1. 4th
IAHR International Symposium on Hydraulic Structures, 9-11 February 2012, Porto, Portugal, ISBN: 978-989-8509-01-7
1
SPILLWAY HYDRAULIC MODELLING –
PERSONAL ADVENTURES AND PEEKS BEHIND THE CURTAIN
D. Campbell1
1
Director of Dam Engineering, Schnabel Engineering, Inc., USA, davec@schnabel-eng.com
Abstract:
This paper explores the relationships between applied researchers and practitioners, both
professionally and through personal experiences. Commentary on the system as perceived by the
author and how it can be improved with greater interaction and understanding is presented. The
commentary is blended with personal reflections on involvement with model studies that influenced
the author and perhaps, in a few circumstances, touched a larger audience.
Keywords: researcher, practitioner, collaboration, hydraulic modelling.
INTRODUCTION
This paper has been written to entertain and to attract the attention of younger professionals that are
passionate about their careers. I hope to have succeeded in at least one of these objectives. Just as
with any craft or profession, work can range from tedium to exhilaration. My early experiences and
my predisposition exposed and convinced me of the merits of the latter. Younger professionals
need to recognize that the passion they bring and the choices they make early in their careers will
likely set the tone for their entire career. The specific path taken is not important; the attitudes that
underscore the activities we choose to undertake make all the difference.
BACKGROUND DISCUSSION
All engineers are, by definition, people who use scientific knowledge to solve problems.
Researchers develop or expand upon scientific principals, lecturers teach others to apply science
based solutions and practitioners directly apply these solutions. Almost all of us have assumed at
least two of these major roles. For the purposes of this paper, the term ‘researcher’ will apply to
‘applied researchers’, those involved in solving complex problems and developing new knowledge
directly applicable by practicing engineers. The tenets of this discussion can readily apply to a
broad range of engineering disciplines founded on scientific investigations and research. A focus
herein on spillway hydraulic modelling is logical since it is within our mutual areas of expertise as
researcher, lecturer and/or practitioner.

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As a practicing design engineer, working almost exclusively on dams for the past 35 years, I am, at
heart, a generalist civil engineer. A generalist dam engineer has to attain reasonable levels of
competency with regard to soils, foundations, geology, structures, hydrology, hydraulics and a
broad array of ancillary civil design activities as they apply to dams; in addition to developing
broad based business survival skills. My primary passion has always been connected with the
hydraulics side of the dam engineering business, so my adventures with spillways, in many
instances, have taken on a personally elevated priority.
The role of practitioners
As background, the vast majority of engineering practitioners are engaged on projects of moderate
scale and limited budgets. Larger projects that can readily benefit from and afford hydraulic model
studies are far fewer in number. The vast majority of design service assignments are confined to
execution of traditional and well-developed design concepts, approaches and features based on
limited budgets, limited client openness to innovative approaches, and project settings and needs
well served by conventional approaches. The inherent tendencies of engineers to resist change
results in slow assimilation of new knowledge into the practitioner’s tool box. Where there is a
lack of readily accessible practical guidance for newer and more advanced spillway design
approaches, that resistance is intensified.
Design consultants traditionally have need to be accomplished in the following areas:
 fundamentals of engineering practice
 applying well documented approaches
 contract terms and conditions
 project scheduling and budgeting
 personnel and project management
 marketing and selling of engineering services
 building and maintaining client relationships
 preparing design drawings and specifications
 overseeing construction activities to validate design compliance
While many consultants are likely to recognize project cost and performance benefits available
through the use of innovative or quasi-experimental approaches, few pursue these options for their
client’s benefit. The design engineer is risk averse and is primarily focused on the development of
engineering solutions fitting their clients’ budgets, schedules and the constraints of project sites,
while limiting risk exposure. Enhanced technical viability, improved robustness and/or economic
advantage are usually resisted if achieving these ends will require a “leap of faith”. Many times the
reluctance to take that leap of faith is based on having to rely on the veracity of work done by
unknown outside parties. Sometimes it is due to an inability or unwillingness to apply fundamental

