failure times, especially the 

Von Thun and Gillette and Reclamation equations. Thus, the recommended values are generally 

a compromise between the results obtained from the MacDonald and Langridge-Monopolis and 

Froehlich relations. Despite this fact, some very fast failures are documented in the literature, 

and this possibility is reflected in the prediction intervals determined from the uncertainty 

analysis. 
 13 

Results — Peak Outflow Estimates 

Peak outflow estimates are shown in Table 4, sorted in order of increasing peak outflow for the 

top-of-joint-use scenario. The lowest peak flow predictions come from those equations that are 

based solely on dam height or depth of water in the reservoir. The highest peak flows are 

predicted by those equations that incorporate a significant dependence on reservoir storage. 

Some of the predicted peak flows and the upper bounds of the prediction limits would be the 

largest dam-break outflows ever recorded, exceeding the 2.3 million ft3/s peak outflow from the 

Teton Dam failure. (Storage in Teton Dam was 289,000 ac-ft at failure). The length of 

Jamestown Reservoir (about 30 miles) may help to attenuate some of the large peak outflows 

predicted by the storage-sensitive equations, since there will be an appreciable routing effect in 

the reservoir itself that is probably not accounted for in the peak flow prediction equations. 

Table 4. — Predictions of peak breach outflow for Jamestown Dam. 

Top of joint use 

(elev. 1432.67 ft) Elev. 1440.0 ft 

Top of flood space 

(elev. 1454.0 ft) 

Maximum design water surface 

(elev. 1464.3 ft) PEAK OUTFLOWS 

Qp, ft3

/s

Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval Prediction 

95% Prediction 

Interval 

Kirkpatrick, 1977 28,900 8,100 — 196,600 42,600 11,900 — 289,900 78,200 21,900 — 531,700 112,900 31,600 — 768,000 

SCS, 1981 67,500 15,500 — 162,000 90,500 20,800 — 217,200 142,900 32,900 — 342,900 188,300 43,300 — 451,900 

Reclamation, 1982, envelope 77,700 15,500 — 163,100 104,100 20,800 — 218,600 164,400 32,900 — 345,200 216,600 43,300 — 455,000 

Froehlich, 1995a 93,800 49,700 — 215,700 145,900 77,300 — 335,600 262,700 139,200 — 604,200 370,900 196,600 — 853,100 

MacDonald and 

Langridge-Monopolis, 1984 167,800 25,200 — 620,900 252,400 37,900 — 933,700 414,100 62,100 — 1,532,000 550,600 82,600 — 2,037,000 

Singh/Snorrason, 1984 

 Qp = f(hd) 202,700 46,600 — 385,200 202,700 46,600 — 385,200 202,700 46,600 — 385,200 202,700 46,600 — 385,200 

Walder and O’Connor, 1997 211,700 33,900 — 755,600 279,300 44,700 — 997,200 430,200 68,800 — 1,536,000 558,600 89,400 — 1,994,000 

Costa, 1985 

 Qp = f(S*hd) 219,500 37,300 — 1,032,000 311,200 52,900 — 1,463,000 464,900 79,000 — 2,185,000 583,800 99,200 — 2,744,000 

Singh/Snorrason, 1984 

 Qp = f(S) 249,600 20,000 — 1,348,000 369,000 29,500 — 1,993,000 578,200 46,300 — 3,122,000 746,000 59,700 — 4,028,000 

Evans, 1986 291,600 17,500 — 1,283,000 453,100 27,200 — 1,994,000 751,800 45,100 — 3,308,000 1,002,000 60,100 — 4,409,000 

MacDonald and 

Langridge-Monopolis, 1984 

 (envelope equation) 

548,700 27,400 — 603,500 824,300 41,200 — 906,700 1,351,000 67,600 — 1,486,000 1,795,000 89,800 — 1,975,000 

Hagen, 1982 640,100 44,800 — 1,344,000 970,000 67,900 — 2,038,000 1,564,000 109,500 — 3,285,000 2,051,000 143,600 — 4,308,000 

Costa, 1985 

 Qp = f(S*hd) (envelope) 894,100 35,800 — 1,091,000 1,289,000 51,600 — 1,573,000 1,963,000 78,500 — 2,395,000 2,492,000 99,700 — 3,040,000 

Costa, 1985 

 Qp = f(S) 920,000 18,400 — 1,932,000 1,478,000 29,600 — 3,104,000 2,548,000 51,000 — 5,351,000 3,470,000 69,400 — 7,288,000 

The equation offered by Froehlich (1995a) clearly had the best prediction performance in the 

uncertainty analysis, and is thus highlighted in the table. This equation had the smallest mean 

prediction error and narrowest prediction interval by a significant margin. 

The results for the Walder and O’Connor method are also highlighted. As discussed earlier, this 

is the only method that considers the differences between the so-called large-reservoir/fasterosion and small-reservoir/slow-erosion cases. Jamestown Dam proves to be a largereservoir/fast-erosion case when analyzed by this method (regardless of the assumed vertical 

erosion rate of the breach—within reasonable limits), so the peak outflow will occur when the 

breach reaches its maximum size, before significant drawdown of the reservoir has occurred. 

Despite the refinement of considering large- vs. small-reservoir behavior, the Walder and 

O’Connor method was found to have uncertainty similar to most of the other peak flow 

prediction methods (about ±0.75 log cycles). However, amongst the 22 case studies that the 

method could be applied to, only four proved to be large-reservoir/fast-erosion cases. Of these, 
 14 

the method overpredicted the peak outflow in three cases, and dramatically underpredicted in one 

case (Goose Creek Dam, South Carolina, failed 1916 by overtopping). Closer examination 

showed some contradictions in the data reported in the literature for this case. On balance, it 

appears that the Walder and O’Connor method may provide reasonable estimates of the upper 

limit on peak outflow for large-reservoir/fast-erosion cases. 

For the Jamestown Dam case, results from the Froehlich method can be considered the best 

estimate of peak breach outflow, and the results from the Walder and O’Connor method provide 

an upper bound estimate. 

NWS-BREACH Simulations 

Several simulations runs were made using the National Weather Service BREACH model (Fread 

1988). The model requires input data related to reservoir bathymetry, dam geometry, the 

tailwater channel, embankment materials, and initial conditions for the simulated piping failure. 

Detailed information on embankment material properties was not available at the time that the 

simulations were run, so material properties were assumed to be similar to those of Teton Dam. 

A Teton Dam input data file is distributed with the model. 

The results of the simulations are very sensitive to the elevation at which the piping failure is 

assumed to develop. In all cases analyzed, the maximum outflow occurred just prior to the crest 

of the dam collapsing into the pipe; after the collapse of the crest, a large volume of material 

partially blocks the pipe and the outflow becomes weir-controlled until the material can be 

removed. Thus, the largest peak outflows and largest breach sizes are obtained if the failure is 

initiated at the base of the dam, assumed to be elev. 1390.0 ft. This produces the maximum 

amount of head on the developing pipe, and allows it to grow to the largest possible size before 

the collapse occurs. Table 5 shows summary results of the simulations. For each of the four 

initial reservoir elevations a simulation was run with the pipe initiating at elev. 1390.0 ft, and a 

second simulation was run with the pipe initiating about midway up the height of the dam. 

Table 5. — Results of NWS-BREACH simulations of seepage-erosion failures of Jamestown Dam. 

Top of joint use 

(elev. 1432.67 ft) Elev. 1440.0 ft 

Top of flood space 

(elev. 1454.0 ft) 

Maximum design water 

surface (elev. 1464.3 ft) 

Initial elev. of piping failure, ft Æ 1390.0 1411.0 1390.0 1415.0 1390.0 1420.0 1390.0 1430.0 

Peak outflow, ft3/s 80,400 16,400 131,800 24,050 242,100 52,400 284,200 54,100 

tp, Time-to-peak outflow, hrs 

(from first significant 

increased flow through the 

breach) 

3.9 2.1 4.0 1.8 4.0 1.4 3.6 1.1 

Breach width at tp, ft 51.6 21.4 63.2 24.8 81.0 33.7 81.0 34.2 

There is obviously wide variation in the results depending on the assumed initial conditions for 

the elevation of the seepage failure. The peak outflows and breach widths tend toward the low 

end of the range of predictions made using the regression equations based on case study data. 

The predicted failure times are within the range of the previous predictions, and significantly 

longer than the very short (0.5 to 0.75 hr) failure times predicted by the Reclamation (1988) 

equation and the first Von Thun and Gillette equation. 

Refinement of the material properties and other input data provided to the NWS-BREACH 

model might significantly change these results. 
 15 

Conclusions

This paper has presented a quantitative analysis of the uncertainty of various regression-based 

methods for predicting embankment dam breach parameters and peak breach outflows. The 

uncertainties of predictions of breach width, failure time, and peak outflow are large for all 

methods, and thus it may be worthwhile to incorporate uncertainty analysis results into future 

risk assessment studies when predicting breach parameters using these methods. Predictions of 

breach width generally have an uncertainty of about ±1/3 order of magnitude, predictions of 

failure time have uncertainties approaching ±1 order of magnitude, and predictions of peak flow 

have uncertainties of about ±0.5 to ±1 order of magnitude, except the Froehlich peak flow 

equation, which has an uncertainty of about ±1/3 order of magnitude. 

The uncertainty analysis made use of a database of information on the failure of 108 dams 

compiled from numerous sources in the literature (Wahl 1998). For those wishing to make use 

of this database, it is available in electronic form (Lotus 1-2-3, Microsoft Excel, and Microsoft 

Access) on the Internet at http://www.usbr.gov/wrrl/twahl/damfailuredatabase.zip. 

The case study presented for Jamestown Dam showed that significant engineering judgment 

must be exercised in the interpretation of predictions obtained from the regression-based 

methods. The results from use of the physically-based NWS-BREACH model were reassuring 

because they fell within the range of values obtained from the regression-based methods, but at 

the same time they also helped to show that even physically-based methods can be highly 

sensitive to the analysts assumptions regarding breach morphology and the location of initial 

breach development. The NWS-BREACH simulations revealed the possibility for limiting 

failure mechanics that were not considered in the regression-based methods. 

References

Costa, John E., 1985, Floods from Dam Failures, U.S. Geological Survey Open-File Report 85-560, Denver, 

Colorado, 54 p. 

Dewey, Robert L., and David R. Gillette, 1993, “Prediction of Embankment Dam Breaching for Hazard 

Assessment,” Proceedings, ASCE Specialty Conference on Geotechnical Practice in Dam Rehabilitation, 

Raleigh, North Carolina, April 25-28, 1993. 

Evans, Steven G., 1986, “The Maximum Discharge of Outburst Floods Caused by the Breaching of Man-Made and 

Natural Dams,” Canadian Geotechnical Journal, vol. 23, August 1986. 

Fread, D.L., 1984, DAMBRK: The NWS Dam-Break Flood Forecasting Model, National Weather Service, Office of 

Hydrology, Silver Spring, Maryland. 

Fread, D.L., 1988 (revised 1991), BREACH: An Erosion Model for Earthen Dam Failures, National Weather 

Service, National Oceanic and Atmospheric Administration, Silver Spring, Maryland. 

Fread, D.L., 1993, “NWS FLDWAV Model: The Replacement of DAMBRK for Dam-Break Flood Prediction,” 

Dam Safety ’93, Proceedings of the 10th Annual ASDSO Conference, Kansas City, Missouri, September 

26-29, 1993, p. 177-184. 

Froehlich, David C., 1987, “Embankment-Dam Breach Parameters,” Hydraulic Engineering, Proceedings of the 

1987 ASCE National Conference on Hydraulic Engineering, Williamsburg, Virginia, August 3-7, 1987, p. 

570-575. 

Froehlich, David C., 1995a, “Peak Outflow from Breached Embankment Dam,” Journal of Water Resources 

Planning and Management, vol. 121, no. 1, p. 90-97. 
 16 

Froehlich, David C., 1995b, “Embankment Dam Breach Parameters Revisited,” Water Resources Engineering, 

Proceedings of the 1995 ASCE Conference on Water Resources Engineering, San Antonio, Texas, August 

14-18, 1995, p. 887-891. 

Hagen, Vernon K., 1982, “Re-evaluation of Design Floods and Dam Safety,” Proceedings, 14th Congress of 

International Commission on Large Dams, Rio de Janeiro. 

Hahn, W., G.J. Hanson, and K.R. Cook, 2000, “Breach Morphology Observations of Embankment Overtopping 

Tests,” 2000 Joint Conference on Water Resources Engineering and Water Resources Planning and 

Management, ASCE, Minneapolis, MN. 

Johnson, F.A., and P. Illes, 1976, “A Classification of Dam Failures,” International Water Power and Dam 

Construction, December 1976, p. 43-45. 

Kirkpatrick, Gerald W., 1977, “Evaluation Guidelines for Spillway Adequacy,” The Evaluation of Dam Safety, 

Engineering Foundation Conference, Pacific Grove, California, ASCE, p. 395-414. 

MacDonald, Thomas C., and Jennifer Langridge-Monopolis, 1984, “Breaching Characteristics of Dam Failures,” 

Journal of Hydraulic Engineering, vol. 110, no. 5, p. 567-586. 

Rousseeuw, Peter J. (1998). “Robust Estimation and Identifying Outliers” in Handbook of Statistical Methods for 

Engineers and Scientists, 2nd ed., Harrison M. Wadsworth, Jr., editor. McGraw-Hill, New York, NY, pp. 

17.1-17.15. 

Singh, Krishan P., and Arni Snorrason, 1984, “Sensitivity of Outflow Peaks and Flood Stages to the Selection of 

Dam Breach Parameters and Simulation Models,” Journal of Hydrology, vol. 68, p. 295-310. 

Soil Conservation Service, 1981, Simplified Dam-Breach Routing Procedure, Technical Release No. 66 (Rev. 1), 

December 1981, 39 p. 

Temple, Darrel M., and John S. Moore, 1994, “Headcut Advance Prediction for Earth Spillways,” presented at the 

1994 ASAE International Winter Meeting, Paper No. 94-2540, Atlanta, Georgia, December 13-16, 1994, 

19 p. 

U.S. Bureau of Reclamation, 1982, Guidelines for Defining Inundated Areas Downstream from Bureau of 

Reclamation Dams, Reclamation Planning Instruction No. 82-11, June 15, 1982. 

U.S. Bureau of Reclamation, 1988, Downstream Hazard Classification Guidelines, ACER Technical Memorandum 

No. 11, Assistant Commissioner-Engineering and Research, Denver, Colorado, December 1988, 57 p. 

Von Thun, J. Lawrence, and David R. Gillette, 1990, Guidance on Breach Parameters, unpublished internal 

document, U.S. Bureau of Reclamation, Denver, Colorado, March 13, 1990, 17 p. 

Wahl, Tony L., 1998, Prediction of Embankment Dam Breach Parameters - A Literature Review and Needs 

Assessment, U.S. Bureau of Reclamation Dam Safety Report DSO-98-004, July 1998, 

http://www.usbr.gov/wrrl/twahl/distilled.dso-98-004.pdf

Walder, Joseph S., and Jim E. O’Connor, 1997, “Methods for Predicting Peak Discharge of Floods Caused by 

Failure of Natural and Constructed Earth Dams,” Water Resources Research, vol. 33, no. 10, October 1997, 

12 p. 
B-5

SOME EXISTING CAPABILITIES AND FUTURE DIRECTIONS FOR

DAM-BREACH MODELING/FLOOD ROUTING

D.L. Fread1

Abstract: Dam-breach modeling and the routing of the unsteady

breach outflow through the downstream river/valley are important

tasks for many Federal, state, local agencies, consultants etc.,

which are charged with or assist those so charged with dam

design, operation, regulation, and/or public safety. A brief

historical summary is provided which covers some of the relevant

procedures for prediction of dam-breach outflows and their extent

of flooding in the downstream river/valley.

Dam-breach modeling can be conveniently categorized as

parametric-based or physically-based. The former utilizes key

parameters: average breach width (bav) and breach formation time

(tf) to represent the breach formation in earthen dams, and thus

compute the breach outflow hydrograph using a numerical time-step

solution procedure or a single analytical equation. Statistics

on observed values for bav and tf have been presented. Also,

various regression equations have been developed to compute peakbreach discharge using only the reservoir volume (Vr) and the dam

height (Hd) or some combination thereof. Physically-based breach

models use principles of hydraulics, sediment erosion, and soil

stability to construct time-stepping numerical solutions of the

breach formation process and the breach outflow hydrograph.

Flood routing is essential for assessing the extent of downstream

flooding due to dam-breach outflows because of the extreme amount

of peak attenuation the unsteady breach outflow experiences

during its propagation through the river/valley. Dam-breach

flood routing models have utilized (1) numerical time-step

solutions of the complete one-dimensional Saint-Venant equations

of unsteady flow; (2) breach peak-flow routing attenuation curves

coupled with the Manning equation to compute peak-flow depths;

and (3) a simplified Muskingum-Cunge flow routing and Manning

equation depth computation. The latter two routing procedures

incur additional error compared to the Saint-Venant routing.

Finally, future research/development directions for dam-breach

prediction are presented.

1. Introduction

A breach is the opening formed in a dam as it fails. The actual

____________________

1

Fread Hydraulic Modeling Services, 622 Stone Road, Westminster, MD 21158, Ph 410-

857-0744
breach failure mechanics are not well understood for either

earthen or concrete dams. Prior to about 1970, most attempts to

predict downstream flooding due to dam failures, assumed that the

dam failed completely and instantaneously. The assumptions of

instantaneous and complete breaches were used for reasons of

convenience when applying certain mathematical techniques for

analyzing dam—break flood waves. These assumptions are somewhat

appropriate for concrete arch dams with reservoir storage volumes

greater than about one—half million acre—ft, but they are not

appropriate for either earthen dams or concrete gravity dams.

Dam-break modeling and the associated routing of the outflow

hydrograph (flood wave) through the downstream river/valley is

of continuing concern to many Federal, state, local, and

international agencies, the private sector, and academia.

Such predictive capabilities are of concern to these entities

since they are charged with or assist those charged with

responsibilities for dam design, operation, regulation, and/or

public safety. This paper presents a perspective on the present

capabilities to accomplish dam-breach modeling and the associated

flood routing.

Dam—breach models may be conveniently categorized as parametric

models or physically—based models. A summary of a relevant

portion of the history of dam-breach modeling and dam-breach

flood routing capabilities is presented in Table 1. A brief

description of both numerical and analytical dam—breach

parametric models, dam-breach physically-based models, and dambreach flood routing models are presented herein.

Finally, future research/development directions in dam-breach

prediction capabilities are presented. These are judged to offer

the most efficient and effective means of improving practical

dam-breach modeling and dam-breach flood routing capabilities.

2. Numerical Parametric Breach Models

Earthen dams which exceedingly outnumber all other types of dams

do not tend to completely fail, nor do they fail instantaneously.

The fully formed breach in earthen dams tends to have an average

width (bav) in the range (O.5<bav/Hd<8) where Hd is the height of the

dam. The middle portion of the range for bav is supported by the

summary report of Johnson and Illes (1976) and the upper range by

the report of Singh and Snorrason (1982). Breach widths for

earthen dams are therefore usually much less than the total

length of the dam as measured across the valley. Also, the

breach requires a finite interval of time (tf) for its formation

through erosion of the dam materials by the escaping water. The

breach formation time is the duration of time between the first

breaching of the upstream face of the dam until the breach is

fully formed. For overtopping failures the beginning of breach

formation is after the downstream face of the dam has eroded away
Table 1. History of Dam-Breach Modeling

and the resulting crevasse has progressed back across the width

of the dam crest to reach the upstream face. This portion of the

failure process could be thought of as the “initiation time”

which is quite distinct from the breach “formation time” or time

of failure (tf). Time of failure (tf) for overtopping initiated

failures may be in the range of a few minutes to usually less

than an hour, depending on the height of the dam, the type of

materials, and the magnitude and duration of the overtopping flow

of the escaping water.

Poorly constructed coal-waste dumps (dams) which impound water

tend to fail within a few minutes, and have average breach widths

in the upper range of the earthen dams mentioned above. Also,

average breach widths are considerably larger for reservoirs with

very large storages which sustain a fairly constant reservoir

elevation during the breach formation time; such a slowly

changing reservoir elevation enables the breach to erode to the

bottom of the dam and then erode horizontally creating a wider

breach before the peak discharge is attained.

Piping failures occur when initial breach formation takes place at

some point below the top of the dam due to erosion of an

internal channel through the dam by the escaping water. Breach

formation times are usually considerably longer for piping than

overtopping failures since the upstream face is slowly being

eroded in the early phase of the piping development. As the

erosion proceeds, a larger and larger opening is formed; this is

eventually hastened by caving-in of the top portion of the dam.
Fread (1971,1977,l988,l993) used a parametric approach to describe

and mathematically model the dynamic breach—forming process. The

mathematical model combined the reservoir level—pool routing

equation with a critical—flow, weir equation in which the weir or

breach was time dependent whose shape and size were controlled by

specified parameters. The numerical time—stepping solution of

these equations produced a discharge hydrograph of breach outflow

including the maximum (peak) discharge. The parametric

description of the dynamic breach is shown in Figure 1.

The breach is assumed to form over a finite interval of time (tf)

and has a final (terminal) breach size of b determined by the

breach side—slope parameter (z) and the average breach width

parameter bav. Such a parametric representation of the breach is

Figure 1. Front View of Dam Showing Formation of Breach.

utilized for reasons of simplicity, generality, wide

applicability, and the uncertainty in the actual failure

mechanism. This approach to the breach description follows that

first used by Fread and Harbaugh (1973) and later in the NWS

DAMBRK Model (Fread;1977, 1988). The shape parameter (z)

identifies the side slope of the breach, i.e., 1 vertical: z

horizontal. The range of z values is from 0 to somewhat larger

than unity. The value of z depends on the angle of repose of the

compacted, wetted materials through which the breach develops.

Rectangular, triangular, or trapezoidal shapes may be specified

by using various combinations of values for z and the terminal

breach bottom width (b), e.g., z=0 and b>0 produces a rectangle

and z>0 and b=0 yields a triangular-shaped breach. The terminal

width b is related to the average width of the breach (bav) by the

following:

b= bav-zHd (1)

in which Hd is the height of the dam. The bottom elevation of the

breach (hb) is simulated as a function of time (tf) according to
the following:

hb =hd-(hd - hbm)(tb/tf)

r

 0<tb<tf (2)

in which hd is the elevation of the top of the dam. The model

assumes the instantaneous breach bottom width (bi) starts at a

point (see Figure 1) and enlarges at a linear or nonlinear rate

over the failure time (tf) until the terminal bottom width (b) is

attained and the breach bottom elevation (hb) has eroded to a

specified final elevation (hbm). The final elevation of the

breach bottom (hbm) is usually, but not necessarily, the bottom of

the reservoir or outlet channel bottom, tb, is the time since

beginning of breach formation, and r is a parameter specifying

the degree of nonlinearity, e.g., r=1 is a linear formation rate,

while r=2 is a nonlinear quadratic rate; the range for r is

1<r<4. The linear rate is usually assumed, although the nonlinear rate is more realistic especially for piping failures;

however, its value is not well identified. The instantaneous

bottom width (bi) of the breach is given by the following:

bi= b (tb/tf)

r

tb<tf (3)

During the simulation of a dam failure, the actual breach

formation commences when the reservoir water surface elevation

(h) exceeds a specified value, hf. This enables the simulation

of an overtopping of a dam in which the breach does not form

until a sufficient amount of water is flowing over the top of the

dam. A piping failure may also be simulated by specifying the

initial centerline elevation of the pipe-breach.

2.1 Statistically-Based Breach Predictors

Some statistically derived predictors for bav and tf. have been

presented in the literature, i.e, MacDonald and LangridgeMonopolis(1984) and Froehlich(1987,l995). Using this data of the

properties of 63 breaches of dams ranging in height from 15 to

285 ft, with 6 of the dams greater than 100 ft, the following

predictive equations are obtained:

bav = 9.5ko(Vr H)

0.25 (4)

tf =0.3Vr

0.53/H0.9 (5)

in which bav is average breach width (ft), tf is time of failure

(hrs), ko = 0.7 for piping and 1.0 for overtopping, Vr is

volume(acre—ft) and H is the height (ft) of water over the breach

bottom (H is usually about the height of the dam, Hd). Standard

error of estimate for bav is ±56 percent of bav, and the standard

error of estimate for tf is ±74 percent of tf.
3. Analytical Parametric Breach Models

A single analytical equation was also developed to predict the

peak outflow from a breached dam. Fread (1981,l984) developed

such an equation which was a critical component of the NWS SMPDBK

(Simplified Dam-Break) model. This equation accounted for the

hydraulic processes of dam-breach outflows, i.e, the simultaneous

lowering of the reservoir elevation as the breach forms by the

escaping reservoir outflow while using the basic breach

parameters (bav,tf), i.e.

Qp=3.1bav[C/(tf + C/Hd

0.5)]3 (6)

in which Qp is the peak breach outflow in cfs, bav is the average

breach width in feet, tf is the breach formation time in hours,

Hd is the height of the dam in feet, and C=23.4 Sa/bav in which Sa

is the reservoir surface area (acres) somewhat above the

elevation of the top of the dam. Recently, a similar but

considerably more complicated approach was reported by Walder and

O’Connor(1997).

Another analytical (single equation) approach for earthen dam—

breaches relies on a statistical regression approach that relates

the observed (estimated) peak dam—breach discharge to some

measure of the impounded reservoir water volume: depth, volume,

or some combination thereof, e.g., Hagen,l982; Evans,l986; Costa,

1988; Froehlich,l995. An example of this type of equation

follows:

Qp=aVr

bHd

c (7)

in which Vr is the reservoir volume, Hd is the height of the dam,

and a, b, c are regression coefficients, e.g., Froehlich(1995)

quantifies these as a=40.1, b=O.295, c=1.24 in which the units for

Qp, Vr, and Hd are cfs, acre-ft and ft, respectively. This

approach is expedient but generally only provides an order of

magnitude prediction of dam-breach peak discharge. It does not

reflect the true hydraulics, but instead mixes the failureerosion process and the hydraulic processes, while ignoring the

important components of time—dependent erosion, weir flow, and

reservoir routing.

4. Physically-Based Breach Erosion Models

Another means of determining the breach properties is the use of

physically-based breach erosion models. Cristofano(l965) modeled

the partial, time-dependent breach formation in earthen dams;

however, this procedure required critical assumptions and

specification of unknown critical parameter values. Also, Harris

and Wagner(1967) used a sediment transport relation to determine

the time for breach formation, but this procedure required

specification of breach size and shape in addition to two
critical parameters for the sediment transport computation; then,

Ponce and Tsivoglou(1981) presented a rather computationally

complex breach erosion model which coupled the Meyer—Peter and

Muller sediment transport equation to the one—dimensional

differential equations of unsteady flow (Saint-Venant equations)

and the sediment conservation equation. They compared the

model’s predictions with observations of a breached landslide—

formed dam on the Mantaro River in Peru. The results were

substantially affected by the judicious selection of the breach

channel hydraulic friction factor (Manning n), an empirical

breach width—flow parameter, and an empirical coefficient in the

sediment transport equation.

Another physically-based breach erosion model (BREACH) for

earthen dams was developed (Fread;1984,1987) which utilizes

principles of soil mechanics, hydraulics, and sediment transport.

This model substantially differed from the previously mentioned

models. It predicted the breach characteristics (size, shape, time

of formation) and the discharge hydrograph emanating from a

breached earthen dam which was man—made or naturally formed by a

landslide; the typical scale and geometrical variances are

illustrated in Figure 2. The model was developed by coupling the

Figure 2. Comparative View of Natural Landslide Dams and Man-Made Dams.

conservation of mass of the reservoir inflow, spillway outflow,

and breach outflow with the sediment transport capacity (computed

along an erosion-formed breach channel. The bottom slope of the

breach channel was assumed to be the downstream face of the dam

as shown in Figure 3. The growth of the breach channel,

conceptually modeled as shown in Figure 4, was dependent on the

dam’s material properties (D50 size, unit weight(g), internal

friction angle (f), and cohesive strength (Ch)).

The model considered the possible existence of the following

complexities: (1) core material properties which differ from

those of the outer portions of the dam; (2) formation of an

eroded ditch along the downstream face of the dam prior to the

actual breach formation by the overtopping water; (3) the

downstream face of the dam could have a grass cover or be

composed of a material such as rip—rap or cobble stones of larger

grain size than the major portion of the dam; (4) enlargement of

the breach through the mechanism of one or more sudden structural
Figure 3. Side View of Dam Showing Conceptualized Overtopping Failure Sequence.

collapses of the breaching portion of the dam due to the

hydrostatic pressure force exceeding the resisting shear and

cohesive forces; (5) enlargement of the breach width by collapse

of the breach sides according to slope stability theory as shown

in Figure 4; and (6) the capability for initiation of the breach

Figure 4. Front View of Dam with Breach Formation Sequence.

via piping with subsequent progression to a free—surface breach

flow. The outflow hydrograph was obtained through a

computationally efficient time-stepping iterative solution. This
breach erosion model was not subject to numerical stability/

convergence difficulties experienced by the more complex model of

Ponce and Tsivoglou (1981). The model’s predictions were

favorably compared with observations of a piping failure of the

large man-made Teton Dam in Idaho, the piping failure of the

small man—made Lawn Lake Dam in Colorado, and an overtopping

activated breach of a large landslide—formed dam in Peru. Model

sensitivity to numerical parameters was minimal. A variation of

+ 30 percent in the internal friction angle and a ± 100 percent

variation in the cohesion parameter resulted in less than ± 20

percent variation in the simulated breach properties and peak

breach outflow. However, it was somewhat sensitive to the extent

of grass cover when simulating man—made dams in which over

topping flows could or could not initiate the failure of the dam.

A brief description of three breach simulations follows:

(1) Teton Dam. The BREACH model was applied to the piping

initiated failure (Fread;1984,1987) of the earthfill Teton Dam

which breached in June 1976, releasing an estimated peak

discharge (Qp) of 2.2 million cfs having a range of 1.6 to 2.6

million cfs. The material properties of the breach were as

follows: Hd=262.5 ft, D50=0.lmm, f=20 deg, Ch=3O lb/ft2, and g=100

lb/ft3. The downstream face of the dam had a slope of 1: 4 and

upstream face slope was 1:2. An initial piping failure of 0.01

ft located at 160 ft above the bottom of the dam commenced the

simulation. The simulated breach hydrograph is shown in

Figure 5. The computed final breach top width (W) of 645 ft

compared well with the observed value of 650 ft. The computed

side slope of the breach was 1:1.06 compared to 1:1.0. The

computed time (Tp) to peak flow was 2.2 hr compared to 1.95-2.12

hr.

(2) Lawn Lake Dam. This dam was a 26 ft high earthen dam with

approximately 800 acre-ft of storage, which failed July 15, 1982,

by piping along a bottom drain pipe (Jarrett and Costa,1984).

The BREACH model was applied (Fread,1987) with the piping breach

assumed to commence within 2 ft of the bottom of the dam. The

material properties of the breach were assumed as follows:

Hd=26 ft, D50=0.25mm, f=25 deg, Ch=l00 lb/ ft2, and g=100 lb/ft3.

The downstream face of the dam had a slope of 1:3 and the

upstream face 1:1.5. The computed outflow was 17,925 cfs, while

the estimated actual outflow was 18,000 cfs. The model produced

a trapezoidal-shaped breach with top and bottom dimensions of 132

and 68 ft, respectively. The actual breach dimensions were 97

and 55 ft, respectively. The mean observed breach width was

about 32 percent smaller than the mean breach width produced by

the model.
 

Figure 5. Teton Dam: Predicted and Observed Breach Outflow

Hydrograph and Breach Properties

(3) Mantaro Landslide Dam. A massive landslide occurred in the

valley of the Mantaro River in the mountainous area of central

Peru on April 25, 1974. The slide, with a volume of

approximately 5.6 x 1010ft, dammed the Mantaro River and formed a

lake which reached a depth of about 560 ft before overtopping

during the period June 6-8, 1974 (Lee and Duncan,1975). The

overtopping flow very gradually eroded a small channel along the

approximately 1 mile long downstream face of the slide during the

first two days of overtopping. Then a dramatic increase in the

breach channel occurred during the next 6—10 hours resulting in a

final trapezoidal-shaped breach channel approximately 350 ft

deep, a top width of some 800 ft, and side slopes of about 1:1.

The peak flow was estimated at 353,000 cfs as reported by Lee and

Duncan (1975), although Ponce and Tsivoglou(l98l) later reported

an estimated value of 484,000 cfs. The breach did not erode down

to the original river bed; this caused a rather large lake about

200 ft deep to remain after the breaching had subsided some 24

hours after the peak had occurred. The landslide material was

mostly a mixture of silty sand with some clay resulting in a D50

size of about 11mm with some material ranging in size up to 3 ft

boulders. The BREACH model was applied (Fread;1984,l987) to the

Mantaro landslide-formed dam using the following parameters:
upstream face slope 1:17, downstream face slope 1:8, Hd=560 ft,

D50=llmm, Ch=30 lb/ft2, f=38 deg, g=100 lb/ft3. The initial breach

depth was assumed to be 0.35 ft. The computed breach outflow is

shown in Figure 6 along with the estimated actual values. The

timing of the peak outflow and its magnitude are very similar as

are the dimensions of the gorge eroded through the dam shown by

the values of D, W, and a in Figure 6. Of particular interest,

the BREACH model produced a depth of breach of 352 ft which

compared to the observed depth of 350 ft.

Figure 6. Mantaro Landslide Dam: Predicted and Observed Breach Hydrograph and Breach

Properties.

Other physically-based breach erosion models include the

following: (1) the BEED model (Singh and Quiroga,1988) which is

similar to the BREACH model except it considers the effect of

saturated soil in the collapse of the breach sides and it routes

the breach outflow hydrograph through the downstream valley using

a simple diffusion routing technique (Muskingum-Cunge) which

neglects backwater effects and can produce significant errors in

routing a dam-breach hydrograph when the channel/valley slope is

less than 0.003 ft/ft; (2) a numerical model (Macchione and

Sirangelo,1988) based on the coupling of the one-dimensional

unsteady flow (Saint-Venant) equations with the continuity

equation for sediment transport and the Meyer-Peter and Muller

sediment transport equation; and (3) a numerical model (Bechteler

and Broich,1993) based on the coupling of the two-dimensional
unsteady flow equations with the sediment continuity equation and

the Meyer—Peter and Muller equation.

