The National Dam 

Safety Program 

Research Needs Workshop:

Seepage through Embankment Dams
Preface 

One of the activities authorized by the Dam Safety and Security Act of 2002 is research 

to enhance the Nation’s ability to assure that adequate dam safety programs and practices 

are in place throughout the United States. The Act of 2002 states that the Director of the 

Federal Emergency Management Agency (FEMA), in cooperation with the National Dam 

Safety Review Board (Review Board), shall carry out a program of technical and archival 

research to develop and support: 

• improved techniques, historical experience, and equipment for rapid and effective 

dam construction, rehabilitation, and inspection; 

• devices for continued monitoring of the safety of dams; 

• development and maintenance of information resources systems needed to 

support managing the safety of dams; and 

• initiatives to guide the formulation of effective policy and advance improvements 

in dam safety engineering, security, and management. 

With the funding authorized by the Congress, the goal of the Review Board and the Dam 

Safety Research Work Group (Work Group) is to encourage research in those areas 

expected to make significant contributions to improving the safety and security of dams 

throughout the United States. The Work Group (formerly the Research Subcommittee of 

the Interagency Committee on Dam Safety) met initially in February 1998. To identify 

and prioritize research needs, the Subcommittee sponsored a workshop on Research 

Needs in Dam Safety in Washington D.C. in April 1999. Representatives of state and 

federal agencies, academia, and private industry attended the workshop. Seventeen broad 

area topics related to the research needs of the dam safety community were identified. 

To more fully develop the research needs identified, the Research Subcommittee 

subsequently sponsored a series of nine workshops. Each workshop addressed a broad 

research topic (listed below) identified in the initial workshop. Experts attending the 

workshops included international representatives as well as representatives of state, 

federal, and private organizations within the United States. 

• Impacts of Plants and Animals on Earthen Dams 

• Risk Assessment for Dams 

• Spillway Gates 

• Seepage through Embankment Dams 

• Embankment Dam Failure Analysis 

• Hydrologic Issues for Dams 

• Dam Spillways 

• Seismic Issues for Dams 

• Dam Outlet Works 

In April 2003, the Work Group developed a 5-year Strategic Plan that prioritizes research 

needs based on the results of the research workshops. The 5-year Strategic Plan ensures 

that priority will be given to those projects that demonstrate a high degree of 
collaboration and expertise, and the likelihood of producing products that will contribute 

to the safety of dams in the United States. As part of the Strategic Plan, the Work Group 

developed criteria for evaluating the research needs identified in the research workshops. 

Scoring criteria was broken down into three broad evaluation areas: value, technical 

scope, and product. The framework adopted by the Work Group involved the use of a 

“decision quadrant” to enable the National Dam Safety Program to move research along 

to produce easily developed, timely, and useful products in the near-term and to develop 

more difficult, but useful, research over a 5-year timeframe. The decision quadrant 

format also makes it possible to revisit research each year and to revise research priorities 

based on current needs and knowledge gained from ongoing research and other 

developments. 

Based on the research workshops, research topics have been proposed and pursued. 

Several topics have progressed to products of use to the dam safety community, such as 

technical manuals and guidelines. For future research, it is the goal of the Work Group to 

expand dam safety research to other institutions and professionals performing research in 

this field. 

The proceedings from the research workshops present a comprehensive and detailed 

discussion and analysis of the research topics addressed by the experts participating in the 

workshops. The participants at all of the research workshops are to be commended for 

their diligent and highly professional efforts on behalf of the National Dam Safety 

Program. 
Acknowledgments 

The National Dam Safety Program research needs workshop on Seepage through 

Embankment Dams was held on October 17-19, 2000, in Denver, Colorado. 

The Department of Homeland Security, Federal Emergency Management Agency, would 

like to acknowledge the contributions of the Association of State Dam Safety Officials 

and URS Corporation in organizing the workshop and developing these workshop 

proceedings. A complete list of workshop facilitators, presenters, and participants is 

included in the proceedings. 
TABLE OF CONTENTS
 

REPORT OF WORKSHOP ON ISSUES, SOLUTIONS AND RESEARCH NEEDS
 

RELATED TO SEEPAGE THROUGH EMBANKMENT DAMS 

vii	 List of Abbreviations 

1.0	 Introduction and Scope of Report
 

2.0	 Executive Summary
 

3.0	 Workshop Process
 

4.0	 Workshop Results for Individual Topics
 

4.1	 Topic 1 - Potential Seepage Problems and Solutions Associated with
 

Penetrations 4.1.1 through Embankment Dams (e.g., Outlet Works
 

Conduits)
 

4.1.1 State-of-the-Practice White Paper
 

4.1.2 State-of-the-Practice Refinement
 

4.1.3 Prioritization of Research and Development Ideas
 

4.1.4 Preliminary Research and Development Plans
 

4.2	 Topic 2 - Filter Design Criteria and Observed Performance (The Concepts of
 

No Erosion and Continuous Erosion Boundaries for Evaluating Filter
 

Compatibility) and Mechanism of Particle Movement and Progression of
 

Internal Erosion
 

4.2.1 State-of-the-Practice White Paper
 

4.2.2 State-of-the-Practice Refinement
 

4.2.3 Prioritization of Research and Development Ideas
 

4.2.4 Preliminary Research and Development Plans
 

4.3	 Topic 3 - Inspection of Dams for Detection of Seepage Problems, Failure
 

Modes Associated with Seepage and Internal Erosion, and Analysis of Risks
 

Associated with Seepage and Internal Erosion
 

4.3.1 State-of-the-Practice White Paper
 

4.3.2 State-of-the-Practice Refinement
 

4.3.3 Prioritization of Research and Development Ideas
 

4.3.4 Preliminary Research and Development Plans
 

4.4	 Topic 4 - Investigation of Seepage Problems/Concerns at Dams, Including the
 

Use of Geophysical Techniques; and Instrumentation and Measurements for
 

Evaluation of Seepage Performance
 

4.4.1	 State-of-the-Practice White Paper
 

4.4.2	 State-of-the-Practice Refinement
 

4.4.3	 Prioritization of Research and Development Ideas
 

I 
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4.4.4	 Preliminary Research and Development Plans
 

4.5	 Topic 5 - Remediation of Seepage Problems through Cutoff or Reduction of
 

Flow and Through Collection and Control of Seepage (Including the Use of
 

Geosynthetics)
 

4.5.1	 State-of-the-Practice White Paper
 

4.5.2	 State-of-the-Practice Refinement
 

4.5.3	 Prioritization of Research and Development Ideas
 

4.5.4	 Preliminary Research and Development Plans
 

4.6	 Topic 6 - Impacts of Aging of Seepage Control/Collection System
 

Components on Seepage Performance
 

4.6.1	 State-of-the-Practice White Paper
 

4.6.2	 State-of-the-Practice Refinement
 

4.6.3	 Prioritization of Research and Development Ideas
 

4.6.4	 Preliminary Research and Development Plans
 

5.0	 Overall Prioritization of Research and Development Ideas
 

6.0	 References
 

II 
TABLE OF CONTENTS
 

EXHIBITS 

Exhibit 3-1	 ASDSO Seepage Advisory Committee and FEMA Project Officer 

Exhibit 3-2	 Workshop Particip ants 

Exhibit 3-3	 Summary of Survey/Questionnaire Responses 

Exhibit 3-4	 Topics Selected for the Workshop 

Exhibit 3-5	 White Paper Authors and Titles 

Exhibit 4-1	 Prioritization of Research and Development Ideas – 

Workshop Topic 1 - Potential Seepage Problems and Solutions 

Associated with Penetrations through Embankment Dams (e.g. Outlet 

Works Conduits) 

Exhibit 4-2	 Research and Development Implementation Plan, R&D Topic 1A – 

Compilation of Case Histories of Seepage Incidents Related to 

Penetrations through Embankment Dams 

Exhibit 4-3	 Research and Development Implementation Plan, R&D Topic 1B – 

Assessing Technology to Detect Voids and Concentrated Seepage 

around Penetrations through Embankment Dams 

Exhibit 4-4	 Research and Development Implementation Plan, R&D Topic 1C – 

Develop Guidelines for Design of Filter Diaphragms Associated with 

Conduits through Embankment Dams 

Exhibit 4-5	 Research and Development Implementation Plan, R&D Topic 1D – 

Guidelines for Inspecting, Monitoring, and Detecting Seepage along 

Penetrations through Embankment Dams 

Exhibit 4-6	 Research and Development Implementation Plan, R&D Topic 1E – 

Development and Deployment of Guidelines for Slip-lining of Outlet 

Works Conduits 

Exhibit 4-7	 Prioritization of Research and Development Ideas – 

Workshop Topic 2 - Filter Design Criteria and Observed Performance 

(The Concepts of No Erosion And Continuous Erosion Boundaries for 

Evaluating Filter Compatibility) And Mechanism of Particle 

Movement And Progression of Internal Erosion 

Exhibit 4-8	 Research and Development Implementation Plan, R&D Topic 2A – 

Classification of Conditions Conducive to Hydraulic Fracturing and 

Cracking 

Exhibit 4-9	 Research and Development Implementation Plan, R&D Topic 2B – 

Develop State-of-the-Practice for Configurations, Dimensions, and 

Construction Methods for Filters and Drains 

Exhibit 4-10	 Research and Development Implementation Plan, R&D Topic 2C – 

Evaluate Mechanism of Piping and Failure in Glacial, Alluvial, and 

Fluvial Environments – Including Consideration of Internal Instability 

III 
TABLE OF CONTENTS
 

Exhibit 4-11 Research and Development Implementation Plan, R&D Topic 2D – 

Evaluation of Mechanical/Geochemical Degradation of Properties of 

Filter Materials, Including Cementation and the Ability to Sustain a 

Crack 

Exhibit 4-12 Research and Development Implementation Plan, R&D Topic 2E – 

Threshold Gradients for Initiating Piping in Cohesive Soils 

Exhibit 4-13 Prioritization of Research and Development Ideas – 

Workshop Topic 3 - Inspection of Dams for Detection of Seepage 

Problems, Failure Modes Associated with Seepage and Internal 

Erosion, and Analysis of Risks Associated with Seepage and Internal 

Erosion 

Exhibit 4-14 Research and Development Implementation Plan, R&D Topic 3A – 

Enhancement of Academic Programs and Professional Development 

Programs Related to Seepage Issues in Dam Design and Rehabilitation 

– “Certification” of Dam Designers, Dam Construction Inspectors, and 

Dam Operators 

Exhibit 4-15 Research and Development Implementation Plan, R&D Topic 3B – 

Develop Guidance for Dam Surveillance Plans Relative to Seepage 

Exhibit 4-16 Research and Development Implementation Plan, R&D Topic 3C – 

Improve Failure Time Estimates for Seepage-Related Failure Modes 

for Existing Dams 

Exhibit 4-17 Research and Development Implementation Plan, R&D Topic 3D – 

Identify Factors for Failure for a) “First Filling” (Including Normally 

Dry Dams/Detention Dams, Maximum Pool, etc.) and b) Long Term, 

for Each Seepage-Related Failure Mode 

Exhibit 4-18 Research and Development Implementation Plan, R&D Topic 3E – 

Expand the Database of Information on Seepage/Piping 

Failures/Incidents for Dams <15 meters in Height 

Exhibit 4-19 Prioritization of Research and Development Ideas – 

Workshop Topic 4 – Investigation of Seepage Problems/Concerns at 

Dams, Including the Use of Geophysical Techniques; and 

Instrumentation and Measurements for Evaluation of Seepage 

Performance 

Exhibit 4-20 Research and Development Implementation Plan, R&D Topic 4A – 

Technology Transfer of Geophysical Techniques for Seepage 

Monitoring 

Exhibit 4-21 Research and Development Implementation Plan, Topic 4B – Test 

Capabilities of Different Geophysical Methods on a Test Embankment 

Exhibit 4-22 Research and Development Implementation Plan, R&D Topic 4C – 

Cross-Discipline Technology Transfer for Investigative Techniques in 

Dams 

IV 
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Exhibit 4-23	 Research and Development Implementation Plan, R&D Topic 4D – 

Do/Can Instruments or Instrument Installations Cause Damage in 

Embankment Dams 

Exhibit 4-24	 Research and Development Implementation Plan, R&D Topic 4E – 

Assess Photo-Monitoring Techniques for Seepage (Infrared Imaging, 

Photo Interpretation, etc.) 

Exhibit 4-25	 Prioritization of Research and Development Ideas – 

Workshop Topic 5 – Remediation of Seepage Problems through 

Cutoff or Reduction of Flow and Through Collection and Control of 

Seepage (Including the Use of Geosynthetics) 

Exhibit 4-26	 Research and Development Implementation Plan, R&D Topic 5A – 

Review of Performance of Seepage Remediation Measures: a) 

Upstream Cutoff Only, b) Upstream Cutoff with Downstream 

Collection, and c) Downstream Collection Only 

Exhibit 4-27	 Research and Development Implementation Plan, R&D Topic 5B – 

Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications 

Exhibit 4-28	 Research and Development Implementation Plan, R&D Topic 5C – 

Evaluate the Performance of In-Place Geotextiles in Seepage Control 

Applications 

Exhibit 4-29	 Research and Development Implementation Plan, R&D Topic 5D – 

Develop Design Criteria for Drainage Pipe Openings and Surrounding 

Material to Prevent Plugging 

Exhibit 4-30	 Research and Development Implementation Plan, R&D Topic 5E – 

Testing of Fabric Clogging Under Steady State Flow Properly 

Simulating Conditions in Dam Applications 

Exhibit 4-31	 Prioritization of Research and Development Ideas – 

Workshop Topic 6 – Impacts of Aging of Seepage Control/Collection 

System Components on Seepage Performance 

Exhibit 4-32	 Research and Development Implementation Plan, R&D Topic 6A ­

Research and Develop Techniques for Remediation and Prevention of 

Contamination of Wells, Drains, and Instrumentation 

Exhibit 4-33	 Research and Development Implementation Plan, R&D Topic 6B – 

Criteria for Frequency of Inspections and Rehabilitation of Horizontal 

Drains, Including Removal of Carbonates 

Exhibit 4-34	 Research and Development Implementation Plan, R&D Topic 6C – 

Research Methods to Control and/or Remove Iron Bacteria Deposits 

from Wells and Drain Systems 

Exhibit 4-35	 Research and Development Implementation Plan, R&D Topic 6D – 

Develop Test Criteria and Procedures for Evaluating Site Vulnerability 

to Physical/Chemical/Biological Deterioration of Seepage Collection 

and Control Systems 

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Exhibit 5-1	 Ranking of Research/Development Ideas Based on Overall Votes at 

the Workshop 

Exhibit 5-2	 Ranking of Research/Development Ideas Based on Overall Votes after 

the Workshop 

Exhibit 5-3	 Ranking of Research/Development Ideas Based on Individual Scores 

for Potential Benefit – Scores Given By Participants after the 

Workshop 

Exhibit 5-4	 Ranking of Research/Development Ideas Based on Individual Scores 

for Probability of Success – Scores Given By Participants after the 

Workshop 

Exhibit 5-5	 Ranking of Research/Development Ideas Based on Individual Scores 

for Cost – Scores Given By Participants after the Workshop 

Exhibit 5-6	 Ranking of Research/Development Ideas Based on Combination of 

Individual Scores for Potential Benefit, Probability of Success, and 

Cost 

Exhibit 5-7	 Best Estimates of Implementation Costs for Research/Development 

Ideas Based on Input from Workshop Participants 

Exhibit 5-8	 Comparison and Combination of Overall Rankings and Combination 

of Individual Scores 

VI 
TABLE OF CONTENTS
 

ATTACHMENTS 

Attachment 1 Pre-Workshop Questionnaire 

Attachment 2 Additional Comments in Response to the Pre-Workshop Questionnaire 

Attachment 3 Survey Forms Sent to Participants after the Workshop 

Attachment 4 White Paper No. 1 - Potential Seepage Problems and Solutions 

Associated with Penetrations through Embankment Dams, Joseph R. 

Kula 

Attachment 5 White Paper No. 2 - The Internal Erosion and Piping Process, by 

Robin Fell and Mark Foster 

Attachment 6 White Paper No. 3 - Assessing The Risk of a Seepage-Related Dam 

Failure by Means of Failure Mode Identification, Risk Analysis, and 

Monitoring Practices, by William O. Engemoen 

Attachment 7 White Paper No. 4 - Investigation Of Seepage Problems/Concerns at 

Dams, Including Use of Geophysical Techniques; and Instrumentation 

and Measurements for Evaluation of Seepage Performance, by Charles 

D. Wagner 

Attachment 8 White Paper No. 5 - Remediation of Seepage Problems through Cutoff 

or Reduction of Flow and through Collection and Control of Seepage 

Including the Use of Geosynthetics, by James R. Talbot, Steve J. 

Poulos, and Ronald C. Hirschfeld 

Attachment 9 White Paper No. 6 - The Impacts of Aging of Seepage 

Control/Collection System Components on Seepage Performance, by 

Danny K. McCook 

Attachment 10 Participants’ Estimates of Implementation Costs for Research and 

Development Ideas 

Attachment 11 Reference List 

REPORT OF WORKSHOP ON ISSUES, 

SOLUTIONS AND RESEARCH NEEDS 

RELATED TO SEEPAGE THROUGH EMBANKMENT DAMS 

VII 
TABLE OF CONTENTS
 

LIST OF ABBREVIATIONS 

Abbreviation Definition 

ADS............................Advanced Drainage Systems
 

A/E.............................Architect/engineer
 

ASCE .........................American Society of Civil Engineers
 

ASDSO ......................Association of State Dam Safety Officials
 

ASTM.........................American Society for Testing of Materials
 

BC ..............................British Columbia
 

CANCOLD ................Canadian Committee on Large Dams
 

Cc ...............................Coefficient of curvature (for soil grain size curve)
 

CEA............................Canadian Electric Association
 

CFR............................Comprehensive Facility Review (USBR)
 

CMP...........................Corrugated metal pipe
 

CPTu...........................Piezocone penetration test
 

Cu ...............................Coefficient of uniformity (for soil grain size curve)
 

DEA ...........................U.S. Drug Enforcement Agency
 

FEMA.........................Federal Energy Management Agency
 

FERC..........................Federal Energy Regulatory Agency
 

GRI.............................Geosynthetics Research Institute
 

HDPE.........................High-density polyethylene
 

ICODS .......................Interagency Committee on Dam Safety
 

ICOLD .......................International Committee on Large Dams
 

IFA.............................International Fabrics Association
 

JPL .............................Jet Propulsion Laboratory
 

MS..............................Master of Science
 

NPDP .........................National Performance of Dams Program
 

NRCS.........................Natural Resources Conservation Service (formerly SCS)
 

NSF............................National Science Foundation
 

OSHA.........................Occupational Safety and Health Administration
 

PhD.............................Doctor of Philosophy
 

R&D...........................Research and development
 

SCS ............................Soil Conservation Service (now NRCS)
 

SPT.............................Standard penetration test
 

TADS .........................Training Aids for Dam Safety
 

TEC ............................Topographic Engineering Center
 

TVA ...........................Tennessee Valley Authority
 

UNSW........................University of New South Wales
 

USACE.......................U.S. Army Corps of Engineers
 

USBR.........................U.S. Bureau of Reclamation
 

USCOLD....................U.S. Committee on Large Dams (now USSD)
 

USGS .........................U.S. Geological Survey
 

USSD .........................United States Society on Dams (formerly USCOLD)
 

VIII 

1.0 INTRODUCTION

INTRODUCTION AND SCOPE OF REPORT 

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

Management Agency (FEMA) and administered by the Association of State Dam Safety 

Officials (ASDSO). This workshop was organized and facilitated by URS Corporation, under 

contract with ASDSO, and under the guidance of the ASDSO Seepage Advisory Committee. 

The product of the workshop is this written report, produced by URS and ASDSO, 

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 issues associated with seepage through embankments and their foundations. The 

objectives of the workshop and the resulting written report were to document: 

1.	 The state-of-practice, as opposed to state-of-the-art, concerning seepage and internal 

erosion of embankment dams and foundations; 

2.	 The short-term (immediate) and long-term research needs of the Federal and non-Federal 

dam safety communities with respect to this issue; and 

3.	 A recommended course of action for the Federal and non-Federal dam safety 

communities to address these needs based on priorities relating to potential benefit, 

probability of success, and cost. 

The workshop was held in Denver, Colorado, on October 17, 18, and 19, 2000. 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-of-the-practice in the field. 

IMPORTANCE OF THE TOPIC 

The importance of consideration of seepage through embankment dams is highlighted by 

some statistics from a recent research program at the University of New South Wales, 

Australia. Professor Robin Fell and two of his graduate students, Mark Foster and Matt 

Spannagle, reviewed records for more than 11,000 large (higher than 15 meter) embankment 

dams. They found: 

•	 136 or 1.2 percent of these dams had failed, with failure defined as an uncontrolled 

release of the reservoir; 

•	 of the failures, 59, or about 44 percent, were caused by seepage and piping; 

•	 another 1.5 percent of the dams were reported to have experienced some type of piping 

incident that did not lead to failure; and 

•	 although failure statistics appear to be better for modern dams (those constructed since 

1950), the failure rate is still about 0.5 percent, with seepage and piping still being a 

common failure mode, in fact the percentage of failures attributable to seepage and piping 

for the modern dams was 52 percent, higher that that for the pre-1950 dams. 

It should be noted that these statistics are based on the information reported in the available 

records, and it is certainly likely that there are seepage incidents, and possibly even failures, 

that have not been reported. 

These sobering statistics clearly indicate that improvement in the understanding of seepage 

and piping should be a significant concern of all modern dam engineers. 

1-1 

2.0 EXECUTIVE SUMMARY

2.0 EXECUTIVE SUMMARY 

A group of 35 individuals was assembled for a three-day workshop on Issues, Solutions, and 

Research Needs Related to Seepage Through Embankment Dams. The group consisted of 27 

invited experts, two facilitators, five members of the ASDSO Seepage Advisory Committee, 

and the FEMA Project Officer for the workshop. The workshop participants were selected to 

provide broad representation of individuals involved in the topic. Participants included 13 

representatives of six different U.S. federal agencies, four representatives from three different 

state dam safety agencies, 12 representatives of eight different consulting companies, three 

independent consultants, two university professors, and one representative of a hydropower 

organization. The group included individuals from 15 different U.S. states and two other 

countries (Canada and Australia). 

During the three days, the workshop participants addressed the following six topics: 

1.	 Potential seepage problems and solutions associated with penetrations through 

embankment dams (e.g., outlet works conduits). 

2.	 Filter design criteria and observed performance (the concepts of no erosion and 

continuous erosion boundaries for evaluating filter compatibility) and mechanism of 

particle movement and progression of internal erosion. 

3.	 Inspection of dams for detection of seepage problems, failure modes associated with 

seepage and internal erosion, and analysis of risks associated with seepage and internal 

erosion. 

4.	 Investigation of seepage problems/concerns at dams, including the use of geophysical 

techniques; and instrumentation and measurements for evaluation of seepage 

performance. 

5.	 Remediation of seepage problems through cutoff or reduction of flow and through 

collection and control of seepage (including the use of geosynthetics). 

6.	 Impacts of aging of seepage control/collection system components on seepage 

performance. 

These specific topics were selected based the results of a survey of the participants that was 

completed in advance of the workshop. 

Each topic was treated in the following manner: 

•	 A “strawman” state-of-the-practice white paper was prepared and presented by one or 

more of the invited experts; a written copy of the white paper was distributed to the 

participants in advance of the workshop. 

•	 The entire group was then led in a facilitated discussion of refinements, modifications, 

and clarifications to the state-of-the-practice. 

•	 The group developed a list of possible research and development ideas for the topic being 

considered. 

•	 The possible research and development ideas were prioritized by the group considering 

potential benefit, probability of success, and cost. 

•	 The top four or five research and development ideas for the topic were assigned to small 

work groups for development of preliminary implementation plans. 

2-1 
2.0 EXECUTIVE SUMMARY

•	 The small work groups reported back to the entire group on their preliminary 

implementation plans. 

The “strawmen” state-of-the-practice white papers are presented in Attachments 4 through 9 

of this report, and brief summaries of these papers are presented in Section 4. The 

discussions of the states-of-the-practice for the six topics are summarized in Section 4 of this 

report, and some of the more significant points from those discussions are presented later in 

this Executive Summary. All of the research and development ideas generated by the group 

for all six topics are presented in Section 4, and the preliminary implementation plans 

developed for the 29 leading ideas generated for all six topics are also presented in Section 4. 

In a closing session on the last day of the workshop and in surveys completed after the 

workshop, the participants provided input for an overall ranking of the leading research and 

development ideas for all six topics. The overall rankings were also based on consideration 

of potential benefit, probability of success, and cost. The overall rankings of the leading 

research and development ideas are discussed in detail in Section 5 and are summarized later 

in this Executive Summary. 

STATE-OF-THE-PRACTICE 

During the state-of-the-practice white paper presentations and the ensuing discussions, it 

became apparent that it is very difficult, if not impossible, to define a single state-of-thepractice for any of the topics being considered. The state-of-the-practice in the area of 

seepage through embankment dams varies from region-to-region and organization-toorganization. Consequently, much of the discussion centered on trying to develop consensus 

among the group of invited experts on what the state-of-the-practice should be for certain 

aspects of practice. All of the discussions on state-of-the-practice are documented in Section 

4, but some of the more significant results of the discussions, in the authors’ opinion, are the 

following, grouped according to the six topics addressed in the workshop: 

PROBLEMS AND SOLUTIONS ASSOCIATED WITH PENETRATIONS THROUGH 

EMBANKMENT DAMS 

1.	 There was a general, but not unanimous, consensus that sand (or sand and gravel) filter 

diaphragms around conduits are preferred over concrete cutoff collars for controlling 

seepage and piping along the sides of outlet works conduits. 

2.	 The existing NRCS/SCS conduit filter diaphragm design criteria were developed for 18 

to 48 inch diameter pipes. There are no widely available criteria for larger pipes. 

3.	 Grouting around conduits is not recommended as a sole solution for prevention of piping. 

Grouting will not likely provide 100 percent encapsulation of the conduit and seepage 

gradients in the “windows” in the grout may actually be higher than the initial gradients 

before grouting. Grouting can be used to fill or partially fill voids created by piping, to 

reduce future settlements, but filter diaphragms or other positive means must be used to 

prevent piping. 

4.	 Bare (unencased) corrugated metal outlet conduits should not be used for new 

construction or replacements in significant or high hazard dams. Although many existing 

dams include bare corrugated metal outlet conduits, their generally poor long-term 

performance argues strongly against their continued use. In addition, studies have shown 

that corrugated metal pipe outlet conduits are inferior to concrete pipe outlet conduits, 

when evaluated on a life-cycle-cost basis. 

2-2 
2.0 EXECUTIVE SUMMARY

5.	 There was a general, but not unanimous, consensus that the springline is the 

recommended minimum height for the top of a conduit cradle, if a cradle is used. 

6.	 There was consensus that permanently pressurized pipes through embankments should be 

either encased (e.g., in concrete) or placed within an outer conduit. 

FILTER DESIGN CRITERIA, OBSERVED PERFORMANCE, AND MECHANISM OF 

PARTICLE MOVEMENT AND PROGRESSION OF INTERNAL EROSION 

1.	 There has been some valuable recent research at the University of New South Wales 

extending previous work on filter design criteria to consideration of “continuous erosion 

boundaries” – the gradation boundaries between “filter” materials that allow some limited 

degree of particle movement but then stabilize and those that allow particles in the base 

material to move continuously. These continuous erosion boundaries should not be 

applied to design of new dams or designs of new dam rehabilitation features, for which 

the established filter design criteria should be used. However, the continuous erosion 

boundaries may be useful in evaluating the risks of piping in existing structures that were 

not designed or constructed strictly according to current filter criteria. 

2.	 At present there remains a lack of understanding of the mechanics of piping on the 

particle level. Such an understanding would help to tie laboratory and field observations 

together into a common understanding of the piping phenomenon. 

3.	 Filters constructed of soil materials should not be over-compacted. In current practice soil 

filter materials are often compacted to a greater degree than necessary. Over-compaction 

of filter materials can result in reduced permeability and increased potential for the filter 

materials to be capable of holding an open crack. Soil filter materials should be 

compacted only to the degree necessary for strength and settlement requirements. It was 

the consensus of the participants that 90 percent of modified Proctor compaction (or 65 to 

70 percent relative density) would be sufficient in almost all cases. 

4.	 After extensive discussion, a general consensus was reached that piping can often be an 

episodic phenomenon. That is, piping with muddy or turbid seepage may occur for some 

period of time, after which the pipe collapses or stabilizes for some period of time, only 

to be followed later by another episode of active piping. It may take many repeated 

episodes of piping before the phenomenon progresses to failure of the dam. The 

importance of this understanding of the piping phenomenon is that the observation of 

clear seepage does not necessarily mean that there is no piping problem. It could simply 

be the case that the observation was made during a period of no active piping. Piping 

should be considered a possibility for any case of uncontrolled seepage. Inspectors should 

also look for evidence of past piping episodes (e.g., silt or sand deposits at or downstream 

of seepage exit points). 

5.	 It was a group consensus that the effectiveness of “crack fillers” or “crack-stoppers” is 

unknown – they may or may not be effective. 

6.	 For design of new structures, it is the state-of-the-practice to assume that fine-grained 

embankment materials crack. 

INSPECTION, FAILURE MODES, AND ANALYSIS OF RISK 

1.	 There are currently two different approaches to quantitative risk analysis for seepage 

through embankment dams. They can be broadly categorized as 1) the statistical-based 

method, and 2) the degree-of-belief-based method. The general consensus is that the 

2-3 
2.0 EXECUTIVE SUMMARY

degree-of-belief-based method is presently considered to be the state-of-the-practice for 

risk analysis for seepage through dams, and this will probably remain so for the 

foreseeable future. At the workshop, the BC Hydro representative requested that it be 

specifically noted that his organization does not presently support the use of detailed 

quantitative risk analysis (with either approach) for dam seepage issues. The reader is 

referred to the report of the March 2000, Logan, Utah Workshop on Risk Analysis for 

Dams for a more extensive treatment of this topic. The results of that workshop are 

presented in another report in FEMA’s National Dam Safety Program Act Report Series. 

2.	 The qualifications, training, and experience of dam inspectors and operators are highly 

variable in the United States. Yet the qualifications, training, and experience of these 

individuals are critical to professional judgments that must be made in operating and 

maintaining a dam. 

INVESTIGATION OF SEEPAGE PROBLEMS/CONCERNS 

1.	 Although actual investigation practices vary widely, it was the consensus of the 

workshop participants that the recommended state-of-the-practice should be that drilling 

should not be done in the core of an existing embankment dam unless absolutely 

necessary, and then only with carefully planned precautions and dry drilling (e.g., auger) 

methods. The risk of hydraulic fracturing is too great to support drilling in the core 

without appropriate justification. 

2.	 It was the consensus of the workshop participants that drilling or test pitting should not 

be done at the downstream toe of a dam with water stored in the reservoir, without 

contingency plans and stockpiling of weighted filter materials (e.g., sand and gravel) to 

be used in the event of a seepage incident. It is also essential that such explorations be 

completed with the on-site presence of experienced personnel with the knowledge to 

react appropriately to any seepage incidents that may occur. 

3.	 It was the consensus of the workshop participants that they generally advised against 

installing piezometers in an embankment core, unless there were very compelling reasons 

for the instruments. The workshop participants felt that, in most cases, piezometers in the 

core do not provide significant additional understanding of the performance of the dam 

beyond that which can be obtained from piezometers in the upstream and downstream 

shells, which are much safer locations for the instruments. 

4.	 Piezometers are tools whose careful installation and subsequent data interpretation, in 

conjunction with other investigative techniques, may provide valuable information in 

diagnosing seepage conditions. However, the limitations of what the piezometers record 

must be recognized, and the piezometer data must be used in conjunction with other 

information (e.g., seepage rates, seepage locations, etc.) to correctly diagnose seepage 

conditions. Since piping channels in embankments are often relatively long, narrow 

features, it is not likely that piezometers will be located at exactly the correct locations to 

provide direct data regarding the piping phenomenon. 

5.	 The dam engineering profession in general remains skeptical or cautious regarding the 

effectiveness of geophysical techniques for investigation of seepage problems, possibly 

because the methods are perceived as not proven sufficiently to establish a high degree of 

confidence. There have been some successful applications of geophysical methods, and 

some of the methods show promise. Successful applications will likely increase in the 

future through research efforts such as those of the Canadian Electric Association. 

2-4 
2.0 EXECUTIVE SUMMARY

REMEDIATION OF SEEPAGE PROBLEMS 

1.	 Although in current practice cutoffs are being used as a sole solution for seepage/piping 

problems, the consensus of the workshop group supports the position that cutoffs should 

always be used together with adequate downstream collection and control systems. What 

constitutes an adequate collection and control system for use in combination with a cutoff 

is subject to engineering judgment. 

2.	 Seepage collection pipes in blanket drains under downstream shells of dams are being 

used – the potential disadvantages (collapse, plugging, drilling into them) of this 

application should be recognized when they are used. 

3.	 The current practice for the use of geotextiles in seepage collection systems varies widely 

among organizations and practitioners involved in dam engineering. After much 

discussion, it was the consensus of the group that a) geotextiles should not be used in 

locations that are both critical to safety and inaccessible for replacement, and b) 

geotextiles can be used in locations that are critical for safety but accessible for 

replacement. However, in the second case the engineer must assess the potential hazard 

posed by failure of the geotextile and the time available to respond and repair or replace 

the geotextile. This position may change in the future based on development of data on 

long-term, in-place performance of geotextiles in dam applications. 

4.	 Several participants related experience with poor performance with the rate of inflow into 

slotted or perforated pipes when the sizes of the openings in the pipes and the gradations 

of the surrounding soil filters were designed according to currently recommended 

guidelines. It appears that the soil particles can partially to substantially plug the 

openings, resulting in limited inflow. This appears to be less of a problem with pipes 

surrounded by gravel than it is for pipes surrounded by sand or sand/gravel mixtures. 

5.	 It was the consensus of the workshop participants that the recommended state-of-thepractice for application of pressure grouting (cement or chemical) in seepage remediation 

should be that a) high-pressure grouting should never be used in the embankment core 

and b) high-pressure grouting is acceptable in rock foundations, with appropriate care. 

However, it was the experience of the group that grouting was often not a permanent 

solution. 

IMPACTS OF AGING OF SYSTEM COMPONENTS 

1.	 Regular and thorough maintenance is essential to the continued effectiveness of relief 

wells. 

2.	 There are reported cases of long-term deterioration of grout curtains. 

3.	 There is some anecdotal information in the profession indicating that some filters may 

have altered over time so that they could hold an open crack after alteration. 

4.	 It was the consensus of the group that corrugated metal pipes should not be used for drain 

pipes in seepage collection systems, because of their record of deterioration. 

RESEARCH AND DEVELOPMENT IDEAS 

Before the research and development ideas were ranked, some of the 29 separate ideas 

generated for the six different topics addressed in the workshop were combined to reduce the 

total number of research and development (R&D) topics to 26. 

2-5 
2.0 EXECUTIVE SUMMARY

Based on all of the input from the participants, it is the authors opinion that the following 

four R&D topics were the leading research and development ideas identified in the 

workshop: 

1.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams (R&D Topic 3E &1A) 

2.	 Enhance Academic Programs and Professional Development and Training Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators (R&D Topic 3A) 

3.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains (R&D Topic 2B) 

4.	 Develop Guidelines for Design of Filter Diaphragms Associated With Conduits Through 

Embankment Dams (R&D Topic 1C) 

These four R&D topics were ranked in the top 10 in all three overall ranking methods used to 

prioritize the research and development ideas and they were ranked 1 through 4 when the 

rankings from the three different methods were averaged, as discussed in detail in Section 5. 

Consequently, it is the authors’ opinion that these four R&D topics are the highest priorities 

for implementation. The R&D topic designations given in parentheses after the research and 

development ideas are the designations assigned during the workshop and used in Sections 4 

and 5 of this report. The preliminary implementation plans for the R&D topics are presented 

in Section 4 using those designations. 

After the four R&D topics listed above, the remaining six ideas in the top 10, based on the 

average of the rankings from the three different methods, were: 

1.	 Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging (R&D Topic 5D) 

2.	 Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including 

Monitoring and Detecting Seepage Along Penetrations Through Embankment Dams 

(R&D Topic 3B & 1D) 

3.	 Technology Transfer of Geophysical Techniques for Seepage Monitoring (R&D Topic 

4A) 

4.	 Evaluate Mechanism Of Piping And Failure In Glacial, Alluvial, And Fluvial 

Environments – Including Consideration Of Internal Instability, and Including 

Consideration of Threshold Gradients for Initiating Piping in Cohesive Soils (R&D Topic 

2C & 2E) 

5.	 Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications (R&D Topic 5B) 

6.	 Assess Technology to Detect Voids and Concentrated Seepage Around Penetrations 

Through Embankment Dams (R&D Topic 1B) 

R&D Topic 5D was ranked in the top 10 according to all three methods used (Ranks of 10, 7, 

and 8), and the other five R&D topics were ranked in the top 10 in two out of the three 

methods used. Consequently, it is the authors’ opinion that these six R&D topics should be 

considered high priority, but not as high as the top four ideas listed above. 

2-6 
2.0 EXECUTIVE SUMMARY

Other R&D topics that received a top 10 ranking in at least one of the three overall ranking 

methods used to prioritize the ideas were: 

1.	 Evaluate the Performance of In-Place Geotextiles in Seepage Control Applications (R&D 

Topic 5C) 

2.	 Testing of Fabric Clogging Under Steady State Flow Properly Simulating Conditions in 

Dam Applications (R&D Topic 5E) 

3.	 Classification of Conditions Conducive to Hydraulic Fracturing and Cracking (R&D 

Topic 2A) 

4.	 Review of Performance of Seepage Remediation Measures: a) Upstream Cutoff Only, b) 

Upstream Cutoff With Downstream Collection, and c) Downstream Collection Only 

(R&D Topic 5A) 

5.	 Research Methods to Control and/or Remove Iron Bacteria Deposits From Wells and 

Drain Systems (R&D Topic 6C) 

6.	 Development and Deployment of Guidelines for Slip-lining of Outlet Works Conduits 

(R&D Topic 1E) 

These R&D topics deserve some consideration for implementation, but at a lower priority 

than the top 10 ideas listed above. 

The remaining 10 R&D topics had significantly less support in the overall rankings of the 

ideas, with none of them ranked in the top 10 in any of the three ranking processes used. 

Section 5 of the report provides some thoughts for possible further combinations of the 

identified R&D topics. 

The participants were also asked to provide estimates of the cost of implementing each of the 

research and development ideas, if they felt qualified to do so. Unfortunately, only 11 

participants felt qualified to provide cost information and the estimates provided varied 

widely. Consequently, the results are not particularly helpful, but they are provided in 

Section 5 and Attachment 10 of this report for completeness. 

In reviewing the leading R&D topics, it is interesting to note that very few of them involve 

basic laboratory or field research. In fact, only R&D Topics 2E, 5D, 1B, 5E, 2A, and 6C 

include such basic research, and none of the top four topics include basic research. Rather, 

most of the R&D topics involve collecting or compiling available information and 

developing guidelines for dissemination to practitioners. In the authors’ opinion, this reflects 

a sense among the workshop participants that the overall topic of seepage through 

embankment dams is relatively mature, and that most seepage problems are the result of 

misuse of available information or lack of knowledge of available information by some 

practitioners. It also seems to reflect a feeling that the information on the overall topic is too 

dispersed for the profession to make the best use of lessons-learned from past performance, 

and that compilation of information into more readily available sources would be beneficial. 

CLOSURE 

The workshop provided a forum for lively and open discussion of important topics related to 

seepage through embankment dams. The discussions resulted in consensus among the invited 

experts on recommendations regarding a number of important, but controversial, aspects of 

the state-of-the-practice. Through the workshop effort, a relatively long list of possible 

research and development ideas was compiled, and that list was prioritized to identify what 

2-7 
2.0 EXECUTIVE SUMMARY

the group believed were the leading ideas for advancement of the state-of-the-practice. The 

group also developed preliminary implementation plans for 29 research and development 

ideas, and those plans are presented in Section 4 of this report. 

2-8 

3.0 WORKSHOP PROCESS

WORKSHOP PROCESS 

This discussion of the workshop process is divided into the following three topics: 

•	 Selection of Workshop Participants 

•	 Selection of Workshop Topics 

•	 Workshop Mechanics 

SELECTION OF WORKSHOP PARTICIPANTS 

The workshop participants were selected jointly by URS and the ASDSO Seepage Advisory 

Committee. Members of the ASDSO Seepage Advisory Committee and the FEMA Project 

Officer for the workshop are listed in Exhibit 3-1. 

Participation in the workshop was by invitation only, and the workshop was not publicly 

advertised. The goal in selecting participants for invitation to the workshop was to have 

broad representation of public and private organizations and individuals involved in dam 

safety seepage issues. To keep the workshop to a manageable size, the number of invited 

experts was limited to 27. When combined with the two URS facilitators, five members of 

the ASDSO Seepage Advisory Committee, and the FEMA Project Officer, the total 

workshop group consisted of 35 individuals. The workshop participants are listed in Exhibit 

3-2. 

The workshop participants were a diverse group, including: 

•	 13 representatives of six different U.S. federal agencies; 

•	 4 representatives from three different state dam safety agencies; 

•	 12 representatives of eight different consulting companies; 

•	 3 independent consultants; 

•	 2 university professors; 

•	 1 representative of a hydropower organization; and 

•	 Individuals from 15 different U.S. states and two other countries (Canada and Australia). 

SELECTION OF WORKSHOP TOPICS 

To accomplish as much as possible within the relatively short duration of the workshop, it 

was judged necessary to pre-select specific topics to be addressed. In pre-selecting the topics, 

it was desired to accomplish two at least partially conflicting goals to the maximum extent 

possible. Those goals were: 

•	 To address what were judged to be the most important and pressing topics regarding 

seepage through embankment dams. 

•	 To cover as much breadth as possible of topics related to seepage through embankment 

dams. 

Considering the three-day duration of the workshop, it was judged that six topics, each being 

addressed for about one-half day, was the maximum number of topics that could be 

addressed in any reasonable depth. It was decided to use a survey of participants, and a few 

3-1 
3.0 WORKSHOP PROCESS

other selected experts who were not available to participate, to develop the topics for the 

workshop. 

URS worked with the ASDSO Seepage Advisory Committee to develop a list of 14 potential 

topics for the workshop. To narrow this list to six topics for the workshop, a 

survey/questionnaire was sent to potential participants. The questionnaire asked each 

individual to select up to eight topics that they thought should be the highest priority for 

consideration at the workshop. In the questionnaire each individual was also asked to list any 

other important topics that he or she believed were not addressed by the 14 listed topics. A 

copy of the questionnaire that was sent to the participants is included as Attachment 1 of this 

report. 

Twenty-seven individuals responded to the questionnaire and the results of their “votes” are 

presented in Exhibit 3-3. The “additional comments” received from the respondents are 

compiled in Attachment 2. 

From a review of the responses, six topics were developed for coverage at the workshop. The 

six selected topics are presented in Exhibit 3-4. As noted above, the six topics were 

developed to meet the two stated objectives: 1) provide coverage of the highest priority 

items identified in the responses; and 2) provide as much breadth of coverage as possible 

within the three-day scope of the workshop. 

WORKSHOP MECHANICS 

The workshop was conducted over three full days, which were divided into six half-day 

periods, each addressing one of the six selected topics. The agenda for each of these six halfdays was as follows: 

•	 One-half to three-quarter hour - Presentation of a “State-of-the-Practice” white paper, 

prepared in advance by one of the participants. 

•	 One-half to three-quarter hour – Facilitated discussion of the white paper by all 

participants, to identify revisions, modifications, and refinements to the “State-of-thePractice” presented by the white paper author. 

•	 One hour – Identification and prioritization of possible research and development ideas 

that could advance the state-of-the-practice. 

•	 One hour – Development of preliminary implementation plans for the highest priority 

research and development ideas. 

At the end of the third day, approximately 1-1/2 hours were devoted to comparing and 

prioritizing all of the “high-priority” research and development ideas that were developed for 

the six different topics. After the workshop had been adjourned, surveys were sent to all 

participants to gather additional input for the prioritization of the research and development 

ideas. 

The discussions, research and development ideas, and preliminary research and development 

plans were captured on flipcharts during the workshop, for compilation in this report. 

Some of the specific aspects of the workshop mechanics are discussed further below. 

3-2 
3.0 WORKSHOP PROCESS

WHITE PAPERS 

After the six topics were selected, some of the workshop participants were invited to prepare 

“white papers” to provide documents that would be “strawmen” for definitions of state-ofthe-practice relative to the six topics. The white paper authors were also invited to put 

forward suggestions for research and development ideas related to their topics, if they so 

desired, but their primary responsibility was to develop “strawmen” for the definition of the 

state-of-the-practice. 

The authors all prepared their white papers for distribution to the participants in advance of 

the workshop. They are owed a debt of gratitude for their contribution to the success of the 

workshop. The white paper authors are all listed in the Exhibit 3-5, and the individual white 

papers are presented in Section 4 of this report. 

DISCUSSIONS OF WHITE PAPERS 

The revisions, modifications, and refinements to the white papers were captured on flipcharts 

during the workshop and are reported in Section 4 of this report. One thing that became 

apparent during the discussions was that “practice” in this field varies significantly from one 

state or region to another and from one agency or organization to another. This makes it very 

difficult to define a singular state-of-the-practice. Consequently, much of the discussion of 

the white papers and the state-of-the-practice consisted of identifying some of the more 

significant differences in practice and attempting to reach a consensus among the group on 

what the state-of-the-practice should be or to identify research and development required to 

determine the appropriate state-of-the-practice. This will become apparent in the discussions 

in Section 4. 

IDENTIFICATION AND PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

For each topic, the potential research and development ideas were compiled from a 

brainstorming process with the entire group. The ideas were listed on flipcharts visible to all 

participants. The research and development ideas for each topic were then prioritized in a 

simple voting process, in which each participant was given a fixed number of “stick-on dots” 

that they could place next to the individual ideas. The number of dots (votes) given to each 

participant was typically about N/3, where N is the total number of research and development 

ideas being considered. The participants were allowed to cast their votes however they saw 

fit; there were no limits on the number of votes that a participant could cast for a particular 

idea. A participant could cast all of his or her votes for one research and development idea, if 

he or she thought it was a high enough priority. Before they cast their votes, the participants 

were instructed to balance the following three criteria in prioritizing the research and 

development ideas: 1) potential benefit, 2) probability of success, and 3) cost. 

All of the research and development ideas and the results of the prioritizations for all six 

topics are presented in Section 4 of this report. 

PRELIMINARY IMPLEMENTATION PLANS 

After the prioritization was completed, the top four or five ideas for each topic were selected 

for development of preliminary implementation plans. The workshop participants were 

divided into small work groups (about 7 or 8 people per group), and each work group was 

assigned the responsibility to develop a preliminary implementation plan for one research 

and development idea. The small groups worked independently for a period of time, and then 

3-3 
3.0 WORKSHOP PROCESS

all of the workshop participants reconvened to hear and discuss reports from all of the small 

work groups. The composition of the small work groups was shuffled for each topic, so that 

the same people were not working together all of the time. One workshop participant was 

assigned the responsibility to serve as the leader of each work group, and this responsibility 

was rotated among almost all participants over the course of the three days. 

The implementation plans developed by the work groups are presented in Section 4 of this 

report. 

OVERALL PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The initial overall prioritization of the 29 leading research and development ideas resulting 

from consideration of the six different topics was completed at the workshop using the same 

voting technique used for prioritizations for the six different topics. Again, participants were 

asked to consider the balance of potential benefit, probability of success, and cost in casting 

their prioritization votes, and, as before, the participants could cast their allotted votes in any 

way they saw fit. Before the prioritization votes were taken, some of the research and 

development ideas were combined, resulting in a reduction in the total number of ideas from 

29 to 26. 

At the end of the workshop, the participants suggested that they would like to have the 

opportunity to cast their prioritization votes again, after they had some time to think further 

about the information discussed at the workshop. Consequently, a survey was sent to all 

workshop participants asking them to provide further input for the prioritization process. The 

implementation plans developed by the small work groups were sent to the participants with 

the survey. The survey was structured so that 1) the participants repeated the voting process 

completed at the end of the workshop, casting votes considering the balance of potential 

benefit, probability of success, and cost, and 2) the participants provided separate scores for 

each of the three criteria for each of the research and development ideas. The participants 

were also asked to provide estimates of the cost of implementing each of the research and 

development ideas, if they felt qualified to do so. Unfortunately, only 11 participants felt 

qualified to provide cost information and the estimates provided varied widely. 

Consequently, the results are not particularly helpful, but they are provided in Section 5 and 

Attachment 10 of this report for completeness. The survey forms sent to the participants are 

presented in Attachment 3. 

The prioritization of the 26 leading research and development ideas is discussed in detail in 

Section 5 of this report. 

3-4 
3.0 WORKSHOP PROCESS

EXHIBIT 3-1 

ASDSO SEEPAGE ADVISORY COMMITTEE 

AND FEMA PROJECT OFFICER 

ASDSO SEEPAGE ADVISORY COMMITTEE 

Organization/Affiliation Name Address Phone/Fax E-mail Address 

Nevada Dam Safety Jason King, P.E. 

West Virginia Dam Safety Brian Long 

Montana Dam Safety Michele Lemieux 

Piedmont Geotechnical Karl Myers 

Consultants 

U.S. Army Corps of Engineers Yvonne Gibbons 

U.S. Bureau of Reclamation Chuck Redlinger 

ASDSO Lori Spragens 

Chief of Appropriations 

NV Division of Water Resources 

122 W. Nye Lane 

Carson City, NV 89706 

WV Office of Water Resources 

Dam Safety 

1201 Greenbrier Street 

Charleston, WV 25311-1088 

MT Dam Safety Program 

P.O. Box 201601 

48 N. Last Chance Gulch 

Helena, MT 59620-1601 

Piedmont Geotechnical Consultants 

P.O. Box 1997 

Roswell, GA 30077 

U.S. Army Corps of Engineers 

201 N. Third Avenue 

Walla Walla, WA 99362 

U.S. Bureau of Reclamation (D-6600) 

P.O. Box 25007 

Denver, CO 80225-0007 

Association of State Dam Safety Officials 

450 Old Vine Street, 2nd Floor 

Lexington, KY 40507 

FEMA PROJECT OFFICER
 

P: 775-687-4381

800-992-0900 

x4381 

F: 775-687-6972 

P: 304-558-0320 

F: 304-558-5905 

P: 406-444-6613 

F: 406-444-0533 

P: 770-752-9205 

Ext. 228 

F: 770-752-0890 

P: 509-527-7618 

F: 509-527-7811 

P: 303-445-2768 

F: 303-445-6463 

P: 859-257-5140 

F: 859-323-1958 

jking@ndwr.state.nv.us 

blong@mail.dep.state.wv.us 

mlemieux@state.mt.us 

kmyers@pgci.com 

Yvonne.R.Gibbons@nww01.usa 

ce.army.mil 

credlinger@do.usbr.gov 

lspragens@damsafety.org 

Organization/Affiliation Name Address Phone/Fax E-mail Address 

Federal Emergency Management 

Agency (FEMA) 

Eugene Zeizel FEMA 

MT-NDSP 

500 C Street, SW, Room 416 

P: 202-646-2802 gene.zeizel@fema.gov 

Washington, DC 20472 

3-5 
3.0 WORKSHOP PROCESS

EXHIBIT 3-2
 

WORKSHOP PARTICIPANTS
 

Organization/Affiliation Name Address Phone / Fax E-mail Address 

U.S. Bureau of Reclamation Bill Engemoen Geotechnical Engineering Group 2 (D8312) P: 303-445-2960 bengemoen@do.usbr.gov 

U.S. Bureau of Reclamation F: 303-445-6472 

P.O. Box 25007 

Denver, CO 80225-0007 

U.S. Bureau of Reclamation Tom Lippert Earth Sciences and Research Lab (D8340) P: 303-445-2330 tlippert@do.usbr.gov 

U.S. Bureau of Reclamation F: 303-445-6341 

P.O. Box 25007 

Denver, CO 80225-0007 

U.S. Bureau of Reclamation John Cyganiewicz U.S. Bureau of Reclamation P: 303-445-3025 jcyganiewicz@do.usbr.gov 

P.O. Box 25007 (D-8311) F: 303-445-6472 

Denver, CO 80225 

Federal Energy Regulatory James Evans Federal Energy Regulatory Commission P: 202-219-2740 james.evans@ferc.fed.us 

Commission, Washington, DC Division Dam Safety and Inspections F: 202-219-2731 

888 First Street, NE, Room 62-63 

Washington, DC 20426 

Federal Energy Regulatory Richard Deubert Federal Energy Regulatory Commission P: 212-273-5933 richard.deubert@ferc.fed.us 

Commission, New York New York Regional Office 

19 West 34th Street, Suite 400 

F: 212-631-8124 

New York, NY 10001 

Federal Energy Regulatory Wayne King Federal Energy Regulatory Commission P: 770-452-3775 wayne.king@ferc.fed.us 

Commission, Atlanta Atlanta Regional Office F: 770-452-2366 

Parkridge 85 North 

3125 Presidential Parkway, Suite 300 

Atlanta GA 30340 

Tennessee Valley Authority Charles Wagner Tennessee Valley Authority P: 423-751-6970 cdwagner@tva.gov 

1101 Market Street, LP 1H-C F: 423-751-4407 

Chattanooga, TN 37402 

National Resources Conservation Danny McCook Soil Mechanics Laboratory P: 817-509-3201 dmccook@ftw.nrcs.usda.gov 

Service Natural Resources Conservation Service F: 817-509-3209 

P.O. Box 6567 

Fort Worth, TX 76115 

3-6 
3.0 WORKSHOP PROCESS

EXHIBIT 3-2
 

WORKSHOP PARTICIPANTS
 

-CONTINUED-
 

Organization/Affiliation Name Address Phone / Fax E-mail Address 

U.S. Army Corps of Engineers, South James Demby South Atlantic Division, Corps of Engineers P: 404-562-5111 james.e.dembyj@usace.army.mil 

Atlantic Division 60 Forsyth Street, S.W. F: 404-562-5122 

Room 9M15 

Atlanta, GA 30303-5111 

U.S. Army Corps of Engineers, Kansas Ray Dridge U.S. Army Corps of Engineers, Kansas City P: 816-983-3691 raymond.g.dridge@usace.army.mil 

City District District 

601 East 12th Street, room 816 

F: 816-426-5462 

Kansas City, MO 64106 

BC Hydro Ken Lum BC Hydro P: 604-528-2406 ken.lum@bchydro.com 

6911 Southpoint Drive F: 604-528-8133 

Burnaby, BC V3N 4X8 

CANADA 

URS Corporation Daniel Johnson URS Corporation P: 303-740-2689 dan_johnson@urscorp.com 

8181 East Tufts Avenue F: 303-694-3646 

Denver, CO 80237 

URS Corporation Joseph Kula URS Corporation P: 301-258-9780 joseph_kula@urscorp.com 

200 Orchard Ridge Drive, Suite 101 F: 301-869-8728 

Gaithersburg, MD 20878 

Schnabel Engineering Ray Martin Schnabel Engineering Associates 

114 North Railroad Avenue 

P: 804-798-0081 

F: 804-798-0048 

rmartin@schnabel-eng.com 

Ashland, VA 23005-1517 

GEI Consultants James Talbot GEI Consultants, Inc. P: 410-586-8772 jtalbot@mindspring.com 

1301 Wagner Street F: 301-494-3824 

Saint Leonard, MD 20685 

GEI Consultants Steve Poulos GEI Consultants, Inc. P: 781-721-4075 spoulos@geiconsultants.com 

1021 Main Street F: 781-721-4073 

Winchester, MA 01890-1970 

Gannett Fleming David Wilson Gannett Fleming Inc. P: 717-763-7211 dwilson@gfnet.com 

P.O. Box 67100 ext. 2448 

Harrisburg, PA 17106 F: 717-763-1808 

3-7 
3.0 WORKSHOP PROCESS

EXHIBIT 3-2
 

WORKSHOP PARTICIPANTS
 

-CONTINUED-
 

Organization/Affiliation Name Address Phone / Fax E-mail Address 

Golder Associates Richard Humphries Golder Associates Inc. P: 770-496-1893 rhumphries@golder.com 

3730 Chamblee Tucker Road F: 770-934-9476 

Atlanta, GA 30341 

GZA GeoEnvironmental William Hover GZA GeoEnironmental Inc. P: 617-630-6258 whover@gza.com 

320 Needham Street F: 617-965-7769 

Newton Upper Falls, MA 02464-1594 

ESA Consultants Debora Miller ESA Consultants, Inc. P: 970-484-3611 dmiller@esacorp.com 

2637 Midpoint Drive, Suite F F: 970-484-4118 

Fort Collins, CO 80525 

Alton P. Davis, Jr. Alton Davis 12 Old Mill Rd. P: 603-539-8010 altondavisjr@nh.adelphia.net 

Engineering Consultant P.O. Box 223 F: 603-539-4697 

West Ossipee, NH 03890 

Independent Consultant Steven Vick 42 Holmes Gulch Way P: 303-838-1443 sgvick@uswestmail.net 

Bailey, CO 80421 F: 303-838-1443 

Independent Consultant Ronald Hirschfeld 47 Emerson Road P: 781-729-8748 rhirsch@mediaone.net 

(formerly GEI) Winchester, MA 01890-3407 F: N/A 

Utah State University Loren Anderson Civil & Environmental Engineering P: 435-797-2938 loren@lab.cee.usu.edu 

Utah State University F: 435-797-1185 

Logan, UT 84322-4110 

University of New South Wales Robin Fell School of Civil and Environmental P: 612-9385- r.fell@unsw.edu.au 

and Independent Consultant Engineering 5035 

University of New South Wales F: 612-9385-

Sydney, AUSTRALIA 2052 6139 

State of Colorado Garrett Jackson Colorado Division of Water Resources P: 719-542-3368 garrett.jackson@state.co.us 

310 East Abriendo, Suite B F: 719-544-0800 

Pueblo, CO 81004 

State of Colorado Dennis Miller Colorado Division of Water Resources P: 970-352-8712 dennis.miller@state.co.us 

810 9th Street, 2nd Floor F: 970-392-1816 

Greeley, CO 80631 

3-8 
3.0 WORKSHOP PROCESS

EXHIBIT 3-2
 

WORKSHOP PARTICIPANTS
 

-CONTINUED-
 

Organization/Affiliation Name Address Phone / Fax E-mail Address 

URS Corporation John France(1) URS Corporation P: 303-740-3812 john_france@urscorp.com 

8181 East Tufts Avenue F: 303-694-3946 

Less Osborne(1) 

Denver, CO 80237 

URS Corporation URS Corporation 

8181 East Tufts Avenue 

Denver, CO 80237 

West Virginia Dam Safety Brian Long(2) WV Office of Water Resources 

Dam Safety 

1201 Greenbrier Street 

Charleston, WV 25311-1088 

Montana Dam Safety Michele Lemieux(2) MT Dam Safety Program 

P.O. Box 201601 

48 N. Last Chance Gulch 

Helena, MT 59620-1601 

Piedmont Geotechnical Consultants Karl Myers(2) Piedmont Geotechnical Consultants 

P.O. Box 1997 

Roswell, GA 30077 

U.S. Army Corps of Engineers Yvonne Gibbons(2) U.S. Army Corps of Engineers 

201 N. Third Avenue 

Walla Walla, WA 99362 

U.S. Bureau of Reclamation Chuck Redlinger(2) U.S. Bureau of Reclamation (D-6600) 

P.O. Box 25007 

Denver, CO 80225-0007 

Federal Emergency Management Eugene Zeizel(3) FEMA 

Agency (FEMA) MT-NDSP 

500 C Street, SW, Room 416 

Washington, DC 20472 

Notes: (1) URS Workshop Facilitator 

(2) Member, ASDSO Seepage Advisory Committee

(3) FEMA Project Officer

P: 303-740-3921 less_osborne@urscorp.com 

F: 303-694-3946 

P: 304-558-0320 blong@mail.dep.state.wv.us 

F: 304-558-5905 

P: 406-444-6613 mlemieux@state.mt.us 

F: 406-444-0533 

P: 770-752-9205 kmyers@pgci.com 

Ext. 228 

F: 770-752-0890 

P: 509-527-7618 Yvonne.R.Gibbons@nww01.usace. 

