The National Dam Safety Program 
Research Needs Workshop: Outlet Works

Report of Workshop 
on Issues, Remedies, and Research 
Needs related to Dam Outlet Works
 
May 25 to 27, 2004 

Denver, Colorado 

Workshop Sponsored by FEMA

Report Prepared by URS 
March 2005 

Preface

One of the activities authorized by the Dam Safety and Security Act of 2002 is research
to enhance the Nations 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 Outlet Works was held
on May 25-27, 2004, in Denver, Colorado.

The Department of Homeland Security, Federal Emergency Management Agency, would
like to acknowledge the contributions of the U.S. Army Corps of Engineers, Hydrologic
Engineering Center, which was responsible for the development of the technical program,
coordination of the workshop, and development of these workshop proceedings. A
complete list of workshop facilitators, presenters, and participants is included in the
proceedings.

TABLE OF CONTENTS


1. Section 1 ONE Introduction.................................................................................... 1-1


1.1 Introduction and scope of report ..............................................................1-1


2. Section 2 TWO Executive Summary ....................................................................... 2-1


2.1 State-of-the-practice.................................................................................2-2


2.1.1 Outlet Works Failure Modes........................................................2-2


2.1.2 Conduit Materials, Selection Criteria, and Construction Methods.....................2-3 


2.1.3 Gates, Valves and Controls..........................................................2-3


2.1.4 Energy Dissipators .......................................................................2-4


2.1.5 Rehabilitation of Conduits ...........................................................2-5


2.1.6 Outlet Works Inspection..............................................................2-6


2.2 Research and Development Ideas ............................................................2-7


2.3 Closure ..........................................................................................2-9


3. Section 3 THREE Workshop Process ..................................................................... 3-1


3.1 Selection of Workshop Participants.........................................................3-1


3.2 Selection of Workshop Topics.................................................................3-1


3.3 Workshop Mechanics...............................................................................3-2


3.4 White Papers ............................................................................................3-2


3.4.1 Discussion of White Papers .........................................................3-3


3.5 Identification and Prioritization of Research and Development Ideas .................3-3 


3.6 Preliminary Implementation Plans...........................................................3-3


3.7 Overall Prioritization of Research and Development Ideas.....................3-4


4. Section 4 FOUR Workshop Results for Individual Topics ....................................... 4-1


4.1 Topic 1  Outlet Works Failure Modes ...................................................4-1


4.1.1 State-of-the-Practice White Paper................................................4-1


4.1.2 State-of-the-Practice Refinement .................................................4-3


4.1.3 Prioritization of Research and Development Ideas......................4-4


4.1.4 Preliminary Research and Development Plans ............................4-4


4.2 Topic 2  Conduit Materials, Selection Criteria, and Construction Methods..........4-4 


4.2.1 State-of-the-Practice White Paper................................................4-4


4.2.2 State-of-the-Practice Refinement .................................................4-6


4.2.3 Prioritization of Research and Development Ideas......................4-7


4.2.4 Preliminary Research and Development Plans ............................4-7


4.3 Topic 3 - Gates, Valves, and Controls .....................................................4-8


4.3.1 State-of-the-Practice White Paper................................................4-8


4.3.2 State-of-the-Practice Refinement ...............................................4-10


4.3.3 Prioritization of Research and Development Ideas....................4-10


4.3.4 Preliminary Research and Development Plans ..........................4-11


4.4 Topic 4  Energy Dissipators.................................................................4-11


4.4.1 State-of-the-Practice White Paper..............................................4-11


4.4.2 State-of-the-Practice Refinement ...............................................4-12


4.4.3 Prioritization of Research and Development Ideas....................4-13


4.4.4 Preliminary Research and Development Plans ..........................4-13


4.5 Topic 5  Rehabilitation of Conduits.....................................................4-14


4.5.1 State-of-the-Practice White Paper..............................................4-14


4.5.2 State-of-the-Practice Refinement ...............................................4-15


4.5.3 Prioritization of Research and Development Ideas....................4-16


4.5.4 Preliminary Research and Development Plans ..........................4-16


4.6 Topic 6  Outlet Works Inspection........................................................4-17


4.6.1 State-of-the-Practice White Paper..............................................4-17


4.6.2 State-of-the-Practice Refinement ...............................................4-20


4.6.2 Prioritization of Research and Development Ideas....................4-21


4.6.3 Preliminary Research and Development Plans ..........................4-21


5. Section 5 FIVE Overall Prioritization Of Research and Development Ideas.............5-1


6. Section 6 SIX References ............................................................. 6-1


EXHIBITS 

Exhibit 3-1 Workshop Participants 

Exhibit 3-2 Topics Selected for the Workshop 

Exhibit 3-3 White Paper Authors and Titles 

Exhibit 4-1 Prioritization of Research and Development Ideas Workshop Topic 1 Outlet Works Failure Modes 

Exhibit 4-2 Research and Development Implementation Plan, R&D Topic 1A Guidelines for Venting Conduits 

Exhibit 4-3 Research and Development Implementation Plan, R&D Topic 1B Best Practices Guide for Conduits through Embankment Dams. 

Exhibit 4-4 Research and Development Implementation Plan, R&D Topic 1C Best Practices for Mechanical and Electrical Design and Automated Control 

Exhibit 4-5 Research and Development Implementation Plan, R&D Topic 1D Developing Lists of Failure Modes for Various Components of Outlet Works Baseline, not Cookbook. 

Exhibit 4-6 Prioritization of Research and Development Ideas Workshop Topic 2  Conduit Materials, Selection Criteria, and Construction Method 

Exhibit 4-7 Research and Development Implementation Plan, R&D Topic 2A Best Practices For Intake Towers  Location, Configuration, Access, Debris/Trash Control, Seismic Performance, and Selective Withdrawals. 

Exhibit 4-8 Research and Development Implementation Plan, R&D Topic 2B Guidance on Application of Tunnels for Outlet Works  Including Microtunnelling in Soft and Hard Ground. 

Exhibit 4-9 Research and Development Implementation Plan, R&D Topic 2C Compile Data on Performance of Conduits With Significant Settlement and Lateral Movement. 

Exhibit 4-10 Research and Development Implementation Plan, R&D Topic 2D Guidance on Seismic Effects on Conduits and How to Analyze and Design for Them Including Embankment Spreading, Fault Offset, and the Propagation of earthquake waves. 

Exhibit 4-11 Prioritization of Research and Development Ideas Workshop Topics 3 and 4  Gates, Valves, Controls and Energy Dissipators 

Exhibit 4-12 Research and Development Implementation Plan, R&D Topic 3A  Best Practices for Selection of Gates and Valves 

Exhibit 4-13 Research and Development Implementation Plan, R&D Topic 4A  Best Practices for Energy Dissipators  Considering Heads, Velocities, Configurations, etc. 

Exhibit 4-14 Research and Development Implementation Plan, R&D Topic 3B  Guidelines for Maintenance and Exercise of Gates and Valves and Cavitation Repairs. 

Exhibit 4-15 Research and Development Implementation Plan, R&D Topic 3C Develop Short Courses with Video/DVD Options on Design, Operation, and Maintenance of Gates and Valves. 

Exhibit 4-16 Prioritization of Research and Development Ideas Workshop Topic 5  Rehabilitation of Conduits 

Exhibit 4-17 Research and Development Implementation Plan, R&D Topic 5A  Design guidance and Guide Specifications for Sliplining. 

Exhibit 4-18 Research and Development Implementation Plan, R&D Topic 5B  Compilation of Case Studies on Outlet Works Rehabilitation  Lessons Learned, Performance, and Comparative Costs. 

Exhibit 4-19 Research and Development Implementation Plan, R&D Topic 5C  Assessment of Microtunnelling and Boring Technologies for Application to Outlet Conduit Rehabilitation. 

Exhibit 4-20 Research and Development Implementation Plan, R&D Topic 5D  Best Practices Guide for Design and Construction Methods to Rebuild Embankment Sections for Conduit Removal and Replacement. 

Exhibit 4-21 Prioritization of Research and Development Ideas Workshop Topic 6  Outlet Works Inspection 

Exhibit 4-22 Research and Development Implementation Plan, R&D Topic 6A Applications of Non-Destructive Testing (NDT) for Inspection of Outlet Works. 

Exhibit 4-23 Research and Development Implementation Plan, R&D Topic 6B  Best Practices for Inspection of Gates, Valves, and Operators, Including Mechanical and Electrical Components. 

Exhibit 4-24 Research and Development Implementation Plan, R&D Topic 6C  Best Practices Guide for Inspection Frequency and Methods of Inspection for Typically Accessible Conduits. 

Exhibit 4-25 Research and Development Implementation Plan, R&D Topic 6D  Inspection of Normally Inundated Structures and Difficult to Access Areas. 

Exhibit 5-1 Ranking of Research/Development Ideas Based on Individual Scores for Potential Benefit - Scores Given By Participants 

Exhibit 5-2 Ranking of Research/Development Ideas Based on Individual Scores for Cost/Ease of implementation - Scores Given By Participants 

Exhibit 5-3 Ranking of Research/Development Ideas Based on Combination of Individual Scores for Potential Benefit and Cost/Ease of implementation 

Exhibit 5-4 Cost-Benefit Comparison of Ranked Research and Development Topics 


ATTACHMENTS 

Attachment 1 Workshop Agenda 
Attachment 2 Research and Development Implementation Plan Form 
Attachment 3 Ranking of Research and Development Ideas Form 
Attachment 4 White Paper No. 1  Outlet Works Failure Modes, Sal Todaro 
Attachment 5 White Paper No. 2  Design and Construction of Outlet Works Conduits for Embankment Dams, Sal Todaro 
Attachment 6 White Paper No. 3  Gates and Valves, Lee Gerbig 
Attachment 7 White Paper No. 4  Energy Dissipators, Henry Falvey 
Attachment 8 White Paper No. 5  Rehabilitation of Pipe Conduit Spillways Through Dams, James Crowder 
Attachment 9 White Paper No. 6  Outlet Works Inspection, Chuck Cooper 


LIST OF ABBREVIATIONS 
Abbreviation Definition 
ASCE American Society of Civil Engineers 
ASDSO Association of State Dam safety Officials 
AWWA American Water Works Association 
CMP Corrugated metal pipe 
EPRI Electric Power Research Institute 
FEMA Federal Emergency Management Agency 
FERC Federal Energy Regulatory Commission 
FRS Flood Retarding Structure 
HDPE High-density Polyethylene 
ICOLD International Committee on Large Dams 
NEHRP National Earthquake Hazard Reduction Program 
NRCS National Resources Conservation Service 
NSRB National Dam Safety Review Board 
REMR Repair, Evaluation, Maintenance, and Rehabilitation 
RFP Request for proposal 
USACE U.S. Army Corps of Engineers 
USBR U.S. Bureau of Reclamation 
USGS U.S. Geologic Survey 
USSD United States Society on Dams 
WRRI Water Resources Research Institute 


SECTION ONE Introduction

1.1 INTRODUCTION AND SCOPE OF REPORT 
This workshop was sponsored by FEMA and was organized and facilitated by URS Corporation. 
The product of the workshop is this written report, produced by URS, documenting the results of 
the workshop. The report will be included in FEMAs National Dam Safety Program Act Report 
Series and will be posted on FEMAs website, http://www.fema.gov/fima/damsafe. 

The workshop consisted of convening and facilitating a group of experts in the field of dam 
outlet works design and maintenance. The objectives of the workshop and the resulting written 
report were to document: 

1. A state-of-practice concerning the cost effective techniques for maintenance and 
replacement of dam outlet works;
2. The short-term (immediate) and long-term research and development needs of the 
Federal and non-Federal dam safety communities with respect to dam outlet works; 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 and 
cost/ease of implementation. 
The workshop was held in Denver, Colorado, on May 25, 26, and 27, 2004. 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. 

SECTION TWO Executive Summary

A group of 22 individuals was assembled for a three-day workshop on Issues, Remedies, and 
Research Needs Related to Dam Outlet Works. Workshop participants were selected to provide 
a broad representation of individuals involved in the topic and included the authors of the six 
white papers presented. Participants included 7 representatives of five different U.S. federal 
agencies, 2 representatives from two different state dam safety and environmental agencies, 7 
representatives of six different consulting companies, 4 independent consultants, one university 
professor, and one representative of a hydropower organization. The group included individuals 
from 10 different U.S. states, the District of Columbia, and Canada. 

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

1. Outlet Works Failure Modes including consideration of failure by seepage and piping along 
the outlet works conduit. 
2. Conduit Materials, Selection Criteria, and Construction Methods including pipe material 
types and their advantages, disadvantages, and appropriate applications; hard foundations; 
soft foundations; pressure conduits (high pressure and low pressure); and non-pressure 
conduits. 
3. Gates, Valves, and Controls, including types of gates and valves and their applications; gate 
and valve locations; gate, valve, and control configurations; rehabilitation, and maintenance. 
4. Energy Dissipators including stilling basins and energy dissipating valves. 
5. Rehabilitation of Conduits including in-place rehabilitation and replacement; capacity  
reservoir evacuation criteria; and economic considerations. 
6. Outlet Works Inspection including discussions about determination of appropriate frequency; 
systems, methods, and techniques; and consideration of design criteria to accommodate 
inspection. 

These specific topics were selected to coincide with the six topics for which white papers were 
prepared and distributed to participants 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 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/ease of implementation. 

The top four or five research and development ideas for the topic were assigned to small work 
groups for development of preliminary implementation plans. 

 The small work groups reported back to the entire group on their preliminary implementation 
plans for each of the selected research and development ideas. 

 Each participant then ranked the identified research and development ideas according to 
considerations of potential benefit and cost/ease of implementation. 

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 also summarized in Section 4 of this report, and 
some of the more significant points from those discussions are presented later in this Executive 
Summary. The research and development ideas generated by the group for all six workshop 
topics, and the preliminary implementation plans developed for the 20 leading ideas generated 
for these topics are also presented in Section 4. 

In the closing session on the last day of 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, and cost/ease of implementation. 
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. 

2.1 STATE-OF-THE-PRACTICE 
During the state-of-the-practice white paper presentations and the ensuing discussions, it became 
apparent that there are several challenges to defining a single state-of-the-practice for any of the 
topics being considered. Much of this may be attributed to the absence of any single, consistent 
set of standards and guidelines covering the various topics discussed that could be used across 
various regions and organizations. The presented white papers provided a basis for further 
discussions of the state-of-the-practice for the various topics discussed. 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 various aspects of outlet works design, maintenance, 
inspection and rehabilitation. All of the discussions on state-of-the-practice are documented in 
Section 4, but some of the more significant insights gleaned from the white papers and the 
ensuing discussions are presented below and are grouped according to the six topics addressed in 
the workshop. 

2.1.1 Outlet Works Failure Modes 
1. The primary causes of outlet works failures are: foundation related failures, structural 
deterioration, the absence of timely rehabilitation and repair, structural failures, 
mechanical failures, failures related to hydraulics, failures related to ice and sediment 
loadings, and operator error. There is also an unwillingness of those involved to 
acknowledge the viability of different failure modes and to devise creative solutions for 
these problems. It has also been observed that many owners/operators will allow a 
known problem to persist without repair for long periods of time. 
2. Methods that can be used to minimize the occurrence of failure of outlet works include: 
having an experienced mechanical engineer design components of the outlet works; using 
reliable standard designs that have been developed and tested over time; locating 
structures on a rock foundation to reduce settlement effects; and addressing air demand 
requirements, seismic loading (particularly of intake towers), ice loading, and vibration 
effects in the design. 
3. The three primary ways of minimizing the failure potential of outlet conduits are: 1) 
Filtering the dam embankment in the vicinity of the outlet conduit to prevent internal 
erosion of the embankment along or near the conduit; 2) Constructing outlet conduits on 
rock foundations when possible; and 3) Designing conduits with redundant features to 
prevent water seepage from the conduit into the embankment resulting in the piping of 
embankment materials. 
4. To minimize the occurrence of control structure failure the following steps are 
recommended: 1) An engineer experienced in the design of gates, valves and mechanical 
systems for dam outlet works should involved with both new design and rehabilitation 
activities; 2) Routinely test, operate and maintain components of control structures; and 
3) replace antiquated and unreliable components of control structures with newer, more 
reliable equipment. 
5. To prevent the uncontrolled erosion of the downstream channel in cases of direct 
discharge, care should be taken in the design and maintenance of discharge mechanisms 
including the use of energy dissipation structures. 

2.1.2 Conduit Materials, Selection Criteria, and Construction Methods 
1. Due to the absence of any single recognized standard for designing dam outlet works 
there is currently great inconsistency in design rationale and review processes for this 
design aspect of small and medium sized embankment dam facilities. The need for a 
single design standard is further underscored by the fact that outlet works have been 
identified as a significant contributor to the occurrence of embankment dam failures. 
2. A single, nationally recognized standard would lead to greater consistency between 
similar project designs, facilitate more effective and consistent review of proposed 
designs, and result in increased potential for safer more reliable facilities. The National 
Dam Safety Review Board (NSRB) is in the process of preparing a manual to be used for 
designing and maintaining outlet works for significant high-hazard dams. The manual 
covers topics for the design, construction, maintenance, and repair of conduits for 
embankment dams. It is recommended that in the interim the guidelines presented in this 
manual be used to form a design basis for smaller facilities. 
3. The use of standards not intended for use in designing pressurized outlet systems for 
embankment dams is the most common practice that introduces additional risk to outlet 
works for smaller embankment dams. 
4. Recommended approaches to the design of outlet conduits on soft foundations include: 1) 
Placement of freestanding pressurized outlet pipe inside of a cast-in-place reinforced 
concrete conduit; 2) Use of a non-pressurized outlet works system; 3) Use of welded steel 
outlet pipe encased in reinforced concrete; 4) Use of articulated joints for the outlet 
conduit; and 5) Protecting the foundations integrity during construction. 

2.1.3 Gates, Valves and Controls 
1. The types of gates commonly used at newer dam sites are: Slide gates, Knife gates, Jet-
flow gates, Clamshell gates, Radial gates, and Hinged Crest gates. Slide gates, also 
known as Sluice gates, are the most common type of gate used for dam outlet works. 
However, it should be noted that there have been frequent problems with leakage of slide 
gates mounted in the unseating direction relative to the head (i.e. the slide gates are 
placed downstream of the headwall). 
2. For applications where the head does not exceed 100 feet, the two types of slide gates 
commonly used are the Cast Iron Slide gate and the Fabricated Slide gate. For 
applications where the head exceeds 100 feet, Bonneted Slide gates and Wheel gates are 
commonly used. Jet-flow gates are commonly used as freely discharging devices. The 
Clamshell gate which is specially designed by the USBR works well in submerged 
installations. 
3. Due to susceptibility to corrosion and the build up of deposits that increase friction and 
affect the operation of its roller train, the use of Roller gates is increasingly avoided even 
though this was a type of slide gate that was also used for high head applications. 
4. Valve types commonly used are: Butterfly valves, Gate valves, Fixed-Cone valves, and 
Sleeve valves. Butterfly valves are commonly used at power plants and water facilities. 
However, problems with the corrosion of the busing or stems of butterfly valves have 
been reported resulting in valves that did not fail in the intended position. A Gate valve 
is a variation of a slide gate, with a circular body and disk. They are often used for guard 
gates upstream of regulating valves, or used for throttling flow in low-head applications. 
A Fixed-Cone valve is commonly used for regulating the flow of water from a dam outlet 
works. Sleeve valves are used as energy dissipaters, both in-line and at the end of a 
conduit and are usually operated to provide precise flow control. 
5. Due to high costs and problems with corrosion, seat erosion, cavitation damage, or 
general maintenance difficulties there has been a decreased use of Needle valves and 
Hollow-Jet valves. 
6. The four basic types of gate operation systems are: manual operators, electric motor-
operators, hydraulic operators, and pneumatic operators. Improved hydraulic fluids 
suitable for outdoor use, the ability to have submerged hydraulic operation, use of better 
seals, and automated operation features has inspired increased use of hydraulic 
components in the design of gates and valves. Hydraulic operation is most often used on 
large gates and valves operating at high head, but is becoming more common for small 
equipment at low heads for particular installations. 
7. The knowledge and experience base in the design and fabrication of gates and valves in 
the United States is continually being eroded with decreased funding for research and 
development in control mechanisms and the increased occurrence of offshore fabrication 
and the disappearance of longstanding US-based designers and manufacturing firms. 

2.1.4 Energy Dissipators 
1. Energy dissipators that have been successfully used at outlet works include: stilling 
basins, baffled apron drops, stepped spillways, impact basins, stilling wells, various types 
of valves, sudden enlargements, in-line orifices, flip buckets, and plunge pools. Most 
outlet works incorporate a combination of different types of energy dissipators. The 
types of energy dissipators used depend on the design reservoir head, discharge 
requirements, and cost constraints of a particular design. However it should be noted that 
problems with backflows in USBR-type stilling basins have been reported. Backflows 
have drawn rock and soil materials into the basins, sometimes leading to ball-milling and 
related damage. Public safety is also a concern for these structures due to the high 
incidence of people using these structures for recreation activities like swimming even 
though egress from basins can be difficult. 
2. USBR Engineering Monograph 25 provides a thorough discussion of the design elements 
for stilling basins, impact basins, flip buckets, and baffled aprons. General guidelines for 
designing outlet works are provided in both USACE Engineering Manual EM 1110-21602 
and in Design of Small Dams published by the USBR. 
3. The combination of chute blocks, which create shear zones, and baffle blocks, which 
create additional turbulence, allows the length of stilling basins to be reduced. The use of 
baffle blocks also allows air content of discharge water to be regulated, and by releasing 
or entraining air in the water flowing through the baffles, water quality of the discharge 
flow is improved. 
4. Although the USBR limits the dimensions and discharges of impact basins to relatively 
low energy levels, the basins have been used successfully at much higher energy levels 
by scaling the recommended dimensions to the larger sizes. 
5. There is lack of widespread, definitive knowledge on reliable repair techniques for 
energy dissipators and lack of specific guidelines on the extent and size of riprap required 
downstream of energy dissipators. 

2.1.5 Rehabilitation of Conduits 
1. Corrugated metal pipe (CMP) commonly serves as the conduit found in small earthen 
embankment dams ranging in height from 10 to 50 feet constructed between 30 and 50 
years ago in the southeastern United States. Compared to conduit materials used in 
newer dams, CMP is highly susceptible to deterioration and becomes a problem when a 
spillway conduit has reached or exceeded its design service life, generally considered to 
be 25 to 30 years. Deterioration of these conduits generally consists of leaking joints, 
corrosion, and holes in the pipe. 
2. The main risk associated with the deterioration of these conduits is piping of the 
surrounding embankment soils into the conduit, which can lead to the eventual failure of 
the earthen embankment. 
3. The four primary remediation options most applicable to earthen embankment dams less 
than 50 feet in height are: 1) Replacement of the existing pipe conduit using cut and 
cover methods; 2) Sliplining the existing conduit; 3) Grouting along the exterior of the 
existing conduit; and 4) constructing either a siphon spillway or short riser and new 
outlet conduit after the existing conduit has been abandoned. Cured-in-place (CIP) 
linings like Insituform have also been used for outlet conduit rehabilitation. 
4. Option 1 typically offers the most thorough rehabilitation for impaired conduits through 
dams, but can be cost-prohibitive. Option 2 offers the possibility of increasing the 
hydraulic capacity of the outlet pipe and increases the service life to the existing conduit 
spillway. Option 3 is classified as a temporary repair solution and does not extend the 
design life of the existing conduit material. The depth of the conduit below the 
embankment surface also limits this method. Option 4 is generally limited to small 
drainage basins with relatively small peak inflows. The installation of the new siphon 
requires excavation of the embankment below normal pool. Siphon spillways do not 
typically exceed 12-inches in diameter and may be constructed of flexible conduit 
materials like PVC, HDPE, or ductile iron. Epoxy paints have become the preferred 
standard for paint used to coat outlet works conduits. 

2.1.6 Outlet Works Inspection 
1. Inspection of cut-andcover outlet works typically includes review of features including: 
the entrance channel; intake structure; conduit(s); terminal structures; and the 
downstream channel. The advantages and disadvantages of each method should be 
assessed with due consideration given to the ease and efficiency with which inspection 
objectives can be met; compliance with health and safety guidelines, and cost. 
2. The purpose of an outlet works inspection program is to ensure that conduits through 
dams are safely and efficiently operated and maintained. While inspection designations 
may differ among the various state and federal agencies/organizations, the types of 
inspections primarily vary according to frequency and scope. 
3. Initial or formal inspections include in depth review of all pertinent data available for the 
outlet works to be inspected. Design and construction data are evaluated relative to 
current state-of-the-art guidelines to identify potential dam safety problems or areas 
requiring particular attention. Detailed crack survey mapping should be used on a 
repeated basis to monitor structural deterioration. 
4. Scheduling periodic outlet works inspections may be influenced by the following factors: 
provision of sufficient notice to dam owners and operators allowing necessary 
arrangements and pre-inspection activities to be completed and needed clearances to be 
obtained; the ability to access most or all of the major components of the outlet works; 
and the opportunity to observe features operating under a wide range of conditions. 
5. Inspections of features like intake structures and upstream conduits that are usually 
submerged require special coordination with the dam owners since the timing of such 
inspections has to be carefully planned. 
6. Good preparation and planning is key to the success of an inspection. Factors to be 
considered include: selection of the inspection team; review of the existing project data 
for the dam to be inspected; and the preparation of a detailed inspection plan. Factors to 
be considered in planning conduit inspections should include: conduit diameter, the 
presence and angle of bends in the conduit, the inclination of the invert slope, and the 
distance between access entry locations. 
7. Specialized inspections of inundated or hard to access features often utilize a combination 
of divers, remotely operated vehicles (ROVs), and closed circuit television (CCTV). 
Considerations that must be accounted for if divers are to be expected to conduct 
inspections include depth, altitude, access, leakage, currents, visibility, size of opening, 
and length of conduit requiring inspection. ROVs are good alternatives to dive 
inspections when conditions like depth, diameter, or length become prohibitive. CCTV 
can be used to inspect submerged portions of intake structures, conduits, and terminal 
structures. 
8. Permanent markers and thorough documentation should be used to facilitate easy location 
of intake structures that are usually submerged. GPS could also be used to aid location of 
inundated structures but a repeatable methodology incorporating reliable equipment 
needs to be developed. 

2.2 RESEARCH AND DEVELOPMENT IDEAS 
Before the research and development ideas were ranked, some 48 separate research and 
development (R&D) ideas were generated for the six different topics addressed in the workshop. 
During this phase, Topic 3 on Gates and Valves and Topic 4 on Energy Dissipators were 
combined and R&D ideas generated for the combined topic. In order to reduce the number of 
R&D ideas to 20, only four ideas from each topic receiving the highest number of votes from 
workshop participants was advanced to the preliminary planning phase. 

Based on all of the input from participants and the combined ranking of R&D ideas assessing 
potential benefit and cost/ease of implementation, the five leading research and development 
ideas (including a two-way tie for 4th position) identified in the workshop are as follows: 

1. Develop a best-practices guide for outlet works conduits through embankment dams, 
emphasizing small embankments. (R&D Topic 1B) 
2. Develop a best-practices guide for selection of gates and valves for outlet works structures. 
(R&D Topic 3A) 
3. Develop guidelines for maintenance and exercise of gates and valves and for cavitation 
repairs for outlet works. (R&D Topic 3B) 
4. Develop a best-practices guide for energy dissipators for outlet works structures, considering 
heads, velocities, and configuration. (R&D Topic 4A) 
5. Design guidance and guide specifications for sliplining outlet conduits. (R&D Topic 5A) 

These five R&D topics were ranked in the top 10 in both of the overall ranking methods used to 
prioritize the research and development ideas assessing potential benefit and overall cost/ease of 
implementation. These R&D ideas were also ranked 1 though 4 when the ranking from both 
ranking methods were averaged as will be discussed in Section 5. Consequently, it is the 
authors opinion that these 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 five R&D topics listed above, the remaining five ideas in the top 10, based on the 
average of the rankings from two ranking considerations were: 

1. Develop a best-practices guide for mechanical and electrical design and for automated 
control for outlet works. (R&D Topic 1C) 
2. Compile case studies on outlet works rehabilitation including lesson learned, performance 
and comparative costs. (R&D Topic 5B) 
3. Develop a best-practices guide for inspection of outlet works gates, valves, and operators, 
including mechanical and electrical components. (R&D Topic 6B) 
4. Develop a list of failure modes for outlet works. (R&D Topic 1D) 
5. Develop a best-practices guide for inspection frequency and method for typically accessible 
outlet works conduits. (R&D Topic 6C) 

R&D topics 1C, 6B and 1D were ranked in the top 10 in both benefit and cost/ease of 
implementation rankings while R&D topic 5B was among the top 10 in the ranking of potential 
benefit, while R&D topic 6C was the second most favorable R&D idea from a cost/ease of 
implementation perspective. Consequently, it is the authors opinion that these five R&D topics 
should be considered high priority, but not as high as the top five ideas previously indicated. 

Other R&D topics that received a top 10 ranking in at least one of the two overall ranking 
methods used to prioritize ideas were: 

1. Develop a best-practices guide for outlet works intake towers, considering such factors as 
location, configuration, access, debris/trash control, seismic performance, and the practice of 
selective withdrawals. (R&D Topic 2A) 
2. Develop a short course with the possibility of a companion video/DVD format on design, 
operation, and maintenance of outlet works conduits. (R&D Topic 3C) 
3. Develop a best-practices guide for design and construction methods to rebuild embankment 
sections removed for outlet conduit removal/replacement. (R&D Topic 5D) 

These R&D topics deserve some consideration for implementation, but at a lower priority than 
the 10 ideas previously indicated. 

The remaining seven R&D topics received marginally less support in the overall rankings of the 
ideas with none of them ranked in the top 10 of either of the two assessment gauges used. 

While a numerical ranking and average were calculated for the purposes of being able to rank all 
of the R&D ideas considered, the graph shown in Exhibit 5-4 indicates clustering of ranking 
data. According to this analysis tool, fifteen R&D ideas could be classified as high benefit with 
low cost/easy to implement, or as providing a high benefit with corresponding high cost/easy to 
implement. 

In reviewing the leading R&D topics, it is interesting to note that none of them involve basic 
laboratory testing. Rather most of the R&D topics involve collecting or compiling available 
information and developing guidelines for dissemination to practitioners and to enable 
consistency in design, maintenance, and inspection activities throughout the field of practice. 
This suggests that the overall challenges associated with various aspects of outlet works design, 
maintenance and inspection result from the absence of documented information, inconsistencies 
among available information, misuse or misapplication of the available information by some 
practitioners, or lack of knowledge of available information by some practitioners. It also seem 
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. 

2.3 CLOSURE 
A review of the leading R&D topics indicates that none of them involve basic laboratory testing. 
Most of the R&D topics involve collecting or compiling available information and developing 
guidelines for dissemination to practitioners to enable consistency in design, maintenance, and 
inspection activities throughout the field of practice. This suggests that the overall challenges 
associated with various aspects of outlet works design, maintenance and inspection result from 
the absence of documented information, inconsistencies among available information, misuse or 
misapplication of the available information by some practitioners, 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. 

SECTION THREE 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 

3.1 SELECTION OF WORKSHOP PARTICIPANTS 
Workshop participants were selected to address the interest and knowledge base of Federal and 
Non-Federal dam owners, engineering practitioners, and academicians. Facilitators (white paper 
authors) were then selected from the participants based upon their recognized knowledge and 
expertise in the identified subject matter. 

The workshop participants were a diverse group, including:

-7 representatives of five different U.S. federal agencies;
-1 representative from a state dam safety agency;
-1 representative from a state environmental agency;
-7 representatives of six different consulting companies;
-4 independent consultants;
-1 university professor;
-1 representative of a hydropower organization; and
-Individuals from 10 different U.S. states, the District of Columbia, and Canada.

3.2 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, the 
following three goals were established. Those goals were: 

-To document the state-of-the-practice concerning cost-effective techniques for maintenance 
and replacement of components associated in dam outlet works. 

-To outline a scope for both the short-term (immediate) and long-term research and 
development needs with respect to dam outlet works. Research and development were 
broadly defined to include technology transfer. 

-To recommend a course of action to address the needs identified based on priorities factoring 
in potential benefit and cost/ease of implementation considerations. 

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. 

The six selected topics are presented in Exhibit 3-2. Furthermore, in order to focus discussion of 
the selected topics, white papers were prepared by invited experts and distributed to participants 
in advance of the workshop for review. A summary of the white paper topics and their authors is 
presented in Exhibit 3-3. 

3.3 WORKSHOP MECHANICS 
The workshop was conducted over three full days divided into six half-day periods. By grouping 
the presentation and discussion of Gates, Valves, and Controls (Topic 3), and Energy Dissipators 
(Topic 4) into one half-day period on the second day, the six selected topics were covered in five 
half-day periods, allowing the last half-day period to be allocated to reviewing, discussing, and 
prioritizing the leading research and development needs. The generic agenda for each of the five 
half-day periods during which the selected topics were discussed was as follows: 

-One-half hour  Presentation of a State-of-the-Practice white paper, prepared in advance 
by one or two (in the case of one paper) of the workshop participants. 