4. Flood Routing

Flood waves produced by the breaching (failure) of a dam are

known as dam—breach flood waves. They are much larger in peak

magnitude, considerably more sharp—peaked, and generally of

much shorter duration with flow acceleration components of a far

greater significance than flood waves produced by precipitation

runoff. The prediction of the time of occurrence and extent of

flooding in the downstream valley is known as flood routing.

The dam-breach wave is modified (attenuated, lagged, and

distorted) as it flows (is routed) through the downstream valley

due to the effects of valley storage, frictional resistance to

flow, flood flow acceleration components, flow losses, and

downstream channel constrictions and/or flow control structures.

Modifications to the dam-break flood wave are manifested as

attenuation (reduction) of the flood peak magnitude, spreadingout or dispersion of the temporal varying flood—wave volume, and

changes in the celerity (propagation speed) or travel time of the

flood wave. If the downstream valley contains significant

storage volume such as a wide floodplain, the flood wave can be

extensively attenuated (see Figure 7) and its propagation speed

greatly reduced. Even when the downstream valley approaches that

of a relatively narrow uniform rectangular—shaped section, there

is appreciable attenuation of the flood peak and reduction in the

wave celerity as the wave progresses through the valley.

Figure 7. Dam-Break Flood Wave Attenuation Along the Routing Reach.
5.1 Flood Routing with Saint-Venant Equations

Dam—breach flood waves have been routed using simulation models

based on numerical solutions of the one—dimensional Saint-Venant

equations of unsteady flow, e.g., DAMBRK (Fread,1977,l978) and

FLDWAV (Fread, 1993). The Saint-Venant equations used in these

models consists of the mass conservation equation, i.e.,

δQ/δx+scδ(A+Ao)/ δt - q=0 (8)

and the momentum conservation equation, i.e.,

smδQ/δt + β(δQ

2/A)/ δx+gA(δh/δx+Sf+Se)-qnx=0 (9)

where h is the water—surface elevation, A is the active cross—

sectional area of flow, Ao is the inactive (off-channel storage)

cross—sectional area, sc and sm are depth-weighted sinuosity

coefficients which correct for the departure of a sinuous in—bank

channel from the x-axis of the valley floodplain, x is the

longitudinal mean flow—path distance measured along the center of

the river/valley watercourse (river channel and floodplain), t is

time, q is the lateral inflow or outflow per lineal distance

along the river/valley (inflow is positive and outflow is

negative), β is the momentum coefficient for nonuniform velocity

distribution within the cross section, g is the gravity

acceleration constant, Sf is the boundary friction slope, Se is the

expansion—contraction (large eddy loss) slope, and nx is the

velocity component of the lateral flow along the x—axis.

5.2 Peak Flow Routing Attenuation Curves

Another flood routing technique SMPDBK (Fread and Wetmore,1984;

Fread, et al.,1991) has been used when the river/valley

downstream from a breached dam is uncomplicated by unsteady

backwater effects, levee overtopping, or large tributaries.

SMPDBK determines the peak flow, depth, and time of occurrence at

selected locations downstream of a breached dam. SMPDBK first

computes the peak outflow at the dam, based on the reservoir size

and the temporal and geometrical description of the breach. The

SMPDBK uses an analytical time-dependent broad-crested weir

equation, Eq.(6), to determine the maximum breach outflow (Qp) in

cfs and the user is required to supply the values of four

variables for this equation. These variables are: (1) the

surface area (As, acres) of the reservoir; (2) the depth (Hd, ft)

to which the breach erodes; (3) the time (tf, hrs) required for

breach formation; and (4) the width (bav, ft) of the breach, and

(5) the spillway flow and overtopping crest flow (Qo) which is

estimated to occur simultaneously with the breach peak outflow.

The computed flood wave and channel properties are used in

conjunction with special dimensionless routing curves (see

Figure 8) to determine how the peak flow will be diminished as it

moves downstream.
 

Figure 8. Routing Curves for SMPDBK Model for Froude No. = 0.25.

The dimensionless routing curves were developed from numerous

executions of the NWS DAMBRK model and they are grouped into

families based on the Froude number associated with the flood

wave peak, and have as their X—abcissa the ratio of downstream

distance (from the dam to a selected cross—section where Qp and

other properties of the flood wave are desired) to a distance

parameter (Xc). The Y-ordinate of the curves used in predicting

peak downstream flows is the ratio of the peak flow (Qp) at the

selected cross section to the computed peak flow at the dam,

QBMAX. The distinguishing characteristic of each member of a

family is the ratio (Vo) of the volume in the reservoir to the

average flow volume in the downstream channel from the dam to the

selected section. To specify the distance in dimensionless form,

the distance parameter (Xc) in feet is computed as follows:

Xc =6Vr/[(1+4(0.5)

m-1Ad] (10)

in which Vr is the reservoir volume (acre—ft), m is a crosssectional shape factor for the routing reach, and Ad, is the

average cross—section area in the routing reach at a depth of Hd.

The volume parameter (Vo) is Vo=Vr/( cXc) in which c represents

the average cross-sectional area in the routing reach at the

average maximum depth produced by the routed flow. The Froude

Number (Fc) is Fc=Vc/(gDc) where Vc and Dc, are the average

velocity and hydraulic depth, respectively, within the routing

reach. Further details on the computation of the dimensionless

parameters can be found elsewhere (Wetmore and Fread,1984;

Fread,et al.,1991).

The SMPDBK model then computes the depth produced by the peak

flow using the Manning equation based on the channel geometry,

slope, and roughness at the selected downstream locations. The

model also computes the time required for the peak to reach each
forecast location and, if a flood depth is entered for the point,

the time at which that depth is reached, as well as when the

flood wave recedes below that depth, thus providing a time frame

for evacuation and possible fortification on which a preparedness

plan may be based. The SMPDBK model neglects backwater effects

created by any downstream dams or bridge embankments, the

presence of which may substantially reduce the model’s accuracy.

However, its speed and ease of use, together with its small

computational requirements, make it an attractive tool for use in

cases where limited time and resources preclude the use of the

DAMBRK or FLDWAV models. In such instances, planners, designers,

emergency managers, and consulting engineers responsible for

predicting the potential effects of a dam failure may employ the

model where backwater effects are not significant.

The SMPDBK model was compared with the DAMBRK model in several

theoretical applications (Fread, et al.,1991) and several

hypothetical dam failures (Westphal and Thompson,l987) where the

effects of backwater, downstream dams/bridges, levee overtopping,

or significant downstream tributaries were negligible. The

average differences between the two models were less than

10 percent for predicted flows, travel times, and depths.

5.3 Numerical Routing with Muskingum-Cunge Equation

Another simple routing model (Muskingum-Cunge with variable

coefficients) may be used for routing dam-breach floods through

downstream river/valleys with moderate to steep bottom slopes

(So>0.003 ft/ft). The spatially distributed Muskingum-Cunge

routing equation applicable to each Dxi subreach for each Dt

j

time step is as follows:

Qi+1

j+1=C1Qij+1 +C2Qij +C3Qi+1j +C4 (11)

The coefficients C0, C1, and C2 are positive values whose sum must

equal unity; they are defined as

C0 = 2 K(1—X) + Dt

j (12)

C1 = (Dt

j-2KX)/C0 (13)

C2 = (Dt

j+2KX)/C0 (14)

C3= [2K(1—X) — Dt]/C0 (15)

C4= qi DxiDt

j/C0 (16)

in which K is a storage constant having dimensions of time, X is

a weighting factor expressing the relative importance of inflow

and outflow on the storage in the Dxi subreach of the river, and

qi the lateral inflow (+) or outflow (-) along the Dxi subreach.
K and X are computed as follows:

K = Dxi/c (17)

X = O.5[1—D/(k’SDxi)] (18)

in which c is the kinematic wave celerity c=k’Q/A, Q is

discharge, S is the energy slope approximated by evaluating Sf for

the initial flow condition, D is the hydraulic depth

A/B where A is the cross-sectional area and B is the wetted

top width associated with Q, and k’ is the kinematic wave ratio,

i.e., k’=5/3-2/3 A(dB/dh)/B2. The bar indicates the variable is

averaged over the Dxi reach and over the Dt

j time step. The

coefficients (C0,C1,C2,C3,C4) are functions of Dxi and Dt

j (the

independent parameters), and D, c, and k’ (the dependent

variables) are also functions of water—surface elevations (h).

These water—surface elevations may be obtained from a steady,

uniform flow formula such as the Manning equation, i.e.,

Q= m/nAR2/3S

1/2 (19)

in which n is the Manning roughness coefficient, A is the crosssectional area, R is the hydraulic radius given by A/P in which P

is the wetted perimeter of the cross section, S is the energy

slope as defined previously, and m is a units conversion factor

(1.49 for U.S. and 1.0 for SI).

5.4 Testing of DAMBRK and SMPDBK

The DAMBRK and SMPDBK models have been tested on several

historical floods due to breached dams to determine their ability

to reconstitute observed downstream peak stages, discharges, and

travel times. Among the floods that have been used in the

testing are: 1976 Teton Dam Flood, 1972 Buffalo Creek (coal-waste

dam) Flood, 1889 Johnstown Dam Flood, 1977 Toccoa (Kelly Barnes)

Dam Flood, the 1997 Laurel Run Dam Flood and others. Some of the

results from the Teton and Buffalo Creek dam-breach tests follow.

The Teton Dam, a 300 ft high earthen dam with 230,000 acre-ft of

stored water and maximum 262.5 ft water depth, failed on June 5,

1976, killing 11 people making 25,000 homeless and inflicting

about $400 million in damages to the downstream Teton-Snake River

Valley. The following observations were reported (Ray, et

al.,1976): the approximate development of the breach,

description of the reservoir storage, downstream cross—sections

and estimates of Manning’s n approximately every five miles,

estimated peak discharge measurements of four sites, flood—peak

travel times, and flood-peak elevations. The critical breach

parameters were tf=1.43 hours, b=80 ft, and z=1.04. The computed

peak flow profile along the downstream valley is shown in

Figure 9. Variations between computed and observed values are
about 5 percent for DAMBRK and 12 percent for SMPDBK. The

Buffalo Creek “coal waste” dam, a 44 ft high tailings dam with

400 acre-ft of storage failed on February 1972, resulting in

 

Figure 9. Profile of peak discharge downstream of Teton.

118 lives lost and over $50 million in property damage. Flood

observations (Davies, et al., 1975) along with the computed

flood—peak profile extending about 16 miles downstream are shown

in Figure 10. Critical breach parameters were tf=0.08 hours,

b=l70 ft, and z=2.6. Comparison of computed and observed flows

indicate an average difference of about 11 percent for both

DAMBRK and SMPDBK.

The Muskingum-Cunge flood routing model was compared with the

DAMBRK (Saint-Venant) model for all types of flood waves (Fread

and Hsu,1993). For dam—breach waves, the routing error

associated with the more simple but less accurate Muskingum-Cunge

model was found to exceed 10 percent when the channel bottom

slope So<0.004/tf

0.89; the error increased as the bottom slope

became more mild and as the time of failure (tf) became smaller.
 

Figure 10. Profile of peak discharge downstream of Buffalo Creek

5 Future Research/Development Directions

Some possible effective future research/development directions

that could improve prediction of dam-breach floods are the

following: (1) use prototype physical experiments to develop

breach models for embankment dams which simulate both breach

“initiation time” and breach “formation time”; first, for clay

embankment dams after Temple and Moore (1997), then for silt/loam

embankments, sand/gravel embankments, and embankments with clay

or concrete seepage-prevention cores; (2) determine the Manning

n flow resistance values for dam-breach floods using both

historical data from such floods and using theoretical approaches

such as the component analysis used by Walton and Christianson

(1980) similar to the Colebrook equation (Streeter,1966). Also,

determine procedures to account for flood debris blockage effects

on Manning n values and the dam effect on bridge openings (the

latter could be simulated as an internal boundary equation

consisting of a discharge-depth rating function which would

represent increasing discharge with increasing flow depth,

followed by decreasing discharge as debris blockage accumulates

with increasing depth, followed by a time-dependent breach of the

debris blocked bridge); (3) develop methodologies, e.g., MonteCarlo simulation (Froehlich,1998), to produce the inherent

probabilistic features of dam-breach flood predictions due to the

uncertainty associated with reservoir inflows, breach formation,

and downstream Manning n/debris effects.
6. References:

Bechteler,W. and Broich,K. (1993). “Computational Analysis of

 the Dam—Erosion Problem,”Advances in Hvdro—Science and

Engineering,Vol.1,edited by S. Wang,Ctr. for Computational

Hydroscience and Engineering, Univ. Mississippi,pp.723-728.

Christofano,E.A.(1965). “Method of Computing Rate for Failure of

Earth Fill Dams,” Bureau of Reclamation,Denver,CO,April.

Costa,J.E. (1988) “Floods from Dam Failures”, Flood Geomorphology,

edited by V.R.Baker,R.C.Kochel, and P.C.Patton,pp.439—463,

 John Wiley,New York.

Davies,W.E., Bailey,J.E., and Kelly, D.B. (1972). “West Virginia

Buffalo Creek Flood: A Study of the Hydrology and Engineering

Geology”, Geological Survey Circular 667,U.S.Geological

Survey, 32pp.

Evans,S.G.(1986). “The Maximum Discharge of Outburst Floods

 Caused by the Breaching of Man-made and Natural Dams”, Can.

Geotech.J.,23,pp.385-387.

Fread,D.L. (1993).“NWS FLDWAV Model: The Replacement of DAMBRK

 for Dam-Break Flood Prediction”,Proceedings of the 10th Annual

Conference of the Association of State Dam Safety Officials,

Inc., Kansas City,MO,pp. 177-184.

Fread,D.L. (1988).“The NWS DAMBRK Model: Theoretical

Background/User Documentation”, HRL-256, Hydrologic Research

Laboratory,National Weather Service, Silver Spring,MD, 315 pp.

Fread,D.L.(1987). “BREACH: An Erosion Model for Earthen Dam

Failures”, HRL-193, Hydrologic Research Laboratory, National

Weather Service,Silver Spring,MD, 34pp.

Fread,D.L.(1984). “A Breach Erosion Model for Earthen Dams”,

Proc. of Specialty Conference on Delineation of

Landslides,Flash Flood, and Debris Flow Hazards in Utah, Utah

State Univ. ,Logan,UT,June 15,3Opp.

Fread,D.L. (1981). “Some Limitations of Contemporary Dam-Break

Flood Routing Models,”Preprint 81-525: Annual Meetinci of

American Society of Civil Engineers,Oct. 17,St.Louis, MO,l5pp.

Fread,D.L.(1977). “The Development and Testing of a Dam-Break

Flood Forecasting Model”, Proc. of Dam-Break Flood Modeling

Workshop, U.S. Water Resources Council, Washington, PC, pp.164-

197.

Fread,D.L. (1971). “Transient Hydraulic Simulation: Breached

 Earth Dams”, Doctoral Dissertation, University of MissouriRolla, Rolla, Missouri, 66pp.
Fread,D.L., and Hsu,K.S. (l993) “Applicability of Two Simplified

Flood Routing Methods: Level-Pool and Muskingum-Cunge”, Proc.

of ASCE National Hydraulic Engineering Conference, San

Francisco,CA,pp.1564-1568.

Fread,D.L.,Lewis,J.M., and Wiele,S.M.(1991).“The NWS Simplified

Dam-Break Flood Forecasting Model”, HRL-256, Hydrologic

Research Laboratory, National Weather Service, Silver Spring,

MD, 47pp.

Fread,D.L. and Harbaugh,T.E. (1973) “Transient Hydraulic

Simulation of Breached Earth Dams”, J. Hydraul Div. ,ASCE, Vol.

99, No.HY1,January l973,pp.139—154.

Froehlich,D.C. (1998). “Personal Communication”, March 11, 1998.

Froehlich, D.C. (1995). “Peak Outflow from Breached Embankment

Dams”, J. of Water Resources Planning and Management, ASCE,

vol.1-2l, No. l,pp.90—97

Froehlich, D.C. (1987). “Embankment—Dam Breach Parameters”,

 Proc. of the 1987 National Conf. on Hydraulic Engr., ASCE, New

York, August,pp. 570-575.

Hagen,V.K.(1982).”Re-evaluation of Design Floods and Dam Safety”,

Paper Presented at 14th ICOLD Congress, Rio de Janeiro

Harris,G.W. and Wagner,D.A. (1967). Outflow from Breached Dams,

Univ of Utah.

Johnson,F.A. and Illes,P. (1976). “A Classification of Dam

Failures”, Water Power and Dam Construction, Dec., pp.43-45.

Lee,K.L. and Duncan,J.M. (1975). “Landslide of April 25, 1974 on

the Mantaro River, Peru”, Nat’l Acad. of Sciences, Washington,

D.C.

Macchiorie,F.and Sirangelo,B. (1988). “Study of Earth Dam

Erosion Due to Overtopping”, Hvdrology of Disasters, Proc. of

Tech. Conf.in Geneva, November 1988, Starosolszky,O. and Melder

O.M. (Editors), James and James, London, pp.212-219.

MacDonald,T.C. and Langridge-Monopolis,J. (1984). “Breaching

Characteristics of Dam Failures”, J.Hydraul.Div., ASCE, Vol.

l10,No.HY5,pp. 567—586.

Ponce,V.M., and Tsivoglou A.J.(1981).“Modeling of Gradual Dam

Breaches”, J. Hvdraul DiV.,ASCE,Vol.107,No.HY6,pp.829-838.

Ray,H.A.,Kjelstrom,L.C.,Crosthwaite,E.G., and Low,W.H. (1976).

“The Flood in Southeastern Idaho from the Teton Dam Failure of

June 5, l976”. Unpublished Open File Report, U.S. Geological

Survey, Boise, ID.
Singh,V.P.,Scarlatos,P.D.,Collins,J.G. and Jourdan,M.R. (1988).

“Breach Erosion of Earthf ill Dams (BEED) Model”, Natural

Hazards, Vol.1, pp.161-180.

Singh,V.P. and Quiroga,C.A. (1988).“Dimensionless Analytical

Solutions for Dam Breach Erosion”, J. Hvdraul.Res., Vol.26,

No.2, pp.179—197.

Singh,K.P. and Snorrason,A. (1982).“Sensitivity of Outflow

Peaks and Flood Stages to the Selection of Dam Breach

Parameters and Simulation Models”, University of Illinois State

Water Survey Division, Surface Water Section, Champaign, IL,

June,17 9pp.

Streeter,V.L. (1966). Fluid Mechanics, pp.253-256, McGraw-Hill,

New York.

Temple,D.M., and Moore,J.S. (1997). “Headcut Advance Prediction

for Earth Spillways.” Trans. of Am. Soc. Agric. Engr.,Vol.40,

No.3, pp.557—562.

Walder,J.S., and O’Connor,J.E. (1997). “Methods for Predicting

Peak Discharge of Floods Caused by Failure of Natural and

Constructed Earthen Dams”, Water Resources Research, Vol.33,

No. 10,pp. 2337—2348.

Walton,R. and Christenson,B.A. (1980). “Friction Factors in StormSurges Over Inland Areas”, Waterways,Ports,Coastal and Ocean

Division,ASCE,106(WW2),pp.261—271,198o.

Wetmore,J.N. and Fread,D.L.(1984). “The NWS Simplified Dam

Break Flood Forecasting Model for Desk-Top and Hand-Held

Microcomputers”, Printed and Distributed by the Federal

Emergency Management Agency (FEMA), 122 pp.

Westphal,J.A. and Thompson,D.B. (1987). “NWS Dambreak or NWS

Simplified Dam Breach, Proceedings, Computational Hvdrology

‘87, Lighthouse Publications, First International Conference

(Hromadka and McCuen, Eds), Anaheim, California.

B-6

1 

Issues, Resolutions, and Research Needs Related to Embankment Dam Failure Analysis 

USDA/FEMA Workshop 

Oklahoma City, June 26-28,2001 

An Introduction to RESCDAM project 

Mikko Huokuna ed. 

Finnis Environment Institute 

1. INTRODUCTION 

Finland’s dams and reservoirs have been constructed mainly for flood control, hydroelectric power 

production, water supply and fish culture, as well as for storing waste detrimental to health or the 

environment. Some of the reservoirs play also a recreational role. At present, there are 55 large 

dams in Finland. According to the Finnish dam safety legislation, 36 dams require a rescue action 

plan. The development of rescue actions based on the risk analysis and the dam-break flood hazard 

analysis was found necessary by the Finnish Ministry of the Interior, the Ministry of the Agriculture 

and Forestry, and the organizations subordinate to these ministries. The launching of the 

RESCDAM project is meant to improve the dam safety sector. The project is financially supported 

by the European Union, the Finnish Ministry of the Agriculture and Forestry, the Finnish Ministry 

of the Interior and the West Finland Regional Environment Centure. 

The RESCDAM project is co-ordinated by the Finnish Environment Institute. The project is being 

carried out in co-operation with: ENEL SpA Ricerca Polo Idraulico e Strutturale (Milan), EDF 

Electricite de France (Paris), the Helsinki University of Technology, the Emergency Services 

College (Kuopio), the Seinäjoki Rescue Centre (Seinäjoki), and the West Finland Regional 

Environment Centre (Vaasa, Seinäjoki). The sub-contractors of the project are the PR Water 

Consulting Ltd. (Helsinki) and Professor Emeritus Eero Slunga (Espoo). 

The activities of the RESCDAM project embrace the risk analysis, the dam-break flood analysis and 

the rescue actions improvement. 

The risk analysis consists of: 

-Assessment of the risk of events or processes that could lead to a dam-break. 

-Assessment of the risks posed by a dam-break flood causing hazards to the 

population, property and the environment downstream from the dam. 

-Depth-velocity dam-break flood danger level curves. 

-Sociological analysis on the reaction of the population during dam-break flooding 

and the related rescue actions and evacuation. 

The dam-break flood hazard analysis consists of: 
2 

-Application of the numerical model for the simulation of dam breach formation to 

the example dam case. 

-Application of the numerical flow models (1- and 2-d models) for dam-break flood 

simulation to the pilot project dam case. 

-Study of the effect of different approaches to model urban areas on flood 

propagation. 

The development of the rescue actions includes: 

-Basic international investigation on how dam-break rescue actions are organised in 

different countries. The evaluation of the requirement for equipment, tools, training 

and exercises. 

-Recommendations to update the existing Finnish dam-break flood rescue guidelines. 

-Evaluation of the opportunities for special training and exercises taking into account 

the need for continuous updating activities. Acquirement of the special rescue 

equipment required and making arrangements for practical training and rescue 

exercises at the example dam. 

-Drawing up rescue action plans for the example dam. 

The results of the RESCDAM project formed a basis for an international seminar and workshop. 

The seminar and workshop took place in Seinäjoki in October 1-5, 2000. The purpose was to create 

a forum for the presentation of and discussion on practical experience in dam safety and emergency 

action planning. The papers presented during theseminar will be included in the RESCDAM final 

report. 

The RESCDAM project started in June, 1999 and will finish in 2001. The project’s final report will 

be available in the form of a CD and on the net. 

2. THE KYRKÖSJÄRVI RESERVOIR PILOT PROJECT 

The Kyrkösjärvi Reservoir, located in the Seinäjoki City, North West Finland, is an off-river 

channel reservoir using the water from the river Seinäjoki, a major tributary of the river Kyrönjoki 

(see Figure 3.2.1. ). This reservoir and its embankment dam were chosen as the area of the pilot 

project in the RESCDAM project. There are several reasons for this choice. The reservoir is in multi 

purpose use (flood control, hydropower production, water supply, cooling water for a thermal 

power plant and recreational use) and it is therefore very important for the local population. The 

area has also been recently surveyed and high accuracy digital maps and a digital terrain model are 

available. The reservoir is located in the City area, with urban areas at risk. The local rescue centre 

has in addition to the Kyrkösjärvi reservoir to deal also with other reservoirs and dams in its area 

and is therefore highly motivated to develop its organisation's skills. 
3 

Figure 1. Map of the Kyrönjoki River basin 

The dam was designed in 1977 and taken into use on February 6, 1981. The reservoir is used as 

flood storage for the River Seinäjoki, which flows trough the city area. There is a hydropower plant 

in the northern part of the lake and a thermal power plant which uses the water from the lake as 

cooling water, at the eastern bank of the reservoir. The volume of the reservoir is 15.8 106 m3 at the 

flood HW-level 81.25 m and 22.3 106 m3 at the emergency HW-level 82.25 m (HW + safety 

margin). 

Seinäjoki river is a tributary of the Kyrönjoki river (drainage area 4.900 km2

).The drainage area of 

the Seinäjoki river upstream of the Kyrkösjärvi reservoir is 813 km2

. Water from Seinäjoki river 

flows to the reservoir trough a canal which begins at Renko Weir (Figure 2.). The discharge through 

the canal between the Renko Weir and the reservoir are at low Reservoir levels or high river levels 
4 

45 m3/s and at low water level differences, at least 25 m3/s. The discharge from the reservoir 

through the turbines of the hydropower plant can be 21 m3/s and through a discharge valve 2 m3/s. 

Kyrkösjärvi dam is a homogeneous embankment dam (Figure 2.). The length of the dam is 12.5 km, 

from which one third is lower than three meters. The maximum height of the dam is about seven 

meters. The core material of the dam is glacial till. 

Figure 2. Kyrkösjärvi Embankment Dam 

3. RISK ASSESSMENT 

3.1 Public response towards dam safety issues 

The sociological research on the public response towards dam safety issues was one part of the 

RESCDAM . It played an important role in this project by concentrating on the attitude of the 

public towards a risk of the Kyrkösjärvi dam-break and on the possible reactions of the people in 

the case of a flood caused by it. By learning the population needs in the field of security matters, the 

research served as one of the tools for creating the emergency action plan in the case of a 

Kyrkösjärvi dam-break and a better preparedness for such an accident. 
5 

The first step of the research included preparation of a questionnaire devoted to the problems of 

dam-breaks in general and in the case of Seinäjoki, as well as to the alarm system. The purpose of 

the questionnaire was to introduce the dam-break issues to the public and to learn their perception 

of such a risk in Seinäjoki. 

At the preparation stage, it was important to construct the questions in such a way as to find out the 

level of public awareness on the dam-break risk problem but not to induce panic. In order to avoid 

unnecessary fears and stress among the public, it was decided that the questionnaire was to be 

accompanied by a short letter of explanation signed by the chief of the local fire brigade. It was 

stressed there that this questionnaire is part of a wider research and that Kyrkösjärvi is only an 

example dam in this study. 

The questionnaire was divided into three parts concentrating on personal data, dam-safety issues 

and comments. One thousand copies were distributed to the households in the 2-hour dam-break 

flood prone area. The copy of the questionnaire was sent by post along with the explanation letter in 

the end of October, 1999. A free-of-charge return envelope addressed to the Finnish Environment 

Institute in Helsinki was also included. Until the end of December, 1999, two hundred eighty five 

responses were received. The results of the questionnaire analysis are available in the paper entitled 

“Public Response Towards Dam Safety Issues – Kyrkösjärvi Dam Pilot Project”. 

Several comments to this questionnaire revealed that dam-break safety issues were a new and 

unexpected subject to the respondents. A few persons stated that a fact that a dam could break had 

never crossed their minds. Nonetheless, the general risk perception among the public proved to be 

low. 

The respondents emphasised the need for decent information on the dam safety issues. However, 

making a decision on the content and the amount of the information disseminated to the public 

creates a problem for the authorities responsible for the public information campaign. On the basis 

of the sociological research and the results of the international workshop on the RESCDAM project, 

a few conclusions were made in the subject of the public information campaign. Information 

presented to the public should be simple and comprehensive. It should stress the safety of a dam and 

simultaneously remind that the EAP has been created to make the dam even more safe. The problem 

of information overburden and its prolonged impact to the public should be tackled while designing 

the information campaign. Since people receive an enormous amount of different information daily, 

it is important to “pack” the information in such a way as to attract their attention. Moreover, the 

impact of the information received will gradually diminish with time and some people will move 

away or into the community. One possible solution to this problem is to create the web pages 

devoted to the dam-break issues and let people know regularly where to seek for the up-dated 

information. 

On the basis of the analysis of the answers and the respondents’ comments, a few recommendations 

for the EAP creation were made. It was recommended that a compact guide for the population on 

how to act in the event of a dam-break should be created. Such a guide should be in a form of a 

leaflet distributed to each household in the flood prone area. The other way of disseminating this 

information would be to include it in the local phone-book. 
6 

Other recommendation deals with the creation of an effective alarm system. In the case of a dambreak fast and effective warning of the population plays a crucial role for their safety. As the results 

of the questionnaire analysis reveal the traditional warning system by sirens might not be the best 

solution. There are a few reasons for such a statement. First, its relative ineffectiveness in the night 

time or when the TV or the radio is on. People fear that they might not hear the alarm sound. A 

second reason derives from the instruction how to act when one hears an alarm signal. Namely, 

people are supposed to go home where they should receive instructions by radio. The weakness of 

such an arrangement in the event of a dam-break is a relatively long time before the inhabitants find 

out what the actual reason of the alarm is. Moreover, there exists also a considerable danger that a 

flood might stop the energy supply which would negatively influence the effectiveness of 

information dissemination. 

At least parts of the EAP should be presented to the local inhabitants during the public information 

meeting. They should be given a possibility to comment and discuss the plan. Their suggestions 

should be taken into consideration in the process of further development of the EAP. 

3.2 The use of physical models 

One part of the RESCDAM was a research carried out at the Laboratory of Water Resources at the 

Helsinki University of Technology. There is a separate report available on that study. 

There were three goals in this part of the project: 1) human stability and manoeuvrability in flowing 

water, 2) permanence of buildings in flowing water and 3) roughness coefficients of forest and 

houses. Human stability and roughness coefficients of forest and houses were studied using physical 

laboratory tests. Experiments on the human stability were conducted testing full scale test persons in 

the 130 m long model basin equipped with towing carriage in the Helsinki University of 

Technology Ship Laboratory. The roughness coefficient was studied in the 50 m long fixed bed 

flume at the Laboratory of Water Resources using scale model forests and houses. The permanence 

of buildings in flowing water was based on literature. 

3.3 Concept and Bases of Risk Analysis for Dams - 

There is a separate report named “Concept and Bases of Risk Analysis for Dams -With an Example 

Application on Kyrkösjärvi Dam” by prof. Eero Slunga. In the conclusions of the report he writes: 

Probabilistic risk analysis is a more rational basis for dam safety evaluation, and provides a deeper 

insight into the risks involved than the traditional standards-based approach. A full risk analysis 

provides a more comprehensive view of dam safety, in that it considers all loading conditions over 

the full range of loads. The analysis procedure itself should not be viewed as a replacement to 

traditional engineering judgement and expertise. Quite the contrary, this process depends heavily on 

the knowledge base of experts. Attaining an exact value of probability for dam failure is not a 

realistic expectation. The utility of this approach is to assess dam safety on relative basis. After 

having assessed the probability of failure for an existing dam, one can investigate -In relative sense 

- the effects that various improvement or remedial measures will have. 
7 

The concept of probabilistic risk analysis may be used for different purposes and at different levels, 

for example: 

- at the dam design stage, to achieve a balanced design and to place the main design 

 effort, where the uncertainties and the consequences seem the greatest; 

- as a basis for decision-making when selecting among different remedial actions and 

 upgrading for old dams within time and financial restraints; 

- to relate dam engineering risk levels to acceptable risk levels established by society for 

 other activities. 

The scepticism to use the probabilistic risk analysis may result from too much emphasis on the third 

and most complex item above, while the benefits from applications such as the first two may be 

overlooked. The application example of the risk analysis of Kyrkösjärvi dam may be included in the 

second one of the above–mentioned items. 

There is concern among practitioners that risk analyses are too subjective, in that there are no clearcut procedures for calculating some failure probabilities, and thus there is too much reliance on 

expert judgement. In fact there are still many areas, where further guidance is required. 

Recommendations for some of the areas that need to be addressed in more detail are listed below: 

- Additional refinement of quantitative analyses. 

- Development of internal erosion analysis methods to be used in a risk analysis format. 

 - Retrospective probability of failure under static loading. 

- Whether societal risk criteria should be applied on a total expected annual risk to life 

basis or on a specific event basis. 

- The concept of average individual risk over the population risk. 

- Prediction of loss of life. 

- Whether upgrading of dams should have criteria applied which were as stringent as for 

new dams. 

- Inconsistent international terminology. 

4. DAM BREAK HAZARD ANALYSES 

4.1 Introduction 

Dam break hazard analyses (DBHA)provides information about consequences of a possible dam 

break for risk estimation and rescue planning. Numerical models are used in DBHA to determine 

the flow through a dam breach and to simulate flood propagation in the downstream valley. 

Kyrkösjärvi reservoir and its embankment dam, located in the Seinäjoki City, North West Finland, 

were chosen as the area of the pilot project in the RESCDAM project. A numerical model for the 

simulation of dam breach formation was used to the determination of dam breach discharges. 

Propagation of flood in different breach scenarios were calculated with 1-d flow model and two 2-d 

models. Also the effect of different approaches to model urban areas on flood propagation were 

studied in the project. 
8 

The 2-d flood calculations and the study on the effect of urban areas on flood propagation were 

made by the partners, EDF Electricite de France (Paris) and ENEL SpA Ricerca Polo Idraulico e 

Strutturale (Milan). According to the preliminary sensitivity analyses the most dangerous breach 

location ( location A) and the HQ1/100 flood condition and mean flow condition (MQ) were chosen 

for DBHA calculations made by the partners EDF and ENEL. The analyses for two other breach 

locations (location B and C) were decided to be done with 1d-flow model. It was also decided that 

1d-model is used to produce a downstream boundary condition for 2d-models. Later it was observed 

that the original modelling area is too small and simulations were extended to the northern area of 

the Seinäjoki city (area behind the railway). The simulations were first made with 1d-model by FEI 

and FEI provided a rating curve for the flow over the railway for the partners. Because in the 

simulations the flow is divided to several streams and the modelling of that area is extremely 

difficult it was decided to calculate the most important cases with 2d-model to the whole area. That 

work was done by FEI by using Telemac-2d model. 