F: 509-527-7811 army.mil 

P: 303-445-2768 credlinger@do.usbr.gov 

F: 303-445-6463 

P: 202-646-2802 gene.zeizel@fema.gov 

3-9 
3.0 WORKSHOP PROCESS

EXHIBIT 3-3
 

SUMMARY OF SURVEY/QUESTIONNAIRE RESPONSES
 

Number of 

Votes 

Rank Possible Topics 

9 12 Identification of potential seepage problems before construction. 

14 9(Tie) Failure modes associated with seepage and internal erosion. 

19 2(Tie) Inspection of dams for detection of seepage problems. 

18 5 Instrumentation and measurements for evaluation of seepage performance. 

15 7(Tie) Investigation of seepage problems/concerns at dams, including the use of 

geophysical techniques. 

4 14 Analysis of seepage flow, including two-dimensional and threedimensional methods. 

17 6 Analysis of risks associated with seepage and internal erosion. 

15 7(Tie) Remediation of seepage problems through cutoff or reduction of flow, 

including the use of geotextiles. 

14 9(Tie) Remediation of seepage problems through collection and control of 

seepage, including the use of geosynthetics. 

6 13 Seepage control systems for new dams. 

19 2(Tie) Impacts of aging of seepage control/collection system components on 

seepage performance. 

12 11 Mechanism of particle movement and progression of internal erosion. 

19 2(Tie) Filter design criteria and observed performance (the concepts of no 

erosion and continuous erosion boundaries for evaluating filter 

compatibility). 

20 1 Potential seepage problems and solutions associated with penetrations 

through embankment dams (e.g., outlet works conduits). 

Note: (1) A total of 27 responses were received. 

(2) Each respondent could vote for up to eight topics; some respondents voted for less

than eight topics. 

3-10 
3.0 WORKSHOP PROCESS

EXHIBIT 3-4 

TOPICS SELECTED 

FOR THE WORKSHOP 

1.	 Potential seepage problems and solutions associated with penetrations through 

embankment dams (e.g., outlet works conduits). 

2.	 Filter design criteria and observed performance (the concepts of no erosion and 

continuous erosion boundaries for evaluating filter compatibility) and mechanism of 

particle movement and progression of internal erosion. 

3.	 Inspection of dams for detection of seepage problems, failure modes associated with 

seepage and internal erosion, and analysis of risks associated with seepage and internal 

erosion. 

4.	 Investigation of seepage problems/concerns at dams, including the use of geophysical 

techniques; and instrumentation and measurements for evaluation of seepage 

performance. 

5.	 Remediation of seepage problems through cutoff or reduction of flow and through 

collection and control of seepage (including the use of geosynthetics). 

6.	 Impacts of aging of seepage control/collection system components on seepage 

performance. 

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3.0 WORKSHOP PROCESS

EXHIBIT 3-5
 

WHITE PAPER AUTHORS AND TITLES
 

Author(s) White Paper Title 

Joseph R. Kula Potential Seepage Problems And Solutions Associated With Penetrations 

Through Embankment Dams 

Robin Fell and Mark Foster The Internal Erosion And Piping Process 

William O. Engemoen Assessing The Risk Of A Seepage-Related Dam Failure By Means Of 

Failure Mode Identification, Risk Analysis, And Monitoring Practices 

Charles D. Wagner Investigation Of Seepage Problems/Concerns At Dams, Including Use Of 

Geophysical Techniques; And Instrumentation And Measurements For 

Evaluation Of Seepage Performance 

James R. Talbot, Steve J. Poulos, Remediation Of Seepage Problems Through Cutoff Or Reduction Of 

and Ronald C. Hirschfeld Flow And Through Collection And Control Of Seepage Including The 

Use Of Geosynthetics 

Danny K. McCook The Impacts Of Aging Of Seepage Control/Collection System 

Components On Seepage Performance 

3-12 

4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS 

In this section of the report, the results of the workshop are presented and discussed 

separately for each of the six topics listed in Exhibit 3-4. For each topic, the following items 

are discussed: 

1. The state-of-the-practice white paper. 

2. Refinements to the state-of-the-practice white paper. 

3. Identification and prioritization of research and development ideas. 

4. Preliminary research and development implementation plans. 

Consideration of each topic resulted in the selection of four or five research and development 

ideas for which preliminary implementation plans were developed. Section 5 of the report 

discusses overall prioritization of the 29 potential research and development plans that were 

developed separately for the six topics considered. 

4.1	 TOPIC 1 – POTENTIAL SEEPAGE PROBLEMS AND SULOUTIONS 

ASSOCIATED WITH PENETRATIONS THROUGH EMBANKMENT DAMS (E.G., 

OUTLET WORKS CONDUITS) 

4.1.1	 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by Joseph R. 

Kula, and the full paper is presented in Attachment 4 of this report. A brief summary of the 

highlights of the paper is presented here. 

Embankment dams are often penetrated by appurtenant structures, such as outlet works and 

spillways. The most common penetration is a conduit serving as either an outlet works or 

spillway conveyance structure. The penetrations can be of various shapes and sizes, and they 

are constructed of a variety of different materials, with the most common ones being concrete 

(both cast-in-place and precast), steel, corrugated metal, and, more recently, plastic. The 

boundaries between the structural materials in the penetrations and the adjacent earth 

materials provide potential preferential paths for seepage. The susceptibility of these 

boundaries to seepage is sometimes exacerbated by the difficulty in compacting fill beside 

and beneath the penetrations, differential settlement of the penetrations, and low stresses 

adjacent to the penetration caused by arching. Ideally, flow through a conduit penetration is 

controlled at or near the upstream end, so that the conduit operates with gravity flow. 

However, there are installations where the control is located at the downstream end and the 

conduit is constantly pressurized to full reservoir head. 

Data collected by the University of New South Wales indicate that about 15 percent of the 

failures (breaches) reported for embankment dams greater than 15m in height were 

associated with conduits passing through the dam, and this represents about one-third of the 

reported failures caused by seepage and piping. The problem appears to have become more 

prevalent in recent years, possibly at least in part because of the aging of older dams. The 

National Performance of Dams Program (NPDP) has collected records of 164 incidents 

related to penetrations through embankment dams. Of these, 87 percent have been occurred 

in the last 20 years and 75 percent in the last 10 years. A survey of state dam safety programs 

was conducted for the 1999 ICODS Dam Safety Technical Seminar No. 6 on conduits. In 

that survey, 14 states reported 1,115 dams with conduits in need of repair; 53 percent being 

corrugated metal pipes (CMPs), 23 percent being steel pipes, and 20 percent being concrete 

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4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

pipes. CMPs appear to be a significant part of the problem. NPDP data indicate that many 

CMPs rust out in less than 25 years, and that one CMP pipe was reported to have rusted out 

in only 17 years. 

Typical problems associated with penetrations through embankment dams include: 1) 

seepage and piping along the conduit or other penetration; 2) erosion into the conduit through 

poor joints, cracks or holes; 3) flow out of the conduit through poor joints, cracks or holes; 

and 4) structural failure from excessive deformations. Seepage and piping along the 

penetration can lead directly to formation of an eroded “pipe” from the downstream to the 

upstream side of the dam, ultimately resulting in formation of a breach. Erosion into a 

conduit can lead to formation of a pipe from the conduit to the reservoir, which again can 

ultimately lead to breach of the dam. The erosion into the pipe will occur at a location where 

the piezometric head in the embankment is higher than the elevation of the defect (joint, 

crack, or hole) in the conduit. Cracks or holes in the conduit wall can be the result of 

structural deterioration, and holes can also result from corrosion (e.g., in CMPs). Flow out of 

the conduit can cause development of a pipe along the outside of the penetration, as in the 

first type of problem described above. This problem is normally associated with pressurized 

conduits. Structural failure can lead to cracks and holes through the walls of a conduit, 

providing the pathways for erosion into or flow out of the conduit. Structural failures can 

occur with any type of conduit, but they are most often associated with flexible pipes (e.g., 

CMPs and plastic pipes), that derive most of their load carrying capability from the 

surrounding backfill. For these types of pipes, if the backfill is not adequately compacted, the 

pipe can deform excessively under load. 

The seepage problems associated with penetrations through embankment dams appear to 

generally be associated with old design standards, poor construction practices, and material 

deterioration. Old design standards (pre-1980) included the use of anti-seepage collars as the 

primary defense against seepage along the penetration. Unfortunately, experience has shown 

that in many cases the anti-seepage collars were not effective, because poor compaction 

around the collars offset (in some cases more than offset) the benefit that they provided. 

Other old design standards that have led to problems include: 1) poor joint details; 2) not 

accounting for settlements resulting from compressible foundations; 3) the lack of support 

cradles for round pipes and the resulting reliance on good compaction in the lower 

“haunches” of the backfill; 4) vertical structural walls, which do not facilitate compaction or 

accommodate settlement; 5) deep and narrow trenches that lead to low stresses because of 

arching; and 6) lack of downstream filters around conduits. Construction practices that have 

contributed to problems include poor joint construction and poor compaction procedures. 

Problems associated with material deterioration require no further discussion. More recently 

practices have improved. Beginning in about 1980, seepage diaphragms to collect and control 

seepage along penetrations have been recommended in place of anti-seepage collars. In 

addition, concrete cradles or full concrete encasements have become more widely used for 

round pipes, structural walls have been battered (e.g., 1H:8V or 1H:10V), and steep, narrow 

trenches have been avoided. There also has been an increased awareness of the importance of 

quality control for construction related to penetrations through embankment dams. 

Inspections are vital to detecting potential problems with conduits and other penetrations, so 

that adverse conditions can be discovered and remedied before they threaten the safety of the 

dam. Direct visual inspections are possible for most conduits larger than about 36 inches in 

diameter, but these inspections require compliance with OSHA regulations for confined 

space entry. Remote camera inspection technology has been evolving rapidly in recent years, 

and in many cases it is the preferred method of inspection. For small conduits remote camera 

4-2 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

inspection is the only practical method of visual inspection. In some cases, it is appropriate to 

supplement visual inspections with geophysical methods such as global seismic 

investigations, localized seismic investigations, laser scanning and profiling, acoustic and 

ultrasonic testing, sonar, and ground penetrating radar. 

Instrumentation and monitoring can also provide valuable information for assessing potential 

problems with penetrations. Structural integrity can be monitored and assessed with strain 

gauges, joint meters, inclinometers, extensometers, settlement plates, and geophysical 

techniques. Seepage can be monitored and assessed with tracers, geophysical methods, 

temperature measurements and thermal imaging, gamma and neutron logging, and acoustic 

devices, in addition to more conventional piezometer installations. 

Where problems have been identified with penetrations, rehabilitation techniques have 

included one or more of the following: replacement, sliplining an existing conduit, cured-inplace pipe liners, filter diaphragms installed around the conduit, grouting, and localized 

patching of structures. To-date trenchless technologies, other than cured-in-place pipe liners, 

have seen limited use in dams. However, as these techniques mature in their applications in 

the sewer industry, it is possible that they may prove applicable to penetrations through 

dams. Trenchless technologies include molded polyethylene pipes, spiral widening systems, 

deformed liners made from high strength polyethylene, pipe bursting, and microtunneling. 

4.1.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

•	 There was a general, but not unanimous, consensus that sand (or sand and gravel) filter 

diaphragms around conduits are preferred over concrete cutoff collars for controlling 

seepage and piping along the sides of outlet conduits. 

•	 The NRCS/SCS filter diaphragm criteria were developed for 18 to 48 inch diameter 

pipes. There are no widely available criteria for larger pipes. Diaphragm dimensions for 

larger pipes are based on engineering judgment based on analysis and evaluation of sitespecific conditions. 

•	 Chimney drains in embankments may serve the same purpose as filter diaphragms, if they 

are located correctly. 

•	 The correct location for a filter diaphragm is dependent on the reservoir head and the 

phreatic surface through the embankment. 

•	 A filter diaphragm must have an outlet to drain any seepage that enters the diaphragm. 

The outlet can be provided by a pipe, connection to a chimney or blanket drain, or any 

one of a number of other suitable means. 

•	 A filter diaphragm will be effective only if the gradation as-installed provides adequate 

filter protection to up-gradient soils. 

•	 Grouting around pipelines is not recommended as a sole solution for prevention of 

piping. Grouting will not likely provide 100 percent encapsulation of the conduit and 

seepage gradients in the “windows” in the grout may actually be higher than the initial 

gradients before grouting. Grouting can be used to fill or partially fill voids created by 

piping, to reduce future settlements, but filter diaphragms or other positive means must 

be used to prevent piping. 

4-3 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

•	 Bare (unencased) corrugated metal outlet conduits should not be used for new 

construction or replacements in significant or high hazard dams. Although many existing 

dams include bare corrugated metal outlet conduits, their generally poor long-term 

performance argues strongly against their continued use. In addition, studies have shown 

that corrugated metal pipe outlet conduits are inferior to concrete pipe outlet conduits, 

when evaluated on a life-cycle-cost basis. 

•	 There was a general, but not unanimous, consensus that the springline is the 

recommended minimum height for the top of a conduit cradle, if a cradle is used. 

•	 Flexible pipes and rigid cradles are not compatible. Flexible pipes (corrugated metal, 

HDPE, etc.) are designed to deflect to a limited degree under load. A rigid cradle 

prevents deflection of the pipe in the cradle, which can lead to overstressing of the walls 

of the pipe. 

•	 There was consensus that permanently pressurized pipes through embankments should be 

either encased (e.g., in concrete) or placed within an outer conduit. 

•	 The workshop participants were not aware of a case in which trenchless technology had 

been used to construct a conduit through an embankment dam. 

•	 It was noted that the discussion on penetrations in this workshop session did not address 

vertical penetrations (e.g., piezometers). 

4.1.3	 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of 15 potential research and 

development ideas, which were then prioritized by the group. The 15 ideas and the results of 

the prioritization are presented in Exhibit 4-1. 

4.1.4	 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top five ideas listed in Exhibit 4-1 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-2 through 4-6. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-1 may not exactly match the ideas listed in Exhibits 4-2 through 4-6. 

4.2	 TOPIC 2 – FILTER DESIGN CRITERIA AND OBSERVED PERFORMANCE 

(THE CONCEPTS OF NO EROSION AND CONTINUOUS EROSION 

BOUNDARIES FOR EVALUATING FILTER COMPATIBILITY) AND 

MECHANISM OF PARTICLE MOVEMENT AND PROGRESSION OF INTERNAL 

EROSION 

4.2.1	 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by Robin Fell and 

Mark Foster, and the full paper is presented in Attachment 5 of this report. A brief summary 

of the highlights of the paper is presented here. 

To provide a complete coverage of the issues, the white paper includes a description of the 

internal erosion process, from initiation through to formation of a breach, and discussions of 

seepage and internal erosion in the dam and in the foundation. 

Historically, nearly 1 in 50 (or approximately 2 percent) of embankment dams larger than 

15m in height have experienced a piping incident through the embankment, foundation, or 

from the embankment to the foundation. Incidents include both failures (a breach resulting 

4-4 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

in uncontrolled release of the reservoir) and seepage “accidents” that did not result in failure. 

Approximately one-third of the reported incidents led to failure. Of all of the reported 

incidents, about 50 percent were in the embankment, 40 percent were in the foundation, and 

10 percent were from the embankment to the foundation. A smaller percentage of incidents 

of piping in the foundation, and particularly those from embankment to foundation, progress 

to failure, than is the case for piping in the embankment. Nearly 50 percent of the reported 

failures occurred on first filling, and 64 percent occurred within the first five years of 

operation. In contrast, about 60 percent of the accidents occurred after the first five years of 

operations. For all failures where the reservoir levels at the times of failure are known, the 

failures occurred with the reservoir at or above its previous maximum level (85 percent of the 

cases) or within 1m of its previous maximum level (15 percent of the cases). Seepage 

gradient alone has been found not to be a good indicator of the likelihood of a piping failure, 

with failures and accidents reported with gradients as low as 0.05. 

The process of a piping failure can be divided into four phases: 1) initiation, 2) continuation 

of erosion, 3) progression to form a pipe, and 4) formation of a breach. Piping can initiate 

from backward erosion (movement of soil particles at a free seepage exit point), a 

concentrated leak (e.g., through a cracked core or along a structural penetration), suffusion 

(internal instability of the soil – the finer components of the soil being washed out of the 

coarser matrix), or “blowout” (heave). Continuation of erosion and formation of a pipe are 

affected by the ability of the pipe to “support a roof.” Case studies suggest that soils with 

more than 15 percent fines are capable of supporting a roof, even if the fines are not plastic. 

In addition, the moisture condition of the soil affects its ability to support a roof, with dry or 

partially saturated soils generally being more likely to support a roof. Stratigraphy can also 

affect the ability to support a roof; for example an overlying cohesive soil layer can provide a 

roof for formation of a pipe in clean cohesionless soil. Potential piping breach mechanisms 

include gross enlargement of the pipe hole, overtopping (resulting from crest settlement or 

sinkhole formation), unraveling of the downstream slope, and downstream slope instability. 

It is suggested that the reason that there are twice as many seepage accidents as there are 

failures by piping is primarily because in accidents the piping process ceased before a breach 

mechanism could develop. The cessation of the process resulted either from 1) some 

characteristic of the zoning of the dam and its foundation, 2) some characteristic of the soil 

and rock materials in the dam and its foundation, 3) the specific seepage conditions at the 

dam, and/or 4) intervention by the dam’s operators. 

The state-of-the-practice for controlling seepage and internal erosion in new dams and dam 

rehabiltations is to include designed filters and high permeability zones within the 

embankment. Erosion from the embankment into rock foundations can be controlled by 

proper foundation preparation (e.g., concrete or shotcrete over open joints in the rock beneath 

the core). Erosion within the foundations can be more difficult to control, but can be 

addressed by providing filters where the seepage will exist or by constructing cutoffs (e.g., 

diaphragm walls in alluvium). 

The issues are more complicated for assessing the safety of existing dams that may not have 

been designed and constructed according to standard practice. In these cases, the actual 

conditions and performance data are compared to the desired state-of-the-practice, and 

engineering judgment is used to decide whether the dam is safe enough. State-of-the-practice 

filter design criteria are sometimes used in this assessment; however, as discussed below this 

approach may be too conservative. Over the past 10 to 15 years, some organizations have 

been using risk assessment methods to provide guidance to the decisions regarding the safety 

4-5 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

of existing dams with respect to seepage. This use of risk assessment methods is considered 

an evolving state-of-the-practice. 

A filter in an embankment dam or its foundation is required to perform two basic functions: 

1) prevent erosion of soil particles from the soil it is protecting and 2) allow drainage of 

seepage water. To achieve this, filters must 1) have an appropriate particle size distributions 

to control and seal the erosion which may have initiated in the base soil, 2) have sufficient 

internal stability, 3) be resistant to segregation and particle breakdown during handling, 

placing, spreading, and compaction, 4) have sufficient permeability and thickness to handle 

the seepage quantity, and 5) be incapable of holding an open crack. Various organizations 

and researchers have recommended filter design criteria that will fulfill these requirements. 

The white paper summarizes recent research by Foster and Fell, at the University of New 

South Wales, that generally supports the criteria currently used by the NRCS and the USBR, 

with a few modifications recommended in the white paper. In their research, Foster and Fell 

found that filters designed according to these criteria can be considered “no erosion” filters – 

that is the filter seals the base material with practically no erosion of the base material. 

“Seals” in this sense means prevents movement of soil particles from the base material. 

The research by Foster and Fell also indicated that filter materials could be coarser than those 

resulting from the “no erosion” criteria, but still prevent “continuous erosion” of the base 

material. As discussed in the white paper, Foster and Fell defined four conditions that they 

applied to their research results: 1) “no erosion,” as defined above, 2) “some erosion,” where 

the filter seals after “some” erosion of the base material, 3) “excessive erosion,” where the 

filter seals, but only after “excessive” erosion of the base soil, and 4) “continuing erosion,” 

where the filter does not seal, but rather allows “continuous” erosion of the base soil. Based 

on their research results, they provide recommendations for “excessive erosion” criteria, 

which they suggest may be applicable in the evaluation of existing dams, particularly in the 

application of risk assessment methods. Foster and Fell recommend that these criteria be used 

only with caution, sufficient site-specific data, and qualified engineering judgment, and they 

specifically recommend that these criteria not be used for design of new dams or dam 

rehabiltations. 

4.2.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

•	 Some participants noted experience indicating that widely graded materials can be 

susceptible to suffusion (internal instability). 

•	 Experience seems to suggest that in some conditions there is a potential for “self-healing” 

to occur before full pipe formation occurs, however, the exact conditions under which 

this occurs are not clearly understood. 

•	 At present there remains a lack of understanding of the mechanics of piping on the 

particle level. Such an understanding would help to tie laboratory and field observations 

together into a common understanding of the piping phenomenon. 

•	 There is a lack of understanding of filter design criteria for coarser materials (gravels and 

coarser). 

•	 Filters constructed of soil materials should not be over-compacted. In current practice soil 

filter materials are often compacted to a greater degree than necessary. Over-compaction 

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4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

of filter materials can result in reduced permeability and increased potential for the filter 

materials to be capable of holding an open crack. Soil filter materials should be 

compacted only to the degree necessary for strength and settlement requirements; this 

would include compacting the filters sufficiently that they would not liquefy if subjected 

to earthquake loading. It was the consensus of the participants that 90 percent of modified 

Proctor compaction (or 65 to 70 percent relative density) would be sufficient in almost all 

cases. It was also noted by some participants that a “method” specification with some 

initial field verification testing may be the best approach to preventing over-compaction 

of filters. 

•	 After extensive discussion, a general consensus was reached that piping can often be an 

episodic phenomenon. That is, piping with muddy or turbid seepage may occur for some 

period of time, after which the pipe collapses or stabilizes for some period of time, only 

to be followed later by another episode of active piping. It may take many repeated 

episodes of piping before the phenomenon progresses to failure of the dam. The 

importance of this understanding of the piping phenomenon is that the observation of 

clear seepage does not necessarily mean that there is no piping problem. It could simply 

be the case that the observation was made during a period of no active piping. Piping 

should be considered a possibility for any case of uncontrolled seepage. Inspectors should 

also look for evidence of past piping episodes (e.g., silt or sand deposits at or downstream 

of seepage exit points). 

•	 It was a group consensus that the effectiveness of “crack fillers” or “crack stoppers” is 

unknown – they may or may not be effective. 

•	 Currently there is not a consensus on thickness requirements for horizontal, vertical, or 

inclined filter zones. Often, constructability is a key factor in determining the minimum 

thickness. In many cases the thickness required to carry expected flows is less than that 

required in construction to assure continuity of the filter zone. 

•	 For design of new structures, it is the state-of-the-practice to assume that fine-grained 

embankment materials crack. 

4.2.3 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of 10 potential research and 

development ideas, which were then prioritized by the group. The 10 ideas and the results of 

the prioritization are presented in Exhibit 4-7. 

4.2.4 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top five ideas listed in Exhibit 4-7 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-8 through 4-12. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-7 may not exactly match the ideas listed in Exhibits 4-8 through 4-12. 

4-7 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

4.3 TOPIC 3 – INSPECTION OF DAMS FOR DETECTION OF SEEPAGE 

PROBLEMS, FAILURE MODES ASSOCIATED WITH SEEPAGE AND 

INTERNAL EROSION, AND ANALYSIS OF RISKS ASSOCIATED WITH 

SEEPAGE AND INTERNAL EROSION 

4.3.1 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by William O. 

Engemoen, and the full paper is presented in Attachment 6 of this report. A brief summary of 

the highlights of the paper is presented here. 

This paper presents the state-of-practice (with a bias to U.S. Bureau of Reclamation 

practices) for the surveillance and monitoring of dams and the use of this information in the 

evaluation of potential risks of a seepage-related failure. 

Reclamation’s current surveillance and monitoring program for high and significant hazard 

dams includes several different components. Typically, Reclamation dams are observed and 

inspected frequently by dam tenders and operations personnel, particularly when the 

reservoirs are at or above normal high operating levels. Annually, representatives from 

Reclamation’s Area Offices complete a detailed examination of each dam and fill out an 

inspection report. Every three years, each dam is subjected to a Periodic Facility Review by a 

team from the Regional Office. Finally, every six years, each dam is subjected to a 

Comprehensive Facility Review (CFR) by a team of specialists from Reclamation’s 

Technical Service Center. The overall process includes visual inspections, collection and 

evaluation of monitoring data, evaluation of failure modes, and assessments of the risks of 

failure. All personnel involved in the process are trained in dam inspection, operation, and 

performance. If potential problems or unacceptable risks are identified for a particular dam it 

is targeted for further evaluation or other appropriate action. 

Surveillance and monitoring programs are different for dams operated by other organizations 

or subject to other jurisdictions. However, the Reclamation program points out several 

important aspects of a good program. First, surveillance and monitoring should be completed 

in a regular, thorough, and prescribed manner. The program needs to be completed by 

appropriately trained and experienced personnel, and available monitoring data should be 

evaluated and considered. Finally, appropriate actions need to be taken in response to the 

findings resulting from the surveillance and monitoring activities. 

Reclamation’s monitoring and surveillance program is guided in many ways by identification 

of potential failure modes and the assessment of risks associated with those failure modes. 

Consequently, the white paper includes a discussion of how Reclamation employs failure 

mode analysis and risk assessment for seepage-related issues, followed by further discussion 

of monitoring and surveillance, all of which is briefly summarized below. 

Failure mode evaluation is used by Reclamation to help identify key aspects of a dam’s 

performance that should be monitored to best detect potential seepage problems. Seepage 

through and under an embankment dam can, given the right situation, lead to failure by any 

one or more of following the potential failure modes: 

Piping – Erosion initiates at a downstream exit point and continues in an upstream direction. 

For this to happen there must be a flow path with water, an unprotected exit for soil particles 

to escape through, erodible material within the flow path, material(s) capable of supporting a 

“pipe” or “roof,” and sufficient seepage gradients. 

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Seepage Erosion or Scour – Loss of material occurs at an erosional surface where 

concentrated flow is located (e.g., a crack in the core or at the dam/foundation contact). 

Internal Erosion by Suffusion (Internal Instability) – The finer-grained particles of a soil are 

washed through the matrix created by the coarser-gained particles. 

High, Confined Pore Pressures in Foundation – High seepage pressures cause blowout-type 

failures, which, in certain circumstances, can be lead to traditional piping – sometimes called 

“piping by heave.” 

The various different seepage and piping failure modes that can develop can be generally 

categorized into three main types – 1) internal erosion through the embankment, 2) internal 

erosion through the foundation, and 3) internal erosion of embankment into/at the foundation. 

After failure modes have been identified, Reclamation uses risk assessment methods to 

evaluate the risks associated with those failure modes. The general formulation of risk used 

by Reclamation is that Risk = [Probability of Loading] x [Probability of Adverse Response 

(Failure), Given the Loading] x [Adverse Consequences, Given the Failure]. Reclamation 

uses three basic types of risk analyses in its dam safety evaluations: 1) a risk-based profiling 

system, 2) CFR risk analysis, and 3) issue evaluation risk analysis. The first two types are 

relatively simple and are used to complete portfolio and screening-level evaluations to 

determine if further studies are needed. The third type is significantly more complex and is 

used when the need for modifications (either structural or non-structural) to a dam is being 

considered. The issue evaluation risk analysis is completed by a team of individuals led by 

two trained facilitators. Typically, the team constructs event trees for the various events 

required to produce a failure according to each of the failure modes. Expert elicitation is then 

used to estimate probabilities for the various branches of the event trees, so that probabilities 

of failure can be calculated. Event trees for seepage-related failure modes typically include 

the following stages: 1) initiation, 2) continuation of internal erosion, 3) progression of the 

internal erosion process, 4) early intervention, 5) breach initiation, and 6) heroic intervention. 

Each stage may be characterized by one or more branches in the event tree. Issue evaluation 

risk analyses are completed for both existing conditions and possible corrective actions to 

assess the risk reduction provided by the corrective actions, and the results are used as part of 

Reclamation’s decision process for implementing corrective actions. 

At Reclamation, the knowledge and understanding developed from failure mode 

identification and risk analysis are used in the monitoring and surveillance program. In many 

ways, they provide guidance on “what to look for and where.” In developing its monitoring 

and surveillance programs, Reclamation incorporates: 1) integration of analysis with 

inspection, 2) emphasis on routine and frequent visual observations, 3) advance identification 

of what to look for and where, 4) inclusion and evaluation of instrumentation data, 5) 

consideration of periodic videotape inspections of outlet works and drainage systems, 6) 

consideration of automated early warning systems, and 7) coordination of monitoring and 

emergency action plans. In its monitoring programs Reclamation also attempts to 1) fight 

complacency, 2) pay close attention to any observed changes, and 3) recognize the 

limitations of instrumentation data (e.g., piezometer data may not provide warning of a 

seepage problem unless it is in exactly the right place). 

4.3.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

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•	 There are currently two different approaches to quantitative risk analysis for seepage 

through embankment dams. They can be broadly categorized as 1) the statistical-based 

method and 2) the degree-of-belief-based method. The general consensus is that the 

degree-of-belief-based method is presently considered to be the state-of-the-practice for 

risk analysis for dams, and this will probably remain so for the foreseeable future. At the 

workshop, the BC Hydro representative requested that it be specifically noted that his 

organization does not presently support the use of detailed quantitative risk analysis (with 

either approach) for dam seepage issues. The reader is referred to the report of the March 

2000, Logan, Utah Workshop on Risk Analysis for Dams (another FEMA/ASDSO 

sponsored workshop) for a more extensive treatment of this topic. That report is also a 

part of FEMA’s National Dam Safety Act Report Series 

•	 Some organizations (the Bureau of Reclamation and some states) are using simplified 

prioritization systems based on risk approaches. However, some believe that these 

approaches are subject to some misinterpretation because the results do not specifically 

address likelihood of occurrences. 

•	 The use of risk analysis in the United States is influenced by the regulatory environment. 

At present the applicability of risk analysis is limited, because most regulatory agencies 

(at both the state and federal levels) do not accept risk analysis as a basis for actions to be 

taken. This situation is likely to change in the future. 

•	 Risk analysis is based on available knowledge about the dam being considered, as are all 

other engineering judgments concerning dams. 

•	 The qualifications, training, and experience of dam inspectors and operators are highly 

variable in the United States. Yet the qualifications, training, and experience of these 

individuals are critical to professional judgments that must be made in operating and 

maintaining a dam. 

•	 Automated monitoring installations for early warning systems need to be designed so that 

they measure parameters that can clearly provide adequate warning. For example, 

tailwater level monitors are sometimes used for early warning, but in many cases they 

will not provide adequate advance warning to the population-at-risk (e.g., the alarm 

would come too late). By contrast, piezometers in the pervious downstream shell of a 

dam may, in the right situation, provide a sensitive measure of changing conditions. 

4.3.3 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of 10 potential research and 

development ideas, which were then prioritized by the group. The 10 ideas and the results of 

the prioritization are presented in Exhibit 4-13. Note that two of the ideas were judged to 

have been addressed by the March 2000 Risk Analysis Workshop in Logan, Utah, and, 

therefore, were not included in the prioritization. In addition, a third idea, which received a 

significant number of votes but did not rank in the top five, was combined with one of the top 

five ideas in the development of implementation plans. 

4.3.4 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top five ideas listed in Exhibit 4-13 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-14 through 4-18. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-13 may not exactly match the ideas listed in Exhibits 4-14 through 4-18. 

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4.4	 TOPIC 4 – INVESTIGATION OF SEEPAGE PROBLEMS/CONCERNS AT 

DAMS, INCLUDING THE USE OF GEOPHYSICAL TECHNIQUES; AND 

INSTRUMENTATION AND MEASUREMENTS FOR EVALUATION OF SEEPAGE 

PERFORMANCE 

4.4.1	 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by Charles D. 

Wagner, and the full paper is presented in Attachment 7 of this report. A brief summary of 

the highlights of the paper is presented here. 

A program to investigate seepage problems and concerns at a dam is typically designed to 

develop a sufficient understanding of the stratigraphic and phreatic features of the dam and 

its foundation. The field investigation program should achieve the following five main 

objectives: 

1.	 augment existing data, 

2.	 assess the subsurface soil and rock conditions of the embankment, abutments, and 

foundation, 

3.	 identify any artesian layers, 

4.	 obtain piezometric data, 

5.	 install additional piezometers strategically to fill any data gaps. 

Methods commonly used in investigating seepage concerns and problems include a) 

geotechnical drilling, sampling, and testing programs, 2) installation and monitoring of 

piezometers and groundwater observation wells, and installation of flumes, weirs, and 

collection pipes to monitor seepage quantities and characteristics (e.g., turbidity, water 

chemistry, and water temperature). Geophysical methods are sometimes included in seepage 

investigation programs, although less frequently than the other methods listed above. 

Any investigation program should begin with a thorough review of pertinent available 

information. Although the extent of available information may vary from extensive for welldocumented dams to nearly nonexistent for many older dams, whatever information is 

available should be thoroughly studied and understood. A thorough understanding of the 

available information will help guide the investigation program and increase its effectiveness 

and efficiency. 

The most commonly used geotechnical investigation method is the Standard Penetration Test 

(SPT) boring. SPT borings provide a) data on subsurface stratigraphy, b) disturbed samples 

for laboratory index testing, and c) blowcounts that provide a measure of in-place 

consistency and density of soils. The SPT borings can be completed with the installation of 

piezometers to provide information on phreatic conditions. If required, undisturbed tube 

samples can be taken in SPT borings, to provide high quality samples for laboratory 

engineering property tests. SPT borings can also be extended into bedrock, using coring or 

augering, if the characteristics of the rock are important to the seepage concerns. One 

drawback of the typical SPT boring is that soil samples are normally taken at five-foot 

vertical intervals in the boring, so they do not provide a continuous profile of the soil strata 

that are penetrated. This can be remedied by taking continuous SPT samples, but at a 

potentially significant increase in investigation cost, particularly for deep borings. In 

addition, care must be exercised if the boring penetrates strata under artesian pressures, 

because the boring provides a direct hydraulic connection between the artesian pressure and 

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the ground surface. In the extreme case, such a boring could provide a pathway for the 

initiation of piping. 

Another common geotechnical investigation method sometimes used in seepage 

investigations is the open test pit or test trench, used to directly expose and examine 

subsurface conditions at shallow depth. 

Piezocone Penetration Tests (CPTu) can be a valuable part of a seepage investigation 

program. The CPTu test is a quick, efficient way to obtain nearly continuous profiles of 

inferred soil property data and piezometric information, with minimal site disturbance. The 

soil property data are inferred from the tip and sleeve resistances and the pore pressure 

readings obtained as the cone is pushed into the ground. Piezometric data are obtained by 

completing piezocone dissipation tests to measure stabilized piezometric levels. There are, 

however, several limitations to the CPTu test. First, the CPTu test does not provide any 

physical soil samples; all of the soil property information must be inferred from the 

piezocone readings. This can be remedied on a site-specific basis by using both SPT and 

CPTu investigations and correlating the results of the two methods. Second, the CPTu test 

equipment cannot penetrate boulders or very hard or dense soils. Third, the practical depth of 

penetration of the CPTu test is less than that of SPT borings. 

Piezometers can be installed in boreholes, and there are some types of piezometers that can 

be installed by pushing them into the subsurface strata without the need for a borehole. 

Piezometers can be either isolated-tip or open-well types. Isolated tip piezometers are those 

that measure the piezometric level within a limited vertical horizon, while open-well type 

piezometers measure the average piezometric level over nearly the entire depth of a borehole. 

The physical compositions of the piezometers can be of several different types (e.g., screened 

pipe sections, porous tips, vibrating wire piezometers, hydraulic piezometers, etc.), and the 

appropriate type of piezometer for each application should be based in large part on the 

required response time for the instrument. Special procedures are required to install 

piezometers in soil strata with artesian pressures (see discussion above regarding SPT 

borings). 

Permeabilities of subsurface strata can be investigated with several different methods, such 

as constant and falling head permeability tests in boreholes or piezometers, CPTu dissipation 

tests, packer pressure tests (in bedrock), and laboratory permeability tests on undisturbed 

samples. 

In some cases, geophysical investigations can be used to help interpret or explore the dams or 

foundations where intrusive methods would be expensive and/or not feasible due to physical 

constraints. Methods of geophysical investigations that have been used in seepage 

investigations include, but are not limited to, ground penetrating radar, spontaneous (self)-

potential surveys, electromagnetic induction surveys, very low frequency surveys, resistivity 

surveys, and seismic refraction surveys. 

Monitoring of piezometers and seepage collection points (weirs, flumes, etc.) should be 

regularly performed so a record of seepage is established. Reservoir and tailwater levels 

should be recorded whenever readings are taken, so that relationships between hydraulic 

head and piezometric levels and seepage quantities can be evaluated. It may also be 

appropriate to collect precipitation and temperature data to allow evaluation of the effects of 

those factors. Dye testing is another method that can be used to investigate seepage paths. 

Colored dyes can be injected into boreholes or released at specific locations in the reservoir, 

and downstream seepage locations can be observed for appearance of the dye. In a similar, 

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water chemistry tests and water temperature measurements can be used to assess potential 

sources of seepage water. 

4.4.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

•	 Although actual investigation practices vary widely, it was the consensus of the 

workshop participants that the recommended state-of-the-practice should be that drilling 

should not be done in the core of an existing embankment dam unless absolutely 

necessary, and then only with carefully planned precautions and dry drilling (e.g., auger) 

methods. The risk of hydraulic fracturing is too great to support drilling in the core 

without appropriate justification. 

•	 It was the consensus of the workshop participants that drilling or test pitting should not 

be done at the downstream toe of a dam with water stored in the reservoir, without 

contingency plans and stockpiling of weighted filter materials (e.g., sand and gravel) to 

be used in the event of a seepage incident. It is also essential that such explorations be 

completed with the on-site presence of experienced personnel with the knowledge to 

react appropriately to any seepage incidents that may occur. 

•	 Care should be taken to avoid building seepage defects into embankments by the 

installation of instruments. A cited example was the installation of hydraulic piezometers 

with the hydraulic tubes running through the embankment core in a transverse direction. 

These tubes could provide pathways for seepage and piping to initiate. 

•	 It was the consensus of the workshop participants that they generally advised against 

installing piezometers in an embankment core, unless there were very compelling reasons 

for the instruments. The workshop participants felt that, in most cases, piezometers in the 

core do not provide significant additional understanding of the performance of the dam 

beyond that which can be obtained from piezometers in the upstream and downstream 

shells, which are much safer locations for the instruments. 

•	 Piezometers are tools whose careful installation and subsequent data interpretation, in 

conjunction with other investigative techniques, may provide valuable information in 

diagnosing seepage conditions. However, the limitations of what the piezometers record 

must be recognized, and the piezometer data must be used in conjunction with other 

information (e.g., seepage rates, seepage locations, etc.) to correctly diagnose seepage 

conditions. Since piping channels in embankments are often relatively long, narrow 

features, it is not likely that piezometers will be located at exactly the correct locations to 

provide direct data regarding the piping phenomenon. 

•	 The dam engineering profession in general remains skeptical or cautious regarding the 

effectiveness of geophysical techniques for investigation of seepage problems, possibly 

because the methods are perceived as not proven sufficiently to establish a high degree of 

confidence. This situation may be caused by a mismatch in engineers expectations and 

the reality of what the methods can produce. Regrettably, this may be the result of some 

geophysical practitioners “over-selling” the capabilities of the various methods. There 

have been some successful applications of geophysical methods, and some of the 

methods show promise. Successful applications will likely increase in the future through 

research efforts such as those of the Canadian Electric Association. 

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•	 The Bureau of Reclamation cited the recent successful use of side-scan sonar in a 

reservoir to assist in locating possible sinkholes in the upstream abutment of a dam. 

•	 All instrumentation in a dam should be part of a carefully designed and implemented 

instrumentation plan that addresses need, purpose, instrumentation types, instrumentation 

locations, and data collection and evaluation. Instrumentation should not be installed 

simply for the purpose of having instrumentation. Similarly, instrumentation data should 

not be collected if it is not processed and evaluated. 

4.4.3	 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of eight potential research and 

development ideas, which were then prioritized by the group. The eight ideas and the results 

of the prioritization are presented in Exhibit 4-19. 

4.4.4	 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top five ideas listed in Exhibit 4-19 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-20 through 4-24. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-19 may not exactly match the ideas listed in Exhibits 4-20 through 4-24. 

4.5	 TOPIC 5 – REMEDIATION OF SEEPAGE PROBLEMS THROUGH CUTOFF 

OR REDUCTION OF FLOW AND THROUGH COLLECTION AND CONTROL OF 

SEEPAGE, (INCLUDING THE USE OF GEOSYNTHETICS) 

4.5.1	 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by James R. 

Talbot, Steve J. Poulos, and Ronald C. Hirschfeld, and the full paper is presented in 

Attachment 8 of this report. A brief summary of the highlights of the paper is presented here. 

There are two principal problems associated with seepage through, around, and beneath an 

embankment dam: piping (internal erosion) and excessive water loss. 

Remedial measures for preventing piping are aimed at controlling seepage so that the 

seepage does not cause internal erosion of soil from the embankment, foundation, or 

abutments of a dam. Remedial measures for preventing piping may not reduce the rate of 

seepage and, in fact, often increase the rate of seepage. 

Remedial measures for reducing water loss are aimed at reducing the quantity of seepage 

through the embankment, foundation, and abutments. Although such measures may reduce 

the pressures and the rate of water flow through a dam, its foundation, or abutments, it is 

nevertheless vital to install proper drainage systems on the downstream side of the dam as the 

primary line of defense against piping. 

The following sequence of activities is often followed to recognize and correct seepage 

problems within a dam: 

•	 field observation of a seepage problem or potential problem; 

•	 information collection and evaluation to determine the cause of the problem; 

•	 design of remedial measures; 

•	 construction of remedial measures; and 

•	 observations of effectiveness of the repairs. 

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The addition of downstream drainage is usually the best solution for controlling seepage in 

embankment dams. Control of seepage can be accomplished by: 

•	 adding a drainage zone by removing a portion of the downstream slope and constructing 

a new filter-drain covered by a reconstructed downstream slope; 

•	 adding a drainage zone by constructing a filter-drain on the existing downstream slope 

and covering the drain with a new downstream shell zone; 

•	 adding an embankment chimney drain to the dam by trenching into the dam and 

backfilling the trench with appropriate filter material; 

•	 installing a toe drain extending into the foundation at the toe of the dam; 

•	 installing a downstream, weighted, blanket drain; 

•	 installing downstream relief wells; 

•	 cleaning existing clogged drains; and 

•	 cleaning existing relief wells. 

The solution that is best-suited to a particular dam will depend on a variety of factors, as 

discussed in the white paper. Some of the more important factors to be considered are a) the 

embankment zoning and foundation stratigraphy, b) the seepage patterns and quantities, c) 

seepage pressures, d) the ability to lower the reservoir for construction, e) the availability of 

construction materials, and f) property constraints and construction access. 

Reducing the amount of seepage through dams will have the benefit of saving water as a 

resource; lowering the seepage pressures within the dam, foundation and abutments (thus 

reducing to some extent the probability of a piping failure); and reducing the required size of 

downstream seepage control systems. It is the opinion of the white paper authors that proper 

downstream drainage collection and safe discharge must always accompany any flowreduction technique. Methods available to reduce the amount of seepage include: 

•	 an upstream blanket constructed with low permeability materials (e.g., soil, asphalt, soil 

cement, roller compacted concrete, concrete, or a geomembrane); 

•	 a “cutoff” or facing on the upstream slope of the dam constructed with low permeability 

material (e.g., soil, soil and bentonite mixtures, soil cement, roller compacted concrete, 

concrete, asphalt, metal, masonry, or a geomembrane); and 

•	 an internal “cutoff” within the dam and foundation constructed of low permeability 

material (e.g., concrete, soil-bentonite mixtures, soil-cement mixtures, sheet piling, or 

grout) – sometimes called diaphragm walls and constructed with such methods as slurry 

trench excavations, deep soil mixing, or jet grouting. 

In the previous paragraph, the term “cutoff” is in quotations because almost no technique 

used for this purpose will actually completely cut off water flow. There always will be 

leakage that must be safely collected and drained on the downstream side of the cutoff. 

Many of the factors affecting the selection of the most appropriate solution for seepage 

reduction are the same as those for seepage collection, as discussed in the white paper. Two 

other significant factors that affect the selection for seepage reduction measures are a) the 

necessity for limiting the potential of hydraulic fracturing when constructing an internal 

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cutoff, and b) the need to provide protection against erosion and animal damage for shallow 

elements such as upstream blankets and upstream facings. 

Geosynthetic materials (geomembranes and geotextiles) have been used in dam remediation 

projects to control and reduce seepage. The white paper authors present some precautions 

regarding use of these materials. When geomembranes are used for blankets or seepage 

barriers, they are vulnerable to puncture during and after installation. The design and 

installation of geomembranes must be done in a such a manner as to minimize this risk. In 

addition, the low friction angle at the geomembrane-soil interface and the possibility of high 

pore water pressures at the interface must be considered in the design. Pending further 

research, the white paper authors recommend that the use of geotextiles as filters be avoided 

in dams. In addition to concerns regarding damage during installation, the white paper 

authors cite two other concerns: a) the potential for the geotextile to tear because of 

movements in the dam, and b) the potential for the geotextile to plug because of the physical 

conditions at the soil-geotextile interface. 

4.5.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

•	 Constructability and construction quality assurance/quality control are critical to 

successful and safe seepage collection/drain system performance. 

•	 Seepage collection pipes in blanket drains under downstream shells of dams are being 

used – the potential disadvantages (collapse, plugging, drilling into them) of this 

application should be recognized when they are used. 

•	 Although in current practice cutoffs are being used as a sole solution for seepage/piping 

problems, the consensus of the workshop group supports the position in the white paper 

that cutoffs should always be used together with adequate downstream collection and 

control systems. 

•	 Seepage collection systems should be designed for significantly greater (3 to 10 times) 

flow capacity than expected. 

•	 The current practice for the use of geotextiles in seepage collection systems varies widely 

amongst organizations and practitioners involved in dam engineering. After much 

discussion, it was the consensus of the group that a) geotextiles should not be used in 

locations that are both critical to safety and inaccessible for replacement, and b) 

geotextiles can be used in locations that are critical for safety but accessible for 

replacement. However, in the second case the engineer must assess the potential hazard 

posed by failure of the geotextile and the time available to respond and repair or replace 

the geotextile. This position may change in the future with data on long-term, in-place 

performance of geotextiles in dam applications. 

•	 Several participants related experience with poor performance with the rate of inflow into 

slotted or perforated pipes when the sizes of the openings in the pipes and the gradations 

of the surrounding soil filters were designed according to currently recommended 

guidelines. It appears that the soil particles can partially to substantially plug the opening, 

resulting in limited inflow. This appears to be less of a problem with pipes surrounded by 

gravel than it is for pipes surrounded by sand or sand/gravel mixtures. 

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•	 The workshop participants were not aware of any currently available guidelines regarding 

the extent and spacing of slots or perforations in pipe walls that can be allowed without 

compromising the structural capacity of the pipe. 

•	 It was the consensus of the workshop participants that the recommended state-of-thepractice for application of pressure grouting (cement or chemical) in seepage remediation 

should be that a) high-pressure grouting should never be used in the embankment core 

and b) high-pressure grouting is acceptable in rock foundations, with appropriate care; 

however, it was the experience of the group that grouting was often not a permanent 

solution. 

4.5.3	 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of 12 potential research and 

development ideas, which were then prioritized by the group. The 12 ideas and the results of 

the prioritization are presented in Exhibit 4-25. 

4.5.4	 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top five ideas listed in Exhibit 4-25 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-26 through 4-30. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-25 may not exactly match the ideas listed in Exhibits 4-26 through 4-30. 

4.6	 TOPIC 6 – IMPACTS OF AGING OF SEEPAGE CONTROL/COLLECTION 

SYSTEM COMPONENTS ON SEEPAGE PERFORMANCE 

4.6.1	 STATE-OF-THE-PRACTICE WHITE PAPER 

The strawman state-of-the-practice white paper for this topic was prepared by Danny K. 

McCook, and the full paper is presented in Attachment 9 of this report. A brief summary of 

the highlights of the paper is presented here. 

This paper discusses the components commonly included in drainage systems for 

embankment dams, the mechanisms of aging that may impact their performance, and 

remedial alternatives. 

Drainage systems in embankment dams may include some or all of the following elements: 

•	 foundation trench and blanket drains with and without collector pipes; 

•	 embankment chimney drains and filters; 

•	 relief wells; 

•	 concrete structural drains; and 

• other miscellaneous features.
 

The mechanics of aging or deterioration of a drainage system may categorized as follows:
 

•	 material deterioration; 

•	 mineralization (encrustation); 

•	 bacterial deposits; 

•	 cementation of filter media; 

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•	 siltation of gravel packs; 

•	 effects of repeated maintenance activities; 

•	 vandalism; and 

•	 impacts of vegetation. 

The drainage components that may be subject to problems caused by aging include: 

•	 granular filter/drain materials, 

•	 pipes, 

•	 well screens, 

•	 fittings, and 

•	 geosynthetics. 

When drainage systems are damaged or deteriorate the systems collect seepage less 

efficiently than intended. Typical problems resulting from damaged or deteriorated drainage 

systems include: 

•	 development of cracks or large openings that can provide pathways for internal erosion 

(piping) of embankment or foundation soils; 

•	 reduced flow capacity and increased pressures due to decreased cross-sectional area; 

•	 leaks or openings in system piping that can lead to internal erosion of surrounding soils; 

•	 increased pore pressures caused by decreased capacity; and 

•	 reduced seepage capacity and increased pressures because of siltation of filters and 

slotted pipes or well screens. 