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hydraulic concepts to sufficiently verify reported findings as an independent reality check on the
conclusions of others. For a few, a newer approach will not be considered until a sanctioned design
procedure is developed for general use.
In general, the broader design engineering community is ill equipped to:
 absorb the tangle of similitude-based findings presented in terms of subscripted and
superscripted Greek symbols
 understand the impacts of model measurement accuracy and non-scalable factors on the
behaviour of a constructed prototype
 comprehend the implications of modelling conditions, such as scale effects on physical
models or the importance of mesh details in CFD analyses
 translate and comprehend academic definitions and terms of art
 fully grasp restrictions imposed by the limited range of parameters explored in a given
research study
The role of researchers
Because I am less learned regarding the roles, responsibilities, obligations and reward structures of
researchers, I will limit my discussion to my general perceptions. Perhaps my caricature will at
least provide a bit of humor for those on the research side of engineering.
In general, spillway hydraulic researchers are:
 highly specialized and have narrowly focused expertise
 focused on research – generating knowledge
 always seeking – looking for the missing piece
 focused on furthering science and theory, developing empirical equations or underlying
basic theory to describe physical processes
 excellent technically – very comfortable with theory, mathematics and technical language
 well trained in experimental methods, data collection, instrumentation, programming
languages and data analysis
 attracted to applied research or solving problems with existing hydraulic structures
 encouraged to collaborate with other researchers and academics
 pressured to publish in peer-reviewed journals
In general, spillway hydraulic researchers are not:
 broadly understanding of how practising engineers work
 prone to grasp broad arenas of knowledge – they are specialists

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 focused on thinking in terms of cost effectiveness or constructability
 used to publishing in terms that facilitate the application of their research by practitioners to
solve problems
 prone to expand text to detail model setups, experimental methods and other factors. that
give context to practitioners
 often rewarded or encouraged to work with practitioners
The practitioner/researcher gap
To best serve our communities as engineers, I believe that all can agree that there is a need for a full
spectrum of integrated services and expertise. I have long contended that if engineers didn’t have
problems communicating, they wouldn’t have any problems. Therefore, to accomplish full
spectrum continuity, we need to reach out to each other and to communicate far more often, so that
we can learn to communicate far more effectively. Building bridges of friendship, mutual respect
and understanding sensitive to each others’ roles and responsibilities will not be easy, but none of
us are attending the 4th
IAHR International Symposium on Hydraulic Structures because we have
chosen the easy path.
While we share our educational foundations, researchers and practitioners have advanced
professionally into very different worlds, characterized by fundamentally different success and
reward systems, an emphasis on either depth or breadth of engineering knowledge and a focus
either on theory or practice. Researchers are well served to contemplate and think deeply.
Practitioners are well served by responding with relative speed and integrating project elements
from a myriad of subdisciplines to build integrated solutions for clients.
As a tangible example, when sending an e-mail to a practicing associate, within or outside of my
company, I have a general expectation that a response will be received within one day. In those
circumstances where a full response cannot be provided quickly, it is the norm to receive either a
brief e-mail or telephone call acknowledging the e-mail, providing a reason for delay and inquiring
about the criticality of a response. When sending an e-mail to an academic, I have a general
expectation of receiving a response within about one week, sometimes longer. This is not an
indictment of academics, but rather a definitive example of the differences in setting, approach and
tempo.
Engineering practice is characterized by “The client needs this tomorrow!” and multitasking on a
daily basis. Research is generally characterized by deeply focused inquiry and a characteristic
mindset that “This is going to require careful consideration”. The applied researcher and the
practitioner have different drivers, pressures and roles (Fig. 1). To interact successfully, we need to
learn to appreciate each other’s perspectives, so we can attune our attitudes and dialogue to
accommodate mutual understanding, deeper discussions and friendships based on trust and mutual
respect. Successful relationship building takes persistence and dedication to purpose, but I believe
that the rewards are well worth the investment.