-One-half hour  Facilitated discussion of the white paper by all workshop participants to 

identify revision, modifications, and refinements to the State-of-the-Practice presented by 

the white paper author(s). 

-One-half hour  Facilitated brainstorming of possible research and development ideas that 
could advance the state-of-the practice. 

-One-quarter hour  Prioritization of possible research and development ideas that could 
advance the state-of-the-practice. 

-One hour  Small work groups established to develop preliminary implementation plans for 
the highest priority research and development ideas. (Typically 4 to 5 participants.) 

-One-half hour  Oral reports from the Implementation Work Groups were given to 
participants on preliminary implementation plans developed. 

Upon conclusion of the fifth half-day session on the third day, approximately 1 hour was devoted 
to reviewing, and discussing all of the leading research and development ideas for which 
preliminary implementations plans had been developed. Approximately 45 minutes were then 
allocated for each of the workshop participants to individually rank each of the research and 
development ideas according to both potential benefit and cost/ease of implementation. 

The discussions, research and development ideas, and preliminary research and development 
plans were captured on flipcharts and comment forms used during the workshop, for compilation 
and inclusion in this report. 

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

3.4 WHITE PAPERS 
After the six topics were selected and prior to the workshop, some of the workshop participants 
were invited to prepare white papers to provide documents that would be strawmen for 
definitions of state-of-the-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 to facilitate 
discussion 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 Exhibit 3-3, and the individual white papers 
are presented in Section 4 of this report. 

3.4.1 Discussion of White Papers 
The revisions, modifications, and refinements to the white papers provided by the participants 
were captured on flipcharts during the workshop and are reported in Section 4 of this report. The 
state-of-the-practice discussions for each of the six selected topics identified key areas of 
deficiency in both design and practice that need to be addressed either through the development 
of uniform standards for the various components of dam outlet works across the country or 
through further research and development initiatives. The discussions also indicated a 
widespread failure to routinely test components of dam outlet works to ensure their proper future 
functioning during the occurrence of an emergency condition. The adverse affects of human 
interference, tampering with operating equipment, and continued facility operations with known 
problems were also identified as pervasive and widespread problems that continued to be in need 
of redress. 

3.5 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 votes for one research and development idea, if he 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/ease of implementation. 

All of the research and development ideas generated in the workshop as well as the results of the 
prioritizations for all six topics are presented in Section 4 of this report. 

3.6 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 4 or 5 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 work independently for a period of time, and then 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. Work group leadership was rotated among workshop 
attendees with responsibility rotated among most of the participants over the course of the three 
days. 

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

3.7 OVERALL PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS 
The overall prioritization of the 20 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 of preliminary ideas considered for each of the six different 
topics. Participants were then asked to make an assessment of each R&D ideas potential benefit 
and associated implementation cost/ease of implementation by assigning a value between zero 
and ten as follows: high potential benefit would be indicated by assigning a value closer to 10, 
while an idea with low potential benefit would be indicated by assigning a value closer to 0; 
favorable low cost or ease of implementation would be indicated by assigning a value closer to 
10, while unfavorable high cost or difficulty to implement the R&D idea would be indicated by 
assigning a value closer to 0. The values for each of the research and development ideas 
assigned by each of the 16 participants were then averaged in order to determine overall rankings 
for each of the research and development ideas according to potential benefit, cost/ease of 
implementation, and on the combination of both factors. 

The prioritization of the 20 leading research and development ideas is discussed in detail in 
Section 5 of this report. 

EXHIBIT 3-1
WORKSHOP PARTICIPANTS

ORGANIZATION NAME ADDRESS PHONE/FAX EMAIL 
BC Hydro Charles Holder 6911 Southpoint Drive 
Burnaby, BC V3N 4X8 
P: 604-528-2418 
F: 604-528-8133 
charles.holder@bchydro.com 
Consultant Jack Cassidy 2884 Saklan Indian Drive 
Walnut Creek, CA 94595 
P: 925-933-5994 
F: 925-287-0802 jcassidys@aol.com 
Consultant Hank Falvey P.O. Box 4 
Conifer, CO 80433 
P: 303-838-4920 
F: 303-825-4920 
h.falvey@worldnet.att.net 
Consultant, URS Lee Gerbig 8181 East Tufts Avenue 
Denver, CO 80237 
P: 303-740-3906 
F: 303-694-3946 
lee_gerbig@urscorp.com 
Consultant Ed Rossilon 6505 West 31st Avenue 
Denver, CO 80214 
P: 303-233-2480 rosie6617@juno.com 
Department of Homeland Security, 
EPR/FEMA 
Gene Zeizel 500 C Street, S.W., Room 416 
Washington, D.C. 20472 
P: 202-646-2802 
F: 202-646-3990 
gene.zeizel@dhs.gov 
Federal Energy Regulatory Commission Dave Ricketts 
San Francisco Regional Office 
901 Market Street, Suite 350 
San Francisco, CA 94103-1778 
P: 415-369-3396 
F: 415-369-3322 dave.ricketts@ferc.gov 
Freese and Nicholls Ron Waters 4055 International Plaza, Suite 200 
Fort Worth, TX 
P: 817-735-7333 
F: 817-735-7490 
rhw@freese.com 
Gannett Fleming Robert Kline, Jr. 
PO Box 67100 
Harrisburg, PA 17106 
P: 717-763-7211 
x. 2657 
F: 717-763-1140 
rkline@gfnet.com 
MWH Americas, Inc. Mark Hammer 2353 130th Avenue NE, Suite 200 
Bellevue, WA 98005 
P: 425-896-6961 mark.a.hammer@mwhglobal.com 
NRCS-NDCSMC Wade Anderson 501 W. Felix, Bldg. 23 
Fort Worth, TX 76115 
P: 817-509-3764 
F: 817-509-3753 
wade.anderson@ftw.nrcs.usda.gov 
Schnabel Engineering Company Jimmy Crowder 5975 Shiloh Road, Suite 114 
Alphraretta, GA 30005 
P: 770-781-8008 
F: 770-781-8003 
jcrowder@schnabel-eng.com 
State of Colorado Mark Haynes 
Dam Safety Branch 
Colorado Division of Water Resources 
1313 Sherman Street, Room 818 
Denver, CO 80203 
P: 303-866-3585 
x. 8276 
F: 303-866-3589 
mark.haynes@state.co.us 
State of New Hampshire Jim Gallagher 
Department of Environmental Serv. 
P.O. Box 95, 6 Hazen Drive 
Concord, NH 03302-0095 
P: 603-271-1961 
F: 603-271-2982 jgallagher@des.state.nh.us 
URS Corporation Sal Todaro 8181 East Tufts Avenue 
Denver, CO 80237 
P: 303-740-2685 
F: 303-694-3946 salvatore_todaro@urscorp.com 
URS Corporation John France 8181 East Tufts Avenue 
Denver, CO 80237 
P: 303-740-3812 
F: 303-694-3946 
john_france@urscorp.com 
URS Corporation Richard Millet 8181 East Tufts Avenue 
Denver, CO 80237 
P: 303-740-3812 
F: 303-694-3946 
richard_millet@urscorp.com 
U.S. Army Corps of Engineers Ken Halstead P.O. Box 1159 
Cincinnati, OH 45201-1159 kenh@lrh.usace.army.mil 
U.S. Army Corps of Engineers Eric Holand P.O. Box 1159 
Cincinnati, OH 45201-1159 
eric.p.holand@saj02.usace.army.mil 
U.S. Army Corps of Engineers Robert Taylor P.O. Box 1159 
Cincinnati, OH 45201-1159 
P: 513-684-3804 
F: 513-684-6361 
robert.e.taylor@lrdor.usace.army.mil 
U.S. Bureau of Reclamation Chuck Cooper 
P.O. Box 25007, Mail Code D8130 
Building 67, Denver Federal Center 
Denver, CO 80225-0007 
P: 303-445-3262 
F: 303-445-6490 
ccooper@do.usbr.gov 
Utah Water Research Laboratory Michael Johnson USU Research Foundation P: 435-797-3176 
F: 435-797-0296 mikejnsn@cc.usu.edu 

EXHIBIT 3-2
WORKSHOP TOPICS

1. Outlet works failure modes including consideration of failure by seepage and piping 
mechanisms along outlet works conduits. 
2. Review of selection criteria, construction methods and the various conduit materials 
utilized in dam outlet works. Discussions included pipe material types and their 
advantages, disadvantages, and appropriate applications; hard foundations, soft 
foundations, and the operation of conduits under various pressure conditions. 
3. Discussion about the role and types of gates, valves, and controls used in the design of 
dam outlet works. Gate, valve, and control configurations, rehabilitation, and 
maintenance considerations were topics that were also discussed. 
4. Discussion about the role and various types of energy dissipators used in dam outlet 
works including stilling basins and energy dissipating valves. 
5. Rehabilitation of pipe conduit spillways through dams including in-place rehabilitation, 
replacement, reservoir evacuation criteria, and economic consideration. 
6. Review of the current state-of-the-practice regarding the frequency and scope of outlet 
works inspection. Systems, methods, techniques, and design criteria to accommodate 
inspection were also included in the discussion. 
REPORT OF WORKSHOP ON ISSUES, 
REMEDIES, AND RESEARCH NEEDS 
RELATED TO DAM OUTLET WORKS 

EXHIBIT 3-3 
WHITE PAPER AUTHORS AND TITLES 

Author(s) White Paper Title/Focus 
Sal Todaro Outlet Works Failure Modes 
Sal Todaro Design and Construction of Outlet Works Conduits for 
Embankment Dams 
Lee Gerbig Gates and Valves 
Henry Falvey Energy Dissipators 
James Crowder Rehabilitation of Pipe Conduit Spillways Through Dams 
Chuck Cooper Outlet Works Inspection 

SECTION FOUR 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 3-2. 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. Preliminary implementation 
plans were developed for four research and development for the combined topic of gates valves, 
controls and energy dissipators. Section 5 of the report discusses overall prioritization of the 20 
potential research and development plans that were developed separately for the six topics 
considered. 

4.1 TOPIC 1  OUTLET WORKS FAILURE MODES 

4.1.1 State-of-the-Practice White Paper 
The strawma n state-of-the-practice white paper for this topic was prepared by Rich Millet and 
Sal Todaro, and is presented in full in Attachment 4 of this report. A brief summary of the 
highlights of the paper is presented here. 

The primary causes of outlet works failures are: foundation related failures, structural 
deterioration, structural failures, mechanical failures, failures related to hydraulics, failures 
related to ice and sediment loadings, and operator error. In addition to being one of the leading 
causes of embankment dam failures, outlet works failures can also result in less catastrophic 
consequences like: the inability to make required reservoir releases; structural or mechanical 
conditions requiring emergency draining of the reservoir; or the uncontrolled release of water 
from the reservoir. The components of outlet works systems generally include intake structures, 
conduits or tunnels, control structures and energy dissipation structures when they are 
incorporated into the overall system design. Therefore failure in one or more parts of these 
system could lead at best to failure of the outlet works, and at worst, result in catastrophic failure 
of the embankment dam. 

Intake structures are those where water enters the outlet works and can be submerged structures, 
tower structures with multiple level inlet ports, or inclined structures located on a dam abutment 
with a single bottom inlet or with multiple level inlet ports. Intake gates, valves, and trash racks 
are the principle mechanical features on intake structures. These features are usually operated by 
mechanical control systems that include manual, motor driven, and hydraulic systems. The 
primary causes of gate and valve malfunction and failure include: the collection of debris, 
cavitation, ice, operator error, malfunctioning of gate operating mechanisms, lack of exercise, 
and deterioration from corrosion. Trash rack failure and malfunction usually result from 
plugging due to sediment, debris, or from plugging with frazil ice. 

The most common failure modes for intake structures are as follows: 

 Poor foundation condition resulting in differential settlement between the intake structure 
and the outlet conduit. Care should be taken to locate intake structures on firm bedrock 
whenever possible; 
 Premature deterioration of intake structures usually resulting from accelerated aging due 
to adverse environmental conditions including: damage from freeze-thaw processes; the 
use of poor concrete materials like alkaline aggregates; and exposure to water with either 
excessively high or low pH values which can accelerate the corrosion of reinforcement 
and cause concrete to deteriorate; 
 Loading from expanding reservoir ice usually resulting in damage to trash racks, gate 
stems, intake towers and piers for intake tower access; 
 Seismic loading from an earthquake resulting in the inoperability of components of the 
intake structures; 
 Accumulation of sediments in intake structures resulting from improper reservoir 
operation, upstream construction, and other land clearing activities like forest fires; 
 Hydraulic failures including cavitation of intake gates or areas at the intake structure or in 
the conduit downstream of the intake gate; 
 Air/Water related failures including the inadequate supply of air to control gates causing 
cavitation and vibration of the intake towers. Air blowback also creates operational 
problems and is caused when air and water are blown violently back into the intake 
structure in the reverse direction through the conduit; and 
 The occurrence of structural fatigue caused by vibration or collapse that results from the 
progressive plugging of the intake structure. 

Methods that can be used to prevent the failure of intake structures include: 

 Locating the intake structure on a rock foundation in order to reduce the magnitude of 
settlement effects; 
 Designing these structures to ensure that air demand requirements to prevent blowback, 
pipe collapse, and cavitation of control gates are satisfied; 
 Designing these structures to account for ice loading. Using bubbler systems to prevent 
ice formation is recommended; 
 Using an experienced mechanical engineer to design the mechanical components of 
outlet works systems; 
 Using reliable standard designs that have been developed and tested over time; 
 Locating the inlets of the intake structure to minimize sediment collection; and 
 Including consideration of vibration affects on trash racks. 

Conduit outlets are usually constructed through dams and can increase the risk of failure of 
embankment dams because of the potential for embankment piping near the conduit. Outlet 
conduits are usually made of cast-in-place concrete or constructed from manufactured pipe while 
pre-cast concrete, plastic, steel and ductile iron are materials commonly used in pipe fabrication. 
The four most common failure modes of outlet conduit through embankment dams are: 

1. Internal erosion of embankment into the conduit; 
2. Pressurized defects in the conduit casing resulting in embankment piping; 
3. Piping of the embankment along the outlet conduit; and 
4. Seepage through a fracture in the embankment near to the conduit. 

The three primary ways of minimizing the failure potential of outlet conduits are: 1) Filtering the 
dam embankment in the vicinity of the outlet conduit to prevent internal erosion of the 
embankment along or near the conduit; 2) Constructing outlet conduits on rock foundations 
when possible; and 3) Designing conduits with redundant features to prevent water seepage from 
the conduit into the embankment resulting in the piping of embankment materials into the 
conduit. By contrast, tunnel outlet works are separated from the dam embankment and are 
generally considered to be a safer than conduits. These tunnels are usually lined with cast in 
place concrete or welded steel. However, even if cost considerations allow a tunnel outlet works 
system to be considered a viable design alternative, construction of the tunnel too close to the 
dam can result in internal erosion of a dams embankment, even though the occurrence is rare. 

As the name implies, a control structure is one in which flow through the outlet works is 
controlled. Control structure location directly impacts the type of control devices used. 
Typically control valves may be located at intake structures, gate chambers or in a valve house at 
the downstream toe of the dam. The most common failure modes of these structures are 
associated with the failure or malfunction of gates, valves, or control systems used to operate 
these devices. To minimize the occurrence of failure therefore, it is recommended that the 
following be done: retain a mechanical engineer experienced in the design of gates, valves and 
mechanical systems for dam outlet works for both new design and rehabilitation activities; 
routinely test, operate and maintain components of control structures; and replace antiquated and 
unreliable gates, valves, and operators with newer, more reliable equipment. 

Finally, in order to prevent the uncontrolled erosion of the downstream channel in cases of direct 
discharge, care should also be taken in the design and maintenance of discharge mechanisms and 
in the use of energy dissipation structures. 

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: 

 Unwillingness of those involved to acknowledge viability of failure modes and resistance to 
thinking outside of the box. 
 Misoperation or lack of operation of outworks components because of the failure of 
automatic control systems stemming from conflicting program instructions, and the 
expiration of these programs. 
 Structural deterioration because of water chemistry and reaction with air and the deterioration 
of concrete because of the presence of hydrogen sulfide (H2S) in the water which can be 
evident in the presence of cavitation. 
 Cavitation because of inadequate air vents. 
 Seismic loading on intake towers. 
 Cracked concrete encasement resulting from earthquake loading and a discussion of 
allowable pressure on metal pipe, and the presence and role of buckled pipe in failure 
mechanisms. 
 Lateral or longitudinal joint offsets also know as embankment spreading due to earthquake 
loading. 
 Rupture of pressurized prestressed concrete cylinder pipe. 
 Plugging of air vents by those annoyed with the sound (e.g. campers). 
 The fact that entities will sometimes operate for a long time with a known problem. 
 Vandalism of operating equipment. 

4.1.3 Prioritization of Research and Development Ideas 
The group brainstorming process resulted in the generation of 11 potential research and 
development ideas, which were then prioritized by the group. The 11 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 4-5. Note that 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 4-5. 

4.2 TOPIC 2  CONDUIT MATERIALS, SELECTION CRITERIA, AND CONSTRUCTION METHODS 

4.2.1 State-of-the-Practice White Paper 
The strawman state-of-the-practice white paper for this topic was prepared by Sal Todaro, and is 
presented in full in Attachment 5 of this report. A brief summary of the highlights of the paper is 
presented here. 

Due to the absence of any single recognized standard for designing dam outlet works there is 
currently great inconsistency in design rationale and review processes for this design aspect of 
small and medium sized embankment dam facilities. The need for a single design standard is 
further underscored by the fact that outlet works have been identified as a significant contributor 
to the occurrence of embankment dam failures. While the similar design of outlet works at all 
small and medium sized embankment dams is not proposed, consistency should exist in the 
guidelines and criteria used to prepare designs for these structures. Design guidelines could 
include recommendations for pipe encasement, the need for redundancy, seepage control, 
methods for addressing compressible foundations, pipe selection, joint details, and criteria for 
reinforced concrete conduit design. 

A single, nationally recognized standard would lead to greater consistency between similar 
project designs, facilitate more effective and consistent review of proposed designs, and result in 
increased potential for safer more reliable facilities. The National Dam Safety Review Board 
(NSRB) is in the process of preparing a manual to be used for designing and maintaining outlet 
works for significant high-hazard dams. The manual covers topics for the design, construction, 
maintenance, and repair of conduits for embankment dams. It is recommended that in the 
interim the guidelines presented in this manual be used to form a design basis for smaller 
facilities. 

By determining best practices for designing and constructing outlet works, and by preparing 
nationally accepted standards to be used for engineering review, important improvements in 
outlet works design methods and construction procedures can be achieved. Furthermore, dam 
safety officials could then require and enforce minimum standards for all new non-federal 
designs, simplifying the task of design engineers by providing a consistent standard for design 
they know will be accepted by review agencies. 

Presently, the use of standards not intended for use in designing pressurized outlet systems for 
embankment dams is the most common practice that introduces additional risk to outlet works 
for smaller embankment dams. Examples of the misapplication of design standards to design 
outlet works include the following: 

 Use of State Highway Department standard plans for culverts and culvert structures 
even though culvert designs for highways were not intended for use in dams. 
 Use of Natural Resources Conservation Service (NRCS) standards for the structural 
design of flood control outlets to design high-hazard pressurized outlet facilities even 
though these standards were not intended for such application, and 
 Use of the precast concrete outlet pipe detail with partial encasement shown in the 
USBRs Design of Small Dams for pressurized outlet works for high-hazard dams. 
This detail allows embankments to be placed directly against the pipe surface which 
is an area where leakage from the pipe joint has direct access to the embankment. 

The creation of an approved standard would therefore reduce the use of inappropriate design 
standards. The USBR and U.S. Army Corps of Engineers (USACE) design standards for outlet 
works combined with the forthcoming NSRB manual could form a basis for preparing a single 
design and construction standard for smaller dam outlet facilities. 

Appropriate modifications that may be required due to variability in foundation conditions 
should also be included in the proposed design manual. Where possible, outlet works structures 
should be founded on firm non-erodable foundations. However, variable foundation conditions 
may result in the founding of outlet works structures upon compressible foundations that are 
subject to differential foundation settlement and movement. Soft foundation conditions incur 
greater risk of embankment piping and structural distress of the conduit. Foundation movements 
are especially dangerous for rigid outlet pipes with open gasketed joints. Therefore outlet 
conduit should be located on uniform foundations whenever possible to prevent abrupt changes 
in conduit settlement. 

Recommended approaches to the design of outlet conduits on soft foundations include: 1) 
Placement of freestanding pressurized outlet pipe inside of a cast-in-place reinforced concrete 
conduit; 2) Use of a non-pressurized outlet works system; 3) Use of welded steel outlet pipe 
encased in reinforced concrete; 4) Use of articulated joints for the outlet conduit; and 5) 
Protecting the foundations integrity during construction. 

While various pipe materials have particular advantages and disadvantages, the ones most 
commonly used for outlet works conduits are: cast-in-place reinforced concrete; welded steel 
pipe encased in reinforced concrete, high density polyethylene (HDPE) pipe, ductile iron pipe, 
and reinforced concrete pressure (RCP) pipe. 

While not usually cons idered as a design alternative where soft ground conditions are 
encountered, tunnel outlet works present several distinct technical advantages when compared to 
cut-and-cover outlet conduit designs, especially for pressurized outlets. These advantages 
include: 

 Elimination of embankment failure modes associated with conduit outlet works. 
 Stream diversion capabilities around the dam site during construction. 
 Construction of tunnel outlet works independent of embankment construction. 
 Embankment placement unobstructed by the outlet conduit 
 Elimination of special compaction requirements, and the need for special filter placement required for conduit systems.

However, tunnel outlet works systems are often more expensive than conduit systems and 
typically involve more cost risk for overruns. Thus, development of cost curves for tunnel 
outlets based on outlet diameter would be helpful allowing engineers to compare cost/ease of 
implementations for preliminary evaluations of tunnel and conduit outlets. The design standard 
would therefore provide a consistent design approach, and allow various design alternatives to be 
evaluated and considered in a systematic and rational manner. 

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: 

 Conduits need to be large enough for inspection and repair. 
 Bends in conduit alignments can eliminate repair/rehabilitation options (e.g. slip-lining). 
 Concrete-encased, welded steel pipe conduits need to be designed for full reservoir pressure 
on the outside of the pipe. Leaks in the encasement and associated buckling failures have 
been caused by pressure between the steel pipe and the encasement. 
 Conduit sizing criteria (e.g. for evacuation) vary among different jurisdictions, and sizing 
criteria do not exist for some jurisdictions. 
 There are a number of negative factors for conduit configurations through embankments in 
addition to those sited in the white paper: 

o Lack of sufficiently detailed geotechnical information along the alignment to calculate 
settlements (total and differential). 
o Differential settlement at material contacts (embankment zones and different 
foundation materials) is expected. 
o Many opportunities exist for improper construction to lead to problems. 

 Diving technologies are available for maintaining, rehabilitating, and replacing deep, 
underwater, upstream gates; however, these technologies are very expensive. 
 Outlet tower/intake configurations vary widely. Examples include freestanding, upstream 
towers; inclined, on-slope, upstream intakes structures; towers within the embankment 
between the upstream toe and the crest, with an upstream, underwater inlet. 
 There has been an increasing desire from some owners and some material manufacturers to 
use plastic pipes (e.g. HDPE), but accepted standards for use of this type of pipe in dams do 
not exist. FEMA is sponsoring a Best-Practices Guide for use of plastic pipe in embankment 
dams, which should address this issue. 
 Some engineers and owners still propose use of corrugated metal pipe (CMP) conduits in 
embankments, but it is unusual. Most regulators will not accept it for high and significant 
hazard dams. 
 Analysis methodologies have improved dramatically: 3-D analysis now available instead of 
1-D; and soil structure interaction included in many programs like FLAC, and Plaxis. 
 For design loads, we are still typically using old guidance (e.g. Marston equations), even with 
a sense that these loads are conservative (i.e. too high). 
 AWWA guidelines and ASCE penstock guidelines are available for steel pipe design. ASCE 
guidelines are more appropriate for high pressure and transient flow. 
 Pressurized downstream control conduits exist in some older facilities and in some retrofits 
for inoperative upstream gates. Proposals for new installations with downstream control are 
typically concrete-encased steel, but there are exceptions. 

4.2.3 Prioritization of Research and Development Ideas 
The group brainstorming process resulted in the generation of 7 potential research and 
development ideas, which were then prioritized by the group. The 7 ideas and the results of the 
prioritization are presented in Exhibit 4-6. 

4.2.4 Preliminary Research and Development Plans 
The top four ideas listed in Exhibit 4-6 were selected for development of preliminary 
implementation plans, and those plans are presented in Exhibits 4-7 through 4-10. In some 
cases, the individual work groups reworded the research and development idea, so the ideas 
listed in Exhibit 4-6 may not exactly match the ideas listed in Exhibits 4-7 through 4-10. 

4.3 TOPIC 3 - GATES, VALVES, AND CONTROLS 

4.3.1 State-of-the-Practice White Paper 
The strawman state-of-the-practice white paper for this topic was prepared by Lee Gerbig, and is 
presented in full in Attachment 6 of this report. A brief summary of the highlights of the paper is 
presented here. 

Releases from outlet works are often controlled to maintain river flows, provide water for 
irrigation, to a water treatment facility, or to an industrial user, and to lower reservoir levels in 
the event of an emergency. Gates and valves are the two general names for the types of 
equipment used to control the release of water in outlet works systems. A gate is a mechanical 
device with a slid ing flat member within a square or rectangular framework or structure that 
controls the flow of water. A valve is usually a circular structure with a sliding member, flat or 
circular, that controls the flow of water. 

The types of gates commonly used at newer dam sites are: Slide gates, Knife gates, Jet-flow 
gates, Clamshell gates, Radial gates, and Hinged Crest gates. Slide gates, also known as Sluice 
gates, are the most common type of gate used for dam outlet works. These devices have a 
movable leaf or disk which slides against bearing surfaces in the frame. The frame is attached to 
a conduit or wall, which provides support against the water load of the gate. The gate leaf is 
moved by a gate stem, which is operated by a manual hand wheel or crank, electric motor-
operator, or hydraulic cylinder. 

For applications where the head does not exceed 100 feet, the two types of slide gates commonly 
used are the Cast Iron Slide gate and the Fabricated Slide gate. As the name implies, both the 
rectangular gate leaf and frame of a Cast Iron Slide gate is fabricated from cast iron. Gate 
leakage from this type of slide gate is usually very low, seldom exceeding 0.1 gal/minute/foot of 
the perimeter of the leaf gate. Fabricated Slide gates are made from a variety of materials 
including steel, stainless steel, and aluminum. The gate leaf uses the metal plate as a sliding 
surface against low friction material attached to the frame. Typical leakage from this type of 
slide gate is 0.05 gal/minute/foot of the perimeter of the leaf gate. 

For applications where the head exceeds 100 feet, Bonneted Slide gates and Wheel gates are 
commonly used. Bonneted slide gates are similar in design to Fabricated Slide gates, except that 
the body is fabricated to completely enclose the gate leaf. This type of slide gate is usually 
embedded in reinforced concrete to provide additional structural reinforcement for the 
pressurized gate body. In Wheel gates, the gate leaf is fitted with multiple wheels that ride on 
rails attached to the face of the structure. It should also be noted that Wheel gates could be 
designed to close by gravity in the event of an emergency. However, one of the main drawbacks 
with Wheel gates is difficult installation due to the critical alignment that is required to achieve 
smooth operation and effective sealing. Due to susceptibility to corrosion and the build up of 
deposits that increase friction and affect the operation of its roller train, the use of Roller gates is 
increasingly avoided even though this was a type of slide gate that was also used for high head 
applications. 

Knife gates and Jet-flow gates are two other variations of the slide gate. While Knife gates are 
not commonly used in the hydropower or dam industry, Jet-flow gates are commonly used as 
freely discharging devices. The gate has a circular opening with a sliding disk that moves over a 
floating, sloping orifice shaped opening. The sloping orifice concentrates the flow to help 
introduce air to prevent cavitation. The Clamshell gate is a special design used by the U.S. 
Bureau of Reclamation consisting of two leafs operating in an arc over the end of a conduit, and 
machined to match the arc of the gate leafs. The gate leafs move in a symmetrical manner to 
provide uniform flow between the two leafs and allow this device to work very well in 
submerged installations. Radial gates have been used for many installations at spillways, canal 
check structures, and canal turnouts. Hinged Crest gates are used at the crest of a spillway, to 
allow flow overtopping the gate to regulate the reservoir or pool elevation. The gate consists of a 
flat or slightly curved plate structure, with a hinge system at the bottom to allow the gate to 
rotate from near vertical to horizontal. 

Valve types commonly used are: Butterfly valves, Gate valves, Fixed-Cone valves, and Sleeve 
valves. Butterfly valves are commonly used at power plants and water facilities and have a 
circular body with a circular disk in the fluid way that rotates around a shaft in the centerline of 
the valve, perpendicular to the flow. The flow velocities through butterfly valves are usually 
limited to 25 to 30 feet per second, although high-performance butterfly valves can operate up 
top 50 feet per second. Butterfly valve operating forces are very low, with very little friction and 
hydraulic effects. They may be operated manually, by electric motor-operators, or by hydraulic 
operation. A Gate valve is a variation of a slide gate, with a circular body and disk. They are 
often used for guard gates upstream of regulating valves, or used for throttling flow in low-head 
applications. A Fixed-Cone valve is commonly used for regulating the flow of water from a dam 
outlet works. This cylindrical valve has a sliding sleeve that covers the opening at the 
downstream end of the valve. Sleeve valves are used as energy dissipaters, both in-line and at 
the end of a conduit and are usually operated to provide precise flow control. Due to high costs 
and problems with corrosion, seat erosion, cavitation damage, or general maintenance difficulties 
there has been a decreased incidence of Needle valves and Hollow-Jet valves. 

The four basic types of gate operation systems are: manual operators, electric motor-operators, 
hydraulic operators, and pneumatic operators. Manual operation usually involves use of a crank 
or handwheel connected to the gate or valve operating mechanism with threaded stems or a 
gearbox arrangement. Electric motor-operators also provide either linear motion with threaded 
stems or rotary motion converted to linear motion. Electric motor-operators are usually designed 
for outdoor applications, with weatherproof enclosures. In the event of an interruption in power, 
hand wheels are usually provided on these units for back up manual operation. Hydraulic 
operation is most often used on large gates and valves operating at high head, but is becoming 
more common for small equipment at low heads for particular installations. Pneumatic operators 
are rarely used for operating gates and valves. The problem with pneumatic operation in typical 
gates and valves is that, with the air, being compressible, it is difficult to maintain a set position. 
Portable drills, portable hydraulic operators, and chain saw operators are the most common 
portable operators that are available to work in conjunction with manual operators. 

With increased equipment reliability and performance, remote and hydraulic operation of gates 
and valves occurs more frequently. Remote sensing may be achieved using electric motor 
operators, hydraulic cylinders, and inclinometers. Improved hydraulic fluids suitable for outdoor 
use, submerged hydraulic operation, use of better seals, and automated operation features has 
inspired increased use of hydraulic components in the design of gates and valves. 

However, the design and fabrication of gates and vales has increasingly shifted overseas with 
major US manufacturers in the process emerging from bankruptcy proceedings. However the 
ultimate effect of offshore fabrication and the disappearance of longstanding US-based gate and 
valve manufactures is the significant decrease in the number of gate designers in the United 
States. Moreover, with government agencies like USBR, USACE, and TVA scaling back dam 
design and construction phases of work, there has also been a corresponding decrease in the 
amount of available research on new equipment and operation. 

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: 

 There are two versions of hoods on fixed-cone valves: in one configuration the hood is 
connected to the body of the valve and moves with the valve, while in the other the hood is 
separate from the body of the valve and stays in a fixed position. 
 A hood on the fixed cone valve limits the applicable head to about 175 feet. 
 A bullnose bottom should be used if a slide gate will be used for regulating the flow. This 
works well up to heads of at least 75 feet, and possibly as much as 100 feet. 
 Although it is desirable to design outlet works with non-pressure conduits, it can be difficult 
to design upstream control for outlet works systems for high heads. There is a lack of 
confidence in the available gates and valves for these high head, flow control applications. 
 Gates intended to close against head may not be as reliable as we would like. 
 AWWA standards for design of stems and operators may not be adequate for dam outlet 
works. The stems can be too easily overloaded and buckle. 
 There have been frequent problems with leakage of slide gates mounted in the unseating 
direction (relative to the head). 
 There is a lack of industry-wide knowledge of the potential for catapulting of gates because 
of insufficient airflow. 
 Butterfly valves and operators can be designed to fail in the open or closed position. Design 
needs to consider which is preferred for that particular installation. If the valve fails in the 
closed position, dampers may be needed to slow the rate of closing to prevent surge damage. 
 There have been problems with the corrosion of butterfly valve bushings or stems, resulting 
in valves that did not close, as intended. 

4.3.3 Prioritization of Research and Development Ideas 
Since this topic had been combined with the topic on energy dissipators, the group brainstorming 
process resulted in the generation of 10 potential research and development ideas for the 
combined topics. The group then prioritized these topics and an overall ranking of research and 
development ideas for the combined topics was generated. The 10 ideas and the results of the 
prioritization are presented in Exhibit 4-11. 