Relief wells are especially susceptible to deterioration and aging. The most common 

problems associated with relief wells have been loss of check valve reliability, corrosion of 

screens and guards, encrustation/mineralization, deterioration of wood staves, vandalism, and 

siltation. To correct these relief well problems the most commonly used maintenance 

procedures include pumping, surging, jetting, acidizing, chlorination (disinfectants), and 

surfactants. Less commonly used relief well maintenance procedures include lime 

application, the Vyredox methods, activated carbon filters, ultraviolet light, ultrasonic 

vibration, and heat treatment (pasteurization). 

Cameras of various types can be used to inspect pipes included in seepage collection 

systems, and recent advances in camera technology have resulted in the ability to inspect 

smaller pipes and this trend in technological advances probably will continue in the future. 

Pipe lining procedures and pipe cleaning procedures (e.g., surging, reaming, and jetting) can 

be used to attempt to rehabilitate pipes in existing seepage collection systems, if the pipes are 

accessible for these procedures or can be made accessible. 

4.6.2 STATE-OF-THE-PRACTICE REFINEMENT 

The discussion of the white paper resulted in the identification of the following items to 

further refine the understanding of the state-of-the-practice: 

4-18 
4.0 WORKSHOP RESULTS FOR INDIVIDUAL TOPICS

•	 Lamping (illuminating with a light) can be a useful method for inspecting the condition 

of horizontal drain pipelines. 

•	 Creosote materials used in some early wooden pipe materials are considered hazardous 

waste. 

•	 Heated, chlorinated water applied to zones in wells, using a packer system, has been 

found to be successful in rehabilitating the wells. 

•	 Regular and thorough maintenance is essential to the continued effectiveness of relief 

wells. 

•	 The workshop group reported knowledge of evidence of long-term deterioration of 

embankment cores due to such occurrences as softening through wetting, mass movement 

during drawdown, suffusion, desiccation, and differential settlement and arching adjacent 

to structures. 

•	 There are reported cases of long-term deterioration of grout curtains. 

•	 There are reported cases of long-term deterioration of foundations due to solutioning and 

washout of in-fill materials (e.g., joint fill or paleokarst collapse features). 

•	 There are problems in drain pipelines with deposits other than iron bacteria and 

carbonates, but to a much more limited extent. 

•	 There is some anecdotal information in the profession indicating that some filters may 

have altered over time so that they could hold an open crack after alteration. 

•	 Weep holes in structural walls (e.g., concrete spillway walls) can plug over time, and may 

require maintenance. 

•	 Tree roots can invade and damage dam drain pipes. 

•	 It was the consensus of the group that corrugated metal pipes should not be used for drain 

pipes in seepage collection systems, because of their record of deterioration. 

4.6.3 PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

The group brainstorming process resulted in the generation of eight potential research and 

development ideas, which were then prioritized by the group. The eight ideas and the results 

of the prioritization are presented in Exhibit 4-31. Note that two ideas, which did not rank in 

the top four were combined with two of the top four ideas in the development of 

implementation plans. 

4.6.4 PRELIMINARY RESEARCH AND DEVELOPMENT PLANS 

The top four ideas listed in Exhibit 4-31 were selected for development of preliminary 

implementation plans, and those plans are presented in Exhibits 4-32 through 4-35. In some 

cases, the individual work groups reworded the research and development idea, so the ideas 

listed in Exhibit 4-31 may not exactly match the ideas listed in Exhibits 4-32 through 4-35. 

4-19 
EXHIBIT 4-1
 

EXHIBIT 4-1 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 1 

POTENTIAL SEEPAGE PROBLEMS AND SOLUTIONS ASSOCIATED WITH 

PENETRATIONS THROUGH EMBANKMENT DAMS (E.G., OUTLET WORKS 

CONDUITS) 

Number of 

Votes Rank Research and Development Idea 

27 1 Compilation of case studies of seepage incidents related to penetrations from 

the National Performance of Dams Program (NPDP) and other resources 

23 2 Assessing techniques for determining locations of voids and concentrated 

seepage around penetrations 

22 3 Guidelines for design of filters and seepage collection facilities for 

penetrations – focusing on conduits larger than 48 inches in diameter. 

19 4 Long-term monitoring and detection guidelines 

18 5 Development and deployment of guidelines for slip-linings 

9 6(Tie) Design requirements for flowable fill for cradles/backfill 

9 6(Tie) Summary documentation of the applicability of geophysical techniques 

7 8 Alternatives/technologies for reducing seepage 

5 9(Tie) Evaluations of trenchless technology for rehabilitation 

5 9(Tie) Technology for locating buried conduits 

5 9(Tie) Guidelines for siphon structures as outlet works replacements 

4 12 Evaluation of long-term reliability of conduits (i.e., plastics) 

3 13(Tie) Use of biodegradable slurry material for filter diaphragm construction 

3 13(Tie) Guidelines for frequency of inspection and evaluation of penetrations 

1 15 The potential of pressure between the core and the penstock during 

drawdown 

4-20 
EXHIBIT 4-2
 

EXHIBIT 4-2 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1A 

COMPILATION OF CASE HISTORIES OF SEEPAGE INCIDENTS RELATED TO 

PENETRATIONS THROUGH EMBANKMENT DAMS 

1. Description 

A. Why is this a priority research/development item? 

Penetrations are the ancillary structures most prone to deterioration and seepage 

leading to failure. 

B. What is the expected outcome? 

Development of a volume of case histories with executive summary of lessons 

learned on issues related to seepage along, into, and out of penetrations through dams. 

2. Project Tasks and Needs 

A. What tasks are to be done? 

B. How is the problem to be solved? 

1) Compile case histories with support documents (literature search, photos, plans, 

specs, etc.) 

a. Compile database/library in ASDSO. 

b. Evaluate and categorize incidents, and select representative cases. 

c. Develop executive summary/statistics/solutions. 

d. Prepare published report. 

e. Develop web site with all case histories. 

f. Develop bibliography. 

2) Federally-funded/ASDSO-funded graduate degree research project 

3) Potential problem: Access to case history documents may be restricted by 

litigation/owner liability issues. 

3. Project Lead and Contact 

A. Who is working in this area? 

Marty McCann, Robin Fell, ICOLD, USCOLD (USSD), U.S. Bureau of Reclamation 

(USBR), U.S. Natural Resources Conservation Service (NRCS), CANCOLD, etc. 

B.	 Who might be able to lead the project? 

Marty McCann, University (Southern, Utah State, many others), Federal agency. 

C. Who are good candidates to complete the work? 

Establish Advisory Committee to direct project, possibly including Robin Fell from 

the University of New South Wales. 

4-21 
EXHIBIT 4-3
 

EXHIBIT 4-3 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1B 

ASSESS TECHNOLOGY TO DETECT VOIDS AND CONCENTRATED SEEPAGE 

AROUND PENETRATIONS THROUGH EMBANKMENT DAMS 

1.	 Description 

A. Why is this a priority research/development item? 

Voids and concentrated seepage are preconditions to rapid failure (~25 percent of 

large dam failures). 

B.	 What is the expected outcome? 

Produce a living document in a form that can be used in the dam profession to guide 

them on techniques to detect voids and concentrated seepage around penetrations. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Literature review.
 

2) Survey of experts/companies/agencies.
 

3) Trials lab/field for reliability resolution.
 

4) Actual projects/case studies.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the wo rk?
 

1) Canadian Electric Authority.
 

2) U.S. Army Corps of Engineers (USACE), Vicksburg Research Laboratory.
 

3) U.S. Bureau of Reclamation.
 

4) The sewer pipe industry.
 

4-22 
EXHIBIT 4-4
 

EXHIBIT 4-4 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1C 

DEVELOP GUIDELINES FOR DESIGN OF FILTER DIAPHRAGMS ASSOCIATED 

WITH CONDUITS THROUGH EMBANKMENT DAMS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Current guidelines are not widely available. 

2) Design of filter diaphragms is important in relation to high percentage of 

reported problems with embankments. 

3) Current guidelines are not applicable to larger conduits. 

4) Current guidelines do not address rehabilitation scenarios.
 

5) Design rationale for current guidelines is not well understood.
 

B.	 Wha t is the expected outcome? 

An expert guidance document, including filter design criteria and separate sections 

for new and rehabilitation projects. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Research ava ilable guidelines. 

2) Develop theoretical rationale and terminology. 

3) Develop guideline document including new design, rehabilitation, and filter 

design.
 

4) Generate work group of individual’s with varied background.
 

5) Lead contact a person with credentials in filter design.
 

6) Important to have team.
 

7) Important for process to generate consensus.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) FEMA, USACE, USBR, FERC, State dam safety agencies, etc.
 

2) FEMA is currently funding some of this work.
 

4-23 
EXHIBIT 4-5
 

EXHIBIT 4-5 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1D 

GUIDELINES FOR INSPECTING, MONITORING, AND DETECTING SEEPAGE 

ALONG PENETRATIONS THROUGH EMBANKMENT DAMS 

1. Description 

A. Why is this a priority research/development item? 

1) Large number of incidents and failures associated with leakage along conduits. 

2) Need to compile existing guidelines and explain rationale behind them. 

3) Need to be aware of changing conditions within a structure that could indicate 

seepage problems or incipient piping. 

4) Need to develop techniques for monitoring. 

B.	 What is the expected outcome? 

1) Guidance document – audience includes designers, operators/owners and 

government agencies. 

2) Develop awareness. 

3) Encourage consistency with respect to monitoring programs and procedures. 

2. Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Research/data gathering
 

a.	 Literature search and survey/questionnaire of “experts” and 

owners/operators. 

b. Compile existing guidelines (USBR, USACE, TVA, NRCS, etc.). 

c.	 Expand on rationale behind current guidelines. 

d. Identify methods available and emerging tools/technology.
 

2) Analysis
 

a.	 Identify methods that have or have not been successful. 

b. Identify emerging technologies that have potential. 

c. Develop format for document.
 

3) Guidelines
 

a.	 Prepare draft guidelines. 

b. Review of draft guidelines by select members of audience. 

c.	 Fina lize guidelines. 

4-24 
EXHIBIT 4-5
 

EXHIBIT 4-5 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1D 

GUIDELINES FOR INSPECTING, MONITORING, AND DETECTING SEEPAGE 

ALONG PENETRATIONS THROUGH EMBANKMENT DAMS 

-CONTINUED3. Project Lead and Contact 

A. Who is working in this area? 

B. Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) USBR, NRCS, USACE, ASDSO, some states, large owners/operators. 

2) University/Academic – MS or Ph.D. thesis, sponsored research (i.e., through 

ASDSO or USCOLD [USSD] scholarship programs). 

3) FEMA is currently funding some of this work through the federal agencies and 

ASDSO. 

4-25 
EXHIBIT 4-6
 

EXHIBIT 4-6 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1E 

DEVELOPMENT AND DEPLOYMENT OF GUIDELINES FOR SLIP-LINING OF 

OUTLET WORKS CONDUITS 

1.	 Description 

A. Why is this a priority research/development item? 

1) This is an economical means of rehabilitating deteriorating outlet works conduits. 

2) There are no guidelines specific to dams: 

a.	 loading conditions are different from other applications. 

b. information from vendors may not be reliable.
 

3) It is being done frequently.
 

B.	 What is the expected outcome?
 

1) Design guideline (cookbook).
 

2) Materials research for loading conditions:
 

a. Suppliers – give them loading conditions and minimum Factor of Safety. 

b. Long term suitability – abrasion – silt load – chemical reactions. 

3) Installation procedures: 

a.	 Grout pressure and mix. 

b.	 Quality Assurance. 

c.	 Welding/joints. 

d.	 Sequencing – unintended side effects. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Determine state-of-practice for design and construction:
 

a.	 ASDSO survey. 

b.	 Available documentation. 

c.	 Vendors. 

d. Performance (case histories). 

2) Identify loading criteria – possible sources: USACE, USBR, NRCS. 

3) Specify long term requirements. 

4) Consolidate information into document. 

4-26 
EXHIBIT 4-6
 

EXHIBIT 4-6 

RESEARCH AND DEVELOPMENT 

IMPLEMENTATION PLAN, R&D TOPIC 1E 

DEVELOPMENT AND DEPLOYMENT OF GUIDELINES FOR SLIP-LINING OF 

OUTLET WORKS CONDUITS 

-CONTIUNED3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) ASDSO.
 

2) Vendors.
 

3) USBR.
 

4) NRCS.
 

B.	 Who might be able to lead the project?
 

1) ASDSO committee for overall design of program.
 

2) Contracted to a subcontractor.
 

C. Who are good candidates to complete the work?
 

1) USBR.
 

2) USACE, Vicksburg Research Laboratory.
 

3) NRCS.
 

REPORT OF WORKSHOP ON ISSUES, 

SOLUTIONS AND RESEARCH NEEDS 

RELATED TO SEEPAGE THROUGH EMBANKMENT DAMS 

4-27 
EXHIBIT 4-7
 

EXHIBIT 4-7 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 2 

FILTER DESIGN CRITERIA AND OBSERVED PERFORMANCE (THE 

CONCEPTS OF NO EROSION AND CONTINUOUS EROSION BOUNDARIES 

FOR EVALUATING FILTER COMPATIBILITY) AND MECHANISM OF PARTICLE 

MOVEMENT AND PROGRESSION OF INTERNAL EROSION 

Number of 

Votes Rank Research and Development Idea 

26 1 Evaluate conditions conducive to hydraulic fracturing and cracking 

24 2(Tie) Guidelines for thickness standards and methods of construction for filters 

24 2(Tie) Evaluate mechanism of piping and failure in alluvial, glacial, and fluvial 

environments; including consideration of internal instability 

19 4 Mechanical/geochemical degradation of the properties of filters; including 

consideration of cementation 

18 5 Cohesive soils – critical gradients related to degree of saturation (?), particle size, 

mineralogy, water chemistry (dispersion), exit face orientation, degree of 

compaction (void ratio) 

13 6 Rate of piping progression 

12 7(Tie) Further verification testing of materials in dams and dam foundations. Both lab 

and field case studies – “excessive” and “continuing” boundaries 

12 7(Tie) Methods for identifying cracks in existing dams 

6 9 Evaluate ability (or not) for sand to maintain a crack 

4 10 Incorporate existing standards of karst (voids) and mining into dam design 

4-28 
EXHIBIT 4-8
 

EXHIBIT 4-8 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2A 

CLASSIFICATION OF CONDITIONS CONDUCIVE TO HYDRAULIC 

FRACTURING AND CRACKING 

1.	 Description 

A. Why is this a priority research/development item?
 

1) It exists.
 

2) It is an initiator of piping.
 

3) It is one of the main causes of piping.
 

B.	 What is the expected outcome?
 

1) Case histories.
 

2) Set of issues/classification.
 

3) Semi-quantified categorization of conditions.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done?
 

1) Identify the mechanisms for discussion/evaluation.
 

2) Develop classification system.
 

3) Evaluate and analyze information gathered.
 

4) Identify research needs.
 

5) Prepare report with classification of conditions.
 

6) Create library of outcome.
 

B.	 How is the problem to be solved?
 

1) Literature search to identify mechanisms.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) University of New South Wales (UNSW) – some.
 

B.	 Who might be able to lead the project?
 

1) Consultant/Agency.
 

C. Who are good candidates to complete the work? 

1) University (with dam qualifications) and consultant/agency as advisor. 

4-29 
EXHIBIT 4-9
 

EXHIBIT 4-9 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2B 

DEVELOP STATE-OF-THE-PRACTICE FOR CONFIGURATIONS, DIMENSIONS, 

AND CONSTRUCTION METHODS FOR FILTERS AND DRAINS 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Lack of consensus.
 

2) They are critical design, construction and cost elements in dams.
 

B.	 What is the expected outcome? 

1) A summary document of the state-of-the-practice, with recommendations for 

minimum thickness, construction techniques, quality assurance, and dimension 

limits within the dam. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Survey of practices by institutions, companies, agencies, and other countries. 

2) Evaluate performance, case histories, and incidents. 

3) Develop rationale for configuration and design layout. 

4) Develop rationale for minimum thicknesses for design and constructability for 

horizontal, vertical, inclined, and finger drains and filters. 

3. Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) USACE, USBR, NRCS, TVA.
 

2) ASDSO Committee.
 

3) University group.
 

4) Consultants.
 

4-30 
EXHIBIT 4-10
 

EXHIBIT 4-10 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2C 

EVALUATE MECHANISM OF PIPING AND FAILURE IN GLACIAL, ALLUVIAL, 

AND FLUVIAL ENVIRONMENTS – INCLUDING CONSIDERATION OF INTERNAL 

INSTABILITY 

1.	 Description 

A. Why is this a priority research/development item? 

1) Mechanisms are poorly understood. 

2) These geologic environments are fairly common. 

3) Many case histories suggest that these conditions are not highly conducive to 

piping failures, but the reason for this is not clear. 

B.	 What is the expected outcome? 

1) Some conclusions regarding the conditions under which these geologic 

environments do or do not present a serious risk of piping failure. 

2) Recommendations on how to address piping concerns in these geologic 

environments when concerns do exist. 

3) A compendium of case histories of failures, incidents, and non-failures. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

1) Survey State dam safety officials and other sources for case histories, both 

published and unpublished. 

2) Contact individuals and organizations with experience in these types of 

environments (e.g., Ralph Peck, Norbert Morgenstern, BC Hydro) to understand 

their interpretation of piping risks posed by the specific geologic environments 

(why do they not lose sleep at night in some cases with significant foundation 

seepage?). 

B.	 How is the problem to be solved? 

1) Screen case histories for selected cases that will be further studied in-depth, 

perhaps with field investigations. 

4-31 
EXHIBIT 4-10
 

EXHIBIT 4-10 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2C 

EVALUATE MECHANISM OF PIPING AND FAILURE IN GLACIAL, ALLUVIAL, 

AND FLUVIAL ENVIRONMENTS – INCLUDING CONSIDERATION OF INTERNAL 

INSTABILITY 

-CONTINUED3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) USACE.
 

2) USBR.
 

3) NRCS.
 

4) Hydro-Quebec, Canada.
 

5) Ontario Hydro, Canada.
 

6) BC Hydro, Canada.
 

7) Vattenfall, Sweden.
 

B.	 Who might be able to lead the project? 

1) A professor with access to multidiscipline graduate students (geology and 

engineering). 

2) Supported by advisors from practice, with expertise in geology and dam 

design/performance. 

3) Possibly a lead agency with support from other agencies (multidiscipline effort). 

C. Who are good candidates to complete the work?
 

1) Utah State University.
 

2) University of Vancouver.
 

3) Virginia Polytechnical University.
 

4) University of New South Wales.
 

5) Consultants or Consulting Companies.
 

4-32 
EXHIBIT 4-11
 

EXHIBIT 4-11 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2D 

EVALUATION OF MECHANICAL/GEOCHEMICAL DEGRADATION OF 

PROPERTIES OF FILTER MATERIALS, INCLUDING CEMENTATION AND THEIR 

ABILITY TO SUSTAIN A CRACK 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Critical part of any dam.
 

2) Dams are aging.
 

3) We are seeing filters plugging up.
 

4) Case histories of problems are occurring.
 

B.	 What is the expected outcome?
 

1) Identify materials for future design and remediation.
 

2) Identify potential problem materials in existing dams.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Identify mechanisms of degradation/cracking etc.
 

2) Review existing filter performance.
 

3) Lab testing for effects of fines, plasticity index, chemical alteration, etc.
 

4) Evaluate/identify possible in situ testing.
 

5) Field investigation.
 

6) Identify types of remediation.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) Government agencies.
 

2) University research centers.
 

4-33 
EXHIBIT 4-12
 

EXHIBIT 4-12 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 2E 

THRESHOLD GRADIENTS FOR INITIATING PIPING IN COHESIVE SOILS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Important for evaluation of older dams with “incorrect filters” or no filters. 

2) Possible applicability to small dams. 

3) Key first step in understanding piping process. 

B.	 What is the expected outcome?
 

1) Determine if there really is a threshold gradient.
 

2) Test results relating threshold gradient to physical properties.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Literature research.
 

2) Test design.
 

3) Lab testing.
 

4) Correlation with case histories.
 

5) Report of findings.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) No known activity at present time.
 

2) Lead – Agency or University with substantial lab resources.
 

3) Specific good candidates:
 

USACE- Vicksburg Research Laboratory, NRCS, USBR, Universities. 

4-34 
EXHIBIT 4-13
 

EXHIBIT 4-13 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 3 

INSPECTION OF DAMS FOR DETECTION OF SEEPAGE PROBLEMS, FAILURE 

MODES ASSOCIATED WITH SEEPAGE AND INTERNAL EROSION, AND 

ANALYSIS OF RISKS ASSOCIATED WITH SEEPAGE AND INTERNAL 

EROSION 

Number of 

Votes Rank Research and Development Idea 

24 1 Identify skill/knowledge needs for dam inspectors/operators and 

training/education/certifications to meet the needs 

23 2 Develop guidance for dam safety professionals to use in the design of new 

surveillance plans and monitoring systems and evaluating existing systems and 

plans 

22 3 Improve precision of estimating failure times for old dams for each failure mode 

(i.e., seepage and erosion) 

19 4 Identify factors for failure in a) first filling (including for flood control 

structures) and b) long term (after first filling) for each internal-erosion-related 

failure mode, for guidance in degree-of-belief failure probability estimates 

18 5 Expand the database of information on failures/accidents for dams <15 meters in 

height 

10 6 Evaluate the effectiveness of remote surveillance and automated warning 

methods(1) 

4 7(Tie) Define the physics of erosion at the fundamental level to increase knowledge of 

the erosion process 

4 7(Tie) Evaluate the “concentrated leak” thesis using past failures 

N/A(2) N/A(2) Continued research on quantitative risk assessment 

N/A(2) N/A(2) Enhance methods for calculating loss-of-life for dam failures 

Notes: (1) After prioritization, this topic was combined with the third-ranked topic for 

development of an implementation plan. 

(2) These topics were eliminated prior to voting, because it was judged that they 

were covered at the Risk Analysis Workshop held in Logan, Utah in March 

2000. 

4-35 
EXHIBIT 4-14
 

EXHIBIT 4-14 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3A 

ENHANCE ACADEMIC PROGRAMS AND PROFESSIONAL DEVELOPMENT 

AND TRAINING PROGRAMS RELATED TO SEEPAGE ISSUES IN DAM DESIGN 

AND REHABILITATION – “CERTIFICATION” OF DAM DESIGNERS, DAM 

CONSTRUCTION INSPECTORS, AND DAM OPERATORS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Lack of understanding of internal erosion by many designers, inspectors, and 

operators. 

2)	 Lack of attention in academic courses. 

3)	 Lack of accessible reference materials. 

4)	 Decrease in number of experienced dam designers who can mentor the next 

generation. 

5) Too many unqualified people who design, inspect, and operate dams. 

B.	 What is the expected outcome? 

1) “Certification” (Georgia Model). 

2) Modules for class use in academic courses and professional development 

programs. 

3) ASDSO/FEMA sponsorship of professional development programs. 

4) Encourage sponsorship of research to focus professors’ interest and support 

graduate students. 

2.	 Project Tasks and Needs 

A. What tasks are to be done?
 

1) Develop training modules (on-line and other).
 

2) Develop guidelines for development of “certification” criteria.
 

3) Recommend research topics and potential sponsors.
 

B.	 How is the problem to be solved? 

1) Sources of funding – NSF; FEMA allocations to state dam safety programs; 

FEMA grants.
 

2) Professional development seminars.
 

3) Co-op training for students.
 

4-36 
EXHIBIT 4-14
 

EXHIBIT 4-14 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3A 

ENHANCE ACADEMIC PROGRAMS AND PROFESSIONAL DEVELOPMENT 

AND TRAINING PROGRAMS RELATED TO SEEPAGE ISSUES IN DAM DESIGN 

AND REHABILITATION – “CERTIFICATION” OF DAM DESIGNERS, DAM 

CONSTRUCTION INSPECTORS, AND DAM OPERATORS 

-CONTINUED3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) TADS program.
 

B.	 Who might be able to lead the project?
 

1) Loren Anderson
 

2) Mike Duncan
 

3) Jim Wright
 

4) Larry Von Thun
 

C. Who are good candidates to complete the work?
 

1) Loren Anderson
 

2) Mike Duncan
 

3) Jim Wright
 

4) Larry Von Thun
 

4-37 
EXHIBIT 4-15
 

EXHIBIT 4-15 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3D 

DEVELOP GUIDANCE FOR DAM SURVEILLANCE PLANS RELATIVE TO 

SEEPAGE 

1.	 Description 

A. Why is this a priority research/development item?
 

1) To provide early warning of problems.
 

2) To utilize and develop new technology.
 

B.	 What is the expected outcome? 

1) To have systems that provide a better likelihood of early detection of seepage 

problems.
 

2) To effectively utilize available money.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Identify new or emerging technologies and add to the list of existing technologies. 

2) Identify parameters to monitor. 

3) Evaluate applicability and effectiveness of each monitoring device for each 

parameter. 

4) Contact specialists in other disciplines: medicine, biolo gy, information 

technology, electrical engineering, and mechanical engineering.
 

5) Consider remote monitoring systems.
 

6) Write a guidance document.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) Agency(s): Lead. 

2) Consultants. 

3) Universities. 

4) Instrumentation providers, instrumentation specialists; including those in other 

disciplines.
 

5) ICOLD, Jerry Dodd.
 

6) USACE – St. Louis; Mike Klosterman, Jim Brown.
 

REPORT OF WORKSHOP ON ISSUES, 

SOLUTIONS AND RESEARCH NEEDS 

RELATED TO SEEPAGE THROUGH EMBANKMENT DAMS 

4-38 
EXHIBIT 4-16
 

EXHIBIT 4-16 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3C 

IMPROVE FAILURE TIME ESTIMATES FOR SEEPAGE-RELATED FAILURE 

MODES FOR EXISTING DAMS 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Key to estimating life loss resulting from failure.
 

2) Statistically, numbers of seepage related failures or incidents are high.
 

3) Existing database is lacking.
 

B.	 What is the expected outcome? 

1) Publication of suggested failure times related to identified variables based on data 

from past failures/incidents.
 

2) Identification of potential future research needs.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Case history research/review.
 

2) Identify variables.
 

3) Determine variables subject to lab testing.
 

4) Develop matrix of variables and failure times.
 

5) Recommended additional research:
 

a) Numerical modeling.
 

b) Lab testing.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) USBR
 

2) University of New South Wale s
 

3) Utah State University
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) See above list. 

2) Add USACE – Vicksburg Research Laboratory, other research/university 

programs, and/or A/E firms. 

4-39 
EXHIBIT 4-17
 

EXHIBIT 4-17 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3D 

IDENTIFY FACTORS FOR FAILURE FOR A) “FIRST FILLING” (INCLUDING 

NORMALLY DRY DAMS/DETENTION DAMS, MAXIMUM POOL, ETC.) AND B) 

LONG TERM, FOR EACH SEEPAGE-RELATED FAILURE MODE 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Risk assessment technology for seepage related issues.
 

2) Many dams/reservoirs have never filled and are high hazard.
 

3) Preponderance of failures are during first filling.
 

B.	 What is the expected outcome?
 

1) Report by NRCS/USBR/USACE.
 

2) Guidance on definition of actual failure modes based on case histories.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Define what constitutes first filling.
 

2) Literature search.
 

3) Review of National Inventory of Dams.
 

4) Select cases with full design and construction documentation.
 

5) Develop opinion of likelihood of various failure modes for each.
 

6) Prepare report for guidance purposes.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) Agencies teamed with consulting community – experts in geotechnical 

engineering.
 

2) USCOLD (USSD)
 

4-40 
EXHIBIT 4-18
 

EXHIBIT 4-18 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 3E 

EXPAND THE DATABASE OF INFORMATION ON SEEPAGE/PIPING 

FAILURES/INCIDENTS FOR DAMS <15 METERS IN HEIGHT 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Large number of dams <15 meters high.
 

2) Proper attention lacking.
 

3) Most likely to exhibit conditions of interest.
 

B.	 What is the expected outcome?
 

1) More information on seepage problems.
 

2) Expanded database for probability of failure.
 

3) Understanding failure modes.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Determine information to be collected. 

2) Determine sub-populations based on dam type, material, etc. 

3) Literature search. 

4) Collect performance information from NRCS, state dam safety organizations, and 

international dam safety organizations.
 

5) Compile and interpret database.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) UNSW, NPDP
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) USSD Committee, ASDSO Committee, NRCS, a university (graduate research). 

4-41 
EXHIBIT 4-19
 

EXHIBIT 4-19 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 4 

INVESTIGATION OF SEEPAGE PROBLEMS/CONCERNS AT DAMS, INCLUDING 

THE USE OF GEOPHYSICAL TECHNIQUES; AND INSTRUMENTATION AND 

MEASUREMENTS FOR EVALUATION OF SEEPAGE PERFORMANCE 

Number 

of Votes Rank Research and Development Idea 

30 1 Technology transfer of geophysical techniques to practical applications in dam safety 

(workshop, documentation, etc.) 

20 2 Determine capabilities of different geophysical methods on a test embankment 

13 3 Technology transfer of investigative techniques from other practices/professions, 

such as the oil fields, mining, environmental investigations, and others 

12 4 Evaluate whether instrumentation installations (e.g., hydraulic tube piezometers) have 

caused damage through investigations of old dams 

8 5 Evaluate photoanalysis/imaging, including infrared imaging, for assessing changes in 

wetting and other seepage-related features 

4 6 Look at data from investigations and instrumentation and assess how, if at all, it has 

been beneficial 

3 7 Evaluate effectiveness of water quality/chemistry data (including temperature data) in 

evaluating seepage 

2 8 Evaluate the effectiveness of dyes and other tracers in assessing seepage conditions 

4-42 
EXHIBIT 4-20
 

EXHIBIT 4-20 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4A 

TECHNOLOGY TRANSFER OF GEOPHYSICAL TECHNIQUES FOR SEEPAGE 

MONITORING 

1. Description 

A. Why is this a priority research/development item? 

1) Lack of communication between geophysicists and geotechnical engineers. 

2) Potentially useful, noninvasive, economical, quick, efficient tools/techniques. 

3) Potential capabilities of techniques are not understood by geotechnical 

community. 

B. What is the expected outcome? 

1) Workshop with proceedings; attended by geotechnical and geophysics 

practitioners. 

2) Guidance document for use of techniques. 

2. Project Tasks and Needs 

A. What tasks are to be done? 

B. How is the problem to be solved? 

1) Organize workshop. 

2) Literature search. 

3) Compile selected short list of topics for workshop, based on interest of 

community. 

4) Geophysicists presentation of capabilities and case histories; positives and 

negatives. 

5) Geotechnical practitioners’ presentation of needs and case histories. 

6) Compile comprehensive comparison; pros and cons. 

7) Prepare guidance document for techniques, and disseminate. 

8) Possibly combine with test embankment. 

4-43 
EXHIBIT 4-20
 

EXHIBIT 4-20 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4A 

TECHNOLOGY TRANSFER OF GEOPHYSICAL TECHNIQUES FOR SEEPAGE 

MONITORING 

-CONTINUED3. Project Lead and Contact 

A. Who is working in this area? 

B. Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) ASDSO/FEMA.
 

2) ASTM.
 

3) Ken Stokee, University of Texas at Austin.
 

4) ASCE.
 

5) USBR.
 

6) USACE.
 

7) USGS.
 

8) Carlos Santamarina, Georgia Tech.
 

9) Bob Whitley.
 

10) James Bay, Student at Utah State University
 

4-44 
EXHIBIT 4-21
 

EXHIBIT 4-21 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4B 

TEST CAPABILITIES OF DIFFERENT GEOPHYSICAL METHODS ON A TEST 

EMBANKMENT 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Engineers are skeptical.
 

2) Benefits are large, if the methods are proven.
 

3) Need to establish limitations and expectations.
 

4) Non-intrusive, no damage.
 

B.	 What is the expected outcome?
 

1) Provide confidence.
 

2) Improved understanding of applications and limitations.
 

3) Weed out ineffective techniques.
 

4) Document (report) findings from engineers’ perspective.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Design test fill; modeling defects, e.g., voids, loose zones, cracks, etc.
 

2) Research and select methods.
 

3) Define performance criteria (what is success?).
 

4) Construct and characterize test fill.
 

5) Perform geophysical tests and interpret results.
 

6) Evaluate all methods, and report.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) CEA (Canadian Electric Association).
 

2) USBR.
 

3) USACE.
 

4) BC Hydro.
 

5) Cons ultants.
 

6) Geophysicists.
 

4-45 
EXHIBIT 4-21
 

EXHIBIT 4-21 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4B 

TEST CAPABILITIES OF DIFFERENT GEOPHYSICAL METHODS ON A TEST 

EMBANKMENT 

-CONTINUEDB.	 Who might be able to lead the project?
 

1) CEA.
 

2) USBR.
 

3) BC Hydro.
 

4) NRCS.
 

C. Who are good candidates to complete the work?
 

1) Contractors/geophysicist.
 

2) Universities.
 

3) Consultants.
 

4) Equipment manufacturers/suppliers.
 

4-46 
EXHIBIT 4-22
 

EXHIBIT 4-22 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4C 

CROSS-DISCIPLINE TECHNOLOGY TRANSFER FOR INVESTIGATIVE 

TECHNIQUES IN DAMS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Limited available technology for seepage investigation. 

2) There may be advances in other industries that could be used to detect seepage in 

dams; these other industries include DOD (Department of Defense), oil fields, 

intelligence, etc. 

B.	 What is the expected outcome? 

1) Identification of existing methods and technologies applicable to seepage 

investigations. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Establish list of parameters/features that need to be identified, measured, 

monitored, etc. (e.g., seepage/water movement, voids, temperature, interface 

conditions, velocities, water pressure, void ratio, etc.). 

2) Review of literature/ prior studies that may have been done for dams. 

3) Identify potential techniques in other industries. 

4) Evaluate identified techniques for their suitability, feasibility, effectiveness, etc. 

for the items established in (1).
 

5) Develop a report summarizing findings.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

1) This is the objective of the study, to identify others having potential applications. 

B.	 Who might be able to lead the project?
 

1) ASDSO.
 

C. Who are good candidates to complete the work?
 

1) Someone like Carlos Santamarina at Georgia Tech.
 

4-47 
EXHIBIT 4-23
 

EXHIBIT 4-23 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4D 

DO/CAN INSTRUMENTS OR INSTRUMENT INSTALLATIONS CAUSE DAMAGE 

IN EMBANKMENT DAMS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Concern that instrument installations can be a source of seepage and potential 

internal erosion.
 

2) May be a gradually deteriorating problem.
 

B.	 What is the expected outcome? 

1)	 Conclusion if there are problems, and, if so, what is the timeframe in which we 

expect they manifest themselves. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Survey dam owners, state representatives, consultant s, and federal agencies for 

instrumentation problems (i.e., when did they stop working, did seepage problem 

occur, etc.). 

2) Correlate the time the problems occurred vs. type of instruments. 

3) Identify remedial measures that might be useful. 

4) Categorize instruments – record locations, head on the instruments etc., types of 

instruments that could be a problem.
 

5) Contact material suppliers about nature of plastic tubing, etc.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) No one is specifically working in this area.
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) USACE.
 

2) USBR.
 

3) ASDSO.
 

4) State of California, Department of Water Resources.
 

4-48 
EXHIBIT 4-24
 

EXHIBIT 4-24 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 4E 

ASSESS PHOTO-MONITORING TECHNIQUES FOR SEEPAGE (INFRARED 

IMAGING, PHOTO INTERPRETATION, ETC.) 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Low cost method.
 

2) Long term monitoring technique.
 

3) Screening technique.
 

4) Early indicator of problems.
 

B.	 What is the expected outcome?
 

1) Overall assessment of value, with report.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Information search – USACE, DEA (Drug Enforcement Agency), USBR, JPL 

(Jet Propulsion Laboratory), NASA, TEC-Fort Belvoir.
 

2) Field calibration/testing of methods – comparison of results.
 

3) Summary report of information.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) Universities – Corne ll, Maine.
 

2) USBR.
 

3) USACE.
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) A university.
 

2) USBR.
 

3) USACE.
 

4-49 
EXHIBIT 4-25
 

EXHIBIT 4-25 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 5 

REMEDIATION OF SEEPAGE PROBLEMS THROUGH CUTOFF OR REDUCTION 

OF FLOW AND THROUGH COLLECTION AND CONTROL OF SEEPAGE, 

(INCLUDING THE USE OF GEOSYNTHETICS) 

Number 

of Votes Rank Research and Development Idea 

24 1 Case study review of performance of seepage remediation projects – distinguishing 

between cutoff only, cutoff combined with adequate downstream drainage/seepage 

collection features, and downstream drainage/seepage collection only 

21 2 Develop a compendium of practices, applications, economics, 

advantages/disadvantages of using geotextiles in dams 

19 3 (Tie) Evaluate the performance of in-place geotextiles 

19 3 (Tie) Develop design criteria for drain collector pipes and surrounding materials to prevent 

plugging 

17 5 Testing of clogging of geotextiles under steady state seepage – properly simulating 

conditions in dam applications 

8 6 Evaluation of performance of biodegradable slurries and other similar materials in the 

construction and performance of French drains 

7 7 (Tie) Look at the deterioration of geosynthetics products under stress (including possible 

“vise-type” stretching 

7 7 Tie) Evaluation of jet grouting, deep soil mixing, and other applicable techniques for 

seepage cutoffs 

2 9 (Tie) Research the applicability of geomembranes for cutoff walls 

2 9 (Tie) Evaluate the design criteria for slots or holes in drain collector pipes 

1 11 Compare the life-cycle costs of grouting versus cutoff walls, with a focus on karst 

terrain 

0 12 Evaluate the applicability of fiber-reinforced concrete and concrete admixtures for use 

in cutoff walls 

4-50 
EXHIBIT 4-26
 

EXHIBIT 4-26 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5A 

REVIEW OF PERFORMANCE OF SEEPAGE REMEDIATION MEASURES: A) 

UPSTREAM CUTOFF ONLY, B) UPSTREAM CUTOFF WITH DOWNSTREAM 

COLLECTION, AND C) DOWNSTREAM COLLECTION ONLY 

1.	 Description 

A. Why is this a priority research/development item? 

1) Validate current design practice. 

2) Reconcile existing disparity among practitioners regarding whether upstream 

cutoff alone is an appropriate remediation approach. 

B.	 What is the expected outcome?
 

1) Recommended practice with compendium of case histories.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Literature search.
 

2) Canvas agencies, consultants, and owners.
 

3) Matrix of evaluation criteria: effectiveness, cost, constructability.
 

4) Collect cases and evaluate.
 

5) Prepare a guidance document.
 

3.	 Project Lead and Contact 

A. Who is working in this area? 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) ASDSO (via university).
 

2) Practicing engineer as sponsor/advisor.
 

4-51 
EXHIBIT 4-27
 

EXHIBIT 4-27 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5B 

COMPILATION OF PRACTICES, APPLICATIONS, EXPERIENCES, ECONOMICS, 

AND ADVANTAGES/DISADVANTAGES OF USING GEOTEXTILES IN DAM 

APPLICATIONS 

1.	 Description 

A. Why is this a priority research/development item? 

1) Geotextiles are being used in applications where perhaps they should not be. 

2) Geotextiles are widely used in small, low hazard dams. 

3) Among many practitioners, there is a strongly held view against geotextiles that 

may not be well based.
 

4) We may find appropriate applications that enhance performance.
 

B.	 What is the expected outcome?
 

1) Report to be widely disseminated.
 

2) Form basis of future guidelines and updates to existing practice.
 

3) Comparison of cost with conventional installation.
 

4) Compilation of case studies.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved?
 

1) Literature review, including lab test data.
 

2) Collect case histories of failures, non-failures, and successes.
 

3) Survey organizations for applications and performance.
 

4) Review of filter design criteria for geotextiles.
 

5) Identify suitable products.
 

6) Advise on constructability issues.
 

7) Guidance on where geotextiles should not be used.
 

8) Summary report of results.
 

4-52 
EXHIBIT 4-27
 

EXHIBIT 4-27 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5B 

COMPILATION OF PRACTICES, APPLICATIONS, EXPERIENCES, ECONOMICS, 

AND ADVANTAGES/DISADVANTAGES OF USING GEOTEXTILES IN DAM 

APPLICATIONS 

-CONTINUED3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) GRI (Geosynthetic Research Institute) at Drexel (R. Koerner).
 

2) USBR.
 

3) French/Germans.
 

4) Landfill industry.
 

5) Geosyntec (J.P. Giroud).
 

B.	 Who might be able to lead the project?
 

1) Embankment dam-oriented person who is open-minded.
 

C. Who are good candidates to complete the work?
 

1) A committee of dam-oriented experts and geotextile experts.
 

4-53 
EXHIBIT 4-28
 

EXHIBIT 4-28 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5C 

EVALUATE THE PERFORMANCE OF IN-PLACE GEOTEXTILES IN SEEPAGE 

CONTROL APPLICATIONS 

1.	 Description 

A. Why is this a priority research/development item? 

1) It is not known if geotextiles are performing as intended in design in dams. 

2) There is significant uncertainty with regard to performance of geotextiles in dams. 

B.	 What is the expected outcome? 

1) Documentation of geotextiles performance. 

2) Recommended practice for use of geotextiles in seepage control applications. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Literature search. 

2) Survey of practice. 

3) Identify projects for in-depth study – dams and other applications. 

4) Identify parameters needed for evaluation (e.g., flows diminished over time). 

5) Gather performance data. 

6) Perform selected forensic investigations, including field and laboratory tests. 

7) Produce report of findings and recommended practice. 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) Geosynthetics Re search Institute – R. Koener.
 

2) ASTM.
 

3) Geosyntec (Rudy Bonaparte, J.P. Giroud).
 

4) IFA (International Fabrics Association).
 

B.	 Who might be able to lead the project?
 

1) ASDSO.
 

2) USBR.
 

C. Who are good candidates to complete the work?
 

1) Consultants.
 

2) Bill Engemoen, USBR.
 

3) Universities.
 

4-54 
EXHIBIT 4-29
 

EXHIBIT 4-29 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5D 

DEVELOP DESIGN CRITERIA FOR DRAINAGE PIPE OPENINGS AND 

SURROUNDING MATERIAL TO PREVENT PLUGGING 

1.	 Description 

A. Why is this a priority research/development item? 

1) There is reported experience of surrounding soils having plugged or partially 

plugged the openings (slots and perforations) in drain collection pipes. 

B.	 What is the expected outcome? 

1) Criteria for appropriate combination of opening size and gradation of backfill 

material. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Define the problem (describe the mechanism/process that creates the problem – 

obtain information from recent USBR work). 

2) Literature search (e.g., ADS studies, Johnson well screen information, dewatering 

contractors, material suppliers). 

3) Develop lab program (large and small scale testing) considering:
 

a) Stress level – crushing.
 

b) Material source – crushed/natural bank run.
 

c) Gradation (Cc, Cu).
 

d) Angularity of particles.
 

e) Shape of pipe wall opening (slots, holes).
 

f) Size of opening.
 

4) Analyze results and prepare recommendations for new designs and existing 

installations. 

5) Document findings in a report. 

4-55 
EXHIBIT 4-29
 

EXHIBIT 4-29 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5D 

DEVELOP DESIGN CRITERIA FOR DRAINAGE PIPE OPENINGS AND 

SURROUNDING MATERIAL TO PREVENT PLUGGING 

-CONTINUED3. Project Lead and Contact 

A. Who is working in this area?
 

1) USACE – Vicksburg Research Laboratory.
 

2) NRCS.
 

3) USBR.
 

B. Who might be able to lead the project? 

C. Who are good candidates to complete the work? 

1) An organization with large laboratory test cell capacity (USACE – Vicksburg 

Research Laboratory, USBR, Utah State University).
 

2) Support from university graduate program.
 

4-56 
EXHIBIT 4-30
 

EXHIBIT 4-30 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 5E 

TESTING OF GEOTEXTILE CLOGGING UNDER STEADY STATE FLOW 

PROPERLY SIMULATING CONDITIONS IN DAM APPLICATIONS 

1.	 Description 

A. Why is this a priority research/development item?
 

1) Because of increased use of geotextiles, we need additional understanding.
 

2) There are currently many misapplications.
 

3) There are reported cases where geotextiles have clogged.
 

B.	 What is the expected outcome?
 

1) A design guidance document for dam applications.
 

2) A conclusion regarding whether geotextiles can be used.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Compile existing studies and data. 

2) Establish parameters for testing (e.g., core vs. filter, various embankment soils vs. 

filter)- consider high stresses typical of embankments. 

3) Set-up testing procedures. 

4) Complete testing program. 

5) Evaluate and prepare written document with recommendations and design criteria. 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) USACE.
 

2) GRI (R. Koerner).
 

3) USBR.
 

4) NRCS.
 

B.	 Who might be able to lead the project?
 

1) USBR.
 

2) ASDSO.
 

C. Who are good candidates to complete the work?
 

1) A university.
 

2) Consultants.
 

4-57 
EXHIBIT 4-31
 

EXHIBIT 4-31 

PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

WORKSHOP TOPIC 6 

IMPACTS OF AGING OF SEEPAGE CONTROL/COLLECTION SYSTEM 

COMPONENTS ON SEEPAGE PERFORMANCE 

Number 

of Votes Rank Research and Development Idea 

28 1 Research and develop techniques for maintaining the operation of relief wells and 

drain collector pipes – include consideration of chemical, physical, and thermal 

methods 

18 2 Develop criteria for frequency of inspection and rehabilitation of horizontal drain 

pipes 

15 3 (Tie) Complete laboratory studies to understand the development of iron bacteria in wells, 

drain pipes, geosynthetics, and soil filter materials - direct the studies toward 

identifying conditions conducive to the development of the bacteria 

15 3 (Tie) Develop a set of test criteria and procedures for evaluating site vulnerability to 

biological or physical/chemical deterioration of drainage collection system 

components 

5 5 Evaluate the rate of dissolution or cementation in soil drain materials 

4 6 Look at materials used in other applications/industries that may prevent biological 

fouling 

3 7 Evaluate the life cycle of bacteria responsible for iron bacteria, for the purpose of 

identifying methods for blocking iron bacteria contamination of wells – this may 

include reduction-oxidation potential methods(1) 

8 8 Evaluate how to clean carbonates from relief wells, including extension into rock 

joints(2) 

Notes: 

(1)	 After prioritization this topic was combined with the first of the third-ranked topic for 

development of an implementation plan. 

(2)	 After prioritization this topic was combined with the second-ranked topic for 

development of an implementation plan. 

4-58 
EXHIBIT 4-32
 

EXHIBIT 4-32 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 6A 

RESEARCH AND DEVELOP TECHNIQUES FOR REMEDIATION AND 

PREVENTION OF CONTAMINATION OF WELLS, DRAINS, AND 

INSTRUMENTATION 

1.	 Description 

A. Why is this a priority research/development item? 

1) Contamination/deterioration of drains and wells leads to reduced effectiveness of 

seepage collection/control systems. 

2) Contamination/deterioration of instruments (piezometers) leads to lengthened 

response times and possibly erroneous performance data. 

B.	 What is the expected outcome? 

1) Recommended designs to reduce the likelihood of contamination. 

2) Recommended procedures/methods to rehabilitate contaminated drains, wells, and 

instruments. 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Collect and evaluate case history information for dams with contamination 

problems and dams without contamination problems. 

2) Collect and evaluate case history information for successful and unsuccessful 

attempts to rehabilitate contaminated drains, wells, and instruments. 

3) Plan and conduct laboratory and field research to investigate and resolve 

questions identified in the case study reviews.
 

4) Develop and publish a report with recommended guidelines.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) USACE, NRCS, USBR, water well industry.
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) USACE, NRCS, USBR, a university (graduate research).
 

4-59 
EXHIBIT 4-33
 

EXHIBIT 4-33 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 6B 

CRITERIA FOR FREQUENCY OF INSPECTIONS AND REHABILITATION OF 

HORIZONTAL DRAINS, INCLUDING REMOVAL OF CARBONATES 

1.	 Description 

A. Why is this a priority research/development item?
 

1) No existing criteria are available.
 

2) There is evidence of drain clogging in existing dams.
 

3) In many cases, drain systems have been neglected by owners.
 

B.	 What is the expected outcome?
 

1) Recommendations for inspection techniques and rehabilitation procedures.
 

2) Recommendations for instrumentation to detect clogging.
 

3) Improve facilities design, inspection, maintenance, and rehabilitation.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

1) Literature survey. 

2) Canvas for case histories. 

3) Review of available technologies in sewer and relief well inspection and 

maintenance.
 

4) Identification of potential problems with maintenance methods.
 

B.	 How is the problem to be solved?
 

1) Guidance document.
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) Sewer industry contractors.
 

2) Industrial pipe cleaners – oil-chemical industries.
 

3) Manufacturing plants.
 

4) Water well contractors.
 

B.	 Who might be able to lead the project?
 

1) USBR.
 

2) USACE.
 

C. Who are good candidates to complete the work?
 

1) Industrial pipe cleaners.
 

4-60 
EXHIBIT 4-34
 

EXHIBIT 4-34 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 6C 

RESEARCH METHODS TO CONTROL AND/OR REMOVE IRON BACTERIA 

DEPOSITS FROM WELLS AND DRAIN SYSTEMS 

1. 	 Description 

A. Why is this a priority research/development item?
 

1) It is a major cause of degradation of wells and drain systems.
 

2) It is a large consumer of maintenance and repair funds.
 

B.	 What is the expected outcome?
 

1) Techniques to control the iron bacteria life cycle level.
 

2) Refinement/optimization of current techniques.
 

3) Automated treatment and systems (e.g., sacrificial anode effect).
 

2.	 Project Tasks and Needs 

A. Wha t tasks are to be done?
 

1) Research life cycle of iron bacteria (biologist).
 

2) Evaluate existing technology:
 

a) Water well industry.
 

b) Water supply engineers.
 

c) Chemists.
 

B.	 How is the problem to be solved?
 

1) Fund Ph.D. student for life cycle research.
 

2) Fund field tests (practical application techniques).
 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) American Waterworks Association.
 

2) USBR.
 

3) USACE.
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) Multidiscipline Advisory Committee.
 

4-61 
EXHIBIT 4-35
 

EXHIBIT 4-35 

RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN 

R&D TOPIC 6D 

DEVELOP TEST CRITERIA AND PROCEDURES FOR EVALUATING SITE 

VULNERABILITY TO PHYSICAL/CHEMICAL/BIOLOGICAL DETERIORATION OF 

SEEPAGE COLLECTION AND CONTROL SYSTEMS 

1.	 Description 

A. Why is this a priority research/development item?
 

1) It is a problem.
 

2) Information is not consolidated or used in dam engineering.
 

3) Could help avoid problems or better design for them.
 

B.	 What is the expected outcome?
 

1) Recommended investigation, sampling, and testing procedures.
 

2) Guide for interpretation of results.
 

2.	 Project Tasks and Needs 

A. What tasks are to be done? 

B.	 How is the problem to be solved? 

1) Information research. 

2) Consulting with experts outside of our field (dam design and construction). 

3) Evaluate and compile information. 

4) Field validate procedures. 

5) Produce guidelines. 

3.	 Project Lead and Contact 

A. Who is working in this area?
 

1) Other industries (chemical, coatings, concrete, well drilling).
 

2) USBR.
 

3) USACE.
 

B.	 Who might be able to lead the project? 

C. Who are good candidates to complete the work?
 

1) USBR.
 

2) USACE.
 

4-62 

5.0 OVERALL PRIORITIZATION

5.0 OVERALL PRIORITIZATION OF RESEARCH AND DEVELOPMENT 

IDEAS 

As discussed in Section 4, the prioritization of the research and development ideas for each 

of the six topics considered in the workshop resulted in the identification of 29 leading ideas 

(4 or 5 ideas for each topic), for which preliminary implementation plans were developed. 

Before the overall prioritization of the leading research and development ideas was 

completed, the workshop participants agreed to combine some of the ideas, reducing the total 

number of research and development ideas to be prioritized to 26. Specifically, R&D Topic 

1A (Compilation of Case Histories of Seepage Incidents Related to Penetrations Through 

Embankment Dams) was combined with R&D Topic 3E (Expand the Database of 

Information on Seepage/Piping Failures/Incidents for Dams <15 meters in Height), R&D 

Topic 1D (Guidelines for Inspecting, Monitoring, and Detecting Seepage Along Penetrations 

Through Embankment Dams) was combined with R&D Topic 3B (Develop Guidance for 

Dam Surveillance Plans Relative to Seepage), and R&D Topic 2C (Evaluate Mechanism Of 

Piping And Failure In Glacial, Alluvial, And Fluvial Environments – Including 

Consideration Of Internal Instability) was combined with R&D Topic 2E (Threshold 

Gradients for Initiating Piping in Cohesive Soils). 

The resulting 26 R&D topics were then prioritized: 1) in a session at the end of the workshop 

and 2) by input provided by the workshop participants after they returned home from the 

workshop. The prioritization of those 26 leading research and development ideas is discussed 

in this section. 

In accordance with the guidance provided by the ASDSO Seepage Advisory Committee, the 

research and development ideas were prioritized considering the following three criteria: 

1.	 Potential benefit. 

2.	 Probability of success. 

3.	 Cost. 

The prioritization was completed in three different ways, as discussed below, and as 

summarized in Exhibits 5-1 through 5-7. 

PRIORITIZATION AT THE END OF THE WORKSHOP 

In a session at the end of the workshop, the participants were asked to prioritize the 26 

leading ideas considering the balance of the three criteria noted above. The research and 

development ideas were posted on flip chart paper displayed on the walls of the room, and 

each participant was given 10 “stick-on” dots with which to cast their “votes.” The 

participants could cast as many votes as they wanted for any particular research and 

development idea, provided that they did not cast more than 10 votes in total. The results of 

this process are summarized on Exhibit 5-1, where the ideas are listed in rank order based on 

the numbers of votes received. As seen in Exhibit 5-1, the top 11 ideas (including a tie for the 

10th position) according to this process are: 

1.	 Enhance Academic Programs and Professional Development and Training Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators 

5-1 
5.0 OVERALL PRIORITIZATION

2.	 Evaluate Mechanism Of Piping And Failure In Glacial, Alluvial, And Fluvial 

Environments – Including Consideration Of Internal Instability, and Including 

Consideration of Threshold Gradients for Initiating Piping in Cohesive Soils 

3.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations through Embankment Dams 

3.	 Technology Transfer of Geophysical Techniques for Seepage Monitoring 

5.	 Develop Guidelines for Design of Filter Diaphragms Associated with Conduits through 

Embankment Dams 

6.	 Evaluate the Performance of In-Place Geotextiles in Seepage Control Applications 

6.	 Research Methods to Control and/or Remove Iron Bacteria Deposits From Wells and 

Drain Systems 

8.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains 

9.	 Assess Technology to Detect Voids and Concentrated Seepage around Penetrations 

through Embankment Dams 

10. Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging 

10. Testing of Fabric Clogging Under Steady State Flow Properly Simulating Conditions in 

Dam Applications 

Note that this list includes ideas tied at ranks 3, 6, and 10. 