Geometry input data for the DBHA was attained from a accurate digital terrain model which was 

available for the project. The results of DBHA were provided as flood maps, tables, water level 

hydrographs and animations for rescue planning. GIS system was used to produce the flood maps 

and the information about buildings and people living under flood risk. 

4.2 Hydrological analysis 

The Hydrological Analysis in RESCDAM project are based on a HBV-hydrological model.The 

Kyrönjoki watershed model is a semi-distributed model with 22 sub-basins. Each sub-basin has 

separate precipitation, temperature and potential evaporation as input. The Kyrönjoki model has a 

flood-area-model which simulates water exchange between river and flood plains. Flood-areamodel is simulated with shorter time steps than the main model. At every reach of river with 

embankments and weir the model calculates water level in river and discharge through the weir over 

the embankment into the flood plain. This part of the model is important during flood. This simple 

hydraulic model is verified against the results from a complete hydraulic model to keep up the 

accuracy of the simulation. 

The Kyrönjoki watershed model is a conceptual model used for operational forecasting in the 

Finnish Environment Institute (Vehviläinen 1994). The watershed model is based on a conceptual 

distributed runoff model, water balance model for lake, river routing model (Muskingum and 

cascade reservoirs) and flood area models. The input variables for the model are daily precipitation, 

temperature and potential evaporation (Class A pan). 

As input for Kyrkösjärvi dam-break simulation three flood situations have been simulated. Floods 

with return period of 20, 100 and 10 000 year have been created or determined with the operational 

hydrological catchment model. The method used to determine 10 000 year flood is based on 

precipitation with return period of 10 000 year. 

More detailed information on the Hydrological analysis of Kyrkösjärvi reservoir and is given in a 

separate report in RESCDAM project. 
9 

4.3 Determination of the Breach Hydrographs 

Determination of flow through a dam breach has lot of uncertainties. In the RESCDAM project a 

numerical model for erosion of a embankment dam (Huokuna 1999) was used for the determination 

of the discharge hydrograph. Hydrographs were also calculated by using a method in which the 

breach opening is increasing linearly when the duration of the breach formation and the width of the 

final breach opening are given. That method to calculate breach formation is available in DYX.10 

flow model and it is also available in many other models, like DAMBRK model. 

In the studies the breach is assumed to happen at three locations at two different hydrological 

conditions. The assumed dam breach locations are presented in the Figure 3. The hydrological 

conditions are the HQ1/100 flood and the mean flow. 

Figure 3. The locations of the assumed dam breach sites. 

The location A in the Figure 3. is the most dangerous location for a possible dam break at 

Kyrkösjärvi dam. The dam is highest at this location (km 5.7 at Figure 2 ) and because of the 

topography of the valley downstream of the dam, the Seinäjoki downtown area could be badly 

flooded if the dam breaks at location A. 
10 

The breach hydrographs for the location A and HQ1/100-flood case are presented in the Figure 4. The 

hydrograph calculated by the erosion model was used in the calculations made by ENEL and EDF. 

Figure 4. Breach hydrographs for the location A in the HQ1/100 –case 

4.4 1-D Flow Modelling 

The 1-d modelling for the dam break hazard analysis of the Kyrkösjärvi reservoir has been done by 

using DYX.10-flow model. The model is based on four point implicit difference scheme developed 

by Danny L. Fread for DAMBRK model. During 1980’s Fread’s algorithm was developed further 

in Finland for river networks. 

The 1-d flow model for the Kyrkösjärvi DBHA covers the area from Renko dam (upstream of 

Kyrkösjärvi Reservoir) to Kylänpää (about 30 km downstream of the reservoir). The cross-sections 

used in the model were taken either from a terrain model or they were measured cross-sections. 

There were 735 cross-sections 22 reaches and 35 junctions in the Kyrkösjärvi 1-d DBHA model 

(breach location A). Some of the reaches were fictive channels (flood plains, connecting channels 

etc.) 

The following cases where studied with the 1-d model: 

-Breach location A Base flow MQ 

-Breach location A Base flow HQ 1/100 

-Breach location C Base flow MQ 

-Breach location C Base flow HQ 1/100
11 

A constant roughness coefficient (Manning n=0.060) was used in all simulation cases. 1-d model 

was also used to run sensitivity analyses of the effect of the size of the breach hydrograph on the 

water level downstream of the dam. A more detailed description of the 1-d flow modelling in the 

RESCDAM-project is given in a separate report. 

4.5 2-D Flow Modelling; Electricite de France 

Electricite de France (EDF) used Telemac-2D model, a 2-dimensional finite element model, in the 

simulation. There were 81161 elements and 41086 points used in the Kyrkösjärvi model. The finite 

element mesh is shown in Figure 5. The mesh size ranges from 8 m to 20 m approximately. The 

river beds, the bridges, the roads, and the railways been highly refined to model accurately the 

propagation. The boundary conditions are solid boundaries everywhere except at the breach, at the 

entrance of river Seinäjoki, and at the output zone. In regular areas such as roads, reservoir dykes, 

and river beds, regular griding has been used. For other features such as railways, embankments, 

constraint lines have been imposed. All these features are quite visible on the mesh. A separate 

report is by EDF is available RESCDAM project.

Figure 5. The Telemac-2D finite element mesh used in the Kyrkösjärvi simulations by EDF. 

4.6 2-D Flow Modelling; ENEL SpA Ricerca Polo Idraulico e Strutturale 

ENEL used FLOOD-2D model, a 2-dimensional finite volume model, in the simulation. 

FLOOD2D has been developed by Enel.Hydro Ricerca Polo Idraulico e Strutturale. The model is 

based on the integration of the Saint Venant equations for two-dimensional flow and it neglects the 

convective terms in the momentum conservation equations. The model requires as basic input only 

the natural ground topography and the estimated Manning's friction factors. 

The two dimensional model was applied to the area below the dam including the City area of 

Seinäjoki. Two sets of topography were used: 
12 

1) Rectangular mesh # 10m without buildings and 

2) Rectangular mesh # 10m with buildings. 

The model has a total number of 446.961 grid points. Depending on the base flow condition 

approximately 55.000 - 70.000 cells of the model became wetted during the computations. There is 

a separate report about calculations in RESCDAM project by ENEL.

4.7 Urban Areas And Floating Debris 

During RESCDAM project the partners EDF and ENEL developed the methods to calculate flood 

wave propagation on urban area. ENEL used the geometry approach to calculate flood propagation 

on urban area. Houses were taken into account in the model geometry. EDF used the porosity 

approach to model flood propagation on urban area. 

There is a separate paper by EDF presenting the results of porosity approach on calculation results 

(Modelling urban areas in dam-break flood-wave numerical simulations). That paper was presented 

in the RESCDAM Seminar. 

ENEL applied the geometry method for the whole calculation area. In the FLOOD2D-model he 

geometry was presented by a grid consisting of rectangles of 10 m times 10 m. ENEL made the 

calculations for MQ and HQ1/100-cases (breach location A) by using two geometry data sets. One 

with buildings and another without buildings. Comparison of those results are given in the final 

report of RESCDAM. Generally the calculated water levels were higher in the cases in which 

buildings were taken in to account (maximum difference about 0.5 m). Also the propagation of a 

flood wave was generally a bit slower when the buildings were taken in to account. However the 

effect on propagation speed was not very large. The effect of buildings on damage hazard 

parameter (flow velocity x depth) was not very large in the case of Seinäjoki DBHA and can not be 

seen to be very important for the planning of emergency actions. 

The effect of urban areas and floating debris in dam-break modelling is presented also in a paper by 

Peter Reiter (Considerations on urban areas and floating debris in dam-break flood modelling), who 

presented the paper in the RESCDAM seminar. 

4.8 Analyses Of The Results 

The following flow calculations were decided to be done by the partners EDF and ENEL: 

RUN 1 Base flow in Seinäjoki River 150 m3/s + breach hydrograph for max reservoir level, 

roughness varies between Stricler 15 (Manning's n=0.06666) and 40 (Manning's 

n=0.025). 

RUN 2 Base flow and breach hydrograph as in RUN 1, roughness is constant for the entire 

modelling area with Strickler 15 (Manning's n=0.06666). 

RUN 3 MQ base flow + breach hydrograph, constant Manning n varying in the entire 

modelling area according to landforms and vegetation and according to the experience 

of EDF and ENEL. 

RUN 4 HQ1/100 base flow + breach hydrograph, other conditions as in RUN 3. 

RUN 5 Conditions of RUN 3 modified according to the partners choice of modelling buildings 

(EDF: porosity, ENEL: geometry) 
13 

RUN 6 Conditions of RUN 4 modified according to the partners choice of modelling buildings 

(EDF: porosity, ENEL: geometry) 

The breach location was assumed to be the location A for all these calculations. The computer runs 

RUN 5 and RUN 6 were done for the whole area only by ENEL, while EDF used a smaller 

example area. 

In the RESCDAM project the meaning of using the different models to simulate the same case was 

not to compare the computational algorithms. The meaning was to get an idea how much the results 

may differ depending on the models and the modellers using their own approaches. The comparison 

of different models and solution algorithms have been done recently in the CADAM-project. 

The partners get the land use data in the 10 m x 10 m grid which was derived from the terrain model 

data. The computation area was divided to 6 land use areas and the modellers used their own 

judgement for choosing the friction factors for different areas. 

In an separate report the results of calculations made by ENEL and EDF are compared together with 

the results of 1-d simulations. The water level comparison is done on different locations 

downstream of the dam. The progression of the dam break flood is also compared on maps. 

According to the comparison the results calculated by EDF and ENEL seems to be relatively close 

to each other. There is more difference between the results of the 2-dimensional models and the 

results of the 1-dimensional model. The 1-dimensional simulations were made only for constant 

Manning’s n (n=0.06) and this is explanation for some differences. However, in the case of very 

complicated topography, like in the Seinäjoki case, the use of 2-dimensional model seem to be more 

reasonable. The use of 1-dimensional model needs a lot of experience because the cross-sections 

have to be put on right locations. The use of 2-dimensional models are more straightforward. 

4.9 DBHA Results For Rescue Actions 

The first DBHA results for emergency action planning where based on 1-d model results and results 

by EDF and ENEL and only the breach location A was considered. Later the calculations for the 

locations A, B and C was made by FEI using 2-dimensional Telemac-2d model. The original final 

element mesh greated by EDF was extended to the area north from the railway station when the 

terrain model data for that area was available. ..Those results were the final results used for 

emergency action planning of the Kyrkösjärvi Reservoir. There is a separate report available in 

RESCDAM on 2-d calculations made by the Finnish Environment Institute. 

The results of DBHA for rescue actions consists of inundation maps, water depth maps, hazard 

parameter maps as well as water level and velocity hydrographs and tables. In the RESCDAM 

project the results were transferred to GIS-system and different results could be analysed together 

with the database information of buildings and inhabitants. That information was used to get 

damage and LOL-estimations. 
14 

5. DEVELOPMENT OF RESCUE ACTIONS 

Developing of rescue services concerning waterbody dams can be compared to the corresponding 

planning obligation of nuclear power plants. These types of accidents are very unlikely, but if an 

accident does occur consequences can be very serious. 

The main area in the preparation of an emergency action plan of a dam must be in organising the 

warning, alerting and evacuation activities. Consequences of a dam failure as well as conditions 

following the accident are so difficult for rescuing, that evacuation before the arrival of flood must 

be the main approach. In addition to the warning and evacuation of population also the automatical 

dam monitoring and notification of a dam break must furthermore be developed. In the seminar of 

RESCDAM project it was very unambiguously stated, that the risk of loosing human lives is 

influenced strongly by the time of the notification of a dam failure. If the failure is not noticed early 

enough, the benefit gained from public warning sirens is lost and people do not have enough time to 

escape from the flood area. 

Failure risk of a dam should be taken into account also in laws controlling building construction. 

Assembly rooms, hospitals, maintenance institution and corrective institutions should not be built in 

the danger area of the dam, because the evacuation of such buildings is very problematic in accident 

situation. Buildings in the danger area should be built so that dam failure will not endanger people 

living in the buildings. 

When preparing for a dam failure, it is especially important to consider human behaviour in crises 

situations. Studies of this topic show that people do not always believe in the reality of warnings. 

Home is “the sanctuary” for people and leaving home is difficult. In the planning and 

implementation of rescue operations the compliance of population with the warning and evacuation 

instructions must always be ensured with vehicles with loudspeaker system rotating in the danger 

area and rescue units going from house to house. 

 Compliance with warnings and instructions given by authorities can be facilitated with 

advance bulletin that is distributed to people in the danger area in advance. In Finland this kind of 

advance informing has primarily been recommended, but not requested. However advance 

informing has significant meaning in the success of rescue operations and thus it should be 

determined. 

The hazard risk assessment of the dam with inundation maps about the flood situation after the 

failure prepared along with the assessment are almost merely the basis for the emergency action 

plan prepared by rescue services. The needs of rescue services must be noticed when presenting the 

flood information and inundation maps. The availability of maps in digital and paper form should 

be further developed. Digital maps were developed during RESCDAM project. These maps can be 

applied to all dams and results and reactions were very positive. 

5.1 Emergency Action Plan For The Kyrkösjärvi Dam 

Emergency action plan of Kyrkösjärvi reservoir is based on a dam-break flood analysis (Chapter 4). 

The dam failure may in the worst case cause a flood that covers over 10 km2

 of population centre 

and over 1300 buildings there. The flood will wet app. 420 00 square metres of built floor area in 
15 

buildings with 0-2 floors. As a whole there is nearly 800 000 square metres of built floor area in the 

flood area, about half of which will stay below the water level. Dam failure will affect directly or 

indirectly lives of many thousands of people. Flood will significantly damage the distribution of 

electricity and energy, water system, road network, sewage and entrepreneurship and servicing in 

the city of Seinäjoki. Situation is then catastrophic in Seinäjoki and the resources of the city of 

Seinäjoki are not adequate considering the situation. Danger of losing human lives depends mainly 

on, how fast the failure is noticed. 

The emergency action plan of the Kyrkösjärvi dam is mainly prepared according to the existing 

Finnish Dam Safety Code of Practice. However among other things the planning of warning of 

population is emphasised so that evacuation is really materialised. Respectively more attention is 

paid among other things to instructions of emergency response centre, medical rescue services and 

informing as well as to the organising of the maintenance of evacuated population. One of the 

purposes of the preparation of the plan was also to facilitate the maintenance and updating of the 

plan. 

Sufficient guarantee to the success of rescue operation must be taken into account when preparing 

the emergency action plan. The basis for the planning should be the worst possible accident 

situation. In the emergency action plan of Kyrkösjärvi the dam failure will occur during natural 

flood in the waterbody. Dam will fail without warning in the worst possible place. Also possible 

other failure situation was considered. 

Preparation of emergency action plan is almost entirely based on the flood information from the 

hazard risk assessment of the dam. Flood information must be prepared in such a form that rescue 

services is able to interpret and process it to it’s own use. During the project inundation maps 

produced with MicroStation- and TeleMac-software from 3D-terrain model were transferred to 

MapInfo- software used by rescue authorities. Actual plans and maps of rescue services were then 

prepared with MapInfo-software. 

Levels according to geographic co-ordinates were prepared from digital inundation maps. These 

levels can be used together with different kind of map material and plans prepared by rescue 

authorities. There is an example of the use of inundation maps in Graph 5. 

Figure 6 .Usage principles of material needed in rescue operations 

Evacuation of population 

Medical rescue services 

Responsibility areas of rescue units 

Coverage area of public warning sirens 

Flood information 

Population database 

Building data base 

Road network 

Basic map 

Inundation maps according to 

- water depth 

- flowing speed of flood 

- damage parameter 
16 

Emergency action plans prepared earlier in Finland are mainly prepared on paper maps. MapInfosoftware (or some other software processing geographical information = GIS) enables the 

processing of information. Several different kinds of database combined to co-ordinates can be 

used to help planning. This kind of database is for example population, road network and building 

register as well as different maps. These considerable improve the quality of planning and facilitate 

the preparing and updating of plans. 

Earlier digital map material was not available in planning of rescue services. The results of 

RESCDAM project are very significant in this area. 

5.2 Recommendations to update the Finnish Dam Safety Code of Practice 

Acts, decrees and instructions concerning dam safety and emergency action plans of the dams today 

are quite sufficient and they form a good basis for the maintenance of dam safety. 

Recommendations for the development of the Finnish Dam Safety Code of Practice presented in 

Appendix XX do not change the present planning practice very much. The recommended changes 

have a great influence on the practical implementation of dam safety. 

Recommended changes to the safety monitoring of the dam would influence among other things the 

periodicity of monitoring. At the moment the risk factor to people, property and environment do not 

have much influence the content of monitoring program. This means that the periodicity of every Pdam is almost the same according to the code. In the future the operational conditions of rescue 

services could influence the monitoring program of the dam. Recommendations include some 

changes to the content of periodic inspections and repairing of monitored deficiencies. 

The most significant change influencing the dam safety concerns the informing. At the moment 

informing about the dam failure risk and about the prepared emergency action plan is directed to 

population in the danger area. The word “should” gives the dam owner and authorities a lot of 

possibilities and has normally lead to a situation that there is no informing at all. During 

RESCDAM project it was observed that advance informing has a great meaning when warning the 

population. In the recommendation it is presented that population in the danger area must be 

informed about the emergency action plan and about the risk of a dam failure. 

The renovation of the rescue services act and decree as well as the regulations and instructions 

passed based on the act and decree influence the most on the dam safety code. These parts of the 

recommendation are mainly about updating the code. 
17 

6. CONLUSIONS 

In the RESCDAM project the main focus was put on the development of rescue actions based on 

the risk assessment and dam-break hazard analysis. The experience and achievements 

(developments) of the International Commission on Large Dams was taken into account in the 

project. The developments in this field from the USA, Canada, Australia, Norway and Sweden were 

also considered while referring to the state of art in risk analysis and using the best available 

practice in calculating the risk of the project example dam – the Kyrkösjärvi dam. 

For the Kyrkösjärvi dam, the detailed study was performed to calculate its risk as good as 

reasonably practical. The calculations were divided into two parts. One dealt with the probability of 

a failure and the other one with the consequences of such a failure. The detailed study of the risk 

identification takes into account all the characteristics of a dam and its foundation as well as the 

history of the dam’s behaviour during its use. The detailed study is recommended to trace all the 

possible hazards which can lead to any kind of a dam failure. The failure in this study was defined 

in terms of a complete breach followed by a significant release of water from the reservoir. The 

detailed risk analysis including the effects of a dam failure provides a tool for the decision-makers 

while selecting among different remedial actions and upgrading for all dams within time and 

financial restraints. It provided also information and basis for the emergency action plan of the dam 

in question. 

On the basis of the project findings the following recommendations for the particular areas of 

development were made: 

-Additional refinement of quantitative analyses. 

-Development of internal erosion analysis methods to be used in a risk analysis 

format. 

-Retrospective probability of failure under static loading. 

-Whether societal risk criteria should be applied on a total expected annual risk to 

life basis or on a specific event basis. 

-The concept of average individual risk over the population risk. 

-Prediction of loss of life. 

-Whether upgrading of dams should have criteria applied which were as stringent as 

for new dams. 

-Inconsistent international terminology. 

Dam break hazard analyses (DBHA)provides information about consequences of a possible dam 

break for risk estimation and rescue planning. Numerical models are used in DBHA to determine 

the flow through a dam breach and to simulate flood propagation in the downstream valley. In the 

RESCDAM-project several modelling approaches have been used in the flow modelling. The 

results shows that with careful modelling and accurate data the results of different modelling 

approaches may be relatively close each other. However, there is a lot of uncertainties in the 

modelling and specially in the one dimensional modelling where the modeller can effect 

dramatically on the results by selecting the locations of cross-sections carelessly. 
18 

The determination of flow hydrographs through the dam breach opening is crucial for the results of 

DBHA. In the RESCDAM project a numerical erosion model for the breach of a embankment dam 

has been used to define the flow hydrographs. There is a lot of uncertainties in the determination of 

breach hydrograph and sensitivity analyses have to be committed to ensure the results. The debris 

flow, clogging of bridges and other structures and erosion of flooded areas are also causing 

uncertainties in the flood simulation and that uncertainty has to be taken into account. 

In the RESCDAM project special methods have been tested to model the flow in urban areas. The 

results of EDF, which used porosity approach, and ENEL, which used geometry approach, are 

promising and they gives good basis for further development. 

The results of DBHA for rescue actions consists of inundation maps, water depth maps, hazard 

parameter maps as well as water level and velocity hydrographs and tables. It is important that the 

results of DBHA are presented in the way that they can be used efficiently in the dam break risk 

estimation and rescue planning. The use of GIS is essential in that purpose. 

Some recommendations for further research topics based on the DBHA of the RESCDAM project: 

-determination of breach formation 

-determination of roughness coefficients 

-the effect of debris flow and urban areas in DBHA 

After the RESCDAM project is completed, it is planned to organise an emergency exercise of the 

Kyrkösjärvi emergency action plan. In connection to this happening the public will receive more 

information about actions during the possible dam break flood. 

After the exercise the improved version of the emergency plan should be presented to the public and 

an information bulletin including instructions how to behave in the case of a flood caused by a dam 

failure should be distributed to the population in the flood prone area. 

If all the above mentioned actions are completed, it will be possible to perform a new sociological 

research to study with the help of a new questionnaire the impact of the information given to the 

public on the potential behaviour patterns in the case of a flood caused by a dam failure. After this 

study it can be studied/checked what impact these changes have/might have on the estimated loss 

of life in the case of a Kyrkösjärvi dam failure. 

Referenses: 

The text in this paper is based on RESCDAM final report which will be available in July 2001. 

The report,and the references used in the text, will be available thru internet and in the form of a 

CD. 
B-7

1

FEMA/USDA WORKSHOP OKLAHOMA CITY JUNE 26, 2001

GUIDELINES FOR ASSIGNING HAZARD POTENTIAL 

CLASSIFICATIONS TO DAMS

by

Alton P. Davis, Jr., P.E. - Independent Consultant

presented at the

FEMA/USDA WORKSHOP ON ISSUES, 

RESOLUTIONS, AND RESEARCH NEEDS RELATED 

TO DAM FAILURE

“FEMA GUIDELINES FOR DAM SAFETY: 

HAZARD POTENTIAL CLASSIFICATION SYSTEM

FOR DAMS”

FEMA Mitigation Directorate: FEMA No. 333

October 1998
2

HAZARD POTENTIAL CLASSIFICATIONS

• Low Hazard Potential

• Significant Hazard Potential

• High Hazard Potential 

LOW HAZARD POTENTIAL 

“Dams assigned the Low Hazard Potential classification 

are those where failure or mis-operation results in no 

probable loss of human life and low economic losses, 

low environmental damage, and no significant 

disruption of lifeline facilities. Losses are principally 

limited to the owner’s property.” 
3

SIGNIFICANT HAZARD POTENTIAL 

“Dams assigned the Significant Hazard Potential 

classification are those dams where failure or misoperation results in no probable loss of human life but 

can cause economic loss, environmental damage, 

disruption of lifeline facilities, or can impact other 

concerns.” 

HIGH HAZARD POTENTIAL 

“Dams assigned the High Hazard Potential 

classification are those where failure or mis-operation 

will probably cause loss of one or more human lives.” 
4

HIGH HAZARD POTENTIAL 

• Loss of One or More Human Lives

• Probable

•Likely to Occur

•Reasonable / Realistic Scenario

• Temporary Occupancy

• High Use Areas 

CONSEQUENCE BASED SYSTEM 

• Adverse Impacts

• Incremental Impacts

• Immediate Impacts

• Current Conditions

• No Allowance for Evacuation
5

SELECTING HAZARD POTENTIAL CLASSIFICATION 

• Presumptive (Phase 1)

• Incremental Hazard Assessment (Phase 2)

• Risk Based Assessment (Phase 3 - Refinement)

PRESUMPTIVE 

• Obvious

• Readily Available Information

• Maps

• Site Reconnaissance
6

INCREMENTAL HAZARD ASSESSMENT 

• Detailed Dam Break Studies

• FEMA Publication No. 94 

“Federal Guidelines For Dam Safety: Selecting & 

Accommodating Inflow Design Floods for Dams.” October 1998

• Defining Incremental Impacts

RISK BASED ASSESSMENT 

• Refinement

• Limited to Loss of Human Life Issues

• Tools, Procedures, Knowledge, Experience

• No Set Procedure Currently Accepted

• Proposed Approach in Draft Guideline
7

GUIDELINE GOALS 

• Repeatable Classification

• Better Understanding by Public

• Standard Terminology

• Periodic Review of Classification

• Record of Decision

FACTORS AFFECTING CLASSIFICATION 

• Loss of Human Life

• Economic Losses

• Lifeline Disruption

• Environmental Damage
8

LIFE LOSS CONSIDERATIONS 

• Designated Day Use / Recreation Areas

• Non-Permanent Structures

• Overnight Recreation Facilities

• Roads / Highways

• Permanent Structures

• Occasional Downstream Recreationist

• Immediate Life Loss

• No Evacuation

Designated Day Use and Recreation Areas

• Golf Courses

• Boating, Rafting, and Kayaking River Sections

• Swimming, Wading, and Beach Areas

• Special Regulation Fisheries: Gold Medal, Wild 

Trout, Catch and Release

• Parks and Picnic Areas

• Sporting Events

• Scenic Attractions
9

Permanent Structures

• Single family homes on fixed (masonry) foundations

• Mobile homes on temporary foundations or single family homes on 

stilts

• Public buildings such as prisons, hospitals, and schools 

• Motels

• Houses of worship

• Condo and apartment complexes

• Commercial and industrial facilities

• Emergency response facilities such as fire, police and public 

works

Mis-Operation

• Mis-operation of a dam or its appurtenant works is the 

sudden accidental and/or non-scheduled operation of a water 

retaining element of a dam that releases stored water to the 

downstream channel in an uncontrolled manner. Misoperation also includes the deliberate release of floodwater 

because of an emergency situation, but without the issuance 

of a timely evacuation warning to the downstream interests 

(Ref. 12 Nigeria, Ref. 13 Dominican Republic). Misoperation also includes the inability to operate a gate in an 

emergency, a condition that could lead to overtopping of the 

dam and potential breach. Mis-operation does not include 

structural failure of the dam.
10

Upstream Damage Potential 

• It is unlikely that loss of human life will occur in the 

reservoir area due to dam failure. A possible exception 

would be during a sunny day breach event when boaters or 

swimmers could be drawn into the breach. These 

possibilities are covered under the concept of the 

occasional hiker or fisherman as outlined in FEMA 

Publication No. 333, and are not considered to represent 

probable loss of human life for purposes of assigning 

hazard potential classifications. If overnight sleeping on 

boats at mariners is allowed, the potential for loss of life 

should be evaluated in accordance with Appendix E.

Lifeline Disruption

• ASCE defines lifelines as transportation systems [highways, airports, 

rail lines, waterways, ports and harbor facilities] and utility systems 

[electric power plants, gas and liquid fuel pipelines, 

telecommunication systems, water supply and waste water treatment 

facilities]. 

• For the purpose of this guideline, lifeline facilities are categorized in 

two groups: “Easy to Restore” and “Difficult to Restore”. Easy to 

restore lifeline facilities are those that generally can be returned to 

service in seven days or less or for which there are alternative

resources or routes available. Difficult to restore lifeline facilities are 

those that will take more then seven days to recover operation or for 

which there are no alternative resources available.
11

Lifeline Disruption

Easy to Restore in Seven Days or Less

• Transportation Infrastructure

• Emergency Shelters

• Fuel Supplies

• Radio and Telephone Centers

• Municipal Services Facilities

• Fiber Optic/Phone Trunk Lines

• Water and Gas Pipelines

• Emergency Response Services

• Evacuation Routes 

Lifeline Disruption

Difficult to Restore in Seven Days or Less

• Potable Water Treatment Facilities

• Wastewater Treatment Facilities

• Power Generation Facilities

• Navigation Facilities

• Communication Facilities

• Fire and Police

• Medical Facilities

• Railroads

• Levies/Flood Control Dams

• Power Transmission Lines
12

ECONOMIC LOSSES 

• Direct Physical Property Damage

• Cleanup Costs

• Repair Costs

• Replacement Costs

• Exclude Owner Economic Losses

• Include Loss of Business Income

• Commercial

• Recreation

• Replacement Water Supply

• Dollar Breakpoint ($1,000,000 Incremental 2001 $)

Economics Losses

• Residential structures

• Industrial buildings

• Commercial and Public buildings

• Railroads 

• Main highways 

• Bridges on main highways and on Township and County roads

• Disruption of utilities (electric, sewer, municipal and agricultural water supply)

• Economic loss due to lost recreation or damage to recreational facilities upstream 

and downstream of the dam

• Loss of commercial navigation

• Agricultural land and buildings

• Costs of alternative transportation or routings
13

ENVIRONMENTAL DAMAGE 

• Habitat and Wetlands

• Toxic and Radiological Waste

• Mine Waste

• Animal Waste

Other Concerns 

• National security issues (dams upstream of military 

facilities)

• Non-jurisdictional dams (No federal or state oversight)

• Native American sites

• Archeological and historic sites

• Facilities not easily evacuated (Assisted living 

establishments, prisons, hospitals)
14

RISK BASED ASSESSMENT

• The purpose of this procedure is to 

differentiate between High Hazard Potential 

and not High Hazard potential. Using the 

procedures outlined in this Appendix, if the 

calculated probable loss of human life 

exceeds 0.33, the dam should be classified 

as High Hazard Potential.

RISK BASED ASSESSMENT

• For estimating incremental life loss only

• Presumptive and incremental hazard methods inadequate

• When 2-feet incremental flooding criteria inadequate

• Use when human occupancy is seasonal

• Based on empirical life loss data

• Use to differentiate between High Hazard Potential and 

Not High Hazard Potential
15

RISK BASED ASSESSMENT

1. Assume failure scenario

2. Define incrementally impacted areas

3. Select time sequence (season, day of week, time of day, etc.)

4. Estimate number of people at risk for time sequence

5. Select empirical fatality rates

6. Compute probability of zero fatalities

7. Determine (time sequence factor)*(zero fatality probability)

8. Add values for all time sequences in 7 above

9. Compute 1.0 minus total time sequence values

10. If result in Step 9 is >0.33, then classify as High Hazard Potential

RISK BASSED ASSESSMENT

• Reference:

“A Procedure for Estimating Loss of Life 

Caused by Dam Failure”

Department of the Interior, Bureau of Reclamation, 

DSO-99-06 September 1999 

by Wayne J. Graham, P.E.
16

GUIDELINE PROCESS 

• Final Draft to ICODS February 6, 2001

• Review and Comment by ICODS

• Peer Review by ASDSO, USCOLD, and ASCE

• FEMA Issue as Guideline

TASK COMMITTEE

Alton P. Davis, Jr. * Chair (Independent Consultant)

Kelvin Ke-Kang Wu* (MSHA)

Wayne J. Graham* (Bureau of Reclamation)

Jerrold W. Gotzmer* (FERC)

Richard W. DeBold (State of New Hampshire)

William Irwin (NRCS)

David S. Bowles (Utah State University)

Alan E. Pearson (State of Colorado)

William Allerton (FERC)

Martin W. McCann (Jack Benjamin & Assoc.)

Terry L. Hampton (Mead & Hunt)

Charles Karpowics (NPS)

James D. Simons (State of North Carolina)

* Developed final draft
B-8

Embankment Dam Failure Analysis 

State Assessment Criteria, Issues and Experience 

Northeastern United States 

By: 

John C. Ritchey, P.E. 

State of New Jersey 

Department of Environmental Protection 

Dam Safety Section 

The Northeast Region of the Association of State Dam Safety Officials includes the states 

of Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New 

Jersey, New York, Pennsylvania, Rhode Island, and Vermont. 

Dams within the region vary in size with a few large dams and many small dams. 

Regardless of size, many of the dams in the region are in close proximity to developed 

areas. It is not uncommon to find 15-foot dams that are rated as high hazard structures. 

Some states within this region find themselves regulating detention basins due to the 

provisions of their state dam safety laws. With developers trying to maximize profit, we 

often find 15 to 20 foot high embankment dams in the middle of residential 

developments. 

Additionally, many of the embankment dams were constructed over 100 years ago using 

combinations of cyclopean concrete, masonry, concrete core walls and earth. This 

sometimes presents unique conditions for modeling dam failures. 

State Assessment Criteria (Current Practices) 

For the purpose of preparing this paper, a survey of states within the Northeast Region 

was conducted to determine current practices in performing dam failure analysis. 

Although response to the survey was low, those that responded are representative of the 

procedures which are used in the Northeast Region. 

Generally within the Northeastern States, it is a requirement that the dam owner obtain 

the services of a licensed professional engineer to undertake a dam failure analysis. 

Analyses are performed for the purpose of determining hazard classifications, spillway 

design floods and for establishing inundation areas for use in Emergency Action Plans. 

Occasionally, state engineers will perform their own dam failure analysis. New Jersey for 

example will perform dam failure analysis on dams owned by the State Divisions of 

Parks and Forestry and Fish and Wildlife when undertaking preliminary engineering or 

establishing inundation areas for Emergency Action Plans. 
 2 

It is common that dam failure analysis be performed for all proposed dam structures in 

order to establish a hazard classification for the proposed dam. Additionally, dam failure 

analysis is required for all high and significant hazard dams in order to establish the 

inundation maps for the required Emergency Action Plan. Dam failure analysis may be 

required to be performed on low hazard dams on a case by case basis. Generally, when 

an inspection report identifies that development has occurred downstream of a dam that 

may increase the hazard classification, a state dam safety office may require that a dam 

failure analysis be performed to identify the inundation areas and therefore assign an 

appropriate hazard classification. Changes within a watershed downstream or upstream 

of a high or significant hazard dam may warrant revisiting the dam failure analysis in 

order to refine inundation limits. Generally, this would be identified to be necessary as 

part of a formal inspection being undertaken on the dam. 