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I have found researchers investigating similar behaviors for similar facilities commonly define
terms and factors differently. Within the research community, this can create a disconnect in
aggregating findings from separate studies and analyses to compile similarities and develop
common truths leading to broader questions and specific design guidance. Issues that create a
minor impediment between researchers will likely provide an overwhelming obstacle to
understanding for an engineering consultant, creating a barrier likely to deter the practitioner from
further inquiry.
Practitioners too often expect rapid turnaround and lower costs for investigations of issues related
to complex hydraulic behaviors, too often expect solutions to be presented using elementary level
mathematics or simple graphs relating two well understood variables, and occasionally expect that
ancillary issues not scoped or contracted at the beginning of the project should be included because
it is obvious, at least to the designer, that the additional information will be needed by the designer
to apply the developed solution.
A limited number of engineering design professionals will actively seek out findings of recent
research activities to identify whether they can beneficially apply these findings to projects, either
now or in the near future. In my efforts to do this, I have found that language barriers exist between
practitioners and researchers, both in linguistic terms of art and in mathematics.
Ideally, with each added piece of evidence, both the empirical and theoretical understanding of
spillway behaviours would benefit the profession as a whole. It is recognized that this ideal is
never achievable, but as a profession, I believe that we can do far better than our historic record
supports. Some concepts on moving in the direction of enhancing cross-discipline understanding
have been touched on. Others will be discussed later in the paper.
Even where a clear benefit exists, few within the design engineering community will regularly
consider application of innovative approaches. We are committed to protect our clients interests, so
Owner and regulator
concerns and needs
New knowledge
Fig. 1 – A simplified researcher-practitioner relationship sketch
Researchers Practitioners
Teaching load
Publishing
Academic politics
Tenure
Budgets
Schedules
Marketing
Keeping up
Increase scientific understanding
Develop design guidance
Do you know how this will be applied?
What’s going wrong with this project?
I need design guidance on that
Can you make this easier to apply?

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risk and cost considerations need to be clearly communicated. Where innovative approaches are
employed, designers need to recognize that the performance of the end product can differ from the
inferences of laboratory findings, through misunderstanding or misapplication of the results or
through ill-advised extrapolations. Therefore, it is incumbent for the design professional to amply
validate approaches, whether innovative or conventional, and to maintain or develop a sufficient
understanding of the hydraulic fundamentals to perform independent reality check verifications
before allowing concepts to be used in designs.
Questions to be asked include:
 What were the purposes and outcomes of the referenced model?
 Do the model findings address all of the issues needed for application to a different project
setting?
 To what extent does the designer need to interpolate or extrapolate findings, and how critical
are these interpolations/extrapolations?
 How confident is the designer with the credentials of the researchers and the veracity of the
referenced modelling work?
The last question will, at a minimum, weigh the importance of the concept considered, the clarity of
the publication, the level of familiarity with the lead researcher, the ability to pragmatically
reconstitute the concepts presented in a manner that aligns with common sense and the likelihood
that the client will be open to the innovative application.
Initial research into a given area (stepped spillways, labyrinth weirs, PK weirs, etc.) is almost
universally undertaken for a specific project, where an innovative concept is considered to have
sufficient viability to merit an at risk research investment. With spillways for dams, the project
setting, required capacity, flow frequency and duration, and facility operational requirements are
unique to each project. Therefore, the translation of model findings from project specific
investigations for application at other locations will generally take either a leap of faith or a
separate site specific spillway model. In general, I have found that publications presenting the
outcome of project specific models tend to provide more tangible and pragmatic findings. In these
circumstances, the design consultant’s contract and interaction with the hydraulic modeller will
usually dictate the development of specific answers to specific issues.
It is common for broader based design guidance research for spillway applications to occur only
after sufficient site specific model studies have been undertaken and sufficient projects have been
constructed to validate an application’s robustness for broader use. Finding a graduate student that
is up to the task is also paramount.
What follows are reflections on a personal journey over the past three and a half decades, with a
focus on those engagements where spillway hydraulic research influenced my thinking or my
career, or exposed me to events and relationships that have provided memories and, hopefully,
some good science.