PRIORITIZATION AFTER THE WORKSHOP 

The participants were asked to repeat this overall prioritization process again, after they 

returned home from the workshop. The participants were sent a table of the 26 leading ideas 

along with the preliminary implementation plans developed at the workshop, and there were 

asked to again cast 10 votes considering the balance of the three identified criteria, using the 

same rules used at the workshop. Twenty-nine individuals provided input to this process, and 

the results are summarized in Exhibit 5-2. The top 12 ideas (including a three-way tie for 10th 

position) according to this overall rating process are: 

1.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

2.	 Enhance Academic Programs and Professional Development and Training Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators 

3.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains 

4.	 Evaluate Mechanism of Piping and Failure in Glacial, Alluvial, and Fluvial Environments 

– Including Consideration of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

5-2 
5.0 OVERALL PRIORITIZATION

5.	 Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including 

Monitoring, and Detecting Seepage Along Penetrations Through Embankment Dams 

6.	 Assess Technology to Detect Voids and Concentrated Seepage around Penetrations 

through Embankment Dams 

7.	 Technology Transfer of Geophysical Techniques for Seepage Monitoring 

7.	 Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications 

7.	 Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging 

10. Develop Guidelines for Design of Filter Diaphragms Associated with Conduits through 

Embankment Dams 

10. Classification of Conditions Conducive to Hydraulic Fracturing and Cracking 

10. Testing of Fabric Clogging Under Steady State Flow Properly Simulating Conditions in 

Dam Applications 

Note that this list includes ideas tied at ranks 7 and 10. 

In addition to the overall ratings summarized in Exhibit 5-2, the participants were asked to 

score the 26 ideas separately for each of the three criteria: potential benefit, probability of 

success, and cost. For each criterion, the participants were asked to score each idea from 1 to 

4, with 1 being most favorable and 4 being least favorable. Again, 29 participants provided 

input to this process. The average scores for the 26 ideas for the three criteria are presented 

separately in Exhibits 5-3, 5-4, and 5-5. In each of those exhibits, the ideas are listed in rank 

order according the average scores for the individual criterion. In Exhibit 5.6, the individual 

scores for the three different criteria are combined by computing an arithmetic average of the 

three individual scores, giving equal weight to each of the criterion. The top 10 topics 

resulting from this process are: 

1.	 Develop Guidelines for Design of Filter Diaphragms Associated with Conduits through 

Embankment Dams 

2.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains 

3.	 Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including 

Monitoring, and Detecting Seepage along Penetrations through Embankment Dams 

4.	 Development and Deployment of Guidelines for Slip-linings of Outlet Works Conduits 

5.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations through Embankment Dams 

6.	 Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications 

7.	 Enhance Academic Programs and Professional Development and Training Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators 

8.	 Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging 

5-3 
5.0 OVERALL PRIORITIZATION

9.	 Review of Performance of Seepage Remediation Measures: a) Upstream Cutoff only, b) 

Upstream Cutoff with Downstream Collection, and c) Downstream Collection Only 

9.	 Classification of Conditions Conducive to Hydraulic Fracturing and Cracking 

Note that this list includes ideas tied at rank 9. 

The participants were also asked to provide estimates of the cost of implementing each of the 

research and development ideas, if they felt qualified to do so. Unfortunately, only 11 

participants felt qualified to provide cost information and the estimates provided varied 

widely. Consequently, the results are not particularly helpful, but they are provided in this 

report for completeness. 

The participants were asked to provide “low,” “best estimate,” and “high” values for the cost 

of implementing each of the 26 research and development ideas. Eleven participants 

provided “best estimate” values, and nine participants provided “low” and “high” values. The 

“best estimate” values are summarized in Exhibit 5-7, which includes low, high, average, and 

median “best estimates,” and a standard deviation of the “best estimates” for each R&D 

topic. In all cases the standard deviations are greater than the average values, illustrating the 

wide range of the estimates. Summaries of the “low” and “high” values are provided in 

Attachment 10 of this report, and they also show wide variations. The individual “low,” “best 

estimate,” and “high” values from the participants are also presented in Attachment 10. A 

panel experienced with the cost of scientific and engineering research may be able to refine 

the estimated cost data provided by the participants to develop more constrained estimates of 

implementation costs. 

COMPARISON AND COMBINATION OF RESULTS FROM DIFFERENT RANKING 

METHODS 

In Exhibit 5-8, the rankings for the 26 research and development ideas from all three methods 

are compared and combined. The overall rankings resulting from the three different 

processes are averaged, and the ideas are listed in order of average ranking. The resulting top 

10 ideas are: 

1.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations through Embankment Dams 

2.	 Enhance Academic Programs and Professional and Training Development Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators 

3.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains 

4.	 Develop Guidelines for Design of Filter Diaphragms Associated with Conduits through 

Embankment Dams 

5.	 Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including 

Monitoring, and Detecting Seepage Along Penetrations through Embankment Dams 

6.	 Technology Transfer of Geophysical Techniques for Seepage Monitoring 

7.	 Evaluate Mechanism of Piping and Failure in Glacial, Alluvial, and Fluvial Environments 

– Including Consideration of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

5-4 
5.0 OVERALL PRIORITIZATION

8.	 Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging 

9.	 Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications 

10. Assess Technology to Detect Voids and Concentrated Seepage around Penetrations 

through Embankment Dams 

OVERALL PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 

In reviewing the results of the overall rankings using the three different methods (Exhibits 5­

1, 5-2, and 5-6), it is seen that the priority order of the ideas varies somewhat among the 

three methods. However, by analyzing the information summarized in Exhibit 5-8, the 

authors believe that priorities among the ideas become clear. To assist in this effort, all of the 

individual top 10 rankings (for the three separate methods) have been indicated by shaded 

boxes in Exhibit 5-8. 

Considering the combination of the number of rankings in the top 10 and the average 

rankings (averages of the individual rankings from all three methods), it is the authors’ 

opinion that the following four topics are clearly the highest priority of the research and 

development ideas considered: 

1.	 Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 

meters in Height, and Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams (R&D Topics 3E & 1A) 

2.	 Enhancement Academic Programs and Professional Development and Training Programs 

Related to Seepage Issues in Dam Design and Rehabilitation – “Certification” of Dam 

Designers, Dam Construction Inspectors, and Dam Operators (R&D Topic 3A) 

3.	 Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods 

for Filters and Drains (R&D Topic 2B) 

4.	 Develop Guidelines for Design of Filter Diaphragms Associated With Conduits Through 

Embankment Dams (R&D Topic 1C) 

All four of these ideas were ranked in the top 10 by all three methods used and they ranked 1 

through 4 in the average ranking (average of individual rankings in the three methods). 

In the authors’ opinion, the next six research and development ideas listed in Exhibit 5-8 

should also be considered high priority research and development ideas, but not as high as 

the top four topics. Those six topics are: 

1.	 Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to 

Prevent Plugging (R&D Topic 5D) 

2.	 Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including 

Monitoring, and Detecting Seepage Along Penetrations Through Embankment Dams 

(R&D Topics 3B & 1D) 

3.	 Technology Transfer of Geophysical Techniques for Seepage Monitoring (R&D Topic 

4A) 

4.	 Evaluate Mechanism of Piping and Failure in Glacial, Alluvial, and Fluvial Environments 

– Including Consideration of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils (R&D Topics 2C& 2E) 

5-5 
5.0 OVERALL PRIORITIZATION

5.	 Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications (R&D Topic 5B) 

6.	 Assessing Technology to Detect Voids and Concentrated Seepage around Penetrations 

through Embankment Dams (R&D Topic 1B) 

Of those six research and development ideas, Topic 5D received top 10 rankings in all three 

methods, but the individual rankings were in the lower range of the top 10 (rankings of 10, 8, 

and 7). The other five ideas all received top 10 rankings in two out of the three methods used. 

The following six other research and development ideas received top 10 rankings in at least 

one of the methods used: 

1.	 Evaluate the Performance of In-Place Geotextiles in Seepage Control Applications (R&D 

Topic 5C) 

2.	 Testing of Fabric Clogging Under Steady State Flow Properly Simulating Conditions in 

Dam Applications (R&D Topic 5E) 

3.	 Classification of Conditions Conducive to Hydraulic Fracturing and Cracking (R&D 

Topic 2A) 

4.	 Review of Performance of Seepage Remediation Measures: a) Upstream Cutoff Only, b) 

Upstream Cutoff With Downstream Collection, and c) Downstream Collection Only 

(R&D Topic 5A) 

5.	 Research Methods to Control and/or Remove Iron Bacteria Deposits from Wells and 

Drain Systems (R&D Topic 6C) 

6.	 Development and Deployment of Guidelines for Slip-linings of Outlet Works Conduits 

(R&D Topic 1E) 

Based on receiving a top 10 ranking in one of the methods, these research and development 

ideas deserve some consideration for implementation, but with less priority than the top 10 

ideas. 

The remaining 10 ideas did not receive top 10 ratings in any of the three methods, and 

therefore should be considered much lower on the priority scale for implementation. 

FURTHER COMBINATIONS OF RESEARCH AND DEVELOPMENT IDEAS 

From a review of the research and development ideas considered at the workshop, the 

authors suggest that, in implementation of research and development plans, consideration be 

given to the following additional combinations of ideas: 

1.	 R&D Topics 2B (Develop State-of-the-Practice for Configurations, Dimensions, and 

Construction Methods for Filters and Drains) and 1C (Develop Guidelines for Design of 

Filter Diaphragms Associated With Conduits Through Embankment Dams). 

2.	 R&D Topics 5B (Compilation of Practices, Applications, Experiences, Economics, and 

Advantages/Disadvantages of Using Geotextiles in Dam Applications) and 5C (Evaluate 

the Performance of In-Place Geotextiles in Seepage Control Applications). 

3.	 R&D Topics 6C (Research Methods to Control and/or Remove Iron Bacteria Deposits 

From Wells and Drain Systems) and 6A (Research And Develop Techniques For 

Remediation And Prevention of Contamination Of Wells, Drains, and Instrumentation). 

5-6 
5.0 OVERALL PRIORITIZATION

4.	 R&D Topics 3B & 1D (Develop Guidance for Dam Surveillance Plans Relative to 

Seepage, Including Monitoring, and Detecting Seepage Along Penetrations Through 

Embankment Dams) and 1B (Assess Technology to Detect Voids and Concentrated 

Seepage around Penetrations through Embankment Dams). 

OBSERVATIONS CONCERNING RESEARCH AND DEVELOPMENT IDEAS 

In reviewing the leading research and development ideas as discussed above, it is interesting 

to note that very few of the ideas involve basic laboratory or field research. In fact, only 

R&D Topics 2E, 5D, 1B, 5E, 2A, and 6C include such basic research, and none of the top 

four topics listed above include basic research. Rather, most of the topics involve collecting 

or compiling available information and developing guidelines for dissemination to 

practitioners. In the authors’ opinion, this reflects a sense among the workshop participants 

that the topic of seepage through embankment dams is relatively mature, and that most 

seepage problems are the result of misuse or misunderstanding of available information or 

lack of knowledge of available information by some members of the engineering community. 

It also seems to reflect a feeling that the information on seepage through embankment dams 

is too dispersed for the profession to make the best use of lessons-learned from past 

performance, and that compilation of information into more readily available sources would 

be beneficial. 

5-7 
EXHIBIT 5-1
 

EXHIBIT 5-1
 

RANKING OF RESEARCH/DEVELOPMENT IDEAS
 

BASED ON OVERALL VOTES AT THE WORKSHOP
 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

3A Enhance Academic Programs and Professional Development 35 

and Training Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of Dam Designers, 

Dam Construction Inspectors, and Dam Operators 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 29 

Alluvial, And Fluvial Environments – Including Consideration 

Of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

3E & 1A Expand the Database of Information on Seepage/Piping 26 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

4A Technology Transfer of Geophysical Techniques for Seepage 26 

Monitoring 

1C Develop Guidelines for Design of Filter Diaphragms 22 

Associated With Conduits Through Embankment Dams 

5C Evaluate the Performance of In-Place Geotextiles in Seepage 18 

Control Applications 

6C Research Methods to Control and/or Remove Iron Bacteria 18 

Deposits From Wells and Drain Systems 

2B Develop State-of-the-Practice for Configurations, Dimensions, 17 

and Construction Methods for Filters and Drains 

1B Assess Technology to Detect Voids and Concentrated Seepage 16 

Around Penetrations Through Embankment Dams 

5D Develop Design Criteria for Drainage Pipe Openings and 15 

Surrounding Material to Prevent Plugging 

5E Testing of Fabric Clogging Under Steady State Flow Properly 15 

Simulating Conditions in Dam Applications 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 12 

Seepage, Including Monitoring, and Detecting Seepage Along 

Penetrations Through Embankment Dams 

1 

2 

3 (Tie) 

3 (Tie) 

5 

6 (Tie) 

6 (Tie) 

8 

9 

10 (Tie) 

10 (Tie) 

12 

Note:	 (1) Participants were asked to cast up to 10 votes, considering the balance of three 

criteria: potential benefit, probability of success, and cost. Each participant could cast 

as many votes as he or she wanted for any particular topic, as long as the total number 

of votes cast did not exceed 10. 

5-8 
EXHIBIT 5-1
 

EXHIBIT 5-1 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON OVERALL VOTES AT THE WORKSHOP 

-CONTINUEDTOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

4B Test Capabilities of Different Geophysical Methods on a Test 11 13 

Embankment 

5B Compilation of Practices, Applications, Experiences, 9 14 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

5A Review of Performance of Seepage Remediation Measures: a) 6 15 

Upstream Cutoff Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

6D Develop Test Criteria and Procedures for Evaluating Site 5 16 

Vulnerability to Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

4C Cross-Discipline Technology Transfer for Investigative 4 17 (Tie) 

Techniques in Dams 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared 4 17 (Tie) 

Imaging, Photo Interpretation, etc.) 

2A Classification of Conditions Conducive to Hydraulic 3 19 (Tie) 

Fracturing and Cracking 

6B Criteria for Frequency of Inspections and Rehabilitation of 3 19 (Tie) 

Horizontal Drains, Including Removal of Carbonates 

2D Evaluation of Mechanical/Geochemical Degradation of 2 21 (Tie) 

Properties of Filter Materials, Including Cementation and the 

Ability to Sustain a Crack 

3C Improve Failure Time Estimates for Seepage-Related Failure 2 21 (Tie) 

Modes for Existing Dams 

6A Research And Develop Techniques For Remediation And 2 21 (Tie) 

Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

1E Development and Deployment of Guidelines for Slip-linings 1 24 

of Outlet Works Conduits 

3D Identify Factors for Failure for a) “First Filling” (Including 0 25 (Tie) 

Normally Dry Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related Failure Mode 

4D Do/Can Instruments or Instrument Installations Cause Damage 0 25 (Tie) 

in Embankment Dams 

Note: (1) Participants were asked to cast up to 10 votes, considering the balance of three 

criteria: potential benefit, probability of success, and cost. Each participant could 

cast as many votes as he or she wanted for any particular topic, as long as the 

total number of votes cast did not exceed 10. 

5-9 
EXHIBIT 5-2
 

EXHIBIT 5-2
 

RANKING OF RESEARCH/DEVELOPMENT IDEAS
 

BASED ON OVERALL VOTES AFTER THE WORKSHOP
 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

3E & 1A Expand the Database of Information on Seepage/Piping 29 1 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

3A Enhance Academic Programs and Professional Development 27 2 

and Training Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of Dam Designers, 

Dam Construction Inspectors, and Dam Operators 

2B Develop State-of-the-Practice for Configurations, Dimensions, 19 3 

and Construction Methods for Filters and Drains 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 17 4 

Alluvial, And Fluvial Environments – Including Consideration 

Of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 16 5 

Seepage, Including Monitoring, and Detecting Seepage Along 

Penetrations Through Embankment Dams 

1B Assess Technology to Detect Voids and Concentrated Seepage 15 6 

Around Penetrations Through Embankment Dams 

4A Technology Transfer of Geophysical Techniques for Seepage 13 7 (Tie) 

Monitoring 

5B Compilation of Practices, Applications, Experiences, 13 7 (Tie) 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

5D Develop Design Criteria for Drainage Pipe Openings and 13 7 (Tie) 

Surrounding Material to Prevent Plugging 

1C Develop Guidelines for Design of Filter Diaphragms 12 10 (tie) 

Associated With Conduits Through Embankment Dams 

2A Classification of Conditions Conducive to Hydraulic 12 10 (tie) 

Fracturing and Cracking 

5E Testing of Fabric Clogging Under Steady State Flow Properly 12 10 (tie) 

Simulating Conditions in Dam Applications 

5C Evaluate the Performance of In-Place Geotextiles in Seepage 11 13 

Control Applications 

Note: (1) Participants were asked to cast up to 10 votes, considering the balance of three 

criteria: potential benefit, probability of success, and cost. Each participant could 

cast as many votes as he or she wanted for any particular topic, as long as the 

total number of votes cast did not exceed 10. 

5-10 
EXHIBIT 5-2
 

EXHIBIT 5-2 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON OVERALL VOTES AFTER THE WORKSHOP 

-CONTINUEDTOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

3C Improve Failure Time Estimates for Seepage-Related Failure 10 14 

Modes for Existing Dams 

1E Development and Deployment of Guidelines for Slip-linings 9 15 (Tie) 

of Outlet Works Conduits 

4B Test Capabilities of Different Geophysical Methods on a Test 9 15 (Tie) 

Embankment 

2D Evaluation of Mechanical/Geochemical Degradation of 8 17 (Tie) 

Properties of Filter Materials, Including Cementation and the 

Ability to Sustain a Crack 

5A Review of Performance of Seepage Remediation Measures: a) 8 17 (Tie) 

Upstream Cutoff Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

6C Research Methods to Control and/or Remove Iron Bacteria 8 17 (Tie) 

Deposits From Wells and Drain Systems 

6D Develop Test Criteria and Procedures for Evaluating Site 8 17 (Tie) 

Vulnerability to Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

3D Identify Factors for Failure for a) “First Filling” (Including 6 21 (Tie) 

Normally Dry Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related Failure Mode 

4C Cross-Discipline Technology Transfer for Investigative 6 21 (Tie) 

Techniques in Dams 

6A Research And Develop Techniques For Remediation And 5 23 

Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

4D Do/Can Instruments or Instrument Installations Cause Damage 2 24 

in Embankment Dams 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared 1 25 (Tie) 

Imaging, Photo Interpretation, etc.) 

6B Criteria for Frequency of Inspections and Rehabilitation of 1 25 (Tie) 

Horizontal Drains, Including Removal of Carbonates 

Note: (1) Participants were asked to cast up to 10 votes, considering the balance of three 

criteria: potential benefit, probability of success, and cost. Each participant could 

cast as many votes as he or she wanted for any particular topic, as long as the total 

number of votes cast did not exceed 10. 

5-11 
EXHIBIT 5-3
 

EXHIBIT 5-3 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR POTENTIAL BENEFIT ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

3A Enhance Academic Programs and Professional Development 

and Training Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of Dam Designers, 

Dam Construction Inspectors, and Dam Operators 

3E & 1A Expand the Database of Information on Seepage/Piping 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

1B Assess Technology to Detect Voids and Concentrated Seepage 

Around Penetrations Through Embankment Dams 

5C Evaluate the Performance of In-Place Geotextiles in Seepage 

Control Applications 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 

Seepage, Including Monitoring, and Detecting Seepage Along 

Penetrations Through Embankment Dams 

5B Compilation of Practices, Applications, Experiences, 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 

Alluvial, And Fluvial Environments – Including Consideration 

Of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

2B Develop State-of-the-Practice for Configurations, Dimensions, 

and Construction Methods for Filters and Drains 

5E Testing of Fabric Clogging Under Steady State Flow Properly 

Simulating Conditions in Dam Applications 

6C Research Methods to Control and/or Remove Iron Bacteria 

Deposits From Wells and Drain Systems 

5D Develop Design Criteria for Drainage Pipe Openings and 

Surrounding Material to Prevent Plugging 

1C Develop Guidelines for Design of Filter Diaphragms 

Associated With Conduits Through Embankment Dams 

1.552 1 

1.672 2 

1.724 3 (Tie) 

1.724 3 (Tie) 

1.741 5 (Tie) 

1.741 5 (Tie) 

1.793 7 

1.862 8 

1.897 9 (Tie) 

1.897 9 (Tie) 

1.983 11 

2.034 12 (Tie) 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being the most 

benefit and 4 being the least benefit. 

5-12 
EXHIBIT 5-3
 

EXHIBIT 5-3 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR POTENTIAL BENEFIT ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

-CONTINUEDTOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

4A Technology Transfer of Geophysical Techniques for Seepage 2.034 12 (Tie) 

Monitoring 

5A Review of Performance of Seepage Remediation Measures: a) 2.034 12 (Tie) 

Upstream Cutoff Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

1E Development and Deployment of Guidelines for Slip-linings 2.138 15 

of Outlet Works Conduits 

6A Research And Develop Techniques For Remediation And 2.172 16 

Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

2D Evaluation of Mechanical/Geochemical Degradation of 2.207 17 (Tie) 

Properties of Filter Materials, Including Cementation and the 

Ability to Sustain a Crack 

4B Test Capabilities of Different Geophysical Methods on a Test 2.207 17 (Tie) 

Embankment 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared 2.207 17 (Tie) 

Imaging, Photo Interpretation, etc.) 

6D Develop Test Criteria and Procedures for Evaluating Site 2.241 20 

Vulnerability to Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

3D Identify Factors for Failure for a) “First Filling” (Including 2.310 21 

Normally Dry Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related Failure Mode 

3C Improve Failure Time Estimates for Seepage-Related Failure 2.345 22 

Modes for Existing Dams 

2A Classification of Conditions Conducive to Hydraulic 2.362 23 

Fracturing and Cracking 

6B Criteria for Frequency of Inspections and Rehabilitation of 2.414 24 

Horizontal Drains, Including Removal of Carbonates 

4D Do/Can Instruments or Instrument Installations Cause Damage 2.552 25 

in Embankment Dams 

4C Cross-Discipline Technology Transfer for Investigative 2.603 26 

Techniques in Dams 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being the most 

benefit and 4 being the least benefit. 

5-13 
EXHIBIT 5-4
 

EXHIBIT 5-4 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR PROBABILITY OF SUCCESS ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

1C Develop Guidelines for Design of Filter Diaphragms 1.48 1 

Associated With Conduits Through Embankment Dams 

3E & 1A Expand the Database of Information on Seepage/Piping 1.55 2 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

1E Development and Deployment of Guidelines for Slip-linings 1.66 3 (Tie) 

of Outlet Works Conduits 

2B Develop State-of-the-Practice for Configurations, Dimensions, 1.66 3 (Tie) 

and Construction Methods for Filters and Drains 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 1.79 5 

Seepage, Including Monitoring, and Detecting Seepage Along 

Penetrations Through Embankment Dams 

5D Develop Design Criteria for Drainage Pipe Openings and 1.83 6 

Surrounding Material to Prevent Plugging 

5B Compilation of Practices, Applications, Experiences, 1.93 7 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

3A Enhance Academic Programs and Professional Development 2.00 8 

and Training Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of Dam Designers, 

Dam Construction Inspectors, and Dam Operators 

6B Criteria for Frequency of Inspections and Rehabilitation of 2.10 9 

Horizontal Drains, Including Removal of Carbonates 

2A Classification of Conditions Conducive to Hydraulic 2.14 10 

Fracturing and Cracking 

5A Review of Performance of Seepage Remediation Measures: a) 2.21 11 

Upstream Cutoff Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

5C Evaluate the Performance of In-Place Geotextiles in Seepage 2.31 12(Tie) 

Control Applications 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being high 

probability and 4 being low probability. 

5-14 
EXHIBIT 5-4
 

EXHIBIT 5-4 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR PROBABILITY OF SUCCESS ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

-CONTINUEDTOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

5E Testing of Fabric Clogging Under Steady State Flow Properly 2.31 12 (Tie) 

Simulating Conditions in Dam Applications 

6A Research And Develop Techniques For Remediation And 2.34 14 

Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

3D Identify Factors for Failure for a) “First Filling” (Including 2.40 15 

Normally Dry Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related Failure Mode 

6C Research Methods to Control and/or Remove Iron Bacteria 2.43 16 

Deposits From Wells and Drain Systems 

2D Evaluation of Mechanical/Geochemical Degradation of 2.53 17 

Properties of Filter Materials, Including Cementation and the 

Ability to Sustain a Crack 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared 2.55 18 

Imaging, Photo Interpretation, etc.) 

6D Develop Test Criteria and Procedures for Evaluating Site 2.59 19 

Vulnerability to Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 2.60 20 

Alluvial, And Fluvial Environments – Including Consideration 

Of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

4A Technology Transfer of Geophysical Techniques for Seepage 2.62 21 

Monitoring 

4B Test Capabilities of Different Geophysical Methods on a Test 2.67 22 

Embankment 

4D Do/Can Instruments or Instrument Installations Cause Damage 2.69 23 

in Embankment Dams 

1B Assess Technology to Detect Voids and Concentrated Seepage 2.79 24 

Around Penetrations Through Embankment Dams 

4C Cross-Discipline Technology Transfer for Investigative 2.84 25 

Techniques in Dams 

3C Improve Failure Time Estimates for Seepage-Related Failure 3.03 26 

Modes for Existing Dams 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being high 

probability and 4 being low probability. 

5-15 
EXHIBIT 5-5
 

EXHIBIT 5-5 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR COST ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

1C Develop Guidelines for Design of Filter Diaphragms 1.55 1 (Tie) 

Associated With Conduits Through Embankment Dams 

1E Development and Deployment of Guidelines for Slip-linings 1.55 1 (Tie) 

of Outlet Works Conduits 

2B Develop State-of-the-Practice for Configurations, Dimensions, 1.59 3 

and Construction Methods for Filters and Drains 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 1.66 4 

Seepage, Including Monitoring, and Detecting Seepage Along 

Penetrations Through Embankment Dams 

4A Technology Transfer of Geophysical Techniques for Seepage 1.83 5 

Monitoring 

2A Classification of Conditions Conducive to Hydraulic 1.93 6 (Tie) 

Fracturing and Cracking 

6B Criteria for Frequency of Inspections and Rehabilitation of 1.93 6 (Tie) 

Horizontal Drains, Including Removal of Carbonates 

5B Compilation of Practices, Applications, Experiences, 2.00 8 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

4C Cross-Discipline Technology Transfer for Investigative 2.09 9 

Techniques in Dams 

5D Develop Design Criteria for Drainage Pipe Openings and 2.12 10 

Surrounding Material to Prevent Plugging 

3D Identify Factors for Failure for a) “First Filling” (Including 2.16 11 

Normally Dry Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related Failure Mode 

5A Review of Performance of Seepage Remediation Measures: a) 2.17 12 

Upstream Cutoff Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

3E & 1A Expand the Database of Information on Seepage/Piping 2.21 13 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being low cost and 

4 being high cost. 

5-16 
EXHIBIT 5-5
 

EXHIBIT 5-5 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON INDIVIDUAL SCORES FOR COST ­

SCORES GIVEN BY PARTICIPANTS AFTER THE WORKSHOP 

-CONTINUEDTOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) NUMBER OF 

VOTES (1) 

RANK 

3A Enhance Academic Programs and Professional Development 2.31 14 

and Training Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of Dam Designers, 

Dam Construction Inspectors, and Dam Operators 

4D Do/Can Instruments or Instrument Installations Cause Damage 2.34 15 

in Embankment Dams 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared 2.38 16 

Imaging, Photo Interpretation, etc.) 

1B Assess Technology to Detect Voids and Concentrated Seepage 2.60 17 

Around Penetrations Through Embankment Dams 

5C Evaluate the Performance of In-Place Geotextiles in Seepage 2.64 18 (Tie) 

Control Applications 

5E Testing of Fabric Clogging Under Steady State Flow Properly 2.64 18 (Tie) 

Simulating Conditions in Dam Applications 

2D Evaluation of Mechanical/Geochemical Degradation of 2.71 20 

Properties of Filter Materials, Including Cementation and the 

Ability to Sustain a Crack 

3C Improve Failure Time Estimates for Seepage-Related Failure 2.72 21 

Modes for Existing Dams 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 2.76 22 

Alluvial, And Fluvial Environments – Including Consideration 

Of Internal Instability, and Including Consideration of 

Threshold Gradients for Initiating Piping in Cohesive Soils 

6A Research And Develop Techniques For Remediation And 2.83 23 (Tie) 

Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

6D Develop Test Criteria and Procedures for Evaluating Site 2.83 23 (Tie) 

Vulnerability to Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

6C Research Methods to Control and/or Remove Iron Bacteria 2.86 25 

Deposits From Wells and Drain Systems 

4B Test Capabilities of Different Geophysical Methods on a Test 3.59 26 

Embankment 

Note: (1) Participants were asked to score each topic from 1 to 4, with 1 being low cost and 

4 being high cost. 

5-17 
EXHIBIT 5-6
 

EXHIBIT 5-6 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON COMBINATION OF INDIVIDUAL SCORES FOR POTENTIAL 

BENEFIT, PROBABILITY OF SUCCESS, AND COST 

INDIVIDUAL SCORES (1) 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) POTENTIAL 

BENEFIT 

PROBABILITY 

OF SUCCESS 

COST AVERAGE 

OVERALL 

SCORE(2 ) 

RANK 

1C Develop Guidelines for Design of Filter Diaphragms 

Associated With Conduits Through Embankment Dams 

2.03 1.48 1.55 1.69 1 

2B Develop State-of-the-Practice for Configurations, 

Dimensions, and Construction Methods for Filters and 

Drains 

1.86 1.66 1.59 1.70 2 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 

Seepage, Including Monitoring, and Detecting Seepage 

Along Penetrations Through Embankment Dams 

1.74 1.79 1.66 1.73 3 

1E Development and Deployment of Guidelines for Sliplinings of Outlet Works Conduits 2.14 1.66 1.55 1.78 4 

3E & 1A Expand the Database of Information on Seepage/Piping 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

1.67 1.55 2.21 1.81 5 

5B Compilation of Practices, Applications, Experiences, 

Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

1.74 1.93 2.00 1.89 6 

3A Enhance Academic Programs and Professional 

Issues in Dam Design and Rehabilitation – “Certification” 

of Dam Designers, Dam Construction Inspectors, and Dam 

Operators 

1.55 2.00 2.31 1.95 7 

5D Develop Design Criteria for Drainage Pipe Openings and 

Surrounding Material to Prevent Plugging 

1.98 1.83 2.12 1.98 8 

5A Review of Performance of Seepage Remediation 

Measures: a) Upstream Cutoff Only, b) Upstream Cutoff 

With Downstream Collection, and c) Downstream 

Collection Only 

2.03 2.21 2.17 2.14 9 (Tie) 

2A Classification of Conditions Conducive to Hydraulic 

Fracturing and Cracking 

2.36 2.14 1.93 2.14 9 (Tie) 

6B Criteria for Frequency of Inspections and Rehabilitation of 

Horizontal Drains, Including Removal of Carbonates 

2.41 2.10 1.93 2.15 11 

4A 

Seepage Monitoring 

2.03 2.62 1.83 2.16 12 

5C Evaluate the Performance of In-Place Geotextiles in 

Seepage Control Applications 

1.72 2.31 2.64 2.22 13 

Development and Training Programs Related to Seepage 

Technology Transfer of Geophysical Techniques for 

Notes: (1) From Exhibits 5-3, 5-4, and 5-5. 

(2) Arithmetic average of the three individual scores. 

5-18 
EXHIBIT 5-6
 

EXHIBIT 5-6 

RANKING OF RESEARCH/DEVELOPMENT IDEAS 

BASED ON COMBINATION OF INDIVIDUAL SCORES FOR POTENTIAL 

BENEFIT, PROBABILITY OF SUCCESS, AND COST 

-CONTINUEDINDIVIDUAL SCORES (1) 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) POTENTIAL 

BENEFIT 

PROBABILITY 

OF SUCCESS 

COST AVERAGE 

OVERALL 

SCORE(2 ) 

RANK 

5E Testing of Fabric Clogging Under Steady State 

Flow Properly Simulating Conditions in Dam 

Applications 

1.90 2.31 2.64 2.28 14 

3D Identify Factors for Failure for a) “First 

Filling” (Including Normally Dry 

Dams/Detention Dams, Maximum Pool, etc.) 

and b) Long Term, for Each Seepage-Related 

Failure Mode 

2.31 2.40 2.16 2.29 15 

1B Assess Technology to Detect Voids and 

Concentrated Seepage Around Penetrations 

Through Embankment Dams 

1.72 2.79 2.60 2.37 16 

4E Assess Photo-Monitoring Techniques for 

Seepage (Infrared Imaging, Photo 

Interpretation, etc.) 

2.21 2.55 2.38 2.38 17 

Glacial, Alluvial, And Fluvial Environments – 

Including Consideration Of Internal Instability, 

and Including Consideration of Threshold 

Gradients for Initiating Piping in Cohesive 

Soils 

1.79 2.60 2.76 2.39 18 

6C Research Methods to Control and/or Remove 

Iron Bacteria Deposits From Wells and Drain 

Systems 

1.90 2.43 2.86 2.40 19 

6A Research And Develop Techniques For 

Remediation And Prevention Of 

Contamination Of Wells, Drains, And 

Instrumentation 

2.17 2.34 2.83 2.45 20 

2D Evaluation of Mechanical/Geochemical 

Degradation of Properties of Filter Materials, 

Including Cementation and the Ability to 

Sustain a Crack 

2.21 2.53 2.71 2.48 21 

4C Cross-Discipline Technology Transfer for 

Investigative Techniques in Dams 

2.60 2.84 2.09 2.51 22 

4D Do/Can Instruments or Instrument Installations 

Cause Damage in Embankment Dams 

2.55 2.69 2.34 2.53 23 

6D Develop Test Criteria and Procedures for 

Evaluating Site Vulnerability to 

Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

2.24 2.59 2.83 2.55 24 

3C Improve Failure Time Estimates for SeepageRelated Failure Modes for Existing Dams 2.34 3.03 2.72 2.70 25 

4B Test Capabilities of Different Geophysical 

Methods on a Test Embankment 

2.21 2.67 3.59 2.82 26 

2C & 2E Evaluate Mechanism Of Piping And Failure In 

Notes: (1) From Exhibits 5-3, 5-4, and 5-5. 

(2) Arithmetic average of the three individual scores.

5-19 
EXHIBIT 5-7
 

EXHIBIT 5-7 

BEST ESTIMATES OF IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT 

IDEAS BASED ON INPUT FROM WORKSHOP PARTICIPANTS(1) 

ESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW(2) HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

1B Assess Technology to Detect Voids and Concentrated 

Seepage Around Penetrations Through Embankment Dams 

10 3500 457.5 100 977.1 

1C Develop Guidelines for Design of Filter Diaphragms 

Associated With Conduits Through Embankment Dams 

7 800 105.6 30 221.2 

1E Development and Deployment of Guidelines for Sliplinings of Outlet Works Conduits 7 100 47.9 40 34.8 

2A Classification of Conditions Conducive to Hydraulic 

Fracturing and Cracking 

9 300 97.6 75 94.6 

2B Develop State-of-the-Practice for Configurations, 

Dimensions, and Construction Methods for Filters and 

Drains 

6 500 78.2 45 135.3 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, 

Alluvial, And Fluvial Environments – Including 

Consideration Of Internal Instability, and Including 

Consideration of Threshold Gradients for Initiating Piping 

in Cohesive Soils 

15 1400 389.3 100 474.1 

2D Evaluation of Mechanical/Geochemical Degradation of 

Properties of Filter Materials, Including Cementation and 

the Ability to Sustain a Crack 

9 1500 364.4 150 472.7 

3A Enhance Academic Programs and Professional 

Issues in Dam Design and Rehabilitation – “Certification” 

of Dam Designers, Dam Construction Inspectors, and Dam 

Operators 

9 1000 317.6 100 401.5 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to 

Seepage, Including Monitoring, and Detecting Seepage 

Along Penetrations Through Embankment Dams 

9 800 123.5 50 220.2 

3C Improve Failure Time Estimates for Seepage-Related 

Failure Modes for Existing Dams 

13 2000 389.3 100 653.0 

3D Identify Factors for Failure for a) “First Filling” (Including 

Normally Dry Dams/Detention Dams, Maximum Pool, 

etc.) and b) Long Term, for Each Seepage-Related Failure 

Mode 

10 1500 219.1 75 413.7 

3E & 1A Expand the Database of Information on Seepage/Piping 

Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to 

Penetrations Through Embankment Dams 

10 500 132.5 60 147.3 

Development and Training Programs Related to Seepage 

4A 

Seepage Monitoring 

Technology Transfer of Geophysical Techniques for 0 300 85.1 50 104.6

Notes: (1)	 Based on input from 11 participants; see Table ATT 10-4, Attachment 10 for 

individual estimates by participants. 

(2)	 "0" estimates in the "low" column are from one participant who thought that each 

of these topics would be combined with another topic, hence the cost was 

included in the cost for the other topic. 

5-20 
EXHIBIT 5-7
 

EXHIBIT 5-7 

BEST ESTIMATES OF IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT 

IDEAS BASED ON INPUT FROM WORKSHOP PARTICIPANTS(1) 

-CONTINUEDESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW(2) HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

4B Test Capabilities of Different Geophysical 

Methods on a Test Embankment 

30 2500 841.8 300 884.5 

4C Cross-Discipline Technology Transfer for 

Investigative Techniques in Dams 

0 500 113.2 50 145.9 

4D Do/Can Instruments or Instrument Installations 

Cause Damage in Embankment Dams 

10 1000 188.2 50 302.1 

4E Assess Photo-Monitoring Techniques for 

Seepage (Infrared Imaging, Photo 

Interpretation, etc.) 

0 1400 246.1 40 413.7 

5A Review of Performance of Seepage 

Remediation Measures: a) Upstream Cutoff 

Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection 

Only 

10 1000 243.9 90 319.8 

5B Compilation of Practices, Applications, 

Experiences, Economics, and 

Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

15 1200 297.5 150 385.7 

5C Evaluate the Performance of In-Place 

Geotextiles in Seepage Control Applications 

10 700 140.9 60 193.8 

5D Develop Design Criteria for Drainage Pipe 

Openings and Surrounding Material to Prevent 

Plugging 

10 1000 182.9 60 291.0 

5E Testing of Fabric Clogging Under Steady State 

Flow Properly Simulating Conditions in Dam 

Applications 

17 1750 296.5 150 477.4 

6A Research And Develop Techniques For 

Remediation And Prevention Of 

Contamination Of Wells, Drains, And 

Instrumentation 

25 2000 409.1 200 593.9 

6B Criteria for Frequency of Inspections and 

Rehabilitation of Horizontal Drains, Including 

Removal of Carbonates 

8 600 103.9 40 165.4 

6C Research Methods to Control and/or Remove 

Iron Bacteria Deposits From Wells and Drain 

Systems 

20 1000 250.0 60 306.6 

6D Develop Test Criteria and Procedures for 

Evaluating Site Vulnerability to 

Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

20 1000 190.0 60 276.0 

Notes: (1) Based on input from 11 participants; see Table ATT 10-4, Attachment 10 for 

individual estimates by participants. 

(2) "0" estimates in the "low" column are from one participant who thought that each 

of these topics would be combined with another topic, hence the cost was 

included in the cost for the other topic. 

5-21 
EXHIBIT 5-8
 

EXHIBIT 5-8
 

COMPARISON AND COMBINATION OF OVERALL RANKINGS
 

AND COMBINATION OF INDIVIDUAL SCORES
 

RANK FOR(1): 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) OVERALL AT 

WORKSHOP(2) 

OVERALL 

AFTER 

WORKSHOP(3) 

COMBINED 

INDIVIDUAL 

SCORES(4) 

AVERAGE 

RANK(5) 

PRIORITY 

OF 

AVERAGE 

RANK 

3E & 1A Expand the Database of Information on Seepage/Piping Failures/Incidents for Dams <15 meters in Height, and 

Compile Case Histories of Seepage Incidents Related to Penetrations Through Embankment Dams 

3 1 5 3.00 1 

3A 

in Dam Design and Rehabilitation – “Certification” of Dam Designers, Dam Construction Inspectors, and Dam 

Operators 

1 2 7 3.33 2 

2B Develop State-of-the-Practice for Configurations, Dimensions, and Construction Methods for Filters and Drains 8 3 2 4.33 3 

1C Develop Guidelines for Design of Filter Diaphragms Associated With Conduits Through Embankment Dams 5 10 1 5.33 4 

3B & 1D Develop Guidance for Dam Surveillance Plans Relative to Seepage, Including Monitoring, and Detecting 

Seepage Along Penetrations Through Embankment Dams 

12 5 3 6.67 5 

4A 3 7 12 7.33 6 

2C & 2E Evaluate Mechanism Of Piping And Failure In Glacial, Alluvial, And Fluvial Environments – Including 

Consideration Of Internal Instability, and Including Consideration of Threshold Gradients for Initiating Piping in 

Cohesive Soils 

2 4 18 8.00 7 

5D Develop Design Criteria for Drainage Pipe Openings and Surrounding Material to Prevent Plugging 10 7 8 8.33 8 

5B Compilation of Practices, Applications, Experiences, Economics, and Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

14 7 6 9.00 9 

1B Assess Technology to Detect Voids and Concentrated Seepage Around Penetrations Through Embankment Dams 9 6 16 10.33 10 

5C Evaluate the Performance of In-Place Geotextiles in Seepage Control Applications 6 13 13 10.67 11 

5E Testing of Fabric Clogging Under Steady State Flow Properly Simulating Conditions in Dam Applications 10 10 14 11.33 12 

2A Classification of Conditions Conducive to Hydraulic Fracturing and Cracking 19 10 9 12.67 13 

5A Review of Performance of Seepage Remediation Measures: a) Upstream Cutoff Only, b) Upstream Cutoff With 

Downstream Collection, and c) Downstream Collection Only 

15 17 9 13.67 14 

Enhance Academic Programs and Professional Development and Training Programs Related to Seepage Issues 

Technology Transfer of Geophysical Techniques for Seepage Monitoring 

Notes: (1) Shaded boxes indicate rankings within the top 10. 

(2) From Exhibit 5-3. 

(3) From Exhibit 5-4. 

(4) From Exhibit 5-5. 

(5) Arithmetic average of ranks from preceding three columns. 

5-22 
EXHIBIT 5-8
 

EXHIBIT 5-8 

COMPARISON AND COMBINATION OF OVERALL RANKINGS 

AND COMBINATION OF INDIVIDUAL SCORES 

-CONTINUEDRANK FOR(1): 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) OVERALL AT 

WORKSHOP(2) 

OVERALL 

AFTER 

WORKSHOP(3) 

COMBINED 

INDIVIDUAL 

SCORES(4) 

AVERAGE 

RANK(5) 

PRIORITY 

OF 

AVERAGE 

RANK 

6C Research Methods to Control and/or Remove Iron Bacteria Deposits From Wells and Drain Systems 6 17 19 14.00 15 

1E Development and Deployment of Guidelines for Slip-linings of Outlet Works Conduits 24 15 4 14.33 16 

4B Test Capabilities of Different Geophysical Methods on a Test Embankment 13 15 26 18.00 17 

6B Criteria for Frequency of Inspections and Rehabilitation of Horizontal Drains, Including Removal of Carbonates 19 25 11 18.33 18 

6D Develop Test Criteria and Procedures for Evaluating Site Vulnerability to Physical/Chemical/Biological 

Deterioration of Seepage Collection and Control Systems 

16 17 24 19.00 19 

4E Assess Photo-Monitoring Techniques for Seepage (Infrared Imaging, Photo Interpretation, etc.) 17 25 17 19.67 20(Tie) 

2D Evaluation of Mechanical/Geochemical Degradation of Properties of Filter Materials, Including Cementation and 

the Ability to Sustain a Crack 

21 17 21 19.67 20(Tie) 

4C Cross-Discipline Technology Transfer for Investigative Techniques in Dams 17 21 22 20.00 22(Tie) 

3C Improve Failure Time Estimates for Seepage-Related Failure Modes for Existing Dams 21 14 25 20.00 22(Tie) 

3D Identify Factors for Failure for a) “First Filling” (Including Normally Dry Dams/Detention Dams, Maximum 

Pool, etc.) and b) Long Term, for Each Seepage-Related Failure Mode 

25 21 15 20.33 24 

6A Research And Develop Techniques For Remediation And Prevention Of Contamination Of Wells, Drains, And 

Instrumentation 

21 23 20 21.33 25 

4D Do/Can Instruments or Instrument Installations Cause Damage in Embankment Dams 25 24 23 24.00 26 

Notes: (1) Shaded boxes indicate rankings within the top 10. 

(2) From Exhibit 5-3.

(3) From Exhibit 5-4. 

(4) From Exhibit 5-5.

(5) Arithmetic average of ranks from preceding three columns.

5-23 

6.0 REFERENCES

6.0 REFERENCES 

All of the white paper authors provided reference lists, which can be found at the back of 

each of the white papers, in Attachments 4 through 9. 

In addition, a list of pertinent references was compiled and is included in Attachment 11. 

Most of this list was provided by Professor Robin Fell, one of the workshop participants, but 

his list was supplemented by contributions from other participants. 

It should be noted that the reference lists included in this document should not be considered 

exhaustive. The existing literature related to seepage through embankment dams is incredibly 

voluminous, and it would not be practical to compile an exhaustive list. In addition, technical 

papers on the topic are regularly being published in journals and conference proceedings, and 

any reference list will quickly become out-of-date. 

6-1 

ATTACHMENT 1 

PRE-WORKSHOP QUESTIONAIRRE 

INVITATION AND QUESTIONNAIRE 

FOR 

ASDSO/FEMA WORKSHOP ON 

ISSUES, SOLUTIONS AND RESEARCH NEEDS 

RELATED TO SEEPAGE THROUGH DAMS 

Dear Colleague: 

URS Corporation has been contracted by ASDSO to convene and facilitate a specialty 

workshop on ISSUES, SOLUTIONS AND RESEARCH NEEDS RELATED TO SEEPAGE 

THROUGH DAMS. The workshop is part of a series of workshops being sponsored by 

FEMA and administered by ASDSO. The workshop will occur on October 17 through 19, 

2000, in the Denver, Colorado metropolitan area. The exact site of the workshop is yet to be 

determined. The product of the workshop will be a written report produced by URS and 

ASDSO documenting the results of the workshop. The report will be included in FEMA’s 

National Dam Safety Program Act Report Series. 

The workshop will consist of convening a group of 20 to 25 experts with respect to dam 

safety associated with seepage through embankments and their foundations. The objectives 

of the workshop and the resulting written report will be to document: 

1.	 The state of practice, as opposed to state-of-the-art, concerning seepage and internal 

erosion of embankment dams and foundations; 

2.	 The short-term (immediate) and long-term research needs of the Federal and non-Federal 

dam safety community with respect to this issue; and 

3.	 A recommended course of action for the Federal and non-Federal dam safety community 

to address these needs based on priorities relating to potential benefit, probability of 

success, and cost. 

We cordially invite you to participate in this workshop. Your time and travel expenses will 

be reimbursed as follows: 

1.	 ASDSO will reimburse you directly for your expenses. 

2.	 A $500 honorarium is available for each participant. 

3.	 Each participant will receive full travel reimbursement. 

Each participant must fill out an Advance Notification Form outlining the anticipated 

reimbursement prior to the workshop and send it to ASDSO. No first class airfares or hotel 

room upgrades will be reimbursed. We will send you the Advance Notification Form after 

you have you have indicated that you plan to participate. After the workshop is completed, 

participants must use an ASDSO Reimbursement Form (which will be provided) and attach 

original receipts to receive reimbursement. 

Could you please respond as soon as possible whether you accept the invitation to 

participate. It would help us a great deal in planning the workshop if you could respond by 

August 9. 

Whether you decide to participate or not, we would like your input in helping to select the 

specific topics that will be addressed in the workshop. Could you please review the 14 

possible topics listed below, and indicate up to eight topics that you think should be the 

7-1 
ATTACHMENT 1 

PRE-WORKSHOP QUESTIONAIRRE 

highest priority for consideration at the workshop. In addition, if there are other topics that 

you think are equally important, but are not encompassed by the 14 listed topics, please list 

those in the space provided. The workshop will be focused on seepage related to 

embankment dams, so please confine your considerations to embankment dams. In 

considering the prioritization for possible topics please remember that one of the purposes of 

the workshop is to identify research needs. Consequently, not just the importance of the 

topic, but also the potential for short-term beneficial research, should be considered. In other 

words, are there topics, which might yield beneficial “low-hanging fruit” in the research field 

– research that is both relatively easily achieved and provides relatively important results.

SEEPAGE TOPICS QUESTIONNAIRE 

Mark Up to Possible Topics 

Eight Topics 

Identification of potential seepage problems before construction. 

Failure modes associated with seepage and internal erosion. 

Inspection of dams for detection of seepage problems. 

Instrumentation and measurements for evaluation of seepage performance. 

Investigation of seepage problems/concerns at dams, including the use of geophysical 

techniques. 

Analysis of seepage flow, including two-dimensional and three-dimensional methods. 

Analysis of risks associated with seepage and internal erosion. 

Remediation of seepage problems through cutoff or reduction of flow, including the use of 

geotextiles. 

Remediation of seepage problems through collection and control of seepage, including the 

use of geosynthetics. 

Seepage control systems for new dams. 

Impacts of aging of seepage control/collection system components on seepage performance. 

Mechanism of particle movement and progression of internal erosion. 

Filter design criteria and observed performance (the concepts of no erosion and continuous 

erosion boundaries for evaluating filter compatibility). 

Potential seepage problems and solutions associated with penetrations through embankment 

dams (e.g., outlet works conduits). 

List below any other topics that you believe are of equal importance to the eight that you 

have marked, but are not encompassed by the 14 topics listed above: 

Thank you for your help, and I hope that you can participate. 

John W. France, PE 

Workshop Facilitator, URS Corporation 

7-2 

ATTACHMENT 2 

RESPONSE TO PRE-WORKSHOP QUESTIONNAIRE 

ADDITIONAL COMMENTS FROM RESPONDENTS
 

ASDSO/FEMA WORKSHOP ON SEEPAGE THROUGH EMBANKMENT DAMS
 

AUGUST 22, 2000 

RESPONDENT A 

1.	 I recently obtained a copy of “Analysis of Embankment Dam Incidents” by Foster, et al, 

University of New South Wales, September 1998. The study included a population of 

11,192 embankment dams, all “large” as defined by ICOLD and all constructed prior to 

1986. Dams in China were excluded as were dams in Japan constructed prior to 1930 

because of lack of reliable data. Of the 11,192 embankment dams, a total of 136 or 1.2 

percent failed. Failure is defined as “collapse or movement of part of a dam or its 

foundation, so that the dam cannot retain water”. Of the 136 failures, 59 failed as a result 

of piping and 46 failed by overtopping. Only 2 failed by earthquake or liquefaction. 88 

out of 2356 (3.8 percent) large embankment dams constructed before 1950 failed; 48 out 

of 8836 (0.5 percent) large embankment dams constructed between 1950 and 1986 failed. 

These are amazing statistics: 

a.	 Over 1 percent of all large embankment dams failed over their lifetime. 

b.	 One large embankment dam in 200 constructed after 1950 and prior to 1986 failed. 

c.	 Nearly half of all failures were triggered by piping. 

The importance of seepage control in new and existing embankment dams cannot be 

overemphasized. 

I was not fully aware that the embankment dam profession had such a poor performance 

record. One percent is, in my opinion, extremely high. Do one percent of other major 

civil engineering structures fail disastrously? I don’t think so, but I don't know for sure. 

2.	 ICOLD Bulletin 95 concerning the use of granular filters in embankment dams is a good 

reference on current design criteria. 

RESPONDENT B 

We need to assemble a compendium of seepage related failure case histories with 

characteristics that would have predicted failure if identified during the design or during 

operation. There is a developing loss of experienced designers and inspectors and we need to 

provide young engineers with a text book that summarizes our experience. 

RESPONDENT C 

Statistical study of historical failure mechanisms for small dams (follow-on to the UNSW 

study for large dams). 

Note that the topic of “penetrations through embankments” was a FEMA sponsored 

workshop and seminar. If we work on that one it should build on what was done there. 

have the publication from that work. 

7-3 

I 
ATTACHMENT 2 

RESPONSE TO PRE-WORKSHOP QUESTIONNAIRE 

RESPONDENT D 

Identification of deficiencies in existing dams and possible remediation. 

Application of geophysical techniques to the investigation of concentrated seepage flow in 

embankments and foundations and karst formations. 

RESPONDENT E 

Training of civil engineers in dam design. (I am not sure how to approach this one, but in my 

experience, many of the recent dams that have failed by piping have been designed by civil 

engineers who did not have any clue how to design to prevent piping. Many such dams are 

small dams built by unsophisticated owners who hire a local civil engineer because he is 

cheap. Maybe the topic should be "how to train owners to understand that they need to hire 

competent dam designers.") 

Training of field inspectors to be aware of problems that show up during construction, but 

that are not anticipated during design. (Teton Dam) 

RESPONDENT F 

As for my thoughts on possible topics, I've included, below, my selections from the list 

included with your questionnaire. My philosophy follows that of many others - - It is best to 

be proactive on prevention (which is facilitated by understanding the processes involved). I, 

therefore, feel the first topic is of special importance. However, since existing structures 

outnumber the dams planned for construction, there needs to be focus on methods for the 

detection of possible problems, or even realizing that there are specific potential issues at a 

structure. These include effects of time on the seepage regime (including the structure, 

foundation, and changes in reservoir operation), as well as the monitoring and control 

systems. Of course, once an issue is identified, the aspect of remediation comes to the fore. I 

think there are quite a few opportunities for research in the areas of problem identification 

and monitoring, and in the remediation arena. Your suggested topics should provide for 

some interesting and informative discussions. 

However, an additional topic that would interest me would be an idea that has generated 

some recent discussions in our office. The subject: reexamining filter criteria for drainage 

systems utilizing slotted or holed drain pipe, possibly developing new criteria. Discussion on 

design of such features would also be covered, including use of geotextiles (drain pipe in two 

stage (gravel/sand) envelope; drain pipe wrapped w/ geotextile in sand envelope; drain pipe 

in gravel envelope enwrapped w/ geotextile). This subject somewhat ties in with several of 

the topics on your original list. This would also be a fairly easily implemented research 

subject. 

RESPONDENT G 

(a) Modeling the whole internal erosion and piping process, from initiation of erosion, 

continuation, progression to form a pipe, and formation of a breach mechanism. (It is the 

details of the whole process, which separates incidents from failures). 

(b) Factors that affect the likelihood of initiation and progression and how these may be used 

to assist in distinguishing between dams which are more likely to experience accidents 

and those which are more likely to fail. 

7-4 
ATTACHMENT 2 

RESPONSE TO PRE-WORKSHOP QUESTIONNAIRE 

(c) The mechanics of erosion and piping in alluvial and fluvioglacial foundation - once again 

with a view to being able to separate incidents from failures. 

(d) Management of internal erosion and piping issues in small dams. 

RESPONDENT H 

The Workshop should clarify whether or not tailings dams are being considered. If they are 

emission criteria become more restrictive and design for minimal seepage, even zero 

discharge, needs to be considered. 

RESPONDENT I 

1.	 Basic Principles - (Source or cause of seepage problems associated with existing dams 

and filter/drain design principles to solve these problems) – Piping/internal erosion, 

cracking, dispersion, role of filters. 

2.	 Inspection, Investigation, and Detection of Seepage or Problems Associated with 

Seepage. 

3.	 Monitoring - Seepage and sediment quantity measurements - Piezometers - what can you 

tell from piezometer data - when to use - how to evaluate data - monitoring with reservoir 

level changes, rainfall, or other events. 