4.3.4 Preliminary Research and Development Plans 
The top four ideas listed in Exhibit 4-11 were selected for development of preliminary 
implementation plans. The ideas directly related to the topics of gates, valves, and controls are 
presented in Exhibit 4-12, Exhibit 4-14, and Exhibit 4-15. In some cases, the individual work 
groups reworded the research and development idea, so the ideas listed in Exhibit 4-11 may not 
exactly match the ideas listed in Exhibit 4-12 and Exhibits 4-14 and 4-15. 

4.4 TOPIC 4  ENERGY DISSIPATORS 

4.4.1 State-of-the-Practice White Paper 
The strawman state-of-the-practice white paper for this topic was prepared by Henry Falvey, and 
is presented in full in Attachment 7 of this report. A brief summary of the highlights of the paper 
is presented here. 

Almost every outlet works requires an energy dissipator so that the high-energy flow from the 
reservoir does not damage the downstream channel or structures. While the laws of conservation 
of energy technically prohibit energy from being dissipated, energy dissipators enable energy 
conversion for high energy water flows by: creating fine grain turbulence; and creating a loss 
through a change in the flows momentum. Wide varieties of structures are available to 
designers to dissipate high head-high energy flows from outlet works. Many designs have been 
developed for site-specific installations that have not appeared in the literature and it should be 
also noted that some of these designs have also not been verified by either modeling or prototype 
tests. 

However, energy dissipators that have been successfully used at outlet works include: stilling 
basins, impact basins, stilling wells, various types of valves, sudden enlargements, in-line 
orifices, flip buckets, and plunge pools. Outlets works can incorporate a combination of 
different types of energy dissipators. The types of energy dissipators used depend on the design 
reservoir head, discharge requirements, and cost constraints of a particular design. 

USBR Engineering Monograph 25 provides a thorough discussion of the design elements for 
stilling basins, impact basins, flip buckets, and baffled aprons. General guidelines for designing 
outlet works are provided in both USACE Engineering Manual EM 1110-2-1602 and in Design 
of Small Dams published by the USBR. 

The USBR defines three types of hydraulic jump stilling basins. The Type I Basin is simply the 
combination of a hydraulic jump with a horizontal apron with energy dissipation accomplished 
by turbulence created within the jump. Type II Basins contain chute blocks located at the end of 
the basin and a dentated end sill. The chute blocks create shear zones that generate fine grain 
turbulence while the end sill prevents downstream erosion and does not contribute significantly 
to energy dissipation. The Type III Basin contains an additional set of baffle blocks within the 
horizontal apron to create additional turbulence. The combination of chute blocks and baffle 
blocks allows the length of the stilling basin to be reduced. 

Reclamation classifies impact basins as Type VI Basins. In these structures energy is dissipated 
by turbulence that is generated when a jet of water makes impact with a vertical wall. Although 
Reclamation limits the dimensions and discharges of impact basins to relatively low energy 
levels, the basins have been used successfully at much higher energy levels by scaling the 
recommended dimensions to the larger sizes. 

Stilling wells are frequently used for low discharge flows into canals. Energy dissipation is 
achieved by the change in momentum between the water entering the well through the pipe and 
the flow up the square well. Flow is controlled by changing the size of the opening using a 
sleeve valve on the bottom of the down comer pipe. 

For applications with high head or high flow requirements, fixed-cone valves are normally used 
to dissipate energy. These valves can use the principle of impinging jets and baffles downstream 
of the valve to provide energy dissipation. It should be noted however, that the distance between 
the end of the fixed cone valve and the hood is critical as severe blowback has been experienced 
in prototype installations where this distance was off by only an inch or two. 

Sudden enlargements occurring within or at the end of a pipeline can be very effective energy 
dissipators. Precautions must be taken during the design of these features to ensure that the 
formation of cavitation within the structure is minimized even though some ranges of operating 
conditions will still generate cavitation. Incorporation of a series of in-line orifices into a 
pipeline also utilizes the energy dissipation function of sudden enlargements. 

Flip buckets are often used at the end of an outlet chute to throw discharge flow away from the 
toe of the dam. Flip buckets are actually not energy dissipation devices although they are 
designated as such in the USBR Engineering Monograph No. 25. Dentates are frequently used 
to spread the compact jet and increase the area over which the jet enters the plunge pool thereby 
decreasing the energy per unit area of the inflow jet. 

Plunge pools are commonly used in combination with flip buckets and are designed to minimize 
the erosion of the downstream channel that a plunging jet of water can cause. Care must be 
taken in the design of these structures since material excavated by a plunging jet of water can 
raise the tailwater in the pool such that it sufficiently drowns out the effects of the flip bucket. 

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: 

 There have been problems with backflows in USBR-type stilling basins. The backflows have 
drawn rock and soil materials into the basins, sometimes leading to ball-milling and related 
damage. 
 There is a lack of available information on ultimate development of plunge pool basins in 
rock including ultimate size and depth. A Swiss engineer is doing some work in this area, as 
is George Annandale, with work to be published soon. 
 There have been cases where energy dissipation characteristics have been affected by valve 
changes. Examples offe red at the workshop include changing geometry/dimensions for 
fixed-cone valve installations and replacement of needle valves with fixed-cone valves. 
 There is a lack of widespread, definitive knowledge about reliable repair techniques for 
energy dissipators  one available source is the USACE REMR documents. 
 There is a lack of specific guidelines on the extent and size of riprap required downstream of 
energy dissipators. This can contribute to a ball-milling problem, if the riprap is small 
enough to be drawn into the stilling basin. Grouted riprap has sometimes been used to 
address this concern. 
 The sleeve valve concept has been modified in some applications to consist of a fixed section 
of pipe with holes and an upstream control valve. This concept has been used for 
intermittent flows with a limited range of discharge. 
 No guidelines are available on the appropriate frequency of inspection of stilling basins. 
 With increased use of failure modes analysis, downstream erosion and undercutting of 
stilling basins or concrete dams is becoming an increasingly frequent concern. Methods for 
reliably evaluating this issue are not readily available. 
 Vandalism leading to ball-milling is a problem which often results from people throwing 
rocks into stilling basins. This has lead to measures to make it more difficult to throw rocks 
into the structures. 
 Public safety can be an issue for stilling basins. People will swim in the basins, and sloping 
downstream ends of the basins can make it difficult for people to get out of them. Steps in 
place of the sloped surface have been used to address this safety concern. 

4.4.3 Prioritization of Research and Development Ideas 
Since this topic had been combined with the topic on gates, valves and controls, the group 
brainstorming process resulted in the generation of 10 potential research and development ideas 
for the combined topics. The group then prioritized these topics and an overall ranking of 
research and development ideas for the combined topics was generated. The 10 ideas and the 
results of the prioritization are presented in Exhibit 4-11. 

4.4.4 Preliminary Research and Development Plans 
The top four ideas listed in Exhibit 4-11 were selected for development of preliminary 
implementation plans. The idea directly related to the topic of energy dissipators is presented in 
Exhibit 4-13. 

4.5 TOPIC 5  REHABILITATION OF CONDUITS 

4.5.1 State-of-the-Practice White Paper 
The strawman state-of-the-practice white paper for this topic was prepared by James Crowder, 
and is presented in full in Attachment 8 of this report. A brief summary of the highlights of the 
paper is presented here. 

Corrugated metal pipe (CMP) commonly serves as the conduit found in small earthen 
embankment dams ranging in height from 10 to 50 feet constructed between 30 and 50 years ago 
in the southeastern United States. Compared to conduit materials used in newer dams, CMP is 
highly susceptible to deterioration and becomes a problem when a spillway conduit has reached 
or exceeded its design service life, generally considered to be 25 to 30 years. Earthfill 
embankments of this vintage were often constructed with CMP spillway conduits passing 
through the base/foundation of the embankment. The deterioration of these conduits generally 
consists of leaking joints, corrosion, and holes in the pipe. 

The main risk associated with the deterioration of these conduits is piping of the surrounding 
embankment soils into the conduit, which can lead to the eventual failure of the earthen 
embankment. Owners of most old embankment dams exhibiting problems with CMP conduits 
usually have a number of concerns or issues that will usually involve several remediation or 
repair options. The four primary options discussed, including the advantages and disadvantages 
of each method, are based upon the experiences of the author in the Southeast United States and 
are mainly limited to CMPs in earthen dams having a maximum height of 50 feet. These options 
include: 

 Replacement of the existing pipe conduit using cut and cover methods; 
 Sliplining the existing conduit; 
 Grouting along the exterior of the existing conduit; and 
 Constructing either a siphon spillway or short riser and new outlet conduit after the existing conduit has been abandoned. 

In order to replace the existing conduit, excavation of the earthen embankment, removal of the 
deteriorated conduit, installation or construction of a new conduit, and backfill of the excavation 
is required. The side slopes of the excavation through embankment dams are typically limited to 
2H: 1V or flatter, in order to facilitate compaction of the replacement backfill against the existing 
embankment. On relatively high embankments in narrow valleys, the excavation required to 
remove the existing low-level conduit may necessitate the removal of nearly the entire dam. The 
replacement option typically offers the greatest operational flexibility among the spillway 
rehabilitation options. This option typically offers the most thorough rehabilitation option for 
impaired conduits through dams, although this option can be cost-prohibitive. 

Sliplining an existing pipe consists of placing a new pipe with a smaller diameter inside the 
existing deteriorated conduit and grouting the annular space between the two pipes. Depending 
on the pipe used, sliplining may increase the hydraulic capacity of the outlet pipe, even when 
reducing the inside diameter of the original pipe by reducing the roughness of the pipe. When 
designed and installed properly, the slipline technique will also add additional years to the 
service life to the existing conduit spillway. A sand diaphragm drain is typically installed around 
the downstream portion of the existing conduit to limit the potential for soil piping as the CMP 
eventually corrodes and deteriorates. 

Grouting along the exterior of an existing conduit is often used to rehabilitate conduits that 
exhibit seepage through joints or deteriorated portions of the existing pipe wall. Grouting fills 
voids that may have been created, and to plug openings in the pipe walls or joints. Cementitious 
or chemical grouts are typically utilized for the purpose. Injection of the materials can be 
performed either from the surface of the embankment or from the interior of the conduit. This 
approach requires the availability of working room for grouting equipment and personnel. Use 
of this method, however, is limited by the depth of the conduit below the embankment surface, 
and whether the remediation is performed with the lake full. Injection of the grout from the 
interior of the pipe typically offers a better opportunity to deliver the grout to specified areas. 
Drilling through the embankment to grout along the conduit is usually performed for small 
diameter conduits or when the pipe is very shallow within the embankment. The greater the 
depth of fill over the conduit, the less certainty the grouting procedures are impacting the 
targeted areas. Drilling through the embankment is not practical for situations in which the lake 
cannot be drained and portions of the conduit within the upstream slope of the dam are to be 
grouted. Moreover, this type of repair is generally classified as temporary and does not extend 
the design life of the existing conduit material. Grouting of the exterior of a conduit pipe also 
retains the stage/discharge relationship of the existing spillway. 

Abandonment consists of completely grouting the interior of the existing CMP with either a 
sand/cement grout or a gravel/sand/cement grout. In either scenario, an expansive chemical 
admixture is typically included in the grout mix to control or reduce shrinkage during curing of 
the grout. Siphons have been used successfully in the southeast but are generally limited to 
small drainage basins with relatively small peak inflows. Siphons can be constructed of flexible 
conduit such as PVC, HDPE, or Ductile Iron. Siphon spillways do not typically exceed 12inches 
in diameter. Abandonment of an existing conduit and construction of a short riser and 
pipe spillway may be considered to be a modified version of the traditional pipe-and-riser 
spillway system or an economical hood inlet spillway system. Usually, the riser invert is set a 
vertical distance below normal pool equal to 1/5 to  of maximum water depth at the upstream 
toe of the dam. The conduit invert should be a minimum depth of 1.5 diameters below the pool 
elevation to avoid the capture of air due to surface water drawdown, and the associated 
slugging under full flow conditions. Installation of the siphon also requires excavation of the 
embankment below normal pool. 

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: 

 There is limited guidance available on siphon outlet design. EPRI published a document a 
number of years ago. 
 Lack of guidelines for design of sliplining rehabilitation, including issues such as design 
criteria, grout characteristics (shrinkage), construction issues, etc. 
 Feasibility of sliplining can be limited by configuration of conduit and associated gates and 
valves  e.g. difficulty often exists in sealing the lining located next to the gate or valve. 
 BC Hydro has done some replacement of underwater, upstream structures, including 
control/guard gates. 
 Cured-in-place (CIP) linings (e.g. Insituform) have been used for outlet conduit 
rehabilitation. 
 NRCS has done one installation in Texas replacing a conduit by augering through an 
embankment dam. NRCS is considering use of microtunneling for other projects. 
 Tunneling and microtunneling through a rock (sometimes soft rock) abutment with a lake tap 
with a full reservoir has been used and example of which was at Standley Lake located in 
Westminster, Colorado. 
 A case was cited where an outlet works in a concrete dam in Texas was rehabilitated to 
replace the upstream gates and line the conduits. The upstream square-to-round transition 
was found to be badly deteriorated and was reformed using Belzona polymer. 
 Epoxy paints have become the preferred standard for paint coatings of outlet works conduits. 
 Repainting of conduits can be very difficult  hard to get moisture and temperature in a 
suitable range for application of a durable coating application; also access is difficult, and in 
some cases impractical, for small diameter conduits. 
 Lead paint on existing structures can cause problems in repainting of conduits and other 
outlet components. There are a few products available that can be used to render the lead 
paint debris non-hazardous. 
 Asbestos in some operating equipment can cause some environmental problems with 
rehabilitation. 

4.5.3 Prioritization of Research and Development Ideas 
The group brainstorming process resulted in the generation of 13 potential research and 
development ideas, which were then prioritized by the group. The 13 ideas and the results of the 
prioritization are presented in Exhibit 4-16. 

4.5.4 Preliminary Research and Development Plans 
The top four ideas listed in Exhibit 4-16 were selected for development of preliminary 
implementation plans, and those plans are presented in Exhibits 4-17 through 4-20. In some 
cases, the individual work groups reworded the research and development idea, so the ideas 
listed in Exhibit 4-16 may not exactly match the ideas listed in Exhibits 4-17 through 4-20. 

4.6 TOPIC 6  OUTLET WORKS INSPECTION 

4.6.1 State-of-the-Practice White Paper 
The strawman state-of-the-practice white paper for this topic was prepared by Chuck Cooper, 
and is presented in full in Attachment 9 of this report. A brief summary of the highlights of the 
paper is presented here. 

Inspection of cut-andcover outlet works typically includes review of features including: the 
entrance channel; intake structure; conduit(s); terminal structures; and the downstream channel. 
While there are several methodologies that may be employed in inspections, the advantages and 
disadvantages of each method should be assessed with due consideration given to the ease and 
efficiency with which inspection objectives can be met; compliance with health and safety 
guidelines, and cost. 

The purpose of an outlet works inspection program is to ensure that conduits through dams are 
safely and efficiently operated and maintained. Factors to be considered in specifying inspection 
programs include inspection frequency; consideration of the systems, methods, and techniques 
used for inspection; and compliance with design criteria. Inspection intervals may vary 
depending on the overall conditions determined from previous inspections and the existence of 
any dam safety concerns. Inspections primarily vary according to scope, and frequency. The 
five types of inspections generally conducted are: initial or formal; periodic or intermediate; 
routine; special; and emergency. 

Initial or formal inspections include in depth review of all pertinent data available for the outlet 
works to be inspected. Design and construction data are evaluated relative to current state-ofthe-
art guidelines to identify potential dam safety problems or areas requiring particular 
attention. During these inspections, an attempt is made to operate all mechanical equipment 
through their full operating range, if possible. Periodic or intermediate inspections are conducted 
between formal inspections and all mechanical equipment may not be tested during a particular 
inspection. Field or operating personnel typically conduct routine inspections. The primary 
focus in these inspections is the current condition of the outlet works. These inspections may be 
scheduled on a regular basis or performed in conjunction with other routine tasks. Special 
inspections are conducted when a unique opportunity, like low water conditions, exist. 
Emergency inspections are performed when an immediate dam safety concern is present or in the 
event of an unusual or potentially adverse condition like those resulting from the occurrence of 
an earthquake. 

Scheduling periodic outlet works inspections may be influenced by the following factors: 
provision of sufficient notice to dam owners and operators allowing necessary arrangements and 
pre-inspection activities to be completed and needed clearances to be obtained; the ability to 
access most or all of the major components of the outlet works; and the opportunity to observe 
features operating under a wide range of conditions. Inspections of features like intake structures 
and upstream conduits that are usually submerged require special coordination with the dam 
owners since the timing of such inspections has to be carefully orchestrated and planned for. 

Factors that should be considered when determining the frequency of inspection for features that 
are usually inundated include: 

 The critical function of the feature to overall dam operations; 
 Operational history and performance record of the feature since its last inspection; 
 Condition of the concrete; 
 Age of the feature; 
 Condition of the embankment and foundation and the presence of faults in the 
foundation;
 Observed seepage; 
 Changes in the discharge capacity of the outlet works; 
 Observed damage or deterioration to visible features in the vicinity of the submerged 
feature; 
 Water quality detrimental to concrete; 
 Consideration of the secondary inspection costs including costs associated with lost water 
and power revenues, to provide inspection access to a feature; 
 Design and construction considerations; 
 Changes in relevant standards or guidelines; 
 Presence of unfavorable stresses conducive to arching; 
 Lack of filters and drainage material around the conduit downstream from the impervious 
zone of the embankment to convey seepage safely; and the 
 Presence of any site conditions that may compromise the safety of the feature, and 
ultimately the safety of the dam. 

The USBR has designated three inspection frequencies at which high hazard dams are inspected 
in order to detect potential dam safety deficiencies at a site. They are: annual, periodic, and 
comprehensive. Generalist engineers familiar with the dam and its operations, who can readily 
distinguish changes from year to year at the site, conduct annual inspections. Periodic 
inspections, also known as Periodic Facility Reviews (PFR) occur on a 6-year cycle and are 
conducted by a team from a regional office of the USBR that includes the regional examination 
specialist. Comprehensive inspections, also known as Comprehensive Facility Reviews (CFR) 
alternate on six-year cycles with the PFR and include examination and evaluation of the dam 
facility by a team of specialists from USBRs Technical Service Center. 

The NRCS requires the sponsor/owner of a dam to be responsible for making inspections after 
the sponsor/owner assumes responsibility for a dam. Special, annual, and formal (once every 5 
years) inspections are performed by personnel trained in conducting the inspections. 

The U.S. Army Corps of Engineers (USACE) performs periodic, intermediate, and informal 
inspections on the basis of project size, importance, or potential hazard as follows: 

 Initial periodic inspection  includes inspection and evaluation of a new earth or rockfill 
dam and is carried out immediately after topping out of the embankment prior to 
impoundment of the pool. 
 Second periodic inspection  performed no later than one year after impoundment is 
initiated. 
 Subsequent periodic inspections  performed at one-year intervals for the next two years 
of dam life. The next two inspections are performed at two-year intervals and then 
extended to a maximum interval of five years. 
 Intermediate inspections  are performed for all or some of the features of dams on a 
five-year inspection cycle, if warranted. Selection is based on consequences of failure, 
age, degree of routine observation, a natural event (e.g. earthquake), performance record 
and history of remedial measures. 
 Informal inspections  are performed by appropriate employees at the project at frequent 
time intervals to identify and report abnormal conditions and evidence of distress. 

Good preparation and planning is key to the success of an inspection. Factors to be considered 
include: selection of the inspection team; review of the existing project data for the dam to be 
inspected; and the preparation of a detailed inspection plan. 

The inspection of outlet works conduits is directly affected by the size of conduit to be inspected. 
A minimum diameter of 36 inches is required if the feature is to be inspected using man entry, or 
a minimum diameter of 48 inches if it is to be inspected by a diver. Specialized inspections of 
inundated or hard to access features often utilize a combination of divers, remotely operated 
vehicles (ROVs), and closed circuit television (CCTV). 

Considerations that must be accounted for if divers are to be expected to conduct inspections 
include depth, altitude, access, leakage, currents, visibility, size of opening, and length of conduit 
requiring inspection. ROVs are good alternatives to dive inspections when conditions like depth, 
diameter, or length become prohibitive. CCTV can be used to inspect submerged portions of 
intake structures, conduits, and terminal structures. They can also be used to inspect structures 
or conduits where confined space entry issues arise. CCTV inspection equipment consists of a 
video camera attached to a self-propelled transport vehicle known as a crawler. An operator 
remotely controls both the transport vehicle and camera and video images are recorded and 
stored for future evaluation and documentation. Modifications to the crawler and to the camera 
size enable CCTV technologies to be applied to a wide range of conduit sizes. 

It is further recommended that permanent markers and thorough documentation be used to 
facilitate easy location of intake structures that are usually submerged. Therefore, factors to be 
considered in planning conduit inspections should include: conduit diameter, the presence and 
angle of bends in the conduit, the inclination of the invert slope, and the distance between access 
entry locations. 

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: 

 Inspection terminology, evident in the use of a term like periodic, differs among different 
agencies and organizations like the USACE, USBR, and FERC. Information in white paper 
on USACE methods, frequency, etc. is not what USACE is currently doing. 
 Inspection activities should include required inspections of gates, valves, and operators. 
Input is needed from mechanical and electrical engineers concerning various elements that 
should be included in required inspections. 
 Required/recommended frequencies of inspections vary among different organizations. 
 GPS could be used to locate underwater structures, so they can be found more easily for 
future inspection. Could be done for new structures or when the structures are actually 
located underwater for existing structures. 
 There is no clear consensus on need for periodic inspection of difficult/inaccessible features. 
 Need to open valves that havent been operated for a long time, especially for low flow 
(small) valves. Owners are reluctant because they are afraid the valve will not close or they 
are afraid of sediment flushing downstream which could result in an environmental problem. 
 Emergency gates are often (sometimes) not exercised and may not work when needed. 
 Full emergency gate exercise under load is rare  USACE has an operating requirement to do 
this test if the gate was designed to operate under load. 
 Hydro-acoustic surveys of stilling basins have been done successfully by the USACE. 
 Dewatering/unwatering of outlet works for gate and conduit inspections can be difficult, 
because of leaky gates or bulkheads. 
 Requirements differ between permit-required and non-permit-required confined spaces. 
 Use of air monitoring devices is recommended for outlet works inspections. 
 There has been some movement toward replacing bulkheads with upstream guard gates as 
has been done by Denver Water. 
 Conduits are not typically surveyed on a periodic basis for elevation and alignment  this is 
typically done only if a problem is identified. 
 Ultrasonic tests can be used to test for material deterioration, however, there can be problems 
distinguishing between good steel and bad steel (it may all look like thickness). 
 Detailed crack survey mapping (on a repeated basis) has been used to monitor structural 
deterioration. 

4.6.2 Prioritization of Research and Development Ideas 
The group brainstorming process resulted in the generation of 7 potential research and 
development ideas, which were then prioritized by the group. The 7 ideas and the results of the 
prioritization are presented in Exhibit 4-21. 

4.6.3 Preliminary Research and Development Plans 
The top four ideas listed in Exhibit 4-21 were selected for development of preliminary 
implementation plans, and those plans are presented in Exhibits 4-22 through 4-25. In some 
cases, the individual work groups reworded the research and development idea, so the ideas 
listed in Exhibit 4-21 may not exactly match the ideas listed in Exhibits 4-22 through 4-25. 

EXHIBIT 4-1
PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS WORKSHOP TOPIC 1 OUTLET WORKS FAILURE MODES

Number of Votes Rank Research and Development Idea 
13* 1 Guidance on air inlets and blow-back. 
11* 2 (Tie) Best practices guide for conduits through small embankment dams. 
11* 2 (Tie) Best practices for mechanical and electrical equipment. 
9* 4 Best practices for automated control of gates and valves. 
8* 5 Developing lists of failure modes for various components of outlet works  baseline, not cookbook. 
6 6 Solutions to H2S issues for structure deterioration. 
3 7 (tie) Develop recommended exercise schedule for outlet works equipment. 
3 7 (tie) Development of requirements for dam and outlet works designers. 
3 7(tie) Application of risk and reliability to assessment of failure modes. 
1 10 Development of guidance for operator training requirements. 
0 11 Development of a no-fault reporting system of incidents not leading to failure. 

* - Idea selected for development. 

Note: Best practices for mechanical and electrical equipment was combined with best practices 
for automated control gates and valves for preliminary plan development. 


EXHIBIT 4-2
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 1A GUIDELINES FOR VENTING CONDUITS

1. Description 
A. Why is this a priority research/development item?
Poor venting can cause operational problems that lead to catastrophic failure.
B. What is the expected outcome?
Better guidelines for design, remediation and operation.

2. Project Tasks and Needs 
A. What tasks are to be done?
A literature search to produce a bibliography of existing information.
B. How is the problem to be solved? 
Additional physical model studies at large and small embankment dams, additional 
analytical work, and additional prototype testing should be conducted. 

3. Project Lead and Contact 
A. Who is working in this area?
Possibly European specialist in this area.
B. Who might be able to lead the project?
Some universities and private laboratories located in the United States.
C. Who are good candidates to complete the work? 
1. The University of Utah and Colorado State University. Both universities have large 
discharge and head capacities that are capable of physically modeling the airflow. 
2. A private independent consultant or a university professor might be a good source for 
the literature review. 


EXHIBIT 4-3
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 1B BEST PRACTICES GUIDE FOR CONDUITS THROUGH EMBANKMENT DAMS

1. Description 
A. Why is this a priority research/development item? 
No established guidelines exist, especially for consultant use. Furthermore, established 
standards that can be enforced by dam safety officials currently do not exist. 
B. What is the expected outcome?
Guidelines for use of design engineers, inspectors, and dam safety officials.

2. Project Tasks and Needs 
A. What tasks are to be done? 
Use the Conduits through Embankment Dams document and expand for use with 
smaller dams. 
B. How is the problem to be solved? 
1. Use the existing FEMA team and expand team with additional state members and 
consultants. 
2. Conduct research into long term performance into conduit materials. 
3. Conduct research into failure of preferred outlet conduit designs. 
4. Compile and evaluate different outlet conduit design standards. 
5. Clearing house for updating design references to be used in the guidelines. ASDSO 
would be an agency to consider. 
6. Develop a brochure for the new document for distribution to the engineering 
community that can also be posted on the FEMA website. Data from the guidelines 
summarized in the brochure could be used to update documents published by 
organizations like the AWWA. The guidelines should be used during the design of 
conduits for embankment dams. 

3. Project Lead and Contact 
A. Who is working in this area?
It is currently not known if anyone is working in this area.
B. Who might be able to lead the project? 
Chuck Cooper currently of the U.S. Bureau of Reclamation. 
C. Who are good candidates to complete the work? 
Mr. Sal Todaro, currently of URS Corporation and independent consultant Ed Rossilson. 


EXHIBIT 4-4
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 1C BEST PRACTICES FOR MECHANICAL AND ELECTRICAL DESIGN AND AUTOMATED CONTROL

1. Description 
A. Why is this a priority research/development item? 
Lack of knowledge leads to failure modes, agencies and consultants could benefit, and 
mechanical/electrical design is often secondary to civil design. 
B. What is the expected outcome?
Transfer of knowledge and technology.

2. Project Tasks and Needs 
A. What tasks are to be done? 
Find knowledgeable people and define a process to gather data and information which 
should be processed into a usable form. 
B. How is the problem to be solved?
No answer provided.

3. Project Lead and Contact 
A. Who is working in this area? 
To the best knowledge of workshop team members no one is currently working in this 
area. 
B. Who might be able to lead the project?
The USBR, USACE, and the USSD.
C. Who are good candidates to complete the work? 
Retirees and experienced designers, operations and maintenance personnel, field 
technicians, gate designers, and manufactures of related components. 


EXHIBIT 4-5
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 1D DEVELOP A LIST OF FAILURE MODES FOR OUTLET WORKS

1. Description 
A. Why is this a priority research/development item? 
Reduce future outlet works failures by making dam designers and owners aware of 
potential failure modes of outlet works components. 
B. What is the expected outcome? 
A compendium of potential failure modes for use in design, inspection, and operation of 
outlet works to ultimately reduce outlet works failures. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Identify forms of failure. 
2. Basic research and literature review of outlet failure modes. 
3. Solicit input from various federal dams, state, dam safety organizations in order to 
develop a list of failure modes 
4. Convene workshop to refine list 
5. Incorporate comments from federal and state agencies 
6. Publish final list. 
B. How is the problem to be solved?
No answer provided.

3. Project Lead and Contact 
A. Who is working in this area?
FERC, the USACE, BC Hydro, USBR, ICOLD and Swede Power.
B. Who might be able to lead the project? 
Dr. David Bowles (Utah State University), Marty McCann of the NPDP, Dr. Des 
Hartford, and Larry Von Thun, consultant. 
C. Who are good candidates to complete the work?
No answer provided.


EXHIBIT 4-6
PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS WORKSHOP TOPIC 2 CONDUIT MATERIALS, SELECTION CRITERIA, AND CONSTRUCTION METHODS

Number of Votes Rank Research and Development Idea 
15* 1 Best practices guidelines for intake towers  configuration, access, debris/trash control, seismic performance, selective withdrawal. 
13* 2 Guidance on application of tunnels to outlet works  including consideration of microtunneling and of soft ground and hard ground tunneling alternatives. 
12* 3 Compile data on performance of conduits through embankments for cases where the conduits have experienced significant settlement (such as some of those shown in the white paper presentation). 
6* 4 Guidance on seismic effects on conduits and how conduits should be analyzed/designed for these effects  embankment spreading, fault offset, propagation of earthquake waves. 
5 5 Measurement of loads on conduits for comparison to predicted loads, 
1 6 (tie) Revision to the ASCE penstock guidelines. 
1 6 (tie) Guidance on use and applicability of siphon outlet works  update earlier EPRI document. 

* - Idea selected for development. 


EXHIBIT 4-7
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 2A BEST PRACTICES FOR INTAKE TOWERS INCLUDING LOCATION,  CONFIGURATION, ACCESS, DEBRIS/TRASH CONTROL, SEISMIC PERFORMANCE, AND SELECTIVE WITHDRAWALS

1. Description 
A. Why is this a priority research/development item? 
1. Changes in the state-of-the-practice in the application of seismic loads. 
2. Changes in water quality requirements. 
3. Past experience with poorly designed and positioned intake towers. 
B. What is the expected outcome?
Development of a best practices guide.

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Identify features of intake towers that merit study. 
2. Survey existing owners and operators of intake towers via the ASDSO. 
3. Gather available literature. 
4. Compile information gathered into a summary document with recommendations. 
B. How is the problem to be solved?
Development of a best practices guide.

3. Project Lead and Contact 
A. Who is working in this area?
The USACE, independent consulting engineers, and the USSD.
B. Who might be able to lead the project?
FEMA.
C. Who are good candidates to complete the work?
The USBR and the USACE.


EXHIBIT 4-8
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 2B GUIDANCE ON APPLICATION OF TUNNELS FOR OUTLET WORKS INCLUDING MICROTUNNELLING IN SOFT AND HARD GROUND 

1. Description 
A. Why is this a priority research/development item? 
1. The high rate of failures due to piping accounting for approximately one quarter 
(25%) of embankment dam failures. 
2. Penetration through dams needs to be eliminated. 

B. What is the expected outcome? 
1. A document or manual to provided guidance to help decide whether to use a tunnel or 
not, and to provide design guidance and costs. 
2. Define appropriate geotechnical conditions for tunnel construction. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Literature search on the use of tunnels and on the rationale for the use of tunnels in 
dams. Case studies where tunnels were used or selected for design should be 
researched and compiled. 
2. Develop pros and cons of the use of tunnels versus conduits in dam outlet works. 
3. Develop selection criteria including relative cost. 
4. Cost benefit analyses of the inclusion of tunnels should be performed. 
B. How is the problem to be solved?
No answer provided.

3. Project Lead and Contact 
A. Who is working in this area? 
To the best knowledge of workgroup team members, no one is currently working in this 
area. 
B. Who might be able to lead the project?
FEMA, ASDSO, USBR, and experienced designers.
C. Who are good candidates to complete the work? 
Former USBR tunnel designers, non-government tunnel designers, experienced tunnel 
expert, and geotechnical designers with tunneling experience. The USACE also has 
experience with microtunneling under levees. 


EXHIBIT 4-9
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 2C COMPILE DATA ON PERFORMANCE OF CONDUITS WITH SIGNIFICANT SETTLEMENT AND LATERAL MOVEMENT

1. Description 
A. Why is this a priority research/development item? 
There are procedures to estimate settlement and lateral movement that have not been validated. 
B. What is the expected outcome? 
Verification of the existing procedures used to estimate settlement and lateral movement. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Gather existing data on USBR and USACE conduits along with site specific conditions. 
2. Collect conduit data and site specific conditions on NRCS dams. 
3. Compare actual settlements and lateral movements with estimates using current design procedures. 
4. Look for site specific conditions or construction procedures that may lead to satisfactory performance. 
5. If current analysis procedures prove incorrect, conduct a computer analysis to fit the data and develop new design guidance. 
B. How is the problem to be solved?
No answer provided.