The most common method of undertaking a dam failure analysis is to utilize the US 

Army Corp of Engineers Flood Hydrograph Package (HEC-1) to establish dam breach 

discharges. For the purpose of establishing downstream flooding limits, output data from 

the HEC-1 is utilized to develop a back water analysis using the US Army Corps of 

Engineers River Analysis System (HEC-RAS) to establish water surface elevations. It is 

estimated that approximately 90% of all dam failure analysis being completed in the 

region is done with this method. 

Many of the states accept the National Weather Service's Dam Break Flood Forecasting 

Model (DAMBRK). However, due to the sensitivity of the DAMBRK model and the 

manipulation of the input necessary to get the program to run (particularly on small 

dams), some states reportedly try to avoid using this model except on large dams. Some 

states reported using the Flood Wave Model (FLDWAV). No state reported any 

difficulties with the FLDWAV model, however, it was the general consensus that limited 

information and training has been made available for the FLDWAV model. Other 

models that were reported to be accepted by the states were the NWS Simplified 

DAMBRK Model, the NRCS's TR-61, WSP2 Hydraulics, and the TR-66, Simplified 

Dam Breach Routing Procedure. 

Pennsylvania reported that they have compared the NWS DAMBRK model and the 

HEC-1 model on specific projects in the past. The results showed that the two models 

give similar outflows, but they have noticed that the NWS model attenuates the 

downstream flood results quicker than that of the HEC-1 model. 

For breach parameters, it is recommended that the engineers performing the analysis 

utilize a range of breach parameters such as those recommended by the Federal Energy 

Regulatory Commission (FERC). In order to achieve results that are conservative, it is 

recommended that the upper level of the average breach width and that the lower end of 

the range of breach times be used so that the resultant breach wave is a worse case 

scenario. The breach should be assumed to be at the location where the dam height is the 

greatest and the breach should occur at the peak of the design storm event. Engineers are 

encouraged to perform sensitivity analysis on their breach parameters to determine the 

reasonableness of their assumptions. 
 3 

Maryland also recommends that the equations developed by Froelich in 1987 (revised 

1995) for determining average breach width and time of failure be used and the results 

compared with the results of the breach analysis using the recommended range of breach 

widths and times. 

Froelich Equations: 

B = 9.5Ko(VsH)0.25 Tf = 0.59(Vs 0.47)/(H 0.91) 

where: 

B = average breach width (ft) 

Tf = time of failure (hrs) 

Ko = 0.7 for piping and 1.0 for overtopping failure 

Vs = storage volume (ac-ft) 

H = height (ft) of water over breach bottom 

Issues with Dam Failure Analysis 

Core walls and concrete or masonry faces 

In the 1920's and 1930's, many dams were built with a concrete or masonry core walls or 

with concrete or masonry downstream or upstream faces. These walls within earthen 

dams have been an issue of discussion when it comes to determine breach parameters to 

be used in a dam breach analysis. 

When a dam with a core wall overtops, the downstream 

face of the dam will erode away. However, the top of 

the dam will only be able to erode down to the elevation 

of the top of the core wall. This will leave the core wall 

to provide the structural stability in the dam. The 

remaining embankment material behind the core wall 

may be saturated and would likely "flow" if the core 

wall were to fail. Generally core walls were designed as 

an impervious barrier to reduce seepage and were not 

designed to provide structural stability. Since the 

downstream fill material has eroded away and the fill 

material behind the structurally questionable core wall is saturated, it could be 

recommended that breach parameters similar to those of a concrete gravity dam be used 

with a very fast to nearly instantaneous time of failure. The width should be established 

based upon the procedures used to construct the core wall (monolithic vs. continuous 

pour). It could be recommended that the downstream face of the dam had eroded away 

on the rising limb of the hydrograph and that the near instantaneous failure of the 

concrete core wall would occur at the peak of the design storm. 

Possible 

Saturated Zone 
 4 

A similar situation exists in dams that were constructed with a masonry face on either the 

upstream or downstream side of the dam or used as a core wall in the dam. In cases 

where the masonry wall is on the downstream face, one could expect if the top layer of 

masonry were to fail and erosion of the earth portion of the dam commence, the masonry 

would unravel as the earth eroded and typical earth dam breach parameters could be used. 

A masonry wall used in the dam as a core wall and on the upstream face of a dam could 

be expected to act similar to the core wall 

situation presented above. In the case with the 

wall on the upstream face, it would be more likely 

to be a near instantaneous since there would be no 

remaining earth fill material upstream or 

downstream of the wall. It couldn't be expected to 

fail typical of a designed masonry dam since the 

wall was not designed to stand alone as a masonry 

dam would have been. 

Core wall example: West Branch Reservoir Dam, Bridgewater, New Jersey 

The West Branch Reservoir Dam is a 39 foot high, 330 foot long, high hazard dam 

constructed in 1929. The dam is an earthen dam with a concrete core wall. The core wall 

is 18 inches wide at the top with a 1H:20V batter on both sides resulting in a base width 

of approximately 5.5 feet resting on bedrock (not keyed). The core wall in this case was 

constructed as a continuous pour over 6 days. 

 

Overtopping of the Washington Forge Pond 

Dam in August 2000. Dam has masonry 

downstream face. 

Construction of core wall at West Branch Reservoir Dam 
 5 

On August 27, 1971, the West Branch Reservoir Dam was overtopped as a result of 

Hurricane Doria. As a result of the overtopping, the downstream fill material was 

washed away exposing the concrete core 

wall. Fortunately the dam did not fail 

however, a quick failure of this dam could 

have been catastrophic. The exposed area of 

the core wall was 22 feet deep and 48 feet 

wide. 

Many have credited the core wall with 

saving the dam from failure. And they may 

have rightfully done so. Without the core, 

the earth fill most likely would have 

continued to erode to the lakeside of the dam 

resulting in a breach of the embankment. 

However, one has to question that if the core wall had not been able to withstand the 

water pressure, would the failure been more catastrophic than a failure of an earth dam 

without a core wall? This is an important point to consider in developing the inundation 

maps for a dam with a core wall. 

The consultant for the Army Corps of Engineers performed a dam failure analysis of this 

dam as part of the Phase 1 inspection report. The consultant use a trapezoidal shaped 

breach with 45-degree side slopes, 190 feet wide at the base (original reservoir floor 

elevation). Six hours was chosen as the time for the breach to form to its maximum size. 

The start of breaching was modeled to begin when the dam first overtops. 

Masonry Wall Example: Edison Pond Dam, Sparta, New Jersey 

The Edison Pond Dam is a small dam in northern New Jersey. The dam is an earthen 

dam approximately 15 feet in height and a portion of the dam possesses a masonry wall 

along the upstream face of the dam. There is no history on the construction of this dam. 

The dam was in a serious state of disrepair. In August 2000, a storm dropped between 14 

and 18 inches of rain on the Edison Pond Dam watershed resulting in the failure of the 

dam. It is uncertain whether the dam failed as a result of piping or overtopping or a 

combination of both. The earth material downstream of the masonry wall was eroded in a 

very narrow breach (3 to 4 foot channel through the embankment) and the masonry wall 

was undermined leading one to believe that piping may have attributed to the failure. 

There was no clear indication that overtopping occurred, however, documentation 

indicates that the normal flow was known to flow over the crest of the dam at this 

location at times when the principal spillway was clogged by beavers. The wall, 

however, did not fail allowing for a slow release of the lake storage. The downstream 

dam survived minimal overtopping during the storm, however, a total failure of the 
 6 

Edison Pond Dam may have resulted in a larger overtopping of the downstream dam and 

hence possible failure. 

 

Views of Edison Pond Dam Failure 

The masonry wall along the upstream face of the Edison Pond Dam was approximately 3 

feet wide. This, in combination with the narrow breach width downstream and a low 

hydraulic head on the wall probably prevented the total failure of the wall. But, had this 

dam overtopped for an extended period of time, a more significant portion of the earthen 

dam may have been eroded making a wider area of exposed masonry wall. This wall 

may not have been able to withstand the water pressures and may have experienced a 

total structural failure. With no earth pressures on the downstream side of the wall, a 

near instantaneous failure could have been expected, resulting in a large release of stored 

water. 

Additional Issues and Research Needs 

Additional issues and research needs that were identified by State engineers in the 

Northeast Region as part of the survey are: 

• Refinement of breach parameters for dams with core walls or vertical concrete or 

masonry walls on the upstream face. 

• Research into and refinement if necessary of breach parameters for small dams. 

• NWS DAMBRK model has problems with large lateral inflows being added 

downstream of a dam 

• State engineers unaware of the latest on the new FLDWAV model. Little or no 

training available. 

• How do models handle debris flow in the flood wave? Currently engineers concerned 

with this issue are using high 'n' values in the overbank areas. 

View of breach across 

crest with masonry wall 

on upstream face 

View of breach 

immediately below 

masonry wall 

View of breach through 

earthen embankment 
 7 

• Forensic Team. The Research Subcommittee of ICODS recommended to FEMA the 

development of a Forensic Team. The intent is that this team would be dispatched to 

the location of dam failures to gather data with respect to the breach and the impacts 

of the failure. State dam safety staffs are spread thin, and when failures occur, 

particularly in a wide spread area similar to the many failures that occurred along the 

east coast as a result of Hurricane Floyd, state engineers have little or no time to 

gather pertinent information with respect to the breach parameters and resultant 

damages. The data gathered by the Forensic Team would be useful for future 

research on dam safety analysis. 

B-9

-1-

Issues, Resolutions, and Research Needs Related to Dam Failure Analysis Workshop

Oklahoma City, Oklahoma

June 26 -28, 2001

Embankment Dam Failure Analysis

by

Francis E. Fiegle II, P. E.

Georgia Safe Dams Program

The Kelly-Barnes Dam failed on November 6, 1977 near Toccoa, Georgia and killed 39 

people that fateful Saturday night. That incident led to the passage of the Georgia Safe Dams Act 

and the formation of the Georgia Safe Dams Program. Since that date, there have been over 300 

dam failures recorded in Georgia. Some of these have been catastrophic and two of these have 

resulted in loss of life. The Kelly Barnes Dam failed in 1977 and unnamed farm pond dam failed 

between Plains, Georgia and Americus which resulted in three deaths on July 5, 1994.

Kelly Barnes Dam Failure

Toccoa Georgia

A few of these dam failures have had good investigative follow-up where the size of the 

breach, initial conditions, and the resulting flood wave depths were measured. For instance, the 

Kelly Barnes Dam failure was thoroughly detailed by a Federal Investigative Board. The

following breach parameters were detailed in the report for the Kelly Barnes Dam which was 38 

feet tall:

• Breach side slopes - right 0.5 H to 1.0V

- left 1.0 H to 1.0 V

• Base width of breach - 40 ft

• Sudden failure

• Estimated peak flow - 24,000 cfs
-2-

However, most of the dams that fail in Georgia have not had these detailed

measurements. Every year in Georgia there are usually three or four dam failures of unregulated 

dams that are reported to our office. The majority of the dam failures have occurred during major 

rainfall events such as Tropical Storm Alberto in 1994, the 100-year flood in middle Georgia in 

1998, and Tropical Storm Allison in 2001.

Lake Collins Dam

Sumter County

Tropical Storm Alberto

July 1994

Clayton County Waste Water Pond Dam

1982
-3-

Pritchard's Lake Dam

Morgan County

March 2001

Unknown Dam

Putnam County

Tropical Storm Allison

June 2001

Over the years, our office has noted that most of the dam breaches have had the following 

general parameters:

- Side slopes 1.0 H to 1.0 V

- Base width of breach equal to height of the dam
-4-

The side slopes are sometimes steeper in more clayey soils and flatter in sandy soils. The 

breach width maybe wider if there is a large impoundment (>than 25 acres).

The breach parameters recommended in the Georgia Safe Dams Program's Engineering 

Guidelines mirror the Breach Parameters recommended by FERC and have been modified by our 

field observations of numerous dam failures.

Table I - Breach Parameters

Earthen- HD 1.0 0.5

engineered

Earthen – HD 1.0 0.1

non-engineered

Slag; Refuse 80% of W 1.0 – 2.0 0.1 to 0.3

Timber Crib HD Vertical 0.1 to 0.3

Rockfill HD

Masonry; Monolith Width Vertical 0.1 to 0.3

Gravity

Vertical or 0.1

Slope of Valley 

Walls

Arch W

Time to 

Failure

Hours

Breach Side Slope

Z

 Breach Width

BR (Feet)

Type of Dam
-5-

Table 2 – Breach Parameters

Definitions

• HD - Height of Dam

• Z - Horizontal Component of Side 

• - Slope of Breach

• BR - Base Width of Breach

• TFH - Time to Fully Form the Breach

• W - Crest Length

Typical Sketch of Breach of Earth Embankment

Our office uses the Boss Dambreak software, which is based on the NWS Dambreak,

developed by Dr. Danny Fread, P. E. Our office assumes that wedge erosion occurs (see

following sketch). Furthermore, the time to failure is conservative for hazard classification of

dams. We use a 6-minute time failure for earth fill dams that are not engineered fills or that we 

have no construction/design information for and 30 minutes for failure of engineered dams. 
-6-

In Georgia, we use dambreak modeling for the following purposes:

• Hazard classification

• Flood inundation mapping

• Emergency action planning

• Incremental spillway capacity design

In closing, over the years our office has used or has seen dambreak modeling and

routings use the following methods:

• NRCS TR66 (1978 to 1982)

• NWS Dambreak

• HECI Dambreak in conjunction with HECII or HECRAS stream routing

• Boss Dambreak (currently used by our office) 

In preparation for this workshop, I surveyed the states east of the Mississippi River. I

received responses from Virginia, North Carolina, West Virginia, South Carolina, Kentucky,

Tennessee, Florida, Ohio, Georgia, and Indiana. The following questions were asked and the

responses are detailed.

1. Who does the dambreak routings?

• Owner of dam - SC, NC, VA, KY, WV, for new dams - FL, TN

• State - SC, OH, GA, NC; TN for existing dams

2. Breach Parameters:

• Breach width varies from height to twice the height of the dam

• Side slopes varies from 0.5 H to 1.0 H to 1V

• Time to failure varies from 6 minutes to 60 minutes

3. What type of dams are routed?

• High hazard - SC, WV, VA, KY, TN, OH, NC, GA

• Significant Hazard - SC, WV, VA

• Low hazard - none

• In Florida and Indiana - various hazards are routed

4. Definition of High Hazard Dams:

• Floods a building that is occupied

• One foot above finished floor

• Well-traveled roadways 6 inches deep

• Use BurRec Guidelines

• Loss of life likely to probably

• Any dam over 60 feet in height or stores more than 5000 acre-feet (Ohio)

• Application of damage index

5. Type of analyses used

• NWS Dambreak (variation of) - TN, SC, KY, OH, WV, NC, GA

• HEC1 Dambreak/HECII and HECRAS - TN, SC, OH, WV, NC, VA

• Visual Observation - NC
-7-

6. Reinventory of Dams Timeframe:

• Annually - high hazard only -SC

• Two Years - high hazard only - NC

• Three Years - significant hazard - NC, SC

low hazard - SC

• Five Years - all hazards - OH, GA

low hazard - NC

• Six Years - all hazards - VA

• Kentucky only reinventories if hazard is noticed

• West Virginia reinventories during routine inspections

• Florida is locally determined (Water Management Districts)

• Tennessee when doing a safety inspections

As a result of this survey, there were several issues identified that need attention. It is 

clear that states need to take the following actions:

• Regularly reinventory dams of all hazard classifications

• Have consistent hazard classification guidelines

• Adopt Quality Assurance/Quality Control Procedures

• Improve technical expertise

The states have requested the following guidance from this workshop based on the

assembled expertise:

• Time to failure guidelines

• Is there time for emergency response to make a difference?

• When to use which model or sets of models (field conditions, etc)?

• What is the level of accuracy for each model?

• Advantages/disadvantages for each model(s)

As a result of the survey, the following immediate dam safety needs were identified by 

the states:

• Combine HECI and HECII or HECHMS and HECRAS into integrated model(s) 

• Finish Floodwave Model

• Provide in depth, hands on training in the use of all models

Finally, the states identified the following Research Needs:

• Input parameters for breach development for earth and rockfill dams

• Depth of overtopping that causes failure

• How does the crest protection influence overtopping failure development?

• How does the embankment protection influence overtopping failure development?

• Forensic investigation of breach failures including the condition of the dam

• Influence of the size of the drainage basin on a "storm in progress" failure
-8-

In closing, I wonder if we in the dam safety community are meeting the public's

expectations in regulating dams, or better yet, are we classifying dams for regulation to meet our 

perception of the public's expectation or some variation there of? If we are using our paradigms 

without adequate explanation to the public and feedback from the "at risk" population, then likely 

we are imposing additional risk to the "at risk" populations that is not justified.
B-10

CREDENTIALS

‰Prep School - Math, Science, Computers,

Statistics

‰Engineering - Calculus, Physics, Thermo, Fluids

‰Grad Courses - Modeling, Meteorology, Hydrology

‰Computers - Punch Cards, Batch Files, XT, AT,

PC, Math Chip, 286, 386, 486, Pentium I, II....

AMATEUR ACADEMIC MODELER

ADJUSTING REALITY

TO FIT THE MODEL

‰DEPT OF NATURAL RESOURCES

‰STATE ENGINEERS OFFICE

‰DAM SAFETY HYDROLOGIST

MATTHEW LINDON, P.E.
Awakening

From the Hypothetical to the Real World

‰HEC I, HEC II courses and experience

‰NWS - DAMBRK/BREACH Course - Exercise

‰Quail Creek dam failure - Calibration opportunity

‰Necessity is the mother of invention

‰Measure, survey, interview, history of event

MODELING

EXPERIENCE

DAM SAFETY HYDROLOGY

20 YEARS

‰ACOE - HEC I, II, HMS, RAS

‰NWS - DAMBRK, BREACH, SMPDBK, DWOPER

‰DHM, FLO2D, TR20, PIPE NETWORK

‰STORM, SPIPE, FLDRTE, BACKWAT

‰SIDECHAN, SPILLWAY, STABLE, QUAKE....
Doubt and Disillusionment

Pity the man who doubts what he’s sure of

‰ HEC I

 - Sensitive to Time Step, Reach Length, Basins

 - Black box for infiltration, lag, runoff, melt....

 - Hydrological routing - No Attenuation

 - Designed for flat farms not wild mountains

‰ HEC II

 - Manning Black Box,

 - 1 dimension limits, boundary conditions

 - Designed for labs and canals - not rivers

‰ Old equations on new high speed computers

‰ Developed by mathematicians, statisticians and

Computer Geeks

CALIBRATION

CORRELATION TO REALITY

‰ NO correlation of BREACH model with reality

 - Piping channel start sensitivity

 - Can’t model actual breach shape and timing

‰ NO correlation of DAMBRK model with reality

 - Manning Roughness Coefficients unreal - 0.1-0.25

 - sensitive to breach size and timing

 - Can’t model trapezoidal migration

 - Can’t converge with Manning increase with depth

‰ Sensitive to Black Box Variables - Mannings

 - Friction, bulking, debris, turbulence, eddys

‰ Limited by time steps and reach lengths - converge?

‰ Supercritical to subcritical hydraulic jumps
Apparent Veracity

Computers lie and liars use computers.

‰Easy inout, user interface, GUI, ACAD, GIS

‰Garbage in garbage out

‰Slick output, graphics, color

‰Windows, WYSIWYG, 3D, Iso views

‰Computer Credibility - must be FACT

‰Models using old theories and methods

‰Lagging physically based, spatial and temporal

‰Computers effect modeling like writing styles

Basis of Uncertainty

Close counts in horseshoes, hand grenades & hydrology

‰Sensitivity analysis of input variables

‰Probabilistic approach

‰Monte Carlo combinations of all

 variables

 - Most probable answer

 - Not best answer

 - Not worst case

‰Fuzziness of results
Problem Solutions

‰ Better Models

 - Eliminate Balck Boxes

 - 2D, 3D - less assumptions

 - incorporate new theory and methods

 - Use spatial and temporal improvements

‰ Qualified modelers

 - Better modelers for better models

 - educate, train, help screens, documentation

 - Use models for intended purpose, scope and scale

‰ Calibrate, Correlate, Calculate

 - Sensitivity analysis on input variables

 - Interpolate rather than extrapolate

‰ Express degree of uncertainty of output

 - Probabilities, confidence, fuzziness, chaos

Good math and science don’t always make good models

New age modelers

Post-modern hydrology - form before function.

‰Ease of operation encourages the unqualified or

unscrupulous to take advantage

‰Not familiar with theory and methods

‰Have not done calculations in head or by hand

‰Don’t understand complex non linear nature of

these multidimensional problems.

‰Know exactly what the models does or don’t use it
Get out of the box.

‰ Natural phenomena are fantastically complex systems

 - Understand little

 - Describe less

 - Model and reproduce even less

‰ Math and Science just our best guess

 - They are tools like slide rules, computers, hammers.

 - “Ology” is the study of, not the perfect understanding.

 - Use a large grain of salt

‰ Observe present and past

 - Paleohydrology

 - Walk up and downstream

 - What does nature want to do

‰ Connect the model with reality

To think outside the box you must get outside.
B-11

A Simple Procedure for Estimating

Loss of Life from Dam Failure

FEMA/USDA Workshop

Issues, Resolutions, and Research

Needs Related to Embankment Dam Failure Analysis

26-28 June 2001

Wayne J. Graham, P.E.

INTRODUCTION

Evaluating the consequences resulting from a dam failure is

an important and integral part of any dam safety study or

risk analysis. The failure of some dams would cause only

minimal impacts to the dam owner and others, while large

dams immediately upstream from large cities are capable of

causing catastrophic losses. Dam failure can cause loss of

life, property damage, cultural and historic losses,

environmental losses as well as social impacts. This paper

focuses on the loss of life resulting from dam failure. 

Included is a procedure for estimating the loss of life that

would result from dam failure. No currently available

procedure is capable of predicting the exact number of

fatalities that would result from dam failure.

PROCEDURE FOR ESTIMATING LOSS OF LIFE

The steps for estimating loss of life resulting from dam

failure are as follows:

Step 1: Determine dam failure scenarios to evaluate.

Step 2: Determine time categories for which loss of life

estimates are needed.

Step 3: Determine area flooded for each dam failure

scenario.

Step 4: Estimate the number of people at risk for each

failure scenario and time category.

Step 5: Determine when dam failure warnings would be

initiated. 

Step 6: Select appropriate fatality rate. 

Step 7: Evaluate uncertainty.

The details of each step are as follows:
Step 1: Determine Dam Failure Scenarios to Evaluate

A determination needs to be made regarding the failure

scenarios to evaluate. For example, loss of life estimates

may be needed for two scenarios - failure of the dam with a

full reservoir during normal weather conditions and failure

of the dam during a large flood that overtops the dam.

Step 2: Determine Time Categories For Which Loss of Life

Estimates Are Needed

The number of people at risk downstream from some dams is

influenced by seasonality or day of week factors. For

instance, some tourist areas may be unused for much of the

year. The number of time categories (season, day of week,

etc.) selected for evaluation should accommodate the varying

usage and occupancy of the floodplain. Since time of day

can influence both when a warning is initiated as well as

the number of people at risk, each study should include a

day category and a night category for each dam failure

scenario evaluated.

Step 3: Determine Area Flooded for Each Dam Failure Scenario

In order to estimate the number of people at risk, a map or

some other description of the flooded area must be available

for each dam failure scenario. In some cases, existing dambreak studies and maps may provide information for the

scenarios being evaluated. Sometimes new studies and maps

will need to be developed. 

Step 4: Estimate the Number of People at Risk for Each

Failure Scenario and Time Category

For each failure scenario and time category, determine the

number of people at risk. Population at risk (PAR) is

defined as the number of people occupying the dam failure

floodplain prior to the issuance of any warning. A general

guideline is to: "Take a snapshot and count the people." 

The number of people at risk varies during a 24-hour period. 

The number of people at risk will likely vary depending upon

the time of year, day of week and time of day during which

the failure occurs. Utilize census data, field trips,

aerial photographs, telephone interviews, topographic maps

and any other sources that would provide a realistic

estimate of floodplain occupancy and usage.
Step 5: Determine When Dam Failure Warnings Would be

Initiated

Determining when dam failure warnings would be initiated is

probably the most important part of estimating the loss of

life that would result from dam failure. Table 1, "Guidance

for Estimating When Dam Failure Warnings Would be

Initiated," was prepared using data from U.S. dam failures

occurring since 1960 as well as other events such as Vajont

Dam in Italy, Malpasset Dam in France and Saint Francis Dam

in California. An evaluation of these dam failure data

indicated that timely dam failure warnings were more likely

when the dam failure occurred during daylight, in the

presence of a dam tender or others and where the drainage

area above the dam was large or the reservoir flood storage

space. Timely dam failure warnings were less likely when

failure occurred at night or outside the presence of a dam

tender or casual observers. Dam failure warnings were also

less likely where the drainage area was small or the

reservoir had little or no flood storage space, i.e, when

the reservoir was able to quickly fill and overtop the dam. 

Although empirical data are limited, it appears that timely

warning is less likely for the failure of a concrete dam. 

Although dam failure warnings are frequently initiated

before dam failure for earthfill dams, this is not the case

for the failure of concrete dams.

Table 1 provides a means for deriving an initial estimate of

when a dam failure warning would be initiated for the

failure of an earthfill dam. The availability of emergency

action plans, upstream or dam-site instrumentation, or the

requirement for on-site monitoring during threatening events

influences when a dam failure warning would be initiated. 

Assumptions regarding when a warning is initiated should

take these factors into account. 
Table 1

Guidance for Estimating When Dam Failure Warnings Would be Initiated (Earthfill 

Dam Type Cause of Failure Special

Considerations

Time of

Failure

When Would Dam Failure Wa

Many Observers at Dam No 

Earthfill Overtopping

100 mi

dam less than

Drainage area at

2 (260 km2)

Day

failure

0.25 hrs. before dam

re

0.

100 mi

dam less than

Drainage area at

2 (260 km2)

Night

failure

0.25 hrs. after dam

re

1.

100 mi

dam more than

Drainage area at

2 (260 km2)

Day

failure

2 hrs. before dam

fa

1 

100 mi

dam more than

Drainage area at

2 (260 km2)

Night

failure

1 to 2 hr. before dam

fa

0 

normal weather)

reservoir,

Piping (full Day

failure

1 hr. before dam

re

0.

Night

failure

0.5 hr. after dam

re

1.

Seismic

Failure

Immediate Day

failure

0.25 hr. after dam

re

0.

Night

failure

0.50 hr. after dam

re

1.

Delayed Failure Day

failure

2 hrs. before dam

re

0.

Night

failure

2 hrs. before dam

re

0.

Notes: "Many Observers at Dam" means that a dam tender lives on high ground and within site of the dam or the dam is visible from the ho

the dam is out of site of nearly all homes and there is no roadway on the dam crest. These dams are usually in remote areas.

the dam crest serves as a heavily used roadway. These dams are typically in urban areas. "No Observers at Dam" means that there is no 

 The abbre

for floodwater.
Step 6: Select Appropriate Fatality Rate

Fatality rates used for estimating life loss should be

obtained from Table 2. The table was developed using data

obtained from approximately 40 floods, many of which were

caused by dam failure. The 40 floods include nearly all

U.S. dam failures causing 50 or more fatalities as well as

other flood events that were selected in an attempt to cover

a full range of flood severity and warning combinations. 

Events occurring outside of the U.S. were included in the

data set. The following paragraphs describe the terms and 

categories that form the basis for this methodology.

Flood Severity along with warning time determines, to a

large extent, the fatality rate that would likely occur. 

The flood severity categories are as follows:

 

1) Low severity occurs when no buildings are washed off

their foundations. Use the low severity category if most

structures would be exposed to depths of less than 10 ft

(3.3 m) or if DV, defined below, is less than 50 ft2/s (4.6

m

2/s).

2) Medium severity occurs when homes are destroyed but trees

or mangled homes remain for people to seek refuge in or on.

Use medium flood severity if most structures would be

exposed to depths of more than 10 ft (3.3 m) or if DV is

more than 50 ft2/s (4.6 m2/s). 

3) High severity occurs when the flood sweeps the area clean

and nothing remains. High flood severity should be used

only for locations flooded by the near instantaneous failure

of a concrete dam, or an earthfill dam that turns into

"jello" and washes out in seconds rather than minutes or

hours. In addition, the flooding caused by the dam failure

should sweep the area clean and little or no evidence of the

prior human habitation remains after the floodwater recedes. 

Although rare, this type of flooding occurred below St.

Francis Dam in California and Vajont Dam in Italy. The

flood severity will usually change to medium and then low as

the floodwater travels farther downstream.
The parameter DV may be used to separate areas anticipated

to receive low severity flooding from areas anticipated to

receive medium severity flooding. DV is computed as follows:

 Qdf -Q2.33

DV = ------------

 Wdf

where:

Qdf is the peak discharge at a particular site caused by dam

failure.

Q2.33 is the mean annual discharge at the same site. This

discharge can be easily estimated and it is an indicator of

the safe channel capacity. 

Wdf is the maximum width of flooding caused by dam failure

at the same site. 

Warning Time influences the fatality rate. The warning time

categories are as follows: 

1) No warning means that no warning is issued by the media

or official sources in the particular area prior to the

flood water arrival; only the possible sight or sound of the

approaching flooding serves as a warning. 

2) Some warning means officials or the media begin warning

in the particular area 15 to 60 minutes before flood water

arrival. Some people will learn of the flooding indirectly

when contacted by friends, neighbors or relatives.

3) Adequate warning means officials or the media begin

warning in the particular area more than 60 minutes before

the flood water arrives. Some people will learn of the

flooding indirectly when contacted by friends, neighbors or

relatives.

The warning time for a particular area downstream from a dam

should be based on when a dam failure warning is initiated

and the flood travel time. For instance, assume a dam with

a campground immediately downstream and a town where

flooding begins 4 hours after the initiation of dam failure. 

If a dam failure warning is initiated 1 hour after dam

failure, the warning time at the campground is zero and the

warning time at the town is 3 hours.

The fatality rate in areas with medium severity flooding

should drop below that recommended in Table 2 as the warning

time increases well beyond one hour. Repeated dam failure
warnings, confirmed by visual images on television showing

massive destruction in upstream areas, should provide

convincing evidence to people that a truly dangerous

situation exists and of their need to evacuate. This should

result in higher evacuation rates in downstream areas and in

a lowering of the fatality rate.

Flood Severity Understanding also has an impact on the

fatality rate. A warning is comprised of two elements: 1)

alerting people to danger and 2) requesting that people at

risk take some action. Sometimes those issuing a flood

warning or dam failure warning may not issue a clear and

forceful message because either 1) they do not understand

the severity of the impending flooding or 2) they do not

believe that dam failure is really going to occur and hence

do not want to unnecessarily inconvenience people. People

exposed to dam failure flooding are less likely to take

protective action if they receive a poorly worded or timidly

issued warning. Warnings are likely to become more accurate

after a dam has failed as those issuing a warning learn of

the actual failure and the magnitude of the resultant

flooding. Precise warnings are therefore more probable in

downstream areas. This factor will be used only when there

is some or adequate warning time.

The flood severity understanding categories are as follows:

1) Vague Understanding of Flood Severity means that the

warning issuers have not yet seen an actual dam failure or

do not comprehend the true magnitude of the flooding. 

2) Precise Understanding of Flood Severity means that the

warning issuers have an excellent understanding of the

flooding due to observations of the flooding made by

themselves or others.
Table 2

Recommended Fatality Rates for Estimating Loss of Life Resulting from D

Flood Severity Warning Time

(minutes)

Flood Severity

Understanding

Fatality 

die)

(Fraction of people at 

Suggested 

HIGH

no warning not applicable 0.75 

15 to 60

vague

many people will remai

issued. No guidance i

failure floodplain aft

the number of people w

Use the values shown a

precise

more than 60

vague

precise

MEDIUM

no warning not applicable 0.15 

15 to 60

vague 0.04 

precise 0.02 

more than 60

vague 0.03 

precise 0.01 

LOW

no warning not applicable 0.01 

15 to 60

vague 0.007 

precise 0.002 

more than 60

vague 0.0003 

precise 0.0002 
Step 7: Evaluate Uncertainty

Various types of uncertainty can influence loss of life

estimates. Quantifying uncertainty is difficult and may

require significant time to achieve. 

Step 1 of this procedure suggests that separate loss of life

estimates be developed for each dam failure scenario. 

Various causes of dam failure will result in differences in

downstream flooding and therefore result in differences in

the number of people at risk as well as flood severity. 

Step 2 suggests that the dam failure be assumed to occur at

various times of the day or week. It is recognized that the

time of failure impacts both when a dam failure warning

would be initiated as well as the number of people who would

be at risk. 

Dam failure modeling serves as the basis for step 3. Dam

failure modeling requires the estimation of: 1) the time for

the breach to form, 2) breach shape and width and 3)

downstream hydraulic parameters. Variations in these

parameters will result in changes in the flood depth, flood

width and flood wave travel time. This will lead to

uncertainty in the: 1) population at risk, 2) warning time

and 3) flood severity. 

Estimating the number of people at risk, step 4, may be

difficult, especially for areas that receive temporary

usage. A range of reasonable estimates could be used.

Step 5 focuses on when a dam failure warning would be

initiated. This warning initiation time could be varied to

determine sensitivity to this assumption. 

The last type of uncertainty is associated with the

inability to precisely determine the fatality rate, step 6. 

There was uncertainty associated with categorizing some of

the flood events that were used in developing Table 2.

Similarly, some of the factors that contribute to life loss

are not captured in the categories shown in Table 2. This

type of uncertainty can introduce significant, but unknown,

errors into the loss of life estimates. Some possible ways

of handling this uncertainty would be to 1) use the range of

fatality rates shown in Table 2, 2) when the flooding at a

particular area falls between two categories (it is unclear

if the flood severity would be medium or low, for example)

the loss of life estimates can be developed using the

fatality rate and range of rates from all categories touched

by the event and 3) historical events can be evaluated to

see if there are any that closely match the situation at the

site under study. 

