Martin Wieland is Chairman of ICOLD’s Committee on Seismic Aspects of Dam Design
In many countries, the sites of large storage dam projects were identified by teams of geologists, hydrologists and dam engineers decades ago, who have also made the first conceptual studies on the possible arrangement of the dam and appurtenant structures. Further project optimisations are then done during the tender and detailed design phases of the project. Geological and other site-specific risks identified during construction may require additional project modifications.
These are very general statements. As every dam is a prototype, the balance between technical, ie safety aspects, and non-technical aspects, i. economic, environmental and social etc, may change. For example, in a dam project in Iran, faults were identified in the footprint of a dam which resulted in the change of an RCC gravity dam to an earth core rockfill dam, when the contractor was already on site. In another arch dam project in Iran, the height of the dam had to be reduced substantially after the start of the project as the cost of the land inundated by the reservoir increased tremendously. These may be unusual cases but project adjustments are not uncommon.
We must also point out that projects are realised by engineers and not by scientists. Engineers must account for many uncertainties as many things are not know in great detail. But the engineers can also not wait until all the baseline data have been provided by scientists. For example, there are major uncertainties involved in the seismic hazard at dam sites. A crucial element has been if faults are crossing a dam site. Earth scientists may need substantial time to determine the slip rates along faults passing through a dam. As strong earthquakes are very rare, this may take many years.
Rather than waiting for this information, the dam engineer may simply select another dam type (or select another site), which is not vulnerable to fault movements such as earth core rockfill dams.
A lot is said about the sustainability of large dams and other projects. In all discussions only non technical aspects are addressed and the most important technical aspect, ie dam safety, is ignored. It is obvious that a dam project must be safe and must remain safe for as long as possible in order to be sustainable. The non technical aspects are also important but subsidiary to dam safety.
Sustainability also means a long service life. This implies that somebody has to take care of a project and provide adequate maintenance to control ageing processes.
Dr Alexander Arch is a civil engineer with Poyry
Hydropower design has evolved considerably in the past 100 years, and in the same way, each project’s design must continuously evolve over its course up until the moment the concrete is poured. Based on the fact that hydropower plants interact with the environment and will be in operation for several decades and even for centuries, engineers shall benefit from the possibility to optimise the design to the utmost extent through to the last possible moment. This is the continual optimisation process that Pöyry focuses on.
The understanding of the specific geological, hydrological and topographical site conditions forms the basis of the overall design concept. In the same way that these specific fundamental conditions will define the feasibility of a project, in-depth market knowledge will drive the project development. Every detail from regulatory procedures to local energy prices must be factored into the design process so that the high-level concept can be optimised. The market conditions will determine what is opportune in Asia or Latin America but is uneconomical in Europe.
Having a clear design concept and profound knowledge of the construction processes are the two fundamental principles to successful hydropower design. Adapting the design criteria to the entire project environment incorporating the particular needs of the client is the basis for a clear, concise and successful design process. From the beginning, the design team integrates all different stakeholders and communicates the evolution and the decisions taken on a day to day basis. This approach allows insight and overall understanding of the concept ensuring that the final product takes into considerations with various stakeholders’ expectations. Every hydropower project is a prototype – no two plants can be approached the same regardless of similarities.
Consequently, hydropower design at Pöyry is a continuous iterative process executed by a connected team and not an "off the shelf" product. A clear vision integrating all acting parties and variables that are unique to each project site together with a lean and transparent decision making process is indispensable for successful development. Apart from the essential technical know-how, geological and hydrological conditions, the design must also take into account the market situation and the capability of the contractors participating in the construction phase. A design requiring a specific construction method might by unfeasible due to the lack of adequate machinery or material.
Interwoven through all these challenges are social – environmental and cultural considerations. Correctly, these are increasingly gaining prominence. Design is fundamental to not, for example, damage archaeological sites, adversely affect local communities or obstruct the environmental habitat. A smart design approach considers these factors from the outset and addresses them at early stages. As hydropower proved to be the backbone for evolving countries, up-to-date findings with respect of environmental and social matters shall be implied in the design avoiding a repetition of already recognized failures within former design approaches.
With so many unique variables for each project, best practice is not to apply the same design, but to apply the same guiding principles. Pöyry’s approach to a successfully designed hydropower plant is a proven multi-disciplinary and expert-based method based on evidence, research and long-term experience fitted to the individual needs of each particular project.
Terry Arnold is North America Dams Practice Leader at MWH Global
A successful hydropower or dam design project includes a few key components that are critical at various stages of the project. From the beginning, the team must have a clear definition of the scope of the project, including design and operating criteria project budget and the timeline. This ensures clear alignment between the design team and the client in order to effectively design the project to meet client objectives. The development of a detailed work plan by the design team provides the proper work flow, a breakdown of roles and responsibilities, and the inter-disciplinary coordination required for complex design projects. The most successful projects ensure that sufficient time is allotted to complete the design and analysis in a logical sequence, with experienced staff in all the relevant disciplines: civil, structural, hydrology and hydraulics, geology/geotechnical, hydromechanical, electrical and instrumentation and controls.
Over the years I have found one of the most important components is having an integrated staff that have worked together on multiple projects. All of the components of a successful project must be met by a team that is efficient and seamlessly integrated. Strong teamwork delivers the client the results they desire, and the most successful projects are delivered when the core of the project team has a strong understanding of each other’s skills, established after a history of working together for years. At MWH Global, we have cultivated an integrated team of dam and hydropower engineers both regionally and internationally with our technical practice group approach, which has led to great success on some landmark projects such as the Panama Canal Third Set of Locks project and the San Vicente Dam Raise.