RESPONDENT J 

Case histories for training – slurry trench, etc.
 

Rehabilitation of relief wells.
 

Maintenance of drains – iron ochre problem.
 

RESPONDENT K 

Identification and analyses of effects of anisotropic permeability (could be grouped in with 

the “analysis of seepage flow, etc.” topic). 

RESPONDENT L 

Time frames associated with piping induced failures for use in estimating warning time: 

1.	 Signs of an impending piping problem. 

2.	 Estimating the elapsed time from the first sign of a piping problem until failure begins. 

3.	 timating the time required to fully develop a breach from a piping induced failure. 

RESPONDENT M 

Evaluation and Remediation of Incompatible Material Zones Within Existing Dams. 

Construction Treatments for the Near-Surface Rock Zone and the Soil-Rock Interface. 

Update on Dispersive Soil Problems. 

7-5 
ATTACHMENT 2 

RESPONSE TO PRE-WORKSHOP QUESTIONNAIRE 

RESPONDENT N 

Influence of other variables on filter performance: 

•	 confining pressure, 

•	 particle mineralogy (cementing agents, microscopic angularity, etc), 

•	 geometry of filter (horizontal, vertical, inclined). 

RESPONDENT O 

Erosion (piping) into foundation openings (voids, joints, etc). 

RESPONDENT P 

1.	 Use of new construction techniques for seepage rehab – i.e. trenchless technology, etc. 

2.	 Research into most common seepage problems (i.e. along conduits, abutment contacts, 

along lifts, through foundations) to focus research would most benefit. 

RESPONDENT Q 

This respondent offered the following suggested changes to the questionnaire topics 

(additions noted in bold italics and deletions noted in strikeout): 

Mark Up Possible Topics 

to Eight 

Topics 

Identification of potential seepage problems and seepage control before construction for new dams. 

Failure modes associated with seepage and internal erosion. 

Inspection of dams for detection of seepage problems. 

Instrumentation and measurements for evaluation of seepage performance. 

Investigation of seepage performance and problems/concerns at dams, including the use of 

geophysical techniques. 

Analysis of seepage flow, including two-dimensional and three-dimensional methods. 

Analysis of risks associated with seepage and internal erosion. 

Remediation of seepage problems through cutoff or collection and control of seepage reduction of 

flow, including the use of geotextiles. 

Remediation of seepage problems through collection and control of seepage, including the use of 

geosynthetics. 

Seepage control systems for new dams. 

Impacts of aging of seepage control/collection system components on seepage performance, 

including geotextiles. 

Mechanism of particle movement and progression of internal erosion and failure modes. 

Filter design criteria and observed performance (the concepts of no erosion and continuous erosion 

boundaries for evaluating filter compatibility). 

Potential seepage problems and solutions associated with penetrations through embankment dams 

(e.g., outlet works conduits). 

REPORT OF WORKSHOP ON ISSUES, 

SOLUTIONS AND RESEARCH NEEDS 

RELATED TO SEEPAGE THROUGH EMBANKMENT DAMS 

7-6 
ATTACHMENT 2 

RESPONSE TO PRE-WORKSHOP QUESTIONNAIRE 

RESPONDENT R 

This respondent offered comments on the questionnaire, as noted below in bold italics: 

Mark Up Possible Topics 

to Eight 

Topics 

Identification of potential seepage problems before construction. 

Failure modes associated with seepage and internal erosion. 

Inspection of dams for detection of seepage problems. (combine with instrumentation? ) 

Instrumentation and measurements for evaluation of seepage performance. 

Investigation of seepage problems/concerns at dams, including the use of geophysical techniques. 

Analysis of seepage flow, including two-dimensional and three-dimensional methods. 

Analysis of risks associated with seepage and internal erosion. (Our organization suggests that a 

balanced view on this important topic be presented such that full discussion is achieved; we have 

some concern about some of the present day practices in risk based evaluations which attempt 

“short cuts”.) 

Remediation of seepage problems through cutoff or reduction of flow, including the use of 

geotextiles. 

Remediation of seepage problems through collection and control of seepage, including the use of 

geosynthetics. 

Seepage control systems for new dams. 

Impacts of aging of seepage control/collection system components on seepage performance. 

Mechanism of particle movement and progression of internal erosion. (including critical gradients) 

Filter design criteria and observed performance (the concepts of no erosion and continuous erosion 

boundaries for evaluating filter compatibility). 

Potential seepage problems and solutions associated with penetrations through embankment dams 

(e.g., outlet works conduits). 

The respondent also offered the following additional comment: 

Case histories and lessons learned. 

7-7 

ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 1
 

AGGREGATE RANKINGS CONSIDERING ALL THREE CRITERIA
 

TOPIC 

NUMBER 

TOPIC NAME VOTES, UP TO 10 TOTAL(1) 

1B Assessing technology to detect voids and concentrated seepage around penetrations 

1C Develop guidelines for design of filter diaphragms associated with conduits through embankments 

1E Development of guidelines for conduit relining 

2A Classification of conditions conducive to hydraulic fracturing/cracking 

2B Develop recommended state of the practice for configuration and dimensions of filters and drains 

2C & 2E Evaluate mechanism of piping and failure in glacial and fluvial sediments, including consideration of 

internal instability; and evaluate threshold gradients for initiating piping in cohesive soils 

2D Evaluation of mechanical/geochemical degradation properties of filter materials including 

cementation and ability to sustain a crack 

3A Enhancement of academic programs and professional development programs related to seepage 

issues in dam design and rehabilitation, possibly including "certifications" of designers, inspectors, 

and operators 

3B & 1D Develop guidance for dam surveillance plans relative to seepage, including guidelines for inspecting, 

monitoring, and detecting seepage along penetrations through embankments 

3C Improve failure time estimates for seepage-related failure modes for existing dams 

3D Identify factors for failure in a) first filling and b) long term for each failure mode (dry dams, 

detention dams, maximum pool, etc.) 

3E & 1A Expand database of information on failures/incidents for dams less than 15 meters high, including 

compilation of case histories of seepage failures/incidents related to penetrations through 

embankments 

Note: (1) Cast votes considering balance of the three criteria: potential benefit, probability 

of success, and cost. Indicate votes with an "X" or some other mark. You can 

cast as many votes as you want for any one topic, as long as your total number of 

votes does not exceed 10. 

7-8 
ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 1 

AGGREGATE RANKINGS CONSIDERING ALL THREE CRITERIA 

-ContinuedTOPIC 

NUMBER 

TOPIC NAME VOTES, UP TO 10 TOTAL(1) 

4A Technology transfer of geophysical techniques for seepage monitoring and investigation 

4B Test capabilities of different geophysical methods on a test embankment 

4C Cross-discipline technology transfer for investigative techniques in dams 

4D Do/can instruments/installations cause damage in dams 

4E Assess photo-monitoring techniques for seepage (IR, photo interpretation, etc.) 

5A Review of performance of seepage remediation measures: a) upstream cutoff only, b) upstream 

cutoff with downstream collection, c) downstream collection only 

5C Evaluate performance of in-place geotextiles in seepage control applications 

5B Compilations of practices, applications, experiences, economics, and advantages/disadvantages of 

using geotextiles 

5D Develop design criteria for pipe openings (slots or perforations) and surrounding material to prevent 

plugging 

5E Testing of fabric (geotextile) clogging under steady state flow, properly simulating conditions in dam 

applications 

6A Research and development techniques for remediation and prevention of contamination of wells, 

drains, and instrumentation 

6B Criteria for frequency of inspection and rehabilitation of horizontal drains, including consideration of 

carbonates 

6C Research methods to control and/or remove iron bacteria deposits from wells and drain systems 

6D Develop test criteria and procedures for evaluating site vulnerability to physical/chemical/biological 

deterioration 

Note: (1) Cast votes considering balance of the three criteria: potential benefit, probability 

of success, and cost. Indicate votes with an "X" or some other mark. You can 

cast as many votes as you want for any one topic, as long as your total number of 

votes does not exceed 10. 

7-9 
ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 2
 

RANKING USING THREE SEPARATE CRITERIA
 

TOPIC 

NUMBER 

TOPIC NAME POTENTIAL 

BENEFIT 

PROBABILITY 

OF SUCCESS 

COST 

RANK 1 to 4 (1) RANK 1 to 4 (2) RANK 1 to 4 (3) 

1B Assessing technology to detect voids and 

concentrated seepage around penetrations 

1C Develop guidelines for design of filter 

diaphragms associated with conduits through 

embankments 

1E Development of guidelines for conduit relining 

2A Classification of conditions conducive to 

hydraulic fracturing/cracking 

2B Develop recommended state of the practice for 

configuration and dimensions of filters and drains 

2C & 2E Evaluate mechanism of piping and failure in 

glacial and fluvial sediments, including 

consideration of internal instability; and evaluate 

threshold gradients for initiating piping in 

cohesive soils 

2D Evaluation of mechanical/geochemical 

degradation properties of filter materials 

including cementation and ability to sustain a 

crack 

3A Enhancement of academic programs and 

professional development programs related to 

seepage issues in dam design and rehabilitation, 

possibly including "certifications" of designers, 

inspectors, and operators 

3B & 1D Develop guidance for dam surveillance plans 

relative to seepage, including guidelines for 

inspecting, monitoring, and detecting seepage 

along penetrations through embankments 

3C Improve failure time estimates for seepagerelated failure modes for existing dams 

3D Identify factors for failure in a) first filling and b) 

long term for each failure mode (dry dams, 

detention dams, maximum pool, etc.) 

3E & 1A Expand database of information on 

failures/incidents for dams less than 15 meters 

high, including compilation of case histories of 

seepage failures/incidents related to penetrations 

through embankments 

Notes: (1) 1 is most benefit and 4 is least benefit 

(2) 1 is high probability and 4 is low probability

(3) 1 is low cost and 4 is high cost

7-10 
ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 2
 

RANKING USING THREE SEPARATE CRITERIA
 

-CONTINUED­
 

TOPIC 

NUMBER 

TOPIC NAME POTENTIAL 

BENEFIT 

PROBABILITY 

OF SUCCESS 

COST 

RANK 1 to 4 (1) RANK 1 to 4 (2) RANK 1 to 4 (3) 

4A Technology transfer of geophysical techniques 

for seepage monitoring and investigation 

4B Test capabilities of different geophysical 

methods on a test embankment 

4C Cross-discipline technology transfer for 

investigative techniques in dams 

4D Do/can instruments/installations cause damage in 

dams 

4E Assess photo-monitoring techniques for seepage 

(IR, photo interpretation, etc.) 

5A Review of performance of seepage remediation 

measures: a) upstream cutoff only, b) upstream 

cutoff with downstream collection, c) 

downstream collection only 

5C Evaluate performance of in-place geotextiles in 

seepage control applications 

5B Compilations of practices, applications, 

experiences, economics, and 

advantages/disadvantages of using geotextiles 

5D Develop design criteria for pipe openings (slots 

or perforations) and surrounding material to 

prevent plugging 

5E Testing of fabric (geotextile) clogging under 

steady state flow, properly simulating conditions 

in dam applications 

6A Research and development techniques for 

remediation and prevention of contamination of 

wells, drains, and instrumentation 

6B Criteria for frequency of inspection and 

rehabilitation of horizontal drains, including 

consideration of carbonates 

6C Research methods to control and/or remove iron 

bacteria deposits from wells and drain systems 

6D Develop test criteria and procedures for 

evaluating site vulnerability to 

physical/chemical/biological deterioration 

Notes: (1) 1 is most benefit and 4 is least benefit 

(2) 1 is high probability and 4 is low probability

(3) 1 is low cost and 4 is high cost

7-11 
ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 3
 

ESTIMATES OF COST
 

TOPIC TOPIC NAME ESTIMATED COST, $1,000s 

NUMBER LOW BEST 

ESTIMATE 

HIGH 

1B Assessing technology to detect voids and concentrated seepage 

around penetrations 

1C Develop guidelines for design of filter diaphragms associated 

with conduits through embankments 

1E Development of guidelines for conduit relining 

2A Classification of conditions conducive to hydraulic 

fracturing/cracking 

2B Develop recommended state of the practice for configuration 

and dimensions of filters and drains 

2C & 2E Evaluate mechanism of piping and failure in glacial and fluvial 

sediments, including consideration of internal instability; and 

evaluate threshold gradients for initiating piping in cohesive 

soils 

2D Evaluation of mechanical/geochemical degradation properties 

of filter materials including cementation and ability to sustain 

a crack 

3A Enhancement of academic programs and professional 

development programs related to seepage issues in dam design 

and rehabilitation, possibly including "certifications" of 

designers, inspectors, and operators 

3B & 1D Develop guidance for dam surveillance plans relative to 

seepage, including guidelines for inspecting, monitoring, and 

detecting seepage along penetrations through embankments 

3C Improve failure time estimates for seepage-related failure 

modes for existing dams 

3D Identify factors for failure in a) first filling and b) long term for 

each failure mode (dry dams, detention dams, maximum pool, 

etc.) 

3E & 1A Expand database of information on failures/incidents for dams 

less than 15 meters high, including compilation of case 

histories of seepage failures/incidents related to penetrations 

through embankments 

4A Technology transfer of geophysical techniques for seepage 

monitoring and investigation 

4B Test capabilities of different geophysical methods on a test 

embankment 

4C Cross-discipline technology transfer for investigative 

techniques in dams 

4D Do/can instruments/installations cause damage in dams 

7-12 
ATTACHMENT 3 

SURVEY FORMS SENT AFTER THE WORKSHOP 

TABLE 3
 

ESTIMATES OF COST
 

-CONTINUED­
 

TOPIC TOPIC NAME ESTIMATED COST, $1,000s 

NUMBER LOW BEST 

ESTIMATE 

HIGH 

4E Assess photo-monitoring techniques for seepage (IR, photo 

interpretation, etc.) 

5A Review of performance of seepage remediation measures: a) 

upstream cutoff only, b) upstream cutoff with downstream 

collection, c) downstream collection only 

5C Evaluate performance of in-place geotextiles in seepage 

control applications 

5B Compilations of practices, applications, experiences, 

economics, and advantages/disadvantages of using geotextiles 

5D Develop design criteria for pipe openings (slots or 

perforations) and surrounding material to prevent plugging 

5E Testing of fabric (geotextile) clogging under steady state flow, 

properly simulating conditions in dam applications 

6A Research and development techniques for remediation and 

prevention of contamination of wells, drains, and 

instrumentation 

6B Criteria for frequency of inspection and rehabilitation of 

horizontal drains, including consideration of carbonates 

6C Research methods to control and/or remove iron bacteria 

deposits from wells and drain systems 

6D Develop test criteria and procedures for evaluating site 

vulnerability to physical/chemical/biological deterioration 

7-13 

White Paper on Potential Seepage Problems and Solutions 

Associated with Penetrations Through Embankment Dams 

ASDSO Seepage Workshop, October 17-19, 2000 – Denver, Colorado 

Prepared by Joseph R. Kula 

INTRODUCTION 

Embankment dams are often penetrated by various ancillary structures. These structures are 

usually, but not always, conduits serving as spillways and outlet works for conveying water 

from the reservoir to the downstream channel. They can be of various shapes, sizes, and 

material types. Typical structures consist of concrete, steel and iron, corrugated metal pipes, 

and plastic pipes, cast-in-place concrete structures, and pre-cast box structures. These 

horizontal structures are often connected to one or more vertical risers or towers, usually 

located upstream of the dam or within the embankment, itself. Valve boxes, manholes and 

other structures can also intersect these structures. Ideally, flow through these penetrating 

conveyance structures is controlled at the upstream end and these structures are under gravity 

flow. Some dams, however, provide control at the downstream end resulting in pressure 

conduits within the dam. 

Penetrations through dams form a discontinuity within the dam embankment or foundation. 

This break in material continuity provides for a preferential seepage path along the 

penetration. Other factors also contribute to the formation of this preferential seepage path, 

including the difficulty in compacting fill along and beneath the penetration and deformations 

(settlement) along the structure over time. In addition, conveyance structures through dams 

can also serve as conduits for internal erosion, through the loss of soil particles through open 

joints or deteriorated/damaged sections. Numerous embankment dams have experienced 

seepage related problems along penetrations including catastrophic dam failures from piping. 

Over the last 20 years, design procedures for dealing with conduits through dams have been 

modified to address these problems. However, many older dams still exist that were designed 

and constructed with outdated procedures. The aging and deterioration of these structures will 

aggravate the problems with penetrations, making this a critical dam safety issue. 

The purpose of this white paper is to discuss the various problems associated with 

penetrations through embankment dams, how they can be investigated, mitigated, monitored, 

and rehabilitated. The paper is divided into the following sections: 

• Historical Data; 

• Typical Problems; 

• Design Features; 

• Methods of Investigation; 

• Instrumentation and Monitoring; and 

• Rehabilitation Techniques. 

HISTORICAL DATA 

According to data collected by the National Performance of Dams Program (NPDP), 

embankment dams that exhibit seepage problems, often experience during the reservoir’s first 

filling. In addition, seepage problems often become worse as the structure ages due to 
deterioration. The NPDP has 164 dam incidents involving outlets and penetrations. Eighty 

seven percent of the incidents were reported in the last 20 years and 75 percent in the last 10 

years. Of these outlet/penetration incidents, 40 percent were due to seepage/piping and 35 

percent due to deterioration. Seepage/piping associated with conduit distortions also were 

reported, but at a rate of about 25 percent that of deterioration. Nine dam failures due to 

conduits were reported in the 1990’s, most of these occurring within the first five years of 

operation. (12) 

Data collected by the University of New South Wales indicates that about half of known 

embankment failures are due to seepage/piping. Of these, about 30 percent are associated 

with conduits passing through the dam. (5) 

A survey of state dam safety programs was conducted for the ICODS Dam Safety Technical 

Seminar No. 6 on conduits. The 14 states that responded reported 1,115 dams with conduits 

in need of repair. Of these, 53 percent were corrugated metal pipes (CMPs), 23 percent were 

steel, and 20 percent were of concrete. NPDP data indicated that many CMPs rusted out in 

less than 25 years with one reported rusting out in as little as 17 years. (4) 

TYPICAL PROBLEMS 

For the purposes of this paper, the problems associated with penetrations through 

embankment dams is divided into four “typical” categories, as described below: 

• seepage/piping along the conduit; 

• erosion into the conduit due to poor joints, cracking, or corrosion; 

• flow out of the conduit; and 

• structural failure from excessive deformations. 

Seepage/Piping Along or Above the Conduit 

The formation of preferential seepage paths along pipe conduits in dams is common and well 

documented. The problem generally occurs because of the difficulty in compacting backfill 

below the springline of a pipe. This often results in a loose, more permeable zone of soil, 

which acts as a conduit for seepage. Unless seepage controls are utilized, this concentrated 

seepage can lead to the internal erosion of soil particles, or piping. Anti-seep collars have been 

found to aggravate the problem, since their use further inhibits compaction, and provides a 

false sense of security. Today, the use of pipe cradles and filter diaphragms are generally 

considered more effective in controlling seepage and piping potential. (5) (8) (11) (16) (17) 

Seepage/piping can also occur above and to the sides of the conduit. Stress distributions in 

the embankment soils in vicinity of the conduit could result in low principle stresses due to 

the rigid conduit. The result can be hydraulic fracturing of the embankment soils and eventual 

seepage/piping initiated along the fracture. This phenomenon can occur on the sides of 

conduits that are constructed in a trench or where the conduit has a sharp corner. Excavating 

a trench through an existing dam to install a conduit can also lead to similar conditions 

conducive to piping above the conduit. (5) 

Seepage/Piping into the Conduit 

Seepage can infiltrate and soil particles can migrate into conduits through open joints, cracks 

in the conduit, and perforations due to corrosion and deterioration. 

2 Attachment 5 White Paper 2.doc 
Leaking joints can result from improper construction or deformations along the pipe profile 

due to foundation settlement from the weight of the embankment. Van Aller (18) discusses 

improper construction techniques, which include: 

•	 damaged pipe ends; 

•	 lack of gaskets, installation of wrong type of gasket, or improper lubrication; 

•	 incorrect joint connecting bands; or 

•	 helically corrugated pipe ends not re-rolled to provide concentric channels for proper joint 

contact. 

If a conduit bears on compressible material, the variable weight of the embankment can 

produce differential settlement along the pipe. Rotation can occur at the joints and break the 

watertight seal and or damage the conduit at the joint. Excessive deformations can also result 

in cracking of the conduit between joints and allowing seepage and/or soil particles to enter 

the conduit. 

Metal conduits are subject to electrolytic corrosion due to the galvanic action between the 

metal and the surrounding soil, groundwater, and water flowing through the pipe. The 

galvanic action results in rusting of the pipe and a gradual decrease in its wall thickness and 

strength. Corrosion of the pipe over time can result in the reduction in wall thickness, 

formation of pipe perforations, and eventual pipe collapse. (8) 

Flow Out of the Conduit 

Open joints, cracks, and perforations in the conduit can also result in flow out of the conduit. 

This could occur under either gravity or pressure flow, but would be more likely under the 

pressure condition. Flow out of the conduit could erode embankment materials from around 

the conduit, forming voids on the exterior of the conduit. This occurrence eventually could 

lead to sinkholes reflected along the slopes of the dam or in piping along the outside of the 

pipe. 

Structural Failure 

Conduits could also fail structurally, if the earth loads acting on it exceed the conduits 

structural capacity. Unlike rigid pipes, flexible metal pipes, such as CMPs derive their 

vertical load carrying capacity from the soil around them. Because the pipes are flexible, they 

are designed to deform somewhat against the adjacent backfill and mobilize lateral resistance 

of the soil. This lateral resistance acting against the sides of the pipe stiffens the shell and 

provides its vertical load carrying capacity. If the backfill under the pipe haunches is not 

adequately compacted, it will not provide the needed lateral resistance or stiffness to the pipe 

to carry the vertical load of the soil above the pipe. This can result in excessive deformations 

of the pipe and eventual structural failure, or collapse of the pipe. (8) 

DESIGN FEATURES 

Old Standards 

Design methods for mitigating the effects of penetrations through embankment dams have 

evolved over the years. Up until about 1980, many agencies and designers relied on antiseepage collars as the primary defense against seepage and piping along conduits. The 

3 Attachment 5 White Paper 2.doc 
objective of the collars was to reduce seepage flow by lengthening the seepage path. 

Unfortunately, case studies have shown that, anti-seepage collars often contributed to seepage 

and piping problems due to the difficulty in compacting backfill around them. Other design 

features which have also contributed to seepage/piping problems include: the lack of 

downstream filters, conduits located in deep and narrow trenches with steep or irregular sides, 

corrugated metal formwork, poor conduit geometry such as overhangs, circular pipe with no 

support, poor joint details, and founding the conduit on compressible soil. Poor compaction 

quality control was also a critical factor resulting in seepage/piping along conduits. (5) 

Current Standards 

In about 1980, design standards for treating penetrations through dams began to change. The 

problems with anti-seepage collars and poor compaction were recognized, and the use of 

downstream filters around conduits replaced anti-seepage collars as the primary defense 

against seepage/piping. Other design elements for mitigating seepage/piping problems 

include: concrete cradles beneath circular pipes, sloping conduit sides at 1:8 or 1:10 to allow 

compaction with rubber tire rollers, use of flatter trench slopes in the core (2:1 min.), and the 

use of steel cylinder concrete pipe to improve performance under deformation. (1) (5) (7) (9) 

(11) (14)

INSPECTION TECHNIQUES 

Typical information of interest for the inspector includes presence and extent of deterioration 

and corrosion, cracks, signs of pipe misalignment, distortion or crushing, nature and condition 

of joints, presence and location of connections with other pipes, water leakage into the 

conduit, water leakage out of the conduit, conduit wall thickness, presence and location of 

blockages and the nature and extent of sediment accumulation. 

Visual Inspections 

For larger diameter pipes, typically greater than 36 inches, direct visual inspection can be 

accomplished by the inspector walking or crawling through the conduit. These types of 

inspections are typically documented using video cameras with an external lighting source. 

However, infrared cameras designed to video in low/no light conditions are also available. 

Although direct visual inspections can provide the most comprehensive information for 

assessing the condition of a conduit, the utility of entering the pipe must be weighed against 

the health and safety of the inspectors. A pipe meets the definition of a confined space under 

the United States Occupational Safety and Health Administration (OSHA) regulations (i.e. 

limited access and egress, not designed for continuous human habitation). OSHA has 

developed strict regulations for protecting the health and safety of personnel working in 

confined spaces. These regulations include requirements for specific training for confined 

space workers, lockout and tag out procedures, monitoring of air quality parameters within the 

confined space, and designation of responsibilities of the personnel. Given the risks, costs and 

relative complexity of working in confined space, there are significant advantages to 

inspecting even relatively large diameter pipes remotely. Furthermore, direct inspection is not 

an option for smaller diameter pipes. (8) 

Remote Video Camera Inspection 

4 Attachment 5 White Paper 2.doc 
Fortunately there are remotely operated vehicle (ROV) video inspection systems that are very 

well suited for inspection of conduits. These systems include rugged, multiple wheel or 

tracked vehicles up to several feet long and equipped with high power lights and articulating 

camera lens. These systems can provide 360-degree cross-sectional views along the entire 

length of a pipe. The systems that are designed for inspection of larger diameter pipes have 

cameras mounted on platforms that the operator can elevate remotely to provide detailed 

views from the invert up to the crown of the pipe. For pipes too small to accommodate a 

remotely operated vehicle, cameras mounted on stiff cable or rods can be pushed through the 

pipe to complete the inspection. Cameras as small as 1.5-inches in diameter are available. 

Video inspections can be documented on videotape including alphanumeric captions and/or 

voice narrative. 

Video inspection systems provide a safer means of inspecting larger conduits and the only 

practical means of inspecting conduits too small for human entry. However, the access 

provided by these systems can be limited significantly by conduit conditions. Conditions such 

as corrosion along the invert may present an un-passable obstacle to a ROV or a push camera. 

Tree roots, sediment and debris may also present significant obstacles for these systems. (1) 

(8) 

Geophysical Methods 

There are a number of new technologies that have potential applications for the inspection of 

conduits in dams. These include: 

•	 global seismic investigations; 

•	 localized seismic investigations such as surface waves, impact-echo, and impulseresponse; 

•	 laser scanning and profiling; 

•	 acoustic and ultrasonic testing; 

•	 sonar; and 

•	 ground penetrating radar. 

Global Seismic Investigations using Spectral-Analysis-of Surface-Waves (SASW) are used 

for identifying potential sink-holes, seeps, and other anomalies by measuring shear stiffness 

profiles of the embankment soils. Testing is conducted along the dam surface at selected 

locations. (13) 

Localized Seismic Investigations are used for evaluating the quality and thickness of the 

conduit wall, for evaluating voids, and the quality of material behind the wall. Methodologies 

include SASW, Impact-echo test using compression waves, and Impulse-response testing 

using flexural waves. (13) 

Laser Scanning and Profiling is used with a camera to data that software computes into 

distances and area. This allows the operator to locate and measure defects such as cracks and 

holes. (15) 

Acoustic and Ultrasonic Testing evaluates the material integrity of conduits, the permeability 

of cracks and the integrity of connectors by interruption of the wave propagation. Acoustic 

methods are used for ceramic materials while ultrasonic testing is used with conductive 

materials. (15) 

5 Attachment 5 White Paper 2.doc 
Sonar can provide the direct measurement of a circular conduits interior diameter. It can also 

measure displacement, corrosion, and level of debris in the conduit. (15) 

Ground Penetrating Radar (GPR) can be used at the surface to locate underground conduits 

or utilities. From inside the conduit GPR can provide information on the conduit wall and soil 

surrounding the conduit. GPR has better application with nonconductive materials such as 

concrete and dry granular soils, which are poor conductors. (15) 

INSTRUMENTATION AND MONITORING 

With advances in automatic data collection and management technology, there are expanding 

applications for automated instrumentation and monitoring of conduits in dams. The two 

most beneficial parameters for measurement are the structural integrity of the conduit and the 

detection of localized seepage/piping. (2) 

Monitoring Structural Integrity 

Problems related to structural integrity include: damage from structural overloading, 

deterioration from corrosion, weathering, or chemical attack, longitudinal stretching from 

settlement of the embankment, or complete failure of the conduit. The instruments for 

monitoring these parameters are available and include: 

•	 strain gages; 

•	 joint meters, inclinometers, extensometers, etc.; 

•	 settlement devices; and 

•	 nondestructive techniques using some of the geophysical techniques previously described. 

Detection of Seepage/Piping 

Seepage/Piping is generally a “localized” problem occurring along a preferential seepage 

path. Detection methods include: leakage monitoring, turbidity measurement, appearance of 

deformation, and study of pore pressure fluctuations. Methods that can help localize the 

seepage path include: 

•	 tracers; 

•	 geophysical methods such as seismic, ground penetrating radar, borings, and water loss 

measurements; 

•	 temperature measurements and thermal imaging; 

•	 gamma and neutron logging; and 

•	 acoustic devices. (2) 

The above technologies are available to the dam safety community and there are no major 

barriers for implementing them in new dams. However, instrument installation costs in 

existing dams can be difficult and costly and represents a significant constraint to 

implementation. 

REHABILITATION TECHNIQUES 

Once an existing conduit is identified as having either a deficiency or the potential for a future 

problem, corrective measures must be considered. These measures can vary widely in 

6 Attachment 5 White Paper 2.doc 
complexity and cost depending on the type and extent of the problem, the size and function of 

the conduit, and the physical limitations of the site. For purposes of this paper, several 

corrective techniques are discussed individually, however, it should be noted that these 

methods could be used in combination to address multiple problems on a single conduit. The 

following paragraphs represent brief descriptions of several techniques to replace, repair and 

rehabilitate conduits. 

Replacement 

If the lake or impounding structure currently serves a useful purpose, or it is desired to retain 

the facility for some future purpose, then rehabilitation is the preferred option. The most 

conventional rehabilitation method consists of removing and replacing the deficient or 

deteriorating conduit. Depending on the desired design life of the rehabilitated facility, 

various different materials and products could be used including concrete, steel, plastic, and 

even corrugated metal. Concrete pipe is by far the most commonly used replacement material 

due to its inherent strength and durability. 

However, the expense to adequately replace a deteriorating conduit can be significant due to 

the relative costs for diversion, excavation, disposal, and backfill, not to mention the 

procurement and installation of the new pipe. These types of repairs can represent a costly 

dilemma for the owners, whom often have little or no financial resource to complete the 

repairs. 

Slipline 

An increasing popular alternative to replacement is “sliplining,” whereby a smaller diameter 

pipe is inserted into the damaged or deteriorating conduit and grouted into place. Sliplining is 

generally employed when it is apparent that the existing conduit has limited design life 

remaining but is in adequate condition at the time of inspection. A successful slipline 

application will resolve “typical” problems such as pipe corrosion, leaking joints and 

occasionally structural failure. However, it is not effective in reducing seepage or piping 

along the outside of the pipe, and therefore may not be a complete solution. When 

appropriate, sliplining can be used in conjunction with other remedial methods to provide a 

complete solution. 

On the surface, sliplining may appear relatively straightforward. However, there are many 

subjects that require attention during the design and construction processes. The following 

items should be considered when contemplating the use of sliplining (18): 

•	 condition of the existing pipe – capable of containing the new pipe and pumped grout; 

•	 hydraulic capacity of slipline pipe – capable of conveying required flow volume with
 

smaller diameter pipe due to increased capacity from smooth wall (as opposed to
 

corrugations);
 

•	 slipliner material – selection of appropriate material (HDPE, PE, PVC, fiberglass,
 

inversion-tube, cast-in-place concrete);
 

•	 slipliner structural capacity – capable of carrying the required load assuming no support
 

from the existing pipe;
 

•	 slipliner joint type – selection of water tight joint (heat fusion, extrusion, glued, Snap-
 

Tite, etc.);
 

•	 installation method – site has enough space available to install pipe; 

•	 annular grout mix – designed to flow through annular space without voids or air pockets; 

and 

•	 differences in load transfer and thermal expansions of various materials. 

7 Attachment 5 White Paper 2.doc 
Sliplining to rehabilitate deteriorated conduits is feasible and relatively economical. In 

addition, the procedure has a successful track record on many dam projects throughout the 

United States. 

Filter Diaphragms 

If the conduit exhibits concentrated seepage and/or piping of soils along the exterior of the 

pipe, a filter diaphragm can be installed to control the seepage and soil particle movement. 

Filter diaphragms are collars of filtering soils constructed around the perimeter of the conduit. 

They are installed along the downstream section of the pipe and are typically about 3 to 4 feet 

thick along the pipe profile. Perpendicular to the pipe axis, they generally extend out from the 

pipe wall a distance equal to 3 times the pipe diameter. The grain size distribution of the 

filtering soils must be compatible with the surrounding embankment and foundation soils 

(14). A detailed procedure of the design of filter diaphragms is presented in the USDA SCS 

Technical Note 709 Dimensioning of Filter Diaphragms for Conduits According to TR-60 

(16) (17).

Grouting 

Voids can be created along the exterior of conduits through concentrated seepage and piping 

along the outside of the conduit or by piping of soils through openings in the conduit. Filling 

these voids or preventing the loss of fines surrounding the pipe can be achieved using cement 

grouts or various chemical grouts without removing the pipe. However, similar to sliplining, 

grouting is not a complete solution. The most successful application will have little to no 

effect on pipe corrosion or structural stability. 

Due to the complexity and sensitive nature of the work, it is important to have an engineer and 

contractor experienced in the application of these grouting techniques on dams. Depending 

on the length and diameter of the conduit, remedial grouting can be a relatively inexpensive 

method for treating voids along the conduit. 

Cement grouts are generally utilized in compaction grouting techniques. Borings are drilled 

from the embankment surface to an area near the exterior of the conduit. Thick grout is 

advanced, under pressure, from the surface through the drill hole to the area of loosened soil. 

The nature of the grout in conjunction with the pressure displaces the soil, thus compacting it 

into the surrounding material. Depending on the size of the pipe and other physical 

restrictions, introduction of compaction grout from within the pipe is also possible. When 

considering the use of pressure grouting techniques in dams, it is important to recognize and 

mitigate the potential for hydraulic fracturing of the embankment material. 

Chemical grouts can be applied to soil adjacent to the pipe to reduce the potential for 

movement of the soil into or along the exterior of the pipe. The grout moves through the pore 

spaces of the soil and eventually bonds the particles together, thus limiting future movement 

(18). It should be noted that micro-fine cement grouts could achieve similar results to those of 

chemical grouts. This application can be achieved from the embankment surface similar to 

compaction grouting, however, it is much more common to drill holes through the pipe wall 

from the interior of the pipe. An obvious limitation of the procedure is that it requires a pipe 

diameter large enough to accept a person and the necessary equipment. (6) 

Localized Patching Techniques 

8 Attachment 5 White Paper 2.doc 
Patching of localized distressed portions of the conduit is another potential repair method if 

the damaged area(s) are accessible to workers. There are a number of products on the market 

including epoxy, cement, and chemical grouts. Some repair techniques make use of preplaced 

aggregate or abrasive resistant aggregate. Welded steel plates are commonly used for 

repairing steel structures. (10) 

Trenchless Technology 

The sewer rehabilitation market has brought many new innovations that, in the future, may be 

applicable to the repair of conduits through dams. Some of these methods use variations of 

the sliplining theme and include: 

• molded polyethylene profiled pipes for non-circular conduits; 

• spiral winding systems using a PVC liner from a continuous PVC profile strip on site; 

• deformed liners made from high strength polyethylene or polyvinyl chloride; 

• cured-in-place liners (inverted polyester lining systems); 

• pipe bursting; and 

• microtunneling techniques. (6) 

There are technical challenges and cost implications associated with many of these newer 

technologies, which must be dealt with before applying them to dam conduit rehabilitation. 

However, as the technology advances, more trenchless technology methods may be an option 

for conduit repair. 

9 Attachment 5 White Paper 2.doc 
LIST OF REFERENCES 

1. Cyganiewicz, John, “Low-Cost Video Inspection of Outlet Works,” Piping Associated 

with Conduits through Embankment Dams, ICODS Dam Safety Technical Seminar 

Proceedings, Editors: J. Michael Duncan, Charles J. Smith, and James K. Mitchell, The 

Federal Emergency Management Agency Emergency Management Institute, Feb. 17-19, 

1999, pp. 180-203. 

2. DiBiagio, Elmo, “Instrumentation Possibilities,” Piping Associated with Conduits through 

Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, Editors: J. Michael 

Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency Management 

Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 97-118. 

3. Duke, John, “Conduit Wall Thickness Survey Techniques,” Piping Associated with 

Conduits through Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, 

Editors: J. Michael Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency 

Management Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 111-118. 

4. Evans, James, “ASDSO Survey of State Experiences Regarding Piping Associates with 

Conduits through Embankment Dams,” Piping Associated with Conduits through 

Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, Editors: J. Michael 

Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency Management 

Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 11-20. 

5. Fell, Robin, “Embankment Dam Incidents Relating to Piping Associated with Conduits,” 

Piping Associated with Conduits through Embankment Dams, ICODS Dam Safety Technical 

Seminar Proceedings, Editors: J. Michael Duncan, Charles J. Smith, and James K. Mitchell, 

The Federal Emergency Management Agency Emergency Management Institute, Feb. 17-19, 

1999, pp. 51-96. 

6. Gray, William, W.S., “Trenchless Technology for Sewer Rehabilitation,” Civil 

Engineering News, March 1996, pp. 24-33. 

7. Guidelines for Controlling Seepage along Conduits Through Embankment Dams, ACER 

Technical Memorandum No. 9, U.S. Department of the Interior, Bureau of Reclamation, 

Denver, Colorado, 1987. 

8. Kula, Joseph R., Zamensky, Gregory A. and King, Timothy, J., “The Inspection and 

Rehabilitation of Corrugated Metal Pipes Used in Embankment Dams,” ASDSO 2000 Annual 

Conference Proceedings. 

9. Lake, Donald W., Jr., “Rehabilitation of Embankment Conduits,” USDA-Soil 

Conservation Service, Syracuse, New York. 

10. Lindsey, Patrick, “Structural Repair of Conduits,” Piping Associated with Conduits 

through Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, Editors: J. 

Michael Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency 

Management Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 285-316. 

11. Martin, Ray, E., “Seepage Control along Conduits Penetrating Embankment Dams,” 

ASDSO 1990 Annual Conference Proceedings, pp. 449-454. 

10 Attachment 5 White Paper 2.doc 
12. Redlinger, Chuck, “NPDP Summary of Incidents,” Piping Associated with Conduits

through Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, Editors: J. 

Michael Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency 

Management Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 21-50. 

13. Stokoe, Ken, “Geophysical Inspection Techniques,” Piping Associated with Conduits 

through Embankment Dams, ICODS Dam Safety Technical Seminar Proceedings, Editors: J. 

Michael Duncan, Charles J. Smith, and James K. Mitchell, The Federal Emergency 

Management Agency Emergency Management Institute, Feb. 17-19, 1999, pp. 204-226. 

14. Talbot, James R., “SCS Filter Studies, Design Procedures and Experiences with Filter 

Diaphragms,” ASDSO Mid-Atlantic Regional technical Seminar, Seepage in Dam Safety: 

Evaluation and Remediation, Baltimore, MD, September 1990. 

15. Thomas, Allen and Laszcynski, Greg, “Probing Pipelines,” Civil Engineering, March 

1998, Vol. 68, No. 3, pp. 13A and 14A. 

16. USDA Soil Conservation Service, Technical Release No. 60 (TR-60), Earth Dams and 

Reservoirs, Washington, DC, 1985. 

17. USDA Soil Conservation Service, Technical Note 709, Dimensioning of Filter Drainage 

Diaphragms for Conduits According to TR-60, South National Technical Center, Fort Worth 

Texas, 1985. 

18. Van Aller, Harold, “Rehabilitation of Failed Corrugated Metal Pipe Spillways,” ASDSO 

Mid-Atlantic Council for Safe Dams Conference, 1996. 

19. Young, Steve, “Grouting Conduits for Abandonment (Fish Lake Dam),” Piping 

Associated with Conduits through Embankment Dams, ICODS Dam Safety Technical 

Seminar Proceedings, Editors: J. Michael Duncan, Charles J. Smith, and James K. Mitchell, 

The Federal Emergency Management Agency Emergency Management Institute, Feb. 17-19, 

1999, pp. 337-350. 

11 Attachment 5 White Paper 2.doc 

ASDSO – FEMA WORKSHOP 

OCTOBER 17TH TO 19TH 2000 

SEEPAGE THROUGH DAMS AND THEIR FOUNDATIONS 

ISSUES, SOLUTIONS AND RESEARCH NEEDS 

THE INTERNAL EROSION AND PIPING PROCESS 

by Robin Fell 

School of Civil and Environmental 

Engineering 

University of New South Wales 

Sydney, Australia 2052 

Email r.fell@unsw.edu.au 

and Mark Foster 

URS Australia Pty. Ltd. 

Level 3, 116 Miller Street 

North Sydney, NSW 2060, Australia 

Email mark_foster@urscorp.com 
1. INTRODUCTION 

This “white paper” is to cover “Filter design criteria and observed performance (the concepts 

of no erosion and continuous erosion boundaries for evaluating filter compatibility) and 

mechanism of particle movement and progression of internal erosion”. 

We have interpreted this to include a description of the internal erosion and piping process, 

from initiation through to formation of a breach (or failure) of the dam, and to include seepage 

and internal erosion in the dam and in the foundation. This is essential for a complete 

coverage of the issues. 

2. THE SEEPAGE AND INTERNAL EROSION PROCESS – FROM INITIATION 

OF EROSION, TO BREACH OF THE DAM 

Seepage, and internal erosion which may lead to piping and breach of a dam occurs through 

the embankment, the foundation, and from the embankment to the foundation. The historic 

frequency of accidents and failures for each of these modes is shown in Table 1. 

Table 1 Historic frequency of piping failures and accidents to embankment dams 

(Foster et al 1998, 2000) 

Mode of failure or accident Frequency of failure or accident in the life of 

the dam x 10-3 

Failure Accident 

Piping through the embankment 3.5 6.7 

Piping through the foundation 1.7 6.2 

Piping from the embankment to 

foundation 

0.2 2.1 

All modes 5.4 15.0 

Notes. Data is for large dams (i.e. = 15m height) up to 1986 

It can be seen that about 2% (or 1 in 50) of embankment dams have historically experienced a 

piping incident. Of these about half are in the embankment, 40% in the foundations, and 10% 

from the embankment to foundation. Fewer incidents of piping in the foundation, and 

particularly from embankment to foundation, progress to failure, than for piping in the 

embankment. About half the failures occur on first filling, or in the first 5 years of operation. 

It is useful to break up the process of internal erosion and piping into four phases – initiation 

and continuation of erosion, progression to form a pipe, and formation of a breach. This is 

shown in figure 1(a) and (b) for piping through the embankment by backward erosion and 

concentrated leak, and figure 1(c) and (d) for piping through the foundation, and from the 

embankment to foundation. 

2 Attachment 5 White Paper 2.doc 
INITIATION CONTINUATION fi fi PROGRESSION fi BREACH/FAILURE

Leakage exits on d/s Continuation of 

side of core and erosion 

backward erosion 

initiates 

Backward erosion Breach mechanism 

progresses back to forms 

the reservoir 

(a) Backward erosion piping in the embankment

INITIATION CONTINUATION fi fi PROGRESSION fi BREACH/FAILURE

Concentrated leak Continuation of Enlargement of Breach mechanism 

forms and erosion erosion concentrated leak forms 

initiates along walls 

of crack 

(b) Concentrated leak piping in the embankment

INITIATION CONTINUATION PROGRESSION BREACH/FAILURE 

Leakage exits from the Continuation of erosion Backward erosion progresses Breach mechanism 

foundation and backward to form a pipe forms 

erosion initiates 

(c) PIPING IN THE FOUNDATION 

INITIATION CONTINUATION PROGRESSION BREACH/FAILURE 

Leakage exits the core Continuation of erosion Backward erosion progresses Breach mechanism 

into the foundation and to form a pipe. Eroded soil is forms 

backward erosion initiates transported in the foundation 

as core erodes into the 

foundation 

(d) PIPING FROM THE EMBANKMENT TO FOUNDATION 

Figure 1 Models for the development of failure by piping (Foster and Fell 1999). 

3 Attachment 5 White Paper 2.doc 
The sequence of events leading to failure by the two models are essentially the same, but the 

mechanisms involved in the initiation and progression stages are different. Backward erosion 

initiates at the exit point of the seepage, and progressive erosion results in the formation of a 

continuous passage or “pipe”. Concentrated leak piping involves the formation of a crack or 

concentrated leak directly from the source of the water to an exit point, and erosion initiates 

along the walls of the concentrated leak. 

Suffusion, or internal instability, is a third potential mechanism, which involves the washing 

of fines from internally unstable soils. Soils which are gap graded, or which have only a small 

quantity of fine soil in a mainly coarse sand or gravel and susceptible to suffusion. 

Filters, or transition zones, control the “continuation” phase of the process 

Potential breach mechanisms are 

• gross enlargement of the pipe hole 

• crest settlement, or sinkhole on the crest leading to overtopping 

• unravelling of the downstream slope 

• instability of the downstream slope. 

The first three mechanisms require the formation of the enlargement of the pipe through the 

dam; the fourth may occur without the formation of a pipe. 

Piping through the foundations may initiate from a concentrated leak, backward erosion, 

suffusion or “blowout” (heave). The latter would be the initiating event, followed by 

backward erosion to form a pipe. Breach may also occur by slope instability and loss of 

freeboard, or gross enlargement of the pipe. 

Piping from the embankment into the foundation may initiate by erosion of the embankment 

into open joints, or coarse soils (eg. gravel with no sand or silt) in the foundation. This may 

involve only erosion of the finer particles in the embankment (a form of suffusion), or the 

whole of the soil, leading to backward erosion in the embankment. 

It should be recognised that the reason there are twice as many accidents as failures by piping 

through the embankment is primarily because in accidents, the piping process ceased before a 

breach mechanism could develop. This is often because filter/transitions may be too coarse to 

prevent the initiation of erosion but may eventually seal, and/or due to the presence of high 

permeability zones downstream. This is exemplified by the performance of central core earth 

and rockfill dams, with no failures, but 19 (or 25%) of the accidents. 

In some cases intervention has also prevented accidents becoming failures. The likelihood of 

successful intervention depends on the type of process which is involved. For example it 

would seem likely that slow erosion processes such as suffusion, or situations which self heal 

(as where filter/transitions are fine enough to eventually seal), are more likely to be detected 

in time for intervention, than for example piping initiated by concentrated leak along a conduit 

in a homogeneous earthfill dam. (We, with J. Cyganiewicz, are part way to preparing a paper 

on this topic). 

3. THE STATE OF PRACTICE 

3.1 General Approach 

4 Attachment 5 White Paper 2.doc 
The state of practice for controlling seepage and internal erosion for new dams is to design the 

dam to include filters and high permeability zones. The filters control the continuation of 

erosion and provided they are designed and constructed to meet modern no-erosion filter 

criteria, we can be confident erosion will not occur in the embankment. 

Erosion from the embankment to the foundations can be controlled by proper foundation 

preparation (eg. concrete or shotcrete over open joints in the rock beneath the core of the 

embankment). Erosion in the foundation is more difficult to control, but can be achieved by 

providing filters where seepage exists, or cutoffs such as diaphragm walls in alluvium. 

The main issues arise for existing dams which have not been designed or constructed with 

these features. In these cases the actual situation coupled with monitoring, is compared to the 

ideal, and engineering judgement, are used to decide whether the dam is safe enough. Some, 

including USBR, NGI, and some Australian Consultants (including URS, SMEC) are using 

risk assessment methods to assist in the decision. This usually involves considering each of 

the processes required to lead to failure as described above. We regard this as the “state of 

practice” and the remainder of the discussion is structured to follow that procedure. 

3.2 Initiation of Erosion 

Table 2 summarizes the means by which internal erosion may initiate. 

Table 2 Means by which internal erosion may be initiated in dam embankments and 

foundations. 

LOCATION MEANS OF INITIATION OF EROSION 

Embankment • Backward erosion 

• Concentrated leak 

- transverse cracking or hydraulic fracturing 

due to horizontal or vertical differential settlement, 

earthquake or slope instability 

- high permeability zone due to poor 

compaction, layers of coarse soil, ice lenses, 

desiccation cracking 

- high permeability zone or cracking 

associated with conduits and walls 

• Suffusion (internal instability) 

Foundation • Backward erosion, including that following “blowout” 

or “heave” 

• Concentrated leak 

- transverse cracking due to hydraulic fracture, 

differential settlement earthquake and slope 

instability 

- high permeability zone due to coarse or 

structured soils (eg. laterite), open jointing or 

solution features in rock, (eg. karst, limestone, 

gypsum); ice lenses 

• Suffusion, and erosion of fine soils into adjacent coarse 

soils or open joints or solution features in rock. 

Embankment to foundation • Backward erosion, initiated by erosion of the 

embankment soils into open joints, coarse soils, or 

5 Attachment 5 White Paper 2.doc 
solution features in the foundation. 

Conduits or walls are a factor in almost half the incidents of piping through embankments. 

Of these processes, most is known, and written regarding concentrated leaks including 

hydraulic fracture (eg. Sherard et al 1963, Sherard et al 1972(a)) and (b), Sherard (1973), 

(1985); Terzaghi and Peck (1967), Von Thun 1996); Charles (1997), Höeg et al (1998); 

suffusion (Sherard (1979), CFGB (1997), Kenney and Lau (1985)); and “Blowout” or heave 

(Sherard et al (1963), Cedergren (1989), Von Thun (1996), Terzaghi and Peck (1967) and 

Skempton and Brogan (1994). 

However, except for “blowout”, internal instability of granular soils and possibly hydraulic 

fracture, the knowledge is rather qualitative, so decision making is also somewhat qualitative 

and judgemental. Foster and Fell (1999, 2000) provide a summary of the factors influencing 

the likelihood of initiation of piping in embankments. The first reference also discusses 

piping in the foundation, but is not so well researched as for embankments. 

Skempton and Brogan (1994) work is interesting in that it shows that erosion of fines in 

internally unstable soils begins to occur at about one third the critical gradient for “blowout”. 

Tables 3 to 8 summarize the factors influencing the likelihood of initiation of erosion in 

embankments. 

Table 3 Influence of factors on likelihood of cracking or wetting induced collapsesusceptibility of core materials (Foster and Fell 2000) 

Factor 

Influence on Likelihood of Cracking or Collapse 

More Likely Neutral Less Likely 

Compaction Poorly compacted, Well compacted, 

density ratio <95% standard compaction 95-98% standard =98% standard compaction 

(1) density ratio (2) compaction density density ratio 

ratio 

Compaction Dry of standard optimum Approx OWC–1% Optimum or wet of standard 

water content water content (approx. OWC – to OWC-2% optimum water content 

3%) 

Soil types (3) Low plasticity clay fines Medium plasticity High plasticity clay fines 

clay fines Cohesionless silty fines 

Notes: (1) For cracking, compaction density ratio is not a major factor. It is more important for wetting induced collapse. 

(2) <93% Standard compaction, dry of OWC, much more likely. 

(3) Soil type is not as important as compaction density and water content. 

6 Attachment 5 White Paper 2.doc 
Table 4 Influence of factors in the likelihood of cracking or hydraulic fracturing – 

features giving low stress conditions (Foster and Fell 2000) 

Factor 

Influence on Likelihood of Cracking or Hydraulic Fracture 

More Likely Neutral Less Likely 

Overall Deep and narrow valley. Reasonably uniform Uniform abutment profile, or 

abutment Abrupt changes in abutment slopes and moderate large scale slope modification. 

profile profile, continuous across steepness, eg. Flat abutment slopes 

core. 0.25H:1V to 0.5H:1V (>0.5H:1V) 

Near vertical abutment slopes 

Small scale Steps, benches, depressions in Irregularities present, Careful slope modification or 

irregularities rock foundation, particularly if but not continuous smooth profile 

in abutment continuous across width of across width of the 

profile core (examples: haul road, core 

grouting platforms during 

construction, river channel) 

Differential 

foundation 

settlement 

Deep soil foundation adjacent 

to rock abutments. Variable 

depth of foundation soils. 

Soil foundation, 

gradual variation in 

depth 

Low compressibility soil 

foundation. 

No soil in foundation 

Variation in compressibility of 

foundation soils 

Core Narrow core, H/W>2, Average core width, Wide core 

characteristics particularly core with vertical 2<H/W<1 H/W<1 

sides 

Core material less stiff than Core and shell Core material stiffer than shell 

shell material materials equivalent material 

stiffness 

Central core Upstream sloping core 

Closure River diversion through No closure section (river 

section closure section in dam, or new diversion through outlet 

(during fill placed a long time after conduit or tunnel) 

construction) original construction 

Table 5 Influence of factors on the likelihood of a concentrated leak –high permeability zone 

(Foster and Fell 2000) 

Factor 

Influence on Likelihood of a High Permeability Zone 

More Likely Neutral Less Likely 

Compaction Poorly compacted, <95% 95-98% standard Well compacted, = 98% 

density ratio standard compaction density compaction density standard compaction density 

ratio (1) ratio ratio 

Compaction Dry of standard optimum Approx OWC-1% to Optimum or wet of standard 

water water content (approx. OWC- OWC-2% optimum water content 

content 3%) 

General 

quality of 

construction 

Poor clean up after wet, dry or 

frozen periods during 

construction. 

Removal of dried, wet or 

frozen layers before resuming 

construction 

No engineering supervision of 

construction 

Good engineering supervision 

Instrumentation Poor compaction around No instrumentation in the core 

details instrumentation, particularly if 

pass through the core 

Characteristics 

of core 

Large variability of materials 

in borrow area, moisture 

Low variability of materials in 

borrow areas 

materials content, conditioning and 

grain size. 

Core materials susceptible to 

shrinkage cracks due to 

Low shrinkage potential. 

Narrow grading 

drying. 

Widely graded core materials 

susceptible to segregation 

Notes: (1) <93% Standard, dry of OWC, much more likely. 

7 Attachment 5 White Paper 2.doc 
Table 6 Influence of factors on the likelihood of a concentrated leak associated with a conduit 

(Foster and Fell 2000) 

Factor 

Influence on Likelihood of a Concentrated Leak 

Much More Likely More 

Likely 

Neutral Less Likely 

Conduit Masonry, brick Steel, cast Cast iron, Concrete encased steel 

Type (1) Corrugated steel iron, not concrete 

encased encased Concrete cast in-situ 

Concrete precast 

Conduit Open joints, or Open joints High quality High quality joints, no 

Joints (1) cracks signs of joints, “open” openings, waterstops 

erosion up to 5mm but 

with waterstops 

Pipe Old, corroded cast Old cast New steel with corrosion 

Corrosion iron or steel iron, steel protection 

(1) 

Conduit 

Details (1) 

Significant 

settlement or deep 

compressible 

Some 

settlement, 

shallow 

Little or no settlement or rock 

foundation 

foundation soils. 

Junction with shaft 

compressible 

foundation 

in embankment soils 

Conduit Narrow, deep, near Medium Wide, side Trench totally in rock, 

Trench 

Details (2) 

vertical sides. 