B-12

1

Workshop on Issues, Resolutions, and Research Needs

Related to Dam Failure Analysis

Current Practice

Natural Resources Conservation Service

by Bill Irwin 1

Introduction

The Natural Resources Conservation Service (NRCS) formerly Soil Conservation Service

(SCS) is the engineer-of-record on over 26,000 of the roughly 77,000 dams currently 

identified in the National Inventory of Dams (NID). NRCS has also engineered over 

3,000,000 dams and ponds that are smaller than the minimum size dam included in the 

National Inventory. Typical dams in the NRCS portfolio are relatively small embankment 

dams built over 30 years ago. Data on NRCS dams in the NID is shown in Figure 1.

NID size dams 26000 26000 26000

25ft+ high 15000 50AF+ storage 23000 30yrs+ old 15000

45ft+ high 2000 500AF+ storage 7000 40yrs+ old 5000

65ft+ high 400 5000AF+ storage 600 50yrs+ old 1000

100ft+ high 40 15000AF+ storage 100 60yrs+ old 400

Figure 1 – NRCS Dam Portfolio 

Current Criteria

The NRCS has developed a significant set of design criteria over the years to accomplish this 

work. The SCS established three levels of hazard classification over as far back as anyone 

can remember and defined the high hazard classification almost fifty years ago as structures 

“...where failure may result in loss of life, damage to homes, industrial and commercial 

buildings, important public facilities, railroads and highways.” 2 This classification and 

subsequent design criteria approach inherently requires evaluation of dam failure parameters. 

The NRCS has provided increasing degrees of criteria and guidance on selection of such 

parameters as techniques for analyzing the consequences of dam failures have advanced.

Current NRCS failure analysis guidance was initially published the late 1970’s as Technical 

Release Number 66 (TR-66), “Simplified Dam Breach Routing Procedure”. This procedure 

is a combined hydrologic-hydraulic method. The hydraulic portion is a simplified version of 

a simultaneous storage and kinematic routing method which accepts a breach hydrograph at 

the upstream end of the reach and routes the flood wave downstream, continuously in time 

and space. The hydrologic portion develops the breach hydrograph based on estimated 

downstream flow characteristics, total volume of flow from dam pool, and expected 

maximum breach discharge (Qmax). The Qmax parameter was estimated from a curve fit of 

the peak discharges from historic dam failures available at the time.

1National Design Engineer, USDA/NRCS, Washington, DC

email: bill.irwin@usda.gov phone: (202)720-5858

2SCS Engineering Memo No. 3, July 16, 1956
2

The procedure was intended to provide a practical “hand-worked” method appropriate for 

typical NRCS dam work. One published report 3 compared the TR-66 procedure with three 

other methods available at the time including the National Weather Service (NWS) and 

Hydraulic Engineering Center (HEC) models. For a 36ft high embankment dam subjected to 

a PMP event, the four methods produced comparable breach profile depths, while the TR-66 

method computed the lowest peak flow at the dam. Computed peak discharges were 

71,355cfs by TR-66, 76,000cfs by Keulegan, 85,950cfs by NWS, and 87,000cfs by HEC-1.

Current NRCS breach peak discharge criteria was initially published in the late 1980”s in 

Technical Release Number 60 (TR-60), “Earth Dams and Reservoirs”. The criteria specifies 

the peak breach discharge (Qmax) to be used to delineate the potential dam failure inundation 

area below the dam and subsequently to determine the dam hazard classification. The 

criteria does not specify downstream breach routing or other hydraulic methodologies to be 

used. Regardless of the stream routing techniques to be used, the minimum peak discharge is 

as follows:

1. For depth of water at dam (Hw) at time of failure  103 feet,

Qmax = 65 Hw

1.85

2. For depth of water at dam (Hw) at time of failure < 103 feet,

Qmax = 1000 Br

1.35 but not less than 3.2 Hw2.5 nor more than 65 Hw1.85, where,

Br = Vs Hw / A and,

Br = breach factor, acres

Vs = reservoir storage at failure, acre-feet

A = cross-sectional area of the embankment, square feet

3. When actual dam crest length(L) is less than theoretical breach width (T) such that,

L < T = (65 H 0.35) / 0.416 use,

Qmax = 0.416 L H 1.5 in lieu of 65 Hw

1.85 in category 1 or 2 above, where,

H = height of dam at centerline, from bottom of breach to top of dam, feet

This suite of expressions for Qmax was derived from a data set of 39 dam failures available 

in the profession or collected from NRCS sources at the time. Figure 2 taken from the 

original work shows the relationship between the peak breach discharge from the 39 sites and 

the peak break discharge predicted by the Qmax criteria.

3 Safety of Existing Dams, National Research Council, National Academy Press, 1983.
3

Figure 2 – Comparison of Predicted vs. Reported Qmax for 39 site data set

Failure Experiences

NRCS has experience a relatively small number of dam failures considering the magnitude of 

its portfolio. However, information from some dramatic NRCS dam failures provides insight 

into NRCS experienced failure modes.

Figure 3 – Obion Creek #36 – looking upstream into reservoir

Obion Creek #36 is a typical NRCS flood control dam from the 1960’s. It was built in 1963 

and failed a year later during the first reservoir filling storm. An Engineering Investigation 

concluded that dispersive soils were a major factor in the failure. Note that the dam was 

constructed with anti-seep collars along the principal spillway pipe as was typical at the time. 
4

Although this failure occurred several years ago, it is still representative of similar dams that 

were built around the same or earlier time periods before needed treatments of dispersive 

soils or needed filter diaphragms around pipe penetrations were recognized. NRCS has had 

several similar piping type failures and does have many similarly designed flood control 

dams that have not yet experienced a significant first filling.

Figure 4 – Coon Creek #41 – note remaining embankment in upper right

Coon Creek #41 is also a typical NRCS flood control dam from the 1960’s. It was built in 

1962 and failed in 1978 during the first significant reservoir filling. An Engineering 

Investigation concluded that stress relief fractured rock in the steep abutment was the major 

factor in the failure. This site was constructed with minimal foundation investigation and 

foundation treatments as was typical at the time. Although this site failure occurred several 

years ago, it is still representative of similar dams that were built in similar geologic settings 

around the same or earlier time periods before such foundation hazards were widely 

recognized or routinely investigated. NRCS has similar flood control dams which have not 

yet experienced a significant first filling. Most recently, Bad Axe #24, a similar site in a 

similar setting built in 1963, failed in a similar fashion last year.

Figure 4 – Ascalmore #11 – looking upstream, note pipe outlet on left
5

Figure 5 – Ascalmore #11 – looking upstream

Ascalmore #11 was built in 1959 and failed last year after trash blocked the pipe spillway 

and a storm quickly filled the flood reservoir. An Engineering Investigation concluded that 

dispersive soils and animal burrow damage in the upper portions of the embankment were 

major factors in the failure. The rough appearance of the embankment surface is due to 

removal of extensive woody vegetation after the breach occurred and before the picture was 

taken. It is interesting to note that the embankment breached in two separate locations and 

the energy of the stored water was not sufficient to erode either breach to the base of the 

dam.

Practical Criteria Needs

The principal NRCS need related to embankment failure analysis continues to be 

determination of the breach inundation area below the dam for purposes of determining 

population at risk, hazard classification, and emergency action planning.

The “hand-worked” hydraulic portion of the old TR-66 method is adequate for only very 

basic hazard class screening on typical rural NRCS dams and ponds. Current software for 

breach flow profile analysis supported with modern computer capabilities is the professional 

norm for developing breach inundation maps and eventually emergency action plans. New 

hydraulic routing software currently being developed in the profession will further advance 

this aspect of dam failure consequence analysis.

The hydrograph portion of the old TR-66 method and subsequently the Qmax equations 

approach of the current TR-60 criteria are still important. This approach can still provide 

adequate dam failure analysis criteria for typical NRCS dams since the embankments are 

small, the area at risk is close to the dam, and agency experience has been a wide variety of 

failure modes. The NRCS workload involving dams requires that a large number of existing 

and potential dams be evaluated without significant topographic or soil site data. Such 

workload without much physical data does not justify a complex analysis. The current 
6

Qmax equation needs to be updated considering newer dam failure data available in the 

profession.

Another NRCS need related more to embankment non-failure analysis is allowable 

overtopping. Agency experience has repeatedly shown that well vegetated dams built with 

well compacted cohesive materials can sustain substantial overtopping flow with minimal 

damage. As NRCS begins a rehabilitation program to rehabilitate aging watershed dams, a 

major issue is increasing the height or spillway capacity of the existing dams to 

accommodate larger required design storms. Research that can increase the confidence level 

of the dam safety profession to accept limited overtopping flow in upgrading these dams 

could eliminate the need for expensive structural upgrades on many existing agency dams.

A last NRCS need related to dam failure analysis is a better tool for risk assessment. Recent 

new authority for NRCS to provide rehabilitation assistance came with the requirement to 

give priority consideration to those existing dams that are the greatest threat to public health 

and safety. NRCS has adopted a risk index system based on the common approach that total 

risk is the product of the probability of loading, the probability of adverse response to that 

loading, and the probability of consequence due to adverse response. Dam failure research 

could provide better tools to define the probability of adverse response.
B-13 

•1

Dam Failure Analyses 

Workshop

Oklahoma City, OK

June 26-28, 2001

Important Areas to Consider in the Investigation 

and Evaluation of Proposed and Existing Dams

• The Embankment Must be Safe Against Excessive Overtopping

by Wave Action Especially During Pre-Inflow Design Flood

• The Slopes Must be Stable During all Conditions of Reservoir

Operations, Including Rapid Drawdown, if Applicable

• Seepage Flow Through the Embankment, Foundation, and

Abutments Must be Controlled so That no Internal Erosion

(Piping) Takes Place and There is no Sloughing in Areas 

Where Seepage Emerges
•2

Important Areas to Consider in the Investigation 

and Evaluation of Proposed and Existing Dams

(Continued)

• The Embankment Must Not Overstress the Foundation

• Embankment Slopes Must be Acceptably Protected Against

Erosion by Wave Action from Gullying and Scour From

Surface Runoff

• The Embankment, Foundation, Abutments and Reservoir

Rim Must be Stable and Must Not Develop Unacceptable

Deformations Under Earthquake Conditions

Design Factors of Safety for Embankment Dams

• End of Construction----------------------------------------------------------FS > 1.3

• Sudden Draw Down From Maximum Pool------------------------------FS > 1.1

• Sudden Draw Down From Spillway Crest or Top of Gates----------FS > 1.2

• Steady Seepage with Maximum Storage Pool---------------------------FS > 1.5

• Steady Seepage With Surcharge Pool-------------------------------------FS > 1.4

• Seismic Loading Condition Factor of Safety----------------------------FS > 1.0

• For Zones with Seismic Coefficients of 0.1 or Less – Pseudostatic

Analysis is Acceptable if Liquefaction Does not Trigger.

• Deformation Analysis are Required if pga  0.15g

For Newmark Procedures, Deformation Should be 2.0 feet.
•3

Stability Analyses Programs to Determine the Factors

of Safety for the Various Loading Conditions

• Computer Programs Such as UTEXAS3 are Used to Determine

the Factors of Safety for the Various Loading Conditions

Previously Discussed

• COE Hand Calculation Method From EM 110-2-1902 are Used

to Confirm a Computer Program Critical Failure Surface for

Important Projects

Lake Blackshear Dam

• Reasons to Prevent Overtopping of an Embankment Even

When Covered With a Good Growth of Grass
•4
•5

Milner Dam

• Control of Seepage Flow Through the Embankment, Foundation,

And Abutments to Prevent Internal Erosion (Piping)

• The Slopes Must be Stable During all Conditions of

Reservoir Operations

• Do Not Permit Unacceptable Deformations Under 

Earthquake Conditions
•6
•7
•8
•9

Santee Cooper East Dam

• The Embankment, Foundation, Abutments, and Reservoir 

Rim Must be Stable and Must Not Develop Unacceptable

Deformations Due to Earthquake Loadings

• Use of Hand Calculations to Confirm Computer Calculations
•10
Dayton Dam Canal Embankment Failure 1

2/12/02

FERC-CRO June 2001 1

Dayton Dam Canal 

Embankment Failure & 

Repair

Michael S. Davis - Lead Engineer

Chicago Regional Office

Federal Energy Regulatory Commission

2/12/02

FERC-CRO June 2001 2

Plan View
Dayton Dam Canal Embankment Failure 2

2/12/02

FERC-CRO June 2001 3

Pertinent Data

• Licensed: 1923 

• Built: 1925 

• Hazard Potential: Low

• Flood of Record: 47,100 cfs (11/10/55)

• Canal Dike Height: 28 feet

• Canal Dike Length: 725 feet

• A substation, owned by a separate entity, is located adjacent to the 

powerhouse.

2/12/02

FERC-CRO June 2001 4

Overflow Spillway
Dayton Dam Canal Embankment Failure 3

2/12/02

FERC-CRO June 2001 5

Canal Embankment – before 

failure

2/12/02

FERC-CRO June 2001 6

Intake
Dayton Dam Canal Embankment Failure 4

2/12/02

FERC-CRO June 2001 7

Canal Embankment – before 

failure

2/12/02

FERC-CRO June 2001 8

Events Leading Up to the Breach

• On July 17, 1996, 16.91 inches of rain over an 18-hour period 

was recorded at the Aurora precipitation gage, which is 

located about 40 miles upstream of the dam. As a result, the 

reservoir rose throughout the following day.

• At 4 p.m., on July 18th, the water level was at about 2 feet 

below the crest of the headgate structure, and rising about 1 

foot per hour. The tailwater was also still rising and was 

beginning to encroach on the substation.

• At that time, the substation owner ordered the plant be taken 

off line so that the power could be cut to the substation. 

• As a result, the level in the canal rose about 3 feet at the 

powerhouse, and began to overtop the canal embankment 

around both sides of the powerhouse.
Dayton Dam Canal Embankment Failure 5

2/12/02

FERC-CRO June 2001 9

The Breach

• With the reservoir still rising and the flow now overtopping the

canal embankment, the canal embankment breached at about 

7 p.m. The breach was initially measured to be about 50 feet 

wide when it reached the foundation. Several secondary 

breaches formed on the embankment as well.

• The resulting breach lowered the canal level and caused a 

differential pressure on the raised headgates. As a result, the

chains holding the gates failed and all four gates slammed into 

the closed position and were severely damaged.

• The flood peaked at about 55,000 cfs later that night (setting a

new flood of record) with the reservoir at about elevation 

507.8 feet, which is 8.9 feet over the crest of the spillway, and 

about 3 inches over the crest of the headgate structure. The 

tailrace reached a peak elevation of 488.9 feet at the 

powerhouse.

2/12/02

FERC-CRO June 2001 10

Cross-section of intake
Dayton Dam Canal Embankment Failure 6

2/12/02

FERC-CRO June 2001 11

Graph

2/12/02

FERC-CRO June 2001 12

July 20, 1996 Inspection

• The next four photographs show the condition of 

the project structures two days after the breach. 

• The inspection was unannounced and was done on 

a Saturday. Access to the site was limited to the 

left bank opposite the side of the canal. 

• The tailrace had receded about 15 feet since the 

breach.
Dayton Dam Canal Embankment Failure 7

2/12/02

FERC-CRO June 2001 13

Breach – 7/20/96

2/12/02

FERC-CRO June 2001 14

Canal Embankment 7/20/96
Dayton Dam Canal Embankment Failure 8

2/12/02

FERC-CRO June 2001 15

Downstream Side at 

Secondary Breach 7/20/96

2/12/02

FERC-CRO June 2001 16

Downstream Right Side of PH 

7/20/96
Dayton Dam Canal Embankment Failure 9

2/12/02

FERC-CRO June 2001 17

July 22, 1996 Inspection

• The next nine photographs show the condition of 

the project structures four days after the breach.

• The tailrace had receded about another 6 to 8 feet 

since the July 20 inspection.

2/12/02

FERC-CRO June 2001 18

Headgate Structure 7/22/96
Dayton Dam Canal Embankment Failure 10

2/12/02

FERC-CRO June 2001 19

Upstream side 7/22/96

2/12/02

FERC-CRO June 2001 20

Upstream Side of Canal 

7/22/96
Dayton Dam Canal Embankment Failure 11

2/12/02

FERC-CRO June 2001 21

Secondary Breach Location 

7/22/96

2/12/02

FERC-CRO June 2001 22

Erosion at House 7/22/96
Dayton Dam Canal Embankment Failure 12

2/12/02

FERC-CRO June 2001 23

Erosion at House 7/22/96

2/12/02

FERC-CRO June 2001 24

Breach – 7/22/96
Dayton Dam Canal Embankment Failure 13

2/12/02

FERC-CRO June 2001 25

Horses on dunes 7/22/96

2/12/02

FERC-CRO June 2001 26

September 30, 1996 Inspection

• On July 25, 1996, the licensee began to place large 

trap rock upstream of the headgate structure to cut 

off the flow. 

• The cofferdam was completed on July 30, 1996.

• The next four photographs show the condition of 

the substantially dewatered canal. 
Dayton Dam Canal Embankment Failure 14

2/12/02

FERC-CRO June 2001 27

Headgate Structure 9/30/96

2/12/02

FERC-CRO June 2001 28

Upstream side 9/30/96
Dayton Dam Canal Embankment Failure 15

2/12/02

FERC-CRO June 2001 29

Breach 9/30/96

2/12/02

FERC-CRO June 2001 30

Breach 9/30/96
Dayton Dam Canal Embankment Failure 16

2/12/02

FERC-CRO June 2001 31

Investigation and Evaluation

• Primary breach was located from Station 6+40 to Station 

7+25, which is 85 feet at the crest.

• Secondary breaches were located at Stations 1+50, 3+00, 

and 4+00.

• Nine borings were taken of the existing embankment and 

foundation. The material was found to be heterogeneous, 

varying from clays, to silt and silty sand, to poorly graded 

sand. Blow counts ranged from 6 to 18. 

• A loose-to-medium-dense silty sand layer about 2 feet thick 

was encountered on the bedrock from the centerline of the 

embankment to its toe.

• The foundation rock is a fine-grained, hard-jointed sandstone 

with numerous horizontal joints and fractures. 

2/12/02

FERC-CRO June 2001 32

Survey Exhibit
Dayton Dam Canal Embankment Failure 17

2/12/02

FERC-CRO June 2001 33

Reconstruction of the Canal Embankment

• Construction began on July 31, 1997.

• The canal embankment was completed in late 

November 1997.

• Repairs to the headgate structure were completed 

in April 1998.

• Generation resumed on May 11, 1998.

• Cost of repairs was about $1,600,000.

2/12/02

FERC-CRO June 2001 34

Exhibit
Dayton Dam Canal Embankment Failure 18

2/12/02

FERC-CRO June 2001 35

Exhibit

2/12/02

FERC-CRO June 2001 36

August 27, 1997 Inspection

• The following two photographs show the progress 

of the reconstruction work.

• At the time of this inspection, the contractor was 

reconstructing the canal invert.
Dayton Dam Canal Embankment Failure 19

2/12/02

FERC-CRO June 2001 37

Filling in Canal Bottom 8/27/97

2/12/02

FERC-CRO June 2001 38

Filling in Breach 8/27/97
Dayton Dam Canal Embankment Failure 20

2/12/02

FERC-CRO June 2001 39

September 30, 1997 Inspection

• The next four photographs show the canal 

embankment substantially completed.

2/12/02

FERC-CRO June 2001 40

Canal Embankment 
Dayton Dam Canal Embankment Failure 21

2/12/02

FERC-CRO June 2001 41

Impervious Core in breach 

9/30/97

2/12/02

FERC-CRO June 2001 42

Cut-outs in canal Embankment 

9/30/97
Dayton Dam Canal Embankment Failure 22

2/12/02

FERC-CRO June 2001 43

Canal Embankment 9/30/97

2/12/02

FERC-CRO June 2001 44

Final Inspection – January 15, 1998.

• Embankment work was completed.

• New gates were being installed in the headgate 

structure.
Dayton Dam Canal Embankment Failure 23

2/12/02

FERC-CRO June 2001 45

Canal Embankment 1/15/98

B-14

Presentation for FEMA / USDA Workshop – 27 June 2001: 

Workshop on Issues, Resolutions, and Research Needs Related to Dam Failure Analysis 

BC HYDRO INUNDATION CONSEQUENCES PROGRAM 

Derek Sakamoto, P.Eng. 

BC Hydro 

Introduction 

BC Hydro is currently working on a program to define a methodology for assessing the consequences 

resulting from a potential dam breach. This Inundation Consequence (IC) Program was initiated in 

February 2000, with the goal of defining guidelines for performing the consequence investigation, which is 

to be followed by the completion of consequences investigations on all BC Hydro’s dam facilities. 

Included in this overview of the IC Program is a brief discussion of BC Hydro and its assets, a summary of 

the legislation and guidelines defining the requirements of the program, followed by a discussion 

highlighting the key components of the IC Program. 

Primary Rationale & Objectives 

The key focus of this program is to provide an improved investigative tool for safety management planning. 

In the case of dam-breach emergency planning, this program will provide decision-makers with realistic 

characterizations of the various situations to which they may have to respond. Investigation into the effect 

of parameters such as dam breach scenarios and temporal variation related to the flood wave propagation 

can be performed. Additionally, severe “non-dam-breach” scenarios, such as the passing of extreme 

floods, can be investigated. 

 A valuable product from these investigations will also be in providing powerful communication tools. 

This will benefit decision-makers by ensuring they are well informed of the magnitude of potential impacts 

related to dam breaches, thus enabling emergency precautions that are proportionate to the consequences 

and uncertainties. Additionally, meeting regulatory approvals and due diligence are key factors. 

BC Hydro 

British Columbia (BC) is the western most of Canada’s provinces, located on the Pacific Ocean along the 

West Coast. BC Hydro itself is a crown corporation, meaning it is a corporation that is owned by the 

province. The corporation, however, is run like a business without subsidies from the government; and like 

other commercial businesses its dividends are provided to its owner which, in this case, is the Province of 

BC. 

BC Hydro owns 61 dams located within 6 operating areas: 

• Columbia River Basin – encompassing the upper region of the Columbia River and draining into 

Washington State, this area produces approximately 50% of BCH power. 

• Peace River Basin – the second largest power generating area, the Peace River joins with the 

Athabasca River in Alberta. 

• Coastal Region – Several smaller dam facilities located along the BC coast. 

• Lower Mainland (Vancouver Region) – housing facilities located near the City of Vancouver. 

• Fraser River Basin – 4 dam facilities draining into the Fraser River. 

• Vancouver Island – a number of dam facilities located on Vancouver Island (southwestern corner of 

BC), taking advantage of the high precipitation of the Pacific West Coast. 

BC Hydro’s assets range from the extremely large Mica Dam to the smaller Salmon River Diversion Dam. 

Mica Dam, a 243 metre high earth-fill dam, is located at the headwaters of the Columbia River; the Salmon 

River Dam is a 5.5 metre earth-fill diversion dam located on the Campbell River system on Vancouver 

Island. 
BC Dam Regulations and Guidelines 

Legislation for dam safety has been recently updated. Managed on a provincial level, the Province of BC 

passed its Dam Safety Regulations in late 1999. The need for defined safety regulations arose from such 

recent incidents as the failure of a private dam in May 1995. Although the breach of this small (6 metre 

high) dam did not result in any loss of life, over $500,000 in damage to property and infrastructure along 

with massive sediment loading into a local river resulted. The Province of BC has established regulations 

which define hazard classifications (Very High, High, Low & Very Low) for dams based on their 

consequence. Based on these hazard classifications, frequency of inspection to ensure the safe operations 

of the dam facilities are outlined as follows: 

Item Very High 

Consequence 

High Consequence Low Consequence Very Low 

Consequence 

Site Surveillance [a] WEEKLY WEEKLY MONTHLY QUARTERLY 

Formal Inspection [b] SEMI-ANNUALLY SEMI-ANNUALLY or 

ANNUALLY 

ANNUALLY ANNUALLY 

Instrumentation AS PER OMS * 

MANUAL 

AS PER OMS * 

MANUAL 

AS PER OMS *

MANUAL 

N/A 

Test Operation of Outlet 

Facilities, Spillway 

gates and other 

Mechanical 

Components 

ANNUALLY ANNUALLY ANNUALLY ANNUALLY 

Emergency 

Preparedness Plan 

UPDATE 

COMMUNICATIONS 

DIRECTORY SEMIANNUALLY 

UPDATE 

COMMUNICATIONS 

DIRECTORY SEMIANNUALLY 

UPDATE 

COMMUNICATIONS 

DIRECTORY 

ANNUALLY 

N/A 

Operation, Maintenance 

& Surveillance Plan 

REVIEW EVERY

7 - 10 YEARS 

REVIEW EVERY

10 YEARS 

REVIEW EVERY

10 YEARS 

REVIEW EVERY

10 YEARS 

Dam Safety Review [c] EVERY 7-10 YEARS 

[d] 

EVERY 10 YEARS 

[d] 

[d] [d]

Further information regarding the BC regulations can be found at the web site: 

http://www.elp.gov.bc.ca/wat/dams/reg_final.html

In addition to the BC regulations a consortium of dam owners in Canada called the Canadian Dam 

Association (CDA) has established guidelines defining key design parameters for dam construction. As 

with the inspection requirements of the provincial regulations, the level of the design requirements are 

based on the consequence classification: 

Consequence 

Category

Earthquake Criteria 

Maximum Design Earthquake (MDE)

Inflow Design 

Flood (IDF) 

Criteria

Very High Maximum Credible 

Earthquake (MCE) 

1/10,000 Probable Maximum 

Flood (PMF) 

High 50% to 100% MCE 1/1000 to 1/10,000 1/1000 to PMF 

Low - 1/100 to 1/1000 1/100 to 1/1000 

Further information regarding the Canadian Dam Association can be found at web site: 

http://www.cda.ca

Inundation Consequence Program 

Building upon the legislative, design and safety requirements, the IC program is focused on defining the 

consequences associated with potential dam breaches. In doing this assessment, four key tasks have been 

defined: 

• Hydraulic modeling 
• Life Safety Model 

• Environmental / Cultural Impact Assessment 

• Economic / Social Impact Assessment 

Hydraulic Modeling 

Previous breach assessment work done by BC Hydro was done during the 1980’s. This analysis provided 

inundation mapping for assumed dam breach scenarios, which were completed using the NWS DAMBRK 

model. In looking to update what was “state of the art” of its time, BC Hydro has opted to update these 

breach studies using the 2-dimensional hydraulic model TELEMAC-2D. The decision to use the 2-

dimensional model is driven by two aspects. The 2-D model offers the ability to simulate complex flow 

patterns, which will be valuable tool in simulating the spread of flood waves over wide areas, or circulation 

and backwater of flows. Additionally, the 2-D output is an integral part of the Life Safety Model discussed 

later. 

There is, however, a need to identify the data requirements in selecting the correct computer model. In 

cases of “low consequence” dams, it may not be necessary to go to the expense and level of effort required 

of the 2-D model when a 1-D model can provide the same, or sufficient results. Two levels of assessment 

in the IC Program may be performed, with 1-D or coarse 2-D models being used on “low consequence” 

dams, and the more detailed 2-D models being used on the “high consequence” facilities. 

Life Safety Model 

BC Hydro is developing the Life Safety Model (LSM), a 2-D computer model which will be used to 

estimate Population at Risk (PAR) and Loss of Life (LOL) in the event of a dam breach. The power of the 

LSM is in the ability to simulate the movement of people over real space as they becoming aware of the 

dam breach, and models how people will escape from a flood. Using national census data, the PAR can be 

distributed over areas being assessed. Various scenarios are prepared distributing the PAR based on time 

of day, day of week, or season. 

This dynamic model will use the flood wave hydrograph produced by TELEMAC-2D as input, simulating 

the movement of the PAR in real time as the flood-wave propagates. The LSM model then simulates how 

the people react to the flood-wave, and their means of escape. A key aspect of this modeling is in 

providing a valuable tool in defining evacuation routes, potential “bottle-necks” in the evacuation plans, 

and highlighting problems associated with high risk areas such as hospitals or schools. 

Environmental / Cultural Impact Assessment 

The dam breach could result in a number of environmental and cultural impacts in areas both upstream and 

downstream of the dam. Three Consequence Types were identified (Physical, Biological, and Human 

Interaction) with 18 resulting Consequence Categories: 

Physical

terrain stability, river channel changes, soil loss / deposition, mobilization of debris, & water quality 

Biological

vegetation, fish, fish incubating, wildlife, productivity of reservoir, & productivity of receiving systems 

Human Interaction

forest, agricultural resources, mineral resources, biological resources, settlement, recreation, & heritage 

Evaluation of these individual consequence categories is based on the net impact the potential dam breach 

could have on them. For each category, a series of “linkage diagrams” have been established. Each link 

defines the resulting effect that the breach can have on the specific category in varying degrees of severity. 

The more severe the impact, the higher up the linkage diagram. 

Economic / Social Impact Assessment 

The initial and key challenge in the economic assessment model was in the identification of all structures 

(residential, institutional, businesses, industries etc.) at risk. Geographic Information Systems (GIS) is 

being utilized to link the various available databases, the location of areas at risk, and the magnitude of the 

impending hazard. Databases that were used to identify areas at risk include: 
• hydraulic model inundation polygon provided in UTM coordinates (TELEMAC-2D output); 

• BC Hydro customer database (providing building location with UTM coordinates & address); 

• BC Assessment Authority database (providing property values, property improvement value, 

construction material, structure use, age, number of floors, etc.) 

GIS also provides a valuable assessment tool in yielding a powerful graphical representation of properties 

at risk. It also yields an easily queried database to assess economic impact based on various scenarios. 

Future work will entail linking the economic losses with respect to social impact on communities in the 

inundation zone. 

IC Program Future 

A pilot program is currently under way to establish guidelines for completing the Inundation Consequence 

assessments. A draft of these guidelines is planned for completion during the summer of 2001 and 

finalized in 2002. Ultimately, inundation consequence assessments will be completed for all the BC Hydro 

sites. 

Presenter: Derek Sakamoto is an engineer with BC Hydro’s Power Supply Engineering (PSE) 

group, and works in the Civil Engineering / Water Resources team. Having been with 

PSE for just over one year, Derek brings to his team over five years in consulting with a 

focus in design, construction and assessment work in hydraulic/hydrologic related 

projects. 

Contact at: (604) 528-7812 (phone); (604) 528-1946 (fax); derek.sakamoto@bchydro.com (email) 

 BC Hydro - 6911 Southpoint Drive (E13), Burnaby, BC, CANADA, V3N 4X8 (mail) 
B-15

Mead & Hunt, June 23, 2001

1

Analyzing Flooding Caused by Embankment Dam Breaches: 

A Consultant’s Perspective

By Ellen B. Faulkner, P.E.

Mead & Hunt, Inc.

Madison/Eau Claire, Wisconsin

Introduction

As engineering consultant to owners of dams throughout the United States, Mead & Hunt

performs dam safety assessments which must be responsive both to the needs of the dam owner

and to the requirements of state and federal regulatory agencies. Frequently, these dam safety

studies include the simulation of a hypothetical dam failure for the purpose of hazard

classification, emergency action planning, or design flood assessment. Each dam failure study

begins with the identification of a critical, but plausible, mode of failure and the selection of

specific parameters which define the severity of the failure. These parameters include the ultimate

dimensions of the breach, the time required to attain these dimensions, and (in the case of

overtopping failures of embankment dams) the depth of overtopping required to initiate a failure.

None of these quantities is easily identified. In many cases, the obvious solution is to

choose the “path of least resistance” - that is, the parameters which will most easily meet with

regulatory acceptance. However, choosing excessively conservative breach parameters may

impose significant costs on the dam owner in the form of new design work and remedial actions,

additional safety studies, or unnecessarily complex or inefficient emergency action plans.

Clearly, the design, construction, and material composition of an earthen embankment

significantly affect how a breach will form. As consultants we are aware that analytical

approaches exist, based on theory, experiment, and experience with real dam failures, for relating

breach size and speed of formation to the characteristics of the embankment. However, these

approaches are not yet well-established enough to use in the regulatory settings in which we

work. One Mead & Hunt study from northern Wisconsin, now almost ten years old but still fairly

representative of the difficulties that may be encountered in this type of study, illustrates how

different approaches to simulating an embankment breach can lead to substantially different

conclusions with respect to design and safety requirements.
Mead & Hunt, June 23, 2001

2

Case Study Setting

The Chalk Hill hydroelectric project is located on the Menominee River on the border between

northeast Wisconsin and Michigan’s Upper Peninsula. Three miles downstream is the White

Rapids project, owned by the same utility. Both dams contain concrete spillway sections and long

earth embankments, but Chalk Hill’s embankment is significantly higher (37 feet) than that at

White Rapids (25 feet). The river valley below both dams is lightly developed, with a mix of

year-round and seasonal residences located near the river and potentially in the dam failure

inundation area.

The studies described below were performed in 1992. They were the most recent of a

series of dam break studies for the dams, which began in 1983 with a HEC-1 storage routing

model which indicated that the hazard related to overtopping embankment failure of either dam

was minimal. In 1987, failures of the embankments were re-analyzed using the NWS-DAMBRK

dynamic routing model. In both the 1983 and 1987 studies, the assumed breach dimensions were

consistent with then-current guidelines, which called for a breach bottom width equal to the

height of the dam.

In 1988, the Federal Energy Regulatory Commission (FERC) issued new guidelines

regarding breach assumptions used for emergency action plans, inflow design flood studies, and

hazard classifications. In the case of breaches in earth embankments, the assumed average breach

width was to be as much as five times the dam height. Reviewing the 1987 reports under these

guidelines, FERC requested a re-analysis for Chalk Hill and White Rapids using a wider breach. 

These analyses were conducted in early 1992. For White Rapids, where the height of the

embankment was just 25 feet and downstream development relatively high on the valley walls, the

re-analysis still indicated no incremental hazard due to overtopping flows; that is, the existing

spillway capacity was adequate. For Chalk Hill, however, the use of a breach width in the high

end of the stipulated range led to an IDF determination about twice the existing spillway capacity. 

