Del Shannon of Schnabel Engineering on Dam Construction and Rehabilitation
February 11, 2021
Schnabel Engineering is an engineering firm that does significant dam design and rehabilitation work across the United States, focusing on geotechnical, structural, hydraulic, and mechanical issues and other important factors. Del Shannon is a principal at Schnabel Engineering and a senior vice president in its dam and levee engineering group. In this interview, he tells Hydro Leader about his work in dam rehabilitation, the advantages of various project delivery methods, and the increasing importance of risk-based dam assessments.
Hydro Leader: Please tell us about your background and how you came to be in your current position.
Del Shannon: My undergraduate degree is in journalism, but I turned out to be the world’s worst journalist. I got a job at an engineering firm helping write proposals and turned out to be pretty good at it. I started hanging out with engineers and realized that I was confident that with the proper training, I could do the same work they did. So I went back to school, got a master’s degree in engineering, and then I got a job at a firm that designed dams.
Early in my career, around 2005–2006, I was the lead designer and engineer of record for one of the first design-build dams in the country. That got me interested in having engineers work with contractors. I thought that there could be tremendous benefit for the industry in creating a team that approached projects from a holistic standpoint, not just from a design or construction standpoint. After working for an engineering firm for 20 years, I worked for contractors for 10 years. That has given me a unique perspective not only on how to design these structures, but also on how to build them. I’m now back in the consulting business. I am a senior vice president of Schnabel Engineering and one of the senior managers in our dam and levee engineering group.
Hydro Leader: Did your civil engineering master’s program specialize in dams?
Del Shannon: No. Few if any master’s programs in the United States focus on dams. That is seen as postgraduate work. My focus in grad school was geotechnical engineering, which is the study of soil, rock, and earthen materials as engineering and construction materials. Working on dams is a natural fit for geotechnical engineers because 90 percent of dams are earthen, and concrete is a lot like rock.
Hydro Leader: Please tell us about Schnabel Engineering.
Del Shannon: Schnabel Engineering was formed in the mid‑1950s along with a slew of other firms, since geotechnical engineering was becoming more and more important at the time. Building foundations and complex structures requires a thorough understanding and knowledge of the soils, rocks, and materials they are built on. Schnabel is primarily based on the East Coast, and recently, it has started expanding into the West. In the 1990s, it formed its dam engineering group. This arm of the company has about 160 people. We’re one of the top dam design engineering firms in the country.
Hydro Leader: What percentage of Schnabel’s work is on dams?
Del Shannon: Schnabel has about 400 people as a whole, and in addition to the 160 people in the dam engineering group, several experts from our geotechnical and tunneling groups work on dam projects, so about 50 percent of our employees work to support projects in the dam and levee engineering group. The dam market is growing by leaps and bounds. The peak of dam building in the United States occurred around the 1960s. Since then, there has been some societal pushback related to the effects of construction on the environment. However, the need for water and power has never subsided, even with the contraction in building. That’s created a bit of a shortfall as the population continues to grow. We need to do some catching up, and it is essential that we maintain our existing structures as they continue to age. That’s one of the main reasons for our tremendous growth.
Hydro Leader: Who are the clients you work with on your dam projects, and who are the owners of the dams Schnabel works on?
Del Shannon: There is a wide range of owners. There are 90,000 dams in the United States, including hydropower dams owned by utilities or municipalities, private owners, states, and the federal government. There are probably a dozen federal agencies that work on and own dams, including the Federal Emergency Management Agency, the National Resources Conservation Service, the U.S. Army Corps of Engineers, and the Bureau of Reclamation. All these entities have dam-safety arms, and we work with all of them.
Hydro Leader: What are the most common types of dam rehabilitation projects Schnabel works on?
Del Shannon: Dams have a number of failure modes related to the ways in which they are most vulnerable. For example, are the foundations and the material underneath the dam stable? Is the dam structure itself stable? Is it degrading over time? Then there’s the hydraulic element. One of the most vulnerable parts of a dam is its spillway. It’s got to be able to pass a storm. If it can’t, it’s vulnerable to failure. We look at spillways and their abilities to pass floods a lot. We do a lot of looking at the quality of concrete. Internal erosion and filters are another major issue with embankment dams and foundations. There are also hydromechanical issues related to elements like gates. If steel gates and valves are poorly maintained over the years or if they are not exercised because they are rarely operated, problems can arise. A rehabilitation project may involve replacing a vulnerable part of a structure, like a spillway or gate. The difficulty is that you have to be able to isolate or shut these things off in order to work on them.