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THE EARLY YEARS
An interesting start
About 30 years ago, with five years of experience in engineering practice, I was assigned to a major
new dam project. As we moved through preliminary engineering, I was able to convince the
project owner on the benefits of a model study for an innovative spillway concept. I initially
worked closely with the lead researcher at a nearby university to accomplish the study goals. It
soon became apparent that acceptable results were not forthcoming and different approaches were
needed to provide solutions. Additionally, the senior professor leading the modelling effort and the
assertive young designer very desirous of obtaining useful results were not a compatible pairing.
The senior researcher was characterized by a strong ego and a narrow perspective on solutions. I
had no prior experience working in a research environment. I was full of ideas and self-confident,
but lacked the art of perspective and relationship building. Had I been better versed in those skills
at that time, we likely could have overcome our differences and found success. Unfortunately, that
was not the case.
In frustration, I visited the department chair and requested he fix the problem or the model study
contract would be terminated and moved to another facility. In response, the chair assigned two
young, untenured hydraulics professors to the hydraulic model study. I was bluffing at the time, so
I was pleased with any changes I could manage to achieve. Because the senior professor was
tenured and highly regarded in the profession, the chair had placated him by allowing him to retain
the rights to publish the model study findings.
The new team collaborated exceptionally well. We tested options in simple terms prior to investing
in detailed model construction. In one instance, wire mesh was initially stapled to a weir surface to
validate the benefit of added roughness prior to adding supplemental elements to the model. In the
end the model study met or exceeded all of its stated goals. The journal paper by the senior
professor (with no co-authors) was well received and considered by some to be a seminal paper on
the topic. In fact, the paper was based primarily on the work of two young, untenured professors
supported by an assertive young design engineer.
I learned several lessons from that experience. Things are not always as they seem is the most
obvious. Second, I had my first real lesson in humility. The two young academics were not put off
in the slightest by not being listed as authors. When discussing the topic at a later date, one of the
young academics simply noted, “That is water over the dam.” The young professors were excited
by the opportunity to participate in the development and execution of a ground-breaking model
study, and they were equally pleased to have succeeded in meeting the project goals. Their broader
goals were sharpening their laboratory skills and seeking tenure. Taking care of my needs and
saving the department from potential embarrassment served them well (both are currently full
professors). It is amazing how much more can be achieved when an individual is not focused on
who gets the credit.

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Lastly, to achieve results in a collaborative environment, compatibility and mutual respect are of
vital consequence. The junior researchers were eager to please and tolerant of my social
inadequacies. Their tolerance made me far more accepting of their ideas and taught me the
importance of building relationships to achieve success. After that project’s second start, we fed off
of each other’s energy and ideas, making the whole vastly more than the sum of the parts.
It’s a small world after all
I’ll now fast forward to 1998 to discuss an event in retrospect. I attended a Schnabel Engineering
sponsored event, the RCC1998 International RCC Dam Seminar and Study Tour. During a study
tour bus ride, I sat next to a Ph.D. candidate named Robert Boes for an extended conversation.
Robert had been invited to present at the seminar to discuss his on-going research on stepped
spillway performance and energy dissipation. He and I had gotten along well and we were
interested in getting to know each other better. I asked Robert how he arrived at his Ph.D. research
topic. He related to me that he was generally interested in dams and since the ETH-Zurich faculty
had considerable expertise with spillways, some type of spillway research seemed an obvious
choice. Robert then recalled sitting in the library for several days combing through journal articles
for topics of interest. At some point, he had come upon an article on the Monksville Dam stepped
spillway model (Fig. 3) from a 1984 ASCE Hydraulics Conference. Robert noted that the final
page of the article discussed research that should be undertaken to allow development of applicable
design approaches for stepped spillways. He then cross-referenced and found that a general
approach for stepped spillway design had not been developed. I then asked Robert if he was
“pulling my leg” (a term of Scottish origin, currently referring to someone being humorously
insincere). After I explained the meaning to Robert, I asked if he recalled who had written that
Fig. 3– Monksville Dam step transition profile (Inset of initial 1:25 scale crest transition model)