Part of the problem at Chalk Hill was an assumed domino failure of White Rapids Dam.

Although White Rapids did not pose a downstream hazard by itself, an overtopping failure of

White Rapids in conjunction with the peak of the dam failure wave from Chalk Hill would affect

residences which were not in the inundation area of White Rapids alone. However, the assumed

failure of White Rapids, consistent with FERC’s approach, occurred at the peak overtopping

stage after the Chalk Hill failure. This scenario would require that the White Rapids embankment

survive about three feet of overtopping before finally failing. If White Rapids could be assumed

to fail at some lesser depth of overtopping, the downstream consequences would be less.
Mead & Hunt, June 23, 2001

3

In most inflow design flood studies, the addition or removal of a few structures to the dam

break inundation zone is of little consequence, as long as at least one inhabited structure is

affected by the flood. In this case, however, each structure determined to be affected was

important because one of the owner’s alternatives was to purchase affected properties.

Physical Model Analysis (NWS-BREACH)

The inflow design flood determination for Chalk Hill Dam involved a number of separate breach

assumptions: the breach formation time and dimensions at Chalk Hill; the formation time and

dimensions at White Rapids; and the depth of overtopping which would certainly cause failure at

White Rapids. (Another issue, related to the evaluation of alternatives for upgrading the spillway

capacity, was whether initially confining Chalk Hill overtopping flows to a low section of the

embankment would successfully promote a non-critical failure in that section.)

We questioned whether the extreme breach parameters used in the first 1992 study were

appropriate, considering two characteristics of the dam. First, the embankments were engineered

and well-constructed -- unlike many dams whose actual historical failures formed the database

that was apparently the foundation for the guidelines. Second, both reservoirs were small and

drawdown would happen quickly. In an attempt to determine whether breach dimensions in the

middle or lower end of the FERC’s suggested range would be consistent with the site-specific

characteristics of the dams, we used the NWS-BREACH program to assess the breach formation

characteristics at both Chalk Hill and White Rapids dams. 

BREACH is a physically based erosion model for embankment dams, and generates a time

sequence of breach dimensions and an outflow hydrograph given an inflow hydrograph, the dam

and reservoir capacity, and geometry and material properties for the embankment. The data

requirements for BREACH include dike material data such as cohesion, angle of internal friction,

void ratio, unit weight, plasticity, and gradation. The availability of almost all of these data

through recent boring studies was another factor which made the physical model approach

practicable for the Chalk Hill study. 

Using the NWS-BREACH model was a new approach in our experience, and one not

approved by the FERC. To anticipate reviewers’ concerns about the accuracy and

conservativeness of the model, we adopted an approach in which we simulated the breach using

the most critical lab test values from both borings at each site. We tested one input variable at a

time, choosing the single test value from the two borings which gave the most severe breach. 

When two tests values were not available, we chose the worst-case value of the input variable,
Mead & Hunt, June 23, 2001

4

based on ranges given in the BRAECH program documentation.

The resulting breach description was significantly different from any of those postulated,

based on written guidelines, in previous studies. Table 1, below, summarizes the differences

between the analyses.

Table 1

Comparison of Chalk Hill Embankment Breach Characteristics Using FERC Guidelines

and NWS-BREACH Program

 Breach

Assumptions

Depth of

Overtopping

Required to

Initiate

Breach (ft)

Breach

Formation

Time

Time for

Breach to

Erode to

Bottom of

Dam

Ultimate

Breach

Bottom

Width

Breach Side

Slope (H:V)

Pre-1988

Studies

0.5 1 hour 1 hour 37 feet (1 x

dam height)

1:1

Studies

Based on

1988

Guidelines

0.5 0.3 hour 0.3 hour 111 feet (3 x

dam height)

1:1

NWSBREACH0.6 > 2 hours 0.1 hour 25 + feet 1:1

There were two major differences between the BREACH results and earlier assumptions. First,

the BREACH program gave a much smaller breach after 2 hours (the time step limit in the

program) than we had previously assumed for a one-half-hour formation time. Second, the

simulated breach eroded very quickly to the bottom of the dam, at which time the peak reservoir

outflow occurred, then continued to slowly widen as the reservoir level dropped. At two hours,

the average breach width was about 1.7 times the height of the dam -- within the range given in

the FERC Guidelines, but near the lower end. The breach was still widening when the program

halted due to time step limits, but the peak outflow had long since passed.

We also performed a sensitivity analysis to the individual material properties input to the

program. Varying each one by plus or minus 25 percent, we found that the maximum changes in
Mead & Hunt, June 23, 2001

5

peak breach outflow were + 10 percent and -28 percent. The most sensitive parameters were

cohesive strength and friction angle. We did not vary any of the parameters in combination with

others, so did not determine how the various properties interacted in affecting the breach.

A separate NWS-BREACH analysis was conducted for the White Rapids project. There,

the simulated breach was larger relative to the dam height. The average breach width at White

Rapids was more than twice the dam height. The White Rapids embankment materials had a

lower unit weight than those at Chalk Hill, were more poorly graded, and were assumed to have

zero cohesion (due to a lack of test data).

Inflow Design Flood Determination

NWS-BREACH develops an outflow hydrograph but does not route it downstream. Therefore,

we used the breach parameters predicted by the NWS-BREACH model as input to the NWSDAMBRK model. The resulting Inflow Design Flood was 85,000 cfs -- still more than the

calculated spillway capacity, but much less than the IDF indicated by the previous study.

The NWS-BREACH study never met with regulatory approval, apparently due to the very

limited track record of the BREACH model and the startlingly less severe breach it predicted than

had been assumed in previous studies. Returning to the more severe guidelines-based breach used

in the previous study, however, we still had an unanswered question. This was the determination

of risk below White Rapids Dam, which was presumed to fail as a result of the Chalk Hill breach

wave. However, for some of the IDF cases considered, White Rapids would be overtopped by

several feet before the Chalk Hill failure occurred. The BREACH model -- even if it had been

accepted -- was of little help in this question, because it predicted a rapid failure at just 0.5 foot of

overtopping. Although that may have been the most likely event, none of the parties involved

were comfortable with it as a “worst-case” scenario. Finally, it was agreed, on the basis of

professional judgement alone, that the White Rapids embankment need not be assumed to

withstand more than two feet of overtopping.

Eventually, the owner of the projects addressed the IDF in two ways. One --

demonstrating that the best ideas are the simplest -- was to retest the radial opening of the

spillway gates. The gates proved to open considerably farther than shown in the design drawings,

resulting in a spillway capacity about 20 percent higher than had previously been computed. 

Secondly, the owner purchased outright or in easements the remaining affected properties, which

were relatively few in number. 

B-16









B-17

1

Current Dam Safety

Research Efforts
2

Hydraulic Design of

Stepped Spillways

James Ruff

and

Jason Ward

Project Background

• Continuation of Dam Safety Research

– Cooperative agreement between CSU & USBR

– spillway overtopping flows

– near prototype scale test facility

• Stepped Spillway Phase

– Start of construction July 1999

– Two summers of testing

– Data analysis and report 2000-2001
3

Overtopping Facility

• Near-prototype scale

• 2H:1V Slope 

• 100 ft concrete chute

• 50ft height

• 10ft wide

– reduced to 4 ft

• 5 ft deep

– 7 ft extended height

• Horsetooth water supply

– approx. 120 cfs max

Objective

Experimental Program

• Air concentration data

• Velocity data

• Visual Observations

Collect data on the characteristics of stepped spillway 

flow and develop a hydraulic design procedure.

• Range of discharges & locations

• Two step heights
4

Stepped Spillway Tests

• Horizontal Steps

• Constructed of lumber and 

plywood

Smooth Spillway Tests

• Steps removed

• Comparison data

Test Series

• First Series

– 25 two-foot steps

– 4 ft tread length

– 2 ft riser height

• Second Series

– 50 two-foot steps

– 2 ft tread length

– 1 ft riser height

• Third Series

– Steps removed

– Comparison data
5

Flow Direction

Nappe Flow

Skimming Flow

Flow Classification

Observations

h = 2.0 ft

Nappe

Q = 20 cfs

Window # 4

Transition

Q = 40 cfs

Window # 4

Skimming

Q = 60 cfs

Window # 3
6

Nappe

Q = 7.1 cfs

Window # 2

Skimming

Q = 21 cfs

Window # 4

Observations, cont’d

h = 1.0 ft

h = 1.0 ft

Q = 60 cfs
7

Friction Factor

Darcy Friction Factor f versus k/dw

0.01

0.10

1.00

10.00

0.01 0.10 1.00 10.00

k/dw

f

Present Study, h = 1ft Present Study, h = 2 ft

Present Study, smooth (k = 0.01 ft) Gaston (1995)

Chamani et. al. (1999) Chamani et. al. equation (2-23)

Tozzi equation (2-16) equation (6-16)













= +

k

d

2.15 0.85log

f

1 w

2

8

avg

w f

U

gd S

f =

k = roughness height

dw = clear water depth

Energy Dissipation, cont’d

Enery Dissipation versus Nh/yc

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0.0 20.0 40.0 60.0 80.0 100.0

Nh/yc

ΔE/Eo

h = 1 ft

h = 2 ft

smooth

eqn. (6-21)

f = 0.30

eqn. (6-21)

f = 0.25

eqn. (6-21)

f = 0.079

2

3

2 8sin

1

cos

8sin 1

3

2

3

1

+













 +











−

Δ

−

c

o

y

Nh

f f

E

E q

q

q

o

o 1

o E

E E

E

E −

=

D

Energy Dissipation

N = number of steps

h = step height

yc = critical depth
8

Hydraulic Design Procedure

• Assume given information

– Total discharge, Q

– spillway width, b

– spillway height, H

– spillway slope, θ = 26.6o

– select step height, h (1.0 ft or 2.0 ft)

• Design Charts:

– friction factor f = f (H, q) versus Nh/yc

– bulking coefficient ε = f (H,q) versus Nh/yc

• Water surface profile computation with f

– dw, Uavg

• Compute energy dissipation

Hydraulic Analysis

of

Articulated Concrete Blocks

Christopher Thornton,Steven Abt,

Chad Lipscomb and Michael Robeson
9

Recent Developments in the Research and Development 

of Articulating Concrete Blocks for Embankment 

Overtopping Protection
10
11

• To evaluate the performance of commercially 

available embankment protection systems under 

various hydraulic conditions

• To develop design criteria for ACB systems

• To determine the effect of a drainage medium under 

ACB systems

Purpose
12

ACB Mats

Placement
13

Placement

Un-Vegetated
14

Vegetated

Vegetated
15

Block Overtopping Tests 

Flume Setup

1

3

2

Overtopping Testing
16

Overtopping Testing

Threshold Levels
17

Threshold Levels

FR

Fi

FD

FG2

FL

FG1

Flow

Stabilizing Forces

FR = Interblock resistance

FG2 = Gravity force normal to slope

Destabilizing Forces

Fi = Impact force (projecting block)

FL = Lift Force

FD = Drag Force

FG1 = Gravity force parallel to slope

Force Balance
18

0 2 4 6 8 10 12 14 16 18 20 22 24 26

Velocity (ft/sec)

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

Shear Stress (lb/ft^2)

Articulated Concrete Blocks

Weight A

Weight B

Design Curves

• Drainage layer has pronounced effect on 

system performance

• At high flows, velocity appears to be 

dominant force

• Performance values consistent between 

overtopping and channelized test protocols

Results
19

Design Criteria

for

Rounded Rock Riprap

Steven Abt 

and 

Humberto Gallegos

• Develop design criteria for rounded/angular 

rock riprap in overtopping flow

• Expand the database of rounded rock riprap to 

include higher embankment slopes

• Increase the understanding of the behavior of 

rounded rock riprap in overtopping flow

Purpose
20

From pump # 1

Pump

# 2

Rock baffle Riprap

Filter layer

Soil embankment

Main sump

Lab floor

Video platform

Wave suppressor Top of flume wall

Flow

Flume Setup

Flume Setup
21

Testing Matrix

Cumulative 

Database
22

y = 0.8505x

R2 = 0.9737

0.1

1

10

0.1 1 10

5.23S0.43qf

0.56

D50

Cu-0.25[1.0805%R+0.4428]-1

Rounded

Angular

Analysis

D50 = 6.58S0.43qf

0.56C

u

0.25(1.0805%R=0.4428)

Results

•Embankment Slopes: 10 to 45 %

•Median Rock Sizes: D50 = 2.4 to 15.3 cm

•Rounded Rock: 55 to 95 %

•Riprap Layer Thickness: 1.5 to 3 D50

•Coefficient of Uniformity: 1.2 to 4.0
23

B-18

Limited Overtopping, Embankment Breach and Discharge 

Issues, Resolutions & Research Needs Related to Dam Failure Analysis: 

Oklahoma Workshop, June 26-28, 2001 

D.M.TEMPLE and G.J.HANSON, USDA-ARS-PSWCRL, 1301 N. Western, Stillwater, OK. 

74075, Phone (405) 624-4135, E-mail dtemple@pswcrl.ars.usda.gov, and 

ghanson@pswcrl.ars.usda.gov. 

ABSTRACT 

Over 10,000 flood control reservoirs constructed with the assistance of the USDA 

provide almost $1 billion in benefits each year. Sixty-two percent of these 10,000 

structures will reach age 50 by 2020. As these structures age additional trapped 

sediment may reduce the flood control capacity of the reservoir, population increases 

and changes in land in the upstream watershed may result in increased runoff, 

population encroachment on the downstream channels may result in structures that 

were designed to protect agricultural land now being depended upon to protect lives 

and homes, and many state dam safety regulatory requirements have also been 

increased since the original construction as a result of federal legislation and/or state 

laws. Because of this, public safety requires that this aging infrastructure be reevaluated and, in some cases, rehabilitated. A key aspect of this re-evaluation is 

prediction of the performance of existing hydraulic structures and channels during 

extreme flood events that may exceed original design conditions. This includes 

prediction of allowable overtopping, rate of embankment breach and failure, and 

resulting discharge. 
INTRODUCTION 

The drought of the 1930’s, followed by flooding in the 1940’s, made the U.S. agriculture 

community keenly aware of the need to keep the water and soil in place. Following 

World War II, numerous management practices to control erosion and reduce flooding 

were implemented with the assistance of the USDA. Included were the upland flood 

control structures constructed under PL-534, PL-566, Pilot, and RC&D watershed 

programs. Approximately $14 billion was invested in more than 10,000 structures that 

presently provide on the order of $1 billion in benefits annually. These flood control 

structures have become an integral part or the nation’s transportation and 

communications infrastructure through their protection of roadways, pipelines, etc. 

As these structures continue to age, additional trapped sediment may reduce the flood 

control capacity of many of these reservoirs. Population increases and changes in land 

use have modified the hydrologic properties of the watersheds upstream of some of 

these structures, resulting in increased runoff of water and/or sediment from a given 

storm. Increasing population and encroachment on the downstream channels have 

resulted in structures that were designed to protect agricultural land now being 

depended upon to protect lives and homes. Many state dam safety regulatory 

requirements have also been increased since the original construction as a result of 

federal legislation and/or state laws. Essentially all of the state dam safety laws were 

written or significantly revised after dam safety concerns were raised in the 1970’s 

following the failure of Teton and Tacoa Falls Dams. Over 70% of USDA-assisted 

projects were in place by that time. Conflicts between the design of the older dams and 

the new dam safety rules are inevitable. Public safety requires that the aging 

infrastructure that includes these dams be re-evaluated and, in some cases, the dams 

rehabilitated and/or modified if they are to continue to serve public needs. 

The Hydraulic Engineering Research Unit of the ARS Plant Science and Water 

Conservation Research Laboratory is conducting research to address the problems 

associated with rehabilitation of the watershed flood control structures and channels, 

and identified as research objectives. Key identified knowledge deficiencies related to 

rehabilitation of watershed flood control structures and channels may be expressed in 

the form of research objectives as: 1) determination of the extent of overtopping that 

may be sustained by a vegetated earth embankment, such as a dam, without resulting 

in embankment breach, and 2) quantification of the processes associated with breach 

such that timing, rate, and geometry of breach may be predicted, and 3) quantification 

of the discharge hydrograph and peak discharge as a result of an embankment breach. 

The results of this research will be incorporated into evaluation tools and software, 

design criteria, and management practices that will allow the continued service and 

increased benefit of the nation’s agricultural watershed flood control infrastructure. 

EARTH EMBANKMENT EROSION RESEARCH 

Although the detailed data on embankment overtopping have been very limited, 

substantial data have been gathered from vegetated spillways, which have experienced 

flood flows. Analyses of these data, combined with laboratory tests and analyses, have 

led to the development of a procedure for evaluation of earth spillway performance 

(NRCS, 1997). The model used in this procedure divides the erosion process into three 

phases. These phases are: 1) the failure of the vegetal cover, if any, and the 
development of concentrated flow, 2) erosion in the area of concentrated flow leading to 

the formation of a vertical or near vertical headcut, and 3) the upstream advance of the 

headcut leading to breach which may also be accompanied by further widening and 

deepening. The three phases describing progressive spillway erosion have also been 

observed for erosion of overtopped earth embankments when the embankment material 

exhibits even a small amount of cohesion (Hanson et al 2001). Therefore, even though 

caution is appropriate in attempting to extend this model directly to prediction of 

embankment breach, the breakdown of the process into these same three phases 

would be appropriate. Because of the short distance through the crest or an 

embankment dam, the concept of allowable overtopping is practically limited to the first 

two phases. 

Tests have been conducted to evaluate the effectiveness of un-reinforced vegetation for 

overtopping protection and the applicability, on steep slopes, of the analysis tools of the 

first two phases of the three phase spillway model (Temple and Hanson, 1998; Hanson 

and Temple, 2001). It was found that the vegetation could provide substantial 

protection and that the relations used for phase 1 and phase 2 erosion of spillways 

could be effectively applied to the steeper embankment slopes. Differences observed 

were associated primarily with the reduced flow depth on the steeper slopes. This 

reduction in flow depth reduced the interaction of the vegetal elements with the turbulent 

flow field as a result of the turbulent scales being less than the length of the individual 

elements. However the effect of this on the flow resistance or protective action of the 

grass appeared to be minor. It was also observed that the decrease in flow depth 

emphasized the effects of discontinuities in the cover or surface. The importance of this 

effect on predicting breach or time to breach is shown by the curves of Figure 1 

(reproduced from Temple and Hanson, 2001). 

The equations used in the development of the curves of Figure 1are those documented 

in NRCS (1997) for the limits of phase 1, vegetal, failure. All curves are based on 

computations for a 3:1 embankment slope. Curve a represents a very high quality 

bermudagrass cover over a soil having a plasticity index of 15. Curve b is for that same 

condition except that the cover or surface exhibits minor discontinuities. A minor 

discontinuity is one that is large enough for the turbulent flow to directly impact the 

erodible material, but small enough that the flow does not concentrate within the 

discontinuity. This would normally imply a maximum dimension of the discontinuity 

parallel to flow on the order of flow depth and/or stem length. Curve d is for the same 

condition except that the discontinuity is large enough to allow the flow to fully 

concentrate, thereby negating any protective effect of the vegetal cover. Curve c is 

added to illustrate the relative importance of the material erodibility. Conditions for 

curve c are the same as for curve b except that the plasticity index of the material is 

reduced to zero to represent a highly erodible condition. The effect is substantially less 

than that indicated by adding discontinuities to the cover or surface. In all cases the 

curves represent failure on the slope and do not address the effects of the impacts of 

high velocity flow on toe or berm areas. Figure 1 illustrates that un-reinforced 

vegetation may be effective in providing overtopping protection, but attention must be 

given to maintenance. 
Figure 1. Potential allowable embankment overtopping based on the point of vegetal 

cover failure for: (a) a good cover of bermudagrass and a material plasticity index of 15; 

(b) a grass cover with minor surface discontinuities and a material plasticity index of 15; 

(c) a grass cover with minor surface discontinuities and a material plasticity index of 0; 

and (d) a grass cover with major discontinuities and a material plasticity index of 15. 

For homogeneous earth embankments, phase 2, concentrated flow erosion, will usually 

represent only a very brief portion of the hydrograph. The combination high stresses 

and low flow depth on the steep embankment slope means that once the flow becomes 

concentrated in the developing discontinuity, erosion to the point of development of a 

vertical or near vertical headcut is normally quite rapid. This phase received some 

attention in the research conducted on steep slopes (Hanson and Temple 2001) and 

embankment overtopping (Hanson et al 2001). These tests verified that phase 2 is 

typically very brief and that the relations used in the spillway model are adequate. An 

important point that was brought out in Hanson and Temple 2001 is that erodibility of 

any given soil may vary several orders of magnitude depending on compaction density, 

and moisture content (Figure 2); indicating that proper measurement of erodibility is 

essential in predicting embankment performance. Erodibility is typically defined by two 

soil parameters, critical stress τc and the detachment coefficient kd. The erosion is 

assumed not to begin until the effective hydraulic stress τe exceeds τc. Once the critical 

stress is exceeded the rate of erosion, dε/dt is assumed to occur at a linear rate 

described by the excess stress equation: 

( ) d e c k

dt

d = τ − τ

ε [1] 
Figure 2. Relationship of a) kd and saturation, b) kd and dry unit weight, c) τc and 

saturation, and d) τc and dry unit weight for laboratory jet tests, and embankment jet 

tests. 

Phase 3, headcut deepening and advance, is a critical part of the breaching process. 

The purpose of the spillway model is the determination of the potential for breach to 

occur. Although this is an important consideration for overtopped embankments, the 

time of breach and the outflow from the breach are also important considerations. This 

means that a two-dimensional model (width of eroded area not considered) is not 

adequate, and erosion following the initial breach needs to be considered. This will 

require the addition of a model component to track headcut width during breach 

development and the quantification of at least two additional phases. These additional 

phases are the downward erosion of the crest of the vertical following submergence of 

the headcut and the widening of the headcut following complete local removal of the 

embankment in the vicinity of the breach. Research presently underway includes 

breaching of embankments such as that shown in Figure 3, and will assist in quantifying 

Dry unit wt (Mg/m3)

1.4 1.5 1.6 1.7 1.8 1.9

Saturation %

40 50 60 70 80 90 100

τ

c (Pa)

0

1

2

Ave τc =0.55 Pa

kd (m3/N-h)

0.0001

0.001

0.01

0.1

Laboratory Compacted

Samples of Soil A

Embankment

Jet Samples

Estimated Value

Based on post 

test samples
the action that occurs during these additional phases. Laboratory tests confirm that 

material properties may have a major impact on the rate of headcut advance, and 

therefore time to breach and breach rate. The headcut erodibility index based relations 

used in the spillway erosion model are semi-empirical and were developed to cover a 

broad range of geologic conditions. They were also developed without consideration of 

such things as pore water changes with position of the headcut. Therefore, as 

discussed by Hanson et al 2001, it should be possible to either refine the relations for 

application to embankment conditions or to replace this approach with an alternate. 

Work is continuing in this area. The focus to date has been on homogeneous 

embankments, but plans are being made to expand the testing program to include other 

types.

Figure 3. Time series of an embankment breach test of a homogeneous non-plastic 

sandy soil conducted at the ARS Hydraulic Laboratory, Stillwater, OK. 

t = 0 min t = 6 min 

t = 12 min 

t = 51 min 

t = 27 min 

t = 39 min 
SUMMARY 

Research efforts at the ARS Plant Science and Water Conservation Research 

Laboratory have resulted in an increased understanding of the erosion processes 

applicable to an overtopped earth embankment. Advances in predicting performance of 

vegetated earth spillways form a point of beginning for quantifying the breach process 

for embankments in a fashion that includes prediction of the extent of overtopping that 

may occur without breach, and the time of breach when breach does occur. However, 

the present spillway model is not considered adequate for this application. 

Additional research is being conducted to allow existing erosion models to be refined 

and extended. With respect to the earth spillway erosion model discussed, this 

involves refinement of existing headcut erosion components and development of 

additional components to address the latter stages of breach development, breach 

widening and breach discharge prediction. Research presently underway will contribute 

to development of these components. 

Research on the ability of un-reinforced vegetation to protect embankment faces has 

shown that grass can substantially increase the time to breach. However, taking 

advantage of this capability will require that attention be given to maintenance of the 

cover and to protecting areas of concentrated attack such as the slope toe. 

Although the research described in this paper focuses on the performance of smaller 

dams of the type constructed with the assistance of the United States Department of 

Agriculture, the results may also be used to better understand the response of larger 

earth dams and will compliment results of research on breach of large dams such as 

that being carried out under the CADAM project (European Commission, 1998a, 1998b, 

1999a, 1999b, 2000). This report discusses the approach being used in USDA 

research, some of the key underlying physical processes that must be considered, and 

the progress being made. 
REFERENCES 

European Commission (1998a) CADAM Concerted Action on Dam Break Modeling, 

Proceedings from the Wallingford Meeting, March 2-3, 1998. 

European Commission (1999b) CADAM Concerted Action on Dam Break Modeling, 

Proceedings from the Munich Meeting, Oct. 8-9, 1998. 

European Commission (1999a) CADAM Concerted Action on Dam Break Modeling, 

Proceedings from the Milan Meeting, May 6-7, 1999. 

European Commission (1999b) CADAM Concerted Action on Dam Break Modeling, 

Proceedings from the Zaragoza Meeting, Nov. 18-19, 1999. 

European Commission (1999b) CADAM Concerted Action on Dam Break Modeling,

Project Report, H. R. Wallingford. Sept. 2000. CD-ROM. 

Hanson, G. J., Cook, K. R., and Hahn, W. (2001) Evaluating Headcut Migration Rates of 

Earthen Embankment Breach Tests. ASAE paper no. 01-012080. 

Hanson, G. J. and Temple, D. M. (2001) Performance of Bare Earth and Vegetated 

Steep Channels Under Long Duration Flows. ASAE paper no. 01-012157. 

Natural Resources Conservation Service. (1997) Earth spillway erosion model. Chapter 

51, Part 628, National Engineering Handbook. 

Temple, D.M. and Hanson, G.J. (1998) “Overtopping of Grassed Embankments.” 

Proceedings of the Annual Conference of State Dam Safety Officials, Las Vegas, NV, 

October 11-16, 1998. CD-ROM 

Temple, D.M. and Hanson, G.J. (2001) “Water Over the Dam.” Prepared for 

Proceedings of the 7th National Watershed Conference, National Watershed Coalition, 

Richmond, VA, May 21-23, 2001. 
B-19

HEC Models for

Dam Break Flood Routing

by

Michael Gee, Ph.D., P.E.

Corps of Engineers Hydrologic Engineering Center

609 2nd Street, Davis, CA 95616

(530) 756-1104

Michael.gee@usace.army.mil

www.hec.usace.army.mil

June 2001 Hydrologic Engineering Center
Hydrologic Engineering Center Mission

Technical

Assistance

Research

and

Development

Training

and

Software

Support

Center of expertise in hydrologic engineering and planning analysis

executing a balanced program of research, training and

technical assistance. Located in Davis, California.

Hydrologic Engineering Center

HEC Products

ÿHydrologic engineering software; Corps,

 Public, International

ÿTechnical Methods and Guidance

ÿTechnical Assistance

ÿPrototype studies, Research and Applications

ÿTraining Courses, Workshops and Seminars
Some HEC History

• 80’s - Simplified techniques, test routing methods

• 90’s

 - NexGen HEC-RAS development for 1-D steady flow

 - UNET (Mississippi Basin Modeling System for

 forecasting)

 - R & U (Alamo Dam, used combination of DAMBRK &

 HEC-RAS

• 2000’s

 - HEC-RAS (unsteady flow)

 - CWMS (Corp Water Management System)

References Hydrologic Engineering Center

In the early ‘80’s HEC looked at using the TVA explicit model for unsteady

flow applications. At that time, a geometric pre-processing program (GEDA)

was developed to compute data tables of geometric properties for USTFLO

from HEC-2 format cross-sections. This capability was later expanded to

prepare DAMBRK and DWOPER geometric data from HEC-2 cross sections.

Research was conducted regarding selection of appropriate flood routing

procedures (HEC, 1980a) and generalized solutions to dam break flood routing

(HEC, 1980b).

UNET (HEC, 2001) has been routinely utilized throughout the Corps for 1-D

unsteady flow modeling for at least the last fifteen years. Many features have

been developed by Dr. Barkau for local needs (HEC, 1998). Of particular

interest and continuing research are issues related to calibration - both

hydrology related (what is the real flow hydrograph) and hydraulics related

(what is the appropriate roughness function for the observed stage hydrograph

and input flow hydrograph). Major developments to UNET (levee breach

connections to off-channel storage areas, etc.) were prompted by large floods in

the Mississippi-Missouri system in ‘93.

Current HEC work involves incorporation of the UNET unsteady flow equation

solver into HEC-RAS. This allows the more complete geometric description of

the river used by RAS to be used as well as RAS’ graphical displays and data

editing capabilities. RAS unsteady flow modeling will support the Corps Water

Management System (HEC, 2000b).
Schematic of the Alamo Dam study area. A DAMBRK model had been

developed of this system by the Seattle Dist. Of the Corps (for the L.A. Dist.).

This model was used to evaluate additional failure scenarios. The DAMBRK

cross sections were converted into RAS sections so that overbank depths and

velocities could be computed. RAS was run as a steady flow model using peak

flows at each section computed by DAMBRK (RAC, 1999).
HEC-RAS Geometric Data

Steps to Develop RAS Data

• Start a New Project

• Enter Geometric data

• Enter Flow and Boundary data

• Establish a Plan and Run

• Evaluate model results

• Adjust model, as necessary

Hydrologic Engineering Center

• River

• Reach

• Junctions

• River Stations

• Cross section

 data entry
Cross-section Plot

Cross-section Data Editor

Hydrologic Engineering Center

• Option: Add Section

• River-Reach-Station

• Input section data

• Station/Elevation Data

• Reach lengths

• Manning’s n

• Bank Stations

• Contract/Expand Coef.
XYZ Perspective Plot

Profile Plot
Use of GIS/DEM data

RAS cross section data can be developed from a digital terrain model using

HEC-GeoRAS, which is an extension to ArcView (HEC, 2000a). This figure

illustrates how the stream centerline and cross section strike lines are chosen by

the user. This example is Las Vegas Wash.
Results of HEC-RAS computations can be viewed using the GIS/DEM data

representation that was used to construct input data. The results that can be

displayed (mapped) include traditional inundated areas for flows modeled as

well as depth and velocity distributions. Ongoing work to extend HEC-RAS for

sediment transport analysis will utilize this information to compute and display

transverse distributions of bed shear stress and stream power (based upon the

local grain size). This example is the Salt River near Phoenix, AZ.
Overview

RAS Unsteady Flow

• Overview

• New Geometric Features for RAS 3.0

• Geometric pre-processor

• Boundary and initial conditions

• Unsteady flow simulation manager

• Post-processor

• Additional graphics/tables to view results

Hydrologic Engineering Center

• Common geometry and hydraulic

 computations for steady & unsteady flow

• Using the UNET equation solver (Dr.

 Robert Barkau)

• Can handle simple dendritic streams to

 complex networks

• Able to handle a wide variety of hydraulic

 structures

• Extremely fast matrix solver
New Geometric Features for

HEC-RAS

• Existing Geometric

 Features all work for

 unsteady flow (XS,

 bridges, Culverts, inline

 weirs/spillways)

• Lateral Weirs/Spillways

• Storage Areas

• Hydraulic Connections

 (weirs, gated spillways,

 and culverts)

Hydrologic Engineering Center

All of the existing hydraulic analysis features in the previous steady flow

versions of HEC-RAS work within the new unsteady flow computation. The

following new features were added to work with unsteady flow, but they also

work in the steady flow simulation:

• Lateral weirs/gated spillways.

• Storage areas: used to model areas of ponded water.

• Hydraulic connections: use to exchange water between storage areas, storage

 areas and a river reach, and between different river reaches.
• For unsteady flow, geometry is pre-

 processed into tables and rating curves

 - Cross sections are processed into tables

 of area, conveyance, and storage

 - Bridges and culverts are processed into a

 family of rating curves for each structure

 - Weirs and gated structures are calculated

 on the fly during unsteady flow calculations

 - Pre-processor results can be viewed in

 graphs and tables

Hydrologic Engineering Center

The pre-processor is used to process the geometric data into a series of hydraulic

properties tables and rating curves. This is done in order to speed up the

unsteady flow calculations. Instead of calculating hydraulic variables for each

cross-section during each iteration, the program interpolates the hydraulic

variables from the tables. The pre-processor must be executed at least once,

but then only needs to be re-executed if something in the geometric data has

changed.

Pre-processing Geometry
Cross sections are processed into tables of elevation versus hydraulic properties

of areas, conveyances, and storage. Each table contains a minimum of 21 points

(a zero point at the invert and 20 computed values). The user is required to set

an interval to be used for spacing the points in the cross section tables. The

interval can be the same for all cross sections or it can vary from cross section to

cross section. This interval is very important, in that it will define the limits of

the table that is built for each cross section. On one hand, the interval must be

large enough to encompass the full range of stages that may be incurred during

the unsteady flow simulations. On the other hand, if the interval is too large, the

tables will not have enough detail to accurately depict changes in area,

conveyance, and storage with respect to elevation.

Cross Section Properties Plot
Hydraulic structures, such as bridges and culverts, are converted into families of

rating curves that describe the structure as a function of tailwater, flow and

headwater. The user can set several parameters that can be used in defining the

curves.

Bridge Hydraulic Properties Plot
Boundary and Initial Conditions

• Boundary conditions must be established

 at all ends of the river system:

 - Flow hydrograph

 - Stage hydrograph

 - Flow and stage hydrograph

 - Rating curve

 - Normal depth

The user is required to enter boundary conditions at all of the external

boundaries of the system, as well as any desired internal locations, and set the

initial flow and storage area conditions in the system at the beginning of the

simulation period.