3. Project Lead and Contact 
A. Who is working in this area?
The USACE and the USBR may be collecting some data.
B. Who might be able to lead the project?
FEMA could assist with the acquisition of data.
C. Who are good candidates to complete the work? 
1. A representative from USBR, USACE, and NRCS is recommended. 
2. State and city agencies that may have some data 
3. Several consultants involved in design, inspection, and analysis of conduits. 


EXHIBIT 4-10
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 2D GUIDANCE ON SEISMIC EFFECTS ON CONDUITS AND HOW TO ANALYZE AND DESIGN FOR THEM INCLUDING EMBANKMENT SPREADING, FAULT OFFSET, AND THE PROPAGATION OF EARTHQUAKE WAVES

1. Description 
A. Why is this a priority research/development item? 
A priority because it is a dam safety concern with limited documented available for analysis and design. 
B. What is the expected outcome? 
A document or chapter or section in a larger document of reference material and design guidance. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Literature research of currently available documentation and design guidance. 
2. Address various types of material i.e. soil, rock, etc., that will be encountered. 
3. Establish a multi-disciplined team/committee to formulate the framework/outline of 
the document and to identify available information and areas of need or where gaps in information exist. 
4. Distinguish the difference between analysis of existing conduits and the design and 
construction of new conduits. 
B. How is the problem to be solved? 
Solicit information from state and federal agencies by surveys/questionnaires dealing with earthquakes where their structures are located. 

3. Project Lead and Contact 
A. Who is working in this area?
The USGS, NEHRP, and the University of California at Berkeley.
B. Who might be able to lead the project?
EPRI, the ASDSO, and the dam safety groups of western states.
C. Who are good candidates to complete the work? 
1. Blast research groups like those at the USACE, and the University of Florida. 
2. The USBR and the USACE, particularly units located in the western states. 
3. Furthermore, since this is a multidiscipline issue, we propose that a professional 
society like ASCE produce a design manual, or solicit papers for a conference and publish the proceedings. 


EXHIBIT 4-11
PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS WORKSHOP TOPIC 3 AND TOPIC 4 GATES, VALVES, CONTROLS AND ENERGY DISSIPATORS

Number of Votes Rank Research and Development Idea 
11* 1 Best practices for selection of gates, valves, and controls  considering heads, velocities, configurations, etc. 
10* 2 Best practices for energy dissipators  considering heads, velocities, configurations, etc. 
9* 3 Guidelines for maintenance and exercise of gates and valves and for cavitation repair. 
7* 4 Develop and present a short course on gates and valves for dams  design, operation, and maintenance  (consider videotaping the course?) 
4 5 Develop expert videos (DVDs) as has been done for other dam safety topics (e.g. Peck, Idriss) for gates and valves and energy dissipators. 
1 6 (tie) Research to develop guidance for variation of air demand for fixed-cone valves 
1 6 (tie) Compile understanding of international efforts in gates and valves and energy dissipators. 
1 6 (tie) Develop guidance for incorporation of seismic requirements into design of gates, valves, and operating systems. 
0 9 (tie) Guidance document for environmentally-acceptable fluids for hydraulic controls. 
0 9 (tie) Develop an information document on current gate and valve manufacturers  domestic and international. 

* - Idea selected for development. 


EXHIBIT 4-12
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 3A BEST PRACTICES FOR SELECTION OF GATES AND VALVES

1. Description 
A. Why is this a priority research/development item? 
 It would aid in transferring information. 
 To aid in preventing errors in selection, operation, and placement of gates and valves. 
B. What is the expected outcome?
An up-to-date manual on selection, operation, and system layout.

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Identify a sponsor like ASME or EPRI. 
2. Identify a team. 
B. How is the problem to be solved?
Team effort with perseverance.

3. Project Lead and Contact 
A. Who is working in this area? 
 Consulting firms. 
 Chinese water resources. 
B. Who might be able to lead the project?
An active consultant.
C. Who are good candidates to complete the work? 
 Consultants. 
 Technical personnel from manufacturers in both the United States and Europe. 
 Western European engineers. 


EXHIBIT 4-13
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 4A BEST PRACTICES FOR ENERGY DISSIPATORS  CONSIDERING HEADS, VELOCITIES, CONFIGURATIONS, ETC.

1. Description 
A. Why is this a priority research/development item? 
Experienced engineers are rapidly becoming fewer and their knowledge and experience needs to be captured. 

B. What is the expected outcome? 
1. Individual publications on each energy dissipator (E.D.). 
2. Report with overview of all energy dissipators with advantages, disadvantages, and applications based on variety of parameters, e.g. head (H) versus flow (Q). 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Develop theoretical model for each E.D. 
2. Gather empirical data for each E.D. 
3. Calibrate theoretical to empirical. 
4. Characterize range of satisfactory behavior. 
5. Identify gaps in range of application. 
6. Identify environmental effects. 
7. Summarize findings in overview report. 
B. How is the problem to be solved? 
 Criteria need to be examined and updated. 
 Lessons learned and experience needs to be captured. 
 Theories were developed years ago and applications need to be assessed. 

3. Project Lead and Contact 
A. Who is working in this area? 
Many people might be working on individual aspects, but it all needs to be brought together. 
B. Who might be able to lead the project?
The laboratories of the USACE (ERDC).
C. Who are good candidates to complete the work? 
Individuals like Jim Gordon, Will Hager, State and Federal Agencies, or Chinese 
researchers/specialists in this area. 


EXHIBIT 4-14
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 3B GUIDELINES FOR MAINTENANCE AND EXERCISE OF GATES AND VALVES AND CAVITATION REPAIRS

1. Description 
A. Why is this a priority research/development item? 
1. It is well documented that poor maintenance of outlet works is a problem and 
represents a dam safety concern. 
2. Currently in cases of emergency, gates and valves are assumed to be operational 
without the exercise of these components on a routine basis. 
B. What is the expected outcome? 
1. Guideline documents for maintenance and exercise of gates and valves. 
2. Training device for dam owners to show the importance of maintaining the facility in 
an operable condition. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Research on known cases of failure of outlet works gates and valves. 
2. Research on corrosion effects of water chemistry on operation and/or maintenance. 
3. Survey federal, state, and large private dam owners, consultants in the field, and dam 
regulators about maintenance concerns, programs, and past experiences. 
4. Impress upon members of academia the importance of maintenance consideration 
along with the design of outlet gates and valves. 
5. Standardize inspection protocol by preparing a review checklist. 
B. How is the problem to be solved? 
ASDSO needs to be the vehicle to develop a document for the procedures and means of 
maintenance and exercise of gates and valves. 

3. Project Lead and Contact 
A. Who is working in this area? 
Currently no one is working in this area to the knowledge of the workgroup team. 
B. Who might be able to lead the project? 
FEMA and ASDSO with contributions from USACE, FERC, and the USBR. 
C. Who are good candidates to complete the work? 
FEMA and ASDSO. 


EXHIBIT 4-15
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 3C DEVELOP SHORT COURSES WITH VIDEO/DVD OPTIONS ON DESIGN, OPERATION, AND MAINTENANCE OF GATES AND VALVES

1. Description 
A. Why is this a priority research/development item? 
We are losing knowledge of senior experts and technology in the United States is 
declining due to not building new dams while at the same time we have an aging 
infrastructure of existing dams that will need rehabilitation. 
B. What is the expected outcome?
A transfer of knowledge and technology to current and future practitioners.

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Develop scope of short course (including such topics as history, state of the practice 
discussions, world practices, lessons learned, and best practices). 
2. Identify target audiences that would include civil engineers, mechanical engineers, 
electrical engineers, and other individuals to be identified whose professional practice 
would be benefited by such a knowledge transfer. 
B. How is the problem to be solved? 
1. Through a contract RFP. The selected contractor needs to bring recognized experts as 
instructors. A major factor in selection will be the knowledge and experience breadth 
of experts brought to the courses. 
2. Evaluation of the video/DVD needs to be an option of the RFP and needs to be 
considered within the structure of the short course. 

3. Project Lead and Contact 
A. Who is working in this area? 
No single entity is working in this area and as such a composite team would be required. 
B. Who might be able to lead the project?
This project could be sponsored by FEMA, ASDSO, USSD, and EPRI.
C. Who are good candidates to complete the work? 
The composite team of members from the sponsoring agencies could be lead by an expert or practicing consulting firm. 


EXHIBIT 4-16
PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS WORKSHOP TOPIC 5 REHABILITATION OF CONDUITS

Number of Votes Rank Research and Development Idea 
14* 1 (tie) Design guidance and guide specifications for sliplining of outlet conduits. 
14* 1 (tie) Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. 
8* 3 (tie) Assessment of microtunneling and boring technologies for application to outlet conduit rehabilitation. 
8* 3 (tie) Best practices guide for design and construction methods to rebuild embankment sections removed for outlet conduit removal/replacement. 
7 5 Design guidance and guide specifications for cured-in-place lining of outlet conduits  considering high velocity flows, end constraints, etc.. 
6 6 (tie) Research/guidance on methods for rehabilitation of conduit deterioration from chemical attack (e.g. H2S). 
6 6 (tie) Best practices guide for abandonment of outlet conduits in-place. 
2 8 (tie) Grout materials research on grout properties for sliplining applications. 
2 8 (tie) Assessment and development of paint technologies for application in damp, cool, confined spaces and for operation in high velocity environments. 
1 10 (tie) Research on aging and thermal properties of HDPE pipe materials and installations. 
1 10 (tie) Applicability and appropriateness of using downstream controls to replace difficult-access upstream gates and valves  special requirements for converting non-pressure pipe to pressure pipe. 
1 10 (tie) Best practices guide for design, construction, and operation of siphon outlet works/spillways. 
1 10 (tie) Consideration of effects on seepage pattern in embankments after relining a leaky conduit. 

* - Idea selected for development. 


EXHIBIT 4-17
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 5A DESIGN GUIDANCE AND GUIDE SPECIFICATIONS FOR SLIPLINING

1. Description 
A. Why is this a priority research/development item? 
1. Potential big market given the large number of projects in need, particularly those that 
have either reached or are fast approaching the end of their service life. 
2. Need cost effective solutions given owners ability to pay i.e. cost sensitivity is 
critical. 
3. Limited information is available, especially for material selection, and primarily from 
pipe suppliers. 
B. What is the expected outcome? 
1. Material selection (paint, pipe, grouts) guide specifications for grouting procedures. 
2. Standard design details, especially for special arrangements. 
3. Distinguish between pressure versus non-pressure conditions. 
4. A list of design considerations including corrosion, erosion, head, flow and hydraulic capacity. 
5. A logic tree to aid in the evaluations of response modes including abandonment, 
sliplining, or other options like excavation and replacement. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Data search 
2. Develop case studies through discussions with designers, owners and contractors. 
Find out what experience exists. 
3. Offer a symposium or conference potentially sponsored by the USSD, at which white papers are presented. 
4. Form a committee to develop guidelines and provide examples. 
5. Work with ASCE, FEMA, and USSD to publish results of all R&D activities previously indicated. 

3. Project Lead and Contact 
A. Who is working in this area?
USBR, NRCS, and consultants.
B. Who might be able to lead the project?
NRCS.
C. Who are good candidates to complete the work? 
USBR, NRCS, pipe suppliers, grout manufacturers, contractors, and designers. 


EXHIBIT 4-18
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 5B COMPILATION OF CASE STUDIES ON OUTLET WORKS REHABILITATION  LESSONS LEARNED, PERFORMANCE, AND COMPARATIVE COSTS

1. Description 
A. Why is this a priority research/development item? 
1. It provides a forum for lessons learned to be discussed. 
2. Allows for the transfer of experiences among practitioners. 
B. What is the expected outcome? 
1. A decision tool for selecting rehabilitation alternatives for a specific application. 
2. Transfer experiences. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Distinguish between low versus high need application 
2. Distinguish access versus pipe size methods. 
3. Survey agencies, private industry, and consultants. 
4. Have a conference or forum from which the proceedings can be published. 
5. Summarize trends similar to USSD and ICOLD publications in a document that should be updated on a periodic basis. 
6. An audit group or committee should be assembled to balance bias with information that is too generalized. 
7. Review case studies to ensure that sensitive specifics about actual projects are removed to eliminate concerns about liability or disclosure of failures. 

3. Project Lead and Contact 
A. Who is working in this area?
ASCE has previously published lessons learned. 

B. Who might be able to lead the project? 
A group committee comprised of engineers with a range of experience in both small and large dams should be comprised of members from professional organizations. 

C. Who are good candidates to complete the work? 
Water Resources Research Institute (WRRI) for land-grant colleges, university professors 
(although a drawback is that this individual may have limited hands-on experience), Earl 
Eiker of USSDs Hydraulics Committee, and ASCEs Hydraulics Structures Committee. 
The knowledge and experience of FEMAs incident response group should be tapped for 
larger-scale problems. The Department of Homeland Security may also fund incident investigations. 


EXHIBIT 4-19
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 5C ASSESSMENT OF MICROTUNNELLING AND BORING TECHNOLOGIES FOR APPLICATION TO OUTLET CONDUIT REHABILITATION

1. Description 
A. Why is this a priority research/development item? 
Because these techniques are being applied to low head dams in limited applications and there are no guidelines. 
B. What is the expected outcome?
Guidelines for appropriate or inappropriate use of these techniques.

2. Project Tasks and Needs 
A. What tasks are to be done? 
A literature search fro application of micro-tunneling in embankment and foundation 
material including upstream seepage cutoffs backing filter systems and stilling systems for steep pipe applications. 
B. How is the problem to be solved? 
Explore contracts and manufacturers associations for funding this research and application. Back up by advisory board of dam consultants. 

3. Project Lead and Contact 
A. Who is working in this area? 
NRCS applications in upgrade of existing FRS facilities about normal water pool as seen at Standley Dams outlet works in Westminster, Colorado where the abutment was rehabilitated. 
B. Who might be able to lead the project? 
The dam groups of the NRCS, Fish and Wildlife, and the Bureau of Indian Affairs, and dam consultants. 
C. Who are good candidates to complete the work?
NRCS national engineering group with the assistance of consulting engineers.


EXHIBIT 4-20
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 5D BEST PRACTICES GUIDE FOR DESIGN AND CONSTRUCTION METHODS TO REBUILD EMBANKMENT SECTIONS FOR CONDUIT REMOVAL AND REPLACEMENT

1. Description 
A. Why is this a priority research/development item? 
1. There are currently no design or construction guidelines for reconstruction of 
breaches through embankment dams for outlet works replacement. 
2. No preferred method of replacement or rehabilitation of outlet works structures has 
been identified. 
3. There is more of a need to replace outlet works than currently practiced. 
4. If the maximum section of a dam is not constructed properly, failure could result. 
5. There are currently unaddressed concerns with the treatment of soft foundations. 
6. New embankments need to be tied into zoning of the existing embankment with draining systems an area of particular concern. 
B. What is the expected outcome? 
Guidelines to address the issues of the reconstruction of partial removal of dam embankments to be used by consultants and dam regulators. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Conduct literature research of existing guidelines like the Levee Design Manual 
developed by the USACE, and case histories. Information gathered from a 
compilation of case studies should be used to develop a set of guidelines for this 
R&D topic. 
2. Survey designers, contractors and designers to develop documentation of experience resources. 
3. Develop guidance documents to be peer reviewed. 
4. Produce the final product in the form of a published set of embankment rebuilding and conduit removal and replacement guidelines. 

3. Project Lead and Contact 
A. Who is working in this area? 
Currently no one is working in this area to the knowledge of the workgroup team. Most 
practitioners have their own independent in-house practices that they follow. 
B. Who might be able to lead the project?
NRCS, ASDSO, and consultants.
C. Who are good candidates to complete the work? 
Mr. David Hammer, formerly of the USACE who has experience with the construction of 
embankments around existing outlets, and who has also authored several papers. Mr. Art 
Walhs with Garnett-Flemming, and Mr. Clark Stanage, formerly of the USACE would 
also be good candidates to conduct this work. 


EXHIBIT 4-21
PRIORITIZATION OF RESEARCH AND DEVELOPMENT IDEAS WORKSHOP TOPIC 6 OUTLET WORKS INSPECTION

Number of Votes Rank Research and Development Idea 
13* 1 Applications of nondestructive testing to inspection of outlet works. 
11* 2 (tie) Best practices for inspection of gates, valves, and operators (mechanical and electrical components). 
11* 2 (tie) Best practices guide for inspection frequency and methods for more-typically accessible outlet works features. 
9* 4 Develop consensus recommendations for inspection of normally inundated structures and very-difficult-to-inspect structures. 
2 5 Use of digital imaging or other technologies to improve the efficiency of crack mapping or defect mapping. 
1 6 (tie) Updating the TADS modules to reflect newer methods, technologies, and standards. 
1 6 (tie) Establish practical and environmentally acceptable methods and materials to seal leaking gates and bulkheads to allow inspection of outlet works. 

* - Idea selected for development. 


EXHIBIT 4-22
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 6A APPLICATIONS OF NON-DESTRUCTIVE TESTING (NDT) FOR INSPECTION OF OUTLET WORKS

1. Description 
A. Why is this a priority research/development item? 
1. Non Destructive Testing provides a unique and consistent technique enabling the inspection of outlet works. 
2. There is currently no clear description of the capabilities of NDT for application to outlet works inspections. 
3. Consistent guidelines of how to interpret the results of non-destructive tests need to be developed. 
B. What is the expected outcome? 
Non-destruction tests being used to confirm the structural integrity of outlet works structures. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Conduct a survey of suppliers or manufacturers of what equipment is available on the market. 
2. An inventory of what is needed that is currently unavailable needs to be made. 
3. The state of the practice today needs to be documented. 
4. A best practices guide on the use of equipment including costs, capabilities, and applications needs to be developed to increase the understanding of non-expert practitioners. 
5. Develop tests to confirm theoretical projections of performance with actual conditions. 

3. Project Lead and Contact 
A. Who is working in this area? 
Mr. Chuck Copper of the USBR, the Vicksburg, MS or Champagne, IL divisions of the USACE, and Hydro Quebec. 
B. Who might be able to lead the project? 
USBR. 
C. Who are good candidates to complete the work? 
USBR. 


EXHIBIT 4-23
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 6B BEST PRACTICES FOR INSPECTION OF GATES, VALVES, AND OPERATORS, INCLUDING MECHANICAL AND ELECTRICAL COMPONENTS

1. Description 
A. Why is this a priority research/development item? 
1. To avoid the failure of these features. 
2. These features are exposed elements and more sensitive than other components of the 
dam and need to be more closely monitored. 
B. What is the expected outcome? 
1. Guidelines for the inspection of mechanical and electrical equipment. 
2. Increased confidence in the reliability of operation of the equipment. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Research existing practices of federal and non-federal dam owner organizations, including international experience e.g. ICOLD. 
2. Consult with equipment manufacturers about recommended practices. 
3. Investigate alternative testing procedures. 
B. How is the problem to be solved? 
1. Developing guidelines. 
2. Consideration of additional state regulations. 

3. Project Lead and Contact 
A. Who is working in this area?
No one to the knowledge of the workgroup team.
B. Who might be able to lead the project? 
Dam Safety organizations like ASDSO, and USSD. 
C. Who are good candidates to complete the work? 
An interdisciplinary team consisting of regulators, dam owners, equipment manufacturers, and mechanical and electrical designers is believed best suited for this work. 


EXHIBIT 4-24
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 6C BEST PRACTICES GUIDE FOR INSPECTION FREQUENCY AND METHODS OF INSPECTION FOR TYPICALLY ACCESSIBLE CONDUITS

1. Description 
A. Why is this a priority research/development item? 
1. No consistency on frequency and methods of inspection. 
2. Problems may be uncovered that may not otherwise be noted where no inspections are done. 
3. May provide guidelines that state or federal agencies may use to require dam owners to follow. 
B. What is the expected outcome? 
1. Inspection guidelines including frequency of inspection tied to hazard potential conduit materials and the age of the outlet. 
2. May influence state or federal policy on outlet inspections. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Literature search on current practices. Develop table of practices and provide a list of references. 
2. List and discuss various remote monitoring techniques and advantages and disadvantages. 
B. How is the problem to be solved? 
1. Solicit input from various dam safety agencies at both the state and federal level, private consultants for inspections versus the type of outlet. 
2. Prepare a question and answer sheet to be answered by private consultants from both state and federal agencies. 
3. Workshop to provide best recommendations. 

3. Project Lead and Contact 
A. Who is working in this area? 
1. ASDSO, ASCE, USSD, USBR, and Mr. Larry Von Thun. This work might also include revisiting the inspection portion of the Model Dam Safety Law. 
B. Who might be able to lead the project? 
FEMA through its internal R&D mechanisms. 
C. Who are good candidates to complete the work? 
The same team leading this project is a good candidate to complete work tasks. 


EXHIBIT 4-25
RESEARCH AND DEVELOPMENT IMPLEMENTATION PLAN, R&D TOPIC 6D INSPECTION OF NORMALLY INUNDATED STRUCTURES AND DIFFICULT TO ACCESS AREAS

1. Description 
A. Why is this a priority research/development item? 
1. This subject is of high priority because this work is often deferred and does not get 
done. 
2. No guidelines currently exist to determine the importance or necessity. 
B. What is the expected outcome? 
1. Develop guidelines for go/no-go procedures that might include consideration of 
outcomes, water quality, design margins, and operation history. 
2. Develop guidelines for inspection frequency. 
3. Develop methods and/or technologies for actually performing inspections. 
4. Possible recommendations or design considerations to facilitate future inspections. 

2. Project Tasks and Needs 
A. What tasks are to be done? 
1. Identify type of structure first. 
2. Data search and case studies to get a feel for the risks that are involved. 
3. Probability and risk assessment of structure to rank priorities. 

3. Project Lead and Contact 
A. Who is working in this area?
No one is currently working in this area to the knowledge of the respondent.
B. Who might be able to lead the project?
The USBR.
C. Who are good candidates to complete the work?
Dam owners and diving and inspection agencies.

SECTION FIVE 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 (with Topic 3 and Topic 4 combined) considered in the workshop resulted in the 
identification of 20 leading ideas (4 ideas for each topic), for which preliminary implementation 
plans were developed. 

The potential benefit and associated implementation cost of each of the 20 R&D topics were 
assigned a score between zero and ten by sixteen workshop participants as will be discussed 
below. The scores, which were based on consideration of the balance of benefit to practice and 
cost/ease of implementation, were then averaged in order to determine overall rankings for each 
of the research and development ideas. 

Potential Benefit 

In order to provide an assessment of potential benefit, workshop participants were asked to use 
the form shown in Attachment 3 to assign a score from 0 to 10 with 0 being least beneficial and 
10 most beneficial. to each of the 20 R&D ideas selected to develop preliminary plans. As may 
be seen on Exhibit 5-1, the top 11 R&D ideas (including a tie for the 10th position) generated by 
assessing this factor provided by 16 participating workshop respondents were as follows: 

1. Best-practices guide for outlet works conduits through embankment dams, emphasizing small 
embankments. (R& D Topic 1B) 

2. Best-practices guide for selection of gates and valves for outlet works structures. (R&D Topic 
3A) 

3. Compilation of case studies on outlet works rehabilitation  lessons learned, performance, 
comparative costs. (R&D Topic 5B) 

4. Best-practices guide for energy dissipators for outlet works structures, considering heads, 
velocities, configuration, etc. (R&D Topic 4A) 

4. Design guidance and guide specifications for sliplining of outlet conduits. (R&D Topic 5A) 

6. Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for 
outlet works. (R&D Topic 3B) 

7. Best-practices guide for mechanical and electrical design and for automated control for outlet 
works. (R&D Topic 1C) 

8. Best-practices guide for inspection of outlet works gates, valves, and operators, including 
mechanical and electrical components. (R&D Topic 6B) 

9. Best-practices guide for outlet works intake towers, considering such factors as location, 
configuration, access, debris/trash control, seismic performance, selective withdrawals, etc. 
(R&D Topic 2A) 

10. Develop a list of failure modes for outlet works. (R&D Topic 1D) 

10. Develop short course (with video/DVD option) on design, operation, and maintenance of 
outlet works gates and valves. (R&D Topic 3C) 

Please note that this list includes ideas tied at ranks of 4 and 10. 

Cost/ Ease of Implementation 

To provide an assessment of cost or perceived difficulty/ease of implementation associated with 
the same 20 R&D ideas selected for preliminary development, workshop participants were asked 
to assign a score for this factor from 0 to 10 with 0 indicating unfavorable high cost/difficulty of 
implementation and 10 indicating favorable low cost or perceived easy implementation. As may 
be seen on Exhibit 5-2, the top 10 R&D ideas as ranked by the same 16 participating workshop 
respondents were as follows: 

1. Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for 
outlet works. (R&D Topic 3B) 

2. Best-practices guide for inspection frequency and methods of inspection for typically 
accessible outlet works conduits. (R&D Topic 6C) 

3. Best-practices guide for selection of gates and valves for outlet works structures. (R&D Topic 
3A) 

3. Best-practices guide for outlet works conduits through embankment dams, emphasizing small 
embankments. (R&D Topic 1B) 

5. Develop a list of failure modes for outlet works. (R&D Topic 1D) 

5. Best practices guide for design and construction methods to rebuild embankment sections 
removed for outlet conduit removal/replacement. (R&D Topic 5D) 

5. Best-practices guide for inspection of outlet works gates, valves, and operators, including 
mechanical and electrical components. (R&D Topic 6B) 

8. Best-practices guide for mechanical and electrical design and for automated control for outlet 
works. (R&D Topic 1C) 

8. Best-practices guide for energy dissipators for outlet works structures, considering heads, 
velocities, configuration, etc. (R&D Topic 4A) 

8. Design guidance and guide specifications for sliplining of outlet conduits. (R&D Topic 5A) 

As seen above, ranking according to this measure resulted in ties at ranks 3, 5, and 8. 

Overall Prioritization of Research and Development Ideas 

In reviewing the results of the overall ranking according to potential benefit (Exhibit 5-1) and 
favorable cost/ease of implementation (Exhibit 5-2), it is seen that the priority order of R&D 
ideas varied somewhat between the two factors assessed. However, by averaging the scores 
from both assessments an overall average score and ranking of the 20 R&D ideas for which 
preliminary plans were developed could be obtained as seen in Exhibit 5-3. The resulting top 10 
ideas are: 

1. Best-practices guide for outlet works conduits through embankment dams, emphasizing small 
embankments. (R&D Topic 1B) 

2. Best-practices guide for selection of gates and valves for outlet works structures. (R&D Topic 3A) 

3. Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. 
(R&D Topic 3B) 

4. Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, 
configuration, etc. (R&D Topic 4A) 

4. Design guidance and guide specifications for sliplining of outlet conduits. (R&D Topic 5A) 

6. Best-practices guide for mechanical and electrical design and for automated control for outlet works. (R&D Topic 1C) 

7. Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative 
costs. (R&D Topic 5B) 

7. Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical 
and electrical components. (R&D Topic 6B) 

9. Develop a list of failure modes for outlet works. (R&D Topic 1D) 

9. Best-practices guide for inspection frequency and methods of inspection for typically 
accessible outlet works conduits. (R&D Topic 6C) 

This combined ranking generated ties at rank 4, 7, and 9 and is believed to indicate some degree 
of prioritization among R&D ideas. The cost-benefit comparison chart shown in Exhibit 5-4 
further indicates that the top 10 R&D ideas from the overall rankings would all generate high 
benefit and had a comparatively low associated implementation cost. 

Based on the combination of the rankings, the following five topics should be considered highest 
priority for research and development: 

 Best-practices guide for outlet works conduits through embankment dams, emphasizing small embankments. (R&D Topic 1B) 
 Best-practices guide for selection of gates and valves for outlet works structures. (R&D Topic 3A) 
 Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. (R&D Topic 3B) 
 Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, configuration, etc. (R&D Topic 4A) 
 Design guidance and guide specifications for sliplining of outlet conduits. (R&D Topic 5A) 

All five of these ideas ranked in the top 10 in both assessments of potential benefit and cost/ease 
of implementation, and were ranked 1 through 4 (with a tie for 4th) in the average ranking. 

The next five research and development ideas listed in Exhibit 5-3 should also be considered 
high priority R&D ideas, but not as high as the first four topics indicated above. These five 
topics are: 

 Best-practices guide for mechanical and electrical design and for automated control for outlet works. (R&D Topic 1C) 
 Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. (R&D Topic 5B) 
 Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical and electrical components. (R&D Topic 6B) 
 Develop a list of failure modes for outlet works. (R&D Topic 1D) 
 Best-practices guide for inspection frequency and methods of inspection for typically accessible outlet works conduits. (R&D Topic 6C) 

R&D topics 1C, 6B and 1D were ranked in the top 10 in both benefit and cost/ease of 
implementation rankings while R&D topic 5B was among the top 10 in the ranking of potential 
benefit, while R&D topic 6C was the second most favorable R&D idea from a cost/ease of 
implementation perspective. Consequently, it is the authors opinion that these five R&D topics 
should be considered high priority, but not as high as the top five ideas previously indicated. 

Other R&D topics that received a top 10 ranking in at least one of the two overall ranking 
methods used to prioritize ideas were: 

 Develop a best-practices guide for design and construction methods to rebuild embankment 
sections removed for outlet conduit removal/replacement. (R&D Topic 5D) 
 Develop a best-practices guide for outlet works intake towers, considering such factors as 
location, configuration, access, debris/trash control, seismic performance, and the practice of 
selective withdrawals. (R&D Topic 2A) 
 Develop a short course with the possibility of a companion video/DVD format on design, 
operation, and maintenance of outlet works conduits. (R&D Topic 3C) 

These R&D topics deserve some consideration for implementation, but at a lower priority than 
the 10 ideas previously indicated. 

The remaining seven R&D topics did not receive top 10 ratings in either of the two assessment 
gauges used, and therefore should be considered much lower on the priority scale for 
implementation. 

Observations Concerning Research and Development Ideas 

As discussed in Section 2, a review of the leading R&D topics indicates that none of them 
involve basic laboratory testing. Rather most of the R&D topics involve collecting or compiling 
available information and developing guidelines for dissemination to practitioners to enable 
consistency in design, maintenance, and inspection activities throughout the field of practice. 
This suggests that the overall challenges associated with various aspects of outlet works design, 
maintenance and inspection result from the absence of documented information, inconsistencies 
among available information, misuse or misapplication of the available information by some 
practitioners, 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. 

EXHIBIT 5-1
RANKING OF RESEARCH/DEVELOPMENT IDEAS BASED ON INDIVIDUAL SCORES FOR POTENTIAL BENEFIT

TOPIC NUMBER RESEARCH/DEVELOPMENT TOPIC(S) SCORE 0 to 10(1) RANK 
1B Best-practices guide for outlet works conduits through embankment dams, emphasizing small embankments. 8.1 1 
3A Best-practices guide for selection of gates and valves for outlet works structures. 7.6 2 
5B Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. 7.5 3 
4A Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, configuration, etc. 7.4 4 
5A Design guidance and guide specifications for sliplining of outlet conduits. 7.4 4 
3B Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. 7.1 6 
1C Best-practices guide for mechanical and electrical design and for automated control for outlet works. 7.0 7 
6B Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical and electrical components. 6.8 8 
2A Best-practices guide for outlet works intake towers, considering such factors as location, configuration, access, debris/trash control, seismic performance, selective withdrawals, etc. 6.7 9 
1D Develop a list of failure modes for outlet works. 6.4 10 
3C Develop short course (with video/DVD option) on design, operation, and maintenance of outlet works gates and valves. 6.4 10 
6C Best-practices guide for inspection frequency and methods of inspection for typically accessible outlet works conduits. 6.2 12 
1A Guidelines for venting outlet works. 6.1 13 
2C Compile data on performance of conduits with significant settlement and lateral movement. 6.1 13 
2D Guidance on seismic effects on conduits and methods for analysis and design to address those effects (e.g. embankment spreading, fault offset, propagation of earthquake waves). 6.1 13 
5D Best practices guide for design and construction methods to rebuild embankment sections removed for outlet conduit removal/replacement. 5.9 16 
6D Guidelines for inspection of normally inundated structures and other difficult-to-access features. 5.4 17 
2B Guidance on application of tunnels for outlet works  including consideration of microtunneling and of both soft-ground and hard-ground tunneling. 5.3 18 
5C Assessment of microtunneling and boring technologies for application to outlet conduit rehabilitation. 5.3 18 
6A Applications of non-destructive testing (NDT) for inspection of outlet works. 5.3 18 

Notes: (1) 0 is lowest benefit and 10 is highest benefit. 