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paper. He admitted that he didn’t recall. At that point, I said, “Would you consider it curious that
you’re currently having a conversation with the lead author (reference to Campbell and Johnson
1984)”. Even with 7 billion people, it can sometimes be a very small world. Also, a seed that was
planted in 1984 (to develop general design guidance for stepped spillways) took 14 years to travel
about 8,000 miles from the conference site before it germinated in Switzerland. Quite amazing! I’d
like to think that several other seeds planted along the way may also have germinated without my
being aware of a connection. A lesson for all of us is to be persistent in keeping creativity alive. If
there are ideas that you are positioned to directly advance, do so. If not, plant seeds regularly in
papers, conversations, presentations and other collaborative venues. As was stated earlier, it is
amazing how much we can all achieve when individuals are not focused on who gets the credit.
The labyrinth makes my acquaintance
I became aware of labyrinth spillways (Fig. 2) in 1984 and immediately became fascinated with the
performance and cost-saving possibilities of these articulated weirs. Several nights and weekends
were initially spent creating a fairly comprehensive labyrinth spreadsheet that provided discharge
rating curves and concrete volume estimates, as well as assigning warning messages that would be
triggered when input data fell outside of the range of tested variables.
Over the next few years, that spreadsheet was tinkered with from time to time to gain a working
familiarity with what worked and what didn’t, from both hydraulic performance and project cost
perspectives. I found that smaller footprint labyrinths were hydraulically less efficient in terms of
discharge per unit width, but the smaller footprint weirs were much more cost effective. Many
questions arose and the limitations in tested labyrinth geometry (W/P≥2) and head (H/P≤0.8)
became increasingly frustrating. The seeds of a broader understanding wouldn’t germinate for
quite some time.
Since labyrinths were still an innovative concept, the standards for recommending one to a client
needed to be high. It took nearly 5 years before a spillway upgrading project came along that
clearly provided performance and project cost benefits compared to conventional weir alternatives.
By that time, the homework done over several years provided a comfort level that left me confident
in understanding the hydraulic and structural design for labyrinths, thereby eliminating the need for
a significant leap of faith.
W: Cycle width
P: Weir height
B: Sidewall length
α: Sidewall angle
a: Half apex width
L: Length of weir (single cycle)
H: Total head upstream of weir
n: Number of cycles
Fig. 2 – Generic labyrinth layout

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A NEW CENTURY
Dog River Dam as the gateway to broader horizons
The Dog River Dam spillway was designed in the early 1990s using hydraulic design methods
developed from model studies performed at the United State Bureau of Reclamation (Reclamation)
Hydraulics Laboratory. The spillway design consisted of six, 9.14 meter wide cycles (W) with a
weir height (P) of 4.57 meters (W/P [horizontal aspect ratio] = 2) and an overall weir length ratio
(L/W) of 4.0. A W/P of 2.0 was the lowest value tested in the Reclamation studies. The Dog River
Reservoir was to provide water supply sufficient to serve its owner for 40 years. However, about
15 years after completion of the original dam construction, water supply demand had outgrown
projections and it became clear that a 3 meter raise of the pool would be necessary to keep pace
with service area water supply demand (Fig. 4). The dam owner indicated that once they had a
permit in hand, they would need a fast-tracked design to get the added water supply on line quickly.
A 3 meter raise of the labyrinth walls would decrease W/P from 2 to 1.2, which would be well
outside of range tested by researchers. Knowing that we’d need a model study to validate
performance for the raised weir, I contacted Kathy Frizell at the Reclamation hydraulics laboratory
to ask if they could perform this work. At the time, Kathy, Darrell Temple, and I were organizing a
spillway research needs conference focused on safety needs for existing dams, so I was in regular
contact with Kathy. In response to the model study request, Kathy stated that she was very
interested in expanding upon the Reclamation’s earlier work and noted that she had an
appropriately sized flume that had just opened up, but the window of opportunity was short.
Knowing the value of this opportunity, Schnabel immediately contracted for the work on behalf of
the owner. When Kathy asked if she should limit the study to the design capacity of the spillway, I
recall saying that it would be far more beneficial to all of us in the long term to limit the study only
by the lesser of the capacity of the flume or the capacity of the flow delivery system. The latter
Fig. 4 – Raised Dog River Dam and labyrinth weir