Boundary and Initial Conditions

• Interior boundary conditions can also be

 defined within the river system:

 - Lateral inflow to a node

 - Uniform lateral inflow across a reach

 - Ground water inflow

 - Time series of gate openings

 - Elevation controlled gate

 - Observed internal stage and/or flow hydrograph
Unsteady Flow Simulation

Manager

Once all of the geometry and unsteady flow data have been entered, the user can

begin performing the unsteady flow calculations. To run the simulation, go to

the HEC-RAS main window and select Unsteady Flow Analysis from the Run

menu.

The unsteady flow computations within HEC-RAS are performed by a modified

version of UNET (HEC, 2001). The unsteady flow simulation is actually a three

step process. First a program called RDSS (Read DSS data) runs. This software

reads data from a HEC-DSS file and converts it into the user specified

computation interval. Next, the UNET program runs. This software reads the

hydraulic properties tables computed by the preprocessor, as well as the

boundary conditions and flow data from the interface and the RDSS program.

The program then performs the unsteady flow calculations. The final step is a

program called TABLE. This software takes the results from the UNET

unsteady flow run and writes them to a HEC-DSS file.

1. Define a Plan

2. Select which

programs to run

3. Enter a starting and

ending date and time

4. Set the computation

settings

5. Press the Compute

button
Post-processing Results

• Used to compute detailed hydraulic

 information for a set of user-specified

 times and an overall maximum water

 surface profile.

• Computed stages and flows are passed

 to the steady flow program for the

 computation of detailed hydraulic results

The Post Processor is used to compute detailed hydraulic information for a set

of user specified time lines during the unsteady flow simulation period. In

general, the UNET program only computes stage and flow hydrographs at user

specified locations. If the Post Processor is not run, then the user will only

be able to view the stage and flow hydrographs and no other output from

HEC-RAS. By running the Post Processor, the user will have all of the

available plots and tables for unsteady flow that HEC-RAS normally produces

for steady flow.

When the Post-Processor runs, the program reads from HEC-DSS the maximum

water surface profile (stages and flows) and the instantaneous profiles. These

computed stages and flow are sent to the HEC-RAS steady flow computation

program SNET. Because the stages are already computed, the SNET program

does not need to calculate a stage, but it does calculate all of the hydraulic

variables that are normally computed. This consists of over two hundred

hydraulic variables that are computed at each cross section for each flow and

stage.
Viewing Unsteady Flow Results

• All of the output that was available for

 steady flow computations is available for

 unsteady flow (cross sections, profile, and

 perspective plots and tables).

• Stage and flow hydrographs

• Time series tables

• Animation of cross section, profile and

 perspective graphs

Stage and Flow Hydrographs

The stage and flow hydrograph plotter allows the user to plot flow hydrographs,

stage hydrographs, or both simultaneously. Additionally, if the user has

observed hydrograph data, that can also be plotted at the same time. The plot

can be printed or sent to the windows clipboard for use in other software.
Animation of Profile Plot

HEC-RAS (or UNET) can be used to simulate the unsteady routing of flood

hydrographs resulting from breaching of dams or levees. The user has many

methods available within the programs to generate the hydrographs. In this

example, a gate operation is used to mimic the failure of a dam embankment.

UNET has the ability to compute flows through levee and embankment

breaches.

Hydrologic Engineering Center

The HEC-RAS software has the ability to animate the cross section profile.

When the user selects Animation, the plot steps thought the computed results in

a timed sequence. The user can control the speed of the animation, as well as

step through individual time steps.

Application of HEC-RAS

to a Dam Break Situation

Hydrologic Engineering Center
Gate Section
Computed Hydrographs

Gate Operation
Weir Type Breach

Future Work

• Dam & Levee Breaching

 - Overtopping

Hydrologic Engineering Center

• Initiation via

 - Water surface elevation

 - Clock (simulation) time

• Growth rate

 - Linear

 - Exponential

• Use weir equations with submergence
Piping Type Breach

Future Work (cont.)

• Dam & Levee Breaching

 - Piping

Hydrologic Engineering Center

• Initiation via

 - Water surface elevation

 - Clock (simulation) time

• Progression

 - Box until top collapses (when top elev. > W.S.)

• Orifice flow transitioning to weir flow
Product Availability

• Internal testing (Teton, MBMS etc.) this

 summer

• General release of HEC-RAS 3.1 - Fall

 of 2001

• Same breaching algorithms to be used

 in HEC-HMS

REFERENCES

HEC, 1977, “Guidelines for Calculating and Routing a Dam-Break Flood,” Research

 Document No. 5, U.S. Army Corps of Engineers, Davis, CA, January 1977.

HEC, 1980a, “Comparative Analysis of Flood Routing Methods,” Research Document

 No. 24, U.S. Army Corps of Engineers, Davis, CA, September 1980.

HEC, 1980b, “Dimensionless Graphs of Floods from Ruptured Dams,” Research Note

 No. 8, U.S. Army Corps of Engineers, Davis, CA, April 1980.

HEC, 1995, HEC-DSS User’s Guide and Utility Program Manuals, U.S. Army Corps of

 Engineers, Davis, CA.

HEC, 1998, “Mississippi Basin Modeling System Development and Application,” Project

 Report No. 36, U.S. Army Corps of Engineers, Davis, CA, April 1998.

HEC, 2000a, “HEC-GeoRAS - An extension of support for HEC-RAS using ArcView,”

 User’s Manual, CPD-76, U.S. Army Corps of Engineers, Davis, CA, April 2000.

HEC, 2000b, “Corps Water Management System (CWMS),” Technical Paper No. 158,

 U.S. Army Corps of Engineers, Hydrologic Engineering Center, June 2000.

HEC, 2001, UNET One-Dimensional Unsteady Flow Through a Full Netwok of Open

 Channels, User’s manual, CPD-66, U.S. Army Corps of Engineers, Davis, CA,

 April 2001.

HEC, 2001, HEC-RAS River Analysis System, Version 3.0 User’s Manual, CPD-68, U.S.

 Army Corps of Engineers, Davis, CA, January 2001.

RAC, 1999, Alamo Dam Demonstration Risk Assessment: Summary Report DRAFT,

 RAC Engineers and Economists and Los Angeles District, U.S. Army Corps of

 Engineers, Davis, CA, January 1977.

USACE, 1993, River Hydraulics, Engineer Manual 1110-2-1416, Headquarters, U.S.

 Army Corps of Engineers, Washington, DC, October 1993.

Hydrologic Engineering Center
B-20

 MORRIS 1 

CADAM & IMPACT: 

European Research Projects Investigating Dambreak 

Modelling and Extreme Flood Processes 

Issues, Resolutions & Research Needs Related to Dam Failure 

Analysis: Oklahoma Workshop, June 26-28, 2001 

M W MORRIS, HR Wallingford, UK 

m.morris@hrwallingford.co.uk

SYNOPSIS 

This paper provides an overview of the CADAM Concerted Action project, 

which was completed in January 2000, and an introduction to the IMPACT 

research project which will commence November / December 2001. Both 

projects have been funded by the European Commission, with the IMPACT 

project addressing key research issues identified during the CADAM 

concerted action project. 

The Concerted Action project on Dambreak Modelling (CADAM) involved 

participants from 10 different countries across Europe and ran between Feb 

98 and. Jan 2000. The aim of the project was to review dambreak modelling 

codes and practice from first principles through to application, to try and 

identify modelling best practice, effectiveness of codes and research needs. 

Topics covered included the analysis and modelling of flood wave 

propagation, breaching of embankments and dambreak sediment effects. 

The programme of study was such that the performance of modelling codes 

were compared against progressively more complex conditions from simple 

flume tests through physical models of real valleys and finally to a real dambreak test case (the Malpasset failure). The study conclusions are presented 

in a final project report, published by both the EC and the IAHR. This paper 

provides a brief summary of the key issues identified. 

The IMPACT project (Investigation of Extreme Flood Processes & 

Uncertainty) focuses research in a number of key areas that were identified 

during the CADAM project as contributing greatly to uncertainty in 

dambreak and extreme flood predictions. Research areas include 

embankment breach (formation and location), flood propagation 

(infrastructure interaction and urban flooding) and sediment movement 

(near and far zones with respect to embankment failure). The uncertainty 

associated with current predictive models and following project research 

will be demonstrated through application to case study material. 

Implications of prediction uncertainty for end users with applications such 

as asset management and emergency planning will also be investigated.
 MORRIS 2 

CADAM – AN INTRODUCTION 

The first legislation in Europe for dam-break risk analysis was presented in 

France in 1968, following the 1959 Malpasset dam-break that was 

responsible for more than 400 injuries. Since then, and especially more 

recently, many European countries have established legal requirements. 

However the techniques applied when undertaking the specified work can 

vary greatly. The perception of risks related to natural or industrial disasters 

has also evolved, leading to public demand for higher standards of safety 

and risk assessment studies. Considering the relatively high mean 

population density within Europe, a dam-break incident could result in 

considerable injury and damage; efficient emergency planning is therefore 

essential to avoid or minimise potential impacts. 

Dam-break analyses therefore play an essential role when considering 

reservoir safety, both for developing emergency plans for existing structures 

and in focussing planning issues for new ones. The rapid and continuing 

development of computing power and techniques during the last 15 years 

has allowed significant advances in the numerical modelling techniques that 

may be applied to dam-break analysis. 

CADAM was funded by the European Commission as a Concerted Action 

Programme that ran for a period of two years from February 1998. Under 

these terms, funding was provided only to pay for travel and subsistence 

costs for meetings, and for project co-ordination. All work undertaken 

during the study was therefore achieved through the integration of existing 

university and national research projects. HR Wallingford co-ordinated the 

project, with additional financial support from the DETR. 

The project continued work started by the IAHR Working Group 

(established by Alain Petitjean following the IAHR Congress in 1995) and 

had the following aims: 

• The exchange of dam-break modelling information between 

participants, with a special emphasis on the links between Universities, 

Research Organisations and Industry. 

• To promote the comparison of numerical dam-break models and 

modelling procedures with analytical, experimental and field data. 

• To promote the comparison and validation of software packages 

developed or used by the participants. 

• To define and promote co-operative research. 

These aims were pursued through a number of objectives: 

• To establish needs of industry, considering a means of identifying dam 

owners, operators, inspectors etc. throughout Europe. 

• To link research with industry needs - encourage participation; 

distribute newsletters to dam owners and other interested parties. 
 MORRIS 3 

• To create a database of test cases (analytical, experimental, real life) 

available for reference. 

• To establish the state-of-the-art guidelines and current best practices for 

dam-break modelling within the technical scope of the Concerted 

Action. This leads towards establishing recommended European 

standard methods, procedures and practices for dam-break assessments. 

• To determine future RTD requirements. 

CONCERTED ACTION PROGRAMME 

The project involved participants from over 10 different countries across 

Europe. All member states were encouraged to participate, with attendance 

at the programme workshops open to all and to expert meetings by 

invitation. Also, links with other experts around the world were welcomed 

to ensure that state-of-the-art techniques and practices were considered. The 

programme of meetings planned for the presentation, discussion and 

dissemination of results and information were as follows: 

Meeting 1 Wallingford, UK. 2/3rd March 98(Expert Meeting) 

A review of test cases and modelling work undertaken by the group up to 

the start of CADAM, followed by a review of test cases considered during 

the previous 6 months. Typical test cases included flood wave propagation 

around bends, over obstructions and spreading on a flat surface (physical 

modelling undertaken in laboratory flumes). 

Meeting 2 Munich, Germany 8/9th October 98(Open Workshop) 

Presentations and discussion on the current state of the art in breach 

formation modelling and sediment transport during dam-break events. 

Meeting 3 Milan, Italy May6/7th 99(Expert Meeting) 

Comparison and analysis of numerical model performance against a 

physical model of a real valley (Toce River, Italy) plus an update on breach 

modelling research. 

Meeting 4 Zaragoza, Spain Nov 18/19th 99 (Symposium) 

Comparison and analysis of numerical model performance against a real 

failure test case (Malpasset failure) plus a presentation of the results and 

conclusions drawn from the work of the Concerted Action over the two-year 

study period. 

MODELLING COMPARISONS 

The programme of tests progressed from simple conditions to test the basic 

numerical stability of modelling codes, through to a real dambreak test case 

– the Malpasset failure. The aim of the programme was to progressively 

increase the complexity of the modelling, and in doing so to try and identify 
 MORRIS 4 

which models performed best under which conditions. Both breach models 

and flood routing models were considered during the project. 

Flood Routing Analysis

Numerical Models The models applied in CADAM ranged from 

commercially available software to codes developed ‘in-house’ by the 

various participants. Participants ranged from ‘End User’ organisations such 

as ENEL (Italy), EDF (France) and Vattenfall (Sweden) to consultancy 

companies and universities undertaking research in this field. Many of the 

European participants codes were 2D codes based on depth averaged Saint 

Venant shallow water equations, but applying different numerical schemes 

utilising different orders of accuracy and source term implementations. 

Codes more familiar to the UK market included DAMBRK and ISIS (1D 

model - implicit finite difference Preissmann Scheme). 

Analytical Tests Initial test cases were relatively simple, with analytical 

solutions against which the numerical modelling results could be compared. 

These tests included: 

• Flume with vertical sides, varying bed level and width. No flow – 

water at rest. 

• Flume with (submerged) rectangular shaped bump. Steady flow 

conditions. 

• Dam-break flow along horizontal, rectangular flume with a dry bed. 

No friction used. 

• Dam-break flow along horizontal, rectangular flume with a wet bed. 

No friction used. 

• Dam-break flow along horizontal, rectangular flume with a dry bed. 

Friction used. 

These tests were designed to create and expose numerical 'difficulties' 

including shock waves, dry fronts, source terms, numerical diffusion and 

sonic points. Results were presented and discussed at the 2nd IAHR Working 

Group meeting held in Lisbon, Nov. 96 (EDF, 1997). 

Flume Tests Following the analytical tests, a series of more complex tests 

were devised for which physical models provided data (Fig 1). The aim was 

to check the ability of the numerical codes to handle firstly, specific 2D 

features, and then important source terms. These tests were: 

• Dam-break wave along a rectangular flume with 90° bend to the left. 

• Dam-break wave along a rectangular flume with a symmetrical 

channel constriction. 

• Dam-break wave along a rectangular flume expanding onto a wider 

channel (asymmetrical). 

• Dam-break wave along a rectangular flume with 45° bend to the left. 
 MORRIS 5 

• Dam-break wave along a rectangular flume with a triangular (weir 

type) obstruction to flow. 

The first three test cases were presented and discussed at the 3rd IAHR 

working Group meeting in Brussels (UCL, June 97) and the remaining two 

at the 1st CADAM meeting in Wallingford (CADAM, March 98). 

Photos courtesy of Sandra Soares, Université Catholique de Louvain, Belgium 

Fig. 1 Shock waves generated from ‘dambreak’ flow around a 45° bend. 

‘Real Valley’ Physical Model A model of the Toce River in Italy was used 

for the analysis of model performance against ‘real valley’ conditions (Fig 

2). The advantage of comparing the numerical models against a physical 

model, at this stage in the project, was that the model data would not include 

any effects from sediment or debris that might mask features of numerical 

model performance. 

Fig. 2 Digital plan model showing the Toce River model 

The model was provided by ENEL and, at a scale of 1:100, represented a 

5km stretch of the Toce River, downstream of a large reservoir. An 

automated valve controlled flow in the model such that a flood hydrograph 

U

a

downstream

upstream

Oblique bore

downstream
 MORRIS 6 

simulating partial or total dam failure could be simulated. Features within 

the downstream valley included a storage reservoir, barrage, bridges and 

villages (Fig 3). 

Photos courtesy of Prof JM Hiver, Université Libre de Bruxelles, Belgium

Fig. 3 Bridge structure on the Toce model and a dambreak flow simulation 

Real Failure Test Case – The Malpasset Failure The Malpasset Dam failure 

was selected as the real case study for the project since: 

• The data was readily available through EDF (France)

• It offered a different data set to the commonly used Teton failure

• In addition to field observations for peak flood levels there were also 

timings for the failure of three power supply centres 

 Data from a physical model study undertaken by EDF in 1964 (Scale 

1:400) was also available 

Modelling focused on the first 15km of valley downstream of the dam for 

which there was field data to compare against model predictions. This 

stretch of valley included features such as steep sided valleys, side valleys / 

tributaries and bridge / road crossings. 

Breach Analysis 

One of the four CADAM meetings was devoted to breach formation and 

sediment and debris effects. A comparison of the performance of breach 

models was undertaken using two test cases. The first test case was based 

on physical modelling work performed at the Federal Armed Forces 

University in Munich. The simulation tested was for a homogeneous 

embankment represented by a physical model approximately 30cm high. 

The second test case was based on data from the Finnish Environment 

Institute, derived from past collaborative research work undertaken with the 

Chinese. This work analysed the failure of an embankment dam some 5.6m 

high (Loukola et al, 1993). 
 MORRIS 7 

SELECTED RESEARCH FINDINGS 

The following sections highlight some selected issues identified during the 

CADAM project: 

Flood Routing

It was not possible to uniquely define a single best model or single best 

approach for dambreak modelling within the scope of the study since the 

various models and approaches performed differently under varying test 

conditions. Equally, a more in-depth analysis of the significant quantities of 

test data collected is now required to understand some of the performance 

features identified. It was possible, however, to identify some recurring 

features and issues that should be considered when defining best practice for 

dambreak modelling. These include (in no particular order): 

Wave Arrival time The speed of propagation of the flood wave is an 

important component of dambreak modelling since it allows emergency 

planners to identify when inundation of a particular area may be expected. 

It was found that 1D and 2D models failed to reproduce this accurately and 

that 1D models consistently under predicted the time (i.e. flood wave 

propagated too quickly) and 2D models consistently over predicted this time 

(i.e. flood wave propagated too slowly). 

Figure 4 shows wave travel times for one set of test data. The 1D models 

(left) show a scatter of results, probably due to the range of numerical 

methods applied. Results shown spread across the observed data. Later 

tests showed a tendency to under predict the wave speed. Many of the 2D 

models used similar numerical methods perhaps resulting in the tight 

clustering of data, however the results here (and repeated later) show a 

consistent over prediction of wave speed (right). 

Fig. 4 Summary of flood wave travel times for 1D models (left) and 

2D models (right) 

Flood wave speed is poorly modelled – 1D models over predict wave speed, 

2D models under predict wave speed. 

0

20

40

60

80

0 10 20 30 40 50

x [m]

t [s]

1

2

3

4

5

0

20

40

60

80

0 10 20 30 40 50

x [m]

t [s]

1

2

3

4

6

5
 MORRIS 8 

Use of 1D or 2D Models It was found that the 1D models performed well 

in comparison with the 2D models for many of the test cases considered. It 

is clear, however, that there are instances where a 2D model predicts 

conditions more effectively than a 1D model. In these situations a 2D model 

should be used or the 1D model should be constructed to allow for 2D 

effects. These situations are where flow is predominantly 2 dimensional 

and include flow spreading across large flat areas (coastal plains, valley 

confluences etc), dead storage areas within valleys and highly meandering 

valleys. Simulation of these features using a 1D model will require 

experienced identification of flow features, reduction of flow cross section 

and addition of headloss along the channel. 

A promising development that may offer a significant increase in model 

accuracy from a 1D model but without the heavy data processing 

requirements of a 2D model, is the use of a ‘patched’ model. This is where 

areas of 2D flow may be modelled using a 2D approach ‘patched’ within a 

1D model (Fig 5). This technique requires further development and 

validation, but seems to offer significant potential. 

In relation to the additional effort required for 2D modelling, 1D models 

perform well but cannot be relied upon to simulate truly 2D flow conditions. 

An experienced modeller is required to apply a 1D model correctly to 

simulate some 2D flow conditions. 

Fig. 5 2D patches within a 1D model to improve model accuracy whilst 

limiting processing requirements 

Modeller Assumptions It was clear just from the test cases undertaken (and 

also supported by an independent study undertaken by the USBR (Graham, 

1998)) that the assumptions made by modellers in setting up their models, 

can significantly affect the results produced. Graham (1998) deliberately 

gave identical topographic and structure data to two dambreak modellers 

and asked them to undertake independent dambreak studies for the same 

a

b

c

A

B

C

Reach 1

Reach 2

Reach 3

a A

c

C

b

B
 MORRIS 9 

site. The results varied significantly, and particularly in terms of flood wave 

arrival times. Variations in breach formation, valley roughness and 

simulation of structures contributed to the differences. 

Modelling assumptions can significantly affect the model results. Different 

modellers may produce different results for an identical study. Care should 

be taken to ensure only experienced modellers are used and that all aspects 

and assumptions made are considered. 

Debris and Sediment Effects It is unusual to find debris and sediment effects 

considered in detail for dambreak studies but it is clear from case studies 

and ongoing research that the movement of sediment and debris under 

dambreak conditions can be extreme and will significantly affect 

topography, which in turn affects potential flood levels. Case studies in the 

US have shown bed level variations in the order of 5 to 10m. 

Debris and sediment effects can have a significant impact on flood water 

levels and should be considered during a dambreak study. These effects 

offer a significant source of error in flood prediction. 

Mesh Convergence The definition of a model grid in 2D models, or the 

spacing of cross sections in 1D models, can significantly affect the predicted 

results. Models should be checked as a matter of routine to ensure that the 

grid spacing is appropriate for the conditions modelled and that further 

refinement does not significantly change the modelling results. 

Mesh or section spacing should be routinely checked when modelling 

Breach Modelling

Existing models are very limited in their ability to reliably predict discharge 

and the time of formation of breaches. Figure 6 below shows a typical 

scatter of modelling results found for the CADAM test cases. Models 

comprised a range of university and commercial codes, including the NWS 

BREACH code. 

It is also clear that there is little guidance available on failure mechanisms of 

structures, which adds to the uncertainty of conditions assumed by 

modellers. 
 MORRIS 10 

Fig. 6 Typical scatter of model results trying to predict breach formation 

There are no existing breach models that can reliably predict breach 

formation through embankments. Discharge prediction may be within an 

order of magnitude, whilst the time of breach formation is even worse. 

Prediction of breach formation time due to a piping failure is not yet 

possible. 

The NWS BREACH model is only calibrated against a very limited data set. 

The author (Danny Fread) confirmed that it is based on approximately 5 

data sets. 

Existing breach models should be used with caution and as an indicative 

tool only. A range of parameters and conditions should be modelled to 

assess model performance and results generated. 

There is a clear need to develop more reliable predictive tools that are based 

on a combination of soil mechanics and hydraulic theory. 

End User Needs

Throughout CADAM, the project focused on the practical needs of end 

users. Attempts were made to quantify a number of issues, both by end 

users and academic researchers alike. The initial response to the question of 

what accuracy models could offer and what was required from end users 

was limited. Without agreement on such issues it is impossible to determine 

whether existing modelling tools are sufficient or not! This perhaps reflects 

the current uncertainty of end users with regards to legislation and 

appropriate safety measures and of modeller’s appreciation of processes and 

data accuracy. It was suggested that the level of modelling accuracy should 
 MORRIS 11 

be appropriate for the site in question (i.e. more detailed for urban areas). 

Water level prediction should be appropriate to the mapping required, and 

the mapping should be at a scale sufficient for emergency planning use (i.e. 

to identify flood levels in relation to individual properties). This suggests an 

inundation mapping scale of approximately 1:5000 for developed areas. 

Inundation maps should be undertaken at a scale appropriate for use in 

emergency planning. For urban areas it is suggested that this should be at a 

scale of 1:5000 or greater. Modelling accuracy should be consistent with the 

detail of mapping required (i.e. for the end user of the data) 

Some Additional Points on DAMBRK_UK and BREACH

During the project, work undertaken by HR Wallingford identified a number 

of potential problems with the DAMBRK_UK and BREACH software 

packages. 

Under certain conditions, it was found that the DAMBRK_UK package 

created artificial flow volume during the running of a simulation. For the 

limited conditions investigated this volume error was found to be as high as 

+13% (Mohamed (1998)). This error tended to be on the positive side, 

meaning that the flood levels predicted would be pessimistic. It may be 

assumed that similar errors exist in the original DAMBRK code. It was 

noted that model performance varied between DAMBRK, FLDWAV 

(released to replace DAMBRK) and BOSS DAMBRK. A detailed 

investigation into the magnitude and implications of these errors has not yet 

been undertaken. 

Similarly, problems were also found with the BREACH software package. 

Under some conditions, predicted flood hydrographs were found to vary 

significantly with only minor modifications to input parameters. This 

erratic behaviour was discovered when considering the differences between 

piping and overtopping failure, by tending the piping location towards the 

crest of the dam. Erratic performance was also confirmed by a number of 

other CADAM members. 

Figure 7 shows a plot of flood hydrographs generated by BREACH for an 

overtopping failure and a piping failure located just 3cm below the crest. 

Logic dictates that these hydrographs should be very similar however the 

results show a significant difference in both the volume of the hydrograph 

as well as the timing. 
 MORRIS 12 

Fig. 7 Different outflow hydrographs produced by breach for an 

overtopping failure and a piping failure located 3cm below the crest. 

CADAM CONCLUSIONS 

The CADAM project has reviewed dambreak modelling codes and practice 

and identified a range of issues relating to model performance and accuracy. 

A number of these issues have been outlined above. When considering all 

aspects contributing to a dambreak study it was found that breach formation 

prediction, debris and sediment effects and modeller assumptions contribute 

greatly to potential prediction errors. 

Full details of all findings and conclusions may be found in the project 

report which has been published by both the EC and the IAHR, and which 

may also be found on the project website at: 

www.hrwallingford.co.uk/projects/CADAM

BEYOND CADAM 

Following completion of the CADAM project, it was a logical extension of 

the work to review the recommendations and develop a programme of 

research work aimed at addressing the key issues. Working within the 

European Commission 5th Framework Research Programme, a major 

research proposal was developed by a new consortium of organisations, 

some of whom had worked on the CADAM project and others whom joined 

the team to provide additional and more varied expertise. This proposal was 

named SECURE (Safety Evaluation of Man Made Water Control Structures 

in Europe) 

Piping Vs Overtopping

0

500

1000

1500

2000

2500

3000

3500

4000

4500

0123456789

time

Outflow (m3/s)

Piping Overtopping
 MORRIS 13 

Funding of European research is undertaken on a competitive basis with a 

finite volume of money with which to fund projects. The original proposal 

initially failed to receive funding and required considerable reworking twice 

before funding was (informally) agreed. During this process the extent of 

the proposed research was significantly reduced. However, the final 

proposal, named IMPACT (Investigation of Extreme Flood Processes & 

Uncertainty), is now subject to contract negotiation with the European 

Commission and research work should commence towards the end of 2001. 

The following sections are drawn from the European Commission 

discussion documents and provide an overview of the proposed work. 

Whilst the work programme is not yet final, it is unlikely to change 

significantly from the work described here. 

THE IMPACT PROJECT - OVERALL AIM 

The problem to be solved in the IMPACT project is to provide means of 

assessing and reducing the risks from the catastrophic failure of dam and 

flood defence structures. 

THE EUROPEAN NEED FOR IMPACT 

In the EU, the asset value of dam and flood defence structures amounts to 

many billions of EURO. These structures include, for example, dams, 

weirs, sluices, flood embankments, dikes, tailings dams etc. Several 

incidents and accidents have occurred which have caused loss of human life, 

environmental and economic damages. For example, in May 1999 a dam 

failed in Southern Germany causing four deaths and over 1 Billion EURO 

of damage. In Spain in 1982, Tous dam failed when still under construction 

with the result of 8 casualties, 100,000 evacuated people and economic 

losses worth 1500 MEuro. In 1997, also in Spain, a dam failed on the 

Guadiamar river, not far from Sevilla, causing immense ecological damage 

from polluted sediments released into the river valley during the failure. The 

dam failure at Malpasset (French riviera) in 1959 caused more than 400 

casualties.

The risk posed by a structure in any area is a combination of the hazard 

created by the structure (e.g. flooding) and the vulnerability of the potential 

impact area to that hazard (e.g. loss of life, economic loss, environmental 

damage). To manage and minimise this risk effectively it is necessary to be 

able to identify the hazards and vulnerability in a consistent and reliable 

manner. Good knowledge of the potential behaviour of the structure is 

important for its proper operation and maintenance in emergency situations 

such as high floods. In addition, prior knowledge of the potential 

consequences of failure of a dam or flood defence structure is essential for 
 MORRIS 14 

effective contingency planning to ensure public safety in such an 

emergency. 

In many areas related to structure failure our current understanding and 

ability to predict conditions is limited, so making the management of risk 

difficult. This project aims to advance the risk management process by 

improving knowledge of, and predictive tools for, the underlying processes 

that occur during and after failure. By both improving knowledge of the 

underlying processes and quantifying probability / uncertainty associated 

with these processes, the effect of these processes within the risk 

management system may be demonstrated and subsequently built into 

consideration the risk management process to improve reliability and safety. 

Many of the ‘underlying processes’ proposed for research were highlighted 

during the recent CADAM European Project as areas requiring further 

research. 

A common problem integral to the failure process is that of sediment and 

debris movement. The sudden release of water from a control structure 

brings with it intensive scour in the flow downstream. Close to the 

structure, the flow is extremely destructive; it can scour aggressively 

material from the riverbed and floor of the valley, changing completely the 

shape of the valley, or even diverting the river from its natural course. The 

flow will uproot vegetation and trees, demolish buildings and bridges and 

wash away animals, cars, caravans etc. The floating debris can be 

transported for substantial distances whilst the heavier material is deposited 

or trapped once the flow velocity attenuates. At a different level, it is the 

erosion of material from an embankment or dam that occurs during 

breaching and hence dictates the rate at which flood water may be released, 

and the location at which this may occur. 

The IMPACT project is of relevance to broad communities of user 

organisations, some of which are Partners in the IMPACT project team. 

The IMPACT project is organised in several complementary and 

interdependent themes to deliver the objectives of the research. 

IMPACT: SCIENTIFIC AND TECHNICAL OBJECTIVES 

The objectives of the IMPACT project are represented schematically in 

Figure 8 below. Specific objectives are therefore to: 

1. Advance scientific knowledge and understanding, and develop 

predictive modelling tools in three key areas associated with the 

assessment of the risks posed by dam and flood defence structures: 

a. the movement of sediment (and hence potential pollutants) generated 

by a failure 
 MORRIS 15 

Fig. 8 Structure of the IMPACT work programme 

b. the mechanisms for the breaching of embankments (dams or flood 

control dykes) and factors determining breach location 

c. the simulation of catastrophic inundation of valleys and urban areas 

following the failure of a structure 

2. Advance the understanding of risk and uncertainty associated with the 

above factors and combine these factors through a single system to 

demonstrate the risk / uncertainty associated with application of the end 

data (i.e. asset management, emergency planning etc.) 

These objectives will be undertaken with careful reference to past and 

ongoing research projects related to these topics, including the CADAM and 

RESCDAM projects. 

 

An important subsidiary objective of the IMPACT Partners is to ensure enduser relevance, acceptance and implementation of the outputs of the 

research. To this end, the IMPACT project Partners will develop the 

methodologies using demonstration sites and applications wherever 

appropriate. The project will include: 

• breaching of large scale test embankments (6m high embankments) to 

investigate breach formation mechanisms and the relationship between 

prototype and laboratory simulation 

• field assessment of sediment movement following large scale 

embankment failure 

• simulation of catastrophic flooding through the streets of a European 

city 

• a combined assessment of extreme flood conditions and prediction 

uncertainty for a real or virtual site comprising dam / flood defence and 

urban area. 

Project Co-ordination 

Sediment 

Movement 

Flood 

Propagation 

Breach 

Formation 

Risk Assessment 

Combined inputs with associated 

uncertainty demonstrated through 

case study application 

Implications for End User 

Applications 
 MORRIS 16 

IMPACT: BENEFITS OF THE RESEARCH PROJECT 

The successful completion of the IMPACT project is expected to lead to: 

• improved scientific knowledge and understanding of extreme and 

aggressive flood flows following the catastrophic failure of a water 

control structure 

• Specific scientific knowledge and understanding relating to breach 

formation through dams and flood defence structures, movement of 

sediment under extreme flood conditions and the simulation of flooding 

in urban areas 

• improved understanding of the risk associated with the potential failure 

of dams and flood defence structures ultimately leading to reduced risks 

of failure and hence a reduction in long-term costs 

• improved understanding of the uncertainty associated with the 

prediction of extreme flood conditions and processes 

• improved public safety through emergency planning and community 

disaster preparedness in the event of a failure

• enhanced prospects for EU-based consultancies in the International 

Water and Hydropower markets 

IMPACT: OVERVIEW OF WORK PROGRAMME 

As shown in Figure 8, the IMPACT project has been structured according to 

5 Theme Areas. These Theme Areas are: 

 Theme 1 Project Integration, Co-ordination and Delivery 

 Theme 2 Breach Formation 

 Theme 3 Flood Propagation 

 Theme 4 Sediment Movement 

 Theme 5 Combined Risk Assessment & Uncertainty 

The objectives and proposed work for each of these Theme Areas is 

presented in more detail below: 

Theme 1 Project Integration, Co-ordination and Delivery

The IMPACT project involves 9 organisations drawn from 8 European 

countries and thus will require careful attention to the management of the 

research to ensure that it delivers it outputs. The project integration, coordination and delivery is a core management function of the project Coordinator. The project integration will be achieved through facilitation of 

communication between each of the project themes and the researchers 

engaged in the work packages. There will be a regular meeting of the 

Theme leaders approximately every four to six months. Where possible, 

these meetings will be scheduled with other project meetings to minimise 

the travel costs. Full team meetings will be held at project workshops, of 

which four are scheduled during the 36-month period. These workshops will 

provide opportunities for representatives of all the research teams to discuss 
 MORRIS 17 

their findings and future approaches. The Co-ordinator (M Morris: HR 

Wallingford) will use the project workshops to review progress and define 

the detailed work programme for the coming months. 

The Co-ordinator will establish a project Internet site with public and 

private areas. The public area will give information on the definitive project 

outputs, whilst the private site with an FTP area will be the main vehicle for 

electronic communication of data, software and results between the 

IMPACT project team members. An Internet based email database will be 

established to allow any interested parties to register their email address for 

receipt of project newsletters, meeting details etc. The Co-ordinator will 

take final responsibility for the documentation and reporting of the project. 