EXHIBIT 5-2
RANKING OF RESEARCH/DEVELOPMENT IDEAS BASED ON INDIVIDUAL SCORES FOR COST/EASE OF IMPLEMENTATION

TOPIC NUMBER RESEARCH/DEVELOPMENT TOPIC(S) SCORE 0 to 10(1) RANK 
3B Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. 6.5 1 
6C Best-practices guide for inspection frequency and methods of inspection for typically accessible outlet works conduits. 6.4 2 
3A Best-practices guide for selection of gates and valves for outlet works structures. 6.3 3 
1B Best-practices guide for outlet works conduits through embankment dams, emphasizing small embankments. 6.3 3 
1D Develop a list of failure modes for outlet works. 6.2 5 
5D Best practices guide for design and construction methods to rebuild embankment sections removed for outlet conduit removal/replacement. 6.2 5 
6B Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical and electrical components. 6.2 5 
1C Best-practices guide for mechanical and electrical design and for automated control for outlet works. 6.1 8 
4A Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, configuration, etc. 6.1 8 
5A Design guidance and guide specifications for sliplining of outlet conduits. 6.1 8 
6D Guidelines for inspection of normally inundated structures and other difficult-to-access features. 5.8 11 
5B Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. 5.5 12 
1A Guidelines for venting outlet works. 5.4 13 
6A Applications of non-destructive testing (NDT) for inspection of outlet works. 5.4 13 
5C Assessment of microtunneling and boring technologies for application to outlet conduit rehabilitation. 5.2 15 
2A Best-practices guide for outlet works intake towers, considering such factors as location, configuration, access, debris/trash control, seismic performance, selective withdrawals, etc. 4.9 16 
2C Compile data on performance of conduits with significant settlement and lateral movement. 4.7 17 
2D Guidance on seismic effects on conduits and methods for analysis and design to address those effects (e.g. embankment spreading, fault offset, propagation of earthquake waves). 4.6 18 
2B Guidance on application of tunnels for outlet works  including consideration of microtunneling and of both soft-ground and hard-ground tunneling. 4.4 19 
3C Develop short course (with video/DVD option) on design, operation, and maintenance of outlet works gates and valves. 3.6 20 

Note: (1) 0 is unfavorable high cost/difficulty of implementation and 10 is favorable low cost/ease of implementation. 


EXHIBIT 5-3
RANKING OF RESEARCH/DEVELOPMENT IDEAS BASED ON THE COMBINATION OF INDIVIDUAL SCORES FOR POTENTIAL BENEFIT AND COST/EASE OF IMPLEMENTATION

TOPIC NUMBER RESEARCH/DEVELOPMENT TOPIC(S) POTENTIAL BENEFIT(1) COST(1) SCORE 0 to 10(2) RANK 
1B Best-practices guide for outlet works conduits through embankment dams, emphasizing small embankments. 8.1 6.3 7.2 1 
3A Best-practices guide for selection of gates and valves for outlet works structures. 7.6 6.3 7.0 2 
3B Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. 7.1 6.5 6.8 3 
4A Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, configuration, etc. 7.4 6.1 6.8 4 
5A Design guidance and guide specifications for sliplining of outlet conduits. 7.4 6.1 6.8 4 
1C Best-practices guide for mechanical and electrical design and for automated control for outlet works. 7.0 6.1 6.6 6 
5B Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. 7.5 5.5 6.5 7 
6B Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical and electrical components. 6.8 6.2 6.5 7 
1D Develop a list of failure modes for outlet works. 6.4 6.2 6.3 9 
6C Best-practices guide for inspection frequency and methods of inspection for typically accessible outlet works conduits. 6.2 6.4 6.3 9 
5D Best practices guide for design and construction methods to rebuild embankment sections removed for outlet conduit removal/replacement. 5.9 6.2 6.1 11 
2A Best-practices guide for outlet works intake towers, considering such factors as location, configuration, access, debris/trash control, seismic performance, selective withdrawals, etc. 6.7 4.9 5.8 12 
1A Guidelines for venting outlet works. 6.1 5.4 5.8 13 
6D Guidelines for inspection of normally inundated structures and other difficult-to-access features. 5.4 5.8 5.6 14 
2C Compile data on performance of conduits with significant settlement and lateral movement. 6.1 4.7 5.4 15 
2D Guidance on seismic effects on conduits and methods for analysis and design to address those effects (e.g. embankment spreading, fault offset, propagation of earthquake waves). 6.1 4.6 5.4 16 
6A Applications of non-destructive testing (NDT) for inspection of outlet works. 5.3 5.4 5.4 16 
5C Assessment of microtunneling and boring technologies for application to outlet conduit rehabilitation. 5.3 5.2 5.3 18 
3C Develop short course (with video/DVD option) on design, operation, and maintenance of outlet works gates and valves. 6.4 3.6 5.0 19 
2B Guidance on application of tunnels for outlet works  including consideration of microtunneling and of both soft-ground and hard-ground tunneling. 5.3 4.4 4.9 20 

Note: (1) The individual scores (potential benefit and cost) are from Exhibits 5-1, and 5-2. 
      (2) Arithmetic average of the two individual scores. 


EXHIBIT 5-4 
COST-BENEFIT COMPARISON OF RANKED R&D TOPICS 


SECTION SIX References

All of the white papers authors provided reference lists in cases where references were cited, 
which can be found in the footnotes or bibliographies provided at the back of the white papers 
presented in Attachments 4 through 9. 

In addition, due to recommendations of several authors that standardized guidelines to be used in 
outlet works design and consistent guidelines for the various topics included in this workshop be 
developed, the following internet addresses may prove useful in locating the most recent outlet 
works publications. 

www.usace.army.mil/publications/ 
www.usbr.gov/pmts/hydraulics_lab/ 
www.ferc.gov/industries/hydropower/safety.asp 
www.info.usda.gov/CED/ 

Attachment 1 

AGENDA 
FEMA WORKSHOP ISSUES, REMEDIES, AND RESEARCH NEEDS RELATED TO DAM OUTLET WORKS
May 25, 26, and 27, 2004 
Denver, Colorado 

Day 1 - Tuesday, May 25, 2004 
8:00 to 8:15 Self- Introductions 
8:15 to 8:30 Workshop Introduction 
8:30 to 9:00 White Paper Presentation  Failure Modes 
9:00 to 9:30 Discussion of State-of-Practice  Failure Modes 
9:30 to 10:00 Brainstorming of R & D Needs  Failure Modes 
10:00 to 10:15 Morning Break 
10:15 to 10:30 Prioritization of R&D Needs  Failure Modes 
10:30 to 11:30 R & D Implementation Work Groups  Failure Modes 
11:30 to 12:00 Implementation Work Group Reports  Failure Modes 
12:00 to 1:00 Lunch 
1:00 to 1:30 White Paper Presentation  Inspection 
1:30 to 2:00 Discussion of State-of-Practice  Inspection 
2:00 to 2:30 Brainstorming of R & D Needs  Inspection 
2:30 to 2:45 Prioritization of R&D Needs  Inspection 
2:45 to 3:00 Afternoon Break 
3:00 to 4:00 R & D Implementation Work Groups  Inspection 
4:00 to 4:30 Implementation Work Group Reports  Inspection 
4:30 to 5:00 Day 1 Closure 

Day 2 - Wednesday, May 26, 2004 
8:00 to 8:30 White Paper Presentation  Energy Dissipators 
8:30 to 9:00 White Paper Presentation  Gates and Valves 
9:00 to 9:30 Discussion of State-of-Practice  Energy Dissipators and Gates and Valves 
9:30 to 10:00 Brainstorming of R & D Needs  Energy Dissipators and Gates and Valves 
10:00 to 10:15 Morning Break 
10:15 to 10:30 Prioritization of R&D Needs  Energy Dissipators and Gates and Valves 
10:30 to 11:30 R & D Implementation Work Groups  Energy Dissipators and Gates and Valves 
11:30 to 12:00 Implementation Work Group Reports  Energy Dissipators and Gates and Valves 
12:00 to 1:00 Lunch 
1:00 to 1:30 White Paper Presentation  Conduits 
1:30 to 2:00 Discussion of State-of-Practice  Conduits 
2:00 to 2:30 Brainstorming of R & D Needs  Conduits 
2:30 to 2:45 Prioritization of R&D Needs  Conduits 
2:45 to 3:00 Afternoon Break 
3:00 to 4:00 R & D Implementation Work Groups  Conduits 
4:00 to 4:30 Implementation Work Group Reports  Conduits 
4:30 to 5:00 Day 2 Closure 

Day 3 - Thursday, May 27, 2004 
8:00 to 8:30 White Paper Presentation  Rehabilitation 
8:30 to 9:00 Discussion of State-of-Practice  Rehabilitation 
9:00 to 9:30 Brainstorming of R & D Needs  Rehabilitation 
9:30 to 9:45 Prioritization of R&D Needs  Rehabilitation 
10:00 to 10:15 Morning Break 
10:15 to 11:15 R & D Implementation Work Groups  Rehabilitation 
11:15 to 11:45 Implementation Work Group Reports  Rehabilitation 
11:45 to 12:45 Lunch 
12:45 to 1:45 Recap and Discussion of R&D Needs 
1:45 to 2:30 Prioritization of Leading R&D Needs 
2:30 to 3:00 Day 3 - Closure 

Attachment 2 

FEMA WORKSHOP ON ISSUES, SOLUTIONS AND RESEARCH NEEDS RELATED TO DAM OUTLET WORKS 
MAY 25, 26, AND 27, 2004 
DENVER, COLORADO 

1. Title/Description of Research/Development Item 

2. Description 
A. Why is this a priority research/development item? 
B. What is the expected outcome? 

3. Project Tasks and Needs 
A. What tasks are to be done? 
B. How is the problem to be solved? 

4. 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? 

Attachment 3 

RANKING OF RESEARCH AND DEVELOPMENT IDEAS 

No. Research and Development Idea Benefit Ranking, 0 to 10(1) Difficulty/ Cost Ranking, 0 to 10(2) 
1 Guidelines for venting outlet works. 
2 Best-practices guide for mechanical and electrical design and for automated control for outlet works. 
3 Best-practices guide for outlet works conduits through embankment dams, emphasizing small embankments. 
4 Develop a list of failure modes for outlet works. 
5 Applications of non-destructive testing (NDT) for inspection of outlet works. 
6 Best-practices guide for inspection frequency and methods of inspection for typically accessible outlet works conduits. 
7 Best-practices guide for inspection of outlet works gates, valves, and operators, including mechanical and electrical components. 
8 Guidelines for inspection of normally inundated structures and other difficult-to-access features. 
9 Best-practices guide for selection of gates and valves for outlet works structures. 
10 Best-practices guide for energy dissipators for outlet works structures, considering heads, velocities, configuration, etc. 
11 Guidelines for maintenance and exercise of gates and valves and for cavitation repairs for outlet works. 
12 Develop short course (with video/DVD option) on design, operation, and maintenance of outlet works gates and valves. 
13 Best-practices guide for outlet works intake towers, considering such factors as location, configuration, access, debris/trash control, seismic performance, selective withdrawals, etc. 
14 Compile data on performance of conduits with significant settlement and lateral movement. 
15 Guidance on application of tunnels for outlet works  including consideration of microtunneling and of both soft-ground and hard-ground tunneling. 
16 Guidance on seismic effects on conduits and methods for analysis and design to address those effects (e.g. embankment spreading, fault offset, propagation of earthquake waves). 
17 Design guidance and guide specifications for sliplining of outlet conduits. 
18 Compilation of case studies on outlet works rehabilitation  lessons learned, performance, comparative costs. 
19 Assessment of microtunneling and boring technologies for application to outlet conduit rehabilitation. 
20 Best practices guide for design and construction methods to rebuild embankment sections removed for outlet conduit removal/replacement. 

Notes: (1) 0 is lowest benefit and 10 is highest benefit. 
       (2) 0 is unfavorable high cost/difficulty in implementation and 10 is favorable low cost/easy implementation. 

Attachment 4 

OUTLET WORKS FAILURE MODES 
FEMA Outlet Works Workshop
May 25- 27, 2004 Denver, Colorado 
By Sal Todaro 

1.0 INTRODUCTION 
This paper overviews the ways in which outlet works can fail and methods that can be used to 
prevent failures. Outlet works features are grouped into four basic structures (1) Intake 
Structures, (2) Conduits and Tunnels (3) Control Structures and (4) Energy Dissipators. Gates, 
valves and other mechanical features are discussed with the structures where they are located. 
Causes of outlet works failures include: foundation related failures, structural deterioration, 
structural failures, mechanical failures, failures related to hydraulics, failures related to ice and 
sediment loadings, and operator error. Methods are recommended to prevent failures in new 
design, by retrofitting existing facilities, and by facility operation. 

The outlet works is an important cause of dam failures, since approximately 25 percent of 
embankment dam failures are associated with the outlet works.1 Outlet works failures can also 
result in less catastrophic consequences than dam failure such as: the inability to make required 
reservoir releases, structural or mechanical conditions requiring emergency draining of the 
reservoir, or the uncontrolled release of the reservoir. 

2.0 INTAKE STRUCTURES 
2.1 Intake Structures 
The intake structure is where water enters the outlet works. Intake structures can be either gated 
or ungated. 

2.2 Types of intake structures and their application 
Intake structures can be submerged structures, tower structures with multiple level inlet ports, 
inclined structures located on an abutment of the dam with a single bottom inlet or with multiple 
level inlet ports. 

2.3 Mechanical Features of Intake Structures 
The principal mechanical features of intake structures are the intake gates and the trash racks. 
Ungated inlets are often fitted for the installation of a removable bulkhead gate that could be 
installed using divers. 

 Intake Gates and Valves- Causes of gate and valve malfunction and failure include: 
debris, cavitation, ice, operator error, and malfunction of gate operating mechanisms, lack 
of exercise, deterioration and corrosion. Use of obsolete equipment is common because it 
is often difficult and costly to replace this equipment. Agencies that would not consider 
driving a Model T car commonly use similar vintage equipment to release water from 
major dams. 

 Control Systems to open and Close Gates and Valves-Mechanical control systems can 
include motor driven, hydraulic, and hand operators. Hydraulic control systems include 
hydraulic power units and hydraulic cylinders to open and close gates and valves. 

 Trash racks- Failure and malfunction of trash racks can result from: plugging due to 
sediment or debris or collapse of trash racks resulting for plugging from frazil ice. 

1 Foster, M., R. Fell, and M. Spannagle. 2000. The statistics of embankment dam failures and accidents. Canadian 
Geotechnical Journal. Volume 37, Number 5, pp. 1000-1024. October. 

2.4 Failure Modes of Intake Structures 
 Foundation Related Failures of Intake Structures - It is important for the designer to 
locate the intake structure on firm bedrock whenever possible. A firm foundation for the 
intake structure is important to reduce differential settlement between the intake structure 
and the outlet conduit. A rock foundation will not only reduce settlements but also 
provide rock mass for anchoring the structure to the rock foundation. Small or 
undetectable settlements at low or submerged inlet structures can be magnified several 
times at high intake towers. No engineer wants to be responsible for the design an intake 
tower that looks like the Leaning Tower of Pisa. Rock foundations can also be used for 
anchoring high intake towers to resist seismic loadings 

 Structural Deterioration - Intake structures can prematurely deteriorate over time because 
of the following: aging; freeze thaw damage which open intake towers can be especially 
susceptible to; poor concrete materials such as alkali aggregates; or poor water quality 
(excessively low or high pH can accelerate corrosion of reinforcement and cause 
deterioration of concrete). 

 Ice loading  Loading from expanding reservoir ice have caused damage to trash racks, 
gates stems, intake towers and piers for intake tower access. 

 Seismic Failure- It is important that intake structures are operable after earthquakes so 
that the outlet works can be used for emergency reservoir evacuation or to provide water 
to surrounding communities following a disaster. 

 Sedimentation of Intake Structures- Sedimentation of intake structures has caused serious 
operational problems at many dams. Sedimentation of intakes can be caused by: improper 
reservoir operation, upstream development, forest fires or design deficiencies. 

 Hydraulic Related Failures- Hydraulic related failures at intake structures could include 
cavitation of intake gates or at areas of the intake structure or in the conduit downstream 
of the intake gate. 

 Air/Water Related Failures - Inadequate air supply to control gates can cause cavitation 
and vibration at intake towers. Another air /water related operational problem is air 
blowback caused by air coming out solution in the conduit violently blowing air and 
water into intake structure. This type of air blowback resulted in serious damage at the 
Bureau of Reclamations Navajo Dam. Air blowback also caused the loss of the trash 
racks at Denver Waters Dillon Dam by ejecting them into the reservoir. 

 Structural fatigue caused by vibration, or collapse as a result plugging such as at Yards 
Creek Dam as seen in Photo 1. 

Photo 1  Collapse of Trash Rack at Yards Creek Dam. 

2.5 Methods to Prevent Failure of Intake Structures 
Methods that can be used to prevent failures of intake structures include the following actions: 

 Locate the intake structure on a rock foundation whenever possible to reduce settlement 
and to provide cohesion and rock mass for anchorage to the foundation rock to increased 
seismic stability 

 Design for air demand requirements to prevent blowback, pipe collapse, and cavitation 
of control gates. 

 Design for ice loading and consider the use of bubbler systems to prevent ice formation. 
Gate stems which will pass through a reservoir ice cover should either have a bubbler 
system to prevent ice formation or the gate stem should be located in an oil filled pipe. 
This is a standard detail that can be supplied by the gate manufacturers. 

 Use a mechanical engineer experienced in design of systems for dams to design the 
mechanical features of the outlet works. This engineer should be responsible for 
selection of intake gates, operators, and operating systems. This engineer should 
conducting inspections of the installation and testing of gates and other critical operating 
systems. 

 Use reliable standard designs that have been developed and tested over time. 
Standardized reliable designs can be used to design most intake structures. Use of 
standardized designs will reduce design time and also help provide the owner with a 
tested design. 

 Use standardized design criteria, for loading condition and allowable stress. 

 Locate the intake structure to reduce sediment and debris accumulation. The design 
may require invert of the intake structure to be located at a higher elevation to reduce 
sediment accumulation. 

 Operate the reservoir to reduce movement of reservoir sediment to the intake 
structure. At Twitchell and Strontia Dams, reservoir fluctuation is minimized since draw 
down lowering of the reservoir can transport sediment to the lower depths of the 
reservoir. 

 Consider the vibration in design of trash racks. 

3.0 CONDUITS AND TUNNELS 
3.1 Conduits and Tunnels for Dams 
Conduits and tunnels are used to convey outlet works discharges from the reservoir through the 
dam. Conduits can be constructed of cast in place or manufactured pipe. Conduit outlets are 
usually constructed through dams and can increase the risk of failure of embankment dams 
because of the potential for embankment piping near the conduit. Tunnel outlet works are 
separated from the dam embankment and are generally considered to be a safer than conduits.2 

3.2 Types of Conduits 
The two general types of outlet conduits through dams are cast in place concrete conduits and 
conduits constructed using manufactured pipe. Pipe materials used to construct outlet conduits 
include of pre-cast concrete, plastic, steel and ductile iron. 

3.3 Tunnels 
Tunnels for dams are usually constructed in hard rock conditions however soft ground tunnels 
have also been used for dam outlet works. Tunnels for dams are usually lined with cast in place 
concrete or welded steel. In some cases (usually in the past) tunnels have been constructed for 
dams without tunnel linings. This practice is not currently accepted for outlet tunnels located 
near embankment dams because of the potential for pressurized water to travel through joints in 
the rock and cause internal erosion of the embankment. 

2 Refer to Conduits through Embankment Dams a guideline developed by FEMA containing the design 
requirements for conduits through embankment dams. Final Draft dated February 2005. 

3.4 Embankment Dam Failure Caused by Outlet Conduits 
Outlet conduits have been found to be responsible for approximately 25 percent of embankment 
dam failures. Four possible failure modes associated with outlet conduits that can result in dam 
failure are shown in Figure 1. Two of the failure modes are caused by a structural failure of the 
outlet conduit, the other two failure modes is caused by preferential seepage paths through the 
embankment near the conduit. These failure modes are discussed in detail in the upcoming 
FEMA guideline for the design of outlet conduits.3 

3 Conduits through Embankment Dams, FEMA. Final Draft dated February 2005. 

Figure 1  Failure Modes for Conduits in Embankment Dams: Internal erosion of embankment into conduit;
Pressurized defect in conduit causing embankment piping; Piping of embankment along outlet conduit; and
Seepage through fracture of embankment near conduit.

3.5 Failure Modes of Tunnel Outlet Works 
Tunnel outlets works adequately separated from the embankment cannot cause the internal 
erosion of the embankment. However, tunnel outlet works constructed too close to a dam can 
result in internal erosion of a dam embankment. Internal erosion of an embankment caused by an 
outlet tunnel is rare but can occur. The outlet tunnel at Willow Creek Dam was constructed under 
the abutment of the dam. Erosion of embankment material through rock joints above the tunnel 
caused a sinkhole at the embankment and required significant repairs to the embankment and the 
tunnel.4 

4 Conduits through Embankment Dams, FEMA. Final Draft dated February 2005.

3.6 Methods of Preventing Failure of Conduits and Tunnels 
Methods that can be used to reduce the potential for failure of outlet conduits through 
embankment include the following actions: 

 Filter the dam embankment near the outlet conduit to prevent the internal erosion of the 
embankment along or near the conduit.5 

 Construct outlet conduits on rock foundations whenever possible. Founding the outlet 
conduit upon a rock will provide several benefits and reduce the potential for settlement 
and cracking of the conduit and therefore reduced potential leakage of from the conduit to 
the embankment or from the embankment into the conduit. Conduits constructed directly 
upon rock foundations can also decrease the contact area between the embankment and 
the conduit and reduce the paths for seepage along the conduit. Constructing the conduit 
into the dam abutment can also reduce the potential for stress concentrations and for the 
embankment near the conduit as seen in Figure 2.6 

Figure 2  Conduit Cast Against Excavated Rock 

 Conduits can be designed with redundant methods to prevent seepage of water from the 
conduit to the embankment and embankment material from piping into the conduit. 
Redundant methods of seepage prevention can include the use of a cast in place concrete 
conduit with water-stopped joints and a welded structural steel liner. This redundant 
design method has been used by the Bureau of Reclamation for pressurized conduits for 
higher head dams or outlets founded upon weak compressible foundation. HDPE pipe 
with welded joints and reinforced concrete encasement with water-stopped joints can also 
be used for a redundant outlet conduit design for lower head dams. 

5 Refer to the upcoming FEMA guideline on conduits through embankment dams for guidance on the design of filters for outlet conduits. 
6 Source: Conduits through Embankment Dams  FEMA Final Draft dated February 2005. 

4.0 CONTROL STRUCTURES 
4.1 The Function of Control Structures 
For the purpose of this paper, the term control structures is used to refer to the location where 
the discharge from the outlet works is controlled. The flow regulating gates for the dam are 
located at the control structure. The regulating can be located: at a valve house at the 
downstream toe of the dam, at an intake structure or at a gate chamber within the dam. Figure 3 
shows these typical locations for control valves.7 

Figure 3  Various Locations for Control Structures (4 Arrangements). 
Arrangement 1 - Intermediate control with downstream access. The control feature is located at an intermediate point within the conduit.  
Arrangement 2 - Intermediate control without downstream access. The control feature is located at an intermediate point within the conduit. 
Arrangement 3 - Upstream control. The control feature is located at the upstream end of the conduit. 
Arrangement 4 - Downstream control. The control feature is located at the downstream end of the conduit. 

7 Source: Conduits through Embankment Dams  FEMA. Final Draft dated February 2005. 

4.2 Control Valves for Outlet Works 
The selection of the valve used to control flow is strongly influenced by the location of the 
control structure. 

 Control Valves Located at Intake Structures- When control valves are located at the 
intake structure, the conduit through the dam is usually not pressurized; this type of 
design is commonly used by the Corps of Engineers for their flood control dams. 
Location for the control valve at the intake structure is also common for small dams 
where slide gates are located at the upstream face of the dam. Sluice gates or bonneted 
slide gates are commonly used to control flow from intake towers. The approach 
conditions for control gates located at intake towers are usually less than ideal; these poor 
approach conditions can affect the performance of the gate and can cause cavitation and 
vibration. When intake gates are used to control flows at heads above approximately 40 
feet, care is required in the design of the intake and selection of the control gate. 

 Control Valves Located in Gate Chambers- When control valves are located in gate 
chambers the flow upstream of the gate chamber is pressurized and the flow downstream 
of the gate chamber is not pressurized (open channel flow conditions.) This type is 
commonly used by the USBR for their outlet works. The approach flow to valves located 
in gate chamber is usually a pressurized conduit with a transition designed to streamline 
flow to the control valve. Conditions upstream of valves located in gate chambers are 
usually trouble free. However, because of the high velocities that can occur downstream 
of a control valve, cavitation can occur downstream of valves at higher head facilities. 
The bonneted slide gate is commonly selected for this application because they perform 
well under a wide range of operating heads and they produce a compact jet which is 
required to allow open channel conditions in the downstream conduit. 

 Control Valves Located a Valve House at the Downstream Toe of the Dam. The entire 
length of the outlet conduit is pressurized when the control valves are located at the 
downstream toe of the dam. This type of design is often used when the outlet works is 
used to supply a pressurized pipeline or a hydroelectric power plant. This type of design 
is almost exclusively used when the head at the valve exceeds 200 feet. The types of 
valves commonly used for this application include the fixed cone valve, the jet flow gate, 
the bonneted slide gate and the sleeve valve. 

4.3 Failure Modes of Control Structures 
Failure modes of control structures are usually associated with the gates, valves, or gate 
operators and control systems. These types of failures do not usually jeopardize the safety of the 
dam, but can limit the ability of the dam to discharge water for normal or emergency releases. 
Photo 2 shows a valve stuck in the closed position because of lack of maintenance. Photo 3 
shows poorly maintained and broken gate operators at an intake tower. Photo 4 shows a failed 
needle valve, this failure resulted in the death of the dam tender. Many of these failures are 
caused poor maintenance and the use of outdated (antique) equipment. 

Photo 2 - Valve stuck in the closed position due to lack of maintenance. 
Photo 3  Broken Gate Operators at an Intake Tower. 
Photo 4 - Failed needle valve. 

4.4 Methods to Prevent Failure of Control Structures 
Methods that can be used to prevent failures of control structures include the following actions: 

 Proper training of all operations and maintenance personnel 
 Regular periodic exercise of all gates and valves to prevent buildup on seats and other 
moving parts that would inhibit operation (minimum of once per year, preferably 3 or 4 
times per year). 
 Note any unusual noises or vibration during operation of equipment, and investigate any 
new observations. 
 Periodically measure electrical current or hydraulic pressure required for gate and valve 
operation. Compare readings with previous measurements to note any deviations 
 When designing new outlet works or outlet works rehabilitations, use a mechanical 
engineer experienced with the design of gates, valves and mechanical systems for dam 
outlet works. 
 Replace outdated and unreliable gates, valves and operators 

5.0 ENERGY DISSIPATORS 
5.1 Energy Dissipators and Their Function 
Energy dissipators are used to reduce channel erosion downstream of outlet works. A more 
thorough discussion of the types of energy dissipators used for outlet work and their application 
can be found in the White Paper prepared for this workshop by Dr. Henry T. Falvey titled 
White Paper on Energy Dissipators. 

5.2 Types of Energy Dissipators 
The more commonly used energy dissipators used for outlet works are: 

 No energy dissipator is used and water discharges directly to the downstream channel. 
As seen in Photo 5 taken at Hubbart Dam a concentrated jet discharging directly to the 
channel downstream of the gate. Initial operation of the gate caused localized channel 
scour which eventually stabilized. 

Photo 5  Hubbart Dam gatehouse and stilling basin. 

 Use a valve that produces a dispersed jet to reduce the potential for downstream channel 
erosion. Fixed cone valves are often used because the produce a dispersed jet that 
reduces the potential for downstream channel erosion. The spray produced by the fixed 
cone valve can result in maintenance problems in cold climates because of the icing that 
often occurs downstream of these valves. 

 Energy dissipating valves - Energy dissipating valves such as the sleeve valve or 
Monovar valves are expensive but can eliminate the need for downstream energy 
dissipating structures. 

 Conventional Concrete Stilling Basin Design- Some commonly reinforced concrete 
stilling basin designs include: the hydraulic jump basin, the Impact basin and the fixed 
cone valve dissipation chamber. 

5.3 Failure Modes of Energy Dissipators 
The principal failure mode for energy dissipators is uncontrolled erosion of the downstream 
channel. 

5.4 Method to Prevent Failure of Energy Dissipators 
The design of energy dissipators for outlet works can usually be accomplished using designs 
standardized by the USBR, USACE, and other large state and federal agencies. These designs 
should be used by the designer whenever possible. 

6.0 CONCLUSIONS 
In order to minimize the occurrence of outlet works failures the following guidelines should be 
followed: 

 Well-trained, experienced engineers should design outlet works; 
 Outlet structures should be located on rock foundations whenever possible; 
 Standardized, reliable designs should be used; 
 Unusual failure modes like those associated with vibration, ice loading, and air/water interactions, should be considered in outlet works design; and 
 Redundancy should be built into the design of all critical elements of outlet works systems. 

Failures of mechanical equipment can usually be traced to the following causes: 

 Lack of exercise 
 Lack of maintenance 
 Deterioration due to erosion, corrosion, and/or cavitation 
 Neglecting operating observed difficulties 
 Operator error or lack of training 

Attachment 5 

DESIGN AND CONSTRUCTION OF OUTLET WORKS CONDUITS FOR EMBANKMENT DAMS 
FEMA Outlet Works Workshop 
May 25  27, 2004  Denver, Colorado 
By Sal Todaro, P.E. 

1.0 Introduction 
This paper addresses outlet works design for smaller dams owned and operated primarily by 
municipalities and private owners. These smaller dams account for most of the nations 
jurisdictional dams. This group of outlet works provides greater design versatility than designs 
produced by federal design agencies and large experienced engineering firms. 

There is no single nationally recognized standard for designing outlet works for dams, and 
inexperienced firms have a greater need for established design guidelines for outlet works. State 
dam safety officials are tasked with reviewing designs that can vary significantly in their design 
approach. On the other hand, outlet works designed by federal agencies and large engineering 
firms use similar designs and are often more consistent in their approach to design. For example, 
outlet works designed by the U.S. Bureau of Reclamation (USBR) are consistent within 
groupings of pressurized and non-pressurized outlet works. 

Not all outlet works should be similarly designed; however, there should be consistent guidelines 
and criteria for preparing these designs. Design guidelines could include recommendations for 
pipe encasement, the need for redundancy, seepage control, methods for addressing compressible 
foundations, pipe selection, joint details, and criteria for reinforced concrete conduit design. 

Consistent guidelines can direct design engineers to safe designs, thus providing state dam safety 
officials assistance in reviewing these designs. Designs developed using thorough, consistent 
standards would result in more consistency between projects and would result in safer, more 
reliable facilities. 

Guidelines currently being prepared by the National Dam Safety Review Board (NSRB) can 
form a basis for design of smaller facilities. The NSRB is preparing a manual for the design, 
construction, maintenance, and repair of conduits for embankment dams. The NSRB manual is 
intended to be used for designing and maintaining outlet works for significant high-hazard dams 
and should be required reading for outlet works designers of both large and small dams. 

2.0 Reducing Embankment Dam Failures Related to Outlet Works Conduits 
Approximately 25 percent of embankment dam failures are related to embankment piping at or 
near the outlet works (Foster et al.)1. By reducing this failure mode, significant dam safety 
improvements would result. Primary embankment dam failures at or near outlet works can be 
attributed to structural defects of the conduit, resulting in piping embankment into or along the 
outside of the conduit (see Figure 1). Because of the extensive erosion that can occur from a 
failure, the exact cause is often difficult to determine. The above-referenced research also shows 
that dam failures associated with outlet works occur rapidly and usually do not provide adequate 
time to respond so that dam failure can be prevented. 

Important improvements in outlet works design methods and construction procedures can be 
achieved by determining the best practice for designing and constructing outlet works, preparing 
nationally accepted standards, and by state and federal dam safety officials enforcing these 
standards. 

1 Foster, M., R. Fell, and M. Spannagle. 2000. The statistics of embankment dam failures and accidents. Canadian 
Geotechnical Journal. Volume 37, Number 5, pp. 1000-1024. October.

3.0 Standards Presently Used for Design of Outlet Works 
3.1 General 
Outlet works are often designed using standards not specifically intended for use in designing 
pressurized outlet system for dams. For example, American Water Works Association (AWWA) 
pressure pipe standards were developed for water supply pipelines; these requirements may not 
be appropriate (without modifications) for the design and construction of outlet pipe under 
embankment dams. 

Outlet pipes have different requirements than water supply pipelines, including long-term 
performance requirements and requirements for construction procedures compatible with the 
design and performance of the embankment dam. Some of the variations between water 
pipelines and outlet works include: 

 Outlet pipe buried under an embankment dam are there for the life of the dam (which 
can be greater than 100 years), thus not allowing the accessibility for repairs as that of 
a water pipeline. The dam may need to be breached to replace an outlet conduit. 
 Outlet pipes under dams are subjected to different foundation movements than 
waterlines; this is especially true during an earthquake. 
 Because public safety issues are associated with dams, outlet works have redundancy 
requirements not required for water pipelines. 
 The consequences from an outlet pipe leak through an embankment dam can be much 
more critical than a water supply pipeline leak. 
 
Engineers not experienced in designing dams and outlet works can inadvertently use 
inappropriate design standards. Examples of misapplication of outlet works design standards include: 

 State highway department standard plans for culverts and culvert structures. These 
standard drawings are simply referred to in design documents to save the engineer 
from designing the outlet works. Culvert designs for highways were not intended for 
use in dams. 