Vertical sides, 

trench in soil 

depth, width, 

slope. 

Excavated 

slopes flatter 

than 1H:1V 

backfilled with concrete 

(backfilled with 

concrete) 

through dam 

Notes: (1) Conduit type, joints, corrosion and details mostly affect piping into the conduit 

(2) Conduit trench details mostly affect piping along the conduit 

Table 7 Influence of factors on the likelihood of a concentrated leak 

associated with a spillway wall (Foster and Fell 2000) 

Factor 

Influence on Likelihood of a Concentrated Leak 

More Likely Neutral Less Likely 

Slope of wall Overhanging Vertical Sloping =0.1H:1V 

Founding Soil, wall subject to settlement Soil or Rock 

material and rotation weathered rock, 

no rotation 

Finish on wall Rough, irregular Smooth, planar 

Concrete collars, Present, particularly if shape Not present 

buttresses, makes compaction of core 

overhangs difficult 

Special No special compaction Careful compaction adjacent 

compaction adjacent to wall to wall 

8 Attachment 5 White Paper 2.doc 
Table 8 Influence of factors on the likelihood of suffusion (Foster and Fell 2000) 

Factor 

Influence on Likelihood of Suffusion 

More Likely Neutral Less Likely 

Particle size distribution: 

• General 

• Gap-graded soils 

(Sherard, 1979) 

• Smooth gradations with 

a tail of fines based on 

Kenney and Lau (1985) 

or Burenkova (1993) 

Gap-graded 

Flat tail in finer 

sizes 

d15c/d15f>5 

Potentially unstable 

Uniform gradation, well 

graded 

d15c/d15f<5 

Stable 

Compaction Density Poorly compacted, 

<95% standard 

95-98% 

standard 

Well compacted, =98% 

standard compaction density 

compaction density 

ratio (1) 

compaction 

density ratio 

ratio 

Permeability High Moderate Low 

Notes: (1) <93% Standard compaction, dry of OWC, much more likely. 

(2) d15c = particle size on coarse side of the distribution for which 15% is finer, d15f = particle size on the fine side of the 

distribution for which 15% is finer. 

A review of case studies by Foster and Fell (1999)showed that the depth and location of 

cracking in the dam core appears to be related to the source of the low stress conditions. 

Piping associated with small scale irregularities in the foundation rock profile generally 

occurs close to the foundation surface, and usually in the lower half of the core height. Cracks 

associated with narrow cores and arching of the core between the shell zones are generally 

located at depths from the crest of 3

1 to 3 2 of the height of the dam. Cracks and piping 

associated with broad changes in the abutment profile are generally located at depths of less 

than 3

1 of the height of the dam, where tension might be expected. 

Some recent experience with central core earth and rockfill dams in Australia is showing that 

cracking is present in the dam core due to yielding of the relatively stiff core which has lacked 

adequate support from dumped, or poorly compacted rockfill. This cracking is not always 

evident at the surface, either because it emerges under the rockfill, or occurred early in the life 

of the dam (due to high instability induced stresses during construction). Test pits through the 

dam crest are needed to locate them. 

Given that 1 in 50 dams have experienced reported incidents, it would seem that overall, more 

than this will have had erosion initiate. We would clearly be greatly better off if we could 

identify dams which have features which make them prone to initiation of erosion. We are 

about to undertake some additional work at UNSW, including generic numerical modelling of 

irregularities in foundation profiles to determine the conditions giving low stresses (which 

might lead to hydraulic fracture and cracking). We hope to get a student to begin research 

cracking of embankment dams during earthquake early in 2001 subject to funding being 

available. 

If we could “test” the embankment, and around conduits for the presence of cracks, we would 

be much better able to identify problem dams. We believe this is an important research area, 

and expect that geophysical (eg. cross-hole or surface to conduit seismic “p” wave or “s” 

wave, or monitoring of seepage temperature will be most productive). We believe some work 

is to be done as part of the Canadian Dam Safety Interest Group research project. 

1.3 Continuation of erosion (or design and construction of filters and transition 

zones). 

9 Attachment 5 White Paper 2.doc 
1.3.1 Some general issues on functional requirements 

Filters in embankment dams and their foundations are required to perform two basic 

functions: 

(a) Prevent erosion of soil particles from the soil they are protecting. 

(b) Allow drainage of seepage water. 

Filters are usually specified in terms of their particle size distribution and are required 

to be sufficiently fine, relative to the particle size of the soil they are protecting to 

achieve function (a), while being sufficiently coarse to achieve function (b) so there 

are conflicting requirements. 

To achieve these functions the ideal filter or filter zone will (ICOLD 1994); 

• not segregate during processing, handling, placing, spreading or compaction 

• not change in gradation (by degradation or break down) during processing 

handling, placing and/or compaction, or degrade with time eg. by freeze-thaw or 

wetting and drying by seepage flow 

• not have any apparent or real cohesion, or ability to cement as a result of chemical, 

physical or biological action, so the filter will not allow a crack in the soil it is 

protecting to persist through the filters 

• be internally stable, that is the finer particles in the filter should not erode from the 

filter under seepage flows. 

• have sufficient permeability (and if a drain, thickness) to discharge the seepage 

flows without excessive build-up of head 

• have the ability to control and seal the erosion which may have initiated by a 

concentrated leak, backward erosion or suffusion (internal instability) in the base 

soil. 

(c) Flow conditions acting on filters 

Figure 2 illustrates the basic flow conditions that can occur between a filter and base 

soil. These are: 

NI Flow normal to the base soil – filter interface, with potentially high gradient 

conditions eg. at the downstream face of the earthfill core, the contact between 

the horizontal drain and the foundations, and within the foundation where 

seepage is across bedding. 

N2 Flow normal to the base soil – filter interface, with low gradient conditions eg. 

at the upstream face of the earthfill core under reservoir drawdown conditions, 

or into the upper zone 2A filter. 

P flow parallel to the interface, eg. at the base of rip-rap layers, or in the 

foundations where seepage is along bedding. 

10 Attachment 5 White Paper 2.doc 
4 

2D 3 

1 

2C 

4 

2A 

3 

2A 

2A 

2B 

P 

P 

P 

N1 

N1 

N N1 2 

N1 

N2 

N1 

N1 

DRAWDOWN 

SEEPAGE 

CONDITION 

SANDY GRAVEL 

SILTY SAND 

SANDY GRAVEL 

ROCK 

LEGEND 

ZONE DESCRIPTION 

1 EARTHFILL 

FILTER/DRAINS 

EARTH OR ROCKFILL 

RIP RAP 

2A 2B 2C 2D 

3 

4 

Figure 2 Flow conditions acting on filters P = Flow parallel to interface; 

N1 = flow normal to interface, high gradient conditions; 

N2 = flow normal to interface, low gradient conditions. 

The erosive stresses are greatest for case N1, and less for N2 because the flow is 

simply draining from the base soil under gravity, not under reservoir water head. 

The erosive action for case P is different, and also less severe than for N1, and as a 

result less conservative (and therefore coarser filters) can sometimes be used for cases 

N2 and P, than for case N1. Cases N1 are often referred to as “critical filters”. 

(d) Filtering concepts 

Figures 3(a) and (b) show the interface between a filter and base soil. The basic 

concept of filter design, is to design the particle size distribution of the filter, so that 

the void in the filter are sufficiently small to prevent erosion of the base soil. 

The void sizes in the filter are controlled by the finer particles, and for design 

purposes, the D15F is usually used to define the void size. Sherard et al (1984(a)) 

showed that for uniformly graded sands and gravels the opening size OF = D15/9. 

Testing by Foster (1999) confirmed this. 

11 Attachment 5 White Paper 2.doc 
12 Attachment 5 White Paper 2.doc

Figure 3 Filtering and self filtering concepts, (a) well graded base soil (b) gap graded, or

concave graded soil, deficient in medium sized particles.

A further basic concept inherent in filter design, is that the base soil, will generally

provide a degree of “self filtering”. Hence in Figure 3, in a well graded base soil, the

coarser particles in the base soil are prevented from eroding into the filter, and they in

turn prevent the medium sized particles in the base soil from eroding, and the medium

sized particles in the base soil prevent the fine particles in the base soil from eroding.

If the base soil is gap graded, or graded concave upwards, so there is a deficiency of

medium sized particles, the self filtering does not occur, and the fine particles in the

base soil will erode through the coarse particles (or suffusion or internal instability

occurs). In these situations, for the filter to be successful in controlling erosion, it

must be able to control the erosion of these finer particles.

1.3.2 Design of critical no-erosion filters

(a) Particle size distributions to give no-erosion critical filters are usually designed using

filter design criteria based on the D85B and D15F sizes ie. the particle sizes for which

85% of the base soil and 15% of the filter is finer.

In widespread use now are the criteria developed by Sherard and Dunnigan and Talbot

at the US Soil Conservation Service laboratories (Sherard and Dunnigan 1985, 1989).

They proposed separate criteria for four soil groups as summarised in Table 9.

WELL GRADED

 BASE SOIL

POORLY GRADED

 BASE SOIL

FILTER

FILTER

(a)

(b)
Table 9 Sherard and Dunnigan (1989) Filter Design Criteria 

C

Base 

Soil 

ategory

Base Soil Description, and 

Percent Finer than 

0.075 mm sieve 

Filter Criteria 

1 Fine silts and clays; 

more than 85% finer 

D 15 F D85 B £ 9 

2 Sands, silts, clays and silty 

and clayey sands; 40 to 85% finer 

D 

15F 

£ 0.7mm

3 Silty and clayey sands and gravels; 

15 to 39% finer D 

15F ( x 4 0.7mm ) 1540 

40 A

85 - -

- £ 

B 

D 

4 Sands and gravels; 

Less than 15% finer 

D 15F £ x 4 D 85B

Foster (1999), Foster and Fell (1999(a)), carried out extensive no-erosion tests using a 

test set-up similar to that of Sherard et al (1984(a),(b)), and reviewed the results of the 

USSCS tests as reported in internal reports by Sherard (Sherard 1985(a) and (b)). 

Table 10 summarises the results. The “proposed criteria for no erosion boundary” are 

intended for applying to the assessment of filter performance of existing dams, and do 

not include any margin of safety. 

Table 10 Summary of results of statistical analysis of proposed criteria for the no-erosion 

boundary 

Base Soil Fines Content Design Criteria of Sherard Range of DF15 for No Erosion Criteria for No Erosion Boundary 

Group (I) and Dunnigan (1989) Boundary 

1 ‡ 85% DF15 £ 9 DB85 6.4 - 13.5 DB85 DF15 £ 9 DB85 (2) 

2 35-85% DF15 £ 0.7mm 0.7 - 1.7mm DF15 £ 0.7mm (2) 

3 <15% DF15 £ 4 DB85 6.8 - 10 DB85 DF15 £7 DB85 

4 15-35% DF15£(40-pp%75mm) x 1.6-2.5DF15 of Sherard and DF15 £ 1.6 DF15d, 

(4DB85-0.7)/25 + 0.7 Dunnigan design criteria Where DF15d = 

(35-pp%75 mm)(4DB85-0.7)/20 + 0.7 

Notes: (1) The subdivision for soil group 2 and 4 was modified from 40% passing 75 mm, as recommended by Sherard and Dunnigan 

(1989), to 35% based on the analysis of the filter test data. The modified soil groups are termed group 2A and 4A. 

The fines content is the % finer than 75 mm after the base soil is adjusted to a maximum particle size of 4.75mm. 

(2) For highly dispersive soils (Pinhole classification D1 or D2 or Emerson Class 1 or 2), it is recommended to use a lower DF15 

for the no erosion boundary. 

(3) For soil group 1 soils, suggest use the lower limit of the experimental boundary, i.e. DF15 £ 6.4 DB85 

(4) For soil group 2A soils, suggest use DF15 £ 0.5mm. 

This work showed that the division between group 2 and 4 soils is better defined on a 

fines content of 35%, than the 40% used by Sherard et al (1984(a),(b)). 

As can be seen the Sherard and Dunnigan (1989) criteria generally have a margin of 

safety but they are not sufficiently conservative to define no-erosion condition for 

dispersive soils and it would be better to adopt D15F £ 6D85B for dispersive type 1 

soils and/or carry out no-erosion tests on the soil and filter. 

UNSW is to carry out further tests on dispersive soils to more clearly define no erosion 

criteria for them. 

(b) Internal instability or suffusion 

Several criteria exist for the assessment of internal instability, including those by 

Sherard (1979), Kenney and Lau (1985) and Burenkova (1993), and Schuler and 

13 Attachment 5 White Paper 2.doc 
Brauns (1993). It should be noted that these criteria only apply to granular soils. There 

are no criteria for cohesive soils eg. gravelly clays. For design purposes the Sherard 

and Dunnigan (1989) method requires “regrading” of these soils to that passing the 

4.75 mm sieve to overcome the problem. UNSW are planning to carry out tests on 

cohesive soils, probably placed as a slurry, to see if criteria can be established. 

(c) Segregation 

Characteristics which make sand-gravel filter segregate on placement include 

(a) a broad grading, particularly with maximum particle size > 75mm 

(b) a low percentage of sand and fine gravel sizes (< 40% finer than 4.75mm) 

(c) poor construction practices eg. end-dumping from trucks, high lift heights, and 

poor control of stockpiling operations. 

Sherard and Dunnigan (1989) suggested using filters with a maximum size not greater 

than 50 mm, and required no less than 40% sand and fine gravel. Ripley (1986) 

recommended for filters in contact with the core: 

• maximum size 19 mm 

• > 60% finer than 4.75 mm 

• < 2% finer than 0.075 mm 

These criteria were based on construction experience. 

Kenney and Westland (1993) carried out laboratory tests and concluded that: 

• all dry soils consisting of sands and gravels segregate in the same general way, 

independent of grain size and grain size distributions 

• dry soils containing fines <0.075 mm, segregate to a smaller extend than soils not 

containing fines 

• water in sandy soils with a mean size finer than 3mm to 4 mm, inhibits segregation 

but has little influence on the segregation of gravels (mean size coarser than 10 

mm to 12 mm). 

The USDA – SCS (1994) and USBR (1987) have adopted a maximum size of 75 mm, 

and limits on the minimum D10F and maximum D90F to limit segregation. The authors 

believe that for narrow or thin filter zones, this may be too large, and recommend the 

use of maximum size of 37 mm or 50 mm in these situations. 

(d) Filter permeability and ability to hold a crack 

The filter must be sufficiently permeable that the seepage flow can pass through it 

without significant build up of pressure. This has been taken account of by using the 

criteria D15F/D15B > 4 or 5; this ensures that the permeability of the filter is 15-20 times 

that of the soil. 

However just as important is to keep the fines content (silt and clay sized particles) to 

a minimum. 

14 Attachment 5 White Paper 2.doc 
Figure 4 Influence of the type and amount of fines on permeability 

of concrete sand, sand-gravel mixture and uniform fine sand 

(ICOLD 1994 from US Army Corps of Engineers, 1986). 

Figure 4 shows the influence on permeability of the type and amount of fines. 

The authors preference is to specify < 2% fines, and the fines be non plastic. Some eg. 

USDA-SCS (1994), USBR (1987) allow up to 5% non plastic fines, but as is evident 

from figure 4, this may reduce the permeability by one or two orders of magnitude 

compared to clean filter materials. The cost in washing to achieve < 2% fines is not 

high, and generally worthwhile. The second advantage of low fines content is that the 

filters are unlikely to hold a crack. 

It is unfortunately not uncommon to be presented with information showing that the 

filters or transition zone in an existing dam were constructed with fines content (% 

passing 0.075mm) greater than the 5% normally accepted as an upper limit, and/or the 

fines are, contrary to accepted practice, plastic. 

15 Attachment 5 White Paper 2.doc 
The question which then arises is whether the filter or transition will “hold a crack”, 

and not perform its filter function. Vaughan and Soares (1982) describe a simple test 

for assessing this. It is described in ICOLD (1994) as follows: 

“A simple test, suitable for use in a field laboratory, has been devised to examine filter 

cohesion. It consists of forming a cylindrical or conical sample of moist compacted 

filter, either in a compaction mould, or in a small bucket such as is used by a child on a 

beach; standing the sample in a shallow tray (if a bucket is used the operation is 

exactly as building a child’s sand castle) and carefully flooding the tray with water. If 

the sample then collapses to its true angle of repose as the water rises and destroys the 

capillary suctions in the filter, then the filter is noncohesive. Samples can be stored for 

varying periods to see if cohesive bonds form with time. This test is, in effect, a 

compression test performed at zero effective confining pressure and a very small shear 

stress, and it is a very sensitive detector of a small degree of cohesion.” 

The authors belief is that it is the combination of fines content, the plasticity of the 

fines, and degree of compaction which is important. One is more likely to accept that 

a filter with excessive and/or plastic fines will collapse, and not hold a crack if it is not 

well compacted. 

Each case should be considered on its merits, and taking into account whether zones 

downstream of the filter may satisfy continuing erosion criteria, so even if the filter 

holds a crack, erosion will eventually seal. 

This is an aspect which needs a more rigorous research program, based on laboratory 

testing and case studies. 

(e) Minimum thickness or width of filters 

The theoretical minimum width or thickness filters designed according to no-erosion 

criteria as detailed above is very small and does not control the dimensions of filters. 

Witt (1986, 1993) carried out some calculations and experiments which demonstrated 

that the depth of penetration soil into the filters is small, even if the filter is somewhat 

coarser than required by the design criteria. 

Using his data it can be shown that 

For, O F D85B = , Depth Penetration 

or = 50 D5F 

and for O F D95B = , Depth Penetration

 = 300 D5F 

Given that opening size O F = D15F/9 (Sherard et al 1984(a)) 

This implies that 

For D15F = 9D85B , Depth Penetration

 = 50 D5F 

16 Attachment 5 White Paper 2.doc 
Sherard and Dunigan (1985, 1989) design criteria range from D15F < 4D85B for type 3 

soils, to D15F £ 9D85B for type 1 soils, so the depth of penetration will be less than 

50D5F for filter designed according to Sherard and Dunnigan criteria. Commonly, 

zone 2A filter would have a D5F less than 0.5mm, so the depth of penetration would be 

less than 25mm. 

Larger depths of penetration, and hence minimum thicknesses would be calculated 

using the Witt (1986, 1993) approach for zone 2A filters penetrating zone 2B, but it is 

not clear if his work would apply to this case. 

1.3.3 Other no-erosion filter design methods 

Lafleur et al (1989, 1993) prefer to work in terms of the opening size of the filter OF and 

consider this in terms of the indicative grain size dI of the base soil. The indicative size is 

determined as shown in Figure 5. This has advantages where, as they do, one is considering 

conventional sand-gravel filter, and geotextiles. They indicate that of the retention ratio RR = 

OF/dI is >> 1, then continuous erosion will occur, and that if RR << 1, clogging (or “blinding”) 

of the base soil/interface may occur, leading to a build up in pore pressure on the filter. This 

is particularly a problem for internally unstable soils, and the fines accumulate upstream of the 

filter, not within it. 

Figure 5 summarizes Lafleur et al (1993) design approach. Note that it is not identical to 

Lafleur (1989) as reported in ICOLD (1994). In particular the retention criteria for aggregate 

filters is D15/5 < dI, not D15/4 < dI, so they have opted for coarser filters than in the ICOLD 

(1994) and Lafleur et al (1989). 

Figure 5 Lafleur et al (1993) method for the design of conventional and geotextile filters 

17 Attachment 5 White Paper 2.doc 
D

Figure 5 does not include design criteria for cohesive soils. Lafleur et al (1989) recommend 

15F £ 0.4mm for non dispersive soils, and D15F £ 0.2mm for dispersive soils. 

Sherard and Dunnigan (1985, 1989) recommend for their group 3 soils, that D15F £ 4 D85B, 

whereas Lafleur et al (1993) recommend for uniform soils, D15F £ 5 D85B. Given that Foster 

(1999), Foster and Fell (1999(a)) showed that erosion would continue for D15F > 9 D95Band 

would be excessive for D15F > 9 D85B , both criteria seem to have some margin of safety 

against large erosion losses. 

Brauns and Witt (1987), Schuler and Brauns (1993, 1997), and Witt (1993), propose that filter 

criteria should be based on a probabilistic analysis to allow for the variability in the particle 

size distributions of the base soil and the filter. Honjo and Veneziano (1989) had a similar 

concept. The authors can see some merit in these approaches, but they are predicated 

implicitly that filters either “fail” or “succeed”. As discussed in Section 3.3.5, the reality is 

that such criteria apply to no-erosion acceptance criteria, and that much coarser filters will 

eventually seal. 

3.3.4 Review of available methods for designing filters with flow parallel to the filters 

ICOLD (1994) summarize testing done at Delft Hydraulics Laboratory (Bakker 1987) to test 

the condition where flow in the filter is along, or parallel to the base soil. Den-Adel et al 

(1994) provides details of a method for designing such filters. 

It is apparent that in these situations, erosion is less likely, and considerably coarser filters 

than obtained from the criteria discussed in Section 3.3.2 and 3.3.3 can be used. 

Figure 6 summarizes some of the Delft Laboratory Testing 

Figure 6 Critical gradient with steady flow parallel to the interface 

(ICOLD 1994 based on Bakker 1987) 

18 Attachment 5 White Paper 2.doc 
In this figure, the hydraulic gradient, eg. equal to the slope of the filter under rip-rap on the 

upstream face of a dam is plotted against D15F/D 50B (D 15 50 /d in figure ). 6 Curves for sandy

base soils with D 50 (d ) = 0.15mm and 0.82 mm are shown. Thus for a uniform sand base 50 

material with a d50 of 0.15 mm on a slope of 2.5 : IV (icv = 0.4), the ratio of D15F/DB50 (D15/d50) 

can be as high as about 8. 

We would be careful in using this approach, particularly in situations where if the filter fails, 

and erosion occurs, it is not practical to repair the damage. 

Having said that, it is common to use more relaxed criteria in non critical conditions eg. 

ICOLD (1993) suggest that for bedding filter under rip-rap, it is found that filters which are 

reasonably well graded between a maximum of 8 to 10 mm, and coarse sand sizes, are 

satisfactory for the great majority of dams. 

3.3.5 Continuing and excessive erosion criteria 

M. Foster (Foster 1999, Foster and Fell 1999(a)), used the test data from Sherard (1985a,b), 

and additional tests using no-erosion test equipment similar to that used by Sherard and 

Dunnigan (1989) to develop the concept of no erosion, some erosion, excessive erosion and 

continuing erosion shown in figure 7. 

CONTINUING 

EROSION 

Continuing Erosion 

Boundary 

No Erosion 

Boundary 

SOME 

EROSION 

NO EROSION 

DF15 

Excessive Erosion 

Boundary 

EXCESSIVE 

EROSION 

Other factor e.g. DB85 

Figure 7 Filter erosion boundaries (Foster 1999) 

The terms are defined as: 

(i) No erosion:- filter seals with practically no erosion of the base material. 

(ii) Some erosion:- filter seals after “some” erosion of the base material. 

(iii) Excessive erosion:- filter seals, but after “excessive” erosion of the base soil. 

(iv) Continuing erosion:- the filter is too coarse to allow the eroded base materials to seal 

the filter. 

Table 11 and figure 8 show the proposed excessive and continuing erosion boundaries. The 

criteria for the excessive erosion boundary are selected from the case studies, and dams which 

experience erosion to this limit may have large piping flow discharges – up to say 1 to 

2m3/sec. Whether a dam can withstand such flows without breaching depends on the 

discharge capacity of the downstream zone, and whether unravelling or slope instability may 

occur. This is discussed in Section 4. 

19 Attachment 5 White Paper 2.doc 
It is also likely that if a dam experiences a piping event, which does eventually seal, it will 

experience another later, as the erosion process continues. 

Table 11 Summary of proposed criteria for the excessive and continuing erosion boundaries 

(Foster 1999, Foster and Fell 1999) 

Base Soil Criteria for Excessive Erosion Boundary Criteria for 

Continuing Erosion 

Boundary 

Soils with DF15 > 9 DB95 

DB95<0.3mm 

Soils with DF15 > 9 DB90 

0.3<DB95<2mm 

For all soils: 

Soils with DB95 > 

2mm and fines 

• Average DF15 >DF15 which gives an 

erosion loss of 0.25g/cm2 in the CEF test, or 

content >35% • Coarse limit DF15 >DF15 which gives an 

erosion loss of 1.0g/cm2 in the CEF test 

DF15 > 9DB95 

Soils with DB95 > DF15 > 9 DB85 

2mm and fines 

content < 15% 

Soils with DB95 > 

2mm and fines 

content 15-35% 

DF15 > 2.5 DF15 design, 

Where DF15 design is given by: 

DF15 design = (35-pp%75mm)(4DB85 – 

0.7)/20 + 0.7 

The criteria listed in Table 11 should only be used with caution, and for serious decision 

making, should be supported by laboratory tests using the filter/transition and core materials 

from the dams, and the results should be tempered with sound dams engineering judgement. Tarbela AD1 Juklavatn Secondary Balderhead Wreck Cove Churchill Falls FF11 Rowallan Viddalsvatn Juktan 

40mm 

Mud Mountain

30 

Range of DF15 for dams with 

poor filter performance 25 

Average DF15 for dams with Contours of 

poor filter performance Erosion Loss

Filter DF15 (mm) 20 

from Filter 

Tests 

1.0g/cm2 

0.5g/cm2 

0.25g/cm 

Range of DF15 for dams with 

good filter performance 15 

No Erosion 10 

Boundary Hyttejuvet 2 

0.1g/cm2 for Soil Group 2 Hills Creek

5 DF15=0.7mm Brodhead 

Songa 

0 

0 5 10 15 20 25 30 35 40 45 50 55 60 

Core material % fine - medium sand (0.075 - 1.18mm) 

Figure 8 Comparison of erosion losses measured in filter tests to dams with poor and good 

filter performance (Foster and Fell 1999) 

20 Attachment 5 White Paper 2.doc 
The procedure has been used in a limited number of dams and has proven to be a valuable aid 

to decision making. 

There are some broader implications to these studies in that it is apparent that for most soils, 

there is a considerable margin between no erosion, and continuing erosion criteria. This 

possibly assists in explaining why, despite the statistical variability in the particle size 

distribution of the base soil and filter, which might on first consideration imply that there was 

a significant potential for piping to occur. There are few, if any, cases of dams with filters 

failing by piping. It is unlikely in most cases that the continuous erosion boundaries criteria 

are exceeded. Figure 9(a) shows this conceptually. 

30 

20 

10 PERCENTAGE OF D15F/D85 B

B

BB 

DES GI N LI MIT = 4 D8 5

NO-EROS ION BOUNDARY = 7 D85

CONTI NUING BOUNDARY L MI IT = 9 D95

1 2 3 4 5 6 7 8 9 10 11 12 

D15F/D85B 

(a) SANDY BASE SOIL 

30 

20 

10 PERCENTAGE OF D15 F/D85 B 

I

I

I

I

I

NO-EROS O N BOUNDARY 

D SI PERS VI E SO L = 6 D85B 

NO-EROS ON BOUNDARY 

DES GN LIMIT = 9 D8 5B 

CONTI NU NG EROS ION BOUNDARY = 9 D95B 

1 2 3 4 5 6 7 8 9 10 11 12 

D15F/D85B 

(b) FINE CLAY AND SILT, LITTLE OR NO SAND SIZED PARTICLES 

Figure 9 Conceptual distribution of D15F/D85B for (a) clean sandy base soil, 

(b) fine clay and silt with little or no sand sized particles; with design, 

no erosion and continuing erosion criteria. 

However it is important to recognise that for fine grained base soils, the separation between 

the Sherard and Dunnigan design limit, no erosion and continuing erosion boundaries is much 

less – Figure 9 (b) and Tables 10 and 11. Hence if the filter design is close to the limiting 

D15F/D85B, very close control on construction will be necessary. 

21 Attachment 5 White Paper 2.doc 
3.3.6 Design of Geotextile Filters 

Geotextile filters are designed based on an equivalent opening size approach. There are 

several design methods. We have decided not to include a review here, but can provide one if 

it is needed. The state of practice seems fairly mature, and it would not seem that much 

research effort is needed. Clogging, and low permeability are problems for geotextile filters. 

3.4 PROGRESSION OF EROSION TO FORMATION AND ENLARGEMENT OF A 

PIPE 

There are two issues affecting the progression of piping through the embankment: 

• The ability of the soil to support a roof of the pipe ie. will the pipe remain open or 

collapse? 

• Enlargement of the hole ie. will the pipe enlarge and how quickly? 

Tables 12, 13 and 14 summarize the factors which influence this. These are based on the 

literature, including Sherard (1953), Terzaghi and Peck (1967), Sherard et al (1972(a) and 

(b)), Arulanandan et al (1975), Vaughan and Soares (1982), Arulanandan and Perry (1983), 

Sherard and Dunnigan (1985), Chapius and Gatien (1986), Peck (1990), Bickel and Juesel 

(1992), Fell et al (1992), Hanson (1992) Hanson and Robinson (1993), Charles et al (1995), 

Von Thun (1996), and a review of case studies (Foster (1999), Foster and Fell (1999). The 

review of case studies showed that fines content was the critical factor in whether a roof could 

be supported. Soils with fines content ‡ 15% were found to be able to hold a roof, even if the 

fines were cohesionless. 

The moisture condition is also important. Dry or partially saturated soils would be expected 

to maintain a roof longer than saturated soils. This may be a factor contributing to the higher 

rate of first filling failures. 

Table 12 Influence of factors on the likelihood of progression of erosion– 

ability to support a roof (Foster and Fell 1999, 2000) 

Factor 

Influence on Likelihood of Fill Materials 

Supporting a Roof of a Pipe 

More Likely Neutral Less Likely 

Fines content (% 

finer than 0.075mm) 

Fines content >15% Fines content <15% and 

>5% 

No fines or fines 

content <5% 

Degree of saturation Partially saturated (first 

filling) 

Saturated 

22 Attachment 5 White Paper 2.doc 
Table 13 Influence of factors on the progression of erosion – 

enlargement of the pipe (limitation of flows) (Foster and Fell 1999, 2000) 

Factor 

Influence on Likelihood of Pipe Enlargement 

More Likely Neutral Less Likely 

Action of filter 

downstream of core Considered in assessment of filter performance 

Filling of cracks by Homogeneous zoning. Zone upstream of core 

washing in of material Upstream zone of capable of crack filling 

from upstream cohesive material (cohesionless soil) 

Restriction of flow by 

upstream zones or 

Homogeneous zoning. 

Very high permeability 

Medium to high 

permeability zone 

In zoned dam, medium 

to low permeability 

concrete element in 

dam 

zone upstream of core upstream of core granular zone upstream 

of core. Central 

concrete corewall and 

concrete face rockfill 

dam 

Table 14 Influence of factors on the progression of erosion ­

likelihood of pipe enlargement (erodibility) (Foster and Fell 1999, 2000) 

Factor 

Influence on Likelihood of Pipe Enlargement 

More Likely Neutral Less Likely 

Soil type Very uniform, fine 

cohesionless sand. 

Well graded material with 

clay binder (6<PI<15) 

Plastic clay (PI>15) 

(PI<6) 

Well graded 

cohesionless soil. 

(PI<6) 

Pinhole Dispersive soils, Potentially dispersive Non-dispersive soils, 

soils, 

Dispersion Test (4) Pinhole D1, D2 Pinhole PD1, PD2 Pinhole ND1, ND2 

Critical shear stress 

(Arulanandan and 

Perry, 1983) 

Soils with c t <4 

dyne/cm2 

Soils with 

4< c t <9 dyne/cm2 

Soils with 

c t >9 dyne/cm2 

Compaction density Poorly compacted, 95-98% standard Well compacted, =98% 

ratio <95% standard compaction density ratio standard compaction 

compaction density density ratio 

ratio (1) 

Compaction water Dry of standard Approx standard OWC- Standard optimum or 

content optimum water content 1% to OWC-2% wet of standard 

(approx. OWC-3% or optimum water content 

less) 

Hydraulic gradient 

across core (2) 

High Average Low 

Note: (1) <93% Standard, dry of OWC, much more likely. 

(2) Even dams with very low gradients, eg. 0.05, can experience piping failure 

(3) PI = Plasticity index 

(4) Using Sherard Pinhole Test 

The most critical issue distinguishing piping failure from accidents appears to be related to the 

limitation of flows through the core in which piping has begun, and the rate of erosion. The 

factors influencing this are summarized in Tables 13 and 14. 

Mechanisms of flow limitation include filtering action (i.e. filters meeting excessive or 

continuing erosion criteria), crack filling by filters upstream of the core, and flow restriction 

from upstream zones eg. rockfill. UNSW is carrying out extensive laboratory testing on the 

factors affecting the rate of erosion, and limiting erosion condition using specially developed 

testing equipment designed to simulate a crack in a dam. Early results indicate that 

23 Attachment 5 White Paper 2.doc 
compaction water content is critical, with rates of erosion up to an order of magnitude higher 

for soils compacted at OWC -1% compared to those compacted at OWC +1%. 

In dam foundations, there are relatively fewer failures than accidents. This seems to be 

related to the conditions needed to “support a roof” being less likely to be met than for piping 

in the embankment. Situations where they are met are where cohesive or cemented soils are 

interlayered with cohesionless soils. 

The “roof” may be provided by a concrete structure, or by cohesive soils. As shown in 

Figure. 10 Filtering of exit points for seepage may limit the progression of erosion. 

Foundation filter 

Unfiltered exit 

Filtered exit Filtered exit Unfiltered exit 

Open-work gravel layer 

Filtered exit 

Bedrock, open-jointed 

Figure 10 Examples of filtered and free exit points for piping through the foundation 

(Foster and Fell 1999) 

“Crack filling” may occur by coarser zones in the foundation, or from the upstream zones of 

the embankment, falling into the pipe. 

For piping from the embankment to foundation, piping is often limited by the size of the open 

joints in the foundation, or by eventual filtering on these joints. 

UNSW is adding to the case studies covered by M. Foster so we can try to better understand 

these processes. We are still seeking good quality case studies from Corps of Engineers, 

Vattenfall, and some Canadian owners, but need more. 

3.5 Formation of a Breach Mechanism 

Table 15 summarizes the mechanics of the breach for failures involving piping through the 

embankment (Foster 1999, Foster and Fell 1999). 

24 Attachment 5 White Paper 2.doc 
Table 15 Mechanism of breach formation, failures 

by piping through the embankment 

Mechanism of Breach Formation No. of Failure Cases 

Gross enlargement of pipe 22 

Crest settlement/sinkhole 3 

Unravelling or sloughing 1 

Instability 1 

Not known 24 

TOTAL 51 

Table 16 summarizes the influence of factors on these mechanisms. These are largely based 

on a review of case studies, (Foster 1999, Foster and Fell (1999) with some data on 

unravelling and sloughing failures from Leps (1973), Olivier (1967) and Solvick (1991). 

Table 16 Influence of factors on the likelihood of breaching 

Influence on Likelihood of Breaching

Factor More Likely Neutral Less Likely 

(a) Gross Enlargement 

Zoning Homogeneous type zoning. Zoned type dam, Zoned type dam with a 

Zoned type dam with a downstream zone of downstream zone of gravel 

downstream zone able to sand or gravel with fines or rockfill 

support a roof 

Storage Volume Large storage volume Small storage volume 

(b) Crest Settlement/Sinkhole 

Freeboard at time of incident (1) <2m freeboard  ̃3m freeboard =4m freeboard 

Crest width Narrow crest Average crest width Wide crest 

Downstream zone (2) Fine grained, erodible Fine grained, non- Rockfill 

erodible 

Gravel 

(c) Unravelling or Sloughing 

Downstream zone Silty sand (SM) Fine grained rockfill. Coarse grained rockfill 

Silty gravel (GM) Gravel with some fines Cohesive soil (CL, CH) 

Flow-through capacity ( Qc) of Qc<<estimated flow-through Qc  ̃ Qp Qc>>Qp 

downstream zone due to piping (Qp) 

(d) Slope Instability 

(d1) Initiation of slide 

Existing stability Analysis and/or evidence Analysis and evidence 

indicates existing marginal indicates significant 

stability margin of safety against 

instability 

Cohesive soils (CL, CH) Clayey/silty sands (SC, Free draining rockfill or 

Downstream zone SM) gravel 

(d2) Loss of freeboard and 

overtopping 

Freeboard at time of <2m freeboard  ̃3, freeboard >4m freeboard 

incident 

Crest Width Narrow crest Average crest width Wide crest 

(d3) Breaching given Fine grained, erodible Fine grained, non- Rockfill

overtopping occurs (2) erodible.

Downstream zone

Gravel

Notes: (1) Much more likely if =1m, very unlikely >5m 

(2) Minor influence. 

Of particular importance in separating accidents and failures, is the presence (or absence) of a 

free draining rockfill zone downstream of the dam core. Dams which have this rockfill are 

25 Attachment 5 White Paper 2.doc 
very unlikely to breach, and have survived large seepage flows. Dams like Teton, which had 

silty sandy gravel downstream, have a limited capacity to cope with seepage flows before 

unravelling or experiencing slope instability. 

Some aspects of the breach process can be calculated eg. unravelling of rockfill, but most rely 

on judgement based on case histories. UNSW is seeking further case history data to develop a 

better understanding of breach mechanisms. 

3.6 Some Other Information 

(a) Timing of incident, reservoir level and gradient 

Foster et al (1998) show that nearly 50% of failures occurred on first filling, and 64% within 

the first 5 years of operation (see Table 17). This is considered to be a combination of 

poorly constructed dams being “found out” as they are first loaded, and the effect of partial 

saturation of the soils during the first filling. The partially saturated soils are likely to be 

more permeable, susceptible to initiation of a crack hold a crack and hold a roof, than 

saturated soils. 

Table 17 Time of incident after construction – piping through the embankment 

Time of Incident 

After Construction 

No. of Cases % of Cases (where known) 

Failures Accidents Failures Accidents 

During construction 1 0 2 0 

During first filling 24 26 48 26 

After first filling and 

during first five years 7 13 14 13 

After first five years 18 60 36 61 

Unknown 1 3 - -

Total No. of Pipe Cases 51 102 100 100 

A review of the reservoir level at the time of failure shows all failures where the reservoir 

level was known occurred when the level was at or above the previous maximum level 

(85%) or within 1 metre of the previous maximum (15%). Hence it appears that the 

reservoir level is important, probably in respect to the initiation of piping. 

It is however apparent that the gradient alone, is not a good indicator of the likelihood of 

piping failure. More important is the continuity of features likely to cause a concentrated 

leak. It is only in so far as they are affected by the width of the core that the gradient/core 

width is important. Piping failures and accidents have occurred at very low gradients (as 

low as 0.05). 

There is some evidence that reservoirs which fill rapidly for the first time are more likely to 

experience piping (Sherard 1985), Høeg et al (1998). 

(a) Piping and breach development time 

Table 18 summarizes the observed piping development time for 51 piping failures through 

the embankment. The piping time is taken as the time from when piping begins, as 

evidenced by a muddy leak, to the embankment breaching. 

26 Attachment 5 White Paper 2.doc 
Table 18 Piping and breach development time for failures by piping through the 

embankment – (Foster 1999, Foster et al 1998) 

Time for Piping and Breach Number of Cases 

Unknown 23 

Not observed, but probably <12 hrs 11 

>24 hrs 3 

12-24 hrs 2 

6-12 hrs 3 

<6 hrs 9 

The relatively short times mean that there is limited scope for intervention. However it 

should be emphasised these data are for failures, not accidents. 

4. RESEARCH NEEDS 

We have attempted to summarize the research needs in table 19, under the phase of the piping 

process. It is hoped that this may provide a starting point for our discussions in Denver. 

27 Attachment 5 White Paper 2.doc 
Table 19 Research Needs – Internal Erosion and Piping (Continued) 

Phase Mode Assessment of Research Issues Possible Research underway 

State of the Art Research Approach and where 

Initiation 

Backward Erosion Cohesionless – Cohesionless soils, effects of Laboratory Tests. None known. 

good particle size (internal instability) 

relative density, fines, exit face 

orientation. 

Cohesive soils – 

Cohesive Soils – Critical gradients 

related to degree of saturation (?) 

Laboratory Tests. None known. 

poor particle size, mineralogy, water 

chemistry (dispersion), exit face 

orientation, degree of compaction 

(void ratio). 

Concentrated leak Poor Is the core cracked? Detection of local seepage Canadian Dam Safety 

in transverse eg. by geophysical or Interest Group 

cracking due to temperature measurement, (CDSIG), Vattenfall 

differential optic cables, (a) (Sweden), Germany 

settlement or slope Detection of cracking eg. by 

instability crosshole or seismic ‘p’ or 

‘s’ wave, (a) 

Poor Is there a crack/void around conduit 

or adjacent walls? 

As above. For conduits use 

surface to conduit seismic (b) 

None known. Used in 

routine work for 

detecting voids around 

sewers (b) 

28 Attachment 5 White Paper 2.doc 
Initiation 

(Cont.) 

Concentrated leak 

in transverse 

Poor to fair Is there slope instability induced 

cracking? 

Recognising situations where 

cracking is likely eg. narrow 

UNSW (G. Hunter) 

cracking due to 

differential 

cores with poorly compacted 

rockfill shoulders. Detection 

settlement or slope 

instability 

as above. 

Fair What conditions lead to differential 

settlement induced cracking? eg. 

due to large and small scale 

foundation irregularity, core hangup on filters 

Numerical modelling of 

typical situations, properly 

modelling relative 

stiffnesses, and cracking 

properties of core material. 

UNSW (C.F. Wan) will 

do some work. 

Plus case studies UNSW (C.F. Wan) 

Concentrated leak Fair (principles What conditions lead to low Subset of above UNSW (C.F. Wan) will 

due to hydraulic well known, stresses sufficient to lead to look at this, but not in 

fracture modelling not hydraulic fracture? How quickly detail. 

accurate) does pore pressure respond to 

reservoir level rises? 

Concentrated leak Poor Under what earthquake loads, dam Numerical modelling None known. UNSW 

due to cracking by 

earthquake 

geometry, dam foundation 

geometry, conduits and walls, does 

cracking and low stressed zones 

(preferably 3D, dynamic) of 

typical situations and dams 

which have cracked. 

may begin in 2001, but 

3D modelling program 

not available. 

(sufficient to subsequently cause 

hydraulic fracture) occur, where, 

Plus 

Case studies. 

and how deep. 

Concentrated leak Poor Are such zones present? As for (a) As for (a) 

due to high 

permeability zones 

in fill or around 

conduits, adjacent 

to walls. 

29 Attachment 5 White Paper 2.doc 
Initiation 

(Cont.) 

Concentrated leak 

due to high 

Poor Are there such zones around 

conduits or adjacent walls? 

As for (b) As for (b) 

permeability 

zones in fill or 

around conduits, 

adjacent to walls. 

Good – mostly What conditions lead to such zones. Summarise situations which UNSW (M. Foster) did 

related to lead to these conditions some of this. More a R 

construction issues. (Case studies, literature & D topic than R. 

review) 

Suffusion Good for granular Conditions leading to suffusion in Laboratory testing with UNSW (CF Wan) to do 

(internal 

instability) 

soils. Poor for soils 

with silt or clay 

silty sandy (gravel) soils, and 

clayey gravel soils. (Is it really a 

varying gradients, void ratio, 

particle size distribution. 

some tests using silty 

and clayey soils as a 

fines. mechanism for cohesive soils?) slurry (artifically 

graded) (but limited in 

extent) 

Continuation No erosion 

criteria, critical 

Good – extensive 

laboratory testing 

No erosion filter criteria for 

dispersive soils. 

No erosion tests (as per 

Sherard et al). 

UNSW (CF Wan) will 

further Test No Erosion 

filters. by several groups 

of researchers. 

Good dam 

No erosion filter criteria for gapgraded soils. 

Filtering Mechanics for 

No erosion tests. 

Laboratory tests on 

criteria for dispersive 

soils. 

M. Locke, University 

performance. cohesionless and cohesive soils. penetration of fines into 

filters. 

of Wollongong is 

investigating this for 

cohesionless soils only 

(we think). 

No erosion Fair to good No erosion criteria for well screens. Laboratory tests to mimic None known. 

criteria, screens Sherard et al No Erosion 

for wells, and Test. 

cracks in 

conduits, and 

joints in rock 

foundations. 

30 Attachment 5 White Paper 2.doc 
Continuation 

(Cont.) 

Continuing and 

excessive erosion 

Fair Continuing and excessive erosion 

criteria for a wide range of soils. 

Laboratory testing using “No 

erosion” set-up, plus review 

UNSW (CF Wan) is 

doing some further 

criteria. of case studies. laboratory and case 

study work. 

Fines content of 

filters – will the 

filter “hold a 

Fair The effect of fines content, 

plasticity and compaction of filters, 

on whether the filter will hold a 

Laboratory testing (but not 

clear how). 

Plus case studies. 

None known. 

crack”. crack. 

Minimum Fair. Depth of penetration of fines (base Laboratory tests Wollongong Uni. (M. 

thickness/depth of 

penetration of 

fines. 

soil) into filter. Locke) – as a byproduct of overall 

mechanics. 

Progression Ability of pipe to Fair Effect of soil classification, fines Laboratory tests, with None known. 

to Form a stay open - in content, degree of compaction, varying conditions and hole 

Pipe embankments degree of saturation, and diameter/shape. 

fluctuations in head and flow, on Plus 

whether a pipe will remain open. Case studies UNSW (CF Wan) will 

assess some case 

studies. 

Ability of pipe to Poor As above, but for foundation soils, Laboratory testing as above. None known 

stay open – in such as alluvials, fluvioglacials etc. 

foundations. Effect of interlayering. Case studies. UNSW (CF Wan) will 

assess some case 

studies. 

Effect of Poor to fair. What zoning will give flow Case studies – embankments, UNSW (CF Wan) will 

limitation of limitation and crack stopping? foundations and embankment assess some case 

flows and “crack to foundations. studies. 

stoppers”. Particle size, critical gradients to Laboratory tests simulating Virginia Tech. (Prof. 

mobilize crack stopping, including crack stopper, core and M. Duncan) was/is 

material from upstream transition filter/transition. planning some tests. 

zones with high fines content. 

31 Attachment 5 White Paper 2.doc 
Progression 

to Form a 

Pipe (Cont.) 

Factors affecting 

the likelihood of 

pipes enlargement 

(erodibility) 

Fair to poor. Effect of soil classification, 

dispersiveness, compaction density 

ratio and water content, degree of 

saturation, flow gradient, water 

chemistry, on rate of erosion, and 

limiting erosion conditions. 

Laboratory tests on 

embankment core materials. 

Laboratory tests on 

foundation soils 

UNSW (CF Wan) is 

carrying out extensive 

testing on embankment 

cores. Illinois Uni. (L. 

Reddi) is developing a 

new erodibility test. 

None known. 

Formation of 

Breach 

Piping through 

embankment 

Fair Conditions leading to Breach by 

unravelling or slope instability 

And 

By gross enlargement, crest 

settlement. 

Flow through “rockfill” 

laboratory tests, plus case 

studies. 

Case studies. 

UNSW (CF Wan) will 

consider some case 

studies. 

As above. 

Piping through 

Foundation 

Piping from 

Embankment to 

Foundation 

Poor 

Poor 

As above 

As above 

As above 

As above 

UNSW (CF Wan) will 

consider some case 

studies. 

UNSW (CF Wan) will 

consider some case 

studies. 

32 Attachment 5 White Paper 2.doc 
5. REFERENCES 

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dams. Journal of the Geotechnical Engineering Division, ASCE. 109(GT5), pp.682-

698. 

Arulanandan, K., Loganathan, P. and Krone, R.B. (1975). Pore and eroding fluid influences 

on the surface erosion of soils. Journal of the Geotechnical Engineering Division, 

ASCE.101(GT1), pp.55-66. 

Bakker, K.J. (1987). Hydraulic Filter Criteria for Banks. European Conference on Soil 

Mechanics and Foundation Engineering, Dublin. 

Bickel, J.O. and Kuesel, T.R. (1992). Tunnel Engineering Handbook. Krieger Publishing 

Company, Flordia. 

Brauns, J. and Witt, K.J. (1987). Proposal for an Advanced Concept of filter Design. Proc. 

9th European Conference on Soil Mechanics and Foundation Engineering. Dublin. 

Burenkova, V.V. (1993). Assessment of suffusion in non-cohesive and graded soils. Filters 

in Geotechnical and Hydraulic Engineering, Brauns, Heibaum & Schuler (eds.), 

Balkema, Rotterdam, pp.357-360. 

Cedergren, H.R. (1989). Seepage, Drainage, and Flow Nets. Third Edition, John Wiley. 

CFGB (1997). Internal Erosion: Typology, Detection, Repair. Barrages and Reservoirs 

No.6. Comité Francais des Grands Barages, Le Bourget-du-lac Cedex. 

Chapius, R.P. and Gatien, T. (1986). An improved rotating cylinder technique for 

quantitative measurements of scour resistance of clays. Canadian Geotechnical 

Journal. 23(1), pp.83-87. 

Charles, J.A. (1997). General Report, Special problems Associated with Earthfill Dams. 

Nineteenth International Congress on Large Dams, Florence, GR Q73, Vol.II, 

pp.1083-1198. 

Charles, J.A., Tedd, P. and Holton, I.R. (1995). Internal erosion in clay cores of British 

dams. Research and Development in the Field of Dams, Crans-Montana, Switzerland, 

Swiss national Committee on Large Dams. Pp.59-70. 

Den-Adel, H., Koenders, M.A. and Bakker, K.J. (1994). The Analysis of Relaxed Criteria for 

Erosion Control Filters. Canadian Geotech. J. Vol.31, pp.829-840. 

Fell, R., MacGregor, J.P., and Stapledon, D.H. (1992). Geotechnical Engineering of 

Embankment Dams. Balkema, 1992. 

Foster, M. and Fell, R. (2000). Use of Event Trees to Estimate the Probability of Failure of 

Embankment Dams by Internal Erosion and Piping. ICOLD 20th Congress on Large 

Dams, Beijing, Q76-R16, 237-259. 

Foster, M.A. (1999). The probability of failure of embankment dams by internal erosion 

and piping. PhD Thesis, School of Civil and Environmental Engineering, University 

of New South Wales, Sydney, Australia. 

Foster, M.A. and Fell, R. (1999). A Method for Assessing Embankment Dam Filters Which 

do not Satisfy Modern Design Criteria. UNICIV Report No. R-376, School of Civil 

and Environmental Engineering, The University of New South Wales. ISBN: 85841 

343 4. 

Hanson, G.J. (1992). Erosion resistance of compacted soils. Transportation Research 

Record 1369, pp.26-30. 

Hanson, G.J. and Robinson, K.M. (1993). The influence of soil moisture and compaction on 

spillway erosion. Transactions of the ASAE. 36(5), pp.1349-1352. 

Høeg, K., Johansen, P.M., Kjærnsli, B. and Torblaa, I. (1998). Internal Erosion in 

Embankment Dams. Research Project Sponsored by Norwegian Electricity Federation 

(EnFO). (In Norwegian with English summary). 

33 
Honjo, Y. and Veneziano, D. (1989). Improved filter criterion for cohesionless soils. Journal 

of Geotechnical Engineering, ASCE, 115 (1), pp.75-94. 

ICOLD (1994). Bulletin 95 – Embankment Dams Granular Filters and Drains. Review and 

Recommendations. ICOLD. 

ICOLD (1994). Bulletin 95, Embankment Dams. Granular Filters and Drains. International 

Commission on Large Dams, Paris. 

Kenney, T.C. and Lau, D. (1985). Internal stability of granular filters. Canadian 

Geotechnical Journal, Vol.22, pp.215-225. 

Kenney, T.C. and Westland (1993). Laboratory study of segregation of granular filter 

materials. Filters in Geotechnical and Hydraulic Engineering, Brauns, Heibaum and 

Schuler (Eds.). Balkema, Rotterdam, pp.313-319. 

Lafleur, J., Mlynarek, J. and Rollin, A.L. (1989). Filtration of Broadly Graded Cohesionless 

Soils. J. Geotech Eng. ASCE, Vol.115, No.12, pp.1747-1768. 

Lafleur, J., Mlynarek, J. and Rollin, A.L. (1993). Filter Criteria for Well Graded 

Cohesionless Soils, in Filters in Geotechnical and Hydraulic Engineering, Editors 

Braun, Helbaum and Schuler. Balkema, Rotterdam, pp.97-106. 

Leps, T.M. (1973). Flow through rockfill dams. In Embankment Dam Engineering, 

Hirschfeld and Poulos eds., John Wiley and Sons, pp.87-107. 

Olivier, H. (1967). Through and overflow rockfill dams – new design techniques. 

Proceedings Institution of Civil Engineers, Vol.36, March, pp.433-464. 

Peck, R. (1990). Interface between core and downstream filter. Proc. H Bolton Seed 

Memorial Symposium, BiTech Publishers, Vol.2, pp.237-251. 

Ripley, C.F. (1986) Discussion of: Internal stability of granular filters. Canadian Geotechnical 

Journal, 23, pp. 255-258. 

Schuler, U. and Brauns, J. (1997). The Safety of Geotechnical Filters. Hydropower and 

Dams, Issue 6, pp.72-74. 

Sherard, J.L. (1953). Influence of soil properties and construction methods on the 

performance of homogeneous earth dams. PhD Thesis, Harvard University. 

Sherard, J.L. (1973). Embankment dam cracking. In Embankment Dam Engineering, 

Hirschfeld and Poulos eds. John Wiley & Sons, New York, pp.271-353. 

Sherard, J.L. (1979). Sinkholes in dams of coarse, broadly graded soils. Thirteenth 

International Congress on Large Dams, New Dehli, ICOLD. Q.49R.2, pp.325-334. 

Sherard, J.L. (1983) Discussion of: Design of filters for clay cores of dams. Journal of 

Geotechnical Engineering ASCE, 109 (9), pp. 1195-1197. 

Sherard, J.L. (1985). Hydraulic fracturing in embankment dams. Proccedings, Symposium 

on Seepage and Leakage from Dams and Impoundments, (Volpe, R.L., and Kelly, 

W.E. eds.), ASCE, pp.115-141.

Sherard, J.L. and Dunnigan, L.P. (1985). Filters and leakage control in embankment dams. 

Proccedings, Symposium on Seepage and Leakage from Dams and Impoundments, 

(Volpe and Kelly eds.), ASCE, pp.1-30. 

Sherard, J.L. and Dunnigan, L.P. (1989). Critical filters for impervious soils. Journal of 

Geotehnical Engineering, ASCE, 115 (7), pp.927-947. 

Sherard, J.L., (1985) Memorandum 1A to 1H, Unpublished reports of filter research carried 

out in the Lincoln, Nebraska, Soil Conservation Service Soil Mechanics Laboratory. 

Sherard, J.L., Decker, R.S. and Ryker, N.L. (1972(a)). Hydraulic fracturing in low dams of 

dispersive clay. Proceedings, Specialty Conference on Performance of Earth and 

Earth-Supported Structures, ASCE, Vol.1, Part 1, pp.653-689. 

Sherard, J.L., Decker, R.S. and Ryker, N.L. (1972(b)). Piping in earth dams of dispersive 

clay. Proceedings, Specialty Conference on Performance of Earth and EarthSupported Structures, ASCE, Vol.1, Part 1, pp.589-626. 