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ultimately controlled. While the needed project spillway capacity was approximately 1700 cms,
model runs were performed for prototype discharges up to 3100 cms (a head of 5.2 meters).
Back to the workshop - Because the above noted workshop had a limit on the number of attendees,
the organizing team had many conversations regarding who to invite. I had recently made the
acquaintance of Bruce Savage, a bright, passionate untenured professor who specialized in CFD
modelling. While I couldn’t justify his attendance on the merits of his experience, I did discuss the
workshop with him and I knew of his eagerness to attend. A last minute cancellation gave me the
opportunity to get an invitation for Bruce to join us for the meeting to be held at a hotel near to the
Reclamation laboratory in Denver.
During the workshop, Bruce was introduced to Kathy and a visit was arranged to see the Dog River
labyrinth model in operation. Recollection of who initiated the discussion has faded, but the three
of us agreed that there would be great merit in having Bruce perform a parallel Dog River labyrinth
model study using CFD. Since Schnabel was not positioned to perform either of the studies, it was
agreed that Schnabel could best participate by collaborating on a paper and by funding Bruce’s
CFD modelling effort. The findings from these companion studies (as reported in Savage, et. al.
2004) indicated that the physical and CFD models for this spillway (Fig. 5) differed by a maximum
of 10% and an average of less than 5%, which is generally within the range of expected variations
between model studies conducted at separate locations.
Schnabel’s underwriting of costs for these analyses and our close collaboration with researchers on
interpretation of findings from these parallel studies initiated a new phase of awareness for our
firm. If we were to truly be a premiere provider of dam engineering services, we had a
responsibility to be personally involved in and financially support the evolution of the state of
design practice. We gained a clear recognition that not only was this the right approach as a
professional, our clients provided feedback that for many projects this was a key differentiator that
led to our selection.
Fig. 5 – Dog River labyrinth physical and CFD models

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Unfolding the mysteries of labyrinths
Shortly after completion of the Dog River modelling, Bruce Savage was appointed to the faculty of
Idaho State University. With Schnabel’s new-found enthusiasm for research collaboration and
support, we supplemented Bruce’s start-up grant to allow him to purchase higher end computer
equipment needed to more quickly process complex three-dimensional CFD analyses. In addition,
Bruce was provided several research stipends to perform additional studies for expanding the
profession’s understanding of labyrinths, including performance over a wider range of heads,
horizontal aspect ratios (W/P) and approach conditions (discussed in Paxson and Savage 2006).
In 2006, Schnabel was retained for rehabilitation or replacement of the Lake Townsend Dam for the
City of Greensboro, North Carolina. That project’s 85 meter long, gated concrete gravity spillway
and adjoining intake and pumping station were suffering from advanced alkali-silica reaction that
severely undermined the spillway’s safety. Additionally, the spillway capacity was insufficient for
meeting current safety standards. The findings of an alternatives analysis showed that replacement
of the existing intake and spillway would be necessary and that construction of a new dam
immediately downstream was the most feasible and cost-effective option. This alternative included
a seven cycle labyrinth with a cycle width of 13 meters, a weir height of 6.1 meters and a total weir
length of 310 meters. To be cost-effective, the labyrinth base slab was to be constructed on
approximately 6 meters of fill, with steps to transition flow to a cross-sloped stilling basin and
discharge channel transition.
As a direct follow up to the Dog River modelling, Schnabel began assessing additional
understanding needed to better leverage the advantages of labyrinth weirs. Within the realm of
modelling, we came to recognize that some questions are better answered using physical models,
some respond better to CFD modelling or others are best resolved by a combination of both
approaches. Given the magnitude of the investment involved for the Lake Townsend Dam
labyrinth (approximately 11000 cubic meters of reinforced concrete) and the complex flow
transitions from labyrinth overflow to a stepped drop to a laterally sloped stilling basin and channel
release transition (Fig. 6), a combination of physical and numerical (CFD) modelling was merited
Fig. 6 – Lake Townsend labyrinth isometric view