 Natural Resources Conservation Service (NRCS) standards for the structural design 
of flood control outlets have been used for designing high-hazard pressurized outlet 
facilities; however, these standards were not intended for such application. 

 NRCS has also developed design standards for articulated outlet pipe design. These 
standards can also be used beyond NRCS intended use. These design standards have 
been used for designing a pressurized outlet at a high-hazard municipal dam on a soft 
foundation. These particular standards should not be used for designing high-hazard 
pressurized outlet works. 

 USBR Design of Small Dams. This may be the best general reference for designing 
reinforced concrete outlet conduits. The NRCS and Design of Small Dams show a 
precast concrete outlet pipe detail with partial encasement, which should not be used 
for pressurized outlet works for high-hazard dams (Figure 2). This detail allows 
embankments to be placed directly against the pipe surface, an area where leakage 
from the pipe joint has direct access to the embankment. 

 Precast pipe under medium height to high embankments. For example, reinforced 
concrete pressure pipe is usually not a good selection for a pressurized outlet pipe 
under a medium height dam. An outlet pipe under a 100-foot-high dam can have 
more than 80 gasketed joints, each of which is a potential leakage source into the 
embankment. 

3.2 Need for Design Guideline for the Design and Construction of Outlet Works Conduits 
Nationally recognized design guidelines are needed for designing outlet works at small- and 
medium-sized dams. Dam safety officials could then require and enforce minimum standards for 
all new non-federal designs, and design engineers tasks would be simplified by having a 
consistent standard for design, one they know review agencies will accept. Such guidelines 
would reduce the use of inappropriate design standards. The USBR and U.S. Army Corps of 
Engineers (USACE) design standards for outlet works combined with the forthcoming NSRB 
manual can form a basis for preparing a single design and construction standard for smaller dam 
outlet facilities. 

4.0 Foundations for Outlet Works 
Good foundations are important for all civil engineering structures, especially for dams and 
outlet works structures. Design engineers must use appropriate measures in determining the 
foundation and potential movements to help eliminate possible outlet works failures. 

4.1 Outlets Constructed on Rigid Foundations 
Outlet works structures should be founded on firm non-erodable foundations whenever possible. 
The alignment of an outlet conduit should be based upon the location of competent foundation 
for the conduit. Outlet works designs and construction specifications should allow for 
adjustments in the alignment during construction after the foundation in the areas of the outlet 
has been exposed. Final alignment adjustments to fit field conditions can improve foundations 
and help ensure that the outlet works structures are founded on firm, uniform foundations. 
Refining the outlet works alignment can also reduce the amount of required excavation or the 
amount of backfill concrete required. Figures 3, 4, and 5 show the construction of an outlet pipe 
excavated into the abutment of a dam. 

Locating the outlet works on a firm rock foundation will decrease settlement and potential for 
structural distress, improve performance during seismic loads, and reduce seepage potential 
adjacent to the conduit. 

4.2 Outlets Constructed on Compressible Foundations 
Outlet works structures founded upon compressible foundation require more attention during 
design and construction, and provide more challenge to the designer and more risks to the dam 
owner than those on firm rock foundations. Outlet conduits on soft and erodable foundations are 
subject to foundation movement, thus incurring greater risks of embankment piping and 
structural distress of the conduit than outlet conduits founded on firm rock foundations. 
Foundation movements are especially dangerous for rigid outlet pipes with open gasketed joints; 
Figure 6 shows a photograph of a failed pipe. 

Outlet conduit should be located on uniform foundations whenever possible to prevent abrupt 
changes in conduit settlement. Because geological condition variables can exist along a conduit 
alignment, uniform foundation is often not possible. Figures 7 and 8 show profiles of foundation 
settlements for cast-in-place outlet conduits at several USBR dams on compressible foundations. 
Soft foundations under embankment dams can settle vertically and spread horizontally. Figure 9 
shows settlement profiles of a failed cast-in-place articulated pipe. Note that the settlement of 
the pipe joints is more abrupt than the cast-in-place conduit design. (The longitudinal 
reinforcement provided by cast-in-place conduits appears to have an effect of smoothing out the 
conduit settlements under the embankment.) 

These figures are important information for engineers conducting outlet conduit settlement 
analyses. It is important to note that foundation settlement conditions can vary significantly 
along an outlet conduit, do not conform to more uniform settlements, and concentrated localized 
settlements can be more severe than predicted by analysis. 

Engineers should question the precision or theoretical settlement analysis conducted to estimate 
the foundation movement of an outlet works. This is especially important if the outlet works has 
gasketed joints that can fail or open when subjected to movements larger than their design 
capacity. Figure 9 shows the estimated deflection and actual deflection of a reinforced concrete 
cylinder pipe that failed under a 100-foot-high embankment. This outlet pipe was designed 
using articulated joint design methods. 

Work by Rutledge and Gould2 has documented longitudinal movement of pipe joints on soft 
foundations. This work shows that settlement and the horizontal joint openings can be erratic 
and non-uniform. Large horizontal movements take place at random selected joints, rather than 
uniformly along the conduit. This type of concentrated movement can open joints of gasketed 
pipe that are not designed for large concentrated horizontal movements. The results of these 
field measurements show that dangerous movements can occur for gasketed pipe outlet works, 
even when the engineer may believe that the pipe has been designed to resist movement 
predicted by analysis. 

Because of the unpredictable random movements that can occur under dam foundations, 
engineers should question the precision of theoretical settlement analysis estimates of outlet 
works conduits. This is especially important if the outlet works has gasketed joints that can fail 
or open when subjected to movements large than their design capacity. 

Techniques historically used by USBR for designing outlet conduits on compressible 
foundations include: 

 Over-excavating foundation and refill with compacted impervious earthfill, 
 Positioning control gates upstream of impervious embankment, 
 Avoiding pressure conduits through impervious embankments unless it is housed in a freestanding pipe, 
 Providing steel lining for pressurized conduits, 
 Avoiding pre-cast concrete pipe except for embankments of small heights (10 to 12 feet), and 
 Protecting the foundation during construction. 

2 Rutledge, P.C., and Gould, J.P. 1973. Embankment-Dam Engineering. Casagrande Volume. John Wiley & Sons. 
New York City, New York. 

Approaches to Design Outlet Conduits on Soft Foundations 

1. Provide a Freestanding Pipe inside of a Reinforced Concrete Conduit. This is a classical 
outlet works design, which locates a freestanding pressurized outlet pipe inside of a cast-
in-place reinforced concrete conduit. The conduit upstream of the embankment case is 
usually pressurized. The design prevents pressurized water from a leaking pipe from 
contacting the embankment. 

2. Provide a Non-Pressurized Outlet Works System. 

3. Welded Steel Outlet Pipe Encased in Reinforced Concrete. This design includes a 
welded steel pipe and reinforced concrete encasement. The theory of this design is that 
the welded steel pipe is ductile, will deform and maintain a watertight conduit, and will 
resist rupture when subjected to foundation movements. The reinforced concrete 
encasement provides a rigid beam to bridge over weak foundation to minimize 
concentrated deflections. The reinforced concrete also provides a redundant water 
passage, capable of resisting internal and external water loads. This design has been 
successfully used by USBR and URS Corporation for new dams as well as retrofits for 
relining outlet works; however, there are no published design criteria for this design 
method. When possible, field joints for welded steel pipe on compressible foundations 
should be welded after embankment construction once the initial foundation settlement 
has occurred. 

4. Articulated Joint Conduit Design. Another outlet design system on soft foundations is 
the use of articulated joints for the outlet conduit. Joint design for outlet work conduits is 
an important area where guidelines are needed, especially for pressurized outlet works on 
compressible foundations. The theory of this design is that the pipe joints are designed to 
deflect and accommodate for longitudinal and rotational deflections of the pipe joints. 
The pipe encasement concrete is provided with open joints to allow the movement of the 
pipe joints. 

There are two important dam safety concerns when an articulated pipe design is used for 
pressurized outlets at high-hazard dams. The first is that theoretically predicting 
deflections and longitudinal movement of joints may not be accurate, and the joints can 
be subjected to movements beyond their safe capacity. The second concern is that the 
encasement concrete at each pipe joint that can provide a leakage path directly to the 
embankment. A gasket or pipe bell failure from excessive settlement will allow 
pressurized flow from the conduit to the embankment. 

5. Treatment of Foundation During Construction. Special construction procedures should 
be provided to protect the foundation integrity, which can degrade when exposed to air, 
moisture, and construction activity. Construction methods used to prepare conduit 
foundations include covering the exposed foundation with a concrete mud mat as soon as 
the excavation to final grade is exposed. 

5.0 Pipe Material Used for Outlet Works Conduits 
The following is a brief description of various pipe material that have been used at embankment 
dams for outlet conduits. The information is intended to form a basis of discussion by group 
members during the conference. 

1. Cast-in-Place Reinforced Concrete and Outlet Works Construction. This design is typical 
construction for larger dam projects, especially projects designed by major federal 
agencies such as USBR and USACE. The design requirements and methods for cast-inplace 
conduits are well documented in USBR and USACE technical publications. These 
conduits are very versatile in their application and can be designed to fit specific project 
requirements and site conditions. Design alternatives for cast-in-place conduit include 
various standard circular and horseshoe shapes. Cast-in-place conduits can house 
freestanding outlet pipes and can also be steel lined when required for water tightness 
(see No. 2 below). This cast-in-place reinforced concrete conduit is often the best 
technical solution for an outlet works conduit, but is an expensive design alternative. 

2. Welded Steel Pipe Encased in Reinforced Concrete. This alternative is similar to cast-inplace 
reinforced concrete construction. The primary difference between the two is that 
steel-lined conduits are designed to be watertight. The encasement concrete is designed 
to resist embankment and foundation loadings, as well as internal and external water 
pressure. The steel liner is usually designed to resist both the internal and external water 
pressure loadings. This design can be used to provide a ductile and watertight conduit for 
compressible foundation conditions. This design has also been used with relatively thin 
non-structural steel linings whose function is to only provide water tightness. 

3. High-Density Polyethylene Pipe. High-density polyethylene (HDPE) pipe has been 
successfully used for low-head water supply outlet works; however, its use for higher 
head and high-hazard dams needs further investigation. This design requires the HDPE 
pipe to be fully encased in concrete. The encasement allows compaction of embankment 
next to the conduit, fills the pipe haunch areas to eliminate this area of difficult 
compaction and potential seepage, prevents pipe deformation from embankment 
loadings, and can provide a redundant conduit system. 

HDPE pipe is a relatively new material to be used for outlet works conduits. Advantages 
of this material include: (1) it is relatively inert and not subject to erosion; (2) it has 
relatively good and because of the smooth wall, lack bond to the concrete and potential 
for radial thermal movement it has potential for; (3) it has fusion-welded joints and is 
seamless; (4) it is ductile and will not crack and act brittle when subjected to differential 
settlements; and (5) it is relatively inexpensive. 

Possible disadvantages include: (1) there is not a long record of its use; (2) it has a large 
expansion coefficient, and the design must account for radial and longitudinal expansion 
and contraction; (3) it has a smooth wall and will not bond to encasement concrete; (4) 
and because of the smooth wall, lack of bond to the concrete and potential for radial 
thermal movement, it has potential for seepage along the outside of the pipe lining, which 
is a design concern especially if large thermal changes can be expected; and (5) buckling 
and collapsing are important design concerns. HDPE pipe has a low modulus of 
elasticity and is relatively weak in buckling when subjected to external water pressure or 
vacuum loads. 

4. Ductile Iron Pipe. Ductile iron pipe has been used for outlet conduits through 
embankment dams. Modern designers encase the pipe in reinforced concrete. Design 
concerns with the use of ductile iron pipe includes corrosion of the pipe and opening of 
the gasketed joints caused by foundation settlement. 

5. Reinforced Concrete Pressure Pipe. RCP pipe is the most commonly used pipe for outlet 
works at small- and medium-head dams. RCP pipe is used for both pressure and non-
pressure applications. This design when used for embankment dams requires either 
partial or full encasement in concrete. Design references for outlet works using RCP pipe 
include NRCS and USBR design references. 

A hard rock foundation is the best application for this pipe because RCP is relatively 
rigid. Large deflections can crack pipe joints or open gasketed joints. Abrupt settlement 
changes can occur under embankment dams, and this pipe can act brittle when subjected 
to concentrated vertical movements (refer to Figure 6). 

The primary advantages of using RCP pipe for outlet conduits are that it is low cost, is 
commonly available, and requires low maintenance. 

Disadvantages of using RCP pipe include: 

 The pipe gasket is the only line of defense against direct seepage into the 
embankment unless the pipe is fully encased with waterstopped encasement joints. 

 RCP pipe was developed for water supply pipelines; however, improved joints can be 
specified for dam use. Each joint is a potential source of leakage. 

 RCP pipe sections are typically only 8 feet long, thus resulting in a large number of 
gasketed joints under the dam. 

 RCP pipe sections provide little or no resistance to longitudinal pipeline movements 
that can result in openings of joints from foundation settlement and spreading joints. 

 RCP outlet pipe under embankment dams can elongate as the dam settles. 

6.0 Tunnel Outlet Works 
Tunnel outlet works are often not considered for dams less than 150 feet high. In the past, tunnel 
outlet works were more common for embankment dams. For example, USBR used a tunnel 
outlet works at an 80-foot-high dam with soft ground tunneling conditions (see Figure 10 [Rye 
Patch Dam Outlet Tunnel]). Tunnels are not usually considered as a design alternative for 
conditions where soft ground conditions are encountered. However, tunnel outlet works have 
several technical advantages when compared to cut-and-cover outlet conduit designs, especially 
for pressurized outlets. These advantages include: 

 A tunnel outlet works is not physically associated with the embankment. Using a 
tunnel outlet will eliminate embankment failure modes associated with conduit outlet 
works. This failure mode accounts for 25 percent of embankment dam failures. 

 Tunnel outlet works often facilitates stream diversion around the dam site during 
construction. 

 Tunnel outlet works construction can take place independently of embankment 
construction. 

 The tunnel outlet works can allow embankment placement, unobstructed by the outlet 
conduit. 

 Tunnel outlets eliminate special compaction requirements required for the conduit. 

 Tunnel outlets eliminate the need for special filter placement and drainage 
requirement, which can also slow embankment construction. 

 Tunnel outlets eliminate the conduit, a critical path item in constructing the 
embankment dam. 

Disadvantages include: 

 Tunnel outlet works are often more expensive than conduit outlet works, especially 
for smaller diameter outlet works. 

 Tunnel construction typically involves more cost risk for overruns than a conduit 
outlet works. 

 Few engineering firms maintain qualified staff for planning, design, and construction 
services for tunnel engineering. 

 Design engineers may not have readily available costing information to compare 
costs of conduit and tunnel outlets. 

6.1 Comparing Conduit and Tunnel Outlet Works 
Tunnel outlet works are generally more expensive than conduit outlet works. However, outlet 
works for medium-size dams incorporating modern design methods and redundancy features can 
also be surprisingly expensive. This is especially true if the outlet works conduit is a pressurized 
system and the design incorporates a gate chamber under the dam with a freestanding discharge 
pipe. An important benefit of the tunnel outlet is that it eliminates the failure mode caused by 
the conduit passing through the embankment. 

Cost curves for tunnel outlets based on outlet diameter would be helpful, allowing engineers the 
ability to compare costs for preliminary evaluations of tunnel and conduit outlets. Also, cost 
curves for outlet tunnels combined with design guidelines for tunnel outlet works design can 
provide a method for engineers to properly evaluate tunnels when planning the design of an 
outlet works. 

7.0 Conclusions 

 Outlet works are a significant cause of embankment dam failures. Approximately 25 
percent of embankment dam failures are related to piping failures at or near the outlet 
works (Foster et al.). By reducing this failure mode, significant dam safety 
improvements would result. 

 There is no single nationally recognized standard for designing outlet works for dams. 
Outlet works are often designed using standards not specifically intended for outlet 
works. 

 Nationally recognized design guidelines are needed for outlet works at small- and 
medium-sized dams. Consistent guidelines can direct design engineers to safe 
designs and provide state dam safety officials guidelines for review. Designs 
developed using thorough, consistent standards would result in more consistency 
between projects and result in safer, more reliable facilities. 

Attachment 6 

WHITE PAPER ON GATES AND VALVES 
FEMA Outlet Works Workshop, May 25  27, 2004  Denver, Colorado 
By Lee C. Gerbig, P.E. 

This white paper is an attempt to present the current state of the art with regards to gates 
and valves for dam outlet works systems. 

Introduction 

The purpose of an outlet works system in a storage reservoir is to control the flow of 
water from the dam into a river, canal, or some other type of channel. The outlet works 
releases can be controlled to maintain river flows, provide irrigation water, provide water 
to a water treatment facility, provide water to an industrial user, lower the reservoir in an 
emergency, or any other of a multitude of options. The outlet works system must be 
capable of regulating the flow of water for the intended purpose, and must be very 
reliable to provide the necessary control whenever needed. In many facilities, the outlet 
works equipment is very reliable, requires very little maintenance, and is often taken for 
granted until something goes wrong. 

This paper will discuss several types of gates and valves that can be used in outlet works, 
from the very basic to the more complex systems. The discussion will also include 
different methods of gate and valve operation and control. 

The terms gate and valve are used interchangeably in many designs and existing 
structures. For the purpose here, a gate is a mechanical device with a sliding flat member 
within a square or rectangular framework or structure that controls the flow of water. A 
valve is usually a circular structure with a sliding member, flat or circular, that controls 
the flow of water. 

This paper will be organized into several sections, including gate descriptions, types of 
operators, typical outlet designs, and current developments. 

Gate and Valve Descriptions 

The following are descriptions of the basic types of gates and valves found in current use 
on dams, and some descriptions of older equipment that may be found. First the 
discussion will cover the current gates and valves used. 

1. Current Gates and Valves 
A. Slide Gates - The most common type of gate used for dam outlet works is the 
basic slide gate, also referred to as a sluice gate. A slide gate has a movable leaf 
or disk, which slides against bearing surfaces in the frame. The frame is attached 
to a conduit or wall, which provides support against the water load of the gate. 
The gate leaf is moved by a gate stem, which is operated by a manual handwheel 
or crank, electric motor-operator, or hydraulic cylinder. 

Slide gates have been used for throttling service on dams with up to 500 feet of 
head when the proper design is provided, and slide gates are often used as guard 
gates for outlet works with discharge valves at the downstream end of the conduit. 

Slide gates can be of various types and designs as follows: 

1) Cast Iron Slide Gate  The cast iron slide gate (also known as a cast iron 
sluice gate) has been used for over a century for controlling the flow of 
water. The square or rectangular gate leaf or disk and frame are 
constructed of cast iron (or in some instances, ductile iron or cast stainless 
steel). Reinforcing ribs are included on the gate leaf for required strength 
and a pocket for attaching the gate stem is provided. Bronze seats are 
attached to the downstream side of the leaf and the upstream side of the 
gate frame to provide a low-friction sliding surface, and to provide a 
metal-to-metal seating surface to reduce leakage. The gate stem is usually 
made of stainless steel, but older designs may use bronze or carbon steel. 
For longer length stems, guides with bronze bushings are provided to 
reduce the stresses due to column loading. Wedges are installed around 
the perimeter of the gate leaf to assist sealing when closed, by forcing the 
leaf against the seats. Gate leakage is usually very low (0.1 gal/min. per 
foot of leaf perimeter). These gates are usually very robust and can be 
used for throttling flow in excess of 90 feet of head, and used for guard 
service for heads in excess of 150 feet. 

Photo 1 - Typical Cast Iron Slide Gate 

2) Fabricated Slide Gate  The fabricated slide gate can be made from a 
variety of materials including, steel, stainless steel, and aluminum. The 
fabricated gate uses welded construction for the gate leaf and frame, with 
reinforcing ribs where needed. The gate leaf uses the metal plate as a 
sliding surface against low friction material (UHMW or similar) attached 
to the frame. Neoprene J-type bulb seals are often attached to the 
perimeter of the leaf to provide additional sealing, eliminating the need for 
wedges. Gate stem design and construction is the same as for cast iron 
gates. Gate leakage is approximately  the leakage form cast iron slide 
gates. 

For higher head applications (above 100 feet of head), the slide gates can
be provided with metal-to-metal seats, eliminating the bulb-type seals. 

a. Bonneted Slide Gate - For high head applications, usually greater 
than 100 feet, bonneted slide gates can be used. Bonneted slide 
gates are similar in design to fabricated slide gates, except that the 
body is fabricated to totally enclose the gate leaf. The gate leaf 
may be fabricated as a flat stainless steel plate without gate seats 
attached or a carbon steel plate with bronze or stainless steel seats 
to slide against bronze or stainless steel seats in the gate body. The 
flat stainless steel plate design will seal at the top at all gate 
openings; whereas the leaf design with seats attached will allow 
water to flow over the top of the leaf at partial gate openings. At 
higher operating heads, stainless steel/bronze seat combinations 
provide low friction, long wear, and cavitation resistant 
characteristics. The bonneted gates use a flush bottom design, with 
no offsets in the flow along the floor of the conduit, providing 
increased discharge capacity and reduced cavitation potential. The 
upstream side of the leaf is designed for reduced downpull and 
effective flow control at all gate openings. 

The bonneted slide gate is usually embedded in reinforced concrete 
to provide additional structural reinforcement for the pressurized 
gate body. 

b. Wheel Gate  Wheel gates are similar in design to slide gates, in 
that there is a square or rectangular leaf, moving vertically over an 
opening in the gate frame. Instead of the leaf sliding on machined 
bearing surfaces, the leaf is fitted with multiple wheels that ride on 
rails attached to the face of the structure. The rails support the 
water load of the gate leaf and frame, and must be installed in good 
alignment to provide a smooth operating surface. The operating 
loads are much lower for a wheel gate, since there is less friction in 
the wheels and axles than there is in the sliding contact on a slide 
gate. Wheel gates can be designed to close by gravity in an 
emergency if necessary. There is usually a bulb-type seal attached 
to the perimeter of the leaf to seal against the gate frame. 

Installation of wheel gates is often difficult because the tracks and frame 
require critical alignment to achieve smooth operation and effective 
sealing. 

Wheel gates can be operated by stem systems similar to the stem design 
for slide gates, and are usually operated by hydraulic cylinders, although 
there are many installations using a wire-rope hoist systems with an 
electric motor operator. Some multiple intake installations use a gantry 
crane that can install one gate in any one of several gate slots when 
needed. 

Photo 2 - Example of a Wheel Gate 

c. Roller Gate  Roller gates are similar to wheel gates, but a roller 
train is used instead of wheels, when moving against the rails. 
Roller gates also have less friction than slide gates, and are capable 
of closure by gravity. Roller gates have fallen out of favor 
because the roller trains are susceptible to corrosion and buildup of 
deposits that increase friction and interfere with operation of the 
rollers and links. 

The operating systems for roller gates are similar to the systems 
used for wheel gates. 

B. Butterfly Valves  Butterfly valves are commonly used at power plants and 
water facilities. A butterfly valve has a circular body with a circular disk in the 
fluidway that rotates around a shaft in the centerline of the valve, perpendicular 
to the flow. The valves may be installed with the shaft vertical, but the valves are 
usually installed with the shaft horizontal. Butterfly valves are relatively 
inexpensive to purchase and install, and as result, they are often used in 
installations that are questionable. The flow velocities through butterfly valves 
are usually limited to 25 to 30 feet per second, although high-performance 
butterfly valves can operate up top 50 feet per second. The flow around the disk 
in the fully open position creates eddies and flow disturbances that can be carried 
to downstream valves unless proper spacing is provided between valves. 
Butterfly valves can be provided with resilient seats for extremely tight shutoff 
capability. 

Butterfly valves are sometimes used for controlling flow, but that has to be done 
with caution. The rotation of the disk does not provide good flow control 
throughout the operating range, resulting in most of the flow control in the mid-
position of operation. It is also difficult to introduce air into the water flow 
immediately downstream of the valve to prevent cavitation. 

Butterfly valve operating forces are very low, with very little friction and 
hydraulic effects. They may be operated manually, by electric motor-operators, 
or by hydraulic operation. Some butterfly valves are counterweighted to close 
upon loss of power in an emergency situation. 

C. Gate Valve  A gate valve is a variation of a slide gate, with a circular body and 
disk. The disk is often wedged into tapered seats to provide tight shutoff. Gate 
valves are often used for guard gates upstream of regulating valves, or used for 
throttling flow in low-head applications. Flow through the valve is fairly 
unrestricted except for the slot around the disk seats. They are relatively 
inexpensive and easy to install, but the larger valves can become quite heavy. 
Knife gates are often manually operated, but the larger sizes are often operated by 
electric motor-operators or hydraulic operation. 

D. Knife Gate  A knife gate is another variation of a slide gate, but is not 
commonly used in the hydropower or dam industry. A knife gates has a circular 
opening in the gate body with a very thin disk that moves across the flow, 
resulting in a very thin valve, face to face. The wetted parts are often made of 
stainless steel to prevent corrosion, and resilient seats are often used for tight 
shutoff. Flow through the valve is fairly unrestricted, with just slight offsets in 
the flow at the seat area. 

Another variation of the knife gate is a Thru Port Knife Gate, which has a disk 
with a circular opening which matches the pipe diameter to provide an 
unobstructed flow through the valve, resulting in no flow losses or cavitation 
potential. 

Knife gates may be operated manually, by electric motor-operators, or hydraulic 
operation. 

E. Fixed-Cone Valve  A fixed-cone valve is commonly used for regulating the 
flow of water from an outlet works in a dam. A fixed-cone valve is a cylindrical 
valve with a sliding sleeve that covers the opening at the downstream end of the 
valve. A cone (usually 90 degrees) is installed at the end of the circular structure 
that disperses the flow radially through the opening between the valve body and 
the sleeve. Flow can be controlled very well at all but the smallest valve 
openings. Seals are provided between the valve body and sleeve to reduce 
leakage. Operating forces are low, since there is only the friction between the 
moving parts and the seals, with little hydraulic forces involved. The valves have 
a high coefficient of discharge, and do not dissipate much energy. They tend to 
produce considerable spray, as a result of the cone at the end. 

Fixed-cone valves can be furnished with hoods attached to reduce the spray, while 
some other installations use an energy dissipation chamber to contain the spray 
and reduce the energy at the downstream end of the structure. Some attempts 
have been made to operate fixed-cone valves submerged, but that requires careful 
study and evaluation. 

Fixed-cone valves can be operated manually or with an electric motor-operator 
through a miter-gear box and shafts or by hydraulic operation. 

Photo 3 - Fixed-Cone Valve with a Hood 

F. Jet-Flow Gate  A jet-flow gate is a variation of a slide gate used as a free 
discharge gate. The gate has a circular opening with a sliding disk that moves 
over a floating, sloping orifice shaped opening. The sloping orifice concentrates 
the flow to help introduce air to prevent cavitation. There is very little energy 
dissipation, resulting in fairly high flow coefficient. Operating forces are high, 
due to the friction between the disk and the seats, and between the disk and the orifice. 

Jet-flow gates have also been used in submerged applications, by expanding the 
downstream discharge pipe to three times the orifice diameter and keeping the 
discharge pipe very short to allow recirculation and prevent cavitation. 

Jet-flow gates can be operated manually, by electric motor-operators or by 
hydraulic operation. 

Photo 4 - Motor-Operated Jet-Flow Gate 

G. Sleeve Valve  Sleeve valves are used as energy dissipaters, both in-line and at 
the end of a conduit. Sleeve valves consist of a section of perforated pipe with 
small tapered holes and a sliding sleeve to uncover the ports required to provide 
the desired discharge. The sleeves are provided with seals to minimize leakage. 
The in-line type valves usually operate with the flow on the exterior of the 
perforated section, flowing inward to dissipate the energy and then the flow 
moves downstream within the conduit. The valves at the end of a conduit are 
usually installed in a vertical position, with the flow moving outward from inside 
the conduit into a stilling well to dissipate energy. Sleeve valves are very 
expensive to purchase, because the manufacturing process is difficult and the 
materials are usually stainless steel and other corrosion/cavitation resistant 
materials. Installation costs are nominal, since the valves are usually just 
connected to the conduit with appropriate flanges. 

Sleeve valves are usually operated to provide precise flow control; they are 
usually operated by either electric motor-operators or hydraulic operation, with 
remote position sensing provided. 

H. Clamshell Gate  The clamshell gate is a special design used by the U.S. Bureau 
of Reclamation. The clamshell gate consist of two leafs operating in an arc over 
the end of a conduit; machined to match the arc of the gate leafs. The leafs move 
in a symmetrical manner to provide uniform flow between the two leafs. There is 
very little energy dissipation, since the flow is much like the flow from an open 
pipe, so an energy dissipation basin or structure is required. Clamshell gates 
work very well in a submerged installation, providing excellent recirculation to 
prevent cavitation. 

Clamshell gates are usually operated by electric motor-operators or hydraulically 
operated. 

I. Radial Gate  Radial gates have been used for many installations at spillways, 
canal check structures, and canal turnouts. They have also been used 
occasionally for outlet works with a top-seal arrangement in a pressurized 
structure. A radial gate consists of a curved plate with reinforcing ribs, and arm 
structure to provide lateral support, and trunnion pins to allow rotation of the gate 
structure. Resilient seals are provided at the bottom and sides to reduce leakage, 
and smooth wall plates are often used to provide a good sealing and sliding surface. 

Operation of radial gates is provided by wire-rope hoists using either manual 
operators or electric motor-operators, or by hydraulic cylinders attached to the 
gate structure. 

Variations of radial gates with a top seal have been used for medium head (100 to 
150 feet) outlet works regulation. The use of the top seal provides a sealing 
surface around the entire perimeter of the gate leaf. The top seals have been 
difficult to maintain, however, and leakage can be a problem. 

Photo 5 - Example of Radial Gate 

J. Hinged Crest Gate  Hinged crest gates are used at the crest of a spillway, to 
allow flow overtopping the gate to regulate the reservoir or pool elevation. The 
gate consists of a flat or slightly curved plate structure, with a hinge system at the 
bottom to allow the gate to rotate from near vertical to horizontal. The crest gates 
are usually wide and short to provide regulation of long spillway structures. 

The operation of crest gates varies considerably. Some gate use torque tube 
arrangement with a hydraulic operator or electric motor-operator at one end. 
Some other installations use hydraulic cylinders, mounted either underneath the 
panel or mounted above the gate on a deck. Still others use a pneumatic bladder 
arrangement under the panel to regulate the gate. 

2. Older Equipment 
A. Needle Valves  Needle valves have been used primarily as free discharge valves 
for outlet works, but on some occasions they have been used for guard valves for 
turbines in power plants. Needle valves are cylindrical valves with an inner 
plunger or needle, with a tapered nose, that moves back and forth to regulate flow 
through the valve. Most needle valves were operated by pressurizing the opening 
or closing chambers within the valve, with reservoir water from within the valve. 
A type of feedback control system was built-in to try to maintain the position of 
the needle. The needle valves were very troublesome, due to build-up of 
corrosion on closely fitting plungers and bodies, operating clearances that 
increased with usage and produced large internal leaks, and control systems with 
close tolerances that tended to plug up or corrode. Some needle valves have 
experienced catastrophic failure due to air entrapment that created large 
unbalanced forces in the opening and closing chambers. As a result, the valves 
slammed shut and ruptured the valve body or upstream piping due to water hammer. 

Some needle valves are mechanically operated, and do not experienced the 
operating difficulty experienced with water-operated valves. Many needle valves 
have been replaced with more modern, trouble-free valves, with better flow 
characteristics. The needle valves also experienced problems with cavitation on 
the needles, due to sub-atmospheric pressure, and leakage past the seats due to 
erosion form high-velocity flow. 

B. Hollow-Jet Valves  Hollow-jet valves have been used for many years by the 
U.S. Bureau of Reclamation and some other entities. The valves are designed as a 
type of reverse needle valve, with the seal at the upstream end of the needle 
instead of downstream, but they are operated either hydraulically or by electric motor-operator. 

Hollow jet valves provided higher discharge coefficients than needle valves, but 
they are very costly to fabricate because of the complex shapes used in the needle 
portion and upstream body. The hollow-jet valves experience seat erosion at 
small openings, and can have cavitation damage at any slight offsets in the 
downstream bodies. 

Gate Operating Systems 

There are several types of operating systems available to operate gates and valves. 
Principally, there are four basic types; manual operators, electric motor-operators, 
hydraulic operators, and pneumatic operators. 

1. Manual Operation 
Manual operation is usually accomplished with a crank or handwheel connected 
to the gate or valve operating mechanism with threaded stems or a gearbox 
arrangement. (Manual operation is also possible with hydraulic operators, and 
will be discussed under hydraulic operation). 

a. Slide gates, gate valves, knife gates, jet-flow gates, and some sleeve 
valves and butterfly valves use a rising stem design, where an operating 
stem rises and lowers to open or close the gate or valve. The stem has 
threads machined onto the upper end, and a crank, handwheel, or gearbox 
is connected to the stem with an operating nut. 

b. Fixed-cone valves, clamshell gates, and some sleeve valves and butterfly 
valves use rotary motion from the crank or handwheel and rotating shaft to 
convert to linear motion through a gearbox arrangement. 

c. Radial gates, wheel gates, roller gates, and crest gates often use a wire  
rope hoist design that can be manually operated with a crank or handwheel 
that turns the wire-rope hoist drums. Usually wheel gates and roller gates 
are too large to operate manually, in a practical sense. 