34
Sherard, J.L., Dunnigan, L.P. and Talbot, J.R. (1984a) Basic properties of sand and gravel 

filters. Journal of Geotechnical Engineering, ASCE, 110 (6), pp. 684-700. 

Sherard, J.L., Dunnigan, L.P. and Talbot, J.R. (1984b) Filters for silts and clays. Journal of 

Geotechnical Engineering, ASCE, 110 (6), pp. 701-718. 

Sherard, J.L., Woodward, R.J., Gizienski, S.F., and Clevenger, W.A. (1963). Earth and 

Earth-Rock Dams, John Wiley & Sons. 

Skempton, A. and Brogan J.M. (1994). Experiments on Piping in Sandy Gravels. 

Geotechnique 44 No.3, 449-460. 

Solvik, Ø (1991). Throughflow and stability problems in rockfill dams exposed to 

exceptional loads, Sixteenth International Congress on Large Dams, Q.67 R.20, 

ICOLD, pp.333-343. 

Terzaghi, K. and Peck, R.B. (1967). Soil Mechanics in Engineering Practice. Second 

Edition, John Wiley. 

US Army Corps of Engineers (1985). Engineering and Design. Seepage Analysis and 

Control for Dams. EM1110-2-1901. 

USBR (1987). Guidelines for Controlling Seepage Along Conduits Through Embankments, 

ACER Technical Memo No.9, U.S. Department of the Interior, Bureau of Reclamation. 

USDA – SCS (1994) 

Vaughan, P.R., and Soares, H.F. (1982). Design of filters for clay cores of dams. Journal of 

Geotechnical Engineering Division, ASCE, 108(GT1), pp.17-31. 

Von Thun, J.L. (1996). Understanding seepage and piping failures – the No.1 dam safety 

problem in the west. ASDSO Western Regional Conference, Lake Tahoe, Nevad. 

Witt, K.J. (1980). Filtrations verhalten und Bemessung von Erdstoff – Filtern. Veroffentl. 

Inst. F. Boden u. Felsmech. Univers. Karlsruhe, Heft 104. 

Witt, K.J. (1993). Reliability Study of Granular Faction. Behaviour of Coarse and Well 

Graded Filters in Filters in Geotechnical and Hydraulic Engineering. Editors Brauns, 

Helbaurn and Schules. Balkema, Rotterdam, pp.35-41. 

35

Assessing the Risk of a Seepage-Related Dam Failure

By Means of Failure Mode Identification, Risk Analysis,

and Monitoring Practices

A “White Paper” for the October 2000 ASDSO/FEMA Seepage Workshop 

William O. Engemoen 

U.S. Bureau of Reclamation 

October 3, 2000 

I. Purpose 

In the survey of interest for workshop topics, the three topics of this paper all received significant 

expressions of interest, and were subsequently combined into a single “white paper.” The three 

topics to be addressed herein, listed in order of the number of votes received, are: 1) inspection 

of dams for detection of seepage problems, 2) analysis of risks associated with seepage and 

internal erosion, and 3) failure modes associated with seepage and internal erosion. This paper 

presents the “state of practice” (admittedly biased towards the practices followed by the Bureau 

of Reclamation) with regards to the surveillance and monitoring of dams, and the subsequent use 

of this information in the evaluation of the potential risks posed from a seepage-related failure at 

a given dam. Potential areas of research relative to these topics are included at the end of the 

paper. 

II. Overview of Reclamation Process for Evaluating Dam Safety Issues 

Reclamation’s inventory of dams includes around 300 major embankments that have the 

potential to result in life loss in the event of failure. Typically, these dams are observed and 

inspected frequently by dam tenders and operations personnel, most likely during the operation 

season when the reservoirs are at their highest levels. However, formal examinations and 

evaluations are done less frequently, but in a thorough and prescripted manner. Annually, 

Reclamation representatives from the nearest Area Office examine the dam and fill out an 

inspection report. Typically, these inspectors are generalist (as opposed to specialist) engineers 

very familiar with the dam and it’s operations, and can readily distinguish changes from year to 

year. All inspectors attend regular training in dam safety inspections. On a 3-year cycle, each 

dam is examined by a team originating in the Regional Office, including the regional 

examination specialist. This examination is referred to a Periodic Facility Review and includes a 

rather thorough review and reporting of all past dam safety and Operation and Maintenance 

(O&M) recommendations made in the past. Finally, on a 6-year cycle, each dam is 

examined/evaluated by a team of specialists from the Technical Service Center that includes an 

Instrumentation Engineer, an Examination Specialist, and a Senior Dam Engineer. This process 

is called a Comprehensive Facility Review (CFR) and includes: a site examination with the Area 

and Regional Office representatives and operational personnel; a thorough review of all 

instrumentation and past performance, as well as suggestions for changes to the monitoring 

program; a review of all available documentation of the original design and construction, 

including all analyses and design assumptions and how they compare to today’s state of practice; 

a discussion of potential failure modes; a new look at the probabilistic earthquake and flood 

1 Attachment 6 White Paper 3.doc 
loadings that would be expected for that site; a determination of the estimated consequences (loss 

of life) in the event of a dam failure; a quantitative evaluation of the risks posed due to the 

various loadings ; and a listing of conclusions, recommendations, and further actions required to 

ensure public safety. 

If the conclusions reached by the CFR team indicate that significant risks may be present at a 

dam, additional higher level studies and risk analyses are then undertaken. Such higher level 

studies may include the collection of additional data, the installation of additional 

instrumentation, changes to the surveillance extent or frequency, performance of specific or 

updated analyses, and likely the performance of a formal, comprehensive analysis of risk 

including detailed event trees and in accordance with established Reclamation methodology. 

The decisions resulting from these studies and additional risk assessments may include: 1) do 

nothing, as risks are not high enough to justify actions; 2) restrict the reservoir, or some similar 

non-structural response; 3) structurally modify the dam to mitigate any deficiency; 4) enhance 

monitoring and emergency management practices to ensure timely detection and warning 

capability that would substantially reduce and hopefully eliminate loss of life; and 5) a 

combination of these measures. A Risk Reduction Analysis would typically be performed to 

provide information to the decision process as to the expected benefits of non-structural and 

structural responses. 

The above overview is a generalized summary of the process Reclamation employs to monitor its 

dams and attempt to detect any potential dam safety deficiencies, whether from flood or 

earthquake loading, or from the static loading which includes the threat of seepage-related 

failure. What follows will be a more detailed discussion of the various processes as they relate to 

the evaluation of the potential for seepage-related dam failure. 

The discussion will start with the failure mode evaluation, as the understanding of how a specific 

dam might fail due to seepage is a key first step. What follows failure modes is logically an 

evaluation of the probability of each failure mode - the risk analysis. Inspection and monitoring 

of the dam is discussed last in the order, to highlight lessons learned, or things to look for, that 

often are discovered during the failure mode and risk analysis process. 

III. Failure Mode Evaluation 

General - In order to best detect potentially threatening seepage problems and to be able to 

understand and estimate the risks posed by seepage, it is important to have a detailed 

understanding of the specific means by which a particular dam might fail under seepage 

conditions. A well thought out discussion and analysis of the specific means by which a given 

dam could fail is referred to as a failure mode evaluation. It is important that this evaluation be 

detailed, rather than too general. For example, saying that the dam could fail by “piping of the 

core” is not sufficient. A far better description would be “erosion of the low plasticity core 

materials through the coarse, openwork shell materials, and into the unprotected toe drain, 

resulting in backward erosion and formation of a sinkhole into the reservoir where the 

subsequent outflow erodes and breaches the embankment.” In other words, the entire failure 

process needs to be understood and logically described. This type of understanding and 

description will help inspectors know where and what to look for during dam surveillance, and 

2 Attachment 6 White Paper 3.doc 
will help the risk analysts better construct event trees and determine probabilities of failure for 

each step of the failure process. With this evaluation, it also helps to identify locations in the 

dam where particular failures are most likely to originate. Openwork foundation soils may be 

present, for example, between stations 3+00 and 6+50 along the dam alignment, or foundation 

grouting or surface treatment may not have extended past a given station on one abutment. This 

type of information may be critical to the inspectors or risk analysts as well. 

Failure mode evaluations are best performed by a small group of very experienced designers and 

geologists and would ideally include at least some individuals with a thorough understanding of 

the dam, site specific knowledge of surveillance and monitoring procedures, and some 

understanding of risk analysis [1]. It is essential that this group carefully study all available 

records of the site geology, design and construction details, and structural performance. 

Attention to detail and thorough discussion will lead to a better development and understanding 

of the failure modes. 

Types of Seepage-Related Failures - Seepage passing through and under an embankment dam 

can, in the right situation, lead to dam failure by one of several mechanisms [2,3,7]. Any dam 

may have one or more of these potential failure modes. 

Piping - Erosion initiates at a downstream exit point of a seepage path within the dam or 

foundation. As soil particles are carried away by the exiting seepage, the erosion process 

continues in a backward (upstream) direction. Classical piping is characterized by the 

formation of an open tunnel extending from the downstream seepage exit point back 

upstream toward the reservoir. For piping to occur, several conditions must be present, 

including: 

- there must be a flow path with water 

- there must be an unprotected (open, unfiltered) exit from which soil can escape 

- there must be erodible material within the flow path that can be transported to 

the exit 

- the material being piped must be able to support a “pipe” or “roof,” or must be 

adjacent to a feature such as a overlying clay layer or concrete structure that 

would provide a “roof” 

-sufficient seepage gradients, or even the presence of a concentrated leak, may be 

required to initiate the erosion process (although that depends on the soil 

erodibility) 

Seepage Erosion, or “Scour” - Loss of material occurs at an erosional surface where a 

concentrated flow is located, such as a crack through a dam or the dam/foundation 

contact. Continued flow causes the erosion to progress, creating a larger and larger 

eroded area. 

Internal Erosion by Suffosion (Internal Instability) - In an internally unstable soil 

(typically gap-graded), flow through this material can cause part of the finer grained 

portion of the soil matrix to be washed through the coarser grained portion of the matrix. 

3 Attachment 6 White Paper 3.doc 
High, Confined Pore Pressures in Foundation - Several different descriptions including 

uplift, heave, and blowout are lumped into this category, and generally describe a 

situation in which the foundation seepage pressures exceed the effective weight of the 

overlying soil, typically at the downstream toe of the dam. Failure scenarios include a 

slope failure or a rupture in the confining layer that in turn might lead to a piping failure. 

It is generally thought that these failure mechanisms would be most likely to occur the 

first time a reservoir reaches a critical elevation, which implies that first filling, new 

water levels that exceed historic highs, and possibly increasing foundation pressures 

would be needed for these to be failure modes. 

Three Major Classifications of Internal Erosion Failure Modes - Based on the work done by 

the University of New South Wales [4,7], Reclamation often evaluates potential internal erosion 

failure modes on the basis of 3 different types: erosion through the embankment, erosion through 

the foundation, and erosion of the embankment into or at the foundation. 

Internal Erosion Through the Embankment - This failure mode is typified by internal 

erosion occurring solely within the embankment, and could include classical piping, 

scour, or suffosion. Erosion would progress by escape of embankment materials into 

downstream areas or zones, and would continue until it eventually reaches the reservoir 

and causes a dam breach. A major subset of this failure mode includes internal erosion 

associated with a penetrating structure such as an outlet works or spillway conduit 

located within the embankment. Studies of case histories suggest that around 50 percent 

of all failures due to embankment erosion appeared to initiate around or near conduits. 

This could be due to a number of factors, including: leaks into or out of the conduit due 

to structure flaws (pipe deterioration, separating joints, differential settlement cracks, 

etc.), poor compaction against the sides of conduits, or stress concentrations in the 

embankment adjacent to the conduit. 

Internal Erosion Through the Foundation - This failure mode is typified by internal 

erosion occurring solely within the foundation, involving only foundation materials 

(which could be soil, rock, or both) in the erosion process. This type of failure could also 

include classical piping, scour, or suffosion, which would start the initiation of erodible 

foundation material. Erosion would then progress by escape of material into downstream 

areas, and would continue backwards until it reached the reservoir. In latter stages of this 

process, the embankment would start caving or stoping into the foundation void, leading 

to ultimate dam breach. 

Internal Erosion of Embankment into/at Foundation - This particular failure mode is 

typified by an internal erosion process involving both the embankment and foundation, 

and includes two distinctly different failure modes: 

• Internal erosion of embankment into the foundation - Erosion initiates at the 

embankment-foundation contact due to a seepage gradient from the embankment 

into the foundation materials, which may be soil or rock. This requires higher 

seepage pressures in the embankment than in the foundation, sufficient 

permeability of the foundation material to allow soil transport, and an unfiltered 

4 Attachment 6 White Paper 3.doc 
exit downstream (or else a sufficient storage volume within the foundation 

material). Once initiated, erosion continues backward until dam breach results. 

Case histories of failures reveal that embankment erosion into rock discontinuities 

is more typical than embankment erosion into pervious foundation soils [4]. 

• Internal erosion by foundation flow at the contact - Erosion begins by a 

concentrated flow of water in the foundation at its contact with the embankment. 

The seepage flow erodes the embankment material into downstream areas of the 

foundation or embankment, ultimately leading to a dam breach. A key 

requirement for this failure mode is the presence of significant flow at the 

embankment/foundation contact. 

IV. Analysis of Risk Posed by Failure Modes 

General - The term “risk” as used by Reclamation [5] is best defined by the equation: 

Risk = [Probability of the Loading] x [Probability of Adverse Response given the Loading] x 

[Adverse Consequences given the Failure]

 Where: 

Probability of the Loading is the annual probability that the load responsible for a failure 

will occur (such as a 100-year flood, a 10,000-year earthquake, etc.) 

Probability of Adverse Response given the Loading is the likelihood that the dam will fail 

under the specific loading (ranges from 0 to 1.0) 

Adverse Consequences given the Failure is typically expressed in terms of the estimated 

number of lives lost given a dam failure 

In Reclamation, there are different levels of risk analyses used at various points in dam safety 

studies, including the following: 

Risk Based Profiling System: This is essentially a “portfolio ranking” tool that utilizes a 

standardized set of questions to calculate a quantitative point total for each dam in a 

given inventory [6]. By applying this profiling system to all dams, an agency then has a 

system that can compare and rate relative risks between their dams. Reclamation has 

only recently developed this system, and is currently developing plans on how to most 

effectively use it for dam safety prioritizing and decision making. 

CFR Risk Analysis: As mentioned earlier, a Comprehensive Facility Review is conducted 

on Reclamation dams every 6 years. As part of this CFR, the Senior Dam Engineer is 

expected to use existing information, judgement, and considerable experience to 

quantitatively estimate the risks posed by various failure modes for a given dam. This 

level of risk analysis is much less detailed and complicated than the team approach 

described below, and is therefore considered more of a screening-level risk analysis. 

Issue Evaluation Risk Analyses: This level of risk analysis is generally the most 

comprehensive type utilized by Reclamation. It is comprised of two trained facilitators 

and a team that usually includes subject experts, design engineers and geologists most 

familiar with the dam, and field personnel responsible for inspection and maintenance of 

5 Attachment 6 White Paper 3.doc 
the structure. This type of analysis includes preparatory time, usually about of week of 

meeting time, and then a fairly lengthy effort to document the processes followed and 

conclusions developed from the risk meetings. 

In general, Reclamation tends to use the first two types of risk assessments to help determine 

what types of further studies are needed on a dam, or the priority in which dams should have 

additional dam studies scheduled, if such studies are needed. The third, and much more 

comprehensive, type of analysis is typically utilized when deciding whether to modify a given 

dam. A very important point to comprehend here with the use of any of these three types of risk 

analyses is that they should serve as a tool to promote a more thorough understanding of the 

technical issues at a dam and help decision makers with determining a prudent course of action. 

A risk analysis is not, by itself, intended to serve as the ultimate “answer” to whether a dam 

safety issue requires remediation. Rather, the risk analysis should compliment other technical 

analyses, non-technical considerations, and judgements, and form an additional consideration 

for deciding future required action. 

Basic Risk Analysis Methods for Analyzing Seepage Risks - There are two primary methods 

for quantifying the risk of seepage-related dam failures: 1) reference to historical databases of 

performance, and 2) decomposition, or the use of event trees. 

Comparison to Historical Performance: A simpler, screening-level risk analysis like that 

performed during a CFR will utilize historical performance data, and generally follow the 

procedure as documented by researchers at the University of New South Wales [4]. In 

essence, a dam is categorized into a particular type of dam (with a resulting failure 

probability from the historical database), receives site specific adjustments due to many 

factors that would affect its susceptibility to internal erosion, and then an adjusted annual 

probability of failure is calculated. Although the method contains some simplifications 

or generalizations, it nonetheless serves as a very useful tool for developing preliminary 

estimates of risks posed by internal erosion failure modes, and is based on a very 

comprehensive look at historical dam performance. 

Event Trees: Higher level risk analysis will typically utilize the event tree method which 

decomposes the failure modes into discrete nodes. Although each specific risk analysis 

for a given dam may require a particular event tree, our experience has shown that a 

“generic” event tree is often satisfactory or at least provides a good starting point. The 

generic tree used by Reclamation is based in large part on the work done by researchers 

at the University of New South Wales [7], but customized for our work. This event tree 

is shown on Figure 1. A separate event tree is typically developed and analyzed for 

each internal erosion failure mode, as there are enough differences between the various 

failure modes to warrant a unique tree for each one. 

Details of Event Tree for Internal Erosion - Following are brief descriptions of each node on 

the event tree, along with some key considerations. Much more detail, including tables which 

list considerations for each node, may be found in Appendix E [3] of Reclamation’s Risk 

Analysis Methodology. 

6 Attachment 6 White Paper 3.doc 
Initiation: Many believe that some type of concentrated leak through the dam or 

foundation is needed to develop an internal erosion problem. An evaluation of case 

histories would support this position over the more unlikely supposition that 

“spontaneous erosion” would suddenly develop where previously no leak existed. Based 

on this assumption, this first node essentially asks the question “What is the probability 

that a concentrated leak exists in the dam (or foundation, depending on which failure 

mode is being analyzed)?” Some of the site specific issues to consider in establishing the 

probability of this node include: the presence and fluctuations of seepage, the location 

and details of any penetrating conduits, the presence of permeable layers, composition of 

core material and likelihood for cracking, the gradations of embankment and foundation 

materials, and the type of foundation treatment. 

Continuation of Internal Erosion: For internal erosion to continue, even given a 

concentrated leak, there needs to be an unprotected exit. Thus, this node seeks the 

probability of an unfiltered exit to the seepage/erosion path. Information to consider in 

estimating this node includes factors such as embankment zoning, the filter compatibility 

of surrounding embankment and foundation materials, and the presence of features such 

as toe drains or relief wells that may not have been designed according to proper filter 

criteria. 

Progression of the Internal Erosion Process: There are three pieces to the consideration of 

whether erosion will progress once the process has initiated at the downstream end of the 

seepage path, and these are shown as three different nodes on the event tree. These three 

nodes are not necessarily conditionally dependent on one another, but nonetheless are all 

considered critical to the progression of the erosion process. 

• Ability to support a roof - This node refers to the ability of the eroded material

to sustain or support a “roof,” either on its own or by the help of an adjacent 

conduit or wall or perhaps an overlying natural material. It is only applicable to 

the classical piping and scour failures, and might be ignored for other erosion 

failure modes. 

• Inability to limit flows - This node refers to the potential for concentrated flow

to be limited by factors such as: washing in and choking of the crack or flow path 

by an upstream material, an internal concrete element such as a diaphragm wall, 

or a physical constraint such the size of a foundation joint. 

• Erodibility of soils - Enlarging of the erosion path is quite dependent on the 

embankment or foundation materials’ erodibility. Considerations in estimating 

this factor include any visual observations of material transport, the plasticity 

index, dispersivity, density, a very low hydraulic gradient, and seepage velocity. 

Early Intervention: At this point in the event tree, it is usually reasonable to address the 

probability that early intervention may stop the process, since at this point there may be 

obvious signs of a developing problem. “Early” intervention refers to actions that would 

be based on an awareness of erosion progression well in advance of any imminent 

7 Attachment 6 White Paper 3.doc 
breach, and might include measures like reverse filters, sinkhole filling, or emergency 

grouting to respond to increasing seepage volumes or observed material transport. The 

“heroic” intervention shown in a later node is distinguished by “all-out” dramatic efforts 

such as draining the reservoir or constructing a breach in another topographic drainage. 

Factors that may influence the success of early intervention include the likelihood of 

observing abnormal behavior, willingness to respond to unusual behavior, the rate at 

which erosion is progressing, and the availability of materials and resources to start 

emergency repairs. 

Breach Initiation: Should intervention be unsuccessful, the probability of a dam breach 

needs to be evaluated. Depending on the nature of the failure mode, dam breach may 

form by one of several mechanisms, including: 1) gross enlargement of the pipe or crack, 

2) crest settlement due to sinkhole, 3) progressive downstream slope failures (raveling or 

sloughing), or 4) a major slope failure due to high pore pressures or weakening of a 

horizontal layer. Some of the factors to consider in the probability of this breaching 

process include embankment zoning, reservoir storage volume, amount of freeboard, 

crest width, and presence of downstream rockfill (flow through capability). 

Heroic Intervention: As mentioned earlier, this node refers to the probability of stopping 

dam breach by all-out efforts that may be attempted once dam failure appears imminent. 

The two primary options considered at this point include the ability to drain the reservoir 

quickly or to construct a breach in a part of the reservoir with low consequences. Factors 

considered include the release capacity of any outlets, the timeliness of decision-makers, 

the availability of a low hazard breach area, and the availability of operators and 

equipment necessary for a breaching operation. 

Once all these nodal probabilities are multiplied, the result is really the middle part of the risk 

equation listed at the beginning of this section - the Probability of Adverse Response given the 

Loading. The next two paragraphs will deal with the other two components of the risk equation. 

Loading - Normally, one would assume that the Probability of the Loading component of the 

risk equation for static failure modes should be equal to one, as the reservoir load is always 

applied to the structure. Even reservoirs that cycle yearly between high and low pools often have 

close to a 100 percent probability of reaching the high pool level each year. For Reclamation 

risk analyses, the static probability of load is therefore usually assumed to be equal to one, 

although there are a few cases where the value would be lower. 

One of those cases is associated with different material types that might be encountered at the 

higher portions of the embankment or abutment that would be wetted only during infrequent 

flood events. An example could be the presence of an erosive sand layer in the dam abutment a 

few feet below the spillway crest. If reservoir levels have only reached this elevation in an 

occasional year over a lengthy operational history, the analysts would likely use a value lower 

than one for the loading probability. The actual operating history would be used to determine the 

probability. 

8 Attachment 6 White Paper 3.doc 
Likewise, it may be that a susceptible portion of the embankment is located within the flood 

surcharge pool, above the normal annual high water level. In this case, it would be advisable to 

include a separate evaluation of this condition and include an annual loading probability 

corresponding to the flood frequency. 

Consequences - The actual loss of life due to a dam failure will depend in large part on the 

amount of available warning time. In turn, the warning time can depend on a number of factors, 

including: frequency of surveillance; readiness, notification ability, and evacuation capability of 

local authorities; distance to the downstream population; whether the failure is occurring at day 

or night; and the failure rate for the particular internal erosion mechanism. From a technical 

standpoint, this is an area where past case histories add some perspective, and once again, the 

University of New South Wales research [4] is of interest. The historical evidence tends to 

support that in dams that survive first filling, later internal erosion problems are more likely to 

end in simply an “accident” rather than a dam failure. This may mean failures develop more 

slowly in older dams. On the other hand, after first filling, failures due to internal erosion solely 

within the foundation or with a through penetrating structure tend to show an increase with age, 

suggesting the possibility of deterioration. 

In terms of the time it took for internal erosion failures to end in dam breach, close to half of the 

case histories had insufficient information regarding the failure time frame. Of those with 

information, most dams failed in less than 12 hours from the detection of a problem. A very few 

took longer than one day, and a few failed in as little as 2 to 3 hours. It would appear that most 

failures probably took less than 6 hours. Obviously, with this type of historical perspective, 

surveillance and emergency management procedures are essential in helping minimize life loss. 

V. Inspection of Dams for Detection of Seepage Risks 

General - Hopefully, the previous sections have emphasized the value of having a good 

understanding of the case histories involving seepage-related failures, a thorough evaluation of 

ways in which a specific dam could fail under seepage loads, and an understanding of the risks 

posed. Some of the lessons learned from these exercises can be used to develop the optimum 

monitoring program for a given dam. 

Components of an Optimum Monitoring Program - The following items are gleaned from the 

lessons learned from actual failures and failure mode evaluation and risk analyses: 

Integrate Analysis with Inspection: The essence of this recommendation is to set up a 

dam safety program that includes inspection as just one component. The other essential 

component is an engineering evaluation of the potential failure modes for a given dam. A 

possible additional element is an assessment of the risk posed by the dam, using a 

portfolio analysis, screening method like the New South Wales approach, or a more 

comprehensive approach utilizing event trees to lay out each step of the failure process. 

By looking thoroughly into the potential weaknesses and vulnerabilities with each dam, a 

better quality monitoring program will result - inspectors will know what to look for. 

9 Attachment 6 White Paper 3.doc 
Emphasize Visual Observation: The benefits of comprehensive visual observations 

cannot be overestimated. Routine and frequent visual inspections are obviously key to 

detecting ongoing internal erosion problems before they progress to failure. The 

frequency of observations may depend on the risks posed, the age of the dam, the design 

features incorporated, and many other factors, and should be carefully evaluated. If 

possible, the same properly trained inspector(s) should make the observations, as they 

will be in the best position to pick up subtle changes in seepage areas. 

Know What to Look For and Where: Obviously, any areas of existing seepage are 

critical, and should be watched closely. Case histories suggest that areas adjacent to 

conduits or penetrating structures within an embankment are particularly vulnerable spots 

for seepage problems. Locations of dramatic topographic changes are also suspect due to 

the possibility of cracking. A thorough failure mode evaluation will likely indicate other 

specific areas with a given dam. 

Include Instrumentation: Total reliance on visual observation is not always sufficient. 

Key instrumentation to help detect seepage problems includes piezometers and seepage 

measurement devices (weirs, flumes, etc.). Changes in water levels, pore pressures, and 

seepage flows can often be discovered earlier if a regular instrument reading program, as 

well as an evaluation of the readings, is established. 

Consider Video-Taping Outlet Works and Drainage Systems: In many older dams, an 

unfiltered exit for seepage may exist in poorly designed outlet works and toe drains or if 

these features have deteriorated badly. Outlet works comprised of corrugated metal pipe 

have been particularly prone to poor construction and deterioration that has led to a high 

rate of incidents of internal erosion. The use of open jointed drain pipe and gravel 

envelopes that don’t satisfy filter criteria presents the possibility of internal erosion of 

finer embankment and foundation materials into the drainage system. Remote controlled 

video cameras that can traverse these pipes have proven valuable in observing the 

condition of otherwise inaccessible systems. 

Consider Automated Early Warning Systems: In some cases, automated piezometers, 

monitoring devices, or stream gages are utilized to provide immediate warning of 

changed conditions in water levels or seepage volumes at the damsite. Surveillance 

cameras trained at key locations can also provide automated observations. These devices 

can be fed to any office or control center that operates 24 hours. 

Tie the Monitoring to an Emergency Action Plan: Detection is an important component 

of warning, but an action plan for notification of authorities and subsequent evacuation 

plans must be in place and practiced to achieve a fully successful warning. 

Limitations of, and Additional Considerations for, Monitoring Programs - Detection of 

impending seepage-related emergencies is a difficult science, perhaps more of an art, and may 

even come down to luck. This statement is made to clarify that monitoring is not a guarantee 

that a dam will not fail from an internal erosion process, but is nonetheless is a proven and 

prudent component of a proactive dam safety program. By recognizing weaknesses of 

10 Attachment 6 White Paper 3.doc 
monitoring and understanding how to best utilize it, the probabilities of averting a problem 

increase. Following are some tips to consider: 

Fight Complacency: Most designers and inspectors realize the significance of first filling 

monitoring (or filling to new historical high water levels), where history has shown that 

dams are most vulnerable. However, once dams have been in service for many 

operational seasons with no hint of any problem, there may be a natural tendency to pay 

less attention to instrumentation data or visual observations. However, seepage-related 

failures can develop unexpectedly, and are often hard to foresee, so it is critical to 

maintain an objective and diligent attention to behavior of an otherwise “satisfactory” 

dam. 

Pay Close Attention to Changes: Any change in behavior at a dam should be taken 

seriously, as it may be a precursor of a developing problem. For seepage-related 

problems, some of the changes to watch for include: 

• New (or enlarging) wet spots or seepage areas - These may indicate new flow

paths are developing or seepage is increasing. Also look for alternate 

explanations such as leakage from a nearby canal or watercourse, recent 

precipitation, increased reservoir levels, etc. 

• Increasing piezometric levels or seepage volumes - As for the above visual

indicators, these instrumentation changes may also indicate new flow paths or 

increasing seepage. However, alternate explanations, as described above, need to 

be evaluated. Changes in otherwise stable instrument readings should be 

immediately reported and checked for accuracy. Increased frequency of 

instrument readings may be advisable as well. 

• Watch seepage behavior carefully during unusual reservoir operations - Changes

in reservoir operation, such as prolonged periods at maximum water levels, 

pronounced drawdowns, or more or less cycling than usual can all trigger changes 

in groundwater and seepage behavior. 

• Sinkhole, depressions, or subsidence on or near the embankment - Any such

feature, especially if newly observed, can be an indicator of internal erosion 

within the dam or its foundation. 

Recognize the Limitations of Instrumentation: It should be recognized that piezometers 

may need to be at just the right location to serve advance warning (i.e. in the concentrated 

leakage path). A belief that seepage problems will be detected because a site has a lot of 

piezometers is false confidence. Seepage measuring devices, because they measure more 

general areas, generate less concern with this issue. However, concerns with weirs and 

flumes include ensuring that they are properly maintained and read, as well as the 

recognition that they are probably not measuring all seepage at a site. Some seepage may 

be flowing underground or into conduits and stilling basins where it cannot be quantified. 

11 Attachment 6 White Paper 3.doc 
VI. Possible Areas of Future Research 

Failure Mode Evaluation -

FM-1: A better understanding of the physics of internal erosion may lead to a better 

understanding of why an erosion process may initiate at one dam and not at a similar 

structure. 

Analysis of Risk -

RA-1: Develop/expand the database of failures and accidents for small dams. (Much of 

the existing data deals with dams higher than 15 meters.) 

RA-2: Continue research regarding the state of knowledge and practice in quantitative 

risk analysis. (Applying probabilities to internal erosion potential is still a bit of an art.) 

RA-3: Study the past failures and theory regarding whether a “concentrated leak” is 

critical to the development of seepage failures or accidents. 

RA-4: Further the development of methods for calculating loss of life estimates resulting 

from dam failures. 

RA-5: Further review the case histories of incidents to determine an acceptable estimate 

of warning time for old dams for each failure mode. Substantial warning can lower 

dramatically the perceived risk of life loss. 

Surveillance and Monitoring -

INSP-1: Study the effectiveness (probably through field testing) of remote surveillance 

and automated warning methods. 

INSP-2: Develop a guidance document, using case histories as possible, for dam safety 

professionals to use in the design of new surveillance plans and monitoring systems and 

to evaluate existing systems and plans. 

12 Attachment 6 White Paper 3.doc 
References 

[1] Fell, R., Bowles, D., Anderson, L., and Bell, G., “The Status of Methods for Estimation of 

the Probability of Failure of Dams for Use in Quantitative Risk Assessment,” paper presented at 

the ICOLD Conference in Beijing, China, September 2000. 

[2] VonThun, J.L., “Understanding Piping and Seepage Failures - The Number 1 Dam Safety 

Problem in the West,” adapted from paper presented at the 1996 Western Regional Conference 

of the Association of State Dam Safety Officials. 

[3] U.S. Bureau of Reclamation Risk Analysis Methodology - Appendix E, “Estimating Risk of 

Internal Erosion and Material Transport Failure Modes for Embankment Dams,” Version 2.4, 

August 18, 2000. 

[4] Foster, M., Fell, R., and Spannagle, M., Analysis of Embankment Dam Incidents, University 

of New South Wales, UNICIV Report No. R-374, September 30, 1998. 

[5] U.S. Bureau of Reclamation Risk Analysis Methodology, Version 3.3, September 1999. 

[6] U.S. Bureau of Reclamation Risk Based Profiling System, May 17, 2000. 

[7] Foster, M., Fell, R. A Framework for Estimating the Probability of failure of Embankment 

Dams by Piping Using Event Tree Methods, UNICIV Report (Draft), April 1999 

13 Attachment 6 White Paper 3.doc 
14 Attachment 6 White Paper 3.doc 

White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

INTRODUCTION 

A basic principle of dam design is to provide as impervious a water barrier as feasible, 

satisfying safety and economic as well as technical requirements. Rims, abutments and 

foundations are integral parts of the water barrier. 

Seepage through embankments, rims, abutments and foundations has been experienced 

by most dam owners. This paper presents what methods have been used to investigate 

and monitor this seepage. 

Depending on the age, the design and construction records will vary greatly. A well 

designed and constructed dam will provide detailed information on the construction 

method and treatment and any known features in the foundation. A dam built with limited 

design may have little or no record of the construction or materials at the site. 

To understand the seepage one must understand the stratigraphy of the area. There are 

various methods to determine the types of material and their condition at the site. They 

vary from drilling, sampling, and testing to more unique methods such as geophysical 

investigations. 

A field investigation program should be set up to determine the stratigraphic and phreatic 

data. This data is required to perform a safety evaluation of the dam with respect to 

seepage or underseepage. If in the study it is proposed to perform a seepage analysis, a 

thorough understanding of the flow and phreatic conditions through the embankment, 

foundation, abutments and rims must be gained. A field investigation program should be 

designed with five main objectives in mind: 

1. Augment already known data, 

2. Assess the subsurface soil conditions, with particular emphasis on soil types, threedimensional stratigraphy, and engineering properties of the embankment, abutment 

and foundation. 

3. Identify the depth, aerial extent and thickness of any artesian layers. 

4. Obtain piezometric data over the entire site at a number of depths. 

5. Install additional piezometers to better define seepage conditions and provide for longterm, groundwater monitoring capabilities. 

Investigation Methods: 

Peizocone Penetration Test (CPTu) and Standard Penetration Test (SPT) can be 

performed to achieve the first three objectives. The CPTu test is a quick, efficient way to 

get quality piezometric and inferred soil property data with minimal site disturbance. SPT 

tests are used to verify blow counts and soil types interpreted from the CPTu results with 

those values obtained from the SPT test. The SPT holes also allow exploration of soil 

layers below the reach of the CPTu rig. 

Push-type and standpipe piezometers can be installed along the crest, abutments, the 

downstream toe, and the valley floor to achieve the fourth objective of the program. 

Below are the requirement and investigations performed at one of TVA’s projects. 

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Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

1. CPTu Testing Procedure and Equipment 

All CPTu tests and equipment were performed in accordance with ASTM Standard 

D3441-86. A cylindrical rod is hydraulically pushed at a rate of 4 ft/min into the soil. 

The rod has a conical tip 1.4 inches in diameter with a 60 degree tip angle. On the 

nonartesian holes, 1.4 inch drive rods were used. A 1.75-inch diameter friction 

reducer was used between the probe and the rods to obtain consistent readings. On 

artesian holes, 1.8-inch diameter rods were used with a 1.9-inch diameter friction 

reducer. All testing was performed using a 20 ton CPTu vehicle capable of a 

maximum 20 ton push and 30 ton pull. 

All testing was performed using a Peizocone probe. A pressure transducer located 

just behind the tip made possible the measurement of pore water pressures during the 

test. Tip resistance, side friction and pore water pressure were measured at 2 cm 

intervals as the probe was pushed into the soil. These values, as well as depth, 

inclination and total pushing force, were recorded. 

Permeabilities 

• Dissipation Testing 

Pore water pressures measured during penetration reflect the volume changes 

induced by the shearing and/or compaction effects of soil, therefore, dissipation tests 

had to be performed to measure hydrostatic pressures. Dissipation tests were 

performed at selected depths in specific holes by stopping the probe penetration and 

allowing the pore water pressures to dissipate. Pore water pressures were recorded 

at specific time intervals until there was no change over a one minute period. Each 

test was performed for a minimum of five minutes. The majority of the dissipation 

tests were performed at downstream locations in order to better understand the 

artesian conditions. 

Preliminary estimates of permeabilities for the embankment fill and foundation material 

were based on the results of dissipation test performed during CPTu tests. 

In this method, it was assumed that, under the given conditions, the cone penetration 

test was more accurately linked with the mechanics associated with a “Pipe-Cavity 

Test.” The rate of rise of the water in the tube is then transformed into soil 

conductivity by the use of the following equation developed by Luthin1

: 

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Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

k = pr

2

ln(Y1/Y2) / S(t2-t1) 

where k is the hydraulic conductivity,

Y1 the distance from the water table to water level in pipe at time t1,

Y2 the distance from water table to water level in pipe at time t2,

r the radius of the pipe,

(t1-t2) the time for water level to change from Y1 to Y2, and

S the shape factor coefficient

• Falling Head tests 

A series of “falling head” tests were conducted in selected piezometers. The general 

procedures for the falling head test consisted of the following steps: 

1. A clear plastic pipe approximately 6 feet in length was attached to the top of the 

existing piezometer standpipe. A tape measure was attached to the side of the 

clear plastic to allow readings during the test. 

2. The pipe was filled to the top with water. The initial level was noted and a stop 

watch started. Readings were taken at regular intervals until the total drop in 

water level exceeded 5 feet, or the test duration exceeded 10 minutes. 

At least 10 readings were recorded for each test. The following relationship, obtained 

from Hoek and Bray2, was used to compute the permeability coefficient, K: 

k= A/ F(t2-t1) x ln(H1/H2) 

where A is the cross section area of the water column 

F the shape factor which depends upon the conditions at the bottom of the 

hole 

• Comparison of Field Test results to Empirical Values 

Empirical values of permeability, based on grain size parameters Dmin, Dmax, and D10, 

were obtained from charts proposed by Hunt3

 and Justin et al.4. 

Backfilling Test Holes 

Because of artesian conditions existent at the downstream valley, the following procedure 

was used to prevent seepage from the holes and avoid potential soil piping. 

1. Installed standpipe at the surface around the rods. 

2. Withdrew the rods slowly to minimize suction pressures and subsequent soil blow-up. 

Generally, the holes tended to collapse at the top of the artesian sand layer. 

3. Measured the ground water level and hole collapse immediately after the rods were 

withdrawn. 

4. Tremie grouted the holes through the standpipe before the truck was moved off the 

hole. Applied a slight amount of air pressure at the top of the standpipe (less than 10 

psi) to help the grout permeate through the collapsed soil. 

Prepared by Charles D. Wagner, TVASeptember, 2000 Page 3 

Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

Nonartesian holes were tremie grouted after 24 hours water levels had been measured. A 

1:1 (by weight) water to portland cement mix with bentonite was found to give satisfactory 

results. Holes in which the grout had settled were topped with grout. 

2. Standard Penetration Testing (SPT) 

The location of these holes was chosen after the CPTu testing program was completed. 

The location was chosen based on the results of the CPTu test in order to correlate the 

CPTu to SPT. The CPTu is a quick and less costly approach to obtain information about 

the soil stratigraphic. 

Testing Procedures and Equipment 

The holes were advanced using a 5-inch wide fishtail bit under a head of bentonite drilling 

mud to ensure borehole stability. Side baffles on the fishtail bit directed the drilling mud 

upwards. As a result, water table measurements could not be directly taken. SPT tests 

were performed every 2.5 feet using a 2.00 in OD sampler. Blow counts were recorded 

for each 6 inches of penetration for a total of 18 inches. The testing procedure utilized a 

safety hammer actuated by the throw of a rope. The rope was wrapped one and onequarter times around the cathead. Based on correlation’s with the CPT test, it is believed 

that this testing procedure delivers 60 percent of the maximum theoretically available 

energy, Seed et. al. 

Backfilling Test Holes 

The backfilling procedure consisted of: 

1. Extracting all drilling equipment from the hole and keeping the hole filled with drilling 

mud. 

2. Lowering a 2-inch diameter PVC tremie pipe to approximately 6 inches from the 

bottom of the borehole. 

3. Attaching a funnel, 8 inches in diameter and 10 inches in length, to the upper end of 

the PVC pipe. 

4. Grouting by gravity feed through the tremie pipe until the borehole was completely 

filled. 

A 1:1 (by weight) water to portland cement mix with 1 percent bentonite was used to 

backfill the holes. Bentonite was added to the grout to increase mix stability by holding 

particles in suspension and minimize shrinkage. 

3. Undisturbed Sampling and Laboratory Testing Program 

A program of subsurface undisturbed sampling may be required, depending on the detail 

of any evaluation or analysis required for the dam and site. The details of a typical 

program is not including in this paper, but may be more suited for a paper on evaluation 

and analysis. 

Prepared by Charles D. Wagner, TVASeptember, 2000 Page 4 

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White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

4. Geophysical Investigations 

Geophysical investigations are conducted at sites to: 

• Identify buried material 

• Determine the presence of contamination plumes, their distribution, direction, and rate 

of movement 

• Characterize natural or manmade hydrogeologic conditions including water bearing 

fractures 

• Locate leaks in dams 

• Stratigraphy 

• Locate subsurface caverns/voids that can develop into sinkholes 

Geophysical testing such as surface surveys help to better interpret or explore the 

interiors of dams where intrusive methods, such as drilling would be expensive and/or not 

feasible due to physical constraints. 

Geophysicists use theories and applications from physics to remotely measure physical 

properties, be it under the ground surface, under water, in the upper atmosphere, or within 

dams. Common techniques employed at dams include spontaneous potential methods, 

ground penetrating radar, and seismic velocity analysis. 

Methods 

Many different methods are used by the geophysicist. A description of those used most 

often during investigations, either singly or in combination. 

• Ground Penetrating Radar (GPR) 

GPR surveys are impulse systems that transmit short duration electromagnetic pulses 

into the ground from an antenna near the surface. These pulses are reflected from 

interfaces with contrasting electrical properties back to the receiver section of the 

antenna connection to the control unit for processing and display. Contrasts in 

electrical properties of material in the earth cause reflections of the radar signal. 

These reflection occur at different soil strata, soil/rock interfaces, rock/air interfaces 

(voids), fractures, manmade objects (drums, underground storage tanks, trenches, 

pits), or any interface that can create a contrast in the dielectric properties. 

Digging a trench and filling it, for example, can create a difference between the 

dielectric properties of the disturbed earth and the undisturbed earth. 

The distance to reflectors on GPR profiles is determined by the echo delay time. The 

time can be converted to apparent depth: 1) if the velocity of the radar pulse can be 

determined; 2) if an object is at a known depth, the depths can be extrapolated; 3) the 

hyperbolic geometry of echo curves can furnish an estimate of depth; and 4) common 

depth points sounding can determine pulse position and depth and have a strong 

dependence on the earth’s moisture content. 

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White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

GPR profiles are continuous and repeatable during different times of the profiles. 

GPR produces digital data that can be processed and filtered to produce data 

enhancements for maximum penetration depth. 

Compared to other geophysical techniques, GPR has a shallower exploration depth. 

GPR does not usually exceed 5 feet in clays, although it has recorded penetrations of 

over 100 feet in sands. GPR profiling depth is greatest in materials having a high 

resistivity, such as coarse sands or gravel; it cannot profile through salt water. 

• Electromagnetic Induction (EM) Surveys 

An EM survey can be used to detect conductivity anomalies, expected to occur above 

caverns or fractures zones in rock. The fractures and caverns provide the major flow 

paths in the rock, and monitor wells can be installed at these locations for remedial 

design. The geophysical surveys can also pinpoint fractures inferred from aerial 

photos. 

The EM can also locate utilities and buried metal debris, in addition to nonmetallic 

burial such as trenches and pits. 

EM equipment is portable and allows data to be collected as fast as the operator can 

walk. Subsurface conductivities (reciprocal resistivities) are collected rapidly and 

continuously as the operator surveys the site with the instrument. Investigations that 

effectively define the location and extent of potential problems areas at shallow depths 

can be performed rapidly. The principal value of the EM method is that it provides 

continuous, high resolution data at a very low cost. 

The EM survey is usually conducted using an induction meter. The EM measures the 

apparent conductivity of the subsurface using the principles of electromagnetic 

induction. The EM consists of two horizontal coplanar loops, one acting as a 

transmitter and the other as a receiver. The transmitter induces eddy currents in the 

earth, which in turn produce a secondary field. The receiver intercepts the secondary 

field in which the EM measures the terrain conductivity by comparing the strength of 

the secondary field to that of the primary. 

The depth of investigation by EM is a function of the intercoil spacing and the 

orientation of the antenna dipoles. The EM with an intercoil spacing of 12 feet and 

used horizontal mode, has an effective depth of analysis of approximately 20 feet. 

The EM with intercoil spacing of 10, 20, and 40 meters and used in the horizontal 

mode, has a maximum depths of analysis of approximately 45, 90, and 180 feet. 

Very Low Frequencies (VLF) 

VLF surveys can locate water-bearing fractures to assist in monitor well 

installation for remedial investigations. This method is particularly well suited for fractures 

in crystalline rocks. 

VLF is commonly conducted using a VLF meter, which uses EM fields to locate fractures. 

The VLF meter uses the magnetic components of the electromagnetic field generated by 

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Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

long-distance radio transmitters in the VLF band. The transmitters are used for longdistance communication between Naval stations. 

• Resistivity 

The resistivity method measures the electrical resistivity of the subsurface that 

includes soil, rock, and groundwater. Resistivity provides information on layering and 

depths of subsurface strata including lateral changes in the surfaces. Risistivity can 

locate water-saturated and unsaturated voids, leaking dams, and map stratigraphic 

and structural features. 

Resistivity surveys can be conducted across a total survey area, as a profile, or as 

soundings at discrete locations. A current is inserted into the ground by a pair of 

surface electrodes. The subsurface resistivity is calculated from the electrode 

separation, applied current, and measured voltage. Most soil and rock minerals are 

electrical insulators (high resistivity), and current flow is conducted primarily through 

the moisture-filled pore spaces within the medium. The resistivity of porous media is 

largely controlled by the amount of pore water, porosity and permeability of the porous 

media, and the dissolved solids concentration of the pore water. 

• Seismic Refraction 

Seismic refraction measures density, thickness, and depth of geological strata using 

sound (acoustic) waves transmitted into the subsurface. Sound waves travel at 

different velocities in various soils and rocks and are reflected at the interface between 

layers. The time is measured from the time source to geophones. The seismic 

source for shallow investigations range from a hammer striking a metal plate to plastic 

explosives. Geophones receive the vibration of the sound energy and translate it to 

an electric signal. The signal is displayed on a seismograph. Time versus distance 

plots of the first-arrival are used to locate depth of strata and possible fractures. 

The seismic refraction method is based on three important assumptions: 

1. Acoustic velocity generally increases with depth 

2. A sufficient acoustic velocity contrast exists between layers to allow differentiating 

between adjacent strata of interest 

3. The layer has sufficient thickness to permit detection 

If these assumptions are not reasonably satisfied at a specific site, this technique may 

provide little usable data or interpretation may become quite involved and expensive. 

Prepared by Charles D. Wagner, TVASeptember, 2000 Page 7 

Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

5. Monitoring 

Piezometric Measurements 

Piezometric measurement locations should be chosen to give a better understanding of 

the seepage pattern through the abutment, foundation or embankment. Piezometers are 

installed for various purposes. The main two reasons are to determine the phreatic head 

in the embankment the other main reason is to determine the pore pressure in a particular 

layer. 

Piezometers have been installed to monitor seepage before, during and after remedial 

measures to determine the effectiveness of the grouting. 

Dye Testing 

Drilling holes to inject dye for dye testing to determine flow path is sometime used. 

Weir Measurements 

Weir measurements are normally taken to monitor any change in the leakage. Seepage 

amounts are usually influenced by headwater level, seasonal and the loss of material, 

such as clay seams. 

These measurements are typically taken at toe drains, springs and other seepage paths. 

Water Quality Tests 

Water quality tests are performed to determine the presence of solids in the runoff from 

drains. These results can be compare to the various material at the site to determine the 

possible origin. 

Grout Monitoring 

Real-time performance monitoring used during grouting includes results from drilling, 

water tests, calculation of grout hole reduction ratios, and dye testing. This monitoring 

allows onsite engineers to track the development of the integrity of the grout curtain and 

focus grouting efforts on specific zones along the grout rows. Also, the results of the 

grouting can be demonstrated from data monitored for 1) discharge from rim leak; 2) 

groundwater elevations down-gradient from the grout curtain; and 3) headwater elevation. 

Prepared by Charles D. Wagner, TVASeptember, 2000 Page 8 

Attachment 7 White Paper 4.doc 
White Paper on Investigation of Seepage Problems/Concerns at Dams, 

Including Use of Geophysical Techniques; and Instrumentation and 

Measurements for Evaluation of Seepage Performance 

1. Luthin, J. N., “Drainage Engineering,” Published by John Wiley and Sons, New York, 

1966. 

2. Hoek, E., and Bray, J. W., “Rock Slope Engineering,” Institute of Mining and 

Metallurgy, London, 1981. 

3. Hunt, R. E., “Geotechnical Engineering Investigation Manual,” McGraw-Hill Series in 

Geotechnical Engineering, McGraw-Hill Book Company, New York, 1984. 

4. Creager, W. P., Justin, J. D., and Hinds, J., “Engineering for Dams - Vol. III: Earth, 

Rockfill, Steel and Timber Dams,” John Wiley and Sons, New York, 1945. 

Prepared by Charles D. Wagner, TVASeptember, 2000 Page 9 

Attachment 7 White Paper 4.doc 

5.0 REMEDIATION OF SEEPAGE PROBLEMS THROUGH 

CUTOFF OR REDUCTION OF FLOW AND THROUGH 

COLLECTION AND CONTROL OF SEEPAGE 

INCLUDING THE USE OF GEOSYNTHETICS 

WHITE PAPER FOR THE ASDSO SEEPAGE WORKSHOP, OCTOBER 17-19, 2000 - DENVER 

James R. Talbot, Steve J. Poulos, and Ronald C. Hirschfeld 

October 2, 2000 

5.1 INTRODUCTION 

5.1.1 Types of Seepage Problems 

The two principal problems associated with seepage through earth dams, their 

foundations, and their abutments are: 

1. Piping 

2. Excessive water loss 

Remedial measures for preventing piping are aimed at controlling seepage so that the 

seepage does not cause internal erosion of soil from the embankment, foundation, or 

abutments of a dam. Remedial measures for preventing piping may not reduce the rate of 

seepage and often increase the rate of seepage. 

Remedial measures for reducing water loss are aimed at reducing seepage through the 

embankment, foundation, and abutments. Although such measures may reduce the 

pressures and the rate of water flow through a dam, its foundation or abutments, it is 

nevertheless vital to install proper drainage systems on the downstream side of the dam as 

the primary line of defense against piping. 

5.1.2 Recognizing and Correcting Seepage Problems 

The following sequence of activity is commonly followed in connection with a correcting 

a seepage problem in a dam: 

1. Field observations indicate that there may be a seepage problem. 

2. Information is gathered to determine the cause of the problem. 

3. Remedial measures are designed. 

4. Remedial construction is carried out. 

5. Observations of the effectiveness of the repairs are made. 

The steps followed in the above sequence are discussed briefly in Sections 5.1.3-7. 

Attachment 8 White Paper 5.doc 
5.1.3 Field Observations That Indicate Seepage Problems 

1. Piping Problems 

a. Springs discharging muddy water or clear water on the downstream side 

of the dam, abutments or downstream valley slopes, through minor 

geologic details in the foundation and abutments, cracks in the 

embankment, compacted layers that are more pervious than their 

neighbors, animal burrows, roots or root holes near live or dead trees, and 

near uprooted trees. 

b. Muddy or clear water flowing next to structures (such as spillways and 

low-level outlet pipes) that penetrate the embankment, foundation, or 

abutments. 

c. Muddy water discharging from spillways or low-level outlet pipes at times 

when the water in the reservoir is clear. 

d. Muddy water or water carrying silts or sands discharging from drains 

(including relief wells) in the embankment, foundation, or abutments. 

e. Depressions or sinkholes anywhere on the embankment or near the 

embankment on either the upstream side or downstream side of the dam. 

f. Increasing or decreasing flow in drains with constant reservoir level. 

2. Excessive Water Loss 

Excessive water loss may occur through the embankment, foundation, or abutments 

without any visible evidence of seepage. Such excessive water loss might only be 

detectable as a visible or measurable drop in the reservoir level when the outlet is 

closed and the weather is dry. Such losses of water are not important if there is 

little value to the water. However, if the water is being used for recreation, power, 

or potable water, the value of the water may be sufficient to investigate and 

perhaps remediate the cause, even though there is no other evidence that there 

may be a piping problem. 

5.1.4 Information Needed to Determine the Cause of the Problem 

1. Piping 

If the cause of a piping problem can be identified, more-effective remedial 

measures can be designed. Some field observations of a piping or potential piping 

problem may give an indication of the cause of the problem—for example, water 

flowing next to a structure that penetrates the dam; deteriorated pipes that 

penetrate the embankment, foundation, or abutments; uprooted trees. Other field 

observations of a piping or potential piping problem may give limited or no 

indication of the cause of the problem—for example, springs on the downstream 

side of the dam; muddy water discharging from drains. If the field observations do 

not indicate a specific cause of piping, the cause may be a minor geologic detail in 

the foundation or abutments or a minor detail of construction. 

The designer of remedial measures against piping should always examine the 

detailed record of the design and construction of the dam to look for those 

“minor” details that could be a cause of piping. Field investigations (such as 

Attachment 8 White Paper 5.doc 
borings and pore-pressure measurements) are likely to be of limited or no value 

because they are likely to be ineffective in uncovering the critical “minor” details. 

2. Excessive Water Loss 

Usually, there will be no visible evidence of excessive water loss that can be used 

for determining the cause. The designer of remedial measures to reduce water 

loss must review the design studies made for construction of the dam, field 

records of the construction, and available records of observations made 

throughout the life of the dam to determine, if possible, the cause(s) of the 

excessive water loss. Because excessive water loss is a function of the overall 

character (not the minor details) of the embankment, foundation, and abutments, a 

field investigation will likely be effective for determining the cause(s) and 

designing remedial measures. 

5.1.5 Design of Remedial Measures 

The design of remedial measures is the subject of subsequent sections of this paper. 

5.1.6 Remedial Work 

During remedial work, the designer must observe the details of the embankment, 

foundation, and abutment that are revealed by the construction activity, because even the 

most detailed field investigations that are made to design the remedial measures cannot 

possibly reveal all the details that may be critical to the effectiveness of the remedial 

measures. 

5.1.7 Observations After Remedial Work Is Completed 

Because it is so difficult to be sure that remedial measures address all the causes of a 

seepage problem, it is essential that field observations be made after remedial work is 

completed to determine whether the remedial measures are effective. 