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to develop the geometries needed to transition flows and dissipate energy in a reliable and cost
effective manner. Blake Tullis of Utah State University’s Utah Water Research Laboratory
(UWRL) teamed with Bruce Savage of Idaho State University to complete the physical and CFD
modelling, respectively. CFD was used for big picture conceptualization of spillway flood flow
patterns and velocity fields, and to assess the relative merits of alternative stepped drops and basin
geometries. The CFD finalist was then modelled in detail in the UWRL flume (presented in Paxson
et. al. 2008).
Throughout the Townsend study, we strengthened our relationship with Blake Tullis and got to
know Brian Crookston, then the graduate student responsible for the Lake Townsend labyrinth
spillway modelling effort. The Lake Townsend Dam model, in part, led Brian to complete his
Ph.D. dissertation on labyrinth spillway hydraulic performance. While considered unlikely, there
was some concern that the approximately 0.3 meter high labyrinth weirs used for the dissertation
work might be subject to error due to scale effects. Schnabel decided to fund fabrication and
testing of a 0.9 meter high, one cycle labyrinth weir (Fig. 7) geometrically mimicking one of the
tested 0.3 meter high weirs. That work, carried out by Brian as a post-doctoral fellow, matched the
findings of its smaller scale cousin, reducing concern related to scale effects and adding another
component validating the findings of Brian’s thesis work. Schnabel also funded Brian in
completing supplemental CFD analyses for high head performance of labyrinth weirs (discussed in
Crookston et. al. 2012).
ONWARD AND UPWARD
The advancement in the understanding of the behaviour of labyrinth weirs over the past several
decades has taken an exceptional but poorly understood concept and converted it into a thoroughly
researched and very well documented design approach that has and will provide cost savings to
Fig. 7 – Large scale labyrinth verification model

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dam owners, and provides a robust, low maintenance, fixed crest spillway alternative. While some
additional research is merited to address some specialized circumstances, labyrinth weir design is
now broadly available for inclusion in every dam engineer’s tool box. As an example of the broad
acceptance of labyrinth weirs, Schnabel Engineering, a small company on the world stage, has
completed design of more than 40 labyrinths. However, as a profession, we are far from having
comprehensively firmed up spillway performance for known spillway configurations, and newer
ideas, such a PK weirs, provide a stream of new questions that demand answers.
Because spillway hydraulics is but a single consideration for practicing dam engineers, our field of
inquiry and interest must be far broader, and necessarily less deep than that of the researcher. As
practitioners, we need the depth of the researcher’s insights as much as the researcher needs the
broader project related challenges presented by practitioners for exploration and, if merited,
comprehensive development. As an additional company initiative within the dam engineering
practice area, Schnabel Engineering is in the early stage of developing a dam engineering research
and development program to annually fund employee proposals for applied research. Interested
employees are encouraged to prepare proposals that define:
 proposed research and/or development activities
 outcome expectations
 costs (internal and external)
 personal investment
 collaborators and commitments (internal and external)
 time frame (with interim milestones, if appropriate)
 end game benefits to the dam engineering profession and to Schnabel Engineering
Practicing engineers are trained to be client and project focused, so this program will require some
initial influence to build broad support. I am confident that once the research and development
program is underway, it will continue on, fuelled by its own merits. While our funding support and
collaborations have historically been directed towards hydraulic structures, it is our intent to expand
those efforts to include foundations, soils, hydrology, structures, concrete materials, operational and
emergency planning and other related civil engineering activities critical to dam safety and dam
project facilities performance.
Additionally, there are many highly trained academics who have chosen to focus primarily on
teaching, and who have more modest research facilities available to them. I believe that this
teaching focused group of academics can provide valuable assistance as liaisons between those
directed towards fundamental and applied research and those dedicated to application of
engineering solutions. Together, we should work to identify how we can best engage teaching
focused academics to assist us in translating theory into practice. Schnabel Engineering is currently
developing one possible approach with a highly regarded university local to one of our dam