The crank or handwheel should be sized to operate the equipment easily and 
provide sufficient force to operate the equipment. The handwheels should be at 
least 12 to 15 inches in diameter for ease of use. Equipment with cranks or 
handwheels is usually designed to operate with no more than 40 pounds of pull on 
the handle or handwheel rim, but the equipment must be designed for much more 
effort (80 to 120 pounds), since some operators can exert much more than 40 
pounds effort if the equipment is stuck or difficult to operate. 

The size of the equipment using manual operation should be carefully considered. 
Although some gates and valves can be operated manually, operation may be so 
slow that it is not practical, and if operation is too difficult, the equipment will not 
be exercised as it should. 

Photo 6 - Manual Operator 

2. Electric Motor-Operators 

Electric motor-operators are used in similar manners as the manual operators, that 
is, either linear motion with threaded stems or rotary motion converted to linear motion. 

An electric motor-operator consists of a high-torque electric motor, gearbox for 
suitable gear reduction and operating speed, pushbuttons, limit switches to control 
stopping positions, torque switches to protect equipment from overloads, 
indicating lights, local position indicators, an in some instances, remote position 
indicators. The high torque electric motors are used to initially start equipment 
open or closed, and operate best on three-phase power due to the high current 
draw during initial operation. The motor-operators will function on single-phase 
power, but size and output is limited. 

The electric motor-operators are usually designed for outdoor applications, with 
weatherproof enclosures. Submerged operation is usually not an option, except 
for extremely short duration. 

Handwheels are usually provided on the units for manual operation if power is interrupted. 

Photo 7 - Electric motor-Operator 

3. Hydraulic Operators 
Hydraulic operation is most often used on large gates and valves operating at high 
head, but is becoming more common for small equipment at low heads for 
particular installations. 

Hydraulic operation typically uses one or more hydraulic cylinders attached to the 
gate or valve, to provide linear motion. The hydraulic cylinder(s) are connected 
to a central hydraulic power unit, with rigid or flexible hydraulic lines. The 
hydraulic line connections should be welded where possible, to reduce the 
potential for leaks at the joints. The hydraulic cylinders can be made fairly 
compact, since high operating pressures are available (2,000 to 3,000 psi, with 
some systems approaching 5,000 psi). The hydraulic cylinders can be designed 
for submerged operation, and can be furnished with electronic sensors for remote 
gate or valve position sensing. 

The hydraulic power units (HPUs) consist of an oil reservoir, one or more electric 
motor-driven hydraulic pumps, control valves, filters, pressure switches to control 
pump and valve operation, relief valves to limit operating pressure, and 
sometimes accumulators to store hydraulic pressure. HPUs can be designed to 
operate more than one gate and/or valve at a facility, by simply adding the 
required control valves, and can be located at fairly long distances from the 
equipment being operated. 

Manual operation can be provided by using a hand pump system instead of an 
HPU. Also, a hand pump may be provided with an HPU for operation during 
electric power interruption. Hand pumps can provide slow operating speeds, but 
some pumps utilize a two-stage pump, with a larger output available at low pressure. 

Accumulators provide operating flexibility when need by providing for limited 
operation during electric power interruption, or for modulating service without 
running the hydraulic pumps and motors frequently. 

Improved hydraulic oils can provide better outdoor performance, and 
biodegradable oils are available where environmental concerns arise. 

Some older gates and valves operated on hydraulic systems using water instead of 
hydraulic oil. The water is stored in tanks above the dam, or the pressure is built 
up by pumps. The principles are the same, but the water systems are usually 
manually operated by opening and closing control valves. The water systems 
have operated for many years, and some are still in service, but corrosion, worn 
and corroded seals, and leaky piping have made many of the systems lacking in 
reliability. Many of the water components, such as cylinders, are very large, since 
high pressure, produced in oil hydraulic systems, is not available. Most water 
systems operated in the range of several hundred psi, instead of several thousand 
for an oil hydraulic system. 

Photo 8 - Hydraulic Power Unit with Accumulators 

4. Pneumatic Operators 
Pneumatic operators are rarely used for operating gates and valves; although one 
successful gate manufacturer currently designs and fabricates hinged crest gates 
using pneumatic bladders at low pressure (Approx. 20 psi). 

The problem with pneumatic operation in typical gates and valves is that, with the 
air, being compressible, it is difficult to maintain a set position. If operating 
forces are high, pneumatic cylinders and control systems become quite large, 
since air pressure is limited to approximately 125 psi. Compressed air is also 
dangerous to work with, because the expansion of the air when released can cause 
great damage. 

Moisture in the compressed air can also create problems at cold temperatures, and 
can cause corrosion to occur in pneumatic equipment. 

5. Portable Operators 
There are several types of portable operators available to work in conjunction 
with manual operators. The manual crank or handwheel operators can usually be 
provided with a square nut or fitting for adapting to a portable operator. 

A. Portable Drill  A portable drill unit is available, which can be mounted on 
a tripod and attached to the crank or handwheel shaft on a manual operator. 
Electric power must be available, and output is usually limited to 
approximately 80 lb. ft. of torque. The drill unit is usually comparable to a 
-inch heavy-duty drill. 

B. Portable Hydraulic Operator  Portable hydraulic operators are available, 
which also connect to the shaft of the manual operator. The portable 
hydraulic operator usually uses a small (5 hp) gasoline engine, hydraulic 
pump, control valve, and a hydraulic motor with flexible hoses to clamp to 
the manual operator. These units are usually mounted on a cart that can be 
easily transported to where needed. 

Photo 9 - Portable Hydraulic Operator 

Another type of portable hydraulic operator connects to a standard hydraulic 
system with quick-connect fittings or other connections, to power a 
hydraulic system or to take the place of the main HPU during an electric 
power interruption. 

C. Chain Saw Operator  Chain saws have been modified to replace the 
cutting chain assembly with a chain-driven operating nut to attach to the 
shaft of a manual operator. These units are lightweight, but very noisy. 

Trends 

In the design of outlet works gates and valves, and outlet works arrangements, there are 
several trends that have been noted. 

1. Remote Operation  More and more designs are being prepared with remote gate 
position sensing and remote or automated operation. The modern gate operating 
systems have reasonably inexpensive means of providing remote gate position 
sensing, and consequently remote control is more attractive. More precise control 
of water flow is provided by remote or automated control, since there is faster 
response to changing conditions. The remote operating systems have also become 
more reliable. Remote sensing is achieved by several means: 

A. Electric Motor-Operators  Electric motor-operators can be furnished 
with position transducers producing a 4 to 20 Ma signal that provides a 
continuous output signal of the gate or valve position. This signal can be 
transmitted by hard wire, optic cable, or radio signal to a control panel or 
computer many miles away. The transducers are built into the operators 
for integral operation, and can be easily modified to produce stepping 
functions or signals at certain openings. 

B. Hydraulic Cylinders  Hydraulic cylinders can be provided with linear 
position transducers also producing a 4 to 20 Ma signal, that function just 
as the transducers on the motor-operators. These transducers san be used 
on hydraulic cylinders submerged in the reservoir for underwater 
operation. 

C. Inclinometers  Some gates that operate with limited rotation, such as 
radial gates and crest gates, can use a transducer known as an inclinometer, 
which measures the angle of a gate member and converts that to gate 
position. These transducers also produce a 4 to 20 Ma signal that functions 
just as the other transducers. 

2. Hydraulic Operation  There appears to be more acceptance on smaller projects 
for hydraulic operation of gates and valves. This practice is favorable for several 
reasons: 

A. Submerged Operation  Hydraulic operators can be designed for 
submerged operation, which may be preferable in some instances. 
Submerged hydraulic cylinders can eliminate long operating stems, and the 
resultant alignment problems. Some stem installations are difficult to 
design, considering access and maintenance issues. 

B. Improved Hydraulic Fluids  Developments in recent years have provide 
hydraulic fluids that are suitable for outdoor use, at most operating 
temperatures. Biodegradable hydraulic fluids are now available that reduce 
the problems with oil leakage in storage reservoirs. 

C. Better Seals  Seals and pipe joint connections have improved to reduce 
leakage and oil spills. Welded pipe connections have virtually eliminated 
oil leaks, and tubing and fitting connections are improved. 

D. Automated Operation  Hydraulic operation lends itself very well to 
automated operation. Where gates and valves are frequently operated for 
optimum flow control, there are no stem threads to wear out, and 
accumulators in the hydraulic systems can reduce pump starts and stops. 
The design of hydraulic cylinders allows for frequent operation without undue wear. 

3. Foreign Design and Manufacturing  In recent years there has been a shift in 
gate and valve design and fabrication to foreign countries. Two large gate 
manufacturers, Hydro Gate and Waterman Industries, have gone through 
bankruptcy. Hydro Gate reorganized and was purchased by the Henry Pratt 
Company, and Waterman is trying to reorganize and scale back, eliminating much 
of their engineering staff. 

Asian countries, such as Korea and Japan, have been designing and/or fabricating 
gates and valves for many years. India is now trying to expand their expertise in 
gate and valve design and manufacturing. Some work is still produced in Europe, 
notably England and Sweden. 

There is a lack of gate designers in the U.S. now, with many steel fabricators 
trying to bid on work, but there are no designers to be found for jobs involving 
design-and-build. Many of the old gate and valve manufacturers have 
disappeared, such as Bingham-Willamette, Allis-Chalmers, Pelton, and Goslin-
Birmingham, with no new companies arising to take their place. 

4. Reduced Government Involvement  Most of the government agencies, such as 
the Bureau of Reclamation, Corps of Engineers, and Tennessee Valley Authority, 
have cut back on their dam design and construction phases of work, resulting in 
less research on new equipment and operation. The government agencies were in 
the forefront of new developments for many years, but that development has really decreased. 

Attachment 7 

White Paper on Energy Dissipators 
FEMA Outlet Works Workshop, May 25  27, 2004  Denver, Colorado 
By Henry T. Falvey1 

INTRODUCTION 

Water passes over or through a dam in a controlled manner through three possible paths. 
These paths are over the spillway, through the penstock, or through an outlet works. The 
purpose of the spillway is to pass flood events past the dam without overtopping the 
structure. Water passing through penstocks goes to hydroelectric turbines to generate 
electricity. Water passing through outlet works is used to control the water level in the 
reservoir and to provide water for irrigation, municipal, or minimum downstream flow 
requirements. 

The outlet works conduit normally passes through the body of the dam. Upstream of the 
centerline of the dam, the pressure in the conduit is almost balanced by the external 
pressure from the water in the dam. However, in the section downstream of the dam 
centerline, the internal pressure can be much higher than the external pressure. A guard 
gate is often placed near the centerline of the dam to avoid the risk of cracks forming in 
the downstream conduit and washing out an earth dam. The conduit downstream of the 
guard gate is either a steel pipe located in a tunnel or it is a chute that forms a part of the 
tunnel. If the downstream conduit is a steel pipe in a tunnel, then the control gate 
structure is located near the downstream toe of the dam. However, if the downstream 
conduit is a chute, then the control gate is located immediately downstream of the 
emergency gate. With a concrete dam, the location of the guard and control gates is not 
critical. They can be found at the axis of the dam or at the downstream face. 

Almost every outlet works requires an energy dissipator so that the high-energy flow 
from the reservoir does not damage the downstream channel or structures. Technically, 
energy is not dissipated in the process. The hydraulic energy is converted into heat 
energy. However, the heat rise in the conversion process is normally so low that it can be 
neglected. Therefore, hydraulic engineers normally refer to the energy conversion process 
as dissipation of the hydraulic energy. The conversion is accomplished by 

 Creating fine grain turbulence, or 
 Creating a loss through a change in momentum of the flow. 

The different types of energy dissipators that have been used at outlet works include, 

 Stilling basins, 
 Baffled Apron Drops, 
 Stepped spillways, 
 Impact basins, 
 Stilling wells, 
 Various types of valves, 
 Sudden enlargements 
 In-line orifices 
 Flip buckets, and 
 Plunge pools. 

The selection of the type of energy dissipator that is used at an outlet works depends upon 
head, discharge, and economical considerations. Often the energy dissipator that is used 
for a specific installation consists of a combination of the types listed above. 

The design of the stilling basins, impact basins, flip buckets, and baffled apron drops has 
been thoroughly discussed in USBR Engineering Monograph No. 25.2 General 
guidelines for the design of outlet works can be found in the US Army Corps of 
Engineers Engineering Manual EM 1110-2-16023 and in the USBR publication Design 
of Small Dams.4 Many of the specialized types of dissipators are described in site-
specific studies. 

The purpose of this paper is to present a state of the art review of current energy 
dissipation devices with respect to their design and selection. 

DESIGN FEATURES 

Stilling basins. The USBR defines three types of stilling basins. The Type I Basin is 
simply a hydraulic jump on a horizontal apron, Figure 1. The energy dissipation is 
accomplished by turbulence within the jump. The Type II Basin contains blocks (chute 
blocks) at the end of the basin and a dentated end sill, Figure 2. The chute blocks create 
shear zones that generate fine grain turbulence. The purpose of the end sill is to prevent 
downstream erosion and does not contribute significantly to energy dissipation. The 
Type III Basin contains an additional set of blocks (baffle blocks) within the horizontal 
apron to create additional turbulence, Figure 3. Cavitation and transverse loads on the 
baffle blocks have required the development of special shapes for high head installations. 
The addition of the chute blocks and the baffle blocks permits the length of the stilling 
basin to be reduced. The energy dissipation for these structures is based on the change in 
momentum of the water through the structure. 

Figure 1. Type I Basin 
Figure 2. Type II Basin 
Figure 3. Type III Basin 

Baffled Apron Drops. The baffled apron drop that is shown in Figure 4 is extremely 
useful in dissipating energy by exerting a force on the water that passes through the 
baffles. The drops are also useful in controlling the air content of the water. With 
approximately seven rows of baffles, the air content of the water becomes saturated. That 
is, if the water is supersaturated or if the water needs more air the baffled apron drop will 
either release air or entrain air to improve the water quality. 

Figure 4. Baffled Apron Drop 

Stepped Spillways. Methods to design a stepped spillway as shown in Figure 5 can be 
found in an excellent book edited by Minor and Hager.5 Although the title indicates that 
the designs are for spillways, the methods outlined in the book can be applied equally 
well to the design of dissipators of outlet works. If the flow depth relative to the step 
height is less than about 0.8, then the energy dissipation is primarily due to changes in 
momentum. This regime is known as nappe flow. For greater depths, energy dissipation 
is primarily due to boundary shear. This regime is known as skimming flow. The exact 
value of the coefficient 0.8 depends upon the slope of the chute. 

Figure 5. Stepped Spillway 

Impact Basins. With an impact basin, the energy is dissipated by turbulence that is 
generated when a jet of water impacts against a vertical wall. After hitting the wall, the 
jet is deflected upward and downwards. A horizontal projection is provided on the top of 
the wall to increase the turbulence in the upstream pool. Although the USBR limits the 
dimensions and discharges to relatively low energy levels, the basins have been used 
successfully at much higher energy levels by scaling the recommended dimensions to the 
larger sizes. The USBR defines impact basins as Type VI Basins, Figure 6. The force that 
the baffle wall exerts on the incoming water jet changes its momentum and thus generates 
the loss. 

Figure 6. Type VI Basin 

Stilling Wells. For low discharges for flows into canals, a stilling well as shown in Figure 
7 is frequently used. The design of stilling wells has been outlined by Falvey6 and Burgi7. 
The energy dissipation is achieved by the change in momentum between the water 
entering the well through the pipe with the diameter and the flow up the square well with 
a side length of width b. The corner fillets and the pedestal in the invert tend to 
maximize the circulation and energy dissipation in the lower portion of the well. The 
flow is controlled by changing the opening, a, using a sleeve valve on the bottom of the 
down comer pipe. Problems have been experienced with the valve operating mechanism 
due to the turbulence in the stilling well. 

Figure 7. Stilling Well 

Valves. With high-head and high flow applications, fixed-cone valves are normally used 
for energy dissipation. These valves use the principle of impinging jets and baffles to 
provide the energy dissipation as shown in Figure 8.8 The ring deflector was damaged 
during operation of the energy dissipator because of a weld failure on the steel cladding.9 
Subsequent inspection found that a large void had been left in the concrete behind the 
steel liner when it was placed. Various modifications of this design concept have been 
developed including hoods on fixed-cone valves that discharge into the atmosphere as 
shown in Figure 9.10 The distance between the end of the fixed cone valve and the hood 
is critical. Severe blowback has been experienced in prototype installations where this 
distance was off by only an inch or two. 

Figure 8. Fixed-cone valve installation 
Figure 9. Hooded Installation of a Fixed-cone Valve 

For high-head and low-flow requirements, the valves are designed on the principle of 
providing small orifices through which the water flows.11, 12 The sudden expansion at the 
downstream side of the orifice is the mechanism that generates the energy dissipation. 
The valves are normally placed in-line as shown in Figures 10 and 11. However, a 40inch 
Monovar valve was used at Terminus Dam in California. In this case, the valve 
discharged freely into the downstream pool. 

Figure 10. Orifice valve 
Figure 11. Monovar Valve 

Sudden Enlargements. A sudden enlargement is a very effective method of dissipating 
energy. The sudden enlargement can occur within or at the end of a pipeline. Two 
examples of sudden enlargements are shown in Figures 12 and 13. The proportions 
shown in Figure 12 are those that minimize the formation of cavitation in the sudden 
enlargement.13 Nevertheless, some ranges of operating conditions will still generate 
cavitation within the structure. The sudden enlargement at the end of the pipeline places 
all the cavitation formation in the downstream tailrace.14 At the Crystal Dam outlet, long 
snake-like vapor filled cavities can be seen during operation. However, these cavitation 
vortices apparently do not generate any adverse effects. 

Figure 12. A sudden Enlargement in a Pipeline with Jet Flow Gates 
Figure 13. A Sudden Enlargement at the End of a Pipeline 

In-line Orifices. Another example of the use of sudden enlargements to dissipate energy 
is the placement of a series of in-line orifices in a pipeline as shown in Figure 14.15 

Figure 14. In-line orifices 

This solution was used at Seven Oaks Dam outlet to provide low flows under a high 
head. Instead of a valve, the terminating structure was an impact basin. Detailed 
computations were necessary to determine the proper number and orifice diameters to 
provide the required energy dissipation under a wide range of reservoir heads without 
generating cavitation downstream of the orifices. 


Elbow Dissipator (ECI Concept)
The energy loss for a 90-degree miter bend is approximately 

Change H @= 1.1 (V^2/2g)

Placing several 90-degree miter bends in a concrete block, as shown in Figure 15, can 
dissipate relatively high heads. The concrete block must be designed to withstand the 
internal pressures and be massive enough to resist overturning from the uneven thrust 
produced as the pressure reduces at each elbow. To date, this concept has not been model 
tested or installed at any prototype location. 

Figure 15. Elbow Energy Dissipator 

Flip Buckets. A flip bucket is often used at the end of an outlet chute to throw the flow 
away from the toe of the dam. These are used in conjunction with plunge pools described 
below. Actually, the flip bucket is not an energy dissipation device although it is 
designated as one in the USBR Engineering Monograph No. 25, as shown in Figure 16. 
Dentates are frequently used to spread the compact jet as it enters the plunge pool as 
shown in Figure 17.16 The literature frequently refers to the energy dissipation effects of 
the jet within the air due to the spreading jet. Actually, very little energy dissipation 
occurs because of the air-water interaction as the jet flies through the air. The principle 
effect of the dentates is to increase the area over which the jet enters the plunge pool. 
This decreases the energy per unit area over which the energy must be dissipated. 

Figure 16. USBR Type X Basin 
Figure 17. Dentates at the End of Chute 

Plunge Pools. A typical plunge pool installation in connection with a flip bucket is shown 
in Figure 18. During the development of a plunge pool, the material that is excavated by 
the plunging jet can form a dam downstream of the plunge pool that will raise the tail 
water sufficiently to drown out the flip bucket. Therefore, many plunge pools are pre-
excavated to alleviate this possibility. The depth and side slopes of this type of plunge 
pool are determined by the soil characteristics. 

Figure 18. Plunge Pool in Connection with a Flip-Bucket 

Another type of plunge pool is shown in Figure 19.17 High-pressure fluctuations develop 
on the invert with this design. Sufficient anchorage and thickness of the floor slabs must 
be provided to prevent their loss during high flows. 

Figure 19. Plunge Pool for an Outlet in a Concrete Dam 

CONCLUSIONS 

Wide varieties of structures are available to designers for energy dissipation of high head 
flows from outlet works. Many of these are described in books and monographs. 
However, many designs have been developed for site-specific installations that have not 
appeared in the literature. Some of these designs have not been verified by either model 
or prototype tests. 

1 Henry T. Falvey & Associates, Inc, Conifer, CO 80433. Email: Falvey@members.asce.org. Tel & Fax: 303 808-4920
2 Peterka, A.J., 1978, Hydraulic Design of Stilling Basins and Energy Dissipators. This monograph is available over the Internet at http://www.usbr.gov/pmts/hydraulics.lab/publications.html. 
3 This can be obtained on the Internet at http:/www.usace.army.mil/usace-docs/eng-manuals/em1110-2-1602. 
4 Hoffman, C.J., 1987, Outlet Works, Chapter X of Design of Small Dams. Third Edition. This book is available over the Internet at http://www.usbr.gov/pmts/hydraulics.lab/publications.html.
5 Minor, H.E, and Hager, W.H., 2000, Hydraulics of Stepped Spillways, A.A. Balkema, Brookfield. 
6 Falvey, H. T. 1962, Hydraulic Model Studies of the Wanship Dam Vertical Stilling Wells, USBR Hydraulic Laboratory Report, HYD 481. 
7 Burgi, P.H., 1973, Hydraulic Model Studies of Vertical Stilling Wells, USBR Hydraulic Laboratory Report, REC-ERC-73-3. 
8 Colgate, D., 1963, Hydraulic Model Studies of the River Outlet Works at Oroville Dam, USBR Hydraulic Laboratory Report, HYD 508. 
9 DeVries, J.J., Hameed. T., and Cheema, M.N., 1994, Hydraulic Model Study of the Oroville Dam River Outlet Works, Center for Water and Wildland Resouces, University of California, Davis. 
10 Beichley, G.L., 1970, Hydraulic Model Studies of an Energy Dissipator for a Fixed Cone Valve at the Ute Dam Outlet Works, USBR Hydraulic Laboratory Report, REC-ERC-70-11. 
11 Burgi, P.H., 1977, Hydraulic Tests and Development of Multijet Sleeve Valves, USBR Hydraulic Laboratory Report, REC-ERC-77-14. 
12 Frizell, K.W., Laboratory Testing of an 8-inch Monovar Valve. 
13 Isbester, T.J., 1974, Hydraulic Model Studies of the Teton Canal Outlet Works Energy Dissipator, USBR Hydraulic Laboratory Report, REC-ERC-74-16. 
14 Burgi, P.H., and Fujimoto, S., 1973, Hydraulic Model Studies of Crystal Dam Spillway and Outlet Works, Colorado River Storage Project, USBR Hydraulic Laboratory Report, REC-ERC-73-22.
15 Ball, J.W., 1963, Progress Report on Hydraulic Characteristics of Pipeline Orifices and Sudden Enlargements used for Energy Dissipation, USBR Hydraulic Laboratory Report, HYD 519. 
16 Cooper, D.R., 1992, Outlet Works for Seven Oaks Dam, Santa Ana River, San Bernardino, County, CA, US Army Corps of Engineers, Technical Report HL-92-14. 
17 Bollaert, E., 2004, Folsom Dam, Numerical Modeling of Hydrodynamic Forces on the Stilling Basin, Aquavision Engineering, Lausanne, Switzerland 

Attachment 8 

White Paper on Rehabilitation of Pipe Conduit Spillways Through Dams 
FEMA Outlet Works Workshop, May 25-27, 2004 
Denver, Colorado 
By James R. Crowder, P.E. 
Schnabel Engineering 

Included in the aging infrastructure of the Southeast United States are hundreds of dams in 
excess of thirty (30) years old. Many of these aging dams are earthfill embankments constructed 
with corrugated metal pipe (CMP) spillway conduits passing through the base/foundation of the 
embankment. Deterioration of the conduit may become a problem when a spillway conduit has 
reached or exceeded its design service life, which is generally considered to be 25 to 30 
years for CMP. The deterioration generally consists of leaking joints, corrosion and holes 
in the pipe. Corrugated Metal Pipes (CMP) are the most susceptible to deterioration. 
Corrugated Metal Pipes were used extensively in small earthen embankment dams in the 
southeast, ranging in height from 10 to 50 feet, in the past 30 to 50 years. The main risk 
associated with the deterioration of these conduits is piping of the surrounding 
embankment soils into the conduit, which can lead to eventual failure of the earthen embankment. 

This paper discusses the repair options that are available to address these deteriorated 
conduits. The options discussed below are based upon the experiences of the author in the 
Southeast United States and are mainly limited to CMPs in earthen dams having a maximum 
height of less than 50 feet. Included in the discussion of each of the options are 
advantages, disadvantages, and design considerations. 

 Option 1  Replacement (Cut and Cover) 
 Option 2 - Slipline the Existing Conduit 
 Option 3  Grouting Along the Exterior of the Conduit 
 Option 4 - Abandon the Existing Conduit 
 Construct Siphon Spillway 
 Construct Short Riser and New Outlet Conduit. 

Option 1 - Replacement 

Replacement, as the name suggests, consists of excavation of the earthen embankment, removal 
of the deteriorated conduit, installation or construction of a new conduit, and backfill of the 
excavation. The side slopes of the excavation through embankment dams are typically limited to 
two horizontal to one vertical (2:1) or flatter, in order to facilitate compaction of the replacement 
backfill against the existing embankment. On relatively high embankments in narrow valleys, 
the excavation required to remove the existing low-level conduit may necessitate the removal of nearly the entire dam. 

The replacement option typically offers the greatest operational flexibility among the spillway 
rehabilitation options. Appurtenances with the ability to completely drain the lake can be 
provided, if desired. Spillway capacity can be increased, or in some cases, controlled to allow for 
flood control improvements or storm water management. 

Removing and replacing the existing conduit typically offers the most thorough rehabilitation 
option for impaired conduits through dams, although this option can be cost-prohibitive. 

The advantages of the replacement option include: 

 Ability to inspect or observe the foundation of the dam 
 Ability to repair areas that may have been damaged by the deteriorating spillway 
 Ability to dramatically change the capacity of the principal spillway 
 Ability to add or improve seepage control measures along the conduit. 
 Capacity to fully drain lake can be provided 

The disadvantages of the replacement option include: 

 Potential high cost of excavating the existing embankment fill to remove the existing conduit 
 The creation of potential seepage paths along the surface of the excavation if proper 
bonding of the replacement backfill is not achieved. 
 The lake must be drained, and remain in a drained condition throughout construction. 
The draining of the lake may be detrimental to both surrounding property values, as well 
to the aquatic life that relies on the lake. 
 Difficulty in diverting normal flows and flood flows during the construction operations 
 Loss of the use of the crest of the dam for pedestrian or vehicular traffic 
 Excavation through the dam may cause conflicts with existing utilities or seepage control 
measures that may be present in the dam 

Option 2 - Sliplining 

Sliplining a pipe consists of placing a new pipe with a smaller diameter inside the existing 
deteriorated conduit and grouting the annular space between the two pipes. The sliplining 
technique can be used in lieu of the replacement or cut and cover method for the rehabilitation of 
the existing outlet pipe. Depending on the pipe used, sliplining may increase the hydraulic capacity of the outlet 
pipe, even when reducing the inside diameter of the original pipe. The reason the hydraulic 
capacity may be increased, even when the diameter of the pipe has been decreased, is due to the 
decrease in roughness of the pipe. Corrugated metal pipes have a relatively high roughness value as 
a result of the corrugations. 

The liner will typically have a roughness value of approximately  of the corrugated metal pipe. When 
designed and installed properly, the slipline technique will add additional years of service life to the existing pipe 
conduit spillway. A sand diaphragm drain is typically installed around the downstream portion of the existing 
conduit to limit the potential for soil piping as the CMP eventually corrodes and deteriorates. 

The advantages of sliplining are many when compared to Option 1. The advantages include: 

 No excavation required through the dam. In cases when either pedestrian or vehicular 
traffic is common or required along the crest of a dam this advantage may be critical. 

 In some cases, a lake can be maintained at or near full when sliplining. When rehabilitating 
a lake in a residential area or adjacent to a golf course green, aesthetics are commonly the 
controlling factor. Keeping a lake full of water duringsummer months, as opposed to 
having a mud flat, is attractive to many clients. In addition, the presence of a full pool allows 
for the maintenance of the existing aquatic habitat within the lake. 

The disadvantages of sliplining can be project threatening. The common disadvantages include: 

 Specialized contractors are required for the installation of the liner and grouting of the 
annular space. Specialized contractors may increase the construction cost. 
 Complete annular space grouting can be a challenge in certain instances. 
 Use of excessive pressure during the grouting of the annular space may cause failure 
or collapse of the liner. Failure of the liner could be critical and could require 
excavation and removal of the conduit system. 
 Partial collapse, irregularities, offset joints or bends in the existing pipe conduit may 
prevent the installation of an adequately sized sliplined pipe. 
 Inability to observe and address internal issues associated with the embankment dam. 

Option 3  Grouting along the Exterior of the Conduit 

Conduits exhibiting seepage through joints or deteriorated portions of the pipe walls can 
be remediated by injecting materials through the walls of the pipe in an attempt to fill 
voids that may have been created and to plug openings in the pipe walls or joints. 
Cementitious or chemical grouts are typically utilized for the purpose. Injection 
of the materials can be performed either from the surface of the embankment or from 
the interior of the conduit. Selection of the approach to injecting the grout depends upon 
the availability of working room for grouting equipment and personnel (i.e. conduit size), 
the depth of the conduit below the embankment surface, and if the remediation is performed with 
the lake full. 

Injection of the grout from the interior of the pipe typically offers a better opportunity to deliver 
the grout to specified areas. Drilling through the embankment to grout along the conduit is 
usually performed for small diameter conduits or when the pipe is very shallow within the 
embankment. The greater the depth of fill over the conduit, the less certainty the grouting 
procedures are impacting the targeted areas. Drilling through the embankment is not practicable 
for situations in which the lake cannot be drained and portions of the conduit within the upstream 
slope of the dam are to be grouted. 

Although costs for this type of rehabilitation are typically lower than the cost of other options, 
this approach is generally considered somewhat of a temporary repair. This option does not 
extend the design life of the material of the conduit. If the damage to the conduit has created 
voids in the surrounding backfill, it is difficult to be certain that the grouting has filled all of the 
voids. 

This option retains the stage/discharge relationship of the existing spillway, which maintains any 
flood control benefits downstream of the dam. However, if the existing spillway capacity is 
insufficient to meet current project requirements, there is no opportunity to alter the capacity of 
the existing conduit. 

To summarize, the advantages to this remediation option include; 

 Relatively low initial cost. 
 Ability to make multiple repairs, if initial attempts are not completely successful 
 Work can be performed without draining the lake, although flow through the conduit 
needs to be controlled when working on the interior of the conduit. 
 Access along the top of the dam may not be impaired. 

The disadvantages to grouting along the conduit exterior include: 

 Inability to be certain that potential voids have been filled. 
 Does not typically provide a permanent repair for an aged conduit. 
 Inability to address spillway capacity issues. 

Option 4  Abandonment of Existing Conduit and Construction of a Siphon 

Abandonment consists of grouting full the existing corrugated metal pipe with either a 
sand/cement grout or a gravel/sand/cement grout. In either scenario, an expansive chemical 
admixture is typically included in the grout mix to control or reduce shrinkage during curing of 
the grout. As with the sliplining option, a sand diaphragm drain is typically installed around the 
downstream portion of the existing conduit to limit the potential for soil piping as the CMP 
eventually corrodes and deteriorates. 

Siphons, as the principal spillway for the rehabilitation of dams, have been used successfully in 
the southeast, but are generally limited to small drainage basins with relatively small peak 
inflows. Because the soil loading is relatively small, siphons can be 
constructed of flexible conduit such as PVC, HDPE, or Ductile Iron. Typically, siphon spillways 
in these applications do not exceed 12-inches in diameter. However, in some instances, 
siphons as large as 15 to 18 inches in diameter have been successfully utilized in small 
dams. Dam owners and surrounding property owners should be aware that the use of 
siphons, as opposed to the more traditional pipe-and-riser spillway systems, generally results in a lake that 
will fluctuate more as a result of the inherit inefficiency of the siphon until priming occurs. 
Siphons prime with a head or water surface elevation between 1 and 1-1/4 times the diameter of the siphon above 
the siphon invert. Once a siphon primes, there is very little increase in outflow as the lake surface rises. 

The advantages of grouting full the existing corrugated metal pipe and installation of a siphon 
include: 

 Lake does not have to be completely drained. Maintaining a partial pool allows for 
the maintenance of some of the aquatic habitat. 
 Installation of siphons can be performed in a relatively short amount of time and are 
typically cost-effective. 
 No visible outlet structure in the lake. 
 Allows for the removal of relatively cool water from deeper areas within the lake to 
promote cold water fish habitat downstream. In areas where trout populations are 
threatened by increasing water temperature, the use of siphons can be used to combat 
the rise in stream temperature. 
 Specialty contractors are not required if quality engineering oversight is available 
during construction. 