5.2 COLLECTION AND CONTROL OF SEEPAGE 

5.2.1 Seepage Control 

The addition of downstream drainage is usually the best solution for seepage problems in 

dams. Several types or methods of drainage have been successfully used for various 

seepage conditions. These methods with their advantages and disadvantages are: 

1. Adding an embankment (chimney) drain to the dam by removing the downstream 

slope to a sloping surface and constructing a filter-drain on the slope while 

replacing the downstream section1. A collection system is usually also added in 

the form of an excavated foundation drain under the downstream shell of the dam. 

a. Applicable condition – Wet areas or springs on the downstream slope 

1

Brodhead Dam, Pennsylvania, reported by Talbot and Ralston, 1985 

Attachment 8 White Paper 5.doc 
from seepage through permeable layers in the dam, or from cracks or other 

anomalies in the dam. Stability problems on the downstream slope caused 

by seepage. 

b. Advantages – Drain intercepts all cracks or other anomalies and permeable 

layers inside the dam where the drain can be confined and protected. 

Protects against development of concentrated leaks in cracks and solves 

stability problems. 

c. Disadvantages – The reservoir is usually drained for stability. Must have 

a high-capacity outlet to avoid reservoir filling if a flood occurs during 

rehabilitation construction. Is major construction and very expensive. 

2. Add an embankment (chimney) drain to dam by constructing a filter-drainage 

zone on the downstream slope of the existing dam and a new shell zone to cover 

the drain and form a new downstream slope. The conditions for installing this 

feature are the same as previous. 

a. Advantages – Intercepts all cracks or other anomalies and permeable 

layers in the dam. Protects against development of concentrated leaks in 

cracks and solves stability problems. Reservoir may not have to be 

drained to construct it. 

b. Disadvantages – Requires larger footprint (property) for the dam. 

Additional shell zone material must be available. 

In all cases where an embankment chimney drain is added to the downstream section of the dam, 

the dam must be designed against slope failure and uplift or blow-off of the downstream 

drain and shell zone with full head of the reservoir at the upstream face of the filter. 

3. Add an embankment (chimney) drain to the dam by trenching into the dam from 

the crest using a trenching machine. The trench is filled with filter material and 

outlets are constructed by trenching to the downstream toe periodically. This 

solution has been used for dry flood control dams where cracking has been a 

problem. 2 

a. Applicable condition – Mainly used for repairing small, dry flood-control 

dams where cracking has occurred and the dam had no embankment drain. 

It could possibly be used where the reservoir was drained for some time to 

allow the dam to dry sufficiently that a trench will remain open for filter 

placement. 

b. Advantages – A chimney drain can be installed inside the dam to protect 

against the development of concentrated leaks. It is relatively simple and 

inexpensive. 

c. Disadvantages – The dam must be dry so that the excavated trench will be 

stable. If the dam is higher than trenching machines can excavate, the top 

of the dam must be removed if the drain is to reach the foundation level. 

4. Provide additional downstream drainage using toe drains – A toe drain may be 

excavated at the downstream toe. The drain should extend to the depth of the 

2

Flood Control Dams in Arizona, reported by Talbot and Deal, 1993 

Attachment 8 White Paper 5.doc 
highly permeable layers in the foundation (taking care that the reservoir is down 

or that a contingency plan is in place to prevent a piping failure) and should 

intercept the contact between the foundation and embankment, if possible. A 

berm is often placed over the drain for additional stability, particularly if the drain 

is constructed beyond the toe of the dam. The drain should consist of filter and 

drainfill zones, and may include collection pipes to carry seepage to a safe outlet. 

a. Applicable conditions – Wet areas, ponding or running water, sand boils, 

or springs at the toe of the dam from seepage through the foundation or 

abutments in permeable layers, cracks, or other anomalies. 

b. Advantages – Can be installed with minimum disturbance to the dam. It is 

best to drain the reservoir, however; they have been installed without 

draining the reservoir when stability has not been a problem. 

c. Disadvantages – The reservoir may have to be drained to provide stability 

during excavation and installation. Drains usually require continued 

maintenance and rejuvenation 

5. Cleaning of existing clogged drains. High-pressure cleaning using jet sprayers 

run through the drain pipe from the outlet have been partially successful for 

cleaning drains clogged with slimes or algae.3 Reaming tools are used for 

removing roots. 

a. Applicable conditions – A common drain-clogging agent is iron-bacteria 

slime or other slimes associated with manganese or sulfur deposits. Algae 

or root growth may also be involved in drain clogging. For all of these 

problems, the effectiveness of the drain diminishes with time and the drain 

may eventually become completely ineffective. 

b. Advantages – Some drainage can be restored without draining the 

reservoir or requiring major design and construction. 

c. Disadvantages – Drain cleaning usually never completely restores the 

drain operation back to its original capacity or to the design intent. 

Cleaning is not a permanent solution and unless the source of the problem 

is resolved, the drains will continue to clog. 

6. Install a downstream blanket drain – Blanket drains are usually thin layers of filter 

material and/or drainfill placed on the foundation and are often used in 

conjunction with other drains such as an embankment drain or toe drain. They 

may serve as an outlet for other drains and to intercept seepage returning to the 

surface of the foundation under the downstream toe of the dam. They must be 

covered with the downstream shell of the dam or a berm extending downstream 

from the dam to confine the drain material and provide stability against uplift. 

3

Ford, Harry (date unknown, reprinted January 1993). “Iron Ochre and Related Sludge Deposits 

in Subsurface Drain Lines” (Circular 671), Florida Extension Service. 

Http://edis.ifas.ufl.edu/BODY_AE026. 

Attachment 8 White Paper 5.doc 
a. Applicable conditions – Wet areas, ponding or running water, sand boils, 

or springs at the toe of the dam from seepage through the foundation in 

permeable layers, cracks, or other anomalies. An excavated toe drain is 

best for these conditions, but a blanket drain may be used when an 

excavated trench is not possible or practical. 

b. Advantages – Can be installed without draining the reservoir when a berm 

is constructed over the blanket downstream. Can be used when stability or 

other problems prevent excavating a toe drain trench. 

c. Disadvantages – Does not reduce uplift pressures under the dam. Requires 

a larger footprint (more space) for the dam. 

7. Addition of downstream relief wells – Relief wells are drilled into the foundation, 

the downstream face, or the abutments. Relief wells may be filled with drainfill 

materials or have a casing inserted with well screens to allow the collection of 

seepage water at a predetermined level. Relief wells may be added to provide 

additional capacity to an existing drainage system or to solve stability problems 

caused by uplift pressures. 

a. Applicable conditions – Relief wells are appropriate if artesian pressure 

exists in layers deeper than is practical for using other drains such as an 

excavated toe drain. 

Under no circumstances should holes or trenches be dug on the 

downstream side of a dam with water in the reservoir, unless a wellthought-out contingency plan is in place to prevent runaway erosion 

into the opening. 

b. Advantages – Usually can be installed without draining the reservoir. 

c. Disadvantages – Are somewhat limited in capacity and effectiveness. 

Require considerable maintenance. 

8. Relief well cleaning – See white paper by Mr. McCook. 

5.3 METHODS FOR REDUCING SEEPAGE THROUGH EMBANKMENT DAMS 

5.3.1 Introduction 

In this paper we cover cutoffs and other flow reduction techniques for existing 

embankment dams. Many of these techniques can be used for new dams. 

Proper downstream drainage collection and safe discharge must always accompany any 

flow-reduction technique. 

Reduction of seepage through dams has the following objectives: 

1. Save water as a resource. 

2. Reduce seepage pressures within the dam, its foundation and abutment, and at the 

downstream toe area, thus reducing to some extent the probability of piping 

failure. 

3. Reduce the required size of seepage-control systems. 

Attachment 8 White Paper 5.doc 
.5.3.2 Alternatives for Reducing Seepage 

1. Upstream blanket 

2. “Cutoff” on upstream face of dam, abutments and foundation 

3. “Cutoff” within dam, abutments and foundation 

5.3.3 Upstream Blanket 

1. Composition: Upstream blankets can be constructed of low-permeability soils or 

artificial impervious barriers such as asphalt, soil cement, roller-compacted 

concrete and concrete. The blankets must be properly filtered at the bottom to 

prevent piping through the blanket and subsequent loss of water. Even relatively 

small flows can substantially increase the water pressures within the dam, 

foundation and abutments. 

2. Advantages: Can be low cost. Can be placed through water in reservoir. Reduces 

flow so that seepage pressures in the dam and abutments are reduced, with the 

result that the likelihood of piping can be reduced and the stability of the dam 

may be improved through reduction of water pressures in the dam, foundation and 

abutments. In particular, upward gradients at the downstream toe are reduced and 

can be reduced below levels that are of concern. 

3. Disadvantages: May require draining of reservoir. May need to cover large areas 

and the cost can be great. Can be difficult to place through reservoir so that the 

blanket is continuous. Difficult to judge how far upstream to carry the blanket, 

since water may bypass blanket anywhere upstream. Must be tied into the 

upstream cutoff. Can not be tied into existing internal cutoff. 

5.3.4 “Cutoff” on Upstream Face 

The term “cutoff” is in quotations because almost no technique used for this purpose will 

actually cut off water flow. There always will be leakage that must be safely collected 

and drained on the downstream side of the cutoff. 

1. Composition: Cutoffs on the upstream face may be composed of compacted 

impervious soil, soil and bentonite mixtures, soil cement, roller-compacted 

concrete, concrete, asphalt, and, rarely, metal or masonry. 

2. Advantages: Reduces water flow on the upstream side and therefore reduces 

seepage to be collected and drained downstream and reduces pressures within the 

dam, abutments and foundation. Is accessible for repair from the upstream face 

by lowering the reservoir. 

3. Disadvantages: Must be protected against wave action. Settlement of the dam 

can cause cracking of the more rigid upstream cutoffs, such as asphalt and 

concrete. Even a compacted soil blanket may crack due to differential 

settlements. Frost action can cause deterioration of the upstream cutoff. Soil 

cutoffs that have dried may develop incipient cracks that may become passages 

for substantial leakage or piping if the water level rises rapidly. Water can bypass 

Attachment 8 White Paper 5.doc 
cutoff if the cutoff is not extended far enough into abutments. An upstream cutoff 

must be accompanied by systems that cut off or control flow through the 

foundation and abutments. 

5.3.5 Internal “Cutoffs” within Dam 

1. Composition: Internal cutoffs may be composed of concrete, soil-bentonite 

mixtures, sheet piles of wood or steel, or grout. 

2. Advantages: Usually can be extended easily to cut off foundation and abutments 

using less material than would be needed for upstream cutoffs or blankets. Thick 

cutoffs are preferable to help avoid difficulties with obstructions during 

installation. Such cutoffs composed of concrete in a slurry trench can be used to 

go deep into the foundations. Some have extended over 200 ft into the 

foundation. Internal cutoffs are protected from damage by frost action. They can 

act as erosion-control barriers to limit damage when a dam is overtopped. 

3. Disadvantages: If the cutoff begins to leak in the future due to movements of the 

dam or deterioration of the materials or poor construction of the cutoff, access to 

find the leak is very difficult if not impossible. Grout curtains injected to cut off 

seepage through a rock foundation can induce high pressures and cracking of the 

dam itself. Unless multiple rows (at least three) of grout holes are used at close 

spacing, cutoff is difficult to achieve. The pressures used must be low to avoid 

hydraulically fracturing the dam. Cutoff must penetrate through obstructions in 

the dam or foundation. These obstructions, if not handled properly can lead to 

future leakage. Sheet piles of wood or steel are particularly susceptible to 

difficulties with obstructions, which often cannot be felt during construction and 

which may open the joints or otherwise damage the sheeting. 

5.4 PRECAUTIONS REGARDING USE OF GEOSYNTHETICS 

5.4.1 Geomembranes 

Geomembranes have been used for blanketing or providing seepage barriers in 

reservoirs.4 The main precaution for their use is that they may be vulnerable to puncture 

during installation or from animal traffic on them after they are installed. Proper 

thickness and strength of the membrane material is important, along with proper bedding 

preparation and cover over the membrane. The constant application of stress by 

individual soil grains on plastics can make them age at substantially increased rates than 

would be the case for an unstressed plastic. In addition, it is important to design for the 

lower friction angle that usually applies at the interface between the soil and membrane. 

Pore pressures also may build up at this interface if the soil is impervious. 

5.4.2 Geotextiles as Filters in Dams 

4

For example, Mt. Elbert Forebay of the Fryingpan-Arkansas Project, U.S. Bureau of 

Reclamation. See http://www.gp.usbr.gov/co/fryarkpf.htm. 

Attachment 8 White Paper 5.doc 
There are two major problems with using geotextiles as filters in dams. These problems 

may possibly be overcome or proven as no problem with research, but until the research 

is completed, the use of geotextiles as filters should be avoided in dams. 

1. Tearing from movements in the dam – The major cause of cracking in earth 

embankment dams is differential settlement of the foundation or the embankment 

soils. The areas over abutments or where the height of the dam changes abruptly 

are the most vulnerable. The main reason for installing filters in dams is to 

intercept all cracks. If the fabric tears in the plane of the crack, it will not serve to 

intercept the crack or as a filter in the plane of the crack. Tearing with 

movements in the dam is likely because: 

a. The geotextile is very thin and will have a very large soil pressure on each 

side of it when installed in a dam. The soil pressure will pinch the fabric 

together from both sides and when movements occur that cause a crack in 

the dam perpendicular to the plane of the fabric, the geotextile will 

undergo stretching by several thousand percent over a short distance, 

which will tear the fabric. 

b. Most dams are constructed of soils that contain rocks or rock fragments 

that are sharp and irregularly shaped. Normal construction practices are 

likely to tear the fabric, unless a substantial bedding (such as a sand layer 

of sufficient thickness) or other protective layer is placed next to the 

geotextile. 

2. Inability of the geotextile to support the seepage discharge face – We hypothesize 

that sand filters function differently from geotextiles where they contact with the 

soil in the dam. The following items explain these differences: 

a. Sand filters placed against a seepage discharge face such as the side of a 

drain trench flow to the soil face and apply a positive pressure to it. The 

sand particles provide a point of contact with the soil face and the distance 

between the points of contact are determined by the gradation of the sand. 

Research has shown that when certain filter gradation criteria are met, the 

soil particles will not move for high gradients and when water is passing 

through the soil (not a crack).5 

b. A fabric by itself does not apply a pressure to the seepage discharge face, 

but is dependent on a material on the other side of the fabric to hold it 

against the discharge face. If the material on the other side of the fabric is 

gravel or stone as in most drainage or transition zones, then the contact 

points where the fabric is held against the discharge face are quite far apart 

compared to sand. The fabric may be loose and actually bulge away from 

the soil between the contact points. Research has shown that when a space 

is left between the filter and the soil discharge face, soil particles will 

move and the filter will clog. If sand must be used on the other side of a 

fabric so it will work properly as a filter, then the sand can provide the 

filter function by itself and the fabric is not needed. 

c. Research is needed to check this hypothesis using testing conditions that 

simulate various conditions for using geotextiles as filters in dams. 

5

Research by U. S. Soil Conservation Service, reported by Sherard, et. all, 1984, 1989. 

Attachment 8 White Paper 5.doc 
5.5 REFERENCES 

1. Ford, Harry (date unknown, reprinted January 1993). “Iron Ochre and Related Sludge 

Deposits in Subsurface Drain Lines” (Circular 671), Florida Extension Service. 

Http://edis.ifas.ufl.edu/BODY_AE026. 

2. Hirschfeld, Ronald C. (1995). “Design, Construction, and Inspection of Embankment 

Dams to Reduce the Risk of Piping,” ICODS Technical Seminar: Seepage, Piping and 

Remedial Measures, Federal Emergency Management Agency, March 23-24. 

3. Hirschfeld, Ronald C. (1999). “Overview of Geotechnical Aspects of Embankment-Dam 

Design,” Embankment-Dam Seminar, sponsored by Tennessee Valley Authority, 

Chattanooga, January 19–21. 

4. Sherard, J. L., and Dunnigan, L. P. (1989). “Critical Filters for Impervious Soils,” 

Journal of Geotechnical Engineering, ASCE, vol. 115, no. 7, pp. 927–947. 

5. Sherard, J. L., Dunnigan, L. P., and Talbot, J. R.(1984). “Basic Properties of Sand and 

Gravel Filters,” Journal of Geotechnical Engineering, ASCE, vol. 110, no. 6, pp. 684–700. 

6. Sherard, J. L., Dunnigan, L. P., and Talbot, J. R.(1984). “Filters for Silts and Clays,” 

Journal of Geotechnical Engineering, ASCE, vol. 110, no. 6, pp. 701–718. 

7. Talbot, J. R., and Deal, C. E. (1993). “Rehabilitation of Cracked Embankment Dams,” 

Geotechnical Practice in Dam Rehabilitation (proceedings of specialty conference 

sponsored by Geotechnical Engineering Division, ASCE; L. R. Anderson, ed.), Raleigh, 

N.C., pp, 267–283. 

8. Talbot, J. R., and Ralston, D. C. (1985). “Earth Dam Seepage Control, SCS Experience,” 

Seepage and Leakage from Dams and Impoundments (proceedings of symposium 

sponsored by Geotechnical Engineering Division, ASCE; R. L. Volpe and W. E. Kelly, 

eds.), Denver, Col., pp. 44–65. 

Attachment 8 White Paper 5.doc 

White Paper on the Impacts of aging of seepage control/collection system components 

on seepage performance 

I. Introduction 

This paper discusses the components commonly included in drainage systems for 

embankments and dams and the mechanisms of aging that may impact their 

performance. The paper also discusses remedial alternatives. 

II. How Drainage Components May Deteriorate 

The components of a drainage system may deteriorate or become damaged from external 

forces including physical, chemical, and biological activity. Some of the ways that 

components become damaged are: 

A. Material deterioration 

1. Deterioration of clay pipes – Pipes may collapse and spread. Then, 

infiltration of soil into joints of clay tiles can occur. 

2. Corrosion of corrugated metal pipe – outlet pipes where they are 

exposed to atmosphere. 

3. Deterioration of wooden well screens in relief wells. 

4. Changes in properties of the granular filters and drains in a system, or 

in a geotextile component of the system. Most common changes are 

siltation and cementation of the granular materials. 

B. Mineralization (encrustation). Groundwater high in dissolved salts can 

contribute to clogging of well screens, perforations in drainpipes, and possibly 

to geotextiles. This process can also contribute to cementation of granular 

media in drains. Cementation of well screens and perforations causes 

reduced capacity. Cementation of granular media can cause loss of selfhealing properties. The USBR Ground Water Manual 6

 lists the most common 

forms of mineral encrustation in wells as: 

1. Precipitation of iron and calcium carbonates as hard, brittle, cement-like 

material adhering to the well screens and also cementing the gravel 

pack or aquifer away from the screen. 

2. Accumulation of iron and manganese hydroxides or hydrated oxides on 

the screen or in the formation next to it. The hydroxides are insoluble, 

jelly-like masses unless oxygen is present. If oxygen is present, the 

minerals oxidize into black, brown, or reddish granules. 

3. Decomposition of lignite beds can result in formation of a slimy black or 

brown viscous material about the screen and in the adjacent aquifer. 

6 United States Bureau of Reclamation. Ground Water Manual. Government Printing Office Stock No. 

024-003-00179-1. Second Edition. 1995. 

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C. Bacterial. Several types of sludge deposits that are associated with 

bacterial activity can be a problem in drainage systems. The types of deposits 

may be classified as ochre, manganese deposits, sulfur slime, and iron sulfide. 

7

 Ochre deposits and associated slimes are usually red, yellow, or tan. Ochre 

is filamentous, amorphous, and is a sticky mass combined with an organic 

matrix that can clog slots, filter media, including geotextiles, and well screens. 

The iron ochre problem is probably the most serious deterioration problem 

associated with drainage systems because it is so widespread. The National 

Water Well Association has a slide presentation 8 and a report on the problem 

is included as Appendix A to the REMR report 9. Testing groundwater 

samples may indicate the potential for the problem to develop. 10 

D. Cementation of filter media. Experience with volcanic sands in chimney 

drains in New Mexico demonstrates that aging and some type of chemical 

reaction of the sands leads to a loss of self-healing characteristics in the 

sands.11 

E. Siltation of gravel packs where the well development was inadequate. 

F. Damage to systems from repeated maintenance activity. Fittings become 

loose during surging, and subsequent maintenance procedures further 

damage the system until repairs are necessary. 

G. Vandalism, especially to outlet pipes and other exposed components. 

H. Impact of vegetation – penetration of roots into drain materials and pipes. 

III. Components subject to aging 

A. Granular filter/drain materials – sand and gravel. Experience with volcanic 

sands in chimney drains in New Mexico demonstrates that aging and a 

chemical reaction of the sands and groundwater leads to cementation and a 

loss of self-healing characteristics in the sands. Siltation and iron ochre 

deposits in well screen filter packs is also a type of deteriorated behavior. 

7 Ford, Harry, Florida Extension Service. ”Iron Ochre and Related Sludge Deposits in 

Subsurface Drain Lines.” Circular 671, reprinted January l993. 

http://edis.ifas.ufl.edu/BODY_AE026. 8 National Ground Water Association. “Iron Bacteria, Sulfur Bacteria, and Water Well Maintenance,” 60 

slides/notes and handout. Ref # A108 $126.50 

9 "Proceedings of REMR Workshop on Research Priorities for Drainage System and Relief Well 

Problems." July, 1989. Compiled by R. E. Leach and H. M. Taylor, Jr., US Army Engineer Waterways 

Experiment Station, Vicksburg, MS.

 Ford, ibid 

11 Communication with Greg Cunningham, SCE, NRCS, Albuquerque, New Mexico 

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B. Pipes, excluding well screens and casing. These components may 

become damaged from external forces such as equipment crushing the pipes 

after installation. A paper presented at the ASDSO annual meeting detailed 

this problem at a Bureau of Reclamation Embankment. 12 Repeated 

maintenance activities in the case of relief wells can also damage the pipes by 

the extreme forces applied in surging the wells. Iron ochre clogging of 

perforations or slots in drainpipe is another common problem. Another 

problem is ultraviolet light attack of exposed pipes. Types of pipes affected 

include: 

1. Asbestos cement 

2. PVC and HDPE – may be particularly susceptible to damage from 

surging in relief wells. 

3. Clay tile pipe 

4. Concrete bell and spigot 

5. Corrugated metal pipe – especially susceptible to corrosion 

damage. This could lead to piping of surrounding filter media and 

crushing of the pipe. 

C. Well screens – in one of the reports in the REMR document, PVC pipe is 

listed as inferior to stainless steel because it is not as robust and resistant to 

damage from cleaning activities such as surging. The Author became familiar 

with the damage to relief well plumbing systems in a study of an embankment 

in Minnesota. The relief wells were replaced with a deep trench drain because 

the repeated maintenance was costly and damaging to the system. Chemical 

applied to relief wells may also contribute to corrosion of the pipes and 

screens in the wells. Various materials have been used for well screen 

material including the following: 

1. Wooden staves 

2. Stainless steel 

3. Brass 

4. PVC or other plastic pipe used for screens 

D. Fittings – elbows, tees, etc. Loosening caused by physical movements, 

loadings, repeated surging in the case of relief wells. 

E. Geosynthetics ­

1. Loss of capacity due to silt plugging 

2. Loss of capacity due to ochre buildup or other biological plugging. 13 

The potential is probably more problematic for non-woven geotextile 

12 Pabst, Mark. U.S. Bureau of Reclamation. “Ochoco Dam Drain Rehabilitation, ” ASDSO Annual 

Meeting, St. Louis, MO. October 10-13, 1999 

13 Mackey, R.E. and G.R. Koerner. “Biological Clogging of Geotextile Filters- A Five Year 

Study,”Geosynthetics 99, Proceedings. International Fabrics Association International. 

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than for woven. 

IV. Consequences of deterioration. When drainage system components deteriorate, 

the system collects seepage less efficiently. Consequently, pressures build up above 

those for which concrete structures or earth blankets were designed. Another 

problem occurs when seepage systems develop cracks or other larger openings and 

lose their filtering capability. Then, the surrounding granular filter media or foundation 

soils can pipe into the seepage control system. As with any piping scenario, 

continued piping can develop into failures. 

A. Reduced flow capacity due to decreased cross-sectional area. Buildup of 

iron ochre in the filter media and in the screens of relief wells is probably the 

most common mode of deterioration in drainage systems. The buildup causes 

increased uplift pressures on clay blankets or concrete structures being 

protected by the wells. Sand boils may develop that were formerly controlled, 

and a rise in piezometric levels for a given reservoir elevation usually 

accompanies the decrease in well capacities. 

B. Leaks in system – piping. When drainage conduits are damaged by 

maintenance activity, subsequent surging pressures can wash out around the 

defects and erode annulus soil and drain fill around the pipes. Piping of 

surrounding filter media and soil can also occur when drainage conduits are 

damaged from corrosion, collapse from loading, separation from consolidation, 

and other mechanisms. Sinkholes are the ground or embankment surface are 

common manifestations of subterranean piping. 

C. Increased pore pressures caused by decreased capacity. This can occur 

most commonly in relief wells, but can also occur in deep trench drains where 

iron ochre buildup is severe. The result of increased pore pressures in the 

foundation may be sand boils developing and uplift pressures increasing 

under concrete appurtenances. 

D. Siltation of filters and slotted pipes or well screens can occur when poor 

check valves allow backwater into the system. This can reduce the flow 

capacity of the system and lessen the benefits of pressure relief. 

V. Relief well maintenance problems. In the REMR report 14, a number of 

relief well problems were identified as common and recurring. The problems were 

associated with excessive maintenance, cost, and effectiveness of the remedial 

measures. The most common ones were: 

A. Check valve reliability. When backwater containing silt fines flows into relief 

wells, siltation of the well screens and surrounding media can occur. 

B. Corrosion of screens and guards 

C. Incrustation or mineralization 

D. Deterioration of wood staves 

"Proceedings of REMR Workshop on Research Priorities for Drainage System and Relief Well 

Problems." July, 1989. Compiled by R. E. Leach and H. M. Taylor, Jr., US Army Engineer Waterways 

Experiment Station, Vicksburg, MS. 

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E. Vandalism 

F. Siltation – separated as a cause from the surface water problem caused by 

poor check valves. This problem occurs when initial well development 

procedures were poor, and a filter cake forms on the well screens or at the 

interface of the screen and filter media, or between the well pack and the 

aquifer. 

G. The most common relief well maintenance procedures mentioned in the 

REMR report 15 were the same as mentioned in the Johnson handbook 16. A 

common treatment program with the Corps of Engineers has been a 5-year 

schedule where chlorine and polyphosphates are added to wells. The 

chemicals are mixed in the well bore with a bailer for 4 hours, allowed to sit 

overnight, and then repeatedly surged the next day. 

1. Pumping 

2. Surging. Also included with this method is carbon dioxide treatment. 

See reference 

3. Jetting 

4. Acidizing. The main effect of acid is the physical dissolving of iron 

deposits. Acids most commonly7 used are hydrochloric acid and 

sulfamic acid. Acid concentrations and contact time are varied 

depending on the concentration of iron bacteria. Often, acid treatment 

followed by disinfectants is the preferred method of well treatment. 

5. Chlorination (Disinfectants) Chlorine is the most widely used 

disinfectant. They are inexpensive, readily available, and proven 

effective. Calcium hypochlorite and sodium hypochlorite are commonly 

used. Important terms are chlorine dosage, chlorine demand, and 

contact time. The usual method provides for either of the two common 

chemicals to obtain a chlorine dosage resulting in a 200-500 mg/l free 

residual of chlorine in the well water. A contact time of 24 hours is 

specified, during which time the well is surged and the residual free 

chlorine checked. Dosage of chlorine is increased if needed to 

maintain the level of 200-500. After 24 hours, the well is pumped free 

and normal operations resumed. In some cases 3 or 4 successive 

treatments are performed to ensure that water outside in the formation 

around the well is affected. 

6. Surfactants – Most common type is polyphosphate. Used in 

concentrations of about 3 percent, together with a minimum of 50 ppm 

of free chlorine residual. Following introduction of the surfactants, the 

wells are surged to distribute the chemical outside the well. At least two 

treatments are usually employed. 

15 ibid 

16 Johnson, 

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H. Alternative or less common relief well maintenance procedures mentioned in 

the REMR report 17 were: 

1. Lime application at the surface 

2. The Vyredox method – forcing oxygen-rich water into an aquifer 

away from the well as a growth medium interceptor for bacteria that 

normally are attracted to the well.’ 

3. Activated carbon filters in the well 

4. Ultraviolet light 

5. Ultrasonic vibration 

6. Heat treatment or pasteurization. 

I. Inspection techniques 

1. Pipe cameras. This type of inspection equipment has become 

commonplace in the commercial plumbing community and is readily 

available. One company sells a complete kit for about $4,800 that is 

capable of inspecting up to 400 feet of as small as 3” diameter line. 

Very sharp bends in drains may limit their use. 

2. Electrical potential – others 

J. Replacement – pipe lining procedures 

K. Pipe cleaning procedures 

1. Surging 

2. Reaming 

3. Jetting with high-pressure nozzles to remove iron deposits. 

The Bureau of Reclamation describes cleaning drains with a highpressure nozzle. 18 

18 United States Bureau of Reclamation. Water Operation and Maintenance Manual No. 188., June, 1999, 

page 13-14. 

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VI. Recommended Research Needs. 

Iron bacteria are the prevalent cause of loss of efficiency in relief wells and foundation drains 

such as trench and blanket drains. Recolonization and regrowth of bacteria colonies in treated 

wells is common. The organisms responsible for iron deposits have not been systematically 

studied because they are difficult to culture in lab environments. Topics associated with this 

problem are probably of highest priority for research. Topics recommended for research into 

aging problems of drainage systems are summarized as follows: 

A. Techniques for culturing iron bacteria for laboratory studies. 

B. Field studies to characterize the nature of iron bacteria populations in 

wells. 

C. Sampling and enumeration techniques for characterizing iron bacteria 

populations in wells. 

D. Field evaluations of disinfectants used for treating iron bacteria in wells. 

This includes quaternary ammonium compounds. Measuring before and after 

concentrations of bacteria is needed to evaluate methods. 

E. Series evaluations involving disinfectants and surfactants, with acids. 

Varying sequences and concentrations. Research on the sequence of 

different methods in treating iron bacteria is important. Research should 

identify both methods most effective, and sequences most effective. 

F. Field heat treatment trials for treating the iron bacteria problem. 

G. Redox potential research such as anoxic blocks in a well. 

H. Quantifying risk of iron ochre buildup from water tests. 

I. Alternative materials in replacement projects. 

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Bibliography 

1. Alford, George and Roy Cullimore. National Ground Water Association. “The 

Application of Heat and Chemicals in the Control of Biofouling Events in Wells,” 

Lewis Publishers, 1999, 181 pages Ref # T889 $81.25. 

2. Cullimore, Dr. Roy, Droycon Bioconcepts Inc. http://www.dbi.sk.ca/droycon/clog.html. 

“Articles on Water Well Biofouling and Clogging,”

 Phone: (306) 585 -1868 Fax: (306)585-3000

3. Dewey, Robert L., “Rehabilitation of a Toe Drain,” ASCE Geotechnical Special 

Publication no. 35, Geotechnical Practice in Dam Rehabilitation. North Carolina 

State University, Raleigh, NC, April, 1993., edited by Loren R. Anderson. pp. 733­

739. 

4. Driscoll, Fletcher G., Johnson Division. Groundwater and Wells, 2nd edition. 1986/ 

1089 pages NGWA Ref # T017 $86.75. 

5. Ford, Harry, Florida Extension Service. ”Iron Ochre and Related Sludge Deposits in 

Subsurface Drain Lines.” Circular 671, reprinted January l993. 

http://edis.ifas.ufl.edu/BODY_AE026 

6. Fourie, A. B., Kuchena, S. M. and Blight, G. E., (1994), "Effect of Biological Clogging 

on the Filtration Capacity of Geotextiles", Proc. 5th IGS Conf., Singapore, 

pp.721-724. 

7. Gould, James P. and Hugh S. Lacy. “Seepage Control in Dam Rehabilitation,” 

ASCE Geotechnical Special Publication no. 35, Geotechnical Practice in Dam 

Rehabilitation. North Carolina State University, Raleigh, NC, April, 1993., edited by 

Loren R. Anderson. pp. 240-255. 

8. Iron Bacteria and Wells (Anthology). National Ground Water Information Center 

1996/ 15 papers. NGWA Ref # K692 $49.00. 

9. Iron Control System for Drip Irrigation, Ilan Bar, NETAFIM Staff Agronomist. 

http://www.netafim.com/netafin/doa_iis.dll/Serve/item/English/1.4.10.1.htm 

10.Kissane, J. and Roy E. Leach, "Redevelopment of Relief Wells, Upper Wood River 

Drainage and Levee District, Madison County, Illinois," REMR-GT-16, [AD-A273 845] 

11.Kissane, Joseph A., "Use of New Well Redevelopment Techniques on Relief Wells in 

Upper Wood River Drainage and Levee District," REMR Bulletin Vol. 5, No. 3, 

September 1988 

12. Klaus, Max Kenneth, “Evaluation and Rehabilitation of Relief Wells,” ASCE 

Geotechnical Special Publication no. 35, Geotechnical Practice in Dam 

Rehabilitation. North Carolina State University, Raleigh, NC, April, 1993., edited by 

Loren R. Anderson. pp. 770-779. 

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on seepage performance 

13.Koerner, R.M., Koerner, George R., Fahim, Amira, and Ragui F. Wilson-Fahmy. 

“Long Term Performance of Geosynthetics in Drainage Applications,” Report 

prepared for National Cooperative Highway Research Program, Transportation 

Research Board, National Research Council., December, 1993. NCHRP Report 367. 

Available from http://nationalacademies.org/trb/bookstore. 

14. Leach, Roy E,. and Glen Hackett, “Evaluation of the Rehabilitation Project for Relief 

Wells at Leesville Dam, Ohio,” REMR Technical Report REMR-67-18. AD A259-197 

15. Leach, Roy, "Determination of Relief Well Infestation with the Use of Bacterial

Activity Test (BAT) Kit," Vol. 5, No. 3, September 1988 REMR Bulletin 

16. Lehr, Jay H., and Glen Hackett, National Water Well Association. “Iron Bacteria 

Occurrence, Problems and Potential Solutions in Water Wells,” Appendix A to the 

Proceedings of REMR Workshop on Research Priorities for Drainage System and 

Relief Well Problems. July, 1989. Compiled by R. E. Leach and H. M. Taylor, Jr., 

US Army Engineer Waterways Experiment Station, Vicksburg, MS. 

17. Mackey, R.E. and G.R. Koerner. “Biological Clogging of Geotextile Filters- A Five 

Year Study,”Geosynthetics 99, Proceedings. International Fabrics Association 

International. 

18. Mansuy, Neil. Edited by Roy Cullimore. National Ground Water Association. Water 

Well Rehabilitation: A Practical Guide to Understanding Well. Lewis Publishers. 

1999. 174 pages. NGWA Ref# T887 $56.25 

19. Mikell, Alfred Thomas, Jr. “Evaluation of Relief Wells at Three Texas Reservoirs for 

Biofouling Potential,” U.S. Army Corps of Engineers Waterways Experiment Station. 

University of Mississippi. 1994. 

20. Mikell, Alfred Thomas, Jr. “Microbial Fouling of Relief Wells and Drains,” U.S. Army 

Corps of Engineers Waterways Experiment Station/Vicksburg District. 

University of Mississippi. 1992. 

21. Mikell, Alfred Thomas, Jr. “Microbiology of Levee Relief Wells,” U.S. Army Corps of 

Engineers Waterways Experiment Station. 1994-95. 

22. Mikell, Alfred Thomas, Jr. ”Microbiology of Levee Relief Wells,” U.S. Army Corps of 

Engineers Waterways Experiment Station. University of Mississippi.1995. 

23. National Ground Water Association. “Iron Bacteria, Sulfur Bacteria, and Water Well 

Maintenance,” 60 slides/notes and handout. Ref # A108 $126.50. 

24. National Ground Water Association. Corrosion and Incrustation of Water Wells 

(Anthology). 1991/ 20 papers. NGWA Ref # K064. $40.00 

25.Ontario Ministry of Agriculture and Food Fact sheet, Iron and Manganese Oxides. 

Problems in Tile Drains, Agdex 752. 

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on seepage performance 

26.Ontario Ministry of Agriculture, Food and Rural Affairs. Agdex # 200/842, March, 

1984. R.W. Irwin, Drain Problems. 

27. Pabst, Mark. U.S. Bureau of Reclamation. “Ochoco Dam Drain Rehabilitation,” 

ASDSO Annual Meeting, St. Louis, MO. October 10-13, 1999. 

28.Pitts, D.J., D.Z. Haman, and A.,G. Smajstrla. “Causes and Prevention of Emitter 

Plugging in Microirrigation Systems.” University of Florida, Cooperative Extension 

Service. http://edis.ifas.ufl.edu/BODY_AE032 

29.Rural Water Advisory Services. “Iron Bacteria in Water Bores”. Queensland, 

Australia. http://www.dnr.qldd.gov.au 

30. Schaffer, Andrew, "Deposition of Calcium Carbonate in Foundation Drain Holes," 

REMR Bulletin Vol. 6, No. 1, February 1989. 

31. Smith, Stuart, Monitoring and Remediation Wells Problem Prevention, Maintenance, 

and Rehabilitation Lewis Publishers. 1995. 174 pages. NGWA Ref# T471 $ 81.25 

32.TECHNICAL REPORT REMR-UNNUMBERED, "Proceedings of REMR Workshop 

on Research Priorities for Drainage System and Relief Well Problems." July, 1989. 

Compiled by R. E. Leach and H. M. Taylor, Jr., US Army Engineer Waterways 

Experiment Station, Vicksburg, MS. NTIS Order Number AD A212 067. 

33.Umble, Art Ph.D., P.E., Manager, Water and Wastewater Operations, Elkhart Public 

Works and Stuart A. Smith, MS, CGWP, Partner, Smith-Comeskey Ground Water 

Science, Ada, Ohio. “A Cautionary Tale: Well Rehabilitation in Elkhart, Indiana's 

South Wellfield,” Presented to Indiana Section, AWWA, Indianapolis, Indiana, 

February 24, 1999. http://www.groundwatersystems.com/inpaper.html 

34. United States Bureau of Reclamation. Ground Water Manual. Government Printing 

Office Stock No. 024-003-00179-1. Second Edition. 1995. 

35.United States Bureau of Reclamation. Research Director’s Office. Project ER99.40, 

“Analysis and Control of Biofouling in Wells, Drains, & Dams. Principal Investigator: 

Sarah L. Wynn. 

36.United States Bureau of Reclamation. Water Operation and Maintenance Manual 

No. 188., June, 1999, page 13-14. 

37. Vance, David B., “Biofouling of Wells – Causes and Solutions,” ARCADIS Geraghty 

and Miller. wysiwyg://25/http://www.2the4.net/biofoul.htm 

38.Vance, David B., “Iron, The Environmental Impact of a Universal Element,” 2 The 4 

Technology Solutions 

39. Vance, David B., Groundwater and Redox Potential,” 2 The 4 Technology Solutions. 

wysiwyg://25/http://www.2the4.net/redox.htm 

Prepared by Danny K. McCook, NRCS September, 2000 Page 3 

Attachment 9 White Paper 6.doc 

EXHIBIT ATT10-1 - SUMMARY OF LOW ESTIMATES OF 

IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT IDEAS, BASED ON INPUT FROM WORKSHOP 

PARTICIPANTS(1) 

ESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

1B Assess Technology to Detect Voids and 

Concentrated Seepage Around Penetrations 

Through Embankment Dams 

5 100 43.3 30 38.2 

1C Develop Guidelines for Design of Filter 

Diaphragms Associated With Conduits 

Through Embankment Dams 

5 50 20.6 20 17.4 

1E Development and Deployment of Guidelines 

for Slip-linings of Outlet Works Conduits 5 80 22.2 20 22.2 

2A Classification of Conditions Conducive to 

Hydraulic Fracturing and Cracking 5 100 33.1 25 28.4 

2B Develop State-of-the-Practice for 

Configurations, Dimensions, and Construction 

Methods for Filters and Drains 

4 50 21.8 20 16.5 

2C & 2E Evaluate Mechanism Of Piping And Failure In 

Glacial, Alluvial, And Fluvial Environments – 10 700 153.9 50 209.4 

Including Consideration Of Internal Instability, 

and Including Consideration of Threshold 

Gradients for Initiating Piping in Cohesive Soils 

2D Evaluation of Mechanical/Geochemical 

Degradation of Properties of Filter Materials, 

Including Cementation and the Ability to 

Sustain a Crack 

7.5 700 131.4 50 208.8 

3A Enhance Academic Programs and 

Professional Development and Training 5 800 120.3 40 242.0 

Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of 

Dam Designers, Dam Construction Inspectors, 

and Dam Operators 

3B & 1D Develop Guidance for Dam Surveillance Plans 

Relative to Seepage, Including Monitoring, and 

Detecting Seepage Along Penetrations 

Through Embankment Dams 

5 100 26.9 20 28.3 

3C Improve Failure Time Estimates for SeepageRelated Failure Modes for Existing Dams 10 1000 143.3 25 305.8 

3D Identify Factors for Failure for a) “First Filling” 

(Including Normally Dry Dams/Detention 

Dams, Maximum Pool, etc.) and b) Long Term, 

for Each Seepage-Related Failure Mode 

7.5 100 29.7 20 28.5 

3E & 1A Expand the Database of Information on 

Seepage/Piping Failures/Incidents for Dams 

<15 meters in Height, and Compile Case 

Histories of Seepage Incidents Related to 

5 100 40.6 25 35.4 

Penetrations Through Embankment Dams 

4A Technology Transfer of Geophysical 

Techniques for Seepage Monitoring 10 100 35.0 25 30.1 

Note: 1.) Based on input from 11 participants; see Table ATT 10-3, Attachment 10 for individual estimates by participants. 
EXHIBIT ATT10-1 - SUMMARY OF LOW ESTIMATES OF 

IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT IDEAS, BASED ON INPUT FROM WORKSHOP 

PARTICIPANTS(1) 

ESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

4B Test Capabilities of Different Geophysical 

Methods on a Test Embankment 

20 1000 327.2 150 385.5 

4C Cross-Discipline Technology Transfer for 

Investigative Techniques in Dams 

8 200 50.8 25 59.2 

4D Do/Can Instruments or Instrument 

Installations Cause Damage in Embankment 

Dams 

8 300 54.2 20 88.3 

4E Assess Photo-Monitoring Techniques for 

Seepage (Infrared Imaging, Photo 

Interpretation, etc.) 

10 300 72.2 20 92.7 

5A Review of Performance of Seepage 

Remediation Measures: a) Upstream Cutoff 

Only, b) Upstream Cutoff With Downstream 

5 500 85.6 40 147.8 

Collection, and c) Downstream Collection 

Only 

5B Compilation of Practices, Applications, 

Experiences, Economics, and 

Advantages/Disadvantages of Using 

Geotextiles in Dam Applications 

10 700 129.4 50 205.7 

5C Evaluate the Performance of In-Place 

Geotextiles in Seepage Control Applications 

8 200 46.4 30 56.5 

5D Develop Design Criteria for Drainage Pipe 

Openings and Surrounding Material to 

Prevent Plugging 

5 500 77.8 20 150.2 

5E Testing of Fabric Clogging Under Steady 

State Flow Properly Simulating Conditions in 

Dam Applications 

15 300 83.9 50 86.7 

6A Research And Develop Techniques For 

Remediation And Prevention Of 

Contamination Of Wells, Drains, And 

Instrumentation 

20 1000 165.6 50 297.4 

6B Criteria for Frequency of Inspections and 

Rehabilitation of Horizontal Drains, Including 

Removal of Carbonates 

5 100 30.8 20 28.2 

6C Research Methods to Control and/or 

Remove Iron Bacteria Deposits From Wells 

and Drain Systems 

10 200 55.6 40 57.0 

6D Develop Test Criteria and Procedures for 

Evaluating Site Vulnerability to 

Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

10 100 37.2 30 25.1 

Note: 1.) Based on input from 11 participants; see Table ATT 10-3, Attachment 10 for individual estimates by participants. 
EXHIBIT ATT10-2 - SUMMARY OF HIGH ESTIMATES OF 

IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT IDEAS, BASED ON INPUT FROM WORKSHOP 

PARTICIPANTS(1) 

ESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

1B Assess Technology to Detect Voids and 15 1000 312.2 200 376.6 

Concentrated Seepage Around Penetrations 

Through Embankment Dams 

1C Develop Guidelines for Design of Filter 8 150 63.7 50 43.5 

Diaphragms Associated With Conduits 

Through Embankment Dams 

1E Development and Deployment of Guidelines 

for Slip-linings of Outlet Works Conduits 

8 150 62.0 50 43.1 

2A Classification of Conditions Conducive to 

Hydraulic Fracturing and Cracking 

10 600 164.4 125 175.9 

2B Develop State-of-the-Practice for 10 120 62.2 70 38.6 

Configurations, Dimensions, and Construction 

Methods for Filters and Drains 

2C & 2E Evaluate Mechanism Of Piping And Failure In 20 2000 649.4 250 774.6 

Glacial, Alluvial, And Fluvial Environments – 

Including Consideration Of Internal Instability, 

and Including Consideration of Threshold 

Gradients for Initiating Piping in Cohesive Soils 

2D Evaluation of Mechanical/Geochemical 10 2000 501.1 200 683.1 

Degradation of Properties of Filter Materials, 

Including Cementation and the Ability to 

Sustain a Crack 

3A Enhance Academic Programs and 

Professional Development and Training 

10 1200 277.2 200 350.8 

Programs Related to Seepage Issues in Dam 

Design and Rehabilitation – “Certification” of 

Dam Designers, Dam Construction Inspectors, 

and Dam Operators 

3B & 1D Develop Guidance for Dam Surveillance Plans 

Relative to Seepage, Including Monitoring, and 

10 300 85.6 60 82.7 

Detecting Seepage Along Penetrations 

Through Embankment Dams 

3C Improve Failure Time Estimates for SeepageRelated Failure Modes for Existing Dams 15 3000 438.3 100 908.4 

3D Identify Factors for Failure for a) “First Filling” 

(Including Normally Dry Dams/Detention 

13 400 131.9 60 123.5 

Dams, Maximum Pool, etc.) and b) Long Term, 

for Each Seepage-Related Failure Mode 

3E & 1A Expand the Database of Information on 

Seepage/Piping Failures/Incidents for Dams 

<15 meters in Height, and Compile Case 

Histories of Seepage Incidents Related to 

20 500 160.0 100 165.4 

Penetrations Through Embankment Dams 

4A Technology Transfer of Geophysical 

Techniques for Seepage Monitoring 

13 500 112.5 75 140.9 

Note: 1.) Based on input from 11 participants; see Table ATT 10-5, Attachment 10 for individual estimates by participants. 
EXHIBIT ATT10-2 - SUMMARY OF HIGH ESTIMATES OF 

IMPLEMENTATION COSTS FOR 

RESEARCH/DEVELOPMENT IDEAS, BASED ON INPUT FROM WORKSHOP 

PARTICIPANTS(1) 

ESTIMATED COSTS IN $1,000s 

TOPIC 

NUMBER 

RESEARCH/DEVELOPMENT TOPIC(S) LOW HIGH AVERAGE MEDIAN STANDARD 

DEVIATION 

4B Test Capabilities of Different Geophysical 

Methods on a Test Embankment 

35 4000 1143.9 250 1400.1 

4C Cross-Discipline Technology Transfer for 

Investigative Techniques in Dams 

13 1000 193.6 100 290.0 

4D Do/Can Instruments or Instrument Installations 

Cause Damage in Embankment Dams 

13 1500 245.3 100 448.6 

4E Assess Photo-Monitoring Techniques for 20 1000 282.2 80 386.8 

Seepage (Infrared Imaging, Photo 

Interpretation, etc.) 

5A Review of Performance of Seepage 

Remediation Measures: a) Upstream Cutoff 

15 1500 262.2 110 443.8 

Only, b) Upstream Cutoff With Downstream 

Collection, and c) Downstream Collection Only 

5B Compilation of Practices, Applications, 

Experiences, Economics, and 

Advantages/Disadvantages of Using 

30 2000 401.1 250 576.5 

Geotextiles in Dam Applications 

5C Evaluate the Performance of In-Place 

Geotextiles in Seepage Control Applications 

12 500 144.1 100 146.7 

5D Develop Design Criteria for Drainage Pipe 14 1500 273.8 80 444.9 

Openings and Surrounding Material to Prevent 

Plugging 

5E Testing of Fabric Clogging Under Steady State 18 1000 298.7 250 291.2 

Flow Properly Simulating Conditions in Dam 

Applications 

6A Research And Develop Techniques For 40 3000 558.9 250 891.2 

Remediation And Prevention Of Contamination 

Of Wells, Drains, And Instrumentation 

6B Criteria for Frequency of Inspections and 9 300 102.7 70 96.5 

Rehabilitation of Horizontal Drains, Including 

Removal of Carbonates 

6C Research Methods to Control and/or Remove 30 1000 271.1 80 344.7 

Iron Bacteria Deposits From Wells and Drain 

Systems 

6D Develop Test Criteria and Procedures for 30 300 130.6 80 89.5 

Evaluating Site Vulnerability to 

Physical/Chemical/Biological Deterioration of 

Seepage Collection and Control Systems 

Note: 1.) Based on input from 11 participants; see Table ATT 10-5, Attachment 10 for individual estimates by participants. 
R&D Topic

ParticipantNo. 1ParticipantNo. 2ParticipantNo. 3ParticipantNo. 4ParticipantNo. 5ParticipantNo. 6ParticipantNo. 7ParticipantNo. 8ParticipantNo. 9 

1B 10 50 5 10 100 80 100 5 30 

1C 5 25 5 5 50 20 50 5 20 

1E 5 25 5 5 30 20 80 10 20 

2A 50 50 10 7.5 30 25 100 5 20 

2B 15 25 5 7.5 50 20 50 4 20 

2C & 2E 250 50 10 15 200 50 700 10 100 

2D 200 50 10 7.5 100 50 700 15 50 

3A 10 50 5 7.5 40 100 800 20 50 

3B & 1D 5 25 5 7.5 40 20 100 10 30 

3C 10 25 10 10 150 50 1000 25 10 

3D 20 50 10 7.5 40 20 100 10 10 

3E & 1A 10 25 10 15 50 50 100 5 100 

4A 10 25 10 10 70 25 100 15 50 

4B 1000 50 50 25 150 150 1000 20 500 

4C 10 25 20 7.5 100 30 200 15 50 

4D 10 50 10 7.5 50 20 300 10 30 

4E 10 25 15 15 150 20 300 15 100 

5A 20 50 15 20 70 40 500 5 50 

5B 50 50 10 25 150 100 700 50 30 

5C 20 50 10 8 40 30 200 10 50 

5D 50 50 5 10 40 20 500 5 20 

5E 50 50 20 15 150 20 300 50 100 

6A 100 50 20 40 150 50 1000 30 50 

6B 5 50 20 7.5 40 25 100 10 20 

6C 100 50 10 40 40 20 200 20 20 

6D 20 50 10 40 40 25 100 30 20 
TABLE ATT 10-4 - INDIVIDUAL "BEST ESTIMATE" IMPLEMENTATION 

COSTS FOR R&D IDEAS 

Estimated costs 

in $1,000's 

R&D Participant Participant Participant Participant Participant Participant Participant Participant Participant Participant Participant 

Topic No. 1 No. 2 No. 3 No. 4 No. 5 No. 6 No. 7 No. 8 No. 9 No. 10 No. 11 

1B 50 100 10 12.5 150 100 500 10 500 100 3500 

1C 25 50 10 6.5 60 50 100 10 30 20 800 

1E 25 50 10 6.5 40 50 100 15 30 100 100 

2A 300 100 20 8.75 40 75 150 10 100 20 250 

2B 45 50 10 8.75 60 50 80 6 30 20 500 

2C & 

2E 

1000 100 25 17.5 250 75 1000 15 300 100 1400 

2D 750 100 25 8.75 150 100 1000 25 150 200 1500 

3A 100 100 10 8.75 50 200 1000 25 100 1000 900 

3B & 

1D 

25 50 10 8.75 50 50 200 15 50 100 800 

3C 50 50 20 12.5 200 100 2000 50 100 200 1500 

3D 75 100 20 10 50 40 300 15 100 200 1500 

3E & 

1A 

50 50 20 17.5 60 100 300 10 250 500 100 

4A 20 50 15 11.25 90 50 300 25 75 0 300 

4B 2500 100 100 30 200 300 2000 30 1000 1000 2000 

4C 50 50 35 10 125 50 500 25 100 0 300 

4D 50 100 25 10 70 50 1000 15 50 100 600 

4E 25 50 25 17.5 175 40 700 25 250 0 1400 

5A 60 100 20 22.5 90 80 1000 10 100 500 700 

5B 100 100 15 27.5 200 200 1000 80 150 200 1200 

5C 50 100 15 10 60 50 300 15 100 150 700 

5D 150 100 10 12 60 50 1000 10 100 20 500 

5E 200 100 25 16.5 200 40 500 80 200 150 1750 

6A 300 100 25 50 200 75 2000 50 200 300 1200 

6B 25 100 25 8.25 60 40 200 15 50 20 600 

6C 500 100 20 50 60 40 600 30 50 300 1000 

6D 60 100 20 50 60 50 200 50 100 400 1000 
TABLE ATT 10-5 - INDIVIDUAL ESTIMATED HIGH IMPLEMENTATION COSTS FOR R&D IDEAS

Estimated costs in $1,000's 

R&D 

Topic 

Participant 

No. 1 

Participant 

No. 2 

Participant 

No. 3 

Participant 

No. 4 

Participant 

No. 5 

Participant 

No. 6 

Participant 

No. 7 

Participant 

No. 8 

Participant 

No. 9 

1B 100 250 25 15 200 200 1000 20 1000 

1C 50 100 25 8 70 100 150 20 50 

1E 50 100 25 8 50 100 150 25 50 

2A 600 250 30 10 50 125 200 15 200 

2B 75 100 25 10 70 100 120 10 50 

2C & 2E 2000 250 50 20 300 200 2000 25 1000 

2D 1500 250 50 10 200 200 2000 50 250 

3A 300 250 25 10 60 400 1200 50 200 

3B & 1D 50 100 25 10 60 100 300 25 100 

3C 100 100 30 15 250 150 3000 100 200 

3D 150 250 30 12.5 60 60 400 25 200 

3E & 1A 100 100 30 20 70 200 500 20 400 

4A 40 100 25 12.5 110 75 500 50 100 

4B 4000 250 200 35 250 500 3000 60 2000 

4C 100 100 50 12.5 150 80 1000 50 200 

4D 100 250 30 12.5 90 100 1500 25 100 

4E 50 100 40 20 200 80 1000 50 1000 

5A 100 250 40 25 110 120 1500 15 200 

5B 200 250 30 30 250 400 2000 150 300 

5C 100 250 30 12 80 100 500 25 200 

5D 300 250 25 14 80 80 1500 15 200 

5E 400 250 40 18 250 80 1000 150 500 

6A 750 250 40 60 250 100 3000 80 500 

6B 50 250 40 9 80 70 300 25 100 

6C 800 250 30 60 80 60 1000 60 100 

6D 100 250 30 60 80 75 300 80 200 

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