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engineering offices. While our discussions are preliminary at this time, we are hopeful that we can
establish a comprehensive long term collaboration to assist in creating and maintaining a center of
excellence for the integration of dam engineering practice. In addition to being a powerful resource
for the profession, this venue would provide Schnabel with additional opportunities for research
and development activities.
Privately owned corporations operate with a deeply vested profit motive. Without profit, we would
cease to exist, so profit is, of necessity, a fundamental operational imperative. Therefore, we have
not undertaken our research and development initiative as a charitable gesture. We have reached an
understanding that a responsible level of support in advancing our profession is recognized and
valued in the marketplace for the tangible benefits it provides our clients. Active involvement in
the development of advances in technology will provide greater exposure to the company, and
astute clients desiring a value oriented consultant with demonstrated technical excellence will
provide sufficient assignments to repay that investment. We know that what we can visualize, we
can achieve. So let us imagine what can be achieved with an enhanced level of advocacy and
broader financial support from throughout the consulting community coupled with an enhanced
level of cooperative interaction with our research oriented engineering associates. Change occurs
slowly and, among engineers, it occurs even more slowly. Our objective should not be to change
the world overnight, but to move us step by step towards a better world. Remember, we are not
attending the 4th
IAHR International Symposium on Hydraulic Structures because we have chosen
the easy path. Let us find common ground and common passions and, together, let us choose the
right path.
ACKNOWLEDGMENTS
My own experiences have been enriched by my interaction with the many hydraulic researchers I have been
fortunate to encounter, work with and get to know personally. In addition to those individuals named or
alluded to in this paper, there are numerous others that have touched me both professionally and personally.
One individual in particular appears to deserve attention.
While I have not had the opportunity to work directly with Jorge Matos, I have had several occasions to truly
get to know him, to learn from him and to be captivated by his humble and quiet passion and his deep
humanity. Trans-Atlantic e-mails have at times been infrequent, but they have never been superficial and
they have always provided me with a source rich with insights, guidance, perspective and depth. Jorge’s
persistence and sense of duty define him as a leader; his insights, accessibility and dedication to purpose
define him as a professional; and his genuine thoughtfulness and contagious enthusiasm define him as a man.
Jorge, thank you for advocating on my behalf and affording me the honor of addressing the 4th
IAHR
International Symposium on Hydraulic Structures.

16. 16
References
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Hydraulic Model Studies. Proceedings of the 2004 Association of State Dam Safety Officials
Annual Conference, electronic media.
Paxson, G. and Savage, B. (2006) Labyrinth Spillways: Comparison of Two Popular U.S.A.
Design Methods and Consideration of Non-standard Approach Conditions and Geometries.
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Structures, Montemor-o-Novo, Portugal, pp. 37-46.
Paxson, G., Crookston, B., Savage, B., Tullis, B., and Lux, F. (2008). The Hydraulic Design
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