The disadvantages of this option include: 

 Some excavation of the dam is required. If the dam is utilized as either a pedestrian 
path or vehicular path, some interruption of service should be anticipated. 
 Inefficient removal of water at heads below 1 to 1-1/4 times the diameter of the pipe, 
which causes excessive fluctuations in the water surface when compared to pipe and 
riser spillways. 
 Not cost effective for large watersheds. 
 Can be susceptible to vandalism, unless protective measures are taken. 
 Limited ability to drain lake deeper than 20 to 25 feet. 
 Inability to keep lakes drained 
 Susceptible to blockage with ice unless special provisions are implemented during 
design and construction 
 Some underwater work may be required 

Option 4  Abandonment of Existing Conduit and Construction of a Short Riser and Pipe Spillway 

This option can be considered a modified version of the traditional pipe-and-riser spillway 
system or an economical hood inlet spillway system. The grouting procedure is the same as for 
option 3. The riser and pipe inverts for this option are set higher in the dam instead of being set 
along the fill/foundation interface. Usually, the riser invert is set a vertical distance below 
normal pool equal to 1/5 to  of maximum water depth at the upstream toe of the dam. For 
example, if the lake depth were approximately 20 feet, the riser invert would be set 4 to 5 feet 
below normal pool. The limiting height of the riser is dictated by both pipe diameter and 
location of the upstream pipe invert (entrance to the pipe) relative to the hydraulic grade 
line. Subatmospheric pressure conditions, that can accompany entrance conditions for steep pipes 
should be avoided. Also, the conduit invert should be a minimum depth of 1.5 diameters below the pool 
elevation to avoid the capture of air due to surface water drawdown, and associated 
slugging under full flow conditions. 


Installation requires excavation of the embankment below normal pool. This excavation depth is 
greater than that required for the installation of a siphon but significantly less than what would be 
required for the removal of the deteriorated conduit. Utilization of this system may require the 
use of bends or elbows along the conduit to allow for the discharge of water at or near the 
downstream toe. A gate is usually installed on the upstream edge of the riser to allow for partial 
draining of the lake. Complete draining of the lake is not feasible with this system. 

The main advantage of this system is its ability to simulate the hydraulic characteristics and 
efficiencies of the traditional pipe-and-riser systems located through the base of the dam. Unlike 
the siphon, both the traditional pipe-and-riser system and this option can accommodate a wide 
variation in base flows into the lake without the corresponding large fluctuations in lake level. 

Because soil loading is relatively moderate, flexible conduits such as ductile iron, PVC, and 
HDPE may be utilized. 

The advantages of such a system include the following: 

 Limited embankment excavation 
 Limited lake level fluctuation, as compared to a siphon spillway. 
 Can be installed without complete draining of the lake. 
 Cost-effective in that the riser height is limited. 

The system does have disadvantages, such as: 

 Cannot be utilized to drain the lake below the invert elevation of the riser. 
 Conduit bends/elbow can be expensive 
 Riser location within the upstream slope allows for an increase chance for vandalism 
in that the riser is only located a short distance from shore 
 Foundation soils for the riser base may be soft which can cause settlement problems 
or raise costs due to over-excavation 
 The height of fall in the conduit is limited. Pipe or culvert spillways should not be 
used for drops, from riser invert to pipe outlet, greater than about 25 feet due to the 
danger of cavitation. 

The owners of most old embankment dams with problem CMP conduits have a number of 
concerns or issues that will usually involve several of the options described above. The engineer 
should attempt to learn of these concerns or issues for each dam owner and present the 
advantages and disadvantages of each of the available repair options. In many instances, 
education of the owner by the engineer may be required to repair the dam in a manner consistent 
with good engineering practices that also meets the requirements or requests of the owner. 

Attachment 9 

White Paper on Outlet Works Inspection 
Federal Emergency Management Agency Outlet Works Workshop 
Denver, Colorado 
May 25  27, 2004
Prepared by Chuck R. Cooper1

1 Civil Engineer, U.S. Bureau of Reclamation, P.O. Box 25007, Denver, Colorado 80225-0007 

Introduction 

Outlet works are generally inspected as part of a thorough inspection of the dam and its 
features. Outlet works are typically either cut-and-cover or tunnels. This white paper 
will focus on the inspection of cut-and-cover outlet works. A cut-and-cover outlet works 
is typically comprised of the following components: 

(1) Entrance channel 
(2) Intake structure 
(3) Conduit(s) 
(4) Terminal structure 
(5) Downstream channel 

The purpose of an outlet works inspection program is to ensure that conduits through 
dams are safely and efficiently operated and maintained. Structural defects and 
deterioration develop progressively over time. A trained and experienced inspector can 
identify defects and potential problems before existing conditions in the dam and conduit 
become serious. This white paper will address the following specific topics relating to 
outlet works inspection: 

 Frequency of inspection 
 Systems, methods, and techniques used for inspection 
 Design criteria to accommodate inspection 

This white paper will not address the inspection of the entrance and downstream 
channels, since they rarely develop dam safety concerns. 

Frequency of Inspection 

Periodic inspection may reveal trends that indicate more serious problems are developing. 
Inspection intervals may vary depending on the overall conditions determined from 
previous inspections and the existence of any dam safety concerns. Periodic inspections 
can vary in scope and purpose and by the organization or personnel (damtender, 
agency/district level, etc.) performing the inspection. 

Types of inspections 

Dam safety organizations and dam owners may employ a variety of inspections during 
the life of an outlet works. These inspections may include the following types 
(Reclamation, 1988a): 

(1) Initial or formal.  Initial or formal inspections include an in depth review of all 
pertinent data available for the outlet works to be inspected. Design and 
construction data are evaluated relative to current state-of-the-art to identify 
potential dam safety problems or areas requiring particular attention. A thorough 
onsite inspection of all features is conducted, and an attempt is made to operate all 
mechanical equipment through their full operating range, if possible. 

(2) Periodic or intermediate.  Periodic or intermediate inspections are conducted 
between formal inspections. An in depth review is made of all pertinent data 
available on the outlet works to be inspected. However, the data review focuses 
on the current status of the outlet works and the data are not evaluated relative to 
current state-of-the-art criteria. A thorough onsite inspection of all features is 
conducted. All mechanical equipment may not be tested during any one 
inspection. Some equipment may be operated at another time or during the next inspection. 

(3) Routine.  Routine inspections are typically conducted by field or operating 
personnel. The primary focus is on current condition of the outlet works. 
Available data may not be reviewed and evaluated prior to the inspection, 
depending on the inspectors familiarity of the outlet works. Inspections may be 
scheduled on a regular basis or performed in conjunction with other routine tasks. 

(4) Special.  A special inspection is conducted when a unique opportunity exists for 
inspection. For example, if low water conditions exist in a reservoir exposing a 
normally inundated structure, a special inspection may be arranged. 

(5) Emergency.  An emergency inspection is performed when an immediate dam 
safety concern is present or in the event of an unusual or potentially adverse 
condition (e.g., immediately following an earthquake). 

The actual terms and meanings used to define the types of inspection may vary between 
dam safety organizations and dam owners. 

Factors influencing scheduling of inspections 

Scheduling of periodic outlet works inspections may be influenced by (Reclamation, 1988b): 

(1) Sufficient notice.  Dam owners and operators may need sufficient time to make 
necessary arrangements, such as pre-inspections associated with lockout/tagout 
and confined space entry, or special equipment or approval for unwatering 
conduits, terminal structures, or pools. This process could require several weeks 
or months depending on the facility. 

(2) Scheduling access.  Access for the inspection should be scheduled when most or 
all of the major components of the outlet works system can be examined. Some 
features such as intake structures and upstream conduits are usually submerged 
and not accessible. Downstream conduits and terminal structures may or may not 
be able to be unwatered and made accessible for inspection. The dam owner or 
operator may be requested to provide notification when reservoir conditions 
permit or when the reservoir can be drawn down to allow the inspection to be 
performed. If the feature to be inspected is normally inundated and inaccessible, 
certain factors (Reclamation, 1985 and 2001) should be considered in determining 
the extent and frequency for inspection such as: 

a. Results of previous hands on inspection or evidence from the inspection 
of the normally accessible portions of the feature. Inspection of the 
normally accessible portion of a feature may provide information on the 
probable condition of the inaccessible portion. 

i. Condition of the concrete.  Cracking, joint separation, or 
significant deterioration. 

ii. Condition of the embankment and foundation.  Excessive post 
construction settlement or alignment distortion of the downstream 
conduit. Excessive embankment settlement or the existence of 
sinkholes on the upstream face along the alignment of the outlet 
works. 

iii. Observed seepage.  Seepage or wet areas observed at the 
downstream toe of the embankment. 

iv. Flow conditions.  Changes in the discharge capacity of the outlet 
works. 

v. Damage and deterioration.  Damage or deterioration of gates and 
metalwork. 

vi. Water quality.  Water quality known to be detrimental to 
concrete, conduit linings, or waterstops. Excessive amounts of 
sand or other material transported by the discharge. 

b. Operational history and performance of the feature, since its previous inspection. 

c. Relative costs for providing access for inspection of the feature, including 
costs associated with lost water and power revenues. 

d. Age of the feature. 

e. Design and construction considerations. 

i. Changes in standards or guidelines.  Design criteria, construction 
techniques, and/or quality of material at the time of construction 
fail to meet current standards or guidelines. 

ii. Foundation conditions.  The conduit was constructed on 
foundation of varying compressibility where there is a potential for 
differential settlement. This may result in cracking of the conduit 
or excessive opening of joints. Differential settlement is also 
possible between the conduit and gate chamber. 

iii. Foundation faults.  The conduit crosses a foundation fault where 
there is the potential for movement or disruption. 

iv. Unfavorable stresses.  The conduit located where conditions are 
conducive to arching and resulting in unfavorable stresses in the 
embankment and/or conduit. These stresses could be conducive to 
hydraulic fracturing of the embankment or stress concentrations on the conduit. 

v. Filters.  Lack of adequate filters and drainage material around the 
conduit downstream from the impervious zone of the embankment 
to safely convey seepage or leakage along the conduit to an exit point. 

f. Critical function of the feature. 

g. Any site conditions which exist that may compromise the safety of the feature. 

(3) Operation.  Certain problems may not normally appear when the feature is dry 
that appear when the feature is being operated. Also, when a feature is operating 
during a period of higher than normal releases may provide information that may 
not have been available to previous inspections. 

The opportunity to optimize both access and operation during a single inspection 
typically is not possible. Inspection objectives may have to alternate from one inspection 
to the next. This may necessitate the need for scheduling special inspections during 
unusual conditions, in addition to regular inspections to provide a comprehensive view of 
the outlet works safety. Special inspections may be required after floods, seismic 
activity, or other unusual events. 

Periodic inspections by selected organizations 

The frequency of periodic inspections varies between organization and dam owners. 
Emergency situations may require much more frequent inspections, such as daily or 
hourly. Situations can arise suddenly that cause serious damage in a short period of time. 
Examples of these problems are operations at full discharge capacity, seismic activity, or 
other special conditions. The need for special inspections should be evaluated after 
occurrence of any of these situations. 

A sampling of periodic inspections as required by selected organizations: 

The Bureau of Reclamation employs the following process (Reclamation, 2001) to 
monitor its significant and high hazard dams and attempt to detect any potential dam 
safety deficiencies: 

 Annually. -Annual inspections are performed by inspectors who are generalist 
(as opposed to specialist) engineers very familiar with the dam and its operations, 
and can readily distinguish changes from year to year. All inspectors attend 
regular training in dam safety inspections. 

 Periodic. - On a 6-year cycle (alternating with the comprehensive facility review 
(CFR), each dam is examined by a team originating in a Reclamation Regional 
Office, including the regional examination specialist. This examination is 
referred to as a Periodic Facility Review (PFR) and includes a rather thorough 
review and reporting of all past dam safety and operation and maintenance 
recommendations. 

 Comprehensive. - On a 6-year cycle (alternating with the PFR), each dam is 
examined/evaluated by a team of specialists from Reclamations Technical 
Service Center that includes an Instrumentation Engineer, an Examination 
Specialist, Mechanical Engineer, and a Senior Dam Engineer. This examination 
is referred to as a CFR and includes not only the PFR activities, but also includes 
technical evaluation of all design, construction, and analysis of the dam. 

The Natural Resource Conservation Service (NRCS) requires the sponsor/owner to be 
responsible for making inspections after they are turned over to the sponsors/owners 
(NRCS, 2003). Special, annual, and formal (once every 5 years) inspections are 
performed by personnel trained in conducting the inspections. If requested by the 
sponsor/owner, NRCS may participate in inspections; provide training to ensure that the 
sponsor/owner understands inspection techniques and the importance of completing 
corrective action; and provide technical assistance to address specific O&M needs. If an 
inspection reveals an imminent threat to life or property, the sponsor/owner shall 
immediately notify all emergency management authorities. 

The U.S. Army Corps of Engineers (USACE) performs periodic, intermediate, and 
informal inspections on the basis of project size, importance, or potential hazard (USACE, 2004): 

 Initial periodic inspection.  The first periodic inspection and evaluation of a new 
earth or rockfill dam is carried out immediately after topping out of the 
embankment prior to impoundment of the pool. 

 Second periodic inspection.  The second periodic inspection for new dams is 
performed no later than one year after impoundment is initiated. 

 Subsequent periodic inspection.  Subsequent periodic inspections are performed 
at one-year intervals for the next two years. The next two inspections are 
performed at two-year intervals and then extended to a maximum interval of five 
years. More frequent inspection intervals are scheduled, if conditions warrant. 

 Intermediate inspection.  For projects on a five-year inspection cycle, an 
intermediate inspection of all or some of the features may be scheduled, if 
warranted. Selection is based on consequences of failure, age, degree of routine 
observation, a natural event (e.g. earthquake), performance record and history of 
remedial measures. Intermediate inspections are also made of any portion of a 
project exposed during dewatering that could not be accomplished during 
scheduled periodic inspection. 

 Informal inspection.  Frequent informal inspections are performed by 
appropriate employees at the project. The purpose of informal inspection is to 
identify and report abnormal conditions and evidence of distress. 

Systems, Methods, and Techniques Used for Inspection 

The success of an inspection will be dependent upon good preparation and planning. 
Any inspection should consider: 

 Selection of the inspection team.  The members of the inspection team will vary 
depending on the needs and resources of the organization or dam owner, type of 
the inspection, results of the data review, and any special requirements. 

 Review of project data.  The amount of available data may vary greatly from 
outlet works to outlet works. The extent of project data review and evaluation 
depends on the type of inspection to be conducted. 

 Preparation of an inspection plan.  A detailed inspection plan should be prepared 
to identify all features to be inspected, problem areas, and areas of potential 
problems. The inspection plan will also identify special logistics, access, or 
equipment requirements. An inspection checklist is typically prepared as part of 
an inspection plan. The checklist is used to identify specific inspection objectives 
and is also useful in developing the final inspection report. 

Methods used for the inspection of the various features of an outlet works are mainly 
dependent upon accessibility. Factors influencing accessibility include: 

 Inundation.  Reservoir operations and water levels may make some features 
unavailable for normal inspection and require specialized inspection services 
(e.g., dive team, remotely operated vehicles). 

 Confined space.  Certain features may require Occupational Safety and Health 
Administration (OSHA) confined space permitting for man-entry, lockout/tagout 
procedures, and preparation of a job hazard analysis (JHA). An alternative to 
man-entry is the use of specialized inspection services (e.g., closed circuit 
television). 

 Size constraints.  Limitations in size may prevent man-entry and require 
specialized inspection services (e.g., closed circuit television). 

Inspection of intake structures 

In most cases, due to the intake structures location in the reservoir, it is either partially or 
fully inundated. If the intake structure is partially inundated, inspection of the structure 
above the water level will be fairly straight forward. However, inspection of the portion 
of the structure below the water level such as the entrance, trashracks, fish screens, ice 
prevention systems, gates/valves, stoplogs, and bulkheads will require specialized 
inspection services. If the intake structure is a tower, it may have a wet well or some 
other access to the control mechanism. Closure of a guard gate or bulkhead may provide 
the ability for inspection of the interior of the tower. 

Problems common to intake structures include deterioration, damage, and misalignment. 
Description of more specific problems related to trashracks, fish screens, ice prevention 
systems, gates/valves, stoplogs, bulkeads, and bridges are beyond the scope of this white 
paper. 

Inspection of conduits 

Generally, outlet works conduits with diameters 36 inches or larger can be inspected by 
man-entry, if proper OSHA precautions are taken. Conduits with diameters smaller than 
36 inches are inaccessible for man-entry and require specialized inspection services. 

Problems common to conduits include obstructions, defective joints, cracking, 
deterioration, and mechanical equipment operation. Signs of these types of problems 
include: water ponding on the invert of the conduit which could be an indication of 
settlement-related problems in certain reaches of the conduit, metallic corrosion of pipe 
or exposed reinforcement, discoloration or staining of concrete surfaces, damaged 
protective coatings, deformation of the conduit circumference, chemical deterioration of 
concrete, joint separation, leakage into or out of the conduit, misalignment of conduit 
sections, plugged drain holes, voids behind the concrete near any observed cracks, joint 
separations, or misalignments, spalled concrete from compression, reinforcement 
corrosion, drummy or hollow-sounding concrete, erosion, abrasion, or damage in 
concrete downstream of gates, offsets, and/or changes in slope, cavitation damage, and 
binding of mechanical equipment. 

Inspection of terminal structures 

The terminal structure may be dry or partially inundated depending on the time of year 
and the schedule of releases through the outlet works. If the terminal structure is partially 
inundated, inspection of the structure above the water level will be fairly straight forward. 
However, inspection of the portion of the structure below the water level such as the 
basin, chute blocks, baffle blocks, or end sill will require specialized inspection services. 

Problems common to terminal structures include deterioration, damage, obstructions, 
misalignment, backfill and foundation deficiencies. 

Specialized inspection 

Specialized inspection includes the use of a dive team, climbing team, remotely operated 
vehicle (ROV), or closed circuit television (CCTV). 

(1) Dive team 
Certain factors should be evaluated when considering a dive inspection: 

a. Depth. - As the depth below the water surface increases, the difficulty of 
performing the dive increases. Divers have a limited amount of time on a 
given dive, and that time decreases with the increased pressures on deeper 
dives. Also, as the dive becomes deeper, more of the allowable dive time 
is spent descending. Allowable dive times can be increased by means 
such as using mixed gas, or diving in a pressurized newt suit. This 
increased dive time at depth comes at an increased cost due to 
requirements for items like larger dive crews, more specialized equipment, 
and a limited number of companies that can actually do the work. 

b. Altitude. - The altitude of the feature to be inspected can greatly affect the 
viability of a dive inspection. This could really be considered a subfactor 
of the depth factor. Due to the lower atmospheric pressure at higher 
altitudes, a diver has an even more limited dive time associated with a given depth of dive. 

c. Access. - Often the entrances to a feature are equipped with trashracks on 
the inlet side. The ability to remove enough of the trashrack bars to allow 
easy entry and egress is important. Since divers in such an environment 
will be utilizing some type of surface-supplied breathing gas, it is 
important that the access point be such that the hoses will be able to be fed 
into the conduit without hanging up.
 
d. Leakage and currents. - Leakage of downstream gates or valves within a 
conduit is a safety factor that can affect whether a dive inspection can be 
safely performed. Any inspection of this type should be performed such 
that the diver enters the conduit against any current and then exits with the 
current. For an outlet works, a submerged conduit will more than likely 
need to be entered from the upstream end. Therefore, the condition of the 
gates and how much amount of leakage is critical with respect to the 
viability of a dive inspection. 

e. Visibility. - The distance a diver can see is important to whether a dive 
inspection is advisable. In the event of zero visibility, little reason would 
exist to pursue a dive inspection, as the shear magnitude of the entire 
surface of a feature would be extremely difficult to inspect by feel. Also, 
in a circular conduit a diver does not have a real edge or other reference 
point to keep track of any findings. If a dive inspection is planned for a 
conduit, consideration should be given to making a large release prior to 
the inspection as a means of flushing sediments from the conduit and then 
allowing some amount of time for the water to settle out prior to diver 
entry. This time will depend on the type of sediments in the water, but 
could vary from a day to a week. 

f. Size. - A conduit should be large enough, so the diver can turn around 
inside and exit head first. The diameter required for inspection would 
depend on the size of the individual diver and also the type of dive 
equipment required. 

g. Length. - As with depth, the conduit length becomes a factor relating to 
the amount of time the diver has available at depth. If the conduit is 
extremely long, it can take much more time to inspect than the diver has 
available. The available dive time for a long conduit can be increased, but 
this can be costly and have extreme safety concerns since the diver does 
not have a direct path to the surface. 

(2) Climbing team 
Although not often required, a climbing team may be utilized to perform inspection of the 
inaccessible portions of intake towers and the walls of terminal structures. 

(3) Remotely operated vehicle 
Inspection using an ROV is a good alternative to dive inspection when conditions such as 
depth, diameter, or length become prohibitive. The ROV can be used to inspect the 
submerged portions of intake structures, conduits, and terminal structures. Divers can be 
used to assist with upstream access by opening trashracks and/or guiding the ROV 
through the racks. Access is also possible from downstream conduit, if the section of 
conduit between the upstream guard gate and downstream regulating gate can be 
unwatered and the ROV placed inside. Cables can be threaded through a special manhole 
bulkhead and the conduit can be rewatered, so the ROV can travel upstream and perform 
the inspection. 

Some of the limitations of an ROV inspection include visibility and the size of the 
conduit. If the conduit diameter is large, the ROV inspection is much more likely to be 
limited to one small path along the conduit, where as a diver can cover a much larger path 
or wider swath as the diver moves down the conduit. Because the diver can use their 
sense of feel, in a limited visibility situation they are able to possibly locate more items of 
interest and then focus in on them with their other senses. With an ROV in a limited 
visibility situation, the only area inspected is the small area directly in front of the 
camera, basically whatever the ROV is bumping into. Sometimes, it can be difficult with 
the ROV to tell exactly where the view seen on the monitor is within the conduit, and 
since ROVs often rely upon a compass, the steel in the conduit lining and/or concrete 
reinforcement can affect the navigation. If CCTV equipment is used in lieu of an ROV, 
the length of cable tether can be measured to determine the location within the conduit. 

(4) Closed circuit television 
CCTV can be used to inspect the submerged portions of intake structures, conduits, and 
terminal structures. CCTV inspection can also be used in structures or conduits where 
confined space entry issues may require permitting prior to physical entry. The OSHA 
regulations define a confined space as having limited access and egress, and not being 
designed for continuous human habitation. This would include not only small conduits, 
but also larger diameter conduits where risks, costs, or system complexity may make 
remote inspection more advantageous. 

CCTV inspection equipment consists of a video camera attached to a self-propelled 
transport vehicle (crawler). The transport vehicle and camera are commonly referred to 
as a camera-crawler. An operator remotely controls both the transport vehicle and 
camera. The camera can provide both longitudinal and circumferential views of the 
interior of the feature. Video images are transmitted from the camera to a television 
monitor, from which the operator can view the conditions within the conduit. The video 
images are recorded onto videotape, compact disc, or digital versatile disc (DVD) for 
future evaluation and documentation. The operator can add voice narrative and 
alphanumeric captions or notations as the inspection progresses. 

Depending on the model, camera-crawlers used in conduits with smaller diameters 
(generally about 4 to 14 inches) have cameras with some pan, tilt, and zoom capabilities, 
a wide range of tether pulling capacity (200 to 1,000 feet), and some steering capabilities. 
Camera-crawlers used in conduits with diameters of 15 inches or larger are steerable, 
have a greater cable tether pulling capacity (500 to 1,500 feet), and have cameras that can 
provide a wider array of optical capabilities, including pan, tilt, and zoom. Actual tether 
limits obtainable in the field, vary greatly depending upon a number of factors such as 
conduit diameter, bends, invert slopes, and existing invert conditions. 

In large diameter conduits, the video camera can be attached to a scissor mechanism 
mounted to the transport vehicle. The scissor mechanism, controlled by the operator, can 
raise or lower the video camera as needed for inspection. In addition, the video camera 
usually has a high powered zoom, which can be used to provide closeup views of areas 
that might be difficult for the transport vehicle to get near. These features allow 
examination of very large conduits with diameters as large as 40 or 50 feet. 

If required, some models of camera-crawlers allow for the attachment of retrieval tools 
such as alligator clamps, grippers, and magnets. These tools can be used to remove light 
debris or damage. The attachment of any type of retrieval tool will require additional 
clearance within the conduit to operate the retrieval tool. Some models of crawlers have 
robotic cutters attached to them. These cutters can be used to remove debris or 
protrusions in concrete, steel, or reinforcement. 

Sometimes the conduit is so small that a transport vehicle cannot be used, or 
obstructions/invert conditions exist that prevent the transport vehicle from traversing the 
conduit. For these types of situations, small color video cameras (1.5 to 3 inches in 
diameter) can be attached to metal or poly-vinyl chloride (PVC) poles and manually 
pushed up the conduit. Push poles are normally used for straight sections of conduit. 
The use of poles for advancement is generally limited to about 400 feet. If bends exist in 
the conduit, a flexible snake device (spring steel wire, coiled wire, or flexible 
polypropylene-jacketed fiberglass push rod) can be used instead of the push poles. The 
color cameras are connected to a video cassette recorder and to a television monitor. The 
snake devices are generally limited to about 75 to 200 feet. 

Design Criteria to Accommodate Inspection 

Intake structures 

Locating submerged intake structures can be very difficult and time consuming. On a 
large dam where the structure is a fair distance from the shore, it is advantageous to have 
some reference points to line up on from two directions. Ideally, if these are permanent 
then they can be used to triangulate in on. For intake structures on small dams where the 
structure is closer to shore, a series of permanent markers can be utilized as a center point 
and a measured length of rope can be used to locate the structure in a radial search using 
the marker as the center point. The series of markers would allow ease of use with 
several water surface elevations. With either of these methods, good documentation is 
needed, so the same points can be used each time. Another possible method is the use of 
an embedded air line which can be used to supply bubbles which can be used to locate it. 
This, of course, requires a compressor, but a small compressor can typically be brought 
on site. Another alternative for locating intake structures involves the use of the Global 
Positioning System (GPS). GPS is a worldwide radio-navigation system formed from a 
constellation of 24 satellites and their ground stations. GPS uses these satellites as 
reference points to calculate positions to a high degree of accuracy. 

Access entry locations (e.g., trashracks) should be in an easily locatable position, such as 
the corner next to the tower. Also, the entry location should be oriented, so it can easily 
be found from inside the structure. If a hatch is near a concrete column, then the column 
can be used for reference. If the hatch is located in the center of the structure it is 
difficult for the diver to determine where the hatch located in the trashracks. The size of 
the hatch or opening provided in the trashracks is recommended to be about 3.5- by 3.0 
feet. The larger hatch size also is beneficial if divers are inserting an ROV. 

The trashracks used for entry locations need to be easily opened or removable by the 
diver. 

Conduits 

If a conduit is going to require inspection by a diver the diameter shouldnt be less than 
48 inches, so the diver can turn around in the conduit. 

The Bureau of Reclamation performed a series of tests in 2002 to evaluate the 
performance capabilities using camera-crawlers in double walled high density 
polyethylene (HDPE) pipe. The results of these performance tests are generally 
applicable for other conduit materials. The following is a summary of those tests: 

(1) Diameter. -The minimum recommended conduit diameter to successfully 
accommodate camera-crawlers is 8 inches. Although camera-crawlers are 
available for conduits smaller than 8 inches, they can be very limited in cable 
tether pulling capacity and generally do not have sufficient traction for use in 
conduit inspection. In addition, the cameras typically only have a fixed lens and 
the transport vehicle is not steerable. Camera-crawlers used in conduits with 
diameters between 8 and 12 inches generally have cameras with some pan, tilt, 
and zoom capabilities, but generally are not steerable. Camera-crawlers used in 
conduits with diameters of 15 inches or larger are steerable, have a greater cable 
tether pulling capacity, and have cameras which can provide a wider array of 
optical capabilities including pan, tilt, and zoom. Where practical, the use of 
conduits with diameters 15 inches or larger is strongly encouraged. This allows 
for the use of more powerful and versatile camera-crawlers. 

(2) Bends. - The maximum recommended bend angle to successfully accommodate 
CCTV inspection equipment is 22.5 degrees. In conduits with diameters of 8 and 
10 inches, the camera-crawler cannot be navigated around bends greater than 
45 degrees, since the camera cannot clear the conduit crown as it travels through 
the bend. If sharper bends are required in conduits with diameters of 8 and 10 
inches, a series of 22.5-degree bends are recommended. Each bend should be 
connected to a minimum 5-foot length of conduit to allow the camera-crawler to 
navigate around the bend segment and provide adequate crown clearance. 
Conduits with diameters of 12 inches or larger can have bends that exceed 22.5 
degrees, but drag friction then reduces the cable tether pulling capacity by as 
much as 75 percent. 

(3) Invert slope inclination. - The maximum recommended invert slope inclination to 
successfully accommodate camera-crawlers is 5 degrees. The difference in invert 
slope inclination between flat and 10 degrees can reduce cable tether pulling 
capacity by as much as 70 percent depending upon the conduit diameter, degree 
of conduit bend, and the invert condition. Flat to 5-degree invert slopes would 
appear to be the most reasonable inclination. Slopes with inclinations greater than 
10 degrees are not recommended, due to the significant loss of traction that occurs 
when camera-crawlers are pulling long cable tethers. If slopes greater than 
5 degrees are required, upstream access locations should be provided within the conduit. 

(4) Distance between access entry locations. - The maximum distance between access 
entry locations can range between 500 and 2,000 feet, but highly depends upon 
the conduit diameter, bends, invert slopes, and invert conditions. The designer 
will need to take these limitations into account when selecting the appropriate 
distance between access entry locations. In conduits with diameters of 8, 10, and 
12 inches, the maximum distance should not exceed about 1,000 feet. This 
assumes that access is available on both ends of the conduit. If access will only 
be available on the downstream end of the conduit, then the maximum distance 
should be limited to about 500 feet. In conduits with diameters of 15 and 18 
inches, the maximum distance should not exceed about 2,000 feet. This assumes 
that access is available on both ends of the conduit. If access will only be 
available on the downstream end of the conduit, then the maximum distance 
should be limited to about 1,000 feet. 

Terminal structures 

Often the most difficult aspect for dive inspection of terminal structures is accessing the 
water. Carrying all of the heavy dive equipment down a riprap slope is a difficult and 
often dangerous task. Providing some means for more easily crossing the riprap such as 
stairs or a narrow concrete section would be useful. Fluctuation of the water level in the 
terminal structure may cause this path to become green with algae and result in a very 
slick surface. 

Other innovative technologies 

Other innovations in inspection systems are currently under development for sewer 
pipelines and for the oil and gas industry. These systems may eventually prove 
applicable to outlet works inspection. These systems involve state-of-the-art lasers 
scanners (digital imaging) and gyroscope technology. Laser scanner systems allow the 
operator to see the total conduit surface with color-coding of conduit defects on a digital 
computer image. Data processing and report preparation are completed using a 
manufacturers proprietary software. Currently, laser scanners are not readily adaptable 
for conduit inspection, since they have some difficulties identifying infiltration, 
corrosion, and conduit ovality. Laser scanners also are limited to conduits in the range of 
8 to 24 inches in diameter. Costs are generally 50 to 75 percent higher than for CCTV. 
However, the major benefit of laser scanners is the ability to produce a digital record, 
which reduces the subjective interpretation of results. Computerized assessment will gain 
wider acceptance as a reliable inspection and evaluation tool as further technological 
advancements are made (Civil Engineering Research Foundation, 2001, . 

There also are a number of geophysical and non destructive testing (NDT) technologies 
that could have application for the inspection of outlet works. These technologies 
include: acoustic and ultrasonic testing, seismic tomography, sonar, electrical resistivity, 
ground penetrating radar, mechanical and sonar calipers, hydro-acoustic surveys, and 
radiography. 

References 

Bureau of Reclamation, Assistant Commissioner  Engineering and Research Center, 
Technical Memorandum No. 6, Guidelines for Determining Whether Normally Inundated 
Outlet-Works Features Should be Examined, 1985. 

Bureau of Reclamation, Training Aids for Dam Safety Module, Inspection of Spillway 
and Outlet Works, 1988a. 

Bureau of Reclamation, Training Aids for Dam Safety Module, Preparing to Conduct a 
Dam Safety Inspection, 1988b. 

Bureau of Reclamation, Directives and Standards FAC 01-07, Review/Examination 
Program for High- and Significant-Hazard Dams, 2001. 

Civil Engineering Research Foundation, CERF Report No. 40551, Evaluation of SSET: 
The Sewer Scanner and Evaluation Technology, 2001. 

Natural Resource Conservation Service, National Operation and Maintenance Manual, 2003. 

U.S. Army Corps of Engineers, EC 1110-2-1156, Draft Safety of Dams  Policy and 
Procedures, 2004.