Project team members will be encouraged to publish the results of the 

research in refereed scientific journals and conferences as appropriate. 

Public outputs from the project will be recorded and made available through 

the public area of the project Internet site. 

Theme 2 Breach Formation

The problem to be solved in this theme is the lack of quantitative 

understanding of the modes and mechanisms involved in the failure of dams 

and flood defence structures. Without such understanding, the rate of 

outflow from a failed structure cannot be assessed and hence the risks posed 

by the structure cannot be assessed with confidence. The approach to the 

research proposed in the IMPACT project is a combination of experimental 

and theoretical investigations, leading to a new modelling procedure for the 

failure of embankments. Three components of failure modes will be 

investigated, internal erosion, overtopping and slope stability during the 

breach enlargement. The methods will be validated as far as possible 

against data from the physical experiments as well as actual failures. The 

large-scale experimental facilities available to the IMPACT partners will 

allow the factors that govern the initiation and growth of breaches to be 

studied under controlled conditions. However, the issue of scaling from the 

laboratory to the prototype scale must be addressed. A novel part of the 

experimental programme is the rare opportunity to include field tests at 

large scale. A test site has been identified in Norway located between 

existing dams where a 6m high embankment may be constructed and then 

tested to failure using controlled flow released from the upper dam. Five 

failure tests are planned. The location and test programme means that no 

damage to infrastructure will occur, also with minimal environmental effect. 

Individual work packages within this Theme Area include: 

• Breach formation processes – controlled failure of 6m high 

embankments to identify key processes 

• Breach formation processes – laboratory physical modelling of 

embankment failure to identify key processes 
 MORRIS 18 

• Model development and comparison - development and comparison of 

breach model performance through use of a common modelling 

framework 

• Breach location – development of a methodology / prototype tool for a 

risk based approach to identifying breach location 

Theme 3 Flood Propagation

The problem to be solved in this theme is to produce reliable modelling 

methods for the propagation of catastrophic floods generated by the failure 

of a water-control structure (often called the dam-break problem). The 

intensity of the flood will depend upon the initial difference in depth 

between the impounded level behind the control structure and the land level 

on the other side. Hence the research in this theme will concentrate upon 

the dam-break flood problem but the techniques will also be applicable to 

the failure of flood embankments. The overall objectives for this theme are: 

• To identify dam-break flow behaviour in complex valleys, around 

infrastructure and in urban areas, and the destructive potential of these 

catastrophic flood waves. 

• To compare different modelling techniques & identify best approach, 

including assessment of accuracy (in relation to practical use of 

software). 

• To adapt existing and develop new modelling techniques for the specific 

features of floods induced by failure of man made structures. 

• To develop guidelines for an appropriate strategy as regards modelling 

techniques, for a reliable and accurate prediction of flooded areas. 

The approach to be adopted is to: 

• compare different mathematical modelling techniques 

• identify the best approaches, including assessment of implementation of 

the methods in industrial software packages 

• check the accuracy and appropriateness of the recommended methods by 

validation of the models against the results from physical 

experimentation. 

• validate the different modelling techniques adopted, both existing and 

newly developed against field data obtained from actual catastrophic 

flood events. 

The research has been organised into two work-packages each subdivided 

into several distinct tasks; for each task there is a Technical Co-ordinator 

and a team of Partners involved in the activities. The two work-packages 

are: 

• Urban flood propagation 

• Flood propagation in natural topographies 
 MORRIS 19 

Theme 4 Sediment Movement

The problem to be solved in this theme is to improve the predictions of the 

motion of sediments in association with catastrophic floods. The nature of 

the problem is different form that in normal flood flows in that the quantity 

and size of sediment will be much greater in the catastrophic flood flow. 

This is an important issue for an accurate prediction of the downstream 

consequences: 

• the river bottom elevation can vary by tens of meters 

• or the river can be diverted from its natural bed (as for the Saguenay 

river tributary – the Lake Ha!Ha! damn failure, Canada, in 1997), 

with the associated impact on the flooded areas. The approach adopted in 

the IMPACT project is to combine physical experiments designed to 

improve our physical understanding of these cases with the development 

and testing of mathematical modelling methods for simulation of these 

flows. The IMPACT Partners will use the extensive experimental facilities 

available to them in undertaking the experimental programme. An output of 

the research will be a set of well-documented experimental investigations of 

flows with transported sediment, which could serve the international 

research community as benchmarks for future theoretical developments 

outside the scope of the current IMPACT project. 

The research is divided into two work-packages that address: 

• near field sediment flow in dam-break conditions 

• geomorphological changes in a valley induced by dam-break flows (far 

field) 

Theme 5 Combined Risk Assessment and Uncertainty

Themes 2-4 outline proposed research into processes that are currently 

poorly understood or poorly simulated by predictive models. An important 

aspect of any process that contributes towards an overall risk assessment 

(i.e. prediction of flood risk) is an understanding of any uncertainty that may 

be associated with prediction of that particular process. For example, a flood 

level may be predicted to reach 20m and an emergency plan developed to 

cope with this. However, if the uncertainty associated with this prediction is 

±2m, then different measures may be taken to manage this event. The 

problem to be solved in this theme, is to quantify the uncertainty associated 

with each process contributing to the risk assessment and to demonstrate the 

significance of this for the end application. This may be in the form of 

uncertainty associated with flood level prediction, flood location, flood 

timing or flood volume – depending upon the particular application of data. 

Uncertainty will be quantified by working closely with the fundamental 

research being undertaken in Themes 2-4 and demonstrated through a 

number of case study applications. The procedure for combining the 
 MORRIS 20 

uncertainty associated with different data will depend upon the process 

itself. This may require multiple model simulations or combination through 

spreadsheet and / or GIS systems as appropriate. 

Having identified process uncertainty and the effect that particular processes 

may have on the end application, it will also be possible to identify the 

importance (with respect to the accuracy of a risk assessment) that each 

process has and hence the effort that should be applied within the risk 

management process to achieve best value for money. 

IMPACT CONCLUSIONS 

Subject to final contract negotiations with the European Commission, the 

IMPACT project should commence towards the end of 2001 and run for a 

period of 3 years. The research findings from this project should enhance 

understanding of extreme flood processes and simulation including breach 

formation, flood routing and sediment movement. It is intended that 

research undertaken for the IMPACT project shall remain focussed upon the 

needs of end users, and active participation by representatives from industry 

worldwide shall be sought. Technical knowledge relating to the specific 

extreme event processes will be presented but also analysed in the context 

of end user applications with the aim of demonstrating not only what is 

known, but also the uncertainty related to that knowledge and how this 

might influence direct applications. 

For more information on this project, and to sign up to the project email list, 

visit the project website (from November 2001) at: 

www.hrwallingford.co.uk/projects/IMPACT 

or contact the project Co-ordinator directly on: 

m.morris@hrwallingford.co.uk

ACKNOWLEDGEMENTS 

The members of CADAM are grateful for the financial support offered by 

the European Community to structure this concerted action programme. 

Without funding for research time or facilities, however, the project relies 

on contributions made by the group members, which is greatly appreciated. 

The teams who undertook modelling comprise: 

Université Catholique de Louvain (Belgium), CEMAGREF (France), 

EDF/LNH (France), Université de Bordeaux (France), INSA Rouen 

(France), Federal Armed Forces University Munich (Germany), ENEL 
 MORRIS 21 

(Italy), Politechnika Gdanska (Poland), Universidade Tecnica de Lisboa 

(Portugal), Universidad de Zaragoza (Spain), Universidad Santiago de 

Compostela (Spain), Vattenfall Utveckling AB (Sweden), University of 

Leeds (UK), HR Wallingford (UK). 

Special thanks should also go to the following organisations that have 

undertaken, or made available data from, physical modelling work: 

Université Catholique de Louvain (Belgium), Université Libre de Bruxelles 

(Belgium), LNEC (Portugal), ENEL (Italy), Federal Armed Forces 

University Munich (Germany), The Finnish Environment Institute. 

REFERENCES 

EDF (1997). Proceedings of the 2nd AIRH Workshop on Dam-break Wave 

Simulation, Lisbon, Nov. 1996. Report LNH HE-43/97/016/B. 

Université Catholique de Louvain (1998). Proceedings of the 3nd AIRH 

Workshop on Dam-break Wave Simulation, Brussels, June 1997. 

CADAM (1998). Proceedings of the 1st CADAM workshop, Wallingford,

March 1998. 

CADAM (1998). Proceedings of the 2nd CADAM workshop, Munich, 

October 1998. 

CADAM (1999). Proceedings of the 3rd CADAM workshop, Milan, May 

1999.

CADAM (1999). Proceedings of the 4th CADAM workshop, Zaragoza, 

November 1999. 

HR WALLINGFORD (2001). IMPACT: Investigation of Extreme Flood 

Processes & Uncertainty. European Commission proposal document, Part 

B, submitted under the Energy, Environment and Sustainable Development 

Programme (Research and Technical Development Activities of a Generic 

Nature), February 2001.

LOUKOLA E, PAN S (1993). Investigation report on dam safety research 

in China. Finnish co-operative research work on dambreak hydrodynamics, 

National Board of Waters and the Environment Series A 167, 92p. 

MOHAMED (1998) Informatic tools for the hazard assessment of dam 

failure. MSc thesis for Mohamed Ahmed Ali Mohamed, IHE Delft, May 

1998. 

B-21

Issues, Resolutions, And Research Needs Related To Dam Failure Analysis 

USDA/FEMA Workshop 

Oklahoma City June 26 - 28, 2001 

Embankment Breach Research in Norway 

Senior Advisor Kjetil Arne Vaskinn, dr.ing. 

Statkraft Grøner AS1

1. INTRODUCTION 

The modern dam building in Norway started around the turn of the century, when we started to 

exploit our hydropower resources. Hydropower is today one of Norway’s major natural 

resources. The development of the resource has resulted in construction of many reservoirs. 2500 

dams are controlled by the Norwegian Water Resources and Energy Directorate (NVE). NVE is 

the dam-safety authority in Norway. The dams controlled by NVE are higher than 4 m or have a 

reservoir capacity exceed 0,5 Mill.(m3

). 

In the beginning most of the dams was masonry or concrete dams. After 1950, large embankment 

dams began to dominate the scene. 

A water reservoir behind a dam represents an enormous energy potential, which might cause 

catastrophic damage in case of a dam failure. The dams therefore pose a risk to the downstream 

area. To manage and minimize this risk effectively it is necessary to be able to identify the 

hazards and vulnerability in a consistent and reliable manner. Good knowledge of the behavior of 

the structure is important for the maintenance and proper operation. In addition, prior knowledge 

of the potential consequences of failure of a dam or flood defense structure is essential for 

effective contingency planning to ensure public safety. 

The issue of dam safety has become more and more important in Norway during the last years 

and much money has been spent to increase the safety level. The dam owner is responsible for 

the safety of his dams. He has to follow the requirement and guidelines from NVE: 

 

} 1

 Statkraft Grøner is one of the major consulting firms in Norway with 300 employee in 

1998 and an annual turnover 42 mill. US dollar. The company has a high expertise in the 

field of research and development, working closely with academic research groups and the 

hydropower industry. The company is fully owned by Statkraft SF, the largest Hydropower 

Company in Norway. Statkraft SF Operates 55 power plants and has ownership in 36 more. 

The average annual production for Statkraft in Norway is 36 TWh (30% of Norway’s total). 

Statkraft SF owns 113 water reservoirs with a capacity of 33,7 billion m3 (40% of 

Norway’s total storage capacity) 
1. Contingency planning for abnormal situations 

2. Safety revisions 

3. Load recording 

4. Damage and accident reporting 

5. Risk analysis 

6. Discussions of the failure probability and studies on impact of failure 

To make sure that the dam-safety work is done in a proper way, NVE has made several 

guidelines. These include “Guidelines for simulation of dam-break”(Backe et al 1999). All the 

dam-break simulations in Norway are made according to these guidelines. 

The system for revisions of dams, developed by NVE, has been operation for several years. The 

experience so far is good. From time to time the result from a safety revision implies that the 

dam-owners have to put in a lot of money to fulfill the requirements. In most cases this is done 

without any discussions. Sometimes, however, there is a discussion between the owner of a dam 

and NVE based on different understanding of the guidelines and a lack of common understanding 

of the basic mechanism in how the strength and stability of the dam can be improved. The focus 

for discussion is now the new guidelines for dam-safety, not yet put into operation. 

The most frequent theme for discussion is whether or not a dam satisfies the requirement to: 

• Stability when exposed to normal loads. 

• Stability with extreme loads e.g. major leakage and resistance against erosion in case of 

overtopping. 

Stability of rock filled dams is determined mostly as a function of the shear strength of the rock 

filling. Stability in case of extreme loads is also dependent of the shear strength, but in these 

cases there is a big uncertainty in the loads. 

The regulations require that the dams can resist a certain leakage through the core. An ongoing 

project (Cost efficient rehabilitation of dams) also put the focus on the breaching mechanism in 

the case of a major leakage. 

Dam break analysis is performed to assess the consequences of dambreak and is a motivating 

factor for the dam safety work. The routines used today to in Norway give a too simplified 

description of the development in the breach in our rock-filled dams. The materials and the way 

the dam is constructed are not taken into consideration. Due to this most of the work done on the 

dam to improve the security will have no visible influence on the development of the dambreak 

and on the downstream consequences of the break, when performing the dambreak simulation. 

This is not logical and gives not incentives to the dam safety work. The result of this can also be a 

wrong classification of a dam. 

Based on these experiences Norway has started a new project with the main objective of 

improving the knowledge in this field. 

Parallel to the planning of a Norwegian project there, European research institutions have been 

working for establishing a common within the filed of dam-safety. The project is called IMPACT 
and is presented in detail by Mark Morris. The problem to be solved in the IMPACT project is to 

provide means of assessing and reducing the risks from the catastrophic failure of dam and flood 

defense structures (quote from the application to EU for funding of IMPACT). 

2. MAJOR OBJECTIVES 

The scope of the project is to improve the knowledge of, and to develop predictive tools for the 

underlying processes that occur during and failure. By doing so the proper decisions can be taken 

for improving the dam safety taking into account the technology and economy. 

The objectives of the project are: 

• To improve the knowledge on the behavior of rock filled dams exposed to leakage. 

• To get knowledge on the developent of a breach. 

This knowledge will be used to: 

• Develop simulation tools that will be used in the planning of dam safety work. 

• Develop new criteria for design of dams 

• Develop criteria for stability and failure mechanics of dams. 

3. PROJECT PLAN. 

The Norwegian project consists of 4 sub-projects: 

1. Shear strengths and permeability of rock-fillings 

2. Stability of the supporting fill and dam-toe in rockfill dams exposed to heavy leakage 

3. Breach formation in embankment-dams (rock-filled dams) 

4. Breach formation in concrete dams 

A rockfill dam is defined as an embankment dam comprising more than 50% by volume of fill 

obtained from rock quarry or rock excavation. (Konov, 2001) 

The IMPACT-project project consist of 4 themes: 

1 Breach Formation 

2 Flood Propagation 

3 Sediment Movement 

4 Combined Risk Assessment and Uncertainty 

Sub-project 3 in the Norwegian project and theme 2 in IMPACT has the same objectives. Some 

of the problems that will be solved in sub-project 1 and 2, will give information that is relevant 

for IMPACT. Through coordination of these to major projects we hope to improve the knowledge 

about embankment dams 

Mark Morris has presented the details of IMPACT. In the following chapters a short description 

of the Norwegian project will be given. 
3.1 Shear strengths and permeability of rock-fillings 

Through the process of reevaluation of rock-filled dams the question of the shear-strength has 

been asked. Very few dams have a documentation of the shear-strength of the rock-fillings based 

on test of the rock materials. In most cases the planning is based on experience from similar damconstructions and geological conditions. 

The main question to answer in the project will be what the correct or best parameters to describe 

the materials are. Physical test and experience will be used. Some tests have been done at some of 

the largest rockfill-dams in Norway. This knowledge will be used to correlate the shear-strength 

from single tests of the rock material to roughness, shape of the grains, pressure strength. 

Permeability or hydraulic conductivity is important for the leakage through the supporting fill and 

for the erosion during a dam failure. Existing knowledge and data on this topic will be collected 

through a literature review. Test of the permeability in the large-scale test dam will be performed. 

3.2 Stability of the supporting fill and dam-toe in rock-filled dams exposed to heavy leakage 

Sub-project no 2 will focus on developing of tools or routines for assesment of the stability of a 

dam exposed to leakage through or over the core. 

The objectives of the tests are: 

1. To find the connection between the drainage capacity through a rock-filled dam, the 

size of the stones, layout of the filling/dam-toe etc. This information will be used 

setup of new guidelines for assessment of old dams and for layout and dimensioning 

of new dams in general and specifically the dam-toe. 

2. To increase the knowledge of the permeability of rock-fillings in general. 

3. To find and verify the connection between different scaling. (1:10, 1:5 and prototype) 

A computer simulation program will be developed to analyze the flow through a rock filling. 

Criteria that tells when a rock-filled dam will collapse either due to erosion of the individual 

stones or a major break along shear flater through the supporting fill, will be developed. 

The simulating program will be tested on physical models in large scale 

3.3 Breach formation in rock-filled dams 

The objective of this sub-project is to improve the understanding of the breach formation process 

that occurs in and through embankments, with a special focus on rockfill dams. 

Breach formation covers factors that will lead to an uncontrolled release of water from the 

structure. The most common modes of failure for an embankment are from water overtopping the 

crest or internal erosion also called piping. The ability to predict the location and rate of 

development of a breach through a flood embankment or dam is limited. 
The most commonly applied approach is the deterministic BREACH model developed in the late 

1970’s at the US National Weather Service (USNWS). Several parametric relationships based 

upon analysis of actual failures of dams are also in use. In Norway the relationship developed by 

Froelich (Backe D et al.1999) is used. 

Most of the tests and analysis have been of homogeneous structures of non-cohesive material. 

The failure of multi-element structures incorporating an impervious core remains poorly 

understood. 

Experimental tests will be undertaken to support the theoretical development of models of the 

failure modes and rates of failure. These tests will be made as part of the IMPACT project. 

Investigation will be made of the factors contributing to breach location and analysis of the likely 

probability of failure resulting from these factors. 

The tests will be completed through “large scale” tests. Based on the results from these tests a 

simulation program will be developed for simulation of the breach formation in these kinds of 

dams. 

3.4 Breach formation in concrete dams 

This subproject will focus on the breach formation in concrete dams. Finite element methods will 

be used. The project will take advantage of the experience of concrete technology for simulation 

of failure of concrete dams. 

There exist several very advanced simulation programs that can be used e.g. ABAQUS. This 

program was developed to help engineers to design the off-shore platforms that are used for oildrilling in the North See. 

4. PHYSICAL/SCALE MODELING 

There will be several test of physical modes in the in the laboratory and in the field (large-scale 

test). This test are necessary in order to find the answers in sub-project 1, 2 and 3 and also for the 

questions asked in theme 2 of IMPACT. 

4.1 Tests in the laboratory. 

There will be laboratory test both in Norway and in UK (Wallingford). The tests in UK will be 

undertaken to examine the different aspects of breach formation. This part of the laboratory 

modeling will use embankments approximately 0.75m in height and the experiments will 

investigate: 

• overtopping failures for water flowing over the crest of an embankment 

• piping failures where fine material is progressively eroded through the body of the 

embankment 
Initial tests will cover homogeneous non-cohesive material – an idealized embankment. Tests 

will then progressively tend towards real embankment designs through the analysis of cohesive 

material and composite structures. Tests will measure flow-rate, the hydraulic heads, and 

evolution of the crest erosion and piping to establish the erosion rates of the material. 

The main issues of the Norwegian laboratory tests are to find out any possible problem with the 

field tests. Several tests of the dam-toe will be made. Focus will be on the following: 

1. Scaling effects 

2. Size of the materials (stones) 

3. Grain size distribution of material 

4. The shape (layout) of the dam-toe 

5. The importance of the downstream-water level. 

In the laboratory we will use to test-flumes: one in the scale 1:5, the second one in scale 1:10. 

According to the plans there will be 13 different tests of the dam-toe. These are shown in table 1. 

 

Key figures for the flumes are shown in table 2. 

Scale 1:10 Scale 1:5 

Width (meter) 2,20 4,0 

Length (meter) 10,0 10,0 

Depth (meter) 0,75 1,43 

Maximum discharge (l/s) 320 600 

 

We will also make some test with the focus of planning of the field test. 

All of the tests in table 1 are used to evaluate the stability of the stones in the outflow area. 

Table 1. Tests in the laboratory

Test no 1 2 3 4 5 6 7 8 9 10 11 12 13

Scale 1:10 * * * * * * *

1:5 * * * *? *? *?

D50 [mm] 500 500 100 300 100

0

200

0

100 100

0

Size of the stones 500 500 500 500 500

Sizing E E E E E E E E V E V E E

Shape Slope 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 1,5 3,0 3,0 1,5 3,0

Water level L L L L L L L L L L L H H

Reproducibilityt

Scale *1 *1 *2 *3 *2 *3

Size of the stones *1 *2 *1 *1 *1 *1 *2 *2

Sizing *1 *1 *2 *2

Slope *1 *2 *1 *2

H/L waterlevel *1 *2 *1 *2

E: Uniform, V: well graded, L: low water level downstream, H: high water level downstream

*: referring to which tests can be compared. E.g.: If we want to study the scaling effects, results from test 1 and 2,

2 and 7, and 5 and 8 should be compared.
Test no 1,2,3,5,7, and 8 will be used to assess if there are some scaling effects. Tests #1 to #8 are 

designed to help in evaluating the effect of the different sizes of the stones in the outflow area. 

The results here will also be used to compare with data from earlier tests and projects: 

• “Safety analysis of rock-filed dams”, Dam safety project 1992. 

• “ Safe remedies for leaking embankment dams”, ICOLD, Rio de Janeiro, 1982. 

• “Flow through and stability problems in rockfill dams exposed to exceptional loads”, Vienna 

1991. 

• “ The risk for internal erosion in rock-filled dams and the calculation of turbulent coefficient 

of permeability”, Norwegian research Council, 1991. 

• “Extreme situations”, Short course in dam safety, 1992. 

The test #2, 9, 10 and #11 are identical except from the differences in the grain size distribution 

of the building material. Two of them are well graded. The other two have a uniform grain size 

distribution. These tests will be used to assess the difference in stability with the same 

characteristic size of the stones, but different grain size distribution. 

Table 3 mixing of material 

Tests #2 , #9, # 10 and #11is identical except for the slope of the downstream side: two of them 

have the slope of 1:3, the two other have a slope equal to 1:1,5. Results from these tests will be 

used to assess the stability of the toe, due to different slopes. 

Test #2 and #12 are identical, the same is #10 and #13 except for difference in the water-level 

downstream of the dam. These tests will be used to compare the effect on the stability due to 

different level down stream of the dam. 

Table 3.Size of material in prototype 

Test Size of stones (mm) mixing 

no. dmax d60 d50 d10 E/V Cu 

1 750 600 500 240 E 2,5 

2 750 600 500 240 E 2,5 

3 150 120 100 48 E 2,5 

4 400 360 300 144 E 2,5 

5 1500 1200 1000 480 E 2,5 

6 1800 1600 1500 640 E 2,5 

7 150 120 100 48 E 2,5 

8 1500 1200 1000 480 E 2,5 

9 750 600 500 120 V 5 

10 750 600 500 240 E 2,5 

11 750 600 500 120 V 5 

12 750 600 500 240 E 2,5 

13 750 600 500 240 E 2,5 

 
The following data will be recorded in the tests: 

• The pressure line in the filling 

• Water-level upstream and downstream of the dam 

• The discharge through the dam (measurd downstream of the dam) 

• The water-level at the downstream edge of the dam_toe 

• The grain size distribution curve. 

• The porosity in a test volume 

• Picture from the test 

• Video recording of the test. 

4.2 The field tests 

The field test will be made downstream of one of the largest reservoir in Norway (The lake 

Røssvatnet). Statkraft SF is the owner of this reservoir and is an active partner in the project. The 

test site is in northern Norway, close to the Arctic Circle. Figure 1 

The dam on this reservoir has just been revised. As a result of the safety revision Statkraft SF has 

made safety improvements on the dam. An overview of the area downstream of the dam is shown 

in figure 2. Figure 3 shows cross-section of the test-site and also a longitudinal section along the 

river. So far the focus in the project has been on the laboratory tests. The results from these test 

will give information and knowledge that will be used for the detailed planning 

We are going to run two different kind of tests: 

• tests of the stability of the dam-toe 

Lysaker/Oslo

Tromsø

Trondheim

Large scale test-site

Arctic circle
• breach tests 

A local contracting firm will be responsible for the building of the dam according to our 

specifications. 

The release of water from the upstream-reservoir has to be done in close cooperation with the 

dam-owner, Statkraft SF. 

The gates at Røssvassdammen have a total capacity up to 500m3

/s. The gates are new and the 

operation of them is easy and flexible. The high capacity through the gates gives us the 

opportunity to simulate breaching in a large reservoir (slow reduction in the water level in the 

reservoir as a function of time) and a small reservoir. 

Prior to the tests we will establish a measurement station for discharge. The capacity of the gate 

as a function of the opening is known. By releasing a known discharge through the gates and 

record the corresponding water level a stage-discharge relationship will be established. 

Exact measurement of the discharge through or over the dam is important. 

There might be a minor price to pay for the release of water, because it normally would have 

been use for hydropower production. Negotiation with Statkraft SF is going on now. 

The following data will be recorded in the tests: 

• The pressure line in the filling 

• Water-level upstream and downstream of the dam 

• The discharge through the dam (measurd downstream of the dam) 

• The water-level at the downstream edge of the dam_toe 

• Picture from the test 

• Video recording of the test. 

• The development of the breach 
 Figure 2 Overview of the test-area. 

 Figure 3. Cross-section and longitudinal section 

Cross section

Longitudinal section

Cross-section

Longitudinal
5. BUDGET AND TIME SCHEDULE 

The whole Norwegian project will run for 3 years with the startup the spring 2001 and with a 

total budget of 7 mill Norwegian Kroner. This close to 900 000 Euros. 

6. PARTNERS 

The Statkraft Grøner AS is the leader of the Norwegian project and also partner in IMPACT. The 

other Norwegian companies involved are: 

• Norconsult AS 

• NGI (Norwegian Geotechnical Institute) 

• SINTEF Energy Research 

• NTNU (Norwegian University for Science and Technology) 

There is established advisory group or steering committee for the project in Norway. This group 

is made up of the major dam owners in Norway, NVE and the Norwegian Electricity Association 

EBL. 

7. REFERENCES 

BACKE D, (1999), Guidelines for Dam-break simulations. NVE 1-1999. (In Norwegian) 

KONOV T, (2001), Taking Stocks of Norway’s dams . In International Water Power & Dam 

Construction. Mai 2001. 

SVENDSEN V N and GRØTTÅ L. (1995), New Requirements for dam safety in Norway.

Hydropower & Dams. May 1995. 

C

PARTICIPANTS

________________________________________________________________________

Steven Abt

Department of Civil Engineering

Colorado State University

Fort Collins, CO 80523-1372

Phone (970) 491-8203

Fax (970) 491-8462

Sabt@engr.ColoState.edu

Cecil Bearden

Planning and Management Division

Oklahoma Water Resources Board

3800 N. Classen

Oklahoma City, OK 73118

Phone (405) 530-8800

Fax (405) 530-8900

crbearden@owrb.state.ok.us

David Bowles

Utah State University

Utah Water Research Laboratory

College of Engineering

8200 Old Main Hill

Logan, UT 84322-8200

Phone (435) 797-4010

Fax (435) 797-2663

David.Bowles@usu.edu

Larry Caldwell

USDA-NRCS

USDA Agricultural Center Bldg.

100 USDA, Suite 206

Stillwater, OK 74074-2655

Phone (405) 742-1257

Fax (405) 742-1126

larry.caldwell@ok.usda.gov
Catalino Cecilio

Catalino B. Cecilio Consulting

2009 Carignan Way

San Jose, CA 95135-1248

Phone (408) 528-9909

Fax (408) 528-9910

cat@cecilio-consulting.com

Alton Davis

Engineering Consultants Inc.

12 Old Mill Rd.

P.O. Box 223

West Ossipee, NH 03890

Phone (603) 539-8010

Fax (603) 539-4697

apdavis@locanet.com

Michael Davis

FERC-Division of Dam Safety and

Inspections

Chicago Regional Office

230 S. Dearborn St., Suite 3130

Chicago, IL 60604

Phone (312) 353-3787

Fax (312) 353-0109

michael.davis@ferc.fed.us

James Evans

FERC-Division of Dam Safety and

Inspections

888 1st Street NE, Rm. 62-73

Washington, DC 20426

Phone (202) 219-2740

Fax (202) 219-2731

james.evans@ferc.fed.us
Ellen Faulkner

Mead & Hunt, Inc.

4527 Kensington Court

Eau Claire, WI 54701

Phone (715) 831-9745

faulkner@meadhunt.com

Ed Fiegle

GA Dept. of Natural Resources

Safe Dams Program

4244 International Pkwy. Ste. 110

Atlanta, GA 30354

Phone (404) 362-2678

Fax (404) 362-2591

ed_fiegle@mail.dnr.state.ga.us

Danny Fread

622 Stone Road

Westminster, MD 21158

Phone (410) 857-0744

dlfread@starpower.net

Mike Gee

US Army Corps of Engineers

Hydrologic Engineering Center

609 Second Street

Davis, CA 95616-4587

Phone (530) 756-1104

Fax (530) 756-8250

Michael.Gee@hec01.usace.army.mil

Wayne Graham

Sediment and River Hyd. Group

Denver Federal Center (D-8540)

Building 67, Room 470

P.O. Box 25007

Denver, CO 80225

Phone (303) 445-2553

Fax (303) 445-6351

wgraham@do.usbr.gov
David Gutierrez

California Dept. of Water

P.O. Box 942836

Sacramento, CA 94236-0001

Phone (916) 445-3092

Fax (916) 227-4759

daveg@water.ca.gov

Terry Hampton

Gannett Fleming

Manager, Dams and Water Resources Engineering

8025 Excelsior Drive

Madison, WI 53717-1900

Phone (608) 836-1500

Fax: (608) 831-3337

thampton@gfnet.com

Greg Hanson

USDA-ARS

1301 N. Western St.

Stillwater, OK 74075

Phone (405) 624-4135 x. 224

Fax (405) 624-4136

ghanson@pswcrl.ars.usda.gov

Mikko Houkuna

Finnish Environment Institute

P.O. Box 140

FIN-00251 Helsinki, Finland

Phone 011 +358 9 160 3371

Fax 011 +358 9 160 2417

Mikko.houkuna@vyh.fi

Bill Irwin

USDA, NRCS

PO Box 2890

Washington, DC 20013

Phone (202) 720-5858

Fax (202) 720-0428

bill.irwin@usda.gov
Matt Lindon

Dam Safety

State Division of Water Rights

PO Box 146300

Salt Lake City, UT 84114-6300

Phone (801) 538-7372

Fax (801) 538-7476

mlindon@state.ut.us

Martin McCann, Jr.

Stanford University

Dept. of Civil and Env. Engineering

Building 540, Room 124

Stanford, CA 94305-4020

Phone (650) 723-1502

Fax (650) 723-8398

mccann@ce.stanford.edu

Mark Morris

HR Wallingford

Howberry Park

Wallingford

Oxon OX10 8BA, United Kingdom

Phone +44 (0) 1491 822283

Fax +44 (0) 1491 825539

mwm@hrwallingford.co.uk

David Moser

Decision Methodologies Division

Institute for Water Resources

7701 Telegraph Road

Alexandria, VA 22315

Phone (703) 428-8066

Fax (703) 428-8435

David.A.Moser@wrc01.usace.army.mil

Bruce Muller

Bureau of Reclamation

U. S. Department of Interior D-6600

P.O. Box 25007

Denver, CO 80225

Phone (303) 445-3238

bmuller@do.usbr.gov
John Ritchey

Dept. of Environmental Protection

Dam Safety Section

P.O. Box 419

Trenton, NJ 08625

Phone (609) 984-0859

Fax (609) 984-1908

jritchey@dep.state.nj.us

John Rutledge

Freese & Nichols, Inc.

4055 International Plaza, Suite 200

Fort Worth, TX 76109

Phone (817) 735-7284

Fax (817) 735-7491

jlr@freese.com

Derek Sakamoto

Power Supply, MEP, Stave Falls

Project

6911 Southpoint Dr (E04)

Burnaby, British Columbia

Canada V3N 4X8

Phone (604) 528-7812

Fax (604) 528-1946

Derek.Sakamoto@BCHydro.bc.ca

Nathan Snorteland

Bureau of Reclamation

U. S. Department of Interior D-8311

P.O. Box 25007

Denver, CO 80225

Phone (303) 445-2395

nsnorteland@do.usbr.gov
Darrel Temple

USDA-ARS

1301 N. Western St.

Stillwater, OK 74075

Phone (405) 624-4141 x. 231

Fax (405) 624-4142

dtemple@pswcrl.ars.usda.gov

Kjetil Arne Vaskinn

Statkraft Groner AS

Olav Tryggvasonsgate

P.O. Box 331

NO-7402 Trondheim, Norway

Phone 011 47 83058575

Fax 011 47 73990202

kav@trh.statkraftgroner.no

Charles Wagner

TVA- River Operations

Sr. Manager, Dam Safety

1101 Market Street LP 3K-C

Chattanooga, TN 37402-2801

Phone (423) 751-6970

Fax (423) 751-6376

cdwagner@tva.gov

Tony Wahl

Water Resources Research Lab

Bureau of Reclamation

U. S. Department of Interior D-8560

P.O. Box 25007

Denver, CO 80225-0007

Phone (303) 445-2155

Fax (303) 445-6324

twahl@do.usbr.gov

Eugene Zeizel

FEMA

500 C. Street S. W.

Washington, DC 20472

Phone (202) 646-2802

Fax (202) 646-3990

gene.zeizel@fema.gov