The Oroville spillway failure in 2017 spooked a lot of people in the industry. That failed during a relatively routine spillway release/flow event. Nobody thought there was a significant problem with that structure, but if you start looking into the history of its design, its geology, and its construction, you can see that there was a problem waiting to happen. The logical next question is, what don’t we know about other structures? How many other structures out there are on the verge of failure?
Hydro Leader: What are some of the major trends in dam construction and rehabilitation today?
Del Shannon: First, there is actually new construction going on. For the first time in a long time, we’re seeing an uptick in new storage, motivated by the facts that water is becoming scarcer and that our population continues to grow. Climate change is part of that. It used to be that you could count on snowpack serving as a supply source to fill reservoirs. It would melt, and you would store it. However, as our climate changes, many entities are realizing that they can no longer rely on snowpack. You need to shift your thinking to more of a runoff scenario where reservoirs are filled year round during periods of high flows. Offstream storage is becoming popular, as is raising existing dams.
Hydro Leader: The cost of replacing infrastructure is always a major concern for dam and reservoir owners. Is Schnabel involved at all in advocating for federal funding for infrastructure?
Del Shannon: We’re acutely aware of the massive costs of infrastructure construction and maintenance. We do advocate for funding for these structures, but we have to be careful to remain politically neutral and offer only our technical expertise. We simply argue for the safe operation of the structures.
Hydro Leader: You spoke earlier about being involved in some of the first design-build dams and the advantages of a holistic perspective that brings together design and construction. Would you expand on those advantages?
Del Shannon: While I’m a big fan of the design-build method, I should clarify that not everybody is. If done correctly, that method can allow you to put downward pressure on costs. Much of the cost of a new construction project relates to risk. In my opinion, in order to effectively manage that risk, you need to assign it to the entity that’s best suited to manage it. For instance, owner-related issues should be managed by the owner. If an owner abdicates responsibility and makes either the contractor or the engineer manage the risk, that drives the price up. The same thing is true of a contractor. If there are a lot of unknowns about the design or there are many things out of the contractor’s control, the contractor will increase its price to cover its risks. The same thing is true of the engineer. If the engineer has a lot of uncertainty, they will be conservative and design an expensive structure.
If you can bring all those entities, including the regulator, to the table and discuss how to appropriately allocate and manage risk, you can lower those prices. Consider the example of the Pine Brook Dam in Boulder, Colorado, which I designed. We designed and built that dam in 18 months for about $4.5 million. A comparable dam was constructed around the same time by the same contractor and a different engineer through the design-bid-build process, meaning that it was designed and then put out to bid and was built by the lowest-bidding contractor. That dam cost $7.5 million. In that particular case, by bringing the right people to the table to manage the risks, we reduced the cost by about 40 percent.
Hydro Leader: What trends do you see in the field of dam construction and rehabilitation?
Del Shannon: When it comes to the evaluation of existing structures, the hydropower world is increasingly shifting to a risk-based outlook. Traditionally, engineering has been deterministic. You derive a specific number from a series of calculations and modeling exercises, and you rely on that number for an idea of what’s going on with your structure. However, the size and complexity of these structures puts limits on the usefulness of that approach. In order to really understand how your dam is performing, you have to have an intimate understanding of the materials used in every element of the dam throughout its three dimensions. You have to have specific, high-quality data from hundreds of thousands, if not millions, of points throughout the structure. It’s not feasible to do that, and as a result, we’re ending up with an incomplete view of the structure from a deterministic standpoint.
The way to address that is by adopting a more-risk-based or probabilistic standpoint, which involves dealing with known vulnerabilities that we call potential failure modes. We evaluate individual potential failure modes using a risk framework to determine whether or not there is a problem. This approach is being promoted by the Federal Energy Regulatory Commission, and it is becoming much more prominent. That’s a big shift.
While risk is an increasingly important element of the evaluation of existing structures, I don’t think deterministic work is going to be supplanted by risk-based work in the design and construction of new structures. We’re still going to do what we’ve always done; however, the potential-failure-modes analysis and risk framework allow us to better design and build new structures with appropriate protective measures.
Del Shannon is a principal at Schnabel Engineering and a senior vice president of Schnabel’s dam and levee engineering group. He can be